Proton-Transfer-Based Azides with Fluorescence Off-On Response for Detection of Hydrogen Sulfide: An Experimental, Theoretical, and Bioimaging Study

This work describes the synthesis of photoactive proton transfer compounds based on the benzazolic core containing the azide group. The compounds present absorption in the UV region and fluorescence emission in the visible region of the spectra with large Stokes shift due to a phototautomerism in the excited state (ESIPT). The azide location on the benzazolic structure presented a noteworthy role on their photophysics, leading to fluorescence quenching. A photophysical study was performed in the presence of NaHS to evaluate their application as an H2S sensor. The methodology employed was the reduction of azides to amines using NaHS to mimic H2S, resulting in an off-on response fluorescence mechanism. The observed photophysical features were successfully used to explore the azides as fluorescent probes in biological media. In addition, DFT and TD-DFT calculations with the CAM-B3LYP/cc-pVDZ and CAM-B3LYP/jun-cc-pVTZ level, respectively, were performed in order to understand the photophysics features of azide derivatives, where the main interest was to investigate the fluorescence quenching experimentally observed in the azide derivatives.