CHARGE-TRANSFER EXCITED-STATES OF ZINC(II) DERIVATIVES OF BETA-SUBSTITUTED DINITROTETRAPHENYLPORPHYRIN

The photophysical properties of the zinc(II) derivatives of five isome rs of dinitrotetraphenylporphyrin were investigated in seven different solvents of varying polarity. The red shift of the optical absorption band and the enhanced oscillator strength of the Q(0,0) transition ar e highly specific of the nature of the isomers. The solvatochromic eff ect on the emission data of the isomers reveals large structural chang es on excitation. The excited state geometries of the isomers involve the partial rotation of the nitro groups about the plane of the porphy rin. The multiexponential decay of the excited singlet state of these isomers suggests a broad angular distribution of the emitting state. T he magnitude of the excited state dipole moment and the low value of t he transition moment of the isomers point to the possible existence of twisted intramolecular charge transfer in the excited singlet state.