Color Variation in Highly Oriented Dye Layers by Polymorphism of Dye Aggregates

In aggregates of polymethine dyes the chromophores are tightly packed, causing strong intermolecular interactions, which lead to shifts of the absorption maxima. Thin layer aggregation (TLA) was used to form seven different polymorphs of a simple heptamethine dye in thin transparent films. It is demonstrated that large areas of uniform aggregate orientation can be achieved, yielding brilliantly colored spherulites, whose anisotropic absorption can be investigated directly in transmission by polarized UV/vis spectroscopy (see the inside front cover for an example).