Hydrogen Bond-Assisted Supramolecular Self-Assembly of Doubly Discotic Supermolecules Based on Porphyrin and Triphenylene

Hydrogen bonding is a powerful driving force for the supramolecular self-assembly of discotic mesogens, and molecular shape also plays an important role in such systems. To study these effects, doubly discotic supermolecules have been synthesized by linking a meso -tetraphenylporphine-4,4′,4′′,4′′′-tetracarboxylic acid (Py) core with four triphenylenes (Tp) arms via either amide or ester bonds. The spacer length between the Py core and Tp disks was C6 and C10, and the alkyl arm length in the Tp disks was C5 and C12, respectively. Compared to the ester-linked Py(Tp) 4 supermolecules, the amide-linked samples exhibited rich crystalline and liquid-crystalline phases, suggesting that the intracolumnar hydrogen-bonding among trans amide bonds was the primary driving force for the self-assembly. X-ray diffraction (XRD) was used to understand the supramolecular self-assembly of the amide-linked Py(Tp) 4 doubly discotic supermolecules. When the spacer length was no shorter than or similar to the triphenylene alkyl arm length, a rectangular boardlike molecular shape was adopted and thus lamellar structures were obtained. When the spacer length was much shorter than the triphenylene alkyl arms, an ellipsoidal overall molecular shape resulted, and thus a regular columnar phase was obtained. From this study, we speculated that hydrogen-bond-induced microphase separation between moieties with different electron affinities in doubly discotic supermolecules may be useful for the practical applications of organic electronics.