Abstract
The photophysical and photochemical properties of the novel hydrazine sensor TAPHP and the TAPDP generated by the cyclization reaction of TAPHP with hydrazine are investigated using the density functional theory and time-dependent density functional theory. The results show that both the excited-state intramolecular proton transfer and intramolecular charge transfer can occur for TAPHP and TAPDP. Analysis of bond parameters and infrared vibrational spectra indicate that hydrogen bonds are enhanced in the first excited state, which is beneficial to excited-state intramolecular proton transfer. The strength of hydrogen bonds is also visualized by using the independent gradient model and topological analysis. The core-valence bifurcation index and bond critical point parameters are further employed to measure hydrogen bonds. The reaction path of proton transfer is obtained through the potential energy curves. The excitation of TAPHP and TAPDP is attributed to the charge transfer excitation, which is determined by the characteristics of the hole-electron distribution. The reaction site and product configuration are verified by atomic charge and 1H-NMR spectra. The negative free energy difference indicates that the reaction between TAPHP and hydrazine can proceed spontaneously. In addition, the absorption and fluorescence spectra agree well with the experimental results, confirming that TAPHP is an excellent sensor of hydrazine.
Highlights
Hydrogen bond (HB) observed in DNA, water, proteins, and other materials (Zhao and Han, 2011; Tanioku et al, 2013; Gole et al, 2014; Ling and Gutowski, 2016; Huang et al, 2018) formed between a hydrogen (H) atom of one molecular fragment D-H and another atom A (i.e., D-H...A) (Li et al, 2011; Wilcken et al, 2013; An et al, 2016, 2017; Ma et al, 2018; Zhao et al, 2019)
We focused on the excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) processes of TAPHP and TAPDP through analyzing bond lengths and bond angles, infrared (IR) vibration spectra, potential energy curves (PECs), and hole-electron distribution, etc
The independent gradient model (IGM), topological analysis, and core-valence bifurcation (CVB) index are employed to visualize the strength of intramolecular Hydrogen bond (HB) as well as electron-hole distribution were obtained by using Multiwfn program (Lu and Chen, 2012a,b)
Summary
Hydrogen bond (HB) observed in DNA, water, proteins, and other materials (Zhao and Han, 2011; Tanioku et al, 2013; Gole et al, 2014; Ling and Gutowski, 2016; Huang et al, 2018) formed between a hydrogen (H) atom of one molecular fragment D-H and another atom A (i.e., D-H...A) (Li et al, 2011; Wilcken et al, 2013; An et al, 2016, 2017; Ma et al, 2018; Zhao et al, 2019). We focused on the ESIPT and ICT processes of TAPHP and TAPDP through analyzing bond lengths and bond angles, infrared (IR) vibration spectra, potential energy curves (PECs), and hole-electron distribution, etc. The independent gradient model (IGM), topological analysis, and core-valence bifurcation (CVB) index are employed to visualize the strength of intramolecular HBs as well as electron-hole distribution were obtained by using Multiwfn program (Lu and Chen, 2012a,b).
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