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

Abstract

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‐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.

Thickness Dependence of the Ambipolar Charge Transport Properties in Organic Field-Effect Transistors based on a Quinoidal Oligothiophene Derivative

“…A better orientation , of the molecules in thinner films could lead to a significant increase in the electron mobility with decreasing film thickness but would also affect hole transport. Previous work has also suggested that ambipolar OFET properties of dicyanomethylene-substituted oligothiophenes strongly depend on the quinoidal or aromatic character of their conjugation paths . The absence of changes in the Raman spectra (data not shown) provides clear evidence that the thickness dependence of field-effect mobilities is not due here to any unexpected modifications in the conjugation structure with film thickness and solution-processing conditions.…”

“…Previous work has also suggested that ambipolar OFET properties of dicyanomethylene-substituted oligothiophenes strongly depend on the quinoidal or aromatic character of their conjugation paths. 17 The absence of changes in the Raman spectra (data not shown) provides clear evidence that the thickness dependence of field-effect mobilities is not due here to any unexpected modifications in the conjugation structure with film thickness and solution-processing conditions. However, the thickness dependence of the charge transport properties in QQT(CN)4 OFETs can also be due to the influence of the film morphology on the electron trap density.…”

Optical and Charge Transport Properties of a New n-Type Solution-Processible Quinoidal Oligothiophene

“…Film morphology was characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). In contrast to ambipolar field-effect properties previously reported in a series of quinoidal oligothiophenes, 19) top-contact QQT(OMe) 2 OFET with Au drain/source electrodes was characterized in air and shows only moderate n-type performance with electron mobility of 5 Â 10 À4 cm 2 V À1 s À1 . Raman spectroscopy measurements were performed in neat films to obtain additional information on the electronic structure of QQT(OMe) 2 in the solid state.…”

“…25) Overall, the solution-processibility, the negligible absorption in the visible region and the n-type performance of the device suggest that QQT(OMe) 2 thin films could be an interesting candidate for organic transparent integrated circuits especially if better morphology and higher crystallinity can be achieved by varying the solutionprocessing conditions or by vapor solvent treatment. Previous work 19) has recently reported ambipolar transport in several quinoidal/aromatic terthiophens and quaterthiophenes. It was also suggested 19,23) that variations in the quinoidal/aromatic conjugated path of the thiophene backbone can result in strong changes in the ambipolar transport properties of these materials.…”

Critical moisture content for microbial growth in dried food‐processing residues

“…As shown in Figure S3, another important feature is the identical Raman spectra measured in as‐prepared QQT(CN)4 thin films spin‐coated from THF and CHCl 3 . This result provides additional evidence that the majority carrier type in the devices is not related to any switching from quinoidal to aromatic biradical structures in the thiophene backbone of QQT(CN)4 molecules 15, 24, 27…”