2, 6-Dialkylphenyldithieno [3, 2-b: 2′, 3′-d] thiophene derivatives (DPCn–DTT) were synthesized and characterized. Effect of alkyl groups on optical characteristics, electrochemical properties, film-forming ability, and field-effect performance was studied. The four compounds DPCn–DTT show almost the same energy levels of the highest occupied molecular orbits and optical energy gaps, but they exhibit different charge carrier ...