NOVEL ELECTRICAL AND OPTICAL-PROPERTIES OF POLY(3-ALKYLTHIOPHENE) AS FUNCTION OF ALKYL CHAIN-LENGTH AND THEIR FUNCTIONAL APPLICATIONS

Electrical (conductivity, mobility), optical (absorption, luminescence) and magnetic (ESR) properties of poly(3-alkylthiophene) were strongly dependent on alkyl chain length, temperature and ambient conditions. These results can be explained by taking fluctuation of electronic band scheme and inter-chain interaction influenced by dimensionality and co-planarity of conjugated main chain which are dependent on the alkyl chain length and its conformation. Properties of mixture of poly(3-alkylthiophene)s with different alkyl chain length were also discussed. Doping characteristics of poly(3-alkylthiophene) dependent on alkyl chain length were discussed in terms of location of dopants in the polymer, modification of crystal structure and polymer-dopant interaction. Especially, unique doping effect of C60 in poly(3-alkylthiophene) was also observed. As example of ambient effect on properties of poly(3-alkylthiophene), characteristics of poly(3-alkylthiophene) in solvent and behavior in poly(3-alkylthiophene) gel were studied and discussed in terms of interactions of solvent molecule with both polymer main chain and alkyl side chain. Various applications of these unique characteristics of poly(3-alkylthiophene) were proposed such as functional electronic element (diodes, FET etc.), EL (electroluminescent diode), optical memory and functional gel elements (bimorph, actuator, etc.). Their characteristics can also be controlled by the alkyl chain and explained in terms of unique electronic band scheme of poly(3-alkylthiophene) dynamically dependent on alkyl chain length and ambient conditions.