Effects of geometrical isomerism on emissive behaviour of heteroleptic cyclometalated Ir(iii) complexes

Abstract

In this study, we report the emissive properties of a heteroleptic cyclometalated Ir(III) complex, [Ir(bzq)₂(PBO)] (bzqH = benzo[h]quinoline; PBOH = 2-(2-hydroxyphenyl)benzoxazole). The complex, [Ir(C^N)₂(N^O)], was synthesised and optically resolved using a chiral column. Two geometrical isomers, trans-(N,N) and cis-(N,N) isomers, were obtained as the major and minor products in an enantiopure form, respectively. Their molecular structures were determined using single crystal X-ray analysis. In the crystalline states, the intermolecular C–H⋯π interaction between PBO⁻ and an H atom in bzq⁻ was the main factor influencing molecular packing. When the complexes were dissolved in CH₂Cl₂ and excited at 430 nm under N₂ atmosphere, yellow (λ_max = 550 nm) and orange emissions (λ_max = 570 nm) were observed for the trans-(N,N) and cis-(N,N) isomers, respectively, with the quantum yield higher for the former than the latter.