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Electron–phonon coupling and vibrational modes contributing to linear electro‐optic effect of the efficient NLO chromophore 4‐( N , N ‐dimethylamino)‐ N ‐methyl‐4′‐toluene sulfonate (DAST) from their vibrational spectra
Author(s) -
Vijayakumar T.,
Hubert Joe I.,
Reghunadhan Nair C. P.,
Jazbinsek Mojca,
Jayakumar V. S.
Publication year - 2009
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.2073
Subject(s) - natural bond orbital , chemistry , hyperpolarizability , intramolecular force , density functional theory , homo/lumo , molecular orbital , raman spectroscopy , hyperconjugation , molecular vibration , solvatochromism , mulliken population analysis , chromophore , hydrogen bond , time dependent density functional theory , computational chemistry , photochemistry , crystallography , stereochemistry , molecule , organic chemistry , physics , optics , polarizability
The optimized geometry and structural features of the most prospective electro‐optic crystal 4‐( N , N ‐dimethylamino)‐ N ‐methyl‐4′‐toluene sulfonate (DAST), and the vibrational spectral investigations have been comprehensively described with the near infrared Fourier transform (NIR FT) Raman and Fourier transform infrared (FT‐IR) spectra supported by the density functional theoretical (DFT) computations to elucidate the contribution of vibrational modes to the linear electro‐optic (LEO) effect. Mulliken population analysis and natural bond orbital (NBO) analysis have also been carried out to analyze the effects of intramolecular charge transfer (ICT), intramolecular hydrogen bonding and hyperconjugative interactions on the geometries. The influence of CT interaction between the phenyl ring and the dimethylamino group of the nonlinear optical (NLO) chromophore on the endocyclic and exocyclic angles, and the electronic effects such as hyperconjugation and back‐donation on the methyl hydrogen atoms have been examined. The concurrent intense activation of Raman and IR activities of the effective conjugation vibrational coordinate, which significantly contributes to the LEO effect resulting from the strong electron–phonon (e/ph) coupling, has been analyzed in detail. The effects of frontier orbitals, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), transition of electron density (ED) transfer and the influence of planarity in the stilbazolium ring on the first hyperpolarizability are also discussed. Copyright © 2008 John Wiley & Sons, Ltd.