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Issue 4, 2002
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Ultrafast charge transfer via a conical intersection in dimethylaminobenzonitrile

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Abstract

The La-like S2 state (2A) of 4-(dimethylamino)benzonitrile was pumped at 267 nm in the gas phase at 130 °C. Nonresonant multiphoton ionization at 800 nm with mass-selective detection then probed the subsequent processes. Whereas ionization at the Franck–Condon geometry only gave rise to the parent ion, fragmentation increased on motion towards the charge-transfer (CT) state. This useful difference is ascribed to a geometry-dependent resonance in the ion. The time constants found are interpreted by ultrafast (≈68 fs) relaxation through a conical intersection to both the CT and the Lb-type S1 state (1B). Then the population equilibrates between these two states within 1 ps. From there the molecule relaxes within 90 ps to a lower excited state which can only be a triplet state (Tn) and then decomposes within 300 ps. Previous experiments either investigated only 1B→CT relaxation—which does not take place in the gas phase or nonpolar solvents for energetic reasons—or, starting from S2 excitation, typically had insufficient time resolution (>1 ps) to detect the temporary charge transfer. Only recently temporary population of the CT state was found in a nonpolar solvent (Kwok et al., J. Phys. Chem. A, 2000, 104, 4188), a result fully consistent with our mechanism. We also show that S2→S1 relaxation does not occur vertically but involves an intermediate strong geometrical distortion, passing through a conical intersection.

Graphical abstract: Ultrafast charge transfer via a conical intersection in dimethylaminobenzonitrile

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Publication details

The article was received on 03 Jan 2002, accepted on 25 Jan 2002 and first published on 18 Feb 2002


Article type: Paper
DOI: 10.1039/B111678A
Citation: Photochem. Photobiol. Sci., 2002,1, 255-262
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    Ultrafast charge transfer via a conical intersection in dimethylaminobenzonitrile

    W. Fuß, K. K. Pushpa, W. Rettig, W. E. Schmid and S. A. Trushin, Photochem. Photobiol. Sci., 2002, 1, 255
    DOI: 10.1039/B111678A

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