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.

The excited state decay process of N-heterocyclic compounds is attracting increasing attention due to their fundamental applications in pharmaceutical and biological sciences.

Excited‐state proton transfer (ESPT) photochemical reactions are attracting increasing attention because of their many applications in materials science and biology. 2‐Mercaptobenzothiazole (MBT) is investigated in solid, protic, and aprotic solvents using vibrational and electronic spectroscopies combined with density functional theory (DFT). The presence of the stable dimer conformer in the solid and solvents was confirmed by vibrational spectroscopy. Steady‐state absorption and fluorescence emission spectra of MBT in different pH solvent environments indicate that the intermolecular hydrogen bonding may reveal important insights into the ESPT mechanisms involving single and double proton transfers. With the aid of DFT and time‐dependent density functional theory calculations, we assigned the observed Raman spectra to the dimer in water and methanol solvents and carried out preliminary investigations into the effect of hydrogen bonding with the solvent on the excited‐state proton transfer process.