The acentric nature of trans-stilbazole crystals and the origin of its NLO response

The X-ray crystal structure and the second order nonlinear optical response of trans-stilbazole are discussed. Given that diffraction intensities are completely insensitive to any small distortion from centrosymmetry, stilbazole X-ray diffraction data are better modelled in the centrosymmetric P21/c space group and cannot be used to distinguish between alternative acentric options. However, second harmonic generation, notable in itself, sheds light on the acentric nature of the crystals and allows the most reasonable structural model to be selected. A previously unobserved low energy photoemission, probably due to through-space charge transfers, is also reported.