Kinetics of spontaneous formation of chiral J-aggregate of N-sulfobutyl oxacarbocyanine.

An oxacarbocyanine with N-sulfobutyl substituents, dye 1, exhibits an ability to form optically active J-aggregates in aqueous solution in the absence of chiral auxiliaries or templates. Optically active J-aggregates are formed in the absence (self-association) and presence of mono- and divalent metal ions. The time course of formation of J-aggregates is described by a sigmoidal time dependence and further characterized by an induction period. The chirality arises either at the step of nucleation or because of conversion of an achiral aggregate (J1) into a chiral one (J2). A monomeric ion pair formed between the anionic dye and the metal cation is the precursor of both aggregates. A red-shifted absorption band, resonance fluorescence, and mono- or bisignate circular dichroism (CD) signals are characteristics of J2. The shape and sign of the CD signal as well as the number of molecules coherently coupled in J2 depend upon the type of metal ion. The presence of N-sulfobutyl groups in 1 results in a relatively high hydrophobicity of the dye molecule, determining the formation of the J2-aggregate.