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

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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


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 π-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-dimethyl-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 π-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° to 80°. (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 π-π stacking distances of 8.665,7.883,7.361 Å, 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 (μβ) approach an unprecedented 900 000 × 10-48 esu, while estimated chromophore figures of merit, μβvec/Mw, approach 1500 × 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.

Original languageEnglish (US)
Pages (from-to)12521-12538
Number of pages18
JournalJournal of the American Chemical Society
Issue number39
StatePublished - Oct 7 2015

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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