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[摘要]：The synthesis, self-assembly, and gelation ability of a series of organogelators based on perylene bisimide (PBI) dyes contg. amide groups at imide positions are reported. The synergetic effect of intermol. hydrogen bonding among the amide functionalities and p-p stacking between the PBI units directs the formation of the self-assembled structure in soln., which beyond a certain concn. results in gelation. Effects of different peripheral alkyl substituents on the self-assembly were studied by solvent- and temp.-dependent UV-visible and CD (CD) spectroscopy. PBI derivs. contg. linear alkyl side chains in the periphery formed H-type p stacks and red gels, whereas by introducing branched alkyl chains the formation of J-type p stacks and green gels could be achieved. Sterically demanding substituents, in particular, the 2-ethylhexyl group completely suppressed the p stacking. Coaggregation studies with H- and J-aggregating chromophores revealed the formation of solely H-type p stacks contg. both precursor mols. at a lower mole fraction of J-aggregating chromophore. Beyond a crit. compn. of the two chromophores, mixed H-aggregate and J-aggregate were formed simultaneously, which points to a self-sorting process. The versatility of the gelators is strongly dependent on the length and nature of the peripheral alkyl substituents. CD spectroscopic studies revealed a preferential helicity of the aggregates of PBI building blocks bearing chiral side chains. Even for achiral PBI derivs., the utilization of chiral solvents such as (R)- or (S)-limonene was effective in preferential population of one-handed helical fibers. AFM studies revealed the formation of helical fibers from all the present PBI gelators, irresp. of the presence of chiral or achiral side chains. Furthermore, vortex flow was found to be effective in macroscopic orientation of the aggregates as evidenced from the origin of CD signals from aggregates of achiral PBI mols. |
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