1. Received: May 25, 2012
Revised: August 8, 2012
Published online: 12 Sep 2012
Center for Nanochemistry, Beijing National Laboratory for Molecular Sciences (BNLMS)
State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University
Beijing , PR China
DOI: /adma
Molecular engineering and chemical self-assembly are combined with materials fabrication to achieve air-stable solution-processable oligothiophene-based field-effect transistors with mobilities up to 6.2 cm2 V−1 s−1, which ranks as the highest among oliogthiophene-based semiconducting materials.

2. High field effect mobilities of OFETs that are beyond 1 cm2 V−1 s−1
6,13-bis(triisopropyl-silylethynyl) pentacene
(TIPS-pentacene)
3.0 cm2 V–1 s–1
J. Am. Chem. Soc., 2011, 133 (22), pp 8732–8739
N ature V O L 4 8 0, 2 2 / 2 9 D E C E M B E R
Upto 3.7 cm2 V–1 s–1
4.6 cm2 V−1 s−1
Zhenan Bao et al
Adv. Mater.2011, 23, 1222–1225
Kazuo Takimiya et al
Adv. Mater. 2007, 19, 678–682
pentacene
1.8 cm2 V–1 s–1
Kilwon Cho et al.
6.30 cm2 V−1 s−1
Appl. Phys. Lett. 94, (2009);
S. G. Mhaisalkar et al

3. organic semiconductors (OSCs) for Field-Effect transistors
Generally required complex physical vapor or vacuum deposition techniques
To enable low-cost manufacturing, materials fabrication through simple solution processing under ambient conditions is highly desirable
OFETs fabricated with solution techniques; electrical properties are inferior to those of the vacuum-deposited devices
More defects and carrier traps in thin films and/or the instability in air.
oligothiophenes and polythiophenes
Promising class of organic semiconductors for solution-processed OFETs
Relatively straightforward synthesis and flexible structural modification
Defects in their solution-processed thin films
Sensitivity to photo-oxidative doping/bleaching hamper the intrinsic charge carrier transport and yield poor transistor performance
- Only very few liquid crystalline semiconductors have been recently demonstrated with improved properties (mobility 10 − 2 ~ 10 − 1 cm2 V−1 s−1).

4. Structure design strategy
lamella-like layered π -stacking structural orders
long-range intermolecular
side-chain interdigitation
long alkyl side-chains
- integrate self-healing capabilities of LC into oligothiophene molecules
self-organize into highly ordered molecular stacks during thermal annealing
Unsubstitution in quaterthiophene or pentathiophene backbones
Some rotational freedom
Oxidative doping stability

5. Synthetic scheme

6. Characterizations λ max = 413 nm (1) and 437 nm (2)
formation of H-aggregates
with close π -stacking in a face-to-face alignment

8. The DSC thermogram of 2 at a scan rate of 10 oC min − 1
A POM image of 2
∼ 135 oC; crystalline-to-liquid crystalline
∼ 160 oC; liquid crystalline-to-isotropic
phase transitions
Fanlike texture in the temperature ranges of
and 155–120 oC for the heating and
cooling procedures, respectively.
Smectic liquid crystalline phase

9. microribbons from a CHCl 3 solvent
via a slow solvent evaporation process.
XRD
STM images of 1 and 2
interlayer distance ( d -spacing) of 40.2 Å for 1 and 47.2 Å for 2
-> slightly larger than the molecular lengths (34.8 Å for 1 and 38.7 Å for 2 ) with the fully-extended alkyl groups

10. The channel length (L) and width (W) were 100 μm and 20 μm, respectively.
Where W/L is the channel width/length, Ci is the insulator capacitance per unit area, and VG
and VT are the gate voltage and threshold voltage, respectively.
Thin film based device; spin-coating
Single crystal based device; polydimethoxysilane (PDMS) stamp transfer method

11. enhanced molecular ordering
π – π stacking induced by thermally-assisted self-assembly of liquid crystals

12. Photoresponsive behavior
on/off ratio on the order of ∼ 10 3
mobility distribution
average mobility of 4.0 cm2 V–1 s–1
With the highest up to 6.2 cm2 V–1 s–1

13. Conclusion
- Oligothiophene based OTFT exhibits air-stable thin-film mobilities as high as 0.2 cm2 V−1 s−1 and an average single-crystal mobility of 4.0 cm2 V−1 s−1 with the highest up to 6.2 cm2 V−1 s−1.
- These results provide new insights into how to combine molecular engineering and
chemical self-assembly with materials fabrication to achieve properties that are desirable for device applications.
- The long alkyl side chains not only increase the molecular solubility allowing for low-cost device fabrication, but also improve the self-assembly ability to form high-quality single crystals.