Theoretical Study of Three Ratiometric 1,8-naphthalimide Fluorescent Probes for Hydrogen Sulfide Detection

Three ratiometric 1,8-naphthalimide fluorescent probes for hydrogen sulfide detection have been studied theoretically by using density functional theory and time-dependent functional theory. From the detailed comparison of the optimized geometries, it is found that the change of substituents has a slight effect on the structure of 1,8-naphthalimide fluorophore, and the effect is mainly located in the part attached to the changed substituent. The change of the electron-withdrawing or electron-donating ability of the substituents on the 1,8-naphthalimide has an effect on the electronic spectra. Based on the analysis of frontier molecular orbital, the intramolecular charge transfer process was found for the three probes and their corresponding products. Finally, the analysis of the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital was elaborated. This work provides a theoretical explanation of the experimental results and thus contributes to the development of novel fluorescent probes in the future.