Controlling the Helicity of Tubular J-Aggregates by Chiral Alcohols

Abstract

The achiral 3,3‘-bis(3-carboxypropyl)-5,5‘,6,6‘-tetrachloro-1,1‘-dioctylbenzimidacarbocyanine dye (C8O3) self-aggregates in aqueous solution to form optically active helical J-aggregates. A three-phasic circular dichroism (CD) spectrum with positive Cotton effect at 568 nm, negative Cotton effect at 582 nm, and positive Cotton effect at 605 nm (+,−,+) is usually found and ascribed to molecular excitons. The predominance of the (+,−,+) signature means that the generation of chirality is enantioselective. The CD signal increases by a factor of about 100 when the chiral (R)-2-octanol is added to an aggregated solution, and the CD signal is further amplified by a factor of about 5 when the alcohol is present in the solvent prior to aggregation. The signature of the CD signal reverses if the enantiomeric (S)-2-octanol is used instead, and for a molar alcohol/dye ratio R of about 20, the spectra become mirror images in good approximation; i.e., the chirality of the alcohol and the CD spectra of aggregates are c...