Anomalous aggregation of squaraine dyes in confined solutions

Enhanced aggregation of squaraine (SQ) dyes in solution capillary layers in contrast to the monomer behavior of the bulk solutions has been observed through differences in electronic absorption spectra of the capillary and bulk SQ solutions of the same concentration. The spectra of the capillary solutions were also different from spectra of SQ condensed films. The spectral differences were dependent on both chemical structure of the dye used and the solvent. It was found that aggregation was stronger in dimethylformamide (DMFA) capillary solutions when compared to the chloroform capillary solutions where aggregation was negligible. It is proposed that the driven force of the observed phenomena is enhanced adsorption of SQ molecules and formation of a liquid crystalline state of the solution near the liquid/solid interface.