Electrogenerated chemiluminescence of the lithium salts of 8-hydroxyquinoline and 2-methyl-8-hydroxyquinoline.

The spectroscopy, electrochemistry, and electrogenerated chemiluminescence (ECL) of [(q)(qH)Li]x (qH=8-hydroxyquinolinato) and [(Meq)(MeqH)Li]x (MeQH=2-methyl-8-hydroxyquinolinato) have been investigated. In both acetonitrile and aqueous solutions, [(q)(qH)Li]x and [(Meq)(MeqH)Li]x have absorption maxima at 320 and 309 nm, respectively. When excited at these wavelengths, the complexes emit around 500 nm (blue-green) in acetonitrile. Photoluminescence efficiencies (phiem) were 0.036 for [(q)(qH)Li]x and 0.012 for [(Meq)(MeqH)Li]x when compared to Ru(bpy)3(2+) (bpy=2,2'-bipyridine) with phiem=0.042. No photoluminescence was observed in aqueous media. The complexes show irreversible oxidative electrochemistry and quasi-reversible reductions in acetonitrile. ECL efficiencies (phiecl) were 0.097 for [(q)(qH)Li]x and 0.080 for [(Meq)(MeqH)Li]x when compared to Ru(bpy)(3)2+ (phiecl=1) in aqueous buffered solution and 0.035 for [(q)(qH)Li]x and 0.028 for [(Meq)(MeqH)Li]x in acetonitrile (0.05 M tri-n-propylamine (TPrA) as an oxidative-reductive ECL co-reactant). The ECL peaks at a potential corresponding to oxidation of both the TPrA and [(q)(qH)Li]x or [(Meq)(MeqH)Li]x. Also, qualitative studies using transmission filters suggest that both complexes emit ECL in approximately the same blue-green region as their photoluminescence, indicating that the same excited state is formed in both experiments.