Oligo(p‐phenylene‐ethynylene)‐Derived Super‐π‐Gelators with Tunable Emission and Self‐Assembled Polymorphic Structures

Linear π‐conjugated oligomers are known to form organogels through noncovalent interactions. Herein, we report the effect of π‐repeat units on the gelation and morphological properties of three different oligo(p‐phenylene‐ethynylene)s: OPE3 , OPE5 , and OPE7 . All of these molecules form fluorescent gels in nonpolar solvents at low critical gel concentrations, thereby resulting in a blue gel for OPE3 , a green gel for OPE5 , and a greenish yellow gel for OPE7 . The molecule–molecule and molecule–substrate interactions in these OPEs are strongly influenced by the conjugation length of the molecules. Silicon wafer suppresses substrate–molecule interactions whereas a mica surface facilitates such interactions. At lower concentrations, OPE3 formed vesicular assemblies and OPE5 gave entangled fibers, whereas OPE7 resulted in spiral assemblies on a mica surface. At higher concentrations, OPE3 and OPE5 resulted in super‐bundles of fibers and flowerlike short‐fiber agglomerates when different conditions were applied. The number of polymorphic structures increases on increasing the conjugation length, as seen in the case of OPE7 with n=5, which resulted in a variety of exotic structures, the formation of which could be controlled by varying the substrate, concentration, and humidity.