Highly stable films of tetranitrotetrapropoxycalix [4]arene (9) with second-order nonlinear optical (NLO) properties and a noncentrosymmetric structure were obtained by a novel crystallization process at 130 ± 140 8C in a dc electric field. The packing of 9 in these films was elucidated by a combination of X-ray diffraction, angle-dependent second-harmonic generation, and scanning force microscopy (SFM).The experimental results agree well with solid-state molecular dynamics calculations for these films. No crystalline phase was observed for nitrocalix [4]arene derivatives with longer or branched alkyl chains; this explains the limited NLO stability of films of these calixarenes. Scanning force microscopy on the aligned films of 9 showed two distinct surface lattice structures: a rectangular lattice (a 9.3, b 11.7 ) and a pseudohexagonal lattice (d % 11.4 ). The combination of these data with the interlayer distance of 8.9 (X-ray diffraction) allowed the packing of molecules of 9 in these structures to be fully elucidated at the molecular level.
A new type of soluble calix [4]arene-based polyimides was prepared by reaction of bis(3aminopropyl) dipropyl functionalized tetranitrocalix[4]arenes with hexafluoroisopropylidene diphthalic anhydride. Spin-coating of these polymers and subsequent electric field poling results in films that are highly transparent above 410 nm and exhibit high and thermally stable second harmonic generation coefficients. These properties make these materials very suitable for frequency-doubling applications in the UV region (820-410 nm).
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