J-aggregate structures in crystals of three bisazomethine dyes

The crystal structures of three bisazomethine dyes, which form J-aggregates in vapor-deposited films, were investigated. The characteristic two-dimensional arrangement of molecules proposed for J-aggregates was recognized in crystals of all three dyes. The observation of unusual bond lengths in one of the dyes at 298 K was resolved by a low temperature study, i.e. 93 K, that showed the existance of conformational disorder at the higher temperature.