Picosecond transient resonance Raman study on the excited-state conformational dynamics of a highly ruffled nickel porphyrin

Picosecond to nanosecond transient resonance Raman spectroscopy was applied to track down the excited-state conformational excursions of Ni^IIT(t-Bu)P [nickel(II) 5,10,15,20-tetra-tert-butylporphyrin] in various solvents with different dielectric properties. From the resonance Raman spectra of Ni^IIT(t-Bu)P obtained by picosecond pulse photoexcitation, the α₄-type conformer was suggested to be dominant in the ¹(d,d) excited state at the initial stage of deactivation processes (∼3 ps). However, only one conformer of αβαβ type was found to persist on the nanosecond time-scale. We also observed that the initial formation of the ¹(d,d) excited state of Ni^IIT(t-Bu)P from the ¹(π,π*) but the subsequent decay of the ¹(d,d) to the ground state is strongly solvent dependent.