The luminescent and reaction mechanisms of a fluorescent probe for the detection of hypochlorous acid: Insights from theory

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2023-06, Vol.294, p.122572, Article 122572
• Main Authors: Li, Huixue, Wang, Xiaofeng, Yuan, Kun, Lv, Lingling, Liu, Kui, Wang, Changqing, Pan, Sujuan, Wang, Peng, Li, Zhifeng
• Format: Article
• Language: English
• Subjects: Fluorescent probe; Luminescent mechanism; Reaction mechanisms; Theoretical study
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2023.122572

The predicted nonradiative rate kic and kisc of BMH were several orders of magnitude larger than its radiative rate kr, so the fluorescence quantum yield of BMH was nearly zero, but the predicted radiative rate kr of BM was much larger than its kic and kisc, its fluorescence quantum yield was more than 90%. [Display omitted] •The predicted internal conversion rate kic and intersystem crossing rate kisc of BMH were several orders of magnitude larger than its predicted radiative rate kr, the excess energy of an excited state was dissipated by nonradiative processes, therefore, the fluorescence quantum yield of BMH was nearly zero.•For BM (the oxidized product of BMH by HClO), the predicted radiative rate kr was much larger than its kic and kisc, so its fluorescence quantum yield was more than 90%.•The reaction for BMH converting into BM consisted of three elementary reactions, firstly the BMH and HClO formed an intermediate product through an addition reaction; secondly the intermediate product further was oxidated by another HClO to form alkylsulfanol (R-S-OH), at last a molecule of water was close to it formed BM.•The solvent effect can decreased the activation energy and be more favorable for these elementary reactions. We have designed and synthesized a novel fluorescent probe BMH for detection of hypochlorous acid (HClO), which can increase dramatically the fluorescence intensity and had ultrafast response, a low detection limit and a wide pH range of application. In this paper, we further studied its fluorescence quantum yield and photoluminescence mechanism theoretically. The calculated results indicated the first excited states of BMH and BM (it was the oxidized product by HClO) were bright states with large oscillator strengths, however, due to more larger reorganization energy of BMH, the predicted internal conversion rate kIC of BMH was four orders of magnitude larger than that of BM; moreover, owing to the effect of heavy atom from sulfur atom in BMH, the predicted intersystem crossing rate kisc of BMH was five orders of magnitude larger than that of BM; meanwhile there was no significant difference found between both the predicted radiative rates kr, thus the calculated fluorescence quantum yield of BMH was nearly zero and that of BM was more than 90%, the data showed the BMH had no fluorescence but its oxidated produce BM possessed strong fluorescence. In addition, the reaction mechanism of BMH transforming into BM has been investigated too, ac