Iterative Divergent/Convergent Approach to Conjugated Oligomers by a Doubling ofMolecular Length at Each Iteration. A Rapid Route to Potential Molecular Wires

摘要

Described is the synthesis of oligo(3-ethylthiophene-ethynylene)s via aniterative divergent convergent approach starting from 3-ethyl-2-(trimethylsilylethynyl)thiophene. Synthesized were the monomer, dimer, tetramer, octamer and 16-mer. The 16-mer is approximately 100 A long in its minimum energy conformational form. At each stage in the iteration, the length of the framework doubles. Only three sets of reaction conditions are needed for the entire iterative synthetic sequence; an iodination, a protodesilylation, and a Pd/Cu-catalyzed cross coupling. The oligomers were characterized spectroscopically and the mass spectrometry data are discussed. The optical properties are presented which show that at the octamer stage, the optical absorbance maximum is nearly saturated. The size exclusion chromatography values for the number average weights, relative to polystyrene, illustrate the tremendous differences in the hydrodynamic volume of these rigid rod oligomers versus the random coils of polystyrene. These differences become quite apparent at the octamer stage. The rigid rod conjugated oligomers may act as molecular wires in molecular electronic devices and they also serve as useful models for understanding analogous bulk polymers.