Wydział Chemii

Anna Szemik-Hojniak

Irena Deperasińska

Katarzyna Ślepokura

Monika Gawłowska

Yuval Erez

2026

Journal of Molecular Structure

1367

146120/1-146120/17

10.1016/j.molstruc.2026.146120

Naukowa

Angielski

Artykuł

In this paper, we present molecular dynamics results of 3-methylamino-4-nitropyridine N-oxide (3M4N) in n-propanol obtained using femtosecond fluorescence conversion and time-correlated single photon counting (TCSPC) techniques. Our main goal was to identify the photoinduced pathways of 3M4N caused by the ortho-substitution of its alkylamino group (-NHCH3) with respect to the nitro group as electron acceptor. Fluorescence up-conversion signals in n-propanol allowed the determination of an ultrafast (200 ∼ 300 fs) intersystem crossing (ISC) between the S₁^FC (ππ*) state and the upper (nπ*) triplet state (T₃).We believe that an efficient ultrafast ISC is strongly influenced by the torsion of the nitro group, isoenergetics of the S₁ state with the triplet (T₃), spin change that takes place simultaneously with the change of electronic configurations [S₁ (π - π*) → T₃ (n - π*)] and significant spin-orbit coupling of T₃ with the S₁ state [the value of Hso (S₁,T₃) is 6.94 cm^-1]. The time constants of the three minima found by TD DFT calculations on the potential energy surface are for the n-π* type S₁(NP) → S₀ transition (0.6 ps), the planar bright structure of the locally excited state S₁ (LE) (3.2 ps) of π -π* character, and the final dark form TICT (8.0 ps), formed from the S₁(LE) state.

Crystal structure, 4-nitropyridine N-Oxide derivatives, Fluorescence up-conversion dynamics, TD-DFT calculations, Ultrafast instersystem crossing

http://dx.doi.org/10.1016/j.molstruc.2026.146120

http://www.elsevier.com