Host–guest control on the formation of pinacyanol chloride H-aggregates in anionic polyelectrolyte solutions

Abstract

The interactions of pinacyanol chloride (PIN), a cationic cyanine dye, with the anionic polyelectrolyte poly(acrylic acid, sodium salt) (PAA) towards enhancing H-aggregation were investigated by electronic absorption spectroscopy. We employed the cucurbit[7]uril (CB7) host to control the formation of these aggregates via host–guest binding interactions with the dye molecules. Absorption spectroscopic studies clearly demonstrate that PAA enhances the formation of PIN H-aggregates. Electrostatic interactions between the cyanine dye molecules and the polyelectrolyte chains assist the formation of H-aggregates at very low dye concentrations (ca. 10 μM). Furthermore, the presence of CB7 was found to effectively disrupt the interactions responsible for dye aggregation. Thus, CB7 completely disrupts the H-aggregates (as well as lower concentrations of J-aggregates) by forming inclusion complexes with PIN. A competing guest, 1-aminoadamantane (AD), was utilised to adjust the extent of aggregation of the cyanine dye. AD regulates aggregate formation by forming an extremely stable complex with CB7 and exerting a tight control on the CB7 concentration available to interact and bind with the dye. Our spectroscopic data clearly indicate that by varying the relative molar ratios of CB7 host, AD and polyelectrolyte acid groups, we can quantitatively control the extent of formation of PIN H-aggregates in these solutions.

Keywords:

• aggregation
• H-aggregates
• cyanine dyes
• cucurbiturils
• molecular recognition

Acknowledgement

The authors are grateful to the National Science Foundation (to AEK, CHE-0600795) for the generous support of this work.