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 defined oligomers is described. The starting monomer is affixed to the solid support so that both ends are free for growth. The polymer-supported n-mer bearing alpha,omega-terminal iodides is divided into two portions. The smaller 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 liberated from the polymer support and then coupled with the polymer-supported portion to form a polymer-supported (3n + 2)-mer with new alpha,omega-terminal iodide end groups. The process is then repeated. The solid-supported material thereby grows in two directions, unlike the common approach of unidirectional growth. This polymer-supported strategy serves as a pseudo high dilution system so that unwanted polymerization does not ensue. Therefore, after each iteration, the oligomer length is more than tripled, making this a rapid growth methodology for precise oligomer syntheses. The methodology is demonstrated by the synthesis of a 17-mer oligo(1,4-phenylene ethynylene) of approximately 120 Å length in seven steps with an overall 20% yield. 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(2,5-thiophene ethynylene)s in an overall 21% yield. The length of the 23-mer is approximately 160 Å.