Short-time dynamics and decay mechanism of 2(1H)-pyridinone upon excitation to the light-absorbing S4(21𝝅𝝅*) state

Teng-Shuo Zhang; Jia-Dan Xue; Xuming Zheng; Bin-Bin Xie; Wei-Hai Fang

doi:10.1063/1.4977763

Short-time dynamics and decay mechanism of 2(1H)-pyridinone upon excitation to the light-absorbing S₄(2¹𝝅𝝅^*) state

J Chem Phys. 2017 Mar 21;146(11):114305. doi: 10.1063/1.4977763.

Authors

Teng-Shuo Zhang¹, Jia-Dan Xue¹, Xuming Zheng¹, Bin-Bin Xie², Wei-Hai Fang²

Affiliations

¹ Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, People's Republic of China.
² Chemistry College, Beijing Normal University, Beijing 100875, People's Republic of China.

PMID: 28330344
DOI: 10.1063/1.4977763

Abstract

The excited-state structural dynamics and the decay mechanism of 2(1H)-pyridinone (NHP) after excitation to the S₄(2¹ππ^*) light-absorbing state were studied using resonance Raman spectroscopy and complete-active space self-consistent field (CASSCF) calculations. The B-band absorption cross-section and the corresponding absolute resonance Raman cross-sections were simulated using a simple model based on time-dependent wave-packet theory. The geometric structures of the singlet electronic excited states and their curve-crossing points were optimized at the CASSCF level of theory. The obtained short-time structural dynamics in easy-to-visualize internal coordinates were then compared with the CASSCF-predicted structural-parameter changes of S₄(2¹ππ^*)/S₃(2¹nπ^*)-MIN, S₄(2¹ππ^*)/S₁(1¹nπ^*)-MIN, and S₄(2¹ππ^*)-MIN. Our results indicate that the initial population of NHP in the S₄ state bifurcates in or near the Franck-Condon region, leading to two predominant (S₄S₃-MIN and S₄S₁-MIN) internal conversion pathways. The lowest-lying S₂(1¹ππ^*) excited state is finally formed via subsequent internal conversions S₃(2¹nπ^*)/S₂(1¹ππ^*)-MIN and S₁(1¹nπ^*)/S₂(1¹ππ^*)-MIN. The enol-keto tautomeric mechanism does not seem to play a role. The decay mechanism in the singlet realm is proposed.