Oligomer Approach: Oligodiacetylenes And Ladderphanes

Polydiaceylenes (PDAs) are linear conjugated polymer constructed by alternative E-olefin and alkyne moieties. PDAs show color change properties which might be contributed by changes in effective conjugation length and interactions between PDA chains (chromophores). Several E-oligodiacetylenes (E-ODAs) have been synthesized and studied. Z-oligodiacetylenes (Z-ODAs) have sporadically explored. A series of tBu-substituted Z-ODAs are synthesized from the reactions of allenyl/propargylic zinc reagents with dithiolane-substituted propargylic aldehydes to form β-thioalkoxy alcohols which undergo stereospecific elimination under Mitsunobu conditions. The stereochemical assignments are based on NOE experiments. The X-ray structure of the hexamer further supports the Z configuration for each of the double bonds in these ODAs. The photophysical properties of these Z-ODAs have been examined. The absorption maxima shift to shorter wavelength upon aggregation. Double-stranded polymeric ladderphane with a hexabenzocoronene (HBC) derivative as linkers is synthesized by the ring-opening metathesis polymerization (ROMP) of the corresponding bisnorbornene monomer using the first-generation Grubbs catalyst. The absorption intensity of the polymer is much lower than that of corresponding monomer. In addition, excimer emission is found in the polymer due to the interactions between adjacent chromophore. Instead of the two dimensional aromatic chromophores being served as linker in ladderphanes, the three dimensional hydrocarbons can be used as linker. Cuneane, the valence isomer of cubane, is applied as linking group in the ladderphane. Double-stranded ladderphane having cuneane linker is synthesized similarly. The STM image of HBC-incorporated ladderphane shows double strained nature and typical properties of polybisnorbornene which would self-assemble to form ordered two-dimensional arrays on the HOPG surface.