Linkage Photoisomerization Mechanism in a Photochromic Ruthenium Nitrosyl Complex: New Insights from an MS-CASPT2 Study

• Published in: Journal of chemical theory and computation Vol. 13; no. 12; pp. 6120 - 6130
• Main Authors: Talotta, Francesco, Heully, Jean-Louis, Alary, Fabienne, Dixon, Isabelle M, González, Leticia, Boggio-Pasqua, Martial
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 12-12-2017
• Subjects: Charge transfer; Chemical Sciences; Density functional theory; Isomers; or physical chemistry; Perturbation theory; Photochromism; Potential energy; Ruthenium; Theoretical and
• ISSN: 1549-9618; 1549-9626
• DOI: 10.1021/acs.jctc.7b00982

The N → O linkage photoisomerization mechanism in a ruthenium nitrosyl complex, [RuCl­(NO)­(py)4]2+, for which a quasicomplete photoconversion between the stable nitrosyl (N-bonded) and metastable isonitrosyl (O-bonded) isomers has been observed under continuous irradiation of the crystal at 473 nm ( Cormary et al. Acta Cryst. B 2009, 65, 612−623 ), is investigated using multiconfigurational second-order perturbation theory (CASPT2). The results support efficient intersystem crossing pathways from the initially excited singlet states to the lowest triplet excited state of metal-to-ligand charge transfer character (3MLCT). The topology of the involved potential energy surfaces corroborates a complex sequential two-photon photoisomerization mechanism involving nonadiabatic processes in agreement with experimental observations and previous density functional theory calculations.