Heteroalkyl‐Substitution in Molecular Organic Semiconductors: Chalcogen Effect on Crystallography, Conformational Lock, and Charge Transport.

The effect of heteroalkyl (‐XR, X = Se, S, O) substitution on a series of molecular semiconductors having a 3,3′‐diheteroalkyl‐2,2′‐bithiophene (XBT) central core is studied. Thus, the selenotetradecyl (‐SeC14H29) SeBT core is investigated by end‐functionalization with two dithienothiophene (DTT), thienothiophene (TT), and thiophene (T) units to give SeBTs 1–3, respectively, for molecular π‐conjugation effect examination. Furthermore, the selenodecyl (‐SeC10H21) and selenohexyl (‐SeC6H13) SeBT cores end‐capped with DTTs to give SeBTs 1B and 1C, respectively, are synthesized for understanding ‐SeR length effects. To address systematically the impact of the chalcogen heteroatom, the newly developed selenoalkyl SeBTs are compared with the previously reported thiotetradecyl (‐SC14H29) DDTT‐SBT (4) and the new tetradecyloxy (‐OC14H29) DDTT‐OBT (5). When fabricating organic field effect transistors by the solution‐shearing method, the devices based on the tetradecylated DDTT‐SeBT (1) exhibit the highest mobility up to 4.01 cm2 V−1 s−1, which is larger than those of the other SeBT compounds and both DDTT‐SBT (4) (1.70 cm2 V−1 s−1) and DDTT‐OBT (5) (9.32 × 10−4 cm2 V−1 s−1). These results are rationalized by a combination of crystallographic, morphological, and microstructural analysis. [ABSTRACT FROM AUTHOR]