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Photoisomerization around a Fulvene Double Bond: Coherent Population Transfer to the Electronic Ground State?
Author(s) -
Ioffe Ilya,
Dobryakov Alexander L.,
Granovsky Alexander A.,
Ernsting Nikolaus P.,
Pérez Lustres J. Luis
Publication year - 2011
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.201001082
Subject(s) - conical intersection , chemistry , photoisomerization , ground state , population , fulvene , photochemistry , intramolecular force , molecular physics , ultrafast laser spectroscopy , atomic physics , isomerization , spectroscopy , physics , quantum mechanics , stereochemistry , biochemistry , demography , sociology , catalysis
Abstract Photoisomerization around a central fulvene‐type double bond is known to proceed through a conical intersection at the perpendicular geometry. The process is studied with an indenylidene–dihydropyridine model compound, allowing the use of visible excitation pulses. Transient absorption shows that 1) stimulated emission shifts to the red and loses oscillator strength on a 50 fs timescale, and 2) bleach recovery is highly nonexponential and not affected by solvent viscosity or methyl substitution at the dihydropyridine ring. Quantum‐chemical calculations are used to explain point 1 as a result of initial elongation of the central CC bond with mixing of S 2 and S 1 states. From point 2 it is concluded that internal conversion of S 1 →S 0 does not require torsional motion to the fully perpendicular state. The S 1 population appears to encounter a sink on the torsional coordinate before the conical intersection is reached. Rate equations cannot model the observed ground‐state recovery adequately. Instead the dynamics are best described with a strongly damped oscillatory contribution, which could indicate coherent S 1 –S 0 population transfer.