We
report the results of photoinduced electron transfer (PET) in
a novel dyad, in which a boron dipyrromethene (BODIPY) dye is covalently
linked to <i>o</i>-carborane (<i>o</i>-Cb). In
this dyad, BODIPY and <i>o</i>-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<sub>1</sub> and S<sub>2</sub> states was examined on the basis of Marcus theory. PET in the S<sub>1</sub> state occurs in the Marcus normal region. Rates are strongly
influenced by the driving force (−Δ<i>G</i>), which is controlled by solvent polarity; thus, PET in the S<sub>1</sub> state is faster in polar solvents than in nonpolar ones.
However, PET does not occur from the higher energy S<sub>2</sub> state
despite large endothermic Δ<i>G</i> values, because
deactivation via internal conversion is much faster than PET
