Giant Macrocycles Composed of Thiophene,Acetylene,and Ethylene Building Blocks

摘要

Fully conjugated giant macrocyclic oligothiophenes with 60pi,90pi,120pi,150pi,and 180pi frames (1,2,3,4 and 5) have been designed,and their butyl-substituted derivatives (1a,2a,3a,4a,and 5a) have been synthesized using modified Sonogashira and McMurry coupling reactions as key steps.The 60-180pi systems 1 -5 are circular with 1.8-6 nm inner cavities and 3.3-7.5 nm outside molecular diameters.Compound 1a containing ten 3,4-dibutyl-2,5-thienylene,eight ethynylene,and two vinylene units has been converted into macrocyclic oligo(3,4-dibutyl-2,5-thienylene-ethynylene) 6a using bromination/dehydrobro-mination procedure.Giant macrocycles 1a-6a exhibit a red shift of their absorption spectra and a fairly strong fluorescence with a large Stokes shift as compared to a linear conjugated counterpart having five thiophene rings.Compounds 1a-6a exhibit multistep reversible redox behaviors with fairly low first oxidation potentials,reflecting their cyclic conjugation.Furthermore,chemical oxidation of 1a-6a with FeCl_3 shows drastic changes of spectroscopic properties due to intramolecular and intermolecular pi-pi interactions.Doping of 1a-3a with iodine forms semiconductor due to its pi-donor properties and pi-pi stacking ability.X-ray analysis of 1a confirmed a round,planar structure with nanoscale inner cavity,and revealed host ability for alkanes and unique packing structure,interestingly,2a and 3a self-aggregate in the solid state to form "molecular wires," which are about 200 nm thick and more than 1 mm long.The internal structures of fibrous aggregates have been investigated by optical microscope,scanning electron microscopy,atomic force microscopy,and X-ray diffraction analyses.