Unraveling the relaxation and photodissociation pathways of electronically excited 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)

Abstract

Femtosecond transient absorption spectroscopy was employed to investigate the excited-state relaxation and photodissociation dynamics of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) in dissolved in dimethyl sulfoxide. By tracking the evolution of the S1 manifold and ground-state recovery, we infer two distinct relaxation routes upon 370 nm excitation at the absorption peak: (1) molecules directly populated into S1 relax back to the ground state S0 sequentially via vibrational relaxation within S1 and S1 → S0 internal conversion (∼4.4 ps) and (2) molecules populated into S2 or higher-lying excited states first feed the S1 manifold (∼0.26 ps) and sequentially relax to highly vibrationally excited S0 (∼0.5 ps). The majority of these molecules cool down through vibrational relaxation, while the minority of them undergo C-NO2 homolytic bond cleavage. Most of the resulting fragments recombine to reform ground-state TATB (∼42 ps), with only a small fraction of NO2 escaping the solvent cage to become the primary photodissociation product. Upon 430 nm excitation at the band edge, only relaxation route (1) is observed, consistent with the nearly exclusive S1 population. Based on these experimental observations, we propose a working model describing the excitation-wavelength-dependent dynamics of TATB, providing a useful reference for understanding analogous nitroaromatic systems.