| 1. |
- 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. - 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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| 2. |
- Kalapos, Peter Pal, et al.
(författare)
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Photoswitching of Local (Anti)Aromaticity in Biphenylene-Based Diarylethene Molecular Switches
- 2022
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 87:15, s. 9532-9542
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Tidskriftsartikel (refereegranskat)abstract
- Photoinduced tuning of (anti)aromaticity and associated molecular properties is currently in the focus of attention for both tailoring photochemical reactivity and designing new materials. Here, we report on the synthesis and spectroscopic characterization of diarylethene-based molecular switches embedded in a biphenylene structure composed of rings with different levels of local (anti)aromaticity. We show that it is possible to modulate and control the (anti)aromatic character of each ring through reversible photoswitching of the aryl units of the system between open and closed forms. Remarkably, it is shown that the irreversible formation of an annulated bis(dihydro-thiopyran) side-product that hampers the photoswitching can be efficiently suppressed when the aryl core formed by thienyl groups in one switch is replaced by thiazolyl groups in another.
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| 3. |
- Kalapos, Peter Pal, et al.
(författare)
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Salicylideneaniline/Dithienylethene Hybrid Molecular Switches: Design, Synthesis, and Photochromism
- 2023
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Ingår i: Journal of Organic Chemistry. - : AMER CHEMICAL SOC. - 0022-3263 .- 1520-6904. ; 89:1, s. 16-26
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Tidskriftsartikel (refereegranskat)abstract
- A hybrid molecular switch comprising salicylideneaniline (SA) and dithienylethene (DTE) moieties around a single benzene ring is reported. Due to an interplay between solvent-assisted enol-keto tautomerization in the former moiety and photochromic electrocyclization in the latter, this dithienylbenzene derivative was found to be photoresponsive at room temperature with a thermally stable closed form. The main photoproduct featuring ring-closed DTE and keto-enamine SA structures could be isolated and converted back to the starting material by irradiation with visible light. The optical properties of the potential structures involved in the overall process were characterized by using density functional theory (DFT) calculations in good agreement with the measured data. The reversibility of the conversion could be tuned by the presence of donor and acceptor substituents, while the introduction of the imine in the form of a benzothiazole moiety enabled photochemistry even in nonprotic solvents.
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| 4. |
- 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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| 5. |
- Oruganti, Baswanth, et al.
(författare)
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Photoinduced Changes in Aromaticity Facilitate Electrocyclization of Dithienylbenzene Switches
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 142:32, s. 13941-13953
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Tidskriftsartikel (refereegranskat)abstract
- The concepts of excited-state aromaticity and antiaromaticity have in recent years with increasing frequency been invoked to rationalize the photochemistry of cyclic conjugated organic compounds, with the long-term goal of using these concepts to improve the reactivities of such compounds toward different photochemical transformations. In this regard, it is of particular interest to assess how the presence of a benzene motif affects photochemical reactivity, as benzene is well-known to completely change its aromatic character in its lowest excited states. Here, we investigate how a benzene motif influences the photoinduced electrocyclization of dithienylethenes, a major class of molecular switches. Specifically, we report on the synthesis of a dithienylbenzene switch where the typical nonaromatic, ethene-like motif bridging the two thienyl units is replaced by a benzene motif, and show that this compound undergoes electrocyclization upon irradiation with UV-light. Furthermore, through a detailed quantum chemical analysis, we demonstrate that the electrocyclization is driven jointly and synergistically by the loss of aromaticity in this motif from the formation of a reactive, antiaromatic excited state during the initial photoexcitation, and by the subsequent relief of this antiaromaticity as the reaction progresses from the Franck-Condon region. Overall, we conclude that photoinduced changes in aromaticity facilitate the electrocyclization of dithienylbenzene switches.
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