Computational Chemistry Study of pH-Responsive Fluorescent Probes and Development of Supporting Software

This study employs quantum chemical computational methods to predict the spectroscopic properties of fluorescent probes 2,6-bis(2-benzimidazolyl)pyridine (BBP) and (E)-3-(2-(1H-benzo[d]imidazol-2-yl)vinyl)-9-(2-(2-methoxyethoxy)ethyl)-9H-carbazole (BIMC). Using time-dependent density functional theory (TDDFT), we successfully predicted the fluorescence emission wavelengths of BBP under various protonation states, achieving an average deviation of 6.0% from experimental excitation energies. Molecular dynamics simulations elucidated the microscopic mechanism underlying BBP's fluorescence quenching under acidic conditions. The spectroscopic predictions for BIMC were performed using the STEOM-DLPNO-CCSD method, yielding an average deviation of merely 0.57% from experimental values. Based on Einstein's spontaneous emission formula and empirical internal conversion rate formulas, we calculated fluorescence quantum yields for spectral intensity calibration, enabling the accurate prediction of experimental spectra. To streamline the computational workflow, we developed and open-sourced the EasySpecCalc software v0.0.1 on GitHub, aiming to facilitate the design and development of fluorescent probes.