• Energy Research
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Rigid and soluble electron donor–acceptor conjugates (3 and 11) that combine π-extended tetrathiafulvalene (exTTF) as an electron donor and C60 as an electron acceptor have been synthesized using oligo-vinylfluorene (oFV) linkers to connect the electroactive entities. Fluorescence and transient absorption measurements confirm that light-induced excitation induces charge-transfer reactions over distances of 28 A in THF. The incorporation of vinylene spacers into oligofluorene molecular wires has been shown both experimentally and theoretically to improve the charge-transfer features significantly to give a β value of 0.075 ± 0.001 A−1. Enhanced π-conjugation caused by higher orbital overlap is responsible for this trend.

We describe for the first time the full reaction coordinate regarding the photoisomerization of red-absorbing norbornadienes (NBDs) to quadricyclanes (QCs). Our studies go beyond steady-state investigations by using an arsenal of time-resolved techniques. Importantly, the red absorption of NBDs is made possible by a different charge-transfer character; adjusting its strength enables control over the photoreversibility of the rearrangement. In the case of strong charge-transfer character (a weakly electron-withdrawing ester and a strongly electron-donating dimethylaniline), photoirradiation with visible light into the delocalized charge-transfer absorption of NBD affords QC reversibly. In stark contrast, UV photoirradiation into the NBD localized excited state leads to a photoinduced degradation and cannot be back-isomerized to NBD under any circumstances. If the charge-transfer character is weak (a weakly electron-withdrawing ester and a weakly electron-donating phenyl), reversibility is seen independently of the photoirradiation light.

A technique known as intensity filtering is introduced to select valence-like virtual orbitals for calculating the local electron affinity, EA(L). Intensity filtering allows EA(L) to be calculated using semiempirical molecular orbital techniques that include polarisation functions. Without intensity filtering, such techniques yield spurious EA(L) values that are dominated by the polarisation functions. As intensity filtering should also be applicable for ab initio or density functional theory calculations with large basis sets, it also makes EA(L) available for these techniques.