Rapid solid-phase syntheses of conjugated homooligomers and [AB] alternating block cooligomers of precise length and constitution

A new iterative divergent/convergent solid-phase synthesis of precisely def ined oligomers is described. The starting monomer is affixed to the solid s upport so that both ends are free for growth. The polymer-supported n-mer b earing alpha,omega-terminal iodides is divided into two portions. The small er portion is converted to the polymer-supported (n + 2)-mer by coupling an alpha,omega-dialkyne to the two iodide ends. The larger portion is liberat ed from the polymer support and then coupled with the polymer-supported por tion to form a polymer-supported (3n + 2)-mer with new alpha,omega-terminal iodide end groups. The process is then repeated. The solid-supported mater ial thereby grows in two directions, unlike the common approach of unidirec tional growth. This polymer-supported strategy serves as a pseudo high dilu tion system so that unwanted polymerization does not ensue. Therefore, afte r each iteration, the oligomer length is more than tripled, making this a r apid growth methodology for precise oligomer syntheses. The methodology is demonstrated by the synthesis of a 17-mer oligo(1,4-phenylene ethynylene) o f approximately 120 Angstrom length in seven steps with an overall 20% yiel d, This solid-supported divergent/convergent tripling protocol is also used for the synthesis of an [AB] alternating block 23-mer containing oligo(1,4 -phenylene ethynylene)s and oligo(2,g-thiophene ethynylene)s in an overall 21% yield. The length of the 23-mer is approximately 160 Angstrom.