Fluorescent deactivation behaviors based on ESIPT and TICT of novel double target fluorescent probe and its sensing mechanism for Al3+/Mg2+: A TD-DFT study

Guotao Sun; Hua Fang

doi:10.1016/j.saa.2023.122718

Fluorescent deactivation behaviors based on ESIPT and TICT of novel double target fluorescent probe and its sensing mechanism for Al³⁺/Mg²⁺: A TD-DFT study

Spectrochim Acta A Mol Biomol Spectrosc. 2023 Sep 5:297:122718. doi: 10.1016/j.saa.2023.122718. Epub 2023 Apr 8.

Authors

Guotao Sun¹, Hua Fang²

Affiliations

¹ Department of Chemistry and Material Science, College of Science, Nanjing Forestry University, Nanjing 210037, People's Republic of China.
² Department of Chemistry and Material Science, College of Science, Nanjing Forestry University, Nanjing 210037, People's Republic of China. Electronic address: susanfang20@gmail.com.

PMID: 37054565
DOI: 10.1016/j.saa.2023.122718

Abstract

Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) methods with integral equation formula polarized continuum model (IEFPCM), the fluorescent behavior and recognizing mechanism of probe N'-((1-hydroxynaphthalen-2-yl)methylene)isoquinoline-3-carbohydrazide (NHMI) for Al³⁺/Mg²⁺ ion were investigated in more detail. Excited state intramolecular proton transfer (ESIPT) process in probe NHMI occurs in the stepwise pattern. The proton H₅ of enol structure (E1) firstly moves from O₄ to N₆ to form single proton-transfer (SPT2) structure, and then the proton H₂ of SPT2 transfers from N₁ to N₃ to form the stable double proton-transfer (DPT) structure. Subsequently, the transformation from DPT to its isomer (DPT1) induces the twisted intramolecular charge transfer (TICT) process. Two non-emissive TICT states (TICT1 and TICT2) were obtained, and TICT2 state quenches the fluorescence observed in the experiment. With the addition of aluminum (Al³⁺) or magnesium (Mg²⁺) ion, TICT process is prohibited by the coordination interaction between NHMI and Al³⁺/Mg²⁺, and the strong fluorescent signal is turned on. For probe NHMI, the twisted C-N single bond of acylhydrazone part leads to the TICT state. This sensing mechanism may inspire researchers to develop new probes from a different direction.

Keywords: ESIPT; Photophysical; Sensing mechanism; TD-DFT; TICT.