| 1. |
- Moberg, Christina, et al.
(författare)
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De unga gör helt rätt när de stämmer staten
- 2022
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Ingår i: Aftonbladet. - 1103-9000.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- 1 620 forskare och lärare i forskarvärlden: Vi ställer oss bakom Auroras klimatkrav
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| 2. |
- Ayub, Rabia, et al.
(författare)
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Triplet State Baird Aromaticity in Macrocycles : Scope, Limitations, and Complications
- 2021
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society. - 1089-5639 .- 1520-5215. ; 125:2, s. 570-584
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Tidskriftsartikel (refereegranskat)abstract
- The aromaticity of cyclic 4nπ-electron molecules in their first ππ∗ triplet state (T1), labeled Baird aromaticity, has gained growing attention in the past decade. Here we explore computationally the limitations of T1 state Baird aromaticity in macrocyclic compounds, [n]CM's, which are cyclic oligomers of four different monocycles (M = p-phenylene (PP), 2,5-linked furan (FU), 1,4-linked cyclohexa-1,3-diene (CHD), and 1,4-linked cyclopentadiene (CPD)). We strive for conclusions that are general for various DFT functionals, although for macrocycles with up to 20 π-electrons in their main conjugation paths we find that for their T1 states single-point energies at both canonical UCCSD(T) and approximative DLPNO-UCCSD(T) levels are lowest when based on UB3LYP over UM06-2X and UCAM-B3LYP geometries. This finding is in contrast to what has earlier been observed for the electronic ground state of expanded porphyrins. Yet, irrespective of functional, macrocycles with 2,5-linked furans ([n]CFU's) retain Baird aromaticity until larger n than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a 3[n]CFU with a specific n is more strongly Baird-aromatic than the analogous 3[n]CPP while the magnetic indices tell the opposite. To construct large T1 state Baird-aromatic [n]CM's, the design should be such that the T1 state Baird aromaticity of the macrocyclic perimeter dominates over a situation with local closed-shell Hückel aromaticity of one or a few monocycles and semilocalized triplet diradical character. Monomers with lower Hückel aromaticity in S0 than benzene (e.g., furan) that do not impose steric congestion are preferred. Structural confinement imposed by, e.g., methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T1 state aromaticity, we reveal the analogy to the Hückel aromaticity of the corresponding closed-shell dications yet observe stronger Hückel aromaticity in the macrocyclic dications than Baird aromaticity in the T1 states of the neutral macrocycles. © 2021 The Authors.
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| 3. |
- Canals, Isaac, et al.
(författare)
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Astrocyte dysfunction and neuronal network hyperactivity in a CRISPR engineered pluripotent stem cell model of frontotemporal dementia
- 2023
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Ingår i: Brain Communications. - 2632-1297. ; 5:3, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- Frontotemporal dementia (FTD) is the second most prevalent type of early-onset dementia and up to 40% of cases are familial forms. One of the genes mutated in patients is CHMP2B, which encodes a protein found in a complex important for maturation of late endosomes, an essential process for recycling membrane proteins through the endolysosomal system. Here, we have generated a CHMP2B-mutated human embryonic stem cell line using genome editing with the purpose to create a human in vitro FTD disease model. To date, most studies have focused on neuronal alterations; however, we present a new co-culture system in which neurons and astrocytes are independently generated from human embryonic stem cells and combined in co-cultures. With this approach, we have identified alterations in the endolysosomal system of FTD astrocytes, a higher capacity of astrocytes to uptake and respond to glutamate, and a neuronal network hyperactivity as well as excessive synchronization. Overall, our data indicates that astrocyte alterations precede neuronal impairments and could potentially trigger neuronal network changes, indicating the important and specific role of astrocytes in disease development.
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| 4. |
- Cid Gomes, Leandro, et al.
(författare)
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Light-driven (cross-)dimerization of terpenes as a route to renewable C15-C30 crudes for fuel and lubricant oil applications
- 2023
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Ingår i: Sustainable Energy & Fuels. - : Royal Society of Chemistry. - 2398-4902. ; 7:3, s. 868-882
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Tidskriftsartikel (refereegranskat)abstract
- Non-fossil hydrocarbons are desirable for transport fuels and lubricant oils to reach a fossil carbon neutral economy. Herein, we show the production of such end-products from crude raw materials via the photosensitized dimerization of terpenes. Terpenes are hydrocarbons originating from renewable sources, such as forestry, industrial bio-waste and photosynthetically active microorganisms. Under irradiation at 365 nm, we observed high conversions of terpenes with conjugated diene segments into their dimers (e.g. 96.1 wt%, 12 h for α-phellandrene), and remarkable results were obtained using simulated and natural sunlight (90.8 wt% and 46.6 wt%, respectively, for α-phellandrene). We show that the lower reactivities of some isomeric monoterpenes could be overcome by a cross-photodimerization with α-phellandrene. We also utilized the cross-photodimerization approach to obtain C15 and C30 products, combining mixtures of isoprene, monoterpenes and sesquiterpenes. Hydrogenation of the terpene dimers gave materials with physical properties suitable as high energy density fuels and lubricant oils. Finally, our preliminary analysis based on recent literature points to the commercial viability of this route to produce fuels and lubricant oils, as well as to a potential for reduction of the environmental impact compared to fossil-based routes.
