Theoretical mechanisms and guided regulation for predicting multicolor fluorescence in NH···N-based dual-ESIPT...

Herein, we present the first systematic theoretical framework for a previously unexplored class of excited-state intramolecular proton transfer (ESIPT) materials featuring dual NH-N type intramolecular hydrogen bonding. A series of representative molecular systems have been rationally designed, employing imidazole rings as proton acceptors and varying the substituents on the amino donors to achieve precise modulation of electron density and hydrogen-bond strength. Theoretical calculations confirm the feasibility of the dual NH-N ESIPT process and reveal tunable multi-color and long-wavelength luminescence properties. Detailed analyses of structural parameters, IR vibrational spectra, and topology, combined with kinetic and thermodynamic investigations, demonstrate effective control over hydrogen bonding strength and elucidate the intrinsic correlation between electron density, emission mechanism, and fluorescence performance. Further insights into the ESIPT mechanism are provided through in-depth potential energy surface exploration and transition-state characterization. This established "Structure-Function-Performance" research paradigm offers a reliable theoretical foundation for subsequent experimental development and application.