Solvent-dependent absorption and electronic relaxation dynamics of iron (III) tetra-4-N-methylpyridylporphine

Solvent-dependent excited-state relaxation dynamics of iron (III) tetra-4-N-methylpyridylporphine (FeTMPyP) were investigated using steady-state and femtosecond spectroscopies. Soret absorption for water-dispersed FeTMPyP consisted of two spectrally broad components centered at 3.12 eV and 2.92 eV, corresponding to π → π^∗and charge-transfer (C-T) transitions. The C-T transition exhibited inverse-dielectric-dependent energy shifts. Following 400-nm excitation, dynamics proceeded by femtosecond internal conversion from the initially prepared π^∗state to the C-T state, followed by solvent-dependent C-T relaxation. The C-T energy shifts and relaxation rates exhibited correlated dielectric dependences. C-T absorption energy and relaxation dynamics of FeTMPyP are sensitive indicators of surrounding dielectric environments.