Push–Pull Heptamethines Near the Cyanine Limit Exhibiting Large Quadratic Electro‐Optic Effect

Abstract

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