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′-dibutylsulfenyl-[2,2′-bi-[4-dicyanovinylene-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 transistors exhibit 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.