Photoinduced Electron Transfer in Branched Bis(ferrocenylacetylene)-C60 Systems : Influence of the Nature of Conjugation
Four new branched 3,4- and 3,5-bis(ferrocenylacetylene)phenyl-C60 molcules, in which the bis-ferrocene donor moieties and C60 acceptor moiety are covalently linked with phenylacetylene linkage through pyrrolidino and pyrazolino rings on the C60 moiety, as abbreviated to be (Fc)2≡Ph-NMPC60 (o- and m-) and (Fc)2≡Ph-PzC60 (o- and m-), respectively, have been prepared in multistep procedures using microwave irradiation, as source of energy. The HOMO–LUMO gaps smaller than 1.25 eV were experimentally determined by cyclic voltammetry (CV) and Osteryoung square-wave voltammetry (OSWV) for (Fc)2≡Ph-PzC60 and (Fc)2≡Ph-NMPC60. In both polar and non-polar solvents, a photoinduced charge-separation (CS) process efficiently takes place in (Fc)2≡Ph-NMPC60 and (Fc)2≡Ph-PzC60 from the singlet excited state of C60 (1C60*), as confirmed by picosecond-time-resolved emission spectroscopy. The CS states were confirmed by nanosecond-transient absorption spectroscopy. The lifetimes of the CS states were evaluated to be ca. 10 ns, which are shorter than those of the similar dyads with phenylenevinylene linkage, suggesting higher electron-hole conductivity through the phenylacetylene linkage.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)