Dual Regulatory Mechanism of Intrinsic Electronegativity and Extrinsic Solvent Polarity for Excited‐State Proton Transfer of BPDI Derivatives

This study conducts theoretical simulations to explore the synergistic regulation of chalcogen‐substituent electronegativity and solvent polarity on the excited‐state proton transfer (ESPT) behavior of three BPDI derivatives (BPDI‐O, BPDI‐S, BPDI‐Se) and clarify the microscopic mechanisms of their excited‐state double proton transfer (ESDPT). Geometric parameter statistics and infrared spectral analysis were performed to investigate the variations of hydrogen bond lengths, bond angles, and O‐H stretching vibrational frequencies in different substituted systems. The results verify prominent hydrogen bond strengthening in the S 1 state for all derivatives, where substituent electronegativity differences induce distinct excited‐state hydrogen bond intensities. Quantum theory of atoms in molecules (QTAIM) topological analysis of bond critical point (BCP) electron density, topological parameters, and hydrogen bond energies confirms that chalcogen electronegativity precisely regulates hydrogen bonding interactions in BPDI systems. Frontier molecular orbitals (FMOs) results show that chalcogen substitution rearranges molecular charge distribution, produces favorable excited‐state charge recombination properties, providing suitable electronic structures for ESPT. Potential energy surfaces (PESs) were constructed to elucidate the stepwise ESPT pathways and behavioral differences of the three derivatives. Comparative analysis reveals that solvent polarity effectively modulates excited‐state hydrogen bond strength and reaction barriers. Nonpolar solvents notably lower the energy barrier of the first proton transfer step (I → II) and greatly promote ESPT reactions. This work clarifies the dual regulatory mechanism of intrinsic atomic electronegativity and extrinsic solvent polarity effects of BPDI derivatives, offering reliable theoretical guidance for molecular design, performance optimization, and optoelectronic applications of novel BPDI functional materials.