Chain folding controlled by an isomeric repeat unit: helix formation versus random aggregation in acetylene-bridged carbazole-bipyridine co-oligomers

Chem Asian J. 2013 Jul;8(7):1579-86. doi: 10.1002/asia.201300132. Epub 2013 May 6.

Abstract

An unprecedented, positional effect of the isomeric repeat unit on chain folding in donor–acceptor-linked oligomers, which contain alternating bipyridine and carbazole moieties that are connected through an acetylinic linkage, is reported. 4,4′-Linked oligomer 1 adopts an intrachain helical conformation (CD-active) in CHCl3/MeCN (20:80 v/v), whereas oligomer 2, which contains an isomeric 6,6′-linkage, forms interchain randomly coiled aggregates (CD-inactive). The substitution position plays a significant role in controlling the variations in electronic effects and dipole moments around the bipyridyl moiety, which are responsible for this observed phenomenon. Two model compounds of oligomers 1 and 2 (3 and 4, respectively) were prepared and their properties were compared. A systematic investigation of the photophysical and CD properties of these structures, as well as theoretical studies, support our conclusions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylene / chemistry*
  • Carbazoles / chemistry*
  • Circular Dichroism
  • Isomerism
  • Polymers / chemical synthesis
  • Polymers / chemistry*
  • Pyridines / chemistry*
  • Solvents / chemistry

Substances

  • Carbazoles
  • Polymers
  • Pyridines
  • Solvents
  • carbazole
  • pyridine
  • Acetylene