Alkyl Chain Orientations in Dicyanomethylene‐Substituted 2,5‐Di(thiophen‐2‐yl)thieno‐[3,2‐b]thienoquinoid: Impact on Solid‐State and Thin‐Film Transistor Performance

Abstract

A series of dicyanomethylene-substituted 2,5-di(thiophen-2-yl)thieno[3,2-b] thieno-quinoids, in which soluble alkyl chains (2-decyltetradecyls) are substituted at different positions (namely, 2,2 ′ -positions (Compound 1 ); 3,3 ′positions (Compound 2 ); 6,6 ′ -positions (Compound 3 )), are strategically designed and successfully synthesized. The photophysical and electrochemical properties as well as molecular packing of these new compounds are thoroughly investigated. Thin fi lm transistor measurements reveal that Compounds 1-3 display markedly different charge transport performance. The solution processed thin fi lm transistors of Compound 2 exhibits the highest electron mobility of up to 0.22 cm 2 V − 1 s − 1 under ambient conditions, one and three orders of magnitude higher than those of Compounds 3 and 1, respectively, demonstrating the strong impact of alkyl chain orientations on transistor performance. Scheme 1 . The chemical structures of some typical thienoquinoidal-type OSCs. Scheme 2 . Synthesis and chemical structures of dicyanomethylene-substituted 2,5-di(thiophen-2-yl)thieno[3,2-b] thienoquinoid derivatives 1 -3 .

Naphtho[2,1-b:3,4-b′]bisthieno[3,2-b][1]benzothiophene-based semiconductors for organic field-effect transistors

“…2. As anticipated, highly πextended naphthobisthienobenzothiophenes show a smaller HOMO-LUMO energy gap than that of the parent naphthodithienothiophene which is attributed to enhanced π- 10 conjugation with the extension of two flanked fused aromatic rings. On the other hand, the energy gap does not change significantly upon incorporation of the fluorine atoms into the naphthobisthienobenzothiophene skeleton; however, the HOMO and LUMO energy levels are significantly stabilized, giving rise 15 to a more air-stable molecular system.…”

“…It was important to find that the branched side-chain analogue, 5 NBTBT-2,6 showed an inferior device performance with a hole mobility of 1.7 × 10 -2 cm 2 /Vs after annealing at 100 °C and decreasing to 3.6 × 10 -3 cm 2 /Vs after annealing at a higher temperature as compared to the straight alkoxy-chain analogues, NBTBT-n (n = 6, 8, and 10). In sharp contrast, upon 10 incorporation of corresponding straight alkoxy-chains i.e. from hexyoxy (C6) to decyloxy (C10), NBTBT-n (n = 6, 8, and 10) exhibited high OFET performance with a hole mobility in the range of 0.10 -0.25 cm 2 /Vs after annealing at 220-240 °C with an average on/off ratio of 10 6 -10 7 .…”

“…9 In addition, incorporation of proper alkyl substituent(s) onto the πconjugated system not only enhances solubility and solution-60 processibility of the resulting materials but also facilitates close molecular packing in the solid state which provides a means to tune the molecular packing. 10 Furthermore, electron-withdrawing fluorine atom, which has a similar radius of hydrogen atom, can be incorporated into the π-65 conjugated backbone to redistribute electron density without altering the molecular geometry and to promote close intermolecular interactions/packing by means of dipole-dipole interactions and thus enhancing carriers transport. 11 Naphtho[2,1-b:3,4-b]dithiophene and its derivatives have been 70 shown to be a promising -conjugated building block to construct efficient organic semiconducting materials for organic photovolatics 12 and thin-film transistors 13 .…”

Recent Advances in Ambipolar Transistors for Functional Applications

“…These improvements finally gave rise to excellent charge carrier mobilities of 0.015 (holes) and 0.168 cm 2 V −1 s −1 (electrons) under ambient conditions. Recently, researchers also explored the novel ambipolar D–A small molecules by attaching different π‐conjugating spacers including thiophene, bithiophene, benzothiophene, benzothiadiazole and thieno[3,2‐ b ]thiophene (TT) to various common groups for instance DPP, NDI derivatives and isoindigo to regulate the intermolecular interactions and energy band structures . Lin et al presented DPP‐derivatives with an A–D–A–D–A construction incorporating DPP core unit and planar bithiophene or TT electron donors .…”

The Influence of Solubilizing Chain Stereochemistry on Small Molecule Photovoltaics

“…), solubilizing groups emerge as important structural components for study and material/device optimization. Indeed, for both oligomers and polymers, side chain type, length, branching, placement, and stereochemistry have independently been shown to influence thin film morphology, charge carrier mobility, and device performance …”