Ultra-High-Response, Multiply Twisted Electro-optic Chromophores: Influence of 蟺-System Elongation and Interplanar Torsion on Hyperpolarizability

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• 作者：Yanrong Shi ; David Frattarelli ; Naoki Watanabe ; Antonio Facchetti ; Elena Cariati ; Stefania Righetto ; Elisa Tordin ; Cristiano Zuccaccia ; Alceo Macchioni ; Staci L. Wegener ; Charlotte L. Stern ; Mark A. Ratner ; Tobin J. Marks
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：October 7, 2015
• 年：2015
• 卷：137
• 期：39
• 页码：12521-12538
• 全文大小：1016K
• ISSN：1520-5126

文摘

The systematic synthesis, structural, optical spectroscopic, and second-order nonlinear optical (NLO) characterization of a series of donor鈥揳cceptor poly-arylene chromophores which have heretofore unachieved 蟺-extension and substantial twisting from planarity, are reported: specifically, two-ring 2TTMC, dicyano(4-(3,5-dimethyl-1-(2-propylheptyl)pyridin-1-ium-4-yl)-3-methylphenyl)methanide; three-ring 3TTMC, dicyano(4鈥?(3,5-dimethyl-1-(2-propylheptyl)pyridin-1-ium-4-yl)-2,2鈥?3鈥?5鈥?6鈥?pentamethyl[1,1鈥?biphenyl]-4-yl)methanide; and four-ring 4TTMC, dicyano(4鈥?(3,5-dimethyl-1-(2-propylheptyl)pyridin-1-ium-4-yl)-2,2鈥?3鈥?6,6鈥?pentamethyl[1,1鈥?4鈥?1鈥?terphenyl]-4-yl)methanide. Single-crystal X-ray diffraction, DFT-optimized geometries, and B3LYP/INDO-SOS analysis identify three key features underlying the very large NLO response: (1) For ring catenation of three or greater, sterically enforced 蟺-system twists are only essential near the chromophore donor and acceptor sites to ensure large NLO responses. (2) For synthetic efficiency, deletion of one ortho-methyl group from o,o鈥?i>,o鈥?i>,o鈥?tetramethylbiaryl junctures, only slightly relaxes the biaryl twist angle from 89.6掳 to 鈭?0掳. (3) Increased arylene catenation from two to three to four rings (2TTMC鈫?3TTMC 鈫?4TTMC) greatly enhances NLO response, zwitterionic charge localization, and thus the ground-state dipole moment, consistent with the contracted antiparallel solid-state 蟺鈥撓€ stacking distances of 8.665 鈫?7.883 鈫?7.361 脜, respectively. This supports zwitterionic ground states in these chromophores as do significant optical spectroscopic solvatochromic shifts, with aryl鈥揳ryl twisting turning on significant intra-subfragment absorption. Computed molecular hyperpolarizabilities (渭尾) approach an unprecedented 900鈥?00 脳 10^鈥?8 esu, while estimated chromophore figures of merit, 渭尾_vec/M_w, approach 1500 脳 10^鈥?8 esu, 1.5 times larger than the highest known values for twisted chromophores and >33 times larger than that of planar donor鈥揳cceptor chromophores.