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| 5. |
- Cid Gomes, Leandro, 1993-
(författare)
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Light-Induced Routes to Sustainable Biocrudes for Fuels and Lubricant Oils
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fossil-based hydrocarbons are at present the ideal compounds for jet fuels and lubricant oils, so their replacement by novel technologies is not easy. Instead, sustainable routes to hydrocarbons, such as sunlight-driven processes, are desired to reduce the environmental impact by the transport sector. Photosynthetic microorganisms can convert water and CO2 into small hydrocarbons, yet, a second step is needed to convert them into jet fuels and lubricant oils. The aim of this thesis is to investigate photochemical routes for this second step.We first explore the triplet photosensitized dimerization of isoprene produced by cyanobacteria. We developed a combined photobiological-photochemical route from CO2 to C10 jet fuel via isoprene that has a climate change impact 80% lower than that of fossil jet fuel. The photosensitizer 1,1-dinaphthylmethanone absorbs in the near-UV light, so natural sunlight can be used with low photosensitizer loading (0.1 mol%). Later, other small conjugated dienes were investigated, providing a deeper understanding of the photodimerization. We concluded that isoprene is the ideal diene to be dimerized into jet fuel, as it has a suitable boiling point that facilitates its harvesting and as it dimerizes more efficiently than the other small volatile dienes.The photodimerization is then expanded to larger substrates to produce lubricant oils and diesel-like fuels. We found that α-phellandrene dimerizes very efficiently (>90%, 12h), and we utilize it in a cross-dimerization with less reactive monoterpenes and with isoprene. We also investigated the influence of light intensity in the reaction of α-phellandrene and the rates of triplet quenching of the photosensitizer by different monoterpenes.A final part of this thesis addresses the need of photochemical routes that can oligomerize unsaturated hydrocarbons other than conjugated dienes. The seminal idea is to use photoacids as catalysts. This journey started by designing a new photoacid based on the anilinium and dibenzotropylium cationic moieties. We found computationally a strong photoacidity, with pKa = -12. We discovered that the photoacidity is operating by a novel mechanism involving a reorganization of charge distribution within the dibenzotropylium moiety upon excitation, which interacts electrostatically with the anilinium moiety and makes the acidic proton of the anilinium unit more acidic.The work described in this thesis provides further understanding of the triplet photosensitized reactions first reported in the early 1960s, and it applies this important organic photoreaction in the context of renewable energy. Furthermore, the last part of this thesis contributes to new interpretations of photoacidity.
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| 6. |
- Dunlop, David, et al.
(författare)
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Excited-State (Anti)Aromaticity Explains Why Azulene Disobeys Kasha's Rule
- 2023
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 145:39, s. 21569-21575
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescence exclusively occurs from the lowest excited state of a given multiplicity according to Kasha's rule. However, this rule is not obeyed by a handful of anti-Kasha fluorophores whose underlying mechanism is still understood merely on a phenomenological basis. This lack of understanding prevents the rational design and property-tuning of anti-Kasha fluorophores. Here, we propose a model explaining the photophysical properties of an archetypal anti-Kasha fluorophore, azulene, based on its ground- and excited-state (anti)aromaticity. We derived our model from a detailed analysis of the electronic structure of the ground singlet, first excited triplet, and quintet states and of the first and second excited singlet states using the perturbational molecular orbital theory and quantum-chemical aromaticity indices. Our model reveals that the anti-Kasha properties of azulene and its derivatives result from (i) the contrasting (anti)aromaticity of its first and second singlet excited states (S-1 and S-2, respectively) and (ii) an easily accessible antiaromaticity relief pathway of the S-1 state. This explanation of the fundamental cause of anti-Kasha behavior may pave the way for new classes of anti-Kasha fluorophores and materials with long-lived, high-energy excited states.
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| 7. |
- El Bakouri, Ouissam, et al.
(författare)
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Strategies for Design of Potential Singlet Fission Chromophores Utilizing a Combination of Ground-State and Excited-State Aromaticity Rules
- 2020
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 142:12, s. 5602-5617
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Tidskriftsartikel (refereegranskat)abstract
- Singlet exciton fission photovoltaic technology requires chromophores with their lowest excited states arranged so that 2E(T-1) < E(S-1) and E(S-1) < E(T-2). Herein, qualitative theory and quantum chemical calculations are used to develop explicit strategies on how to use Baird's 4n rule on excited-state aromaticity, combined with Huckel's 4n + 2 rule for ground-state aromaticity, to tailor new potential chromophores for singlet fission. We first analyze the E(T-1), E(S-1), and E(T-2) of benzene and cyclobutadiene (CBD) as excited-state antiaromatic and aromatic archetypes, respectively, and reveal that CBD fulfills the criteria on the state ordering for a singlet fission chromophore. We then look at fulvenes, a class of compounds that can be tuned by choice of substituents from Baird-antiaromatic to Baird-aromatic in T-1 and S-1 and from Huckel-aromatic to Huckel-antiaromatic in S-0. The T-1 and S-1 states of most substituted fulvenes (159 of 225) are described by singly excited HOMO -> LUMO configurations, providing a rational for the simultaneous tuning of E(T-1) and E(S-1) along an approximate (anti)aromaticity coordinate. Key to the tunability is the exchange integral (K-H,K-L), which ideally is constant throughout the compound class, providing a constant.E(S-1 - T-1). This leads us to a geometric model for the identification of singlet fission chromophores, and we explore what factors limit the model. Candidates with calculated E(T-1) values of similar to 1 eV or higher are identified among benzannelated 4npelectron compound classes and siloles. In brief, it is clarified how the joint utilization of Baird's 4n and Huckel's 4n + 2 rules, together with substituent effects (electronic and steric) and benzannelation, can be used to tailor new chromophores with potential use in singlet fission photovoltaics.
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| 8. |
- El Bakouri, Ouissam, et al.
