Tuning the dimensionality of functional thiazolo[5,4-d]thiazole based supramolecular polymers via competitive interactions

Abstract

The supramolecular organization of functional molecules at the mesoscopic level influences their material properties. Typically, planar π-conjugated (disc- or linear-shaped) molecules tend to undergo one-dimensional (1D) stacking, whereas two-dimensional (2D) organization from such building blocks is seldom observed in spite of their technological potential. Herein, we rationally achieve both 1D and 2D organizations from a single planar, π-conjugated molecular system via competitive interactions. We exemplify this concept through the supramolecular polymerization of amide functionalized thiazolo[5,4-d]thiazole chromophores into micron-sized, highly crystalline 2D sheets and 1D nanofibers in a range of different solvents. Solution-grown 2D sheets and 1D nanofibers with intermolecular hydrogen bonding were obtained for n-octyl and n-hexadecyl chain bearing derivatives, respectively. Molecular dynamics simulations reveal that for n-octyl derivatives weak C–H⋯S and C–H⋯N interactions between the π-conjugated cores of lateral monomers are dominant leading to 2D sheets, whereas with n-hexadecyl chains, enhanced van der Waals interactions of side-chains lead to 1D growth. For intermediate alkyl chain length (n-dodecyl), a competition between these two interactions leads to a combination of both 1D nanofibers and 2D sheets. The highly crystalline 2D sheets exhibit over two orders of magnitude higher electrical conductivity compared to their amorphous counterpart. We envisage that the strategy of competitive interaction could potentially be applicable to other heteroatom bearing chromophores to achieve tuneable soft functional materials.