Substituent effects on the excited-state properties of platinummeso-tetraphenylporphyrins

A study has been undertaken to examine the effect of peripheral substitution on the photophysics of platinum tetraarylporphyrins. The aim of the study was to provide better dyes for oxygen sensing. Substitution of electron rich aryl groups results in red shifts for both the absorption and emission spectra. These observations are explained using simple molecular orbital theory. The lifetime of the excited singlet state for platinum tetraphenylporphyrin is calculated to be shorter than 0.7 psec. The radiative rate constants are on the order of 10³ sec^–1 while nonradiative rate constants are on the order of 10⁴ sec^–1. The model used is sufficiently flexible to be applied to all Pt and Pd porphyrins.