Mechanism of quenching of the triplet states of organic compounds by tris-(β-diketonato) complexes of iron(III), ruthenium(III) and aluminium(III)

Abstract

The rate constants for quenching of the triplet states of sixteen different organic molecules by tris(acetylacetonato)-iron(III), -ruthenium(III) and -aluminium(III) and by tris(dipivaloylmethanato)-iron(III) in benzene solution have been measured using the technique of laser photolysis. As each level in the quencher becomes accessible for electronic energy transfer there is a marked rise in quenching ability with increasing triplet energy to a plateau value and no further increase in quenching rate constant is observed until a further excited state of the quencher is reached. This characteristic dependence on the energy of the triplet states being quenched and on the spectroscopically determined energy levels of the complexes establishes energy transfer as the mechanism of quenching. Orbital overlap and spin statistical factors are shown to be important parameters in determining the efficiencies of quenching by these coordination complexes.