Finely Tuned Electron/Hole Transport Preference of Thiazoloisoindigo-based Conjugated Polymers by Incorporation of Heavy Chalcogenophenes

Abstract

A series of copolymers of thiazoloisoindigo (TzII) with different chalcogenophene trimers were synthesized to systematically investigate the chalcogen effect on their charge transport properties. When only the middle thiophene ring of terthiphene (T-T-T) is replaced by heavier chalcogenophenes, a preference (expressed by the ratio of μe/μh) towards electron transport was observed descending from T-T-T to T-Se-T then to T-Te-T (Se and Te stand for selenophene and tellurophene, respectively). On the other hand, with the increased number of heavier chalcogenophenes, a preference toward hole transport was observed descending from Se-T-Se to Se-Se-Se then to Se-Te-Se. This phenomenon is well-explained by the balance between the aromatic resonance energy of the chalcogenophenes and the electronegativity of the chalcogens. Specifically, P(TzII-T-Se-T) displayed relatively balanced ambipolar property (μhmax and μemax of 3.77 and 1.59 cm2·V−1·s−1 with a μe/μh of 0.42), while P(Tzll-Se-Te-Se) exhibited the best preference to hole transfer with a μe/μh of 0.09. P(Tzll-T-Te-T) exhibited the best preference to electron transfer with a μe/μh, of 16 and the μemax of 0.64 cm2·V−1·s−1 which is the highest electron mobility among the known conjugated polymers containing tellurophenes.