Regio-regular polythiophenes used in diodes which are not light emitting or photovoltaic. High quality, processable thin film polymer films can be made. The thin film can have a thickness of about 50 nm to about one micron, and the conductive thin film can be applied by spin casting, drop casting, screening, ink-jetting, transfer or roll coating. The polythiophenes can be homopolymers or copolymers. The regio-regular poly(3-substitutedthiophene) can be derivatized so that the 3-substituent is an alkyl, aryl, or alkyl/aryl moiety with a heteroatom substitution in either the .alpha.- or beta-position of the 3-substituent.