ATR Analysis: Quantifying Molecular and Bulk Responses in Guest-Host Poled Polymers with Push-Pull Heptamethine Chromophores.

This study reports a systematic experimental and analytical workflow for evaluating push-pull heptamethine chromophores (PPH-phores) and their poled guest-host polymers for electro-optic (EO) applications. Attenuated total reflection (ATR) spectroscopy was used to accurately measure the optical birefringence and the DC/AC EO coefficients (r33 values) of poled films, establishing a direct correlation between molecular properties and bulk material responses. Sellmeier analysis of refractive-index dispersion quantified the nonresonant and low-energy resonance contributions and, combined with Kuzyk's two-component model, enabled reliable extraction of key parameters, including the order parameter (⟨P2⟩), dipole moment, and linear polarizability of PPH-phores. Incorporating the experimentally determined ⟨P2⟩, the rigid oriented gas model was applied to derive the first hyperpolarizability (β) of PPH-phore directly from measured r33 values. Across a comprehensive evaluation of 15 PPH-phores and 20 guest-host polymers, we identified an ultralarge dressed β of up to -34,000 × 10-30 esu and a linear polarizability of up to 9.31 × 10-22 cm3, the highest values reported to date for PPH-phores, which collectively translate into large r33 values in poled polymers. This integrated workflow accelerates structure-property relationship studies and facilitates the discovery and optimization of PPH-phores, supporting the scalable development of high-performance organic EO materials.