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 a series of push-pull heptamethines containing the tricyanofuran (TCF) acceptors and indoline or benzo[e]indoline donors are reported. 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. A transmission-mode electromodulation spectroscopy is used to study the electric-field-induced changes in optical absorption and refraction of polymer films doped with heptamethine chromophores, and 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 is obtained. The study opens a path for developing organic materials based on cyanine-like merocyanines for complementary metal oxide semiconductor -compatible, fast, efficient, and low-loss electro-optic modulation. A series of heptamethines based on tricyanofuran acceptor and (benzo)indoline donors are reported. These heptamethines can attain a highly delocalized cyanine-like electronic ground state, even closer to the ideal cyanine-limit than symmetrical cyanines. The electric-field-induced changes in optical absorption of guest-host polymers are studied to demonstrate large quadratic electro-optic effect of materials with improved figure-of-merit.image

Automated summary

This study reports a series of heptamethines based on the tricyanofuran acceptor and indoline or benzo[e]indoline donors. These dipolar chromophores can attain a highly delocalized cyanine-like electronic ground state, even closer to the ideal polymethine state than symmetrical cyanines. A transmission-mode electromodulation spectroscopy is used to demonstrate a large and thermally stable quadratic electro-optic effect with high efficiency-loss figure-of-merits. The study opens a path for developing organic materials for fast, efficient, and low-loss electro-optic modulation.