Photoinduced electron transfer from silyl end-capped sexithiophene to benzoquinone derivatives studied by laser photolysis

Photoinduced electron transfer from the electron-donating bis(dimethyl-n-octylsilyl)sexithiophene, (DSi6T), to the electron-accepting benzoquinone derivatives, BQs, in polar benzonitrile has been investigated with laser photolysis method. The employed benzoquinone derivatives include 1,4-benzoquinone (BQ), 2,5-dichloro-1,4-benzoquinone (Cl₂BQ), 2,6-dimethyl-1,4-benzoquinone (Me₂BQ), tetrafluoro-1,4-benzoquinone (F₄BQ) and 2-methyl-1,4-benzoquinone (MeBQ). The electrochemical measurements showed pronounced effect of the substituted groups on the reduction potentials of BQs, and consequently on the driving forces of the electron transfer of the DSi6T/BQs mixture systems. Such effect of the driving forces for electron-transfer reactions of DSi6T/BQs mixture systems have been examined by utilizing the femtosecond and nanosecond laser flash photolysis, in addition the complementary steady state absorption and fluorescence techniques. Upon excitation of DSi6T with 440 nm laser light, the electron-transfer reactions from the triplet excited state of DSi6T to BQs were confirmed by observing the transient absorption bands of DSi6T radical cation in the visible region. The excellent electron donating properties of DSi6T suggests its potential to be a photoactive unit in the bulk heterojunction solar cells.