Insights into H-aggregates and CH⋯O hydrogen bond mediated self-assembly of pyromellitic bisimide

Abstract

Weak intermolecular interaction directed self-assembly of two synthetic pyromellitic bisimides containing L-amino acids are illustrated. UV/vis study reveals a blue shift with increasing concentration for phenylalanine-appended pyromellitic bisimide and molecular organization has been successfully transformed from nanospheres to microspheres. By contrast, the leucine analogue shows no shift in UV/vis bahavior with concentration, and has foam like morphology. X-Ray crystallography reveals that both the Phe and Leu side chains are in trans position in the reported bisimides. The phenylalanine-appended pyromellitic bisimide packed in H-aggregration which further self-assembled through CH⋯O hydrogen bond formation whereas the leucine analogue exhibits sheet like packing structure in the solid state. Such drastic changes in the self-assembly pattern are clear and striking evidence of the importance of weak intermolecular interactions. Moreover, the bisimides recognize tryptophan methyl ester in aprotic solvents.