Synthesis of Phenyleneethynylene Macrocycle Bearing Optically Active Amide Groups Undergoing Reversible Sol−Gel Transformation

Abstract

Cyclic phenyleneethynylene 3 bearing optically active amide groups was synthesized by the Sonogashira−Hagihara coupling of ʟ-alanine-derived 3,5-dibromobenzamide 1 and 1,3-diethynylbenzene 2. The formation of 3 was confirmed by MALDI−TOF mass spectrometry along with ¹H/¹³C-NMR and IR spectroscopies. A solution of 3 in CHCl₃ turned into gelled state upon standing for 30 min, and the gel returned into fluid state by vibration. The sol−gel transformation was confirmed by dynamic viscoelastic measurement, wherein the storage modulus became larger than loss modulus around the angular frequency at 0.18 rad/s. A membrane of 3 fabricated by spin-coating on a quartz cell exhibited negative Cotton effects at 291 nm and 305 nm assignable to chirally assembled phenyleneethynylene moieties.