Electronic excitations and first hyperpolarizability of 2-methyl-4-nitroaniline clusters

Authors

  • Maxime Guillaume,

    1. Laboratoire de Chimie Théorique Appliquée, Facultés Universitaires Notre-Dame de la Paix, 61 rue de Bruxelles, B-5000 Namur, Belgium
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  • Edith Botek,

    1. Laboratoire de Chimie Théorique Appliquée, Facultés Universitaires Notre-Dame de la Paix, 61 rue de Bruxelles, B-5000 Namur, Belgium
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  • Benoît Champagne,

    Corresponding author
    1. Laboratoire de Chimie Théorique Appliquée, Facultés Universitaires Notre-Dame de la Paix, 61 rue de Bruxelles, B-5000 Namur, Belgium
    • Laboratoire de Chimie Théorique Appliquée, Facultés Universitaires Notre-Dame de la Paix, 61 rue de Bruxelles, B-5000 Namur, Belgium
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  • Frédéric Castet,

    1. Laboratoire de Physico-Chimie Moléculaire, UMR 5803 CNRS, Université Bordeaux I, 33405 Talence, Cedex, France
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  • Laurent Ducasse

    1. Laboratoire de Physico-Chimie Moléculaire, UMR 5803 CNRS, Université Bordeaux I, 33405 Talence, Cedex, France
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Abstract

The crystal packing effects upon the static and dynamic first hyperpolarizability of 2-methyl-4-nitroaniline (MNA) clusters have been addressed at the TDHF/AM1 level. Due to electrostatic interactions, in 1-D arrays of MNA unit cells extending along the a crystallographic axis, the effective hyperpolarizability strongly increases whereas stacking unit cells along the b or c axes leads to a reduction of these quantities. These effects are magnified in the case of frequency-dependent quantities. The first hyperpolarizability variations can mostly be related to bathochromatic and hypsochromatic shifts as well as to changes in transition dipole moments of the low-energy excited states that dominate the UV/visible absorption spectra. From calculations performed at the CIS/INDO/S level of approximation, these dominant excited states present an important intramolecular charge transfer character and bathochromatic (hypsochromatic) shifts are associated with increase (decrease) of the transition dipole moments. In addition, a large number of intermolecular charge-transfer excited states have been detected. In the small MNA aggregates as well as in clusters extending only along the b or c crystallographic axes, these excited states possess small transition dipole moments. On the other hand, when stacking MNA unit cells along the a axis the electrostatic interactions induce a decrease of the excitation energies and an increase of the transition dipole moments of these intermolecular charge transfer states. As a consequence, they account for a nonnegligible contribution to the first hyperpolarizability. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

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