Site-selection and Zeeman spectroscopy of the S₁↔S₀ transition of magnesiumporphin in N-octane at 4·2 K

Abstract

Site selection spectroscopy combined with a study of the Zeeman effect of the MgP · ethanol complex (MgP = magnesiumporphin) in a n-octane single crystal is reported. The splitting of the ¹ E_u state is identified with the 0-0 _y transition 195 cm^-1 above the 0-0 _x transition. The value of the electronic orbital angular momentum Λ = 4·4 and the Jahn-Teller interaction is very weak. Laser excitation into the 0-0 _x transition leads to reversible photochemistry. In this process the interaction of ethanol with the porphin nucleus is attenuated and the crystal field splitting reduced to 22 cm^-1. The photochemistry enables optical hole burning from which the homogeneous widths of the 0-0 transitions are determined. SCF-PPP calculations are performed to mimick the MgP · ethanol complex. The calculations satisfactorily explain the differences between the ethanol complex and its photoproduct.