Variation of charge transfer kinetics in structurally closely related dyads with rhenium photosensitizers

The kinetics for photoinduced charge separation and thermal charge-recombination processes in three donor–bridge–acceptor molecules with rhenium(I) tricarbonyl diimine photosensitizers were investigated. Time resolved luminescence and transient absorption spectroscopies reveal that in addition to driving force effects, differences in bridge-mediated electronic donor–acceptor coupling among the three dyads play important roles. Notably, it is seen that charge separation depends strongly on whether initial photoexcitation involves promotion of an electron towards or away from a phenothiazine electron donor. Thermal charge recombination rates are found to differ by a factor of 2 between two isomeric dyads due to an electronic coupling effect.