A porphyrin-based gelator assembly which is reinforced by peripheral urea groups and chirally twisted by chiral urea additives

A novel porphyrin (1b) bearing four urea groups at its periphery was synthesized. This compound tends to aggregate into one-dimensional direction, resulting in an organogel phase in anisole and diphenyl ether solvents. The gel can be formed even at 0.125 wt/vol% in anisole and the sol-gel phase transition temperatures (T_gel) are as high as 120-140°C, indicating that 1b acts as an excellent gelator for these specific solvents. The spectroscopic studies and electron-micrographic observations support the view that the π-π stacking interaction among porphyrin moieties and the hydrogen-bonding interaction among urea moieties operate synergistically to give rise to a stable one-dimensional aggregate structure indispensable for gel formation. Further interestingly, chiral urea derivatives are bound to this aggregate to twist it in a chiral manner. This is a unique example for a rationally-designed organogelator including a porphyrin core and urea peripheral groups.