Monolithic nonlinear optical chromophores with extended conjugate bridge: Large refractive index, high thermal and electro-optic stability

Abstract

Monolithic electro-optic (EO) molecular glasses are promising materials for optical waveguide device owing to their high chromophore loading density, high refractive indices and large EO coefficients (r33 values) for the optimization of in-device figure of merit (n3r33). However, the stability of EO molecular glasses including the poling induced r33 stability, chemical stability under both high temperature and high voltage in poling is still an obstruction for their real application. Herein, we used the chemical structural optimization, by means of introducing a large conjugated electron-bridge indacenodithiophene (IDT), to synthesize a monolithic EO molecular glass IDTC. Comprehensive properties of excellent glass-forming ability, high thermal stability (Td = 315 °C), and high glass transition temperature (Tg = 137 °C) was achieved in monolithic IDTC thin films. More significantly, refractive index of monolithic film was exceptionally high (n = 1.8294 @ 1310 nm and n = 1.7645 @1550 nm). The poled IDTC film exhibited the r33 value of 87.6 pm/V with large figure of merit (n3r33: 536 pm/V @1310 nm), and the EO activity can be retained over 85% of the initial value after 300 h annealing at 85 °C. Meanwhile, it was found that there is no decomposition of IDTC in poled films after high temperature and high voltage poling as well as long term annealing. The poled chromophores are recyclable EO materials for the sustainable application in low-cost EO devices.