Modular Synthesis and Interface Engineering of Guest–Host Polymers Containing Highly Asymmetrical Push–Pull Heptamethines for Electro-Optics

Push–pull
heptamethine chromophores (PPH-phores) containing
Michler’s base donor moieties exhibit limited solubility and
low loading density during film processing of guest–host electro-optic
(EO) polymers. To address the issues, we designed and synthesized
asymmetrical derivatives of Michler’s base through steric and
electronic modifications, yielding 11 highly asymmetrical PPH-phores
that incorporate various meso-substituents and strong
tricyanofuran acceptors. These diverse structural variations regulate
the electronic polarization and solution processability of the PPH-phores,
further determining their first hyperpolarizabilities (β values)
and optimal loading densities in guest–host polymers. The approach
effectively increased the loading levels of PPH-phores in poled guest–host
polymers by 23%, resulting in a substantial enhancement in the EO
coefficients (r33 values) of the materials.
Furthermore, for high-field poling of sandwiched EO polymer films,
inserting a solution-processable ultrathin SnO2 barrier
layer dramatically reduced the leakage current during poling, thereby
improving the poling efficiency of guest–host films. Together,
the modular synthesis and interface engineering presented in this
study achieved large r33 values, up to
149.1 pm/V at 1304 nm, from the poled films containing highly asymmetrical
PPH-phores, representing the best EO activities to date for PPH-phores
in poled polymer systems.