Nonadiabatic Dynamics Simulation Predict Intersystem Crossing in Nitroaromatic Molecules on a Picosecond Time Scale

Abstract

Previous time‐resolved spectroscopic experiments and static quantum‐chemical calculations attributed nitronaphthalene derivatives one of the fastest time scales for intersystem crossing within organic molecules, reaching the 100 fs mark. Nonadiabatic dynamics simulations on three nitronaphthalene derivatives challenge this view, showing that the experimentally observed ∼100 fs process corresponds to internal conversion in the singlet manifolds. Intersystem crossing, instead, takes place on a longer time scale of ∼1 ps. The dynamics simulations further reveal that the spin transitions occur via two distinct pathways with different contribution for the three systems, which are determined by electronic factors and the torsion of the nitro group. This study, therefore, indicates that the existence of sub‐picosecond intersystem crossing in other nitroaromatic molecules should be questioned.

Role of Ultrafast Internal Conversion and Intersystem Crossing in the Nonadiabatic Relaxation Dynamics of ortho-Nitrobenzaldehyde

“…Nonetheless, the simulations provide strong evidence that the IC cascade from S 4 to S 1 is significantly faster than ISC. The obtained few-ps time constant is also consistent with results reported for other nitro-aromatic compounds and nicely matches an experimental estimate of the ISC time constant in o NBA (2.7 ps) …”

“…Nonetheless, the simulations provide strong evidence that the IC cascade from S 4 to S 1 is significantly faster than ISC. The obtained few-ps time constant is also consistent with results reported for other nitro-aromatic compounds 71 and nicely matches an experimental estimate of the ISC time constant in oNBA (2.7 ps). 27 Oftentimes, the time constants obtained from fitting the adiabatic populations cannot be mapped one-to-one to the experimentally measured time constants.…”

Intersystem Crossing and Triplet Dynamics in an Iron(II) N-Heterocyclic Carbene Photosensitizer

“…While such a characterization is often approximately performed by simple inspection of the orbitals involved in the leading configurations of the excited-state configuration interaction vector, this task can be tedious for a large number of states. 71 Alternatives include dipole moments 72 or transition dipole moments 73 or quantitative analysis of the transition-density matrix, 74 as it will be done in this work.…”

Revisiting the non-fluorescence of nitroaromatics: presumption versus reality

“…As the initially populated π, π* S 1 states of some of them relax, the nitro group can twist out of the plane of the ring and may assume an asymmetric pyramidal geometry, as in 1-nitronaphthalene. 21 This distortion of the nitro group in π, π* S 1 states promotes highly effective transitions to n, π* triplet states with the same geometry. 22 Preventing such distortions of the nitro group can suppress ISC and decreases k ISC by orders of magnitude.…”