Theoretical investigation of dual hydrogen-bonding interactions and ESIDPT mechanism associated with halogen substituted 2,5-bis(4,5-diphenyl-1H-imidazol-2-yl)benzene-1,4-diol derivatives.

CONTEXT: In this work, using the TDDFT method, we mainly focus on exploring the photo-induced excited state dual hydrogen-bonding interactions for halogen element substituted 2,5-bis(4,5-diphenyl-1H-imidazol-2-yl)benzene-1,4-diol (BDIBD) derivatives (i.e., BDIBD-FF, BDIBD-FCl and BDIBD-FBr). Analyses of chemical bond properties, bond lengths and bond angles, infrared (IR) spectral shifts, as well as the simulated core-valence bifurcation (CVB) parameters, we find upon excitation dual hydrogen bonds of BDIBD-FF, BDIBD-FCl, and BDIBD-FBr are strengthened in the S1 state. Variations about photo-induced charge further reveal the excited state intramolecular double proton transfer (ESIDPT) tendency. By constructing potential energy surfaces (PESs), we not only clarify the stepwise ESIDPT mechanism for BDIBD derivatives, but also present the halogen element regulated ESIDPT behaviors.

METHODS: Based on Gaussian 16 program, all BDIBD derivatives were optimized using DFT and TDDFT methods with D3-B3LYP and TZVP theoretical levels. By comparing geometries variations and exploring core-valence bifurcation indexes for predicting hydrogen-bonding strength using Multiwfn 3.8, dual hydrogen-bonding interactions were analyzed. Potential energy surfaces with transition state forms were explored to reveal the ESIDPT mechanism.