Poly(3-decylthiophene) Radical Anions and Cations in Solution: Single and Multiple Polarons and Their Delocalization Lengths in Conjugated Polymers

Optical absorption spectra of anions and cations of poly­(3-decylthiophene) (P3DT) in solution were identified as single polarons. Pulse radiolysis of P3DT in THF determined the spatial extent of one negative polaron to be ∼11.5 thiophene units by observing transient absorption of P3DT^–• radical ions, which are prinicpally free ions, at 850 nm with ε = (7.25 ± 0.47) × 10⁴ M^–1 cm^–1 and bleaching of the neutral absorption band at 450 nm. P3DT^–• was formed in a combination of diffusive reactions and fast “step” processes. Similarly, a positive polaron of P3DT was estimated to delocalize over ∼8.7 thiophene units by pulse radiolysis in chloroform. Chemical reduction by sodium and oxidation by FeCl₃ injected multiple charges into a single P3DT chain while showing absorption spectra in the early stages of reaction resembling those observed by pulse radiolysis. The results indicated that multiple polarons exist in a single chain of P3DT before coalescing into bipolarons or transforming into other forms of polaron.