Photoinduced electron transfers (ET) from trimethoxybenzene to excited quinones were studied in polar and apolar solvents by flash photolysis and photoacoustic calorimetry. In apolar solvents, back-ET was also observed. The enthalpy, entropy and volume changes of these ET were measured and compared with those from dimethylaniline to excited pyrene. ET to a triplet quinone in an apolar solvent involves a structural volume increase, indicating the formation of a loose ion pair, whereas ET to the singlet state of pyrene leads to a volume contraction. ET from tetramethylbenzidine to excited C-60 was also measured in benzonitrile and benzene and the formation of a ground-state complex in benzene was detected. The rates of the photoinduced and back-ET were measured and interpreted with nonadiabatic theories and with the intersecting-state model. It is shown that the size of the reactants has a negligible effect on the kinetics of these reactions and that nonspecific solvent effects are only significant for very exothermic reactions.