EXCITON-POLARITON AND CHARGE TRANSFER STATES IN POLYMORPHS OF QUASI-METALLIC CRYSTALS OF DYES

The reflection spectra of different crystalline forms of two dyes, pseudoisocyanine iodide (PIC) and 2,4-bis (4-diethylamino-2-hydroxy phenyl) cyclobutadienediylium-1,2-diolate (HEAPS), have been investigated in order to gain understanding of dye aggregation. The study involves clarification of earlier conflicting results for PIC and the examination of polymorphs of HEAPS. The discovery of another crystalline form of PIC is also reported. Crystal spectra are presented which indicate the possible relation to the J-band observed in dye aggregation