Photoinduced Solvent Ligation to Nickel(II) Octaethylporphyrin Probed by Picosecond Time-Resolved Resonance Raman Spectroscopy

Abstract

Pump/probe picosecond time-resolved resonance Raman spectra of nickel(II) octaethylporphyrin (NiOEP) in pyridine were observed in the time range −5 to +1000 ps. The spectra demonstrate generation of the vibrationally and electronically excited (d,d) state (B1g) immediately after the excitation to the ππ* state of the macrocycle, subsequent vibrational relaxation, and the formation of six-coordinate exciplex, B1g(L)2 (L = pyridine). Singular value decomposition analysis was applied to a series of picosecond time-resolved Raman spectra to investigate whether a five-coordinate complex was generated prior to the formation of the six-coordinate species. The results indicate insignificant population of the five-coordinate species preceding the formation of B1g(L)2 and suggest concerted coordination of two solvent molecules to axial positions of the (d,d) excited NiOEP. The formation process of the B1g(L)2 species is discussed.