Polymorphism in Squaraine Dye Aggregates by Self?Assembly Pathway Differentiation: Panchromatic Tubular Dye Nanorods versus J?Aggregate Nanosheets

A bis(squaraine) dye equipped with alkyl and oligoethyleneglycol chains was synthesized by connecting two dicyanomethylene substituted squaraine dyes a phenylene spacer unit. The aggregation behavior of this investigated in non-polar toluene/tetrachloroethane (98:2) solvent mixture, which revealed competing cooperative self-assembly pathways into supramolecular polymorphs entirely different packing structures UV/Vis/NIR absorption properties. pathway can be controlled the cooling rate from heated solution monomers. For both polymorphs, quasi-equilibrium conditions between monomers respective aggregates established to derive thermodynamic parameters insights mechanisms. AFM measurements nanosheet structure height 2 nm for thermodynamically more stable polymorph tubular nanorod helical pitch 13 diameter 5 kinetically favored polymorph. Together wide angle X-ray scattering measurements, models were derived: consists brick-work type nanosheets that exhibit red-shifted bands as typical J-aggregates, while eight polymer strands intertwined form chimney-type structure. aggregate covers large spectral range 550 875 nm, cannot rationalized conventional exciton theory. By applying Essential States Model considering intermolecular charge transfer, spectrum adequately reproduced, revealing broad is due pronounced donor-acceptor overlap within nanorods. latter also responsible bathochromic shift observed result slip-stacked arranged chromophores.