Time-resolved resonance Raman study of the primary photoprocesses of nickel(II) octaethylporphyrin in solution

Two-color pump-probe time-resolved resonance Raman studies with 3 ps time resolution were carried out for nickel(II) octaethylporphyrin in toluene and tetrahydrofuran solutions. Reliable proofs have been obtained for the existence of both conformational changes and vibrational heating/cooling in the primary photoprocess. Conformational changes from ruffled to planar structures, which were monitored by time evolution of the v10∗ bands at 1616–1629 cm−1, took place in the excited (d,d) state within 15 ps following photoexcitation, while the core expansion of the macrocycle occurs immediately after the excitation energy transfer from the (π,π∗) to (d,d) states. Intensity changes of the v4∗ and v7∗ bands in the anti-Stokes Raman spectra revealed that the conversion of the electronic excess energy into vibrational heating/cooling occurs with time constants of 5–8 ps and is dependent on pump wavelength.