Highly thermally stable binary cross-linkable organic nonlinear optical materials based on different Diels–Alder or Huisgen cycloaddition reactions†

The development of binary crosslinkable electro-optic materials with 100 wt% chromophores, which possess an ultrahigh electro-optic coefficient and high long-term alignment stability, has been a crucial goal. Anthracene–maleimide and maleimide–furan-based Diels–Alder (DA) reactions and azide–alkyne-based Huisgen cycloaddition reaction were developed for making highly efficient binary cross-linkable tetrahydroquinoline-based chromophores QLD1 and QLD3–QLD6. A polymer cross-linked network was formed by these three reactions at different temperatures after electric field poling orientation, which greatly improved the stability of the materials. Electro-optic coefficients of up to 234–312 pm V⁻¹ and glass transition temperatures as high as 118–160 °C were achieved in these cross-linked films owing to their high chromophore density (5.24–5.71 × 10²⁰ molecules per cm³) and large hyperpolarizability. Long-term and high-temperature stability tests showed that after heating at 85 °C for over 500 h, 93.45 and 95.13% of the initial r₃₃ value was maintained for the poled and cross-linked electro-optic films 2 : 1 QLD5/QLD6 and 1 : 1 QLD1/QLD3, respectively. These results provide a very effective molecular engineering approach to systematically design binary cross-linked electro-optic materials for high performance device applications.