Theoretical investigation on the sensing mechanism of a triphenylamine-benzofuran derived fluorescent probe for the detection of H2Sn

Sensing mechanism of the benzo-bodipy based fluorescent probe for Hypochlorous acid detection: Invalidity of photoinduced electron transfer

In vivo real-time detection of hypochlorous acid (HClO) in biological systems plays a crucial role in diagnosing immune-related diseases. Experimentally, a benzo-bodipy probe based on the photo-induced electron transfer (PeT) sensing mechanism has been developed for live fluorescence imaging. However, there have been no theoretical studies conducted to substantiate the precision of the sensing mechanism. This paper employs density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods to investigate the fluorescence detection mechanism of benzo-bodipy derivatives (BBy-T and BBy-TO), proposing a detection approach based on dark nπ* state quenching. The study reveals that the fluorescence quenching mechanism of BBy-T is primarily regulated by a thiomorpholine moiety, involving a dark nπ* state transition non-radiatively. Furthermore, this paper explains the fluorescence enhancement observed in BBy-TO. Theoretical investigations demonstrate, based on frontier molecular orbitals (FMOs) and hole-electron analysis, that the fluorescence enhancement for BBy-TO is not governed by the previously proposed intramolecular charge transfer (ICT) mechanism in experiments but rather follows a locally excited (LE) ππ* pattern. This work offers new insights for the design of novel fluorescence probes based on bodipy and benzo derivatives, expanding the understanding of their fluorescence properties.

Photophysical Properties of (E)-1-(4-(Diethyla-mino)-2-hydroxybenzylidene)-4,4-dimethylthiosemicarbazide Compound and Its Triple Fluorescence Emission Mechanism: A Theoretical Perspective

In view of the application prospects in biomedicine of (E)-1-(4-(diethyla-mino)-2-hydroxybenzylidene)-4,4-dimethylthiosemicarbazide (DAHTS), the behavior of excited-state dynamics and photophysical properties were studied using the density functional theory/time-dependent density functional theory method. A series of studies indicated that the intramolecular hydrogen-bond (IHB) intensity of DAHTS was enhanced after photoexcitation. This was conducive to promoting the excited-state intramolecular proton-transfer (ESIPT) process. Combining the analysis of the IHB and hole-electron, it revealed that the molecule underwent both the ESIPT process and the twisted charge-transfer (TICT) process. Relying on exploration of the potential energy surface, it was proposed that the different competitive mechanisms between the ESIPT and TICT processes were regulated by solvent polarity. In acetonitrile (ACN) solvent, the ESIPT process occurred first, and the TICT process occurred later. In contrast, in the CYH solvent, the molecule first underwent the TICT process and then the ESIPT process. Furthermore, we raised the possibility that the TICT behavior was the cause of weak fluorescence emission for the DAHTS in CYH and ACN solvents. By the dimer correlation analysis, the corresponding components of triple fluorescence emission were clearly assigned, corresponding to the monomer, dimer, and ESIPT isomer in turn. Our work precisely elucidated the photophysical mechanism of DAHTS and the attribution of the triple fluorescence emission components, which provided valuable guidance for the development and regulation of bioactive fluorescence probes with multiband and multicolor emission characteristics.