| 1. |
- Gotfredsen, Henrik, et al.
(författare)
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Donor-Acceptor-Functionalized Subphthalocyanines for Dye-Sensitized Solar Cells
- 2018
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Ingår i: ChemPhotoChem. - : Wiley-VCH Verlagsgesellschaft. - 2367-0932. ; 2:11, s. 976-985
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Tidskriftsartikel (refereegranskat)abstract
- Boron subphthalocyanines (SubPcs) are attractive as light harvesting materials in photovoltaic devices. Here we present the synthesis, optical and electrochemical properties, and device performances of a series of donor-acceptor-functionalized SubPc derivatives incorporating a carboxylic acid for anchoring onto TiO2. Liquid- and solid-state dye-sensitized solar cells (DSCs) were prepared from three compounds, and a triad system consisting of two aniline donor moieties and a benzothiadiazole acceptor moiety was found to exhibit the highest power conversion efficiency (PCE) in the series (PCE=1.54 %; solid-state device). The compounds were prepared by stepwise acetylenic coupling reactions. In addition, we present the synthesis and optical properties of a SubPc derivative incorporating three anilino-substituted 1,1,4,4-tetracyanobutadiene units, prepared by the [2+2] cycloaddition between three ethynyl units at the SubPc periphery and three tetracyanoethylene molecules followed by electrocyclic ring-opening reactions.
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| 2. |
- Kilde, Martin Drohse, et al.
(författare)
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Norbornadiene-dihydroazulene conjugates
- 2019
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Ingår i: Organic and Biomolecular Chemistry. - : Royal Society of Chemistry (RSC). - 1477-0539 .- 1477-0520. ; 17:33, s. 7735-7746
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Tidskriftsartikel (refereegranskat)abstract
- The introduction of various photochromic units into the same molecule is an attractive approach for the development of novel molecular solar thermal (MOST) energy storage systems. Here, we present the synthesis and characterisation of a series of covalently linked norbornadiene/dihydroazulene (NBD/DHA) conjugates, using the Sonogashira coupling as the key synthetic step. Generation of the fully photoisomerized quadricyclane/vinylheptafulvene (QC/VHF) isomer was found to depend strongly on how the two units are connected - by linear conjugation (a para-phenylene bridge) or cross-conjugation (a meta-phenylene bridge) or by linking to the five- or seven-membered ring of DHA - as well as on the electronic character of another substituent group on the NBD unit. When the QC-VHF system could be reached, the QC-to-NBD back-reaction occurred faster than the VHF-to-DHA back-reaction, while the latter could be promoted simply by the addition of Cu(i) ions. The absence or presence of Cu(i) can thus be used to control whether heat releases should occur on different or identical time scales. The experimental findings were rationalized in a computational study by comparing natural transition orbitals (NTOs). Moreover, the calculations revealed an energy storage capacity of 106-110 kJ mol(-1) of the QC-VHF isomers, which is higher than the sum of the capacities of the individual, separate units. The major contribution to the energy storage relates to the energetic QC form, while the major contribution to the absorption of visible light originates from the DHA photochrome; some of the NBD-DHA conjugates had absorption onsets at 450 nm or beyond.
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| 3. |
- Kjaer, Christina, et al.
(författare)
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Luminescence Spectroscopy of Rhodamine Homodimer Dications in Vacuo Reveals Strong Dye-Dye Interactions
- 2019
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Ingår i: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 20:4, s. 533-537
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Tidskriftsartikel (refereegranskat)abstract
- Being alone or together makes a difference for the photophysics of dyes but for ionic dyes it is difficult to quantify the interactions due to solvent screening and nearby counter ions. Gas-phase luminescence experiments are desirable and now possible based on recent developments in mass spectrometry. Here we present results on tailor-made rhodamine homodimers where two dye cations are separated by methylene linkers, (CH2)(n). In solution the fluorescence is almost identical to that from the monomer whereas the emission from bare cation dimers redshifts with decreasing n. In the absence of screening, the electric field from the charge on one dye is strong enough to polarize the other dye, both in the ground state and in the excited state. An electrostatic model based on symmetric dye responses (equal induced-dipole moments in ground state) captures the underlying physics and demonstrates interaction even at large distances. Our results have possible implications for gas-phase Forster Resonance Energy Transfer.
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| 4. |
- Olsen, Stine T., et al.
(författare)
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Dark Photoswitching Induces Coulomb Blockade Diamond Collapse
- 2015
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:27, s. 14829-14833
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Tidskriftsartikel (refereegranskat)abstract
- A derivative of the photochromic molecule dihydroazulene (DHA) undergoes bias-induced switching into its vinylheptafulvene (VHF) conformation when inserted into a silver junction. This dark switching mechanism, which induces a collapse of the Coulomb blockade diamonds, is explained by quantum calculations on the molecular transport junction. Analysis of the nonequilibrium populations of molecular redox states explains the observed bias threshold. Predictions are made that another DHA derivative will not, in future experiments, exhibit bias-induced switching. Thus, the dark switching mechanism depends on the structure of the photoswitch. The methodology applies to any molecular junction and offers a versatile tool for answering mechanistic questions.
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| 5. |
- Skov, Anders B., et al.
(författare)
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Excited‐State Topology Modifications of the Dihydroazulene Photoswitch Through Aromaticity
- 2019
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Ingår i: ChemPhotoChem. - : Wiley. - 2367-0932. ; 3:8, s. 619-629
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Tidskriftsartikel (refereegranskat)abstract
- The gain and loss of aromaticity plays a key role in organic chemistry and in the prediction of rate‐determining steps. Herein, we explore the concept of aromaticity in photoisomerization reactions. Benzannulated derivatives of the dihydroazulene‐vinylheptafulvene (DHA‐VHF) photoswitch were investigated using transient absorption spectroscopy and time‐dependent density functional theory to elucidate the effect of built‐in aromaticity on the switching properties. We found that benzannulation hampered the switching ability by enhancing an already existing barrier on the excited state surface. This enhancement was found to arise from a significant loss of aromaticity in the DHA‐to‐VHF transition state on the excited state potential energy surface. The VHF was found to be highly aromatic on the excited state surface, showing a reversal of aromaticity compared to the ground state. The barrier was found to be dependent on the position of benzannulation, since one derivative was found to switch as fast as the non‐benzannulated molecule although with lower efficiency, whereas another derivative completely lost the ability to undergo reversible photoswitching. The findings herein provide novel principles for the design of molecular photoswitches, shedding new light on excited state aromaticity, as previous discussions have mainly considered excited state aromaticity to be beneficial to switching. Our findings show that this view must be reconsidered.
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