(författare)
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Three-Dimensional Fully π-Conjugated Macrocycles : When 3D-Aromatic and When 2D-Aromatic-in-3D?
- 2022
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:19, s. 8560-8575
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Tidskriftsartikel (refereegranskat)abstract
- Several fully π-conjugated macrocycles with puckered or cage-type structures were recently found to exhibit aromatic character according to both experiments and computations. We examine their electronic structures and put them in relation to 3D-aromatic molecules (e.g., closo-boranes) and to 2D-aromatic polycyclic aromatic hydrocarbons. Using qualitative theory combined with quantum chemical calculations, we find that the macrocycles explored hitherto should be described as 2D-aromatic with three-dimensional molecular structures (abbr. 2D-aromatic-in-3D) and not as truly 3D-aromatic. 3D-aromatic molecules have highly symmetric structures (or nearly so), leading to (at least) triply degenerate molecular orbitals, and for tetrahedral or octahedral molecules, an aromatic closed-shell electronic structure with 6n + 2 electrons. Conversely, 2D-aromatic-in-3D structures exhibit aromaticity that results from the fulfillment of Hückel’s 4n + 2 rule for each macrocyclic path, yet their π-electron counts are coincidentally 6n + 2 numbers for macrocycles with three tethers of equal lengths. It is notable that 2D-aromatic-in-3D macrocyclic cages can be aromatic with tethers of different lengths, i.e., with π-electron counts different from 6n + 2, and they are related to naphthalene. Finally, we identify tetrahedral and cubic π-conjugated molecules that fulfill the 6n + 2 rule and exhibit significant electron delocalization. Yet, their properties resemble those of analogous compounds with electron counts that differ from 6n + 2. Thus, despite the fact that these molecules show substantial π-electron delocalization, they cannot be classified as true 3D-aromatics.
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| 9. |
- Escayola, Silvia, et al.
(författare)
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Guidelines for Tuning the Excited State Huckel-Baird Hybrid Aromatic Character of Pro-Aromatic Quinoidal Compounds**
- 2021
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Ingår i: Angewandte Chemie International Edition. - : John Wiley & Sons. - 1433-7851 .- 1521-3773. ; 60:18, s. 10255-10265
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Tidskriftsartikel (refereegranskat)abstract
- Pro-aromatic molecules have higher-energy diradicaloid states that are significantly influenced by resonance structures in which conjugated rings take on Huckel-aromatic character. Recently, it has been argued that there are also pro-aromatic molecules that adopt central units with 4n pi-electron Baird-aromatic character in the T-1 state, although detailed analysis suggests that these compounds are better labelled as T-1 Huckel-Baird hybrid molecules where Huckel-aromaticity dominates. Herein, we consider a series of symmetrically substituted conjugated rings with potential Baird aromaticity in the lowest excited triplet and singlet states. Our computational results allow us to establish general guidelines for the rational design of molecules with excited state Huckel/Baird aromaticity in pro-aromatic quinoidal compounds. We found two main strategies to promote high Baird aromatic character: 1) anionic and small conjugated rings with electron donating groups as substituents and small exocyclic groups with electron withdrawing substituents, or 2) electron deficient conjugated rings with exocyclic electron-donor substitution.
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| 10. |
- Escayola, Silvia, et al.
(författare)
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In the quest of Huckel-Huckel and Huckel-Baird double aromatic tropylium (tri)cation and anion derivatives
- 2023
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Ingår i: Journal of Physical Organic Chemistry. - : John Wiley & Sons. - 0894-3230 .- 1099-1395. ; 36:1
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Tidskriftsartikel (refereegranskat)abstract
- Besides the most common form of aromaticity involving a pi-ring, hexaiodobenzene and hexakis(phenylselenyl)benzene dications also present sigma-aromaticity in the outer ring formed by the main group substituents. These two compounds are considered sigma- and pi-double aromatic, and their characterization is of special interest to the fields of organic and structural chemistry. In this work, we decided to explore the double aromaticity in substituted tropylium cations for three reasons: (i) the seven neutral halogen substituents of the tropylium cations will, without oxidation, lead to 14 sigma-electrons (a 4n + 2 Huckel number); (ii) tropylium cations are highly stable and can be easily generated experimentally; and (iii) whereas in substituted benzenes the distances between substituents in the optimized structures or X-ray crystals are too large to allow strong sigma-aromaticity, these distances are expected to be shorter in substituted tropylium cations. Yet, instead of the expected sigma-aromaticity, we found that the most stable geometries are highly puckered, meaning that delocalization in both pi- and sigma-systems is lost. Our results, which include also the tropylium anion and trication in the singlet and triplet state, show that there is a need to open a lone pair hole by oxidation to generate sigma-aromaticity. Among the systems studied, only triplet C7Br7+3 with an internal Huckel aromatic tropylium ring and an external incipient Baird aromatic Br-7 ring shows double pi- and sigma-aromaticity. This result, however, is functional-dependent and reveals that (C7Br73+)-C-3 is at the borderline for onset of double aromaticity.
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| 11. |
- Gazdag, Tamás, et al.
