Charge transfer excited states of zinc(II) derivatives of β-substituted dinitrotetraphenylporphyrin

Abstract

The photophysical properties of the zinc(II) derivatives of five isomers 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 are highly specific of the nature of the isomers. The solvatochromic effect on the emission data of the isomers reveals large structural changes on excitation. The excited state geometries of the isomers involve the partial rotation of the nitro groups about the plane of the porphyrin. The multiexponential decay of the excited singlet state of these isomers suggests a broad angular distribution of the emitting state. The magnitude of the excited state dipole moment and the low value of the transition moment of the isomers point to the possible existence of twisted intramolecular charge transfer in the excited singlet state.