Diarylethenes with intramolecular donor-acceptor structures for photo-induced electrochemical change

Diarylethenes with donor-acceptor groups were synthesized to induce electrochemical switching by light. Photoisomerization was induced by 1,2-bis(2-methyl-1-benzob]thiophen-3-yl)perfluorocyclopentene (BTF, 1) unit, while the 3,4-ethylenedioxythiophene (T) and nitro (N) groups were directly connected to BTF, to extend π-electron delocalization. Spectral change to a longer wavelength through photochromism was significant in the donor-acceptor structures (6), accompanied by an increase in the molar absorption coefficients, than those of the unsubstituted BTF (1) or the BTF substituted with only acceptor group (2c and 3c). A significant peak shift toward lower redox energy was observed when the molecules were converted from an open isomer to a closed isomer. The plot of the reduction potentials ((E_1/2^red, V vs Ag/AgCl) vs LUMO energy eV) for the diarylethenes indicates that the reduction potential is strongly dependent on the nature of the substituents around the diarylethene unit. When 6 was applied to a photocell of Au/PC/ITO glass, in which PC is the polystyrene containing 6, it became possible to switch the conductivity of the cell through the film by UV-vis irradiation, as estimated by the I-V plot on a photocell. The conductivity of the cell exposed to UV light was three times larger than that of the cell exposed to visible light, and 10 times larger than that of the cell containing 3, indicating the importance of the push-pull structure for π-electron connectivity through the donor-BTF-acceptor.