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.
Zhang et al. (Thu,) studied this question.