Bisperfluorophenyl-Substituted Thiophene Oligomers. Organic Semiconductors with Complementary-Type Carrier Mobility
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Bisperfluorophenyl-Substituted Thiophene Oligomers. Organic Semiconductors with Complementary-Type Carrier Mobility Antonio Facchetti1, Howard E. Katz2, and Tobin J. Marks*1 1 Department of Chemistry and the Materials Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA. 2 Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey 07974, USA. ABSTRACT The design, synthesis, and properties of two mixed perfluorophenyl-thiophene oligomers 5,5'''-diperfluorophenyl-2,2':5',2'':5'',2''':5''',2'''':5'''',2'''''-quaterthiophene (2) and 5,5’-bis{1-[4(thien-2-yl)-2,3,5,6-tetrafluorophenyl)]}-2,2'-dithiophene (3) are presented. Molecular characterization included the following techniques: multinuclear NMR, DSC and TGA, optical UV-Vis and photoluminescence spectroscopy, and cyclic voltammetry. Thin films can be easily grown by vacuum evaporation and have been characterized by optical UV-Vis and photoluminescence, XRD, and field-effect transistor measurements. Electron and hole mobilities of 0.06-0.08 cm2/(V s) and 0.001-0.003 cm2/(V s) were found for 2 and 3, respectively. INTRODUCTION During the last several years, organic-based electronic and electro-optic materials have attracted considerable attention due to the remarkable progress in organic light-emitting devices (OLEDs), organic thin film transistors (OTFT), photovoltaic cells, and photodetectors. In particular in the TFT area, the characteristics and performance of some organic semiconductors have made such devices viable for applications requiring large area coverage, mechanical flexibility, and low overall cost.1 However, the full development of this field requires the availability of both efficient p- (hole-transporting) and n-channel (electron-transporting) semiconductors. Indeed, most organic FET semiconductors are p-channel, meaning that positive charge carriers (holes) can be injected and made to move through the material. Far fewer studies have focused on the design and transport characteristics of organic n-channel compounds, into which negatively charged carriers (electrons) can be injected and made mobile.2 We report here the synthesis of two new mixed perfluorophenyl (FP)/thiophene (T) oligomers 2 and 3 (Figure 1) and compare their properties with those of the formal all-thiophene parent 1 (α6T), which is one of the most studied organic p-type semiconductors. F F
F S
F
S
F S S
S S
S
F
S
F
S F
F F
2 (FPTTTTFP)
S F
1 (α6T)
F
S
F S
F
F S
F
3 (TFPTTFPT)
Figure 1. The perfluorophenyl-thiophene oligomers.
S
F F
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Drain
Source Gold (50 nm) Organic Semiconductor (50 nm) HMDS (monolayer)
Gold (50 nm)
SiO2 (300 nm) n+-Si Gate
Figure 2. TFT device configuration and measurements These compounds and the corresponding vacuum-deposited thin films have been fully characterized by a variety of physical techniques. Electrical measurements were performed in the top-contact thin film transistor configuration. EXPERIMENTAL DETAIL Materials. The reagents 5-bromo-2,2':5',2''-terthiophen
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