Push-pull Heptamethines Near The Cyanine Limit Exhibiting Large Quadratic Electro-Optic Effect.

Harnessing the quadratic electro-optic (QEO) of near-infrared polymethine chromophores over broad telecom wavelength bands is a subject of immense potential but remains largely under-investigated. Herein we report a series of push-pull heptamethines containing the tricyanofuran (TCF) acceptors and indoline or benzo[e]indoline donors. These dipolar chromophores can attain a highly delocalized "cyanine-like" electronic ground state in solvents spanning a wide range of polarities, in some cases even closer to the ideal polymethine state than symmetrical cyanines. We use a transmission-mode electromodulation spectroscopy to study the electric-field-induced changes in optical absorption and refraction of polymer films doped with heptamethine chromophores, and obtain large and thermally stable QEO effect with high efficiency-loss figure-of-merits that compare favorably to those from dipolar polyenes in poled or unpoled polymers and III-V semiconductors. Our study opens a path for developing organic materials based on cyanine-like merocyanines for CMOS-compatible, fast, efficient, and low-loss electro-optic modulation. This article is protected by copyright. All rights reserved.