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

Abstract

A combination of the advanced chemometrics method with quantum mechanics calculation was for the first time applied to explore a facile yet efficient analysis strategy to thoroughly resolve femtosecond transient absorption spectroscopy of ortho-nitroaniline (ONA), served as a model compound of important nitroaromatics and explosives. The result revealed that the ONA molecule is primarily excited to S3 excited state from the ground state and then ultrafast relaxes to S2 state. The internal conversion from S2 to S1 occurs within 0.9 ps. One intermediate state S* was identified in the intersystem crossing (ISC) process, which is different from the specific upper triplet receiver state proposed in some other nitroaromatics systems. The S1 state decays to the S* one within 6.4 ps and then intersystem crossing to the lowest triplet state within 19.6 ps. T1 was estimated to have a lifetime up to 2 ns. The relatively long S* state and very long-lived T1 one should play a vital role as precursors to various nitroaromatic and explosive photoproducts.

Photodissociation Dynamics of the Highly Stable ortho-Nitroaniline Cation

“…Tables S4 and S5 contain the excited state energies and oscillator strengths for ONA + at the S 0 and D 0 geometries, respectively; only the EOM-CCSD results are shown. Although no calculations of ONA + excited states have been reported to the best of our knowledge, our calculated energy for the neutral ONA S 1 state of 3.79 eV at the TD-CAM-B3LYP level is reasonably close to literature values for the S 1 energy of TATB (3.63 eV at the TD-B3LYP/6-311++G­(d,p) level) and ONA (3.06 eV at the same level in water) …”

“…Although no calculations of ONA + excited states have been reported to the best of our knowledge, our calculated energy for the neutral ONA S 1 state of 3.79 eV at the TD-CAM-B3LYP level is reasonably close to literature values for the S 1 energy of TATB (3.63 eV at the TD-B3LYP/ 6-311++G(d,p) level) 10 and ONA (3.06 eV at the same level in water). 53 The results in Figure 2 show that ONA behaves quite differently from other related nitroaromatic molecules. Previous studies by our group showed that ortho-nitrotoluene, a closely related molecule to ONA, went from a C−NO 2 torsional angle of 26.0 to 35.5°upon ionization.…”

Excited-state dynamics and electron transfer process of 1,3,5-triamino-2,4,6-trinitrobenzene

“…Therefore, we must analyse the transition according to the following information: rst, TATB is a photosensitive EM which undergoes colour changes from yellow to green or darker under light irradiation/photolysis, which has been attributed to the formation of a long-lived radical in the T 1 state; 22 and second, intersystem crossing to the T 1 state is likely to happen in this case. 29 On the basis of the foregoing arguments, it would be reasonable to assign the decay of the relaxed S 1 state to the S 1 / T 1 transition in this work. The Kohn-Sham orbitals, electron distribution, and orbital energies are in good agreement with this interpretation.…”

Modulating the Roaming Dynamics for the NO Release in ortho-Nitrobenzenes

“…Moreover, these calculations do not consider direct dissociation from the triplet state, and additionally, the assignment of translational energy components based on a single classical trajectory may not be statistically valid . Theoretical and time-resolved experimental studies show that the motions localized on the nitro group are primarily responsible for the nonadiabatic dynamics in the excited electronic states of nitrobenzene and reveal that irrespective of the initial excitation energy, an ultrafast internal conversion followed by an intersystem crossing results in populating the T 1 state, which is invariant to the nature of substitution on the nitrobenzene. − Lin and co-workers, based on the excitation energy dependence of the slow-to-fast ( s / f ) branching ratio, have surmised that the fast components appear due to direct dissociation from the T 1 state, while the slow component from the S 0 state, in concurrence with other experimental investigations. , In contrast, many theoretical reports suggest both the fast and slow translational energy components are due to a second intersystem crossing from T 1 to S 0 surface, , which is in accord with the time-resolved photoelectron measurements …”

“…In this work, we examine, holistically, the trends in the branching ratio of slow-to-fast ( s / f ) translational energy components for the NO release obtained by a velocity map imaging technique following 266 nm photolysis of nitrobenzene and a series of ortho -substituted nitrobenzenes, viz., o -nitrotoluene, o -nitroanisole, o -nitroaniline, and o -nitrophenol. It has been reported that for nitrobenzene, o -nitrotoluene, o -nitroaniline, and o -nitrophenol time-resolved experiments following 266 nm excitation reveal ultrafast decay of the initially excited state to the T 1 state; however, the corresponding NO release experiments following 266 nm excitation for various ortho -nitrobenzenes, with the exception of nitrobenzene, are conspicuously missing. The experimental results are interpreted using DFT [B3LYP/6-311++g (d,p)] calculations, wherein it is proposed that the dynamics on the T 1 surface along the minimum energy path dictates the s / f branching ratio.…”