The present invention describes thin film transistors in which the active channel layer is a thin film of a polycyclic aromatic compound, such as, pentacene, prepared by solution processing a soluble precursor of the polycyclic aromatic compound on a substrate followed by heating to a moderate temperature to convert the precursor back to the polycyclic aromatic compound. The soluble precursors of the polycyclic aromatic compounds are organic solvent-soluble Diels-Alder adducts of polycyclic aromatic compounds, such as, oligothiophene, perylene, benzo[ghi]perylene, coronene and a polyacene with a variety of dienophiles that contain at least one heteroatom. The Diels-Alder adducts can be converted back to pentacene by retro-Diels-Alder reaction at moderate (60-250° C.) temperatures both in bulk, in solution or as thin-films.