The photophysics of free-base hemiporphyrazine: a theoretical study

The photophysics of free-base hemiporphyrazine has been studied by theoretical computations based on time dependent density functional theory and multiconfigurational complete active space methods. The results confirm that the dual emission spectrum of hemiporphyrazine is due to the formation at the excited state of different tautomers, but the emission at longer wavelength, originally attributed to a vibronically induced radiative decay from the tautomer with both central hydrogens linked to pyridine rings, is now ascribed to a dipole allowed transition, occuring either from that tautomer or from the tautomer with the two hydrogens linked to one pyridine and one isoindole ring.