Investigations of fluorescence emission Mechanism: Formation of ring-like structures by interactions influenced by hydroxyl group and deprotonation.

[Display omitted] • The fluorescence quenching of the probes P1 and P2 is due to the PET process, while the strong fluorescence of P3 originates from the ICT process. • The differences in hydroxyl positions and deprotonation are responsible for the different intramolecular interactions of the products. • The deprotonated form of the product is the real experimental product, and only this product emits strong fluorescence in the NIR fluorescence region. As one of the gaseous signaling molecules in biological systems, hydrogen sulfide(H 2 S) is involved in numerous physiological processes and diseases. Therefore, rapid, effective, and real-time detection of H 2 S is of great importance. Based on its excellent optical properties, dicyanoisophorone has attracted much attention in recent years, and a large number of corresponding probes have been developed to detect H 2 S in biological systems. In this paper, the fluorescence mechanisms of three dicyanoisophorone-based fluorescent probes are investigated and the near-infrared (NIR) fluorescence attribution of the products is discussed by density-functional theory and time-dependent density-functional theory methods. Frontier molecular orbital analysis shows that the non-fluorescence of the probes is attributed to the photo-induced electron transfer process. Structural change and reduced density gradient analyses indicate that the position of the hydroxyl group and the deprotonation have a non-negligible influence on the interactions within the products. The five- or six-membered ring-like structures formed by interactions make the molecule stain as a planar and the fluorescence emission, while the twist exists the fluorescence quenching. In addition, spectral information shows that the emission of NIR fluorescence originates from the deprotonated form of the product. [ABSTRACT FROM AUTHOR]