Molecular Origins of the High-Performance Nonlinear Optical Susceptibility in a Phenolic Polyene Chromophore: Electron Density Distributions, Hydrogen Bonding, and ab Initio Calculations

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• 作者：Tze-Chia Lin ; Jacqueline M. Cole ; Andrew P. Higginbotham ; Alison J. Edwards ; Ross O. Piltz ; Javier P茅rez-Moreno ; Ji-Youn Seo ; Seung-Chul Lee ; Koen Clays ; O-Pil Kwon
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：May 9, 2013
• 年：2013
• 卷：117
• 期：18
• 页码：9416-9430
• 全文大小：585K
• 年卷期：v.117,no.18(May 9, 2013)
• ISSN：1932-7455

文摘

The molecular and supramolecular origins of the superior nonlinear optical (NLO) properties observed in the organic phenolic triene material, OH1 (2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile), are presented. The molecular charge-transfer distribution is topographically mapped, demonstrating that a uniformly delocalized passive electronic medium facilitates the charge-transfer between the phenolic electron donor and the cyano electron acceptors which lie at opposite ends of the molecule. Its ability to act as a 鈥減ush鈥損ull鈥?蟺-conjugated molecule is quantified, relative to similar materials, by supporting empirical calculations; these include bond-length alternation and harmonic-oscillator stabilization energy (HOSE) tests. Such tests, together with frontier molecular orbital considerations, reveal that OH1 can exist readily in its aromatic (neutral) or quinoidal (charge-separated) state, thereby overcoming the 鈥渘onlinearity-thermal stability trade-off鈥? The HOSE calculation also reveals a correlation between the quinoidal resonance contribution to the overall structure of OH1 and the UV鈥搗is absorption peak wavelength in the wider family of configurationally locked polyene framework materials. Solid-state tensorial coefficients of the molecular dipole, polarizability, and the first hyperpolarizability for OH1 are derived from the first-, second-, and third-order electronic moments of the experimental charge-density distribution. The overall solid-state molecular dipole moment is compared with those from gas-phase calculations, revealing that crystal field effects are very significant in OH1. The solid-state hyperpolarizability derived from this charge-density study affords good agreement with gas-phase calculations as well as optical measurements based on hyper-Rayleigh scattering (HRS) and electric-field-induced second harmonic (EFISH) generation. This lends support to the further use of charge-density studies to calculate solid-state hyperpolarizability coefficients in other organic NLO materials. Finally, this charge-density study is also employed to provide an advanced classification of hydrogen bonds in OH1, which requires more stringent criteria than those from conventional structure analysis. As a result, only the strongest OH路路路NC interaction is so classified as a true hydrogen bond. Indeed, it is this electrostatic interaction that influences the molecular charge transfer: the other four, weaker, nonbonded contacts nonetheless affect the crystal packing. Overall, the establishment of these structure鈥損roperty relationships lays a blueprint for designing further, more NLO efficient, materials in this industrially leading organic family of compounds.