Side chain-directed assembly of large discotic π-conjugated molecules: Toward tuning and stabilization of mesophases

A representative π-conjugated motif, perylenediimide (PDI), when functionalized with taper-shaped semi-fluoroalkyl chains at one of its imide positions, self-assembled into various ordered phase structures depending on the type of side chains at the other imide position. Asymmetrical substitution by semi-fluoroalkyl/alkyl chains allowed the PDI molecule to form a rectangular columnar liquid crystalline mesophase while semi-fluoroalkyl/triethyleneglycol-substitution resulted in a lamellar-packed crystalline mesophase. In both mesophases, the immiscible nature of superhydrophobic/hydrophobic or superhydrophobic/hydrophilic segments works as the major droving force to lead semi-fluoroalkyl/alkyl or semi-fluoroalkyl/oxyethyleneglycol nano-domains, resulting in high stability of the mesophases with the wide temperature range over 100ºC. The compound decorated with tapered semi-fluoroalkyl chains at the both imide positions exhibited complicated crystalline ordered phases with high thermal stability.