(författare)
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An Exploration of Substituent Effects on the Photophysical Properties of Monobenzopentalenes
- 2024
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Ingår i: ChemPhysChem. - : Wiley-VCH Verlagsgesellschaft. - 1439-7641 .- 1439-4235. ; 25:7
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Tidskriftsartikel (refereegranskat)abstract
- Monobenzopentalenes have received moderate attention compared to dibenzopentalenes, yet their accessibility as stable, non-symmetric structures with diverse substituents could be interesting for materials applications, including molecular photonics. Recently, monobenzopentalene was considered computationally as a potential chromophore for singlet fission (SF) photovoltaics. To advance this compound class towards photonics applications, the excited state energetics must be characterized, computationally and experimentally. In this report we synthesized a series of stable substituted monobenzopentalenes and provided the first experimental exploration of their photophysical properties. Structural and opto-electronic characterization revealed that all derivatives showed 1H NMR shifts in the olefinic region, bond length alternation in the pentalene unit, low-intensity absorptions reflecting the ground-state antiaromatic character and in turn the symmetry forbidden HOMO-to-LUMO transitions of ~2 eV and redox amphotericity. This was also supported by computed aromaticity indices (NICS, ACID, HOMA). Accordingly, substituents did not affect the fulfilment of the energetic criterion of SF, as the computed excited-state energy levels satisfied the required E(S1)/E(T1)>2 relationship. Further spectroscopic measurements revealed a concentration dependent quenching of the excited state and population of the S2 state on the nanosecond timescale, providing initial evidence for unusual photophysics and an alternative entry point for singlet fission with monobenzopentalenes.
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| 12. |
- Jafri, Syed Hassan Mujtaba, 1979-, et al.
(författare)
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Nanomolecular electronic devices based on AuNP molecule nanoelectrodes using molecular place-exchange process
- 2020
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Ingår i: Nanotechnology. - : IOP PUBLISHING LTD. - 0957-4484 .- 1361-6528. ; 31:22
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Tidskriftsartikel (refereegranskat)abstract
- The implementation of electronics applications based on molecular electronics devices is hampered by the difficulty of placing a single or a few molecules with application-specific electronic properties in between metallic nanocontacts. Here, we present a novel method to fabricate 20 nm sized nanomolecular electronic devices (nanoMoED) using a molecular place-exchange process of nonconductive short alkyl thiolates with various short chain conductive oligomers. After the successful place-exchange with short-chain conjugated oligomers in the nanoMoED devices, a change in device resistance of up to four orders of magnitude for 4,4 '-biphenyldithiol (BPDT), and up to three orders of magnitude for oligo phenylene-ethynylene (OPE), were observed. The place-exchange process in nanoMoEDs are verified by measuring changes in device resistance during repetitive place-exchange processes between conductive and nonconductive molecules and surface-enhanced Raman spectroscopy. This opens vast possibilities for the fabrication and application of nanoMoED devices with a large variety of molecules.
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| 13. |
- Jorner, Kjell, et al.
(författare)
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Degradation of Pharmaceuticals through Sequential Photon Absorption and Photoionization in Amiloride Derivatives
- 2020
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Ingår i: Cell Reports Physical Science. - : Elsevier BV. - 2666-3864. ; 1:12
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Tidskriftsartikel (refereegranskat)abstract
- Haloaromatic drug molecules of the amiloride family are plagued by photodegradation with associated toxicity. Herein, we report on the photodegradation of analogs of amiloride, which are known to undergo photosubstitution in water. Model compounds built on the same scaffold undergo clean photosubstitution also in alcoholic solvent, where a certain amount of photodehalogenation is normally expected. Available evidence points to a mechanism starting with photoexcitation followed by photoionization to give a radical cation intermediate. Subsequent substitution reaction with the protic solvent is assisted by a general base, possibly strengthened by the proximal solvated electron. Recombination with the solvated electron generates the observed product. Quantum chemical computations reveal that excited state antiaromaticity is relieved when an electron is ejected from the photoexcited molecule by the second photon. The mechanism indicated here could have wide applicability to photoinduced degradation of similar heteroaromatic compounds in the environment, as well as to a class of increasingly popular synthetic photoredox methods.
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| 14. |
- Karas, Lucas J., et al.
(författare)
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Electron-driven proton transfer relieves excited-state antiaromaticity in photoexcited DNA base pairs
- 2020
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 11:37, s. 10071-10077
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Tidskriftsartikel (refereegranskat)abstract
- The Watson-Crick A.T and G.C base pairs are not only electronically complementary, but also photochemically complementary. Upon UV irradiation, DNA base pairs undergo efficient excited-state deactivation through electron driven proton transfer (EDPT), also known as proton-coupled electron transfer (PCET), at a rate too fast for other reactions to take place. Why this process occurs so efficiently is typically reasoned based on the oxidation and reduction potentials of the bases in their electronic ground states. Here, we show that the occurrence of EDPT can be traced to a reversal in the aromatic/antiaromatic character of the base upon photoexcitation. The Watson-Crick A.T and G.C base pairs are aromatic in the ground state, but the purines become highly antiaromatic and reactive in the first 1(pi pi)* state, and transferring an electron and a proton to the pyrimidine relieves this excited-state antiaromaticity. Even though proton transfer proceeds along the coordinate of breaking a N-H pi-bond, the chromophore is the pi-system of the base, and EDPT is driven by the strive to alleviate antiaromaticity in the pi-system of the photoexcited base. The presence and absence of alternative excited-state EDPT routes in base pairs also can be explained by sudden changes in their aromatic and antiaromatic character upon photoexcitation.
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| 15. |
- Mayer, Peter J., et al.
(författare)
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Structure–Property Relationships in Unsymmetric Bis(antiaromatics) : Who Wins the Battle between Pentalene and Benzocyclobutadiene?
