Quenching of organic singlets and triplets by a complex containing NiII, CoII or MnII

Abstract

The quenching of anthracene fluorescence and biacetyl and 1-bromonaphthalene phosphorescence by M^II(4-picoline)₄(NCS)₂ complexes, where M^II is Ni^II, Co^II or Mn^II, respectively, has been studied in liquid and glassy solutions and the data are compared with theoretical energy-transfer mechanisms.

The chosen donor–acceptor pairs form, in the solid state, clathrates with significant ground-state interactions: no such association was observed in solution that might influence the luminescence decay processes. In particular, a diffusion-controlled process occurred for the systems involving excited singlet anthracene—M^II complexes in methanol and in cyclohexanol and its mixtures; an encounter-controlled process of an exchange nature occurred for the system triplet biacetyl—M^II complex in water; finally a dipolar and/or exchange quenching process took place in the system triplet 1-bromonaphthalene—M^II complex. These results correlated satisfactorily with an electronic energy transfer mechanism; alternative quenching processes were also considered, i.e. electron transfer, heavy-atom effect, spin-catalysed deactivation and exciplex formation, but were found to correlate poorly with the observed behaviour of the various systems studied.