Thermal-Responsive Second Harmonic Generation in Poly(Ethylene Oxide)/Chromophore Crystalline Films*

Amorphous, high-glass transition temperature polymer materials containing electric-field-poled nonlinear optical (NLO) chromophores have shown promise in optical information processing applications. A major hurdle in using hybrid polymer/NLO chromophore materials is that the chromophore orientation will randomize over time, drastically impairing and reducing widespread use. Here, we present that films composed of poly(ethylene oxide)/ 2-chloro-4-nitroaniline (PEO/CNA) host-guest crystalline complexes exhibit stable and long-term second harmonic generation (SHG) activity, which is a result of the alignment of chromophore molecules during film crystallization. Differential scanning calorimetry (DSC) and grazing incidence wide-angle X-ray scattering (GIWAXS) confirmed the formation of the crystalline complex structure. SHG results indicate the non-centrosymmetric structure in PEO/CNA crystalline complex, and SHG intensity is maintained while at room temperature for weeks. Furthermore, the hybrid films exhibit thermal-responsive SHG activity in which SHG intensity sharply decreases as the melting temperature of the film is approached due to the phase transition from a crystalline to a liquid state.