Ambipolar Organic Field-Effect Transistors from Cross-Conjugated Aromatic Quaterthiophenes; Comparisons with Quinoidal Parent Materials

This contribution presents an electrochemical, Raman spectroscopic, and theoretical study probing the differences in molecular and electronic structure of two quinoidal oligothiophenes (3',4'-dibutyl-5,5 ''-bis(dicyanomethylene)-5,5 ''-dihydro-2,2':5',2 ''-terthiophene and 5,5'-bis(dicyanomethylene)-3-hexyl-2,5-dihydro-4,4'-dihexyl-2,2',5,5'-tetrahydro-tetrathiophene) with terminal tetracyanomethylene functionalization and aromatic oligothiophenes where acceptor moieties are positioned at lateral positions along the conjugated chain (6,6'-dibutylsulfanyl-[2,2-bi-[4-dicyzinovinylene-4H-cyclopenta[2,1-b:3,4-b']dithiophene]). In this way, the consequences of linear and cross conjugation are compared and contrasted. From this analysis, it is apparent that organic field-effect transistors fabricated with cross-conjugated tetrathiophene semiconductors should combine the benefits of an electron-donor aromatic chain with strongly electron-accepting tetracyanomethylene substituents. The corresponding organic field-effect transistor ambipolar transport with rather similar hole and electron mobilities. Moreover, n-channel conduction is enhanced to yield one of the highest electron mobilities found to date for this type of material.