Strong difference between optical properties and morphologies for J-Aggregates of similar cyanine dyes

Abstract

Optical properties and morphologies of molecular aggregates of two similar cyanine dyes (BIC and TDBC) have been studied. The dyes have the same 5,5′,6,6′-tetrachlorobenzimidacarbocyanine chromophore part and differ just in one methyl group in alkyl chains. Due to such a similarity of the dye molecular structures, their aggregates are often supposed to have similar structure. However the difference in optical properties was reported in some publications assuming different structures of the J-aggregates. Indeed, we have found distinct morphologies for BIC and TDBC J-aggregates: spherical species for BIC J-aggregates and rod-like ones for TDBC J-aggregates. The difference in morphologies and, hence, structures is the reason of unlike optical properties of these J-aggregates.