Novel Functionalised 2-phenylquinoxaline Ligand for Tuning Luminescence in Ir(III) Complexes

Abstract

Luminescent iridium(III) complexes have emerged as promising alternatives to traditional organic fluorescent dyes for optical applications, especially to their exceptional photophysical characteristics including long-lived phosphorescence, broad Stokes shifts, and superior photostability which are particularly advantageous for real-time imaging and targeted diagnostics. In this study, a series of novel 2-phenylquinoxaline-based ligands were synthesised in good yields (61–84%) and fully characterised using a several of analytical techniques including ¹H, ¹³C, and ¹⁹F NMR, IR spectroscopy, and high-resolution mass spectrometry. Two heteroleptic iridium(III) complexes, [Ir(L₃)₂(bpy)]PF₆ and [Ir(L₄)₂(bpy)]PF₆, were successfully isolated and their characterisation and electronic properties investigated. Spectroscopic studies, including UV–vis absorption and time-resolved luminescence measurements, revealed strong phosphorescent emission in the red region of the visible spectrum (λem = 650–672 nm), with emission lifetimes in range of hundred nanoseconds in aerated acetonitrile. These findings demonstrate the potential of functionalised quinoxaline ligands for tuning the photophysical behaviour of Ir(III) complexes in luminescent applications.