- 2020
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 85:8, s. 5158-5172
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Tidskriftsartikel (refereegranskat)abstract
- According to the currently accepted structure-property relationships, aceno-pentalenes with an angular shape (fused to the 1,2-bond of the acene) exhibit higher antiaromaticity than those with a linear shape (fused to the 2,3-bond of the acene). To explore and expand the current view, we designed and synthesized molecules where two isomeric, yet, different, 8 pi antiaromatic subunits, a benzocyclobutadiene (BCB) and a pentalene, are combined into, respectively, an angular and a linear topology via an unsaturated six-membered ring. The antiaromatic character of the molecules is supported experimentally by H-1 NMR, UV-vis, and cyclic voltammetry measurements and X-ray crystallography. The experimental results are further confirmed by theoretical studies including the calculation of several aromaticity indices (NICS, ACID, HOMA, FLU, MCI). In the case of the angular molecule, double bond-localization within the connecting six-membered ring resulted in reduced antiaromaticity of both the BCB and pentalene subunits, while the linear structure provided a competitive situation for the two unequal [4n]pi subunits. We found that in the latter case the BCB unit alleviated its unfavorable antiaromaticity more efficiently, leaving the pentalene with strong antiaromaticity. Thus, a reversed structure-antiaromaticity relationship when compared to aceno-pentalenes was achieved.
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| 16. |
- Ottosson, Henrik
(författare)
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A focus on aromaticity : fuzzier than ever before?
- 2023
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 14:21, s. 5542-5544
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The field of aromaticity has grown five-fold in the last two decades as revealed by Merino et al. in their Perspective "Aromaticity: Quo Vadis" where they ask where the field is heading (Chem. Sci., 2023, https://doi.org/10.1039/D2SC04998H). Numerous computational tools for aromaticity analysis have been introduced and novel classes of molecules that exhibit aromatic (or antiaromatic) features have been explored experimentally. Hence, the aromaticity concept is broader and possibly fuzzier than ever. Yet, earlier it also triggered vigorous debates after periods when new analysis tools emerged, and it survived. Today's debate reveals that the field is vital and that new knowledge is produced. Yet, as much as we ask where the field is moving, we should ask "Aromaticity: Cui Bono?"; who utilizes the aromaticity concept and who benefits from it? Especially, who benefits from it being overly fuzzy and who does the opposite? It is an exciting debate. We should get out of it with a better understanding of the chemical-bonding phenomenon labelled aromaticity.
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| 17. |
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| 18. |
- Pati, Avik K., et al.
(författare)
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Tuning the Baird aromatic triplet-state energy of cyclooctatetraene to maximize the self-healing mechanism in organic fluorophores
- 2020
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences (PNAS). - 0027-8424 .- 1091-6490. ; 117:39, s. 24305-24315
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Tidskriftsartikel (refereegranskat)abstract
- Bright, photostable, and nontoxic fluorescent contrast agents are critical for biological imaging. "Self-healing" dyes, in which triplet states are intramolecularly quenched, enable fluorescence imaging by increasing fluorophore brightness and longevity, while simultaneously reducing the generation of reactive oxygen species that promote phototoxicity. Here, we systematically examine the self-healing mechanism in cyanine-class organic fluorophores spanning the visible spectrum. We show that the Baird aromatic triplet-state energy of cyclooctatetraene can be physically altered to achieve order of magnitude enhancements in fluorophore brightness and signal-to-noise ratio in both the presence and absence of oxygen. We leverage these advances to achieve direct measurements of large-scale conformational dynamics within single molecules at submillisecond resolution using wide-field illumination and camera-based detection methods. These findings demonstrate the capacity to image functionally relevant conformational processes in biological systems in the kilohertz regime at physiological oxygen concentrations and shed important light on the multivariate parameters critical to self-healing organic fluorophore design.
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| 19. |
- Poater, Jordi, et al.
(författare)
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Single-Not Double-3D-Aromaticity in an Oxidized Closo Icosahedral Dodecaiodo-Dodecaborate Cluster
- 2023
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 145:41, s. 22527-22538
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Tidskriftsartikel (refereegranskat)abstract
- 3D-aromatic molecules with (distorted) tetrahedral, octahedral, or spherical structures are much less common than typical 2D-aromatic species or even 2D-aromatic-in-3D systems. Closo boranes, [BnHn](2-) (5 = n = 14) and carboranes are examples of compounds that are singly 3D-aromatic, and we now explore if there are species that are doubly 3D-aromatic. The most widely known example of a species with double 2D-aromaticity is the hexaiodobenzene dication, [C6I6](2+). This species shows p-aromaticity in the benzene ring and s-aromaticity in the outer ring formed by the iodine substituents. Inspired by the hexaiodobenzene dication example, in this work, we explore the potential for double 3D-aromaticity in [B12I12](0/2+). Our results based on magnetic and electronic descriptors of aromaticity together with B-11{H-1} NMR experimental spectra of boron-iodinated o-carboranes suggest that these two oxidized forms of a closo icosahedral dodecaiodo-dodecaborate cluster, [B12I12] and [B12I12](2+), behave as doubly 3D-aromatic compounds. However, an evaluation of the energetic contribution of the potential double 3D-aromaticity through homodesmotic reactions shows that delocalization in the I-12 shell, in contrast to the 10s-electron I-6(2+) ring in the hexaiodobenzene dication, does not contribute to any stabilization of the system. Therefore, the [B12I12](0/2+) species cannot be considered as doubly 3D-aromatic.
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| 20. |
- Preethalayam, Preethanuj, et al.
