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Computational Photochemistry of the Azobenzene Scaffold of Sudan I and Orange II Dyes: Excited‐State Proton Transfer and Deactivation via Conical Intersections
Author(s) -
Guan PeiJie,
Cui Ganglong,
Fang Qiu
Publication year - 2015
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201402743
Subject(s) - photochemistry , excited state , intramolecular force , chemistry , conical intersection , ground state , diabatic , chromophore , hydrogen bond , chemical physics , atomic physics , molecule , physics , stereochemistry , organic chemistry , adiabatic process , thermodynamics
We employed the complete active space self‐consistent field (CASSCF) and its multistate second‐order perturbation (MS‐CASPT2) methods to explore the photochemical mechanism of 2‐hydroxyazobenzene, the molecular scaffold of Sudan I and Orange II dyes. It was found that the excited‐state intramolecular proton transfer (ESIPT) along the bright diabatic 1 ππ* state is barrierless and ultrafast. Along this diabatic 1 ππ* relaxation path, the system can jump to the dark 1 n π* state via the 1 ππ*/ 1 n π* crossing point. However, ESIPT in this dark state is largely inhibited owing to a sizeable barrier. We also found two deactivation channels that decay 1 ππ* keto and 1 n π* enol species to the ground state via two energetically accessible S 1 /S 0 conical intersections. Finally, we encountered an interesting phenomenon in the excited‐state hydrogen‐bonding strength: it is reinforced in the 1 ππ* state, whereas it is reduced in the 1 n π* state. The present work sets the stage for understanding the photophysics and photochemistry of Sudan I–IV, Orange II, Ponceau 2R, Ponceau 4R, and azo violet.