| Abstract
| - The squaraine dye bis(2,4,6-trihydroxyphenyl)squaraine (SqH) was earlier reported to form J-type dimeraggregates in acetonitrile solutions at higher concentrations. Subsequent studies have suggested thatconcentration-dependent changes in the absorption spectrum of SqH in acetonitrile could be attributed toshifts in the acid−base equilibrium due to the presence of water as an impurity. In this work, we describe ourstudies on the effect of varying acid and dye concentration on the absorption spectra of the bromo and iodosubstituted dyes, bis(3,5-dibromo-2,4,6-trihydroxyphenyl)squaraine (SqBr) and bis(3,5-diiodo-2,4,6-trihydroxyphenyl)squaraine (SqI). Analysis of the changes in the absorption spectra as a function of dyeconcentration and the nature of the solvent composition confirmed the formation of J-type dimer aggregatesin aprotic solvents in this class of dyes. Further confirmation for the formation of the J-type dimer aggregatescould be obtained by comparing the differences in the triplet excited state properties of the neutral andaggregated forms of the dyes using time-resolved spectroscopy.
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