Reference interaction site model study of self-aggregating cyanine dyes.

Area of Science:

• Supramolecular chemistry
• Physical chemistry
• Dye aggregation

Background:

• Cyanine dyes are crucial in various applications.
• Understanding their aggregation behavior in solution is key to controlling their properties.
• Previous models often lack accuracy in predicting complex aggregation structures.

Purpose of the Study:

• To model the aggregation of cyanine dyes in aqueous solutions.
• To investigate the stability and structural transitions of dye aggregates.
• To develop a predictive model for self-assembly in water.

Main Methods:

• Utilized the reference interaction site model (RISM) and supramolecular approach.
• Studied various modifications of the hypernetted-closure (HNC) expression for excess free energy.
• Employed partial wave approximation with semiempirical corrections for excluded volume and hydrogen bonding.

Main Results:

• The RISM-HNC model accurately predicted binding and dimerization energies, aligning with experimental data.
• Hydrated H-dimers were found to be more stable than hydrated J-dimers.
• Complexes of more than four monomers self-assemble into ladderlike structures, a novel finding.

Conclusions:

• The developed model provides reliable predictions for cyanine dye aggregation.
• Hydrated H-dimers represent the most stable dimeric form.
• A structural transition to ladderlike aggregates occurs for larger dye complexes, explained by the proposed model.