Studies on the interaction of achiral cationic pseudoisocyanine with chiral metal complexes

Abstract

The effect of chiral metal complexes ([Co(en)₃]I₃·H₂O, cis-[CoBr(NH₃)(en)₂]Br₂, K[Co(edta)]·2H₂O and [Ru(phen)₃](PF₆)₂) on the polymer-bound J-aggregates in aqueous mixtures of pesudoisocyanine (PIC) iodine and poly(acrylic acid, sodium)(PAAS) have been studied by UV–vis absorption, circular dichroism (CD) and fluorescence spectra. At low concentration, the PIC monomers could self-assemble to form supermolecules by binding to each of the COO⁻groups on the polymer chains through electrostatic interactions. After the addition of chiral metal complexes to the formed PIC-PAAS J-aggregates, we found that only the chiral multiple π-conjugated phenanthroline metal complexes could transfer their metal-centered chiral information to the formed J-aggregates. The chiral J-aggregates showed a characteristic induced circular dichroism (ICD) in the visible region of J-band chromophore, and the ICD signals depend on the absolute configuration, concentration of the chiral multiple π-conjugated metal complexes, as well as temperature. More interestingly, the supramolecular chirality of the polymer supported PIC J-aggregates could be memorized even after the addition of an excess opposite chiral complex enantiomers. This is in sharp contrast to the behavior in the high concentrated NaCl induced PIC-J aggregates, in which the optical rotation of a mixture of two enantiomers varies linearly with their ratio.