Photoinduced Electron Transfer in a BODIPY-ortho-Carborane Dyad Investigated by Time-Resolved Transient Absorption Spectroscopy

We report the results of photoinduced electron transfer (PET) in a novel dyad, in which a boron dipyrromethene (BODIPY) dye is covalently linked to o-carborane (o-Cb). In this dyad, BODIPY and o-Cb act as electron donor and acceptor, respectively. PET dynamics were investigated using a femtosecond time-resolved transient absorption spectroscopic method. The free energy dependence of PET in the S-1, and S-2 states was examined on the basis of Marcus theory. PET in the S-1, state occurs in the Marcus normal region. Rates are strongly influenced by the driving force (-Delta G), which is controlled by solvent polarity; thus, PET in the S-1 state is faster in polar solvents than in nonpolar ones. However, PET does not occur from the higher energy S-2 state despite large endothermic Delta G values, because deactivation via internal conversion is much faster than PET.