Soluble regioregular polythiophene derivatives as semiconducting materialsfor field-effect transistors

Soluble regioregular polythiophene derivatives with chiral alkyl side chain s, bulky side chains, and carboxylic side chains have been synthesized. The ir thin-film field-effect transistor performance and structural characteris tics have been investigated. The above properties were found to be strongly affected by the nature of the side chains. Poor molecular ordering and low crystallinity were found for regioregular polythiophenes with bulky or car boxylic-substituted side chains, and their resulting transistor devices sho wed poor field-effect mobilities (less than 10(-5)-10(-4) cm(2)/(V s)). A c hiral alkyl-substituted regioregular polythiophene showed high crystallinit y. However, its pi-pi overlap distance between the polythiophene backbones increase substantially (i.e., to similar to 4.3 vs 3.8 Angstrom for regiore gular poly(3-hexylthiophene) (PHT)) through the introduction of methyl bran ches in the side chains. The field-effect mobility of this polymer is reaso nably high for solution-processable conjugated polymers (i.e., of the order of 10(-3) cm(2)/(Vs)), but is still an order of magnitude lower than for r egioregular PHT. These studies provide an initial basis for further structu ral design and molecular engineering of soluble regioregular polythiophenes with potentially improved transistor performance.