Explore the influence of intramolecular hydrogen bond formation sites on the fluorescence mechanism

In this contribution, the fluorescence mechanism of HBT-HBZ, a fluorescent probe used to detect HClO content in living cells and tap water, and its structure after oxidation by HClO (HBT-ClO) have been discussed based on density functional theory (DFT) and time-dependent density functional theory (TDDFT). At the same time, the impact of the probe conformation and the proton transfer site within the excited state molecule on the fluorescence mechanism has been revealed. Combined with infrared vibrational spectra and Atoms-in-molecules theory, the strength of intramolecular hydrogen bonds in HBT-HBZ and HBT-ClO and their isomers are demonstrated qualitatively. The relationship between the strength of intramolecular hydrogen bonds and dipole moments is discussed. The potential energy curves demonstrate the feasibility of intramolecular proton transfer. The weak fluorescence phenomenon of HBT-HBZ in solution is quantitatively explained by the frontier molecular orbital and hole electron analysis due to charge separation. Moreover, when strong cyan fluorescence occurs in solution, the corresponding molecular structure should be HBT-ClO(T). The impact of the intramolecular hydrogen bond formation site on the molecule as a whole is also investigated by electrostatic potential analysis.