(författare)
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Azaboracyclooctatetraenes reveal that the different aspects of triplet state Baird-aromaticity are nothing but different
- 2023
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Ingår i: Journal of Physical Organic Chemistry. - : John Wiley & Sons. - 0894-3230 .- 1099-1395. ; 36:1
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Tidskriftsartikel (refereegranskat)abstract
- The Baird-aromaticity of BN/CC cyclooctatetraene isosteres (azaboracyclooctatetraenes) in their lowest triplet states (T1) has been explored through computations of various aromaticity indices that describe the different aspects of aromaticity (magnetic, electronic, energetic and geometric). While cyclooctatetraene (COT) is aromatic in its T1 state following Baird's 4n rule, we now reveal that the degrees of Baird-aromaticity of its BN/CC isosteres vary with aromaticity aspect considered. The thermodynamically most stable octagonal B4N4H8 isomer, having an alternating B and N pattern (borazocine, B4N4COT-A), is only weakly aromatic or nonaromatic in T1 according to energetic and electronic indices, while magnetic descriptors suggest it to have about two thirds the Baird-aromaticity of T1 state COT (3COT). The extent of Baird-aromaticity of intermediate BN/CC isosteres also varies markedly with aromaticity aspect considered. The strong aromaticity of 3B4N4COT-A according to magnetic descriptors can be linked to the symmetries of the orbitals involved in the virtual transitions from occupied to unoccupied orbitals, which describe the response of a molecule in an external magnetic field. However, the magnetic aspect of T1 state Baird-aromaticity (response aromaticity) is not related to the electronic and energetic aspects (intrinsic aromaticity), findings that underline earlier observations on differences between the various aspects of the aromaticity phenomenon (or phenomena).
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| 21. |
- Proos Vedin, Nathalie, 1992-
(författare)
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Shining Light on the Molecular Jewellery : Excited State (Anti)Aromaticity Assessment of Small Heterocycles
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis explores the lowest excited states of heteroaromatics. Focus is put on how to properly examine and define their degree of aromaticity or antiaromaticity, as well as on the factors influencing this excited state (anti)aromaticity (ES(A)A) and other photochemical phenomena of importance.Firstly, the inorganic version of cyclooctatetraene (COT), borazocine (B4N4H8), and intermediate isosteres are studied. The determination of aromatic character in the T1 state is found to be ambiguous, with different conclusions drawn depending on the descriptor employed. The importance of applying several aromaticity indices to ensure proper characterisation is reaffirmed, and it is suggested that more such challenging cases should be identified.Focus is then shifted to the character of the lowest excited states, which in heterocycles is not limited to π,π*. Because of the in-plane lone-pair nσ orbital(s) provided by the heteroatom(s), the photochemically most relevant states (S1 and T1) are often of n,π* character. This is also the case for equivalent compounds like carbenes. The aromatic character of such odd-π-electron states, which do not conform to the well-known Baird's rule for excited (π,π*) states, is explored. The analysis requires separation of the π-electron spins (α and β), in accordance with Mandado's rule. When the two contributions are added together a residual may emerge, and the result is found to depend on factors such as electronegativity and symmetry. Examples of all possible outcomes are identified, with some ground state aromatic compounds even becoming more aromatic in the excited state than in S0.The findings are also related to the order of the lowest excited states and whether this is possible to predict. Factors affecting the energy of the nσ orbital, such as electronegativity, bond angle and intraorbital repulsion, influence this. Possibilities for tuning the order are presented.Finally, the photochemical process of triplet state photoionisation is investigated. No general relation between the degree of ES(A)A and the photoionisation potential is observed, and thus, the factors that affect these parameters are explored more closely. Aspects related to how strongly the electrons are held and to symmetry are found to influence both.The work presented in this thesis enhances our understanding of the degree of aromaticity and antiaromaticity in excited heterocycles, and clarifies the approach with which to assess it. Insight into how this parameter relates to the character of the lowest excited state and other significant properties is also provided. The generality of the findings are discussed, paving the way towards predictive schemes for future applications within fields such as catalysis, medicine and beyond.
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| 22. |
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| 23. |
- Rana, Anup, et al.
(författare)
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A combined photobiological-photochemical route to C10 cycloalkane jet fuels from carbon dioxide via isoprene
- 2022
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Ingår i: Green Chemistry. - : Royal Society of Chemistry. - 1463-9262 .- 1463-9270. ; 24, s. 9602-
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Tidskriftsartikel (refereegranskat)abstract
- The hemiterpene isoprene is a volatile C5 hydrocarbon with industrial applications. It is generated today from fossil resources, but can also be made in biological processes. We have utilized engineered photosynthetic cyanobacteria for direct, light-driven production of bio-isoprene from carbon dioxide, and show that isoprene in a subsequent photochemical step, using either near-UV or simulated or natural solar light, can be dimerized into limonene, paradiprene, and isomeric C10H16 hydrocarbons (monoterpenes) in high yields under photosensitized conditions (above 90% after 44 hours with near-UV and 61% with simulated solar light). The optimal sensitizer in our experiments is di(naphth-1-yl)methanone which we use with a loading of 0.1 mol%. It can also easily be recycled for subsequent photodimerization cycles. The isoprene dimers generated are a mixture of [2 + 2], [4 + 2] and [4 + 4] cycloadducts, and after hydrogenation this mixture is nearly ideal as a drop-in jet fuel. Importantly the photodimerization can be carried out at ambient conditions. However, the high content of hydrogenated [2 + 2] dimers in our isoprene dimer mix lowers the flash point below the threshold (38 °C); yet, these dimers can be converted thermally into [4 + 2] and [4 + 4] dimers. When hydrogenated these monoterpenoids fully satisfy the criteria for drop-in jet fuels with regard to energy density, flashpoint, kinematic viscosity, density, and freezing point. Life-cycle assessment results show a potential to produce the fuel in an environmentally sustainable way.
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| 24. |
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| 25. |
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| 26. |
- Rasmussen, Josefine, 1988-, et al.
