Photophysics of aromatic molecules with low-lying πσ* states: excitation-energy dependence of fluorescence in jet-cooled aromatic nitriles

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DOIResolve DOI: http://doi.org/10.1021/jp050889b
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TypeArticle
Journal titleThe Journal of Physical Chemistry A
Volume109
Issue32
Pages71217126; # of pages: 6
AbstractExcitation-energy dependence of fluorescence intensity and fluorescence lifetime has been measured for 4-dimethylaminobenzonitrile (DMABN), 4-aminobenzonitrile (ABN), 4-diisopropylaminobenzonitrile (DIABN), and 1-naphthonitrile (NN) in a supersonic free jet. In all cases, the fluorescence yield decreases rather dramatically, whereas the fluorescence lifetime decreases only moderately for S1 (ππ*, Lb) excess vibrational energy exceeding about 1000 cm-1. This is confirmed by comparison of the normalized fluorescence excitation spectrum with the absorption spectrum of the compound in the vapor phase. The result indicates that the strong decrease in the relative fluorescence yield at higher energies is due mostly to a decrease in the radiative decay rate of the emitting state. Comparison of the experimental results with the TDDFT potential energy curves for excited states strongly suggests that the decrease in the radiative decay rate of the aminobenzonitriles at higher energies is due to the crossing of the ππ* singlet state by the lower-lying πσ*C≡N singlet state of very small radiative decay rate. The threshold energy for the fluorescence “break-off” is in good agreement with the computed energy barrier for the ππ*/πσ* crossing. For NN, on the other hand, the observed decrease is in fluorescence yield at higher excitation energies can best be attributed to the crossing of the ππ* singlet state by the πσ* triplet state.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada; NRC Steacie Institute for Molecular Sciences
Peer reviewedYes
NPARC number12327458
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Record identifier13348e2e-21c9-40c2-a1dd-c5923ebfb3eb
Record created2009-09-10
Record modified2017-03-23
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