UV–Vis, Fluorescence, and Resonance Raman Spectroscopic and Density Functional Theoretical Studies on 3-Amino-1,2,4-triazole: Microsolvation and Solvent-Dependent Nonadiabatic Excited State Decay in Solution

Abstract

The microsolvation and photophysics of 3-amino-1,2,4-triazole (3AT) after excitation to the light-absorbing S2(nπ*) state were studied by using resonance Raman spectroscopy and single component artificial force-induced reaction (SC-AFIR) in a global reaction route mapping (GRRM) strategy. The vibrational spectra were assigned on the basis of experimental data and density functional theory (DFT) calculations. The resonance Raman spectra of 3AT were measured to probe the excited state structural dynamics in the Franck–Condon region. The conformations of 3AT­(CH3CN)1, 3AT­(CH3OH)2, and 3AT­(H2O)2 clusters were determined by combining vibrational spectrum experiments and B3LYP/6-311++G­(d,p) computations. DFT calculations were carried out to obtain the minimal excitation energies of the lower-lying singlet excited states, and the curve-crossing points. It was revealed that the short-time structural dynamics of 3AT were dominated by the N–N stretching coordinates. An excited state decay mechanism is proposed: 3AT is initially excited to the S2(nπ*) state, then the conical intersection (CI) of the S2(nπ*)/S1(ππ*) potential energy surfaces is crossed, and 3AT then decays to the lower solvent-dependent excited state S1(ππ*). It subsequently returns to the S0 state, accompanied by a large Stokes fluorescence shift, which was interpreted as the stabilized S1(ππ*) excited state bonding to several water molecules via intermolecular hydrogen bonding.

Absorption, fluorescence, Raman spectroscopic and density functional theoretical studies on the singlet and triplet excited state decay of 3-amino-5-mercapto-1,2,4-triazole

“…29 Recently, we also reported several solvent-dependent hydrogen bonding molecules, i.e., 5-(methylthio)-1,3,4-thiadiazole-2(3H)-thione (MTTN), 3amino-1,2,4-triazole (3AT), 4,6-dimethyl-2-mercaptopyrimidine (DMMP), and 2-mercaptobenzothiazole by Raman spectroscopy and density functional theory calculations. [30][31][32][33][34] These results revealed that solvent hydrogen bonding can stabilize the thione isomers and the thione 4 thiol tautomerization may occur in a higher excited state, which was greatly controlled by the solvent character and UV light wavelength.…”

“…In our recent reports, methanol was shown to form stronger hydrogen bonds with solute molecules than water. 31,32 Thus, the weakness of n 8 in methanol may be the result of stronger solute-solvent hydrogen bonding. This suggests that structural dynamics are solvent and hydrogenbonding dependent along the reaction coordinates in the Franck-Condon region.…”

Spectroscopic and theoretical insights into hydrogen bonding clusters, triplet species, and the relaxation mechanism of the light (1ππ*) excited state of 4-methyl-1,2,4-triazole-3-thione

“…The 488 nm Raman spectra were obtained using an apparatus with a triple monochromator (TriVista TR557m Princeton Instruments) equipped with a 488 nm laser line (Coherent, CVI MellESGrIOT). 40,41 The 488 nm excitation laser line was produced with a CVI MellesGriotargon-ion laser (543-AP-A01). A backscattering geometry was adopted for the collection of the Raman-scattered light through reflective optics, which imaged the light onto a liquid nitrogen-cooled CCD camera mounted on the exit of the spectrograph.…”

Excited‐state proton transfer via higher excited state in 2‐mercaptobenzothiazole: Absorption, fluorescence, Raman spectroscopic study, and theoretical calculation

“…Resonance Raman spectra were also obtained by excitation at 488 nm with the use of an experimental apparatus consisting of a triple monochromator (TriVista TR557, Princeton Instruments) equipped with the argon ion laser as the 488‐nm excitation light source (power: 20 mW at the sample) and a liquid‐nitrogen‐cooled charge‐coupled device (CCD) array (Princeton Instruments, LN/2048X512.B/I, UVAR); further details of this experimental arrangement may be found elsewhere . A backscattering geometry was employed for collection of the Raman‐scattered light by reflective optics that imaged the light onto the CCD, which was mounted at the exit of the spectrograph.…”