Theoretical study on the luminescent and reaction mechanism of dansyl‐based fluorescence probe for detecting hydrogen sulfide

The photophysical and photochemical properties of the sulfonyl azide-based fluorescent probe DNS-Az and its reduction product DNS by hydrogen sulfide (H₂S) have been investigated theoretically. The calculated results indicated the first excited states of DNS-Az was dark state (oscillator strength less than 0.03) and DNS was bright state (oscillator strength more than 0.1), which determined the predicted radiative rate k_r of DNS-Az was much smaller than that of DNS, meanwhile, due to more larger reorganization energy of DNS-Az, its predicted internal conversion rate k_ic was four times larger than that of DNS; moreover, owing to the effect of heavy atom from sulfur atom in DNS-Az, its predicted intersystem crossing rate k_isc was seven times larger than that of DNS, thus the calculated fluorescence quantum yield of DNS-Az was only 2.16% and that of DNS was more than 77.2%, the above factors is the basis for DNS-Az molecule to function as a fluorescent probe. Regarding both DNS-Az and DNS molecules, their maximum Huang-Rhys factors, which are less than unity, signify the reliability of 0-0 transitions between their S₀ and S₁ electronic states. In addition, for DNS, our simulated emission peak of the 0-0 transition is 515 nm, a value that exhibits enhanced accuracy and coherence when compared to the experimental datum of 528 nm. The reaction mechanism of DNS-Az generating DNS by H₂S has been investigated too, according to the potential energy profile, we found that the fluorescent probe firstly protonated, then this organic ion broke down into DNS with the aid of a proton.