Tailoring intramolecular charge transfer (ICT) dynamics for dual emission: A route to single-molecule white light emission

Abstract

Herein, we present an imidazole-based single-molecule white light-emitting organic luminophore with efficient intramolecular charge transfer characteristics. Steady-state studies indicate that the lowest excited state is primarily governed by the local excited state in less-polar solvents, while charge transfer character dominates in more-polar solvents. The fine-tuning of both locally excited and charge transfer states via the combination of solvent or variable pH environment leads to the simultaneous dual-emission behavior, enabling near-white-light emission. The intramolecular hydrogen bonding leads to structural planarity, which in turn enhances the quantum yield in the solution state. The twisted cyano phenyl rings inhibit the aggregate caused quenching, resulting in the solid state emission also. A thorough theoretical study is performed. As the dielectric constant of the solvent increases, intramolecular charge separation becomes more pronounced, leading to larger dipole moment differences between the ground and excited states. This enhanced separation strengthens solvent stabilization of the excited states, which in turn appears as red shifts in the UV-Visble spectra. Moreover, the luminophore showcases remarkable mechanochromic luminescence, shifting from vibrant blue to intense green upon mechanical stress and effortlessly reverting via solvent diffusion, highlighting its reversible and robust response. These findings pave the way for next-generation single-molecule luminescent materials with tunable and multifunctional optical properties.