A novel electron-rich cyclopentadithienothiophene (9H-thieno[3,2-b]thieno[2 '',3 '':4',5[thieno[2',3'3,4]cyclopenta[1,2-d]thiophene, CDTT) is reported by an optimized one-pot procedure involving two sequential lithiation/acylation steps. Three novel copolymers containing the varied electron-deficient acceptors 2,1,3-benzothiadiazole (BT), 5,6-difluoro-2,1,3-benzothiadiazole (DFBT) and naphtho[1,2-c:5,6-c]bis[1,2,5] -thiadiazole (NT) were prepared by Stile polymerization. These three polymers show promising charge transport properties in transistor devices, with PCDTT-BT exhibiting unipolar hole mobility up to 0.67 cm(2) s(-1) in top gate devices utilizing gold source drain electrodes. Changing to a bilayer electrode of Al/Au resulted in ambipolar transistor behavior, with PCDTT-DFBT exhibiting balanced hole and electron mobilities of 0.38 and 0.17 cm(2) s(-1) respectively. These results clearly demonstrate that CDTT is a promising new building block for conjugated polymers.