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 (‐SeC 14 H 29 ) 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 (‐SeC 10 H 21 ) and selenohexyl (‐SeC 6 H 13 ) 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 (‐SC 14 H 29 ) DDTT‐SBT ( 4 ) and the new tetradecyloxy (‐OC 14 H 29 ) 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 cm 2 V −1 s −1 , which is larger than those of the other SeBT compounds and both DDTT‐SBT ( 4 ) (1.70 cm 2 V −1 s −1 ) and DDTT‐OBT ( 5 ) (9.32 × 10 −4 cm 2 V −1 s −1 ). These results are rationalized by a combination of crystallographic, morphological, and microstructural analysis.