Deciphering a novel mechanism for single-component white light emission: synergistic effects of ESIPT and excimers

Abstract

The development of novel single-component white light materials is crucial for advancing the progress of efficient, low-cost, and environmentally friendly optoelectronic devices. However, the complex luminescence mechanisms of full-spectrum emitters pose significant challenges to the development of white light materials. In this study, the luminescence mechanisms of three molecules (CF₃-HTTH, CF₃-MTTH, and CF₃-MTTM) are investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The focus is placed on elucidating the white light emission mechanism of CF₃-HTTH, where a unique combination of excited-state intramolecular proton transfer (ESIPT) and excimer formation effectively generates triple fluorescence (Enol*, Keto*, and excimer). The ground-state and excited-state properties of the three systems are simulated, revealing that the enhanced intramolecular hydrogen bonding in CF₃-HTTH and CF₃-MTTH facilitates the ESIPT process. Both systems undergo a single ESIPT process, despite CF₃-HTTH having two potential proton transfer sites. Consequently, CF₃-HTTH and CF₃-MTTH emit blue (Enol*) and green (Keto*) fluorescence. In the excited state, the two CF₃-HTTH and CF₃-MTTM monomers approach each other and undergo parallel slippage, maximizing the π–π overlap area between the monomers. This increases intermolecular interactions, promoting excimer formation and resulting in red fluorescence emission. The effective synergy between ESIPT and excimer formation provides valuable theoretical guidance for the design of highly efficient single-molecule white light-emitting materials.