RADIATIONLESS DECAY VIA ESIPT OF THE FIRST EXCITED SINGLET OF THE HEMIPORPHYRAZINE

It is proposed that free base hemiporphyrazine, a phthalocyanine analo gue where two opposite isoindoles are replaced by pyridines, should ex hibit excited state intramolecular proton transfer (ESIPT). This conje cture is based on MNDO/CI computations, according to which the most st able positions of the two inner hydrogens are inverted upon excitation to the first excited singlet. The computed barriers for hydrogen migr ation are large both for the synchronous and the asynchronous path, bu t they are in line with those previously computed by the same method f or the ground state migration of the inner hydrogens of free base porp hines, a process which is known by NMR measurements to be fast at room temperature.