DFT/TDDFT investigation on the D-π-A type molecule probes 4-(5-R-thiophen-2-yl)-2-isobutyl-2H-[1,2,3]triazolo[4,5-e][1,2,4] triazolo[1,5-a]pyrimidines: fluorescence sensing mechanism and roles of weak interactions

We performed DFT/TDDFT investigation on the sensing mechanism of the D-pi-A type fluorescence probes 4-(5-R-thiophen-2-yl)-2-isobutyl-2H-[1,2,3]triazolo[4,5-e][1,2,4] triazolo[1,5-a]pyrimidines (ITTP1, ITTP2, ITTP3), which are designed for detecting 2,4,6-trinitrophenol (TNP) explosive. Theoretical calculations reveal that the fluorescence sensing mechanism was induced by the combination of the pi-pi stacking interaction and photo-induced electron transfer. The blueshift in the UV-Vis spectrum of the ITTP sensors was correlated with the decrease in electron-donating ability of the molecule probes and was further evidenced by the calculated H-1 NMR spectra and D-CT index. The roles of the weak interactions: pi-pi stacking and hydrogen-bonding interaction for the probes fluorescence sensing process were analyzed, and the pi-pi stacking interaction was verified to be the dominant for the fluorescence sensing. The present finding should be useful for the future design of explosive fluorescent probes and the interpretation of the sensing mechanisms.