Optical and spectroscopic properties of substituted oxa- and thiazole luminophores metalated with platinum metals

Abstract

The cyclometalated [M(pbo)En]PF6(M = Pd(II), Pt(II)), [M(pbo)2En]PF6 (M = Rh(III), Ir(III)), and [Rh(C∧N)2En]PF6 ((C∧N)− are the deprotonated forms of 2-phenylbenzoxazole (pbo), 2,5-diphenyloxazole (dpo), 2-phenylbenzothiazole (pbt), 2-biphenyl-4-yl-5-phenyloxazole (bpo), and 2-biphenyl-4-yl-6-phenylbenzoxazole (bpbo) and En is ethylenediamine) complexes are studied by 1H NMR spectroscopy, IR spectroscopy, and electronic absorption and emission spectroscopy. Metalation of luminophores leads to the formation of five-membered {M(C∧N)} cycles in the composition of plane-square and octahedral complexes of the cis-C,C structure. In addition to the intraligand (IL) π-π* optical transitions in the UV region, the complexes are characterized by long-wavelength metal-to-ligand charge-transfer (MLCT) absorption bands in the region of 366–416 nm. The phosphorescence of the complexes in the visible region (482–531 nm) is attributed to radiative transition from the mixed IL/MLCT electronically excited state. The temperature quenching of the phosphorescence of complexes is attributed to the thermally activated population of metal-centered electronically excited states with subsequent nonradiative deactivation.