A bio-inspired organic semiconductor 5,5 0-diphenylindigo shows excellent and well-balanced ambipolar transistor properties; its hole and electron mobilities are 0.56 and 0.95 cm 2 V À1 s À1 , respectively. The enhanced performance is attributed to the extended p-p overlap of the phenyl groups as well as the characteristic packing pattern that is a hybrid of the herringbone and brickwork structures. The ambipolar transistor characteristics are analyzed considering its operating regions, where a large unipolar saturated region appears due to the difference of the electron and hole threshold voltages. Scheme 1 Structures of indigo derivatives.

n-Channel organic transistors with excellent air stability are realized on the basis of charge-transfer complexes, (BTBT)(TCNQ), (BTBT)(F 2 TCNQ), (BSBS)(F 2 TCNQ), and (BTBT)(F 4 TCNQ), where BTBT is benzothieno[3,2b]benzothiophene, BSBS is benzoseleno[3,2-b]benzoselenophene, and F n TCNQ (n = 0, 2, and 4) are fluorinated 7,7,8,8-tetracyanoquinodimethanes. These complexes consist of mixed stacks of essentially neutral molecules, and the transistors are air stable even after several-month storage in ambient conditions.

On the basis of an excellent transistor material, [1]benzothieno[3,2-b][1]benzothiophene (BTBT), a series of highly conductive organic metals with the composition of (BTBT)2XF6 (X = P, As, Sb, and Ta) are prepared and the structural and physical properties are investigated. The room-temperature conductivity amounts to 4100 S cm(-1) in the AsF6 salt, corresponding to the drift mobility of 16 cm(2) V(-1) s(-1). Owing to the high conductivity, this salt shows a thermoelectric power factor of 55-88 μW K(-2) m(-1), which is a large value when this compound is regarded as an organic thermoelectric material. The thermoelectric power and the reflectance spectrum indicate a large bandwidth of 1.4 eV. These salts exhibit an abrupt resistivity jump under 200 K, which turns to an insulating state below 60 K. The paramagnetic spin susceptibility, and the Raman and the IR spectra suggest 4kF charge-density waves as an origin of the low-temperature insulating state.

A new series of benzobisthiadiazole (BBT)-based donor-acceptor copolymers, namely PBBT-FT, PBBT-T-FT, and PBBT-Tz-FT, with different π-conjugated bridges have been developed for polymer thin film transistors (TFTs). It was found that inserting different π-conjugated bridges into the polymer backbone 10 allowed tailoring of the opto-electrical properties, molecular organizations, and accordingly, the ambipolar transport of the TFTs. The UV-Vis-NIR spectra of all three polymers were similar with the low band gaps around 1.1 eV. While the lowest unoccupied molecular orbital (LUMO) energy levels were also similar (around −3.8 eV), their highest occupied molecular orbital (HOMO) energy levels varied from −5.05 to −5.42 eV due to the different π-conjugated bridges. Importantly, their TFTs exhibited 15 different ambipolar transport. p-Type dominant TFT performances with the hole mobility (µ h ) reaching 0.13 cm 2 V −1 s −1 were observed for the prototype polymer PBBT-FT. However, the device based on PBBT-T-FT with thiophene bridges displayed lower but more balanced hole (µ h ) and electron (µ e ) mobilities of 6.5×10 −3 and 1.2×10 −3 cm 2 V −1 s −1 , respectively. The device based on PBBT-Tz-FT with the thiazole units exhibited more evenly balanced hole and electron mobilities (µ h /µ e = 0.45) along with a 20 significantly enhanced µ e~0 .02 cm 2 V −1 s −1 . These different semiconducting features were ascribed to different molecular orientations and film morphologies revealed by wide-angle X-ray scattering (WAXS) and atomic force microscopy (AFM).a Maximum values of the hole/electron mobilities measured under vacuum (10 −4 -10 −5 mbar). The average values are in parentheses (from 5 to 10 devices). The hole/electron mobilities under optimized annealing conditions are indicated in boldface.Three new benzobisthiadiazole-based donor-acceptor copolymers, namely PBBT-FT, PBBT-T-FT, and PBBT-Tz-FT, with different π-conjugated bridges were developed for polymer thin film transistors (TFTs). It was shown that inserting different π-conjugated bridges into the polymer backbone allows tailoring of the opto-electrical properties, molecular organizations, and accordingly, the type of charge carriers in the TFTs.

Novel mixed stack charge-transfer complexes (DMeO-BTBT)(Fn-TCNQ) show air-stable n-channel transistor performance in the thin films and single crystals.