Photoinduced electron transfer in xerogel fabricated by covalently bound polycondensation of chromophore-contained alkoxysilanes

A series of alkoxysilane derivatives containing chromophores were chosen as pairs of donor and acceptor in organic-inorganic hybrid material (OIHM), in which photoinduced electron transfer (PET) emerged. The modified Rehm-Weller equation was employed to decide the free energy change of PET reaction where parameters such as reduction potential and zero-zero transition energy of acceptor, and the oxidation potential of donor were measured. The occurrence of PET in OIHM was observed by fluorescence quenching of acceptor chromophore after photo-excitation, and this process was affected by the molar ratios between donor and acceptor. Such efficient PET process can only be observed when donor and acceptor moieties were covalently bound in OIHM. A controlled experiment showed that the PET was difficult to occur when polycondensation reaction would not take place between donor and acceptor. This sol-gel method played an important role to covalently bind two chromophores together and facilitate PET process. Kinetic measurement of fluorescence decay determined the rate of PET, where the efficiency of PET was up to 86% when donor/acceptor = 1/2. This hybrid system provided further understanding of electron transfer reaction within solid state material and gave the potential usage of hybrid materials in optoelectronics.