Investigation of ultrafast excited state dynamics of 2,2′,4,4′,6,6′-hexanitrostilbene using femtosecond transient absorption spectroscopy

Abstract

A study on the dynamics and structures of the excited states of 2,2′,4,4′,6,6′-hexanitrostilbene shows equilibrium between vibrationally hot S1 (S*1) and S1 states with lifetimes of 0.8 and 6 ps, respectively.

A Combination of Chemometrics and Quantum Mechanics Methods Applied to Analysis of Femtosecond Transient Absorption Spectrum of Ortho-Nitroaniline

“…In addition, 0.59 ps lifetime of S 2 → S 1 was reported for a benzophenone derivative (p-iodobenzophenone) in acetonitrile media 37 . Longer relaxation time with 0.8 ps lifetime was observed from the femto-TA transient absorption spectrum of HNS for its S 2 → S 1 decay in acetontrile media 28 . The ab initio MD study on the uracil in solution 42 , which exhibited good consistency with the experimental observations, also found that 50% of the excited trajectories are still trapped in S 2 after 1 ps, indicating that the depopulation of the S 2 state slowly occur due to internal conversion to the S 1 .…”

“…Figure 2 shows 2D plot of the spectrum, which covers the range from 400 nm to 710 nm and possess a long delay time of 400 ps. The negative signals (blue region) in the 400–460 nm range should correspond to the ground state bleaching (GSB) or stimulated emission (SE) 28 41 . The positive signals in the region of 460–710 nm should involve in excited state absorption mixed with the simulated emission from the high vibration excited states to the low ones.…”

“…However, there are very limited studies on the decay of the electronically excited states of the nitro- and amino- aromatic explosives since the process is ultrafast and exothermic, involving in the safety. Only recently, with the aid of a simple singular-value decomposition (SVD) method, Chu 28 used femto-second transient absorption to study the relaxation dynamics behavior of 2, 2′, 4, 4′, 6, 6′-hexanitrostilbene (HNS) after excitation at 266 nm and proposed a relaxation process of S 2 → S * → S 1 → T 1 . Thereby, elucidation of the initial decay and the dynamics behavior of excited electronic states has been quietly absent and highly desirable for the explosives.…”

“…Compared to 400 nm excitation wavelength used in PNA system, we used shorter excitation wavelength for ONA in order to gain insight into the relaxation process in higher excited levels. The short excitation wavelength close to 266 nm were adopted in the femto-TA spectra of some compounds 4 37 38 39 40 , including HNS 28 . The MCR-ALS in combination with QM calculation is for the first time adopted to explore an efficient resolving method to obtain a comprehensive description of a complete decay evolution process of the electronic excited states of ONA, which will provide valuable information for developing facile yet efficient analysis method for resolving the transient absorption spectrum used in the other fields.…”

Observation of Excited νs(NO2) and Relaxation Process of HNS in Solution by CARS Technique

“…have been observed [2, 18−21]. The evolution of excited state of HNS has also been observed by the ultrafast absorption experiments [22]. The thermal decomposition of HNS has been analyzed by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) [20].…”