Luminescence of porphyrins and metalloporphyrins. Part 4.—Fluorescence of substituted tetraphenylporphyrins

Abstract

Fluorescence quantum yields and excited singlet-state lifetimes were measured for a series of substituted tetraphenylporphyrins in benzene solution. The rate constants for non-radiative deactivation of the excited singlet state correlated with the Hammett constant of the substituent for both electron withdrawing and electron donating substituents. From the Hammett plots, it was concluded that the fluorescence properties of tetraphenylpophyrin were not particularly sensitive to substituents at the para position of the phenyl ring.

Efficient fluorescence quenching was observed with a porphyrin/quinone unit and, here, the fluorescence quantum yield decreased with increasing polarity of the solvent. This effect was interpreted in terms of partial charge separation within the excited singlet state.