Centrosymmetric molecules for second harmonic generation

Research News: The requirement of a non-centrosymmetric structure for second harmonic generation (SHG) was until recently assumed necessarily to apply to the smallest building block, the molecule. However, non-centrosymmetric aggregates of centrosymmetric molecules can exist, and their SHG properties are considered here. Derivatives of squaraines are taken as examples. Finally, the role of intermolecular charge transfer in Langmuir-Blodgett film-forming materials for SHG-both within the monolayers and across the boundary-is discussed.