The low-lying {pi}{sigma}* state and its role in the intramolecular charge transfer of aminobenzonitriles and aminobenzethyne

Journal Article · Mon Apr 28 04:00:00 EDT 2008 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.2901976· OSTI ID:21104038

Lee, Jae-Kwang; Fujiwara, Takashige; Kofron, William G ^[1]; Zgierski, Marek Z; Lim, Edward C ^[2]

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1. Department of Chemistry and Center for Laser and Optical Spectroscopy, University of Akron, Akron, Ohio 44325-3601 (United States)
2. Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa K1A 0R6 (Canada)

Electronic absorption spectra of the low-lying {pi}{pi}* and {pi}{sigma}* states of several aminobenzonitriles and 4-dimethylaminobenzethyne have been studied by time-resolved transient absorption and time-dependent density functional theory calculation. In acetonitrile, the lifetime of the {pi}{sigma}*-state absorption is very short (picoseconds or subpicosecond) for molecules that exhibit intramolecular charge transfer (ICT), and very long (nanoseconds) for those that do not. Where direct comparison of the temporal characteristics of the {pi}{sigma}*-state and the ICT-state transients could be made, the formation rate of the ICT state is identical to the decay rate of the {pi}{sigma}* state within the experimental uncertainty. These results are consistent with the {pi}{sigma}*-mediated ICT mechanism, L{sub a} ({pi}{pi}*){yields}{pi}{sigma}*{yields}ICT, in which the decay rate of the {pi}{sigma}* state is determined by the rate of the solvent-controlled {pi}{sigma}*{yields}ICT charge-shift reaction. The {pi}{pi}*{yields}{pi}{sigma}* state crossing does not occur in 3-dimethylaminobenzonitrile or 2-dimethylaminobenzonitrile, as predicted by the calculation, and 4-aminobenzonitrile and 4-dimethylaminobenzethyne does not exhibit the ICT reaction, consistent with the higher energy of the ICT state relative to the {pi}{sigma}* state.

• OSTI ID: 21104038
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 16 Vol. 128; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABSORPTION
ABSORPTION SPECTRA
ACETONITRILE
AMINES
AROMATICS
DENSITY FUNCTIONAL METHOD
EXCITED STATES
LIFETIME
REACTION KINETICS
SOLVENTS
TIME DEPENDENCE
TIME RESOLUTION
TRANSIENTS