Luminescence of porphrins and metalloporphyrins. Part 6.—Luminescence of aluminium(III) tetraphenylporphine and its µ-oxo dimer

Abstract

Aluminium(III) tetraphenylporphine possesses a tightly bound axial ligand, the nature of which influences the photophysical properties. As the spin–orbital coupling character of the ligand increases (OH^– < OOCCH^–₃ < F^– < Cl^– < Br^– < I^–), the singlet excited state lifetime and the fluorescence quantum yield decrease whilst the quantum yield for formation of the excited triplet state increases. The observations can be interpreted in terms of an internal heavy-atom enhanced intersystem-crossing mechanism, and for these compounds internal conversion is unimportant. However, for the µ-oxo dimer internal conversion accounts for some 46% of the decay route for the excited singlet state although there is little evidence to suggest pronounced exciton coupling between the two porphyrin rings.