Building Blocks for n-Type Molecular and Polymeric Electronics. Perfluoroalkyl- versus Alkyl-Functionalized Oligothiophenes (nT; n = 2−6). Systematics of Thin Film Microstructure, Semiconductor Performance, and Modeling of Majority Charge Injection in Field-Effect Transistors

Abstract

The solid-state properties and FET electrical behavior of several series of alpha,omega- and beta,beta'-fluorocarbon- and alkyl-substituted and unsubstituted oligothiophenes nTs (n = 2-6) are compared and contrasted. The thin films were grown by slow vacuum deposition over a range of substrate temperatures and/or by casting from solution and were investigated by X-ray diffraction and scanning electron microscopy. Our results indicate that vacuum deposition at 60-80 degrees C affords films with remarkably similar microstructures despite the extensive H --> F substitution. Trends in observed d spacing versus molecular core extension provide quantitative information on molecular orientation. Field-effect transistor measurements performed for all systems and having the same device structure, components, and fabrication conditions demonstrate that all nTs functionalized with fluorocarbon chains at the thiophene termini are n-type semiconductors, in contrast to the p-type activity of the remaining systems. One of these systems, alpha,omega-diperfluorohexyl-4T, exhibits a mobility of 0.22 cm2/(V s) and an Ion:Ioff ratio of 10(6), one of the highest so far reported for an n-type organic semiconductor. The effect of substitution regiochemistry on FET majority charge carrier was additionally studied, in the case of a 6T core, by shifting the fluorocarbon substituents from the terminal to the central thiophene units. Finally, we propose a simple theoretical model for electrode/organic interfacial carrier injection. The results suggest why modest substituent-induced changes in the injection barrier can produce working n-type materials.

Trends in molecular design strategies for ambient stable n-channel organic field effect transistors

“…-fold increase in the carrier injection rate when the injection barrier is lowered by 0.27 eV. 243 Yu and co-workers reported two air stable isomers of trifluoromethyltriphenodioxazine 5b and 5c. 244 Both are n-channel materials with mobilities of 0.07 and 0.03 cm 2 V À1 s…”

Charge dynamics through pi-stacked arrays of conjugated molecules: effect of dynamic disorder in different transport/transfer regimes

“…[32] and [33] . We extend this study here to the electronic coupling fluctuations of sexithiophene, a molecule that can be considered a prototype for an entire class of organic semiconductors [9,34] and is therefore a reference also for many theoretical studies. [35] A supercell containing 48 molecules of sexithiophene was build replicating the crystal unit cell 2, 3 and 4 times respectively along the crystallographic axes a, b, and c (a=44.70 Å, b=7.81 Å, c=6.03 Å).…”

DFT STUDY ON LOW MOLECULAR WEIGHT α,α-DITERT-BUTYL-4H-CYCLOPENTA[2,1-b,3;4-b'] DITHIOPHENE AND α,α-DITERT-BUTYL-4H-CYCLOPENTA[2,1-b,3;4-b']DITHIOPHENE S-OXIDE BRIDGED DERIVATIVES

“…[1][2][3][4][5][6][7][8][9] However, the synthesis, reactivity as dienes in Diels-Alder reactions, and photochemical and electrochemical behavior of other thiophene-related molecules such as thiophene S,S-dioxide, and thiophene S-oxide have also been investigated. [10][11][12][13][14][15][16][17][18][19][20] The orbital energies and electrochemical properties of thiophene S-oxide monomers have been studied theoretically using MP2/6-31G*.…”