(författare)
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CONSENSYS: Controllern – en outforskad aktör i omställningen mot hållbara energisystem : Resultat och praktiska implikationer
- 2024
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Denna rapport är en sammanfattning av de huvudresultat och praktiska implikationer som forskningsprojektet Controllern – en outforskad aktör i omställningen mot hållbara energisystem (CONSENSYS) [2019-006322] resulterat i. CONSENSYS har pågått 2020-2023 och har finansierats av Energimyndighetens forskningsprogram MESAMs (Människa, Energisystem och Samhälle) andra omgång (Energimyndigheten, 2019). En controller är en specialist inom ekonomistyrning och agerar vanligtvis som rådgivare för ledningen eller ekonomichefen. Controllern ansvarar för att samla in ekonomisk information från olika avdelningar och presentera resultatet för ledningsgruppen eller ekonomiavdelningen inom större organisationer. Allt fler controllers arbetar idag även med hållbarhetsarbete som att upprätta en organisations hållbarhetsredovisning enligt internationella ramverk och att utveckla hållbarhetsarbetet. I det här arbetet är det även centralt att integrera finansiella data med olika typer av hållbarhetsdata.Projektets syfte har varit att studera controllerns roll i energiintensiva företags energi- och hållbarhetsstyrning. Med den här rapporten hoppas vi kunna sprida insikter och kunskap om energi- och hållbarhetsstyrning med ett särskilt fokus på controllerns roll. Rapporten riktar sig därmed i första hand till controllers och ekonomichefer, men också till andra funktioner såsom energi- och hållbarhetsansvariga som i sitt arbete på olika sätt samarbetar med controllers. Projektet har studerat företag inom svensk energiintensiv industri. I ljuset av det ökade fokus energi- och hållbarhetsfrågor får idag bör dock flera av de utmaningar vi identifierar förekomma även i andra industrier och projektets resultat och praktiska implikationer bör därför vara till nytta även för företag i andra industrier.
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| 27. |
- Rasmussen, Josefine, 1988-
(författare)
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Management control for sustainability : Activities and procedures for energy management in industrial companies
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis takes its point of departure in the important role of the industrial sector in mitigating climate change through a reduced energy use. There is a lack of understanding for how energy management should be organised and implemented in industrial companies. The aim of this thesis is therefore to analyse the management control activities and procedures used by energyintensive industrial companies for energy management and one of its key elements—energy efficiency investments. The thesis also examines how so-called non-energy benefits are considered for energy efficiency investments and their role in driving these investments. The thesis consists of a cover essay and four appended papers, one of which is based on a systematic literature review of benefit concepts applied in the context of energy efficiency investments. The remaining papers build on three empirical studies in Swedish manufacturing and process industries with a particular focus on the pulp and paper industry.Energy management is an important aspect of sustainability for the industrial sector. This thesis advances the understanding of management control for energy management by bridging the theoretical domains of energy management and sustainability management control. The thesis acknowledges both the strategic and operational dimensions of energy management, going beyond the predominating operational perspective, and illuminates the way in which both dimensions are reflected in management control practices. The role of established organisational arrangements spanning different functions and levels is identified. A framework for categorising non-energy benefits is also developed, which may facilitate their inclusion in the investment process. However, the configuration of management control activities and procedures applied for the investment process is essential for the extent to which non-energy benefits can be acknowledged during investment decision-making. Through its emphasis on management control activities and procedures for energy management, this thesis contributes to the managerial path of sustainability management control, providing both theoretical and managerial contributions. Altogether, the four studies constituting this thesis illuminate the need for adequate tools and methods in the transition to a sustainable industrial sector and the role of management control configurations in this endeavour.
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| 28. |
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| 29. |
- Shoji, Yoshiaki, et al.
(författare)
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Inside Cover : An Element-Substituted Cyclobutadiene Exhibiting High-Energy Blue Phosphorescence (Angew. Chem. Int. Ed. 40/2021)
- 2021
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Ingår i: Angewandte Chemie International Edition. - : John Wiley & Sons. - 1433-7851 .- 1521-3773. ; 60:40, s. 21598-21598
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Tidskriftsartikel (refereegranskat)abstract
- The ground- and excited-state properties of a diazadiboretidine (DADBT) derivative, an isoelectronic heterocyclic analogue of cyclobutadiene, are reported by Henrik Ottosson, Hiromi Nakai, Tadaaki Ikoma, Takanori Fukushima, and co-workers in their Research Article on page 21817. While the B2N2 ring of the DADBT derivative adopts a rhombic geometry in the ground state, it turns to a square geometry with a nonaromatic character in the lowest triplet state. Notably, the DADBT derivative displays blue phosphorescence in solution, providing insight into the photophysical properties of heterocyclic pi-systems.+
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| 30. |
- Slanina, Tomáš, et al.
