THE CHAMELEON DYE 1,7-BIS(DIMETHYLAMINO)HEPTAMETHINE

Communication: The influence of the alignment and density of dye molec ules on the spectroscopic properties of aggregates can be studied part icularly well in J-aggregates of 1,7-bis(dimethylamino)heptamethine (B DH(+)). Four different arrangements of BDH(+) molecules can be obtaine d without changing the molecular structure simply by using different c ounterions. The relationship between structure and linear spectroscopi c properties-including the color of crystals containing BDH(+)-is disc ussed.