Mechanism of Ultrafast Intersystem Crossing in 2‐Nitronaphthalene

Abstract

Nitronaphthalene derivatives efficiently populate their electronically excited triplet states upon photoexcitation through ultrafast intersystem crossing (ISC). Despite having been studied extensively by time‐resolved spectroscopy, the reasons behind their ultrafast ISC remain unknown. Herein, we present the first ab initio nonadiabatic molecular dynamics study of a nitronaphthalene derivative, 2‐nitronaphthalene, including singlet and triplet states. We find that there are two distinct ISC reaction pathways involving different electronic states at distinct nuclear configurations. The high ISC efficiency is explained by the very small electronic and nuclear alterations that the chromophore needs to undergo during the singlet–triplet transition in the dominating ISC pathway after initial dynamics in the singlet manifold. The insights gained in this work are expected to shed new light on the photochemistry of other nitro polycyclic aromatic hydrocarbons that exhibit ultrafast intersystem crossing.

Synthesis of Green Emitting Multi‐substituted Dibenzodioxins and Related Heteroacenes and Computational Investigation of Substituent Effects on Emission Spectra

“…The intersystem crossing (ISC) along the nitro twisting coordinate of the S 1 state can be considered as another possible reason behind the non‐fluorescent or less fluorescent nature of the nitro compounds. Similar to the results reported in literature we have also observed the possible role of the triplet states due to the interaction with the S 1 state along the nitro twist path (change of <C−C−N−O dihedral angle) starting from the planar geometry (Figures S38‐S41). This indicates that some population may be transferred to the triplet states from the S 1 state and thereby the fluorescence is likely to be reduced.…”

“…The IC process will populate the S 1 state and subsequent deactivation channels will operate through the IC (S 1 ‐S 0 ) and ISC processes. Similar S 2 ‐S 1 IC processes are very common in nitro compounds …”

“…This TICT state of nitro compounds have been reported by different groups in past. The non‐radiative decay channel quenching the fluorescence due to the twisted nitro group has already been described elaborately by several theoretical and experimental groups . The presence of fluorescent planar S 1 minima and the simultaneous existence of the nitro‐twisted S 1 minima with exclusive charge transfer towards the nitro moiety has been observed by them.…”

Finite-temperature Wigner phase-space sampling and temperature effects on the excited-state dynamics of 2-nitronaphthalene

“…In this work, we systematically investigate the effects of Wigner sampling at finite temperature on the excited-state dynamics of the organic chromophore 2-nitronaphthalene (2NN). The deactivation mechanism of 2NN has been previously established by us employing nonadiabatic dynamics simulations, 23 and it is summarized in Fig. 1.…”

Visualizing spin degrees of freedom in atoms and molecules

“…This spin-orbit coupling contains key features that change the shape of an energy eigenstate as well as affecting chemical properties such as dissociation energy [1][2][3][4]. Given the growing recognition that phenomena such as spin-orbit coupling play an important role in some chemical reactions [5][6][7], there is a need for tools to help better understand these processes.…”