Controlled Self-Assembly of C3-Symmetric Hexa-peri-hexabenzocoronenes with Alternating Hydrophilic and Hydrophobic Substituents in Solution, in the Bulk, and on a Surface

In this work, we introduce a class of C-symmetric hexa-peri-hexabenzocoronenes (HBCs) 1 with alternating hydrophilic and hydrophobic substituents to achieve control over the self-assembly of discotic nanographene molecules. Our studies show that the following structural parameters and experimental conditions are essential for tailoring the formation of the liquid-crystalline phase in the bulk as well as the self-assembly in solution and on surfaces: (1) steric demand of alkyl and alkylphenyl substituents; (2) noncovalent hydrophilic-hydrophobic interactions of the substituents; and (3) processing conditions, such as the type and mixture of solvents of different polarities along with the nature of the surface. The substitution of HBC with linear alkyl side chains possessing less steric demand (1b) leads to high crystallinity in the bulk solid state and at the liquid-solid interface, and the additional feature of alternating hydrophilic and hydrophobic substituents promotes a high aggregation tendency in polar/apolar solvent mixtures. In contrast, bulky branched alkyl chains (1a) and alkylphenyl substituents (1c) induce liquid crystallinity over the whole temperature range measured. While la does not show pronounced self-assembly in solution, compound 1c displays, even at high temperatures, aggregation in polar/apolar solution due to the intermolecular "locking" of peripheral phenyl groups. After solution deposition on a surface, distinct fiber formation is observed for the HBC derivatives, which is related to the solution self-assembly behavior. The present work provides further insight into the molecular design and self-assembly of discotic nanographene materials.