Second-harmonic generation in pure p-nitroaniline and in composites with polystyrene by flash evaporation

A new metastable phase of p-nitroaniline has been formed by flash evaporation from a toluene solution. This phase generates extremely strong second-harmonic radiation at 532 nm when illuminated with a near-infrared laser beam at 1064 nm. This observation is surprising since the stable crystalline phase exhibits no second harmonic and suggests that the new structure lacks a center of symmetry. The second-harmonic intensity decays over several days for the pure compound but remains unchanged over 3 months for the composite with polystyrene. Such nonlinear-optical materials are important for optoelectronic devices such as electro-optic modulators and switches used in telecommunications.