Theoretical analyses of the effects on the linear and quadratic nonlinear optical properties of N-Arylation of pyridinium groups in stilbazolium dyes

Benjamin J. Coe, David Beljonne, Henryk Vogel, Javier Garín, Jesús Orduna

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    Abstract

    N-Arylation of the pyridinium electron acceptor unit in stilbazolium chromophores has been found by previous experimental hyper-Rayleigh scattering and electronic Stark effect (electroabsorption) spectroscopic studies to lead to substantial increases in the static first hyperpolarizability β0 (Coe, B. J. et al. Adv. Funct. Mater. 2002, 12, 110; 2003, 13, 347). We show here that INDO/SCI calculations on the isolated cations trans-4′-(dimethylamino)-N-R-4-stilbazolium (R = methyl 1, phenyl 2, 2,4-dinitrophenyl 3, or 2-pyrimidyl 4) predict only slight red-shifts in the energy of the intramolecular charge-transfer (ICT) transition and accompanying relatively small changes in β0 on moving along the series. The inclusion of acetonitrile solvent using a polarizable continuum model affords a somewhat better agreement with the experimental data, especially the red-shifting of the ICT transition and the increase in β0 on going from 1 to 4. Time-dependent density functional theory (TD-DFT), finite field, and coupled perturbed Hartree-Fock calculations reproduce even more closely the empirical data and trends; the latter two approaches lead to the highest quadratic nonlinear optical (NLO) response of the studied chromophores for 3, for which the predicted β0 is ca. 50-100% larger than that of the analogous N-methylated cation 1. Although the TD-DFT and INDO/SCI approaches give quite different results for ground- and excited-state dipole moments, the overall conclusions of these two methods regarding the ICT absorption and NLO responses are similar. © 2005 American Chemical Society.
    Original languageEnglish
    Pages (from-to)10052-10057
    Number of pages5
    JournalJournal of Physical Chemistry A
    Volume109
    Issue number44
    DOIs
    Publication statusPublished - 10 Nov 2005

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