Polythiophene was functionalized with redox-active ferrocenylborane pendent groups. A postpolymerization modification procedure was applied, in which silylated polythiophene was reacted with BBr3 to give a polymer with pendent BBr2 groups. The dibromoboryl functionalities were then further elaborated by first treating the intermediate with FcSnMe(3) to introduce the ferrocenyl moieties and then with an arylcopper derivative ArCu (Ar = 2,4,6-trimethylphenyl (Mes), 2,4,6-tri-isopropylphenyl (Tip)) to sterically stabilize the boron centers. Using similar methods, two quaterthiophene derivatives were also prepared. The number-average molecular weight (M-n) of the polymers was determined by gel permeation chromatography (GPC) relative to narrow PS standards to range from 9400 to 14 600 Da. The polymer structure was further confirmed by MALDI-TOF mass spectrometry and by multinuclear NMR spectroscopy. H,H-NOESY spectroscopy and single crystal X-ray diffraction experiments on the quaterthiophene derivatives were used to gain insight into the conformation of the oligomers and polymers in solution and the solid state. The electronic structure of the oligo- and polythiophenes was studied in detail by UV-vis spectroscopy and electrochemical measurements.