Twisted π-Electron System Electrooptic Chromophores. Structural and Electronic Consequences of Relaxing Twist-Inducing Nonbonded Repulsions

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• 作者：Yiliang Wang ; David L. Frattarelli ; Antonio Facchetti ; Elena Cariati ; Elisa Tordin ; Renato Ugo ; Cristiano Zuccaccia ; Alceo Macchioni ; Staci L. Wegener ; Charlotte L. Stern ; Mark A. Ratner ; Tobin J. Mark
• 刊名：Journal of Physical Chemistry C
• 出版年：2008
• 出版时间：May 29, 2008
• 年：2008
• 卷：112
• 期：21
• 页码：8005 - 8015
• 全文大小：740K
• 年卷期：v.112,no.21(May 29, 2008)
• ISSN：1932-7455

文摘

The synthesis, structural and spectroscopic characterization, and nonlinear optical response properties of a “slightly” twisted zwitterionic 4-quinopyran electrooptic chromophore FMC, 2-{4-[1-(2-propylheptyl)-1H-pyridine-4-ylidene]cyclohexa-2,5-dienylidene}malononitrile, are reported. X-ray diffraction data and density functional theory (DFT) minimized geometries confirm that deletion of the four o-, o′-, o′′-, and o′′′-methyl groups in the parent chromophore TMC-2, 2-{4-[3,5-dimethyl-1-(2-propylheptyl)-1H-pyridin-4-ylidene]-3,5-dimethylcyclohexa-2,5-dienylidene}malononitrile, relaxes the arene−arene twist angle from 89.6 to 9.0°. These geometrical changes result in a significantly increased contribution of the quinoidal structure to the molecular ground state of FMC (versus TMC-2), reduced solvatochromic shifts in the optical spectra, and a diminished electric-field-induced second-harmonic (EFISH) generation derived molecular hyperpolarizability (μβ = −2340 × 10⁻⁴⁸ esu of DFMC, the dendrimer derivative of FMC, vs −24000 × 10⁻⁴⁸ esu of TMC-2) in CH₂Cl₂ at 1907 nm. Pulsed field gradient spin–echo (PGSE) NMR spectroscopy and EFISH indicate that the levels of FMC aggregation in solution are comparable to those of TMC-2 (monomers and dimers) in CH₂Cl₂ solution. B3LYP and INDO/S computation of chromophore molecular structure, aggregation, and hyperpolarizability trends are in good agreement with experiment.