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

作者：Shi Yanrong; Frattarelli David; Watanabe Naoki; Facchetti Antonio; Cariati Elena; Righetto Stefania; Tordin Elisa; Zuccaccia Cristiano; Macchioni Alceo; Wegener Staci L; Stern Charlotte L; Ratner Mark A; Marks Tobin J

来源：Journal of the American Chemical Society, 2015, 137(39): 12521-12538.

DOI：10.1021/jacs.5b04636

The systematic synthesis, structural, optical spectroscopic, and second-order nonlinear optical (NLO) characterization of a series of donor-acceptor poly-arylene chromophores which have heretofore unachieved pi-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'-(3,5-dimethyl-1-(2-propylheptyl)pyridin-1-ium-4-yl)-2,2',3',5',6'-pentamethyl[1,1'-biphenyl]-4-yl)methanide; and four-ring 4TTMC, dicyano (4 ''-(3,5-ciimethyl-1- (2-propylheptyl)-pyridin-1-ium-4-yl)-2,2',3 '',6,6'-pentamethyl[1,1':4',1 ''-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 pi-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',o '',o'"-tetramethylbiaryl junctures, only slightly relaxes the biaryl twist angle from 89.6 degrees to similar to 80 degrees. (3) Increased arylene catenation from two to three to four rings (2TTMC -> 3TTMC -> 4TTMC) greatly enhances NLO response, zwitterionic charge localization, and thus the ground-state dipole moment, consistent with the contracted antiparallel solid-state pi-pi stacking distances of 8.665 -> 7.883 -> 7.361 angstrom, respectively. This supports zwitterionic ground states in these chromophores as do significant optical spectroscopic solvatochromic shifts, with aryl-aryl twisting turning on significant intra-subfragment absorption. Computed molecular hyperpolarizabilities (mu beta) approach an unprecedented 900 000 X 10(-48) esu, while estimated chromophore figures of merit, mu beta(vec)/M-w, approach 1500 X 10(-48) esu, 1.5 times larger than the highest known values for twisted chromophores and >33 times larger than that of planar donor-acceptor chromophores.

• 出版日期2015-10-7
• 单位西北大学