Fluorescence study of some deformed zinc(II) porphyrins

The effect of deformation in the porphyrin ring on the emission properties of a series of zinc(II) derivatives of basket handle porphyrins is reported Emission from the upper excited S-2 state is observed in all zinc(II) deformed porphyrins. The porphyrin ring deformation results in red shifts of both the S-1 and S-2 emission bands and perturbed lifetimes of the S-1 state. Decreased quantum yields and increased intersystem crossing rates are also caused by porphyrin ring deformation. The decrease in the S-1 fluorescence yields can be interpreted in terms of an enhancement of the non-radiative rate, whereas a reduction in the energy gap between the S-2 and S-1 states results in low S-2 quantum yields relative to planar derivatives.