Thin layers of polymethine dye salts were prepared by a fast spin coating process. Depending on the aggregation tendency of the dye molecules four different layer types were obtained, consisting respectively of polycrystallines, randomly distributed molecules, randomly distributed J-aggregates, and large-scale oriented J-aggregates. The latter are formed by a hitherto unknown self-organization (Thin Layer Crystallization, TLC) process in the solid state. The layers were investigated by dichroic optical spectroscopy. The spectra were compared with spectroscopic and structural data obtained for single crystals of the same compounds. Conclusions were drawn concerning the layer structure and the self-organization process. The layer structure could be influenced by the aggregation parameters temperature and air humidity.