Fragile arrangements of self-organized J aggregates of pseudoisocyanine dye at a glass/solution interface

Self-organized J aggregates of a 1,1'-diethyl-2,2'-cyanine (pseudoisocyanin e: PIC) dye produced at a soda lime glass/solution interface (J(L) aggregat e) were characterized. The dye concentration dependence of J(L) aggregation showed a quasi-adsorption behavior owing to formation of the aggregates at anionic sites on the glass surface. An increase in the PIC concentration a ccompanied a slight red shift of the J(L) band as well as a decrease in the fluorescence lifetime. The results suggested that the J(L) aggregate posse ssed relatively fragile arrangements. In order to discuss the structures of the aggregates, we proposed a new approach to estimating the number of int eracting molecules (N) in the aggregate on the basis of a thermodynamic con sideration for self-association of molecules and an adsorption isotherm. Th en, we estimated N to be 6 in the J(L) aggregates when N is assumed to be u nchanged. According to extended dipole model calculations for a brickstone or staircase structure with N = 6, the concentration dependence of the opti cal properties of the J(L) band was reasonably explained by assuming loose and fragile arrangements of PIC molecules in the aggregates. The amorphous solid surface of the glass was shown to be the origin for fragile arrangeme nts of PIC molecules in the J(L) aggregates.