Temperature and heavy atom effects on the free base corrole tautomerization

Abstract

Corroles represent a peculiar family of contracted tetrapyrrolic macrocycles with a direct pyrrole– pyrrole linkage and the free base derivatives show pronounced nonplanar distortions due to sterical hindrances imposed by three protons in the macrocycle core. To date, studies on the excitation energy deactivation pathways in corroles have mainly focused on the radiative deactivation of the lowest singlet S1 state, and the fluorescence spectra, quantum yields and lifetimes have been measured and discussed for a number of the free base corrole derivatives [1]. At the same time the singlet to triplet S1–T1 intersystem crossing was found to be the main excitation energy deactivation route in corroles as it is for most of related tetrapyrrolic macrocycles, except highly distorted compounds [2]. Recently, the individual ground state absorption and fluorescence features have been distinguished for the two NH tautomers (see Scheme 1) of the free base meso-triarylcorroles