(författare)
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Impact of Excited-State Antiaromaticity Relief in a Fundamental Benzene Photoreaction Leading to Substituted Bicyclo[3.1.0]hexenes
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 142:25, s. 10942-10954
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Tidskriftsartikel (refereegranskat)abstract
- Benzene exhibits a rich photochemistry which can provide access to complex molecular scaffolds that are difficult to access with reactions in the electronic ground state. While benzene is aromatic in its ground state, it is antiaromatic in its lowest ππ∗ excited states. Herein, we clarify to what extent relief of excited-state antiaromaticity (ESAA) triggers a fundamental benzene photoreaction: the photoinitiated nucleophilic addition of solvent to benzene in acidic media leading to substituted bicyclo[3.1.0]hex-2-enes. The reaction scope was probed experimentally, and it was found that silyl-substituted benzenes provide the most rapid access to bicyclo[3.1.0]hexene derivatives, formed as single isomers with three stereogenic centers in yields up to 75% in one step. Two major mechanism hypotheses, both involving ESAA relief, were explored through quantum chemical calculations and experiments. The first mechanism involves protonation of excited-state benzene and subsequent rearrangement to bicyclo[3.1.0]hexenium cation, trapped by a nucleophile, while the second involves photorearrangement of benzene to benzvalene followed by protonation and nucleophilic addition. Our studies reveal that the second mechanism is operative. We also clarify that similar ESAA relief leads to puckering of S1-state silabenzene and pyridinium ion, where the photorearrangement of the latter is of established synthetic utility. Finally, we identified causes for the limitations of the reaction, information that should be valuable in explorations of similar photoreactions. Taken together, we reveal how the ESAA in benzene and 6π-electron heterocycles trigger photochemical distortions that provide access to complex three-dimensional molecular scaffolds from simple reactants.
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| 31. |
- Vajravel, Sindhujaa, et al.
(författare)
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Toward combined photobiological-photochemical formation of kerosene-type biofuels : which small 1,3-diene photodimerizes most efficiently?
- 2023
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Ingår i: Photochemical and Photobiological Sciences. - : Springer. - 1474-905X .- 1474-9092. ; 22:8, s. 1875-1888
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Tidskriftsartikel (refereegranskat)abstract
- A transition from fossil- to bio-based hydrocarbon fuels is required to reduce greenhouse gas emissions; yet, traditional biomass cultivation for biofuel production competes with food production and impacts negatively on biodiversity. Recently, we reported a proof-of-principle study of a two-step photobiological–photochemical approach to kerosene biofuels in which a volatile hydrocarbon (isoprene) is produced by photosynthetic cyanobacteria, followed by its photochemical dimerization into C10 hydrocarbons. Both steps can utilize solar irradiation. Here, we report the triplet state (T1)-sensitized photodimerization of a broader set of small 1,3-dienes to identify which structural features lead to rapid photodimerization. Neat 1,3-cyclohexadiene gave the highest yield (93%) after 24 h of irradiation at 365 nm, followed by isoprene (66%). The long triplet lifetime of 1,3-cyclohexadiene, which is two orders of magnitude longer than those of acyclic dienes, is key to its high photoreactivity and stem from its planar T1 state structure. In contrast, while isoprene is conformationally flexible, it has both photochemical and photobiological advantages, as it is the most reactive among the volatile 1,3-dienes and it can be produced by cyanobacteria. Finally, we explored the influence of solvent viscosity, diene concentration, and triplet sensitizer loading on the photodimerization, with a focus on conditions that are amenable when the dienes are produced photobiologically. Our findings should be useful for the further development of the two-step photobiological–photochemical approach to kerosene biofuels.
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| 32. |
- Yan, Jiajie, et al.
(författare)
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Photochemistry Driven by Excited-State Aromaticity Gain or Antiaromaticity Relief
- 2023
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Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 29:19
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Forskningsöversikt (refereegranskat)abstract
- Gain of aromaticity or relief of antiaromaticity along a reaction path are important factors to consider in mechanism studies. Analysis of such changes along potential energy surfaces has historically focused on reactions in the electronic ground state (S-0), but can also be used for excited states. In the lowest pi pi* states, the electron counts for aromaticity and antiaromaticity follow Baird's rule where 4n pi-electrons indicate aromaticity and 4n+2 pi-electrons antiaromaticity. Yet, there are also cases where Huckel's rule plays a role in the excited state. The electron count reversals of Baird's rule compared to Huckel's rule explain many altered physicochemical properties upon excitation of (hetero)annulene derivatives. Here we illustrate how the gain of excited-state aromaticity (ESA) and relief of excited-state antiaromaticity (ESAA) have an impact on photoreactivity and photostability. Emphasis is placed on recent findings supported by the results of quantum chemical calculations, and photoreactions in a wide variety of areas are covered.
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| 33. |
- Zeng, Weixuan, et al.
(författare)
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Excited state character of Cibalackrot-type compounds interpreted in terms of Hückel-aromaticity : a rationale for singlet fission chromophore design
- 2021
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 12:17, s. 6159-6171
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Tidskriftsartikel (refereegranskat)abstract
- The exact energies of the lowest singlet and triplet excited states in organic chromophores are crucial to their performance in optoelectronic devices. The possibility of utilizing singlet fission to enhance the performance of photovoltaic devices has resulted in a wide demand for tuneable, stable organic chromophores with wide S1–T1 energy gaps (>1 eV). Cibalackrot-type compounds were recently considered to have favorably positioned excited state energies for singlet fission, and they were found to have a degree of aromaticity in the lowest triplet excited state (T1). This work reports on a revised and deepened theoretical analysis taking into account the excited state Hückel-aromatic (instead of Baird-aromatic) as well as diradical characters, with the aim to design new organic chromophores based on this scaffold in a rational way starting from qualitative theory. We demonstrate that the substituent strategy can effectively adjust the spin distribution on the chromophore and thereby manipulate the excited state energy levels. Additionally, the improved understanding of the aromatic characters enables us to demonstrate a feasible design strategy to vary the excited state energy levels by tuning the number and nature of Hückel-aromatic units in the excited state. Finally, our study elucidates the complications and pitfalls of the excited state aromaticity and antiaromaticity concepts, highlighting that quantitative results from quantum chemical calculations of various aromaticity indices must be linked with qualitative theoretical analysis of the character of the excited states.
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