Cyclometalated rhodium complexes of phenyl- and diphenyl-substituted oxazole and thiazole luminophores

Abstract

Cyclometaleted rhodium complexes of oxazole and thiazole luminophores [Rh(C∧N)2En]Cl [(C∧N)−, deprotonated forms of 2,5-diphenyloxazole, 2-phenylbenzothiazole, 2-(biphenyl-4-yl)-6-phenylbenzoxazole, and 2-(biphenyl-4-yl)-5-phenyloxazole; En — ethylenediamine] were obtained and characterized by the methods of 1H NMR, IR, and electron absorption and emission spectroscopy. Two cyclometallated ligands in the inner sphere of the complexes are in the cis-C,C positions. Cyclometallating of the luminophores results both in a red shift of intraligand π-π*-optical transitions (Δν ∼1.2 kK) as compared to free luminophores and in the appearance of a long-wave band (λmax 376–392 nm) of a mixed nature: metal-ligand charge transfer/intraligand transition. Alongside with the internal conversion to a low-energy state of the metal-ligand charge transfer/ intraligand transition, the emission degradation of photoexcitation energy results in the intraligand π-π*-fluorescence of the complexes (λmax 390–423 nm) at room temperature.