Organic field-effect transistor (OFET) as the heart elementof organic/molecular electronics has attracted particular attention recently. Pentacene, is a bench mark molecular material of OFETs with high mobility and on/off ratio. However, the photo degradation of pentacene limits its commercial potential. Here, a pentacene analog, heteroacene DBTDT has been synthesized in three simple and controlled steps. This material possesses high ionization potential and high thermal and photostability, as confirmed by electrochemistry, TGA, and UV-vis spectra. Devices with mobility above 0.5 cm² V^–1 s^–1 and on/off ratio over 10⁶ were obtained at substrate temperature at 36 °C. All these results suggested that DBTDT will be extremely valuable for applications in plastic organic electronics.

Figure 1 Molecular structure of oentacene and DBTDT.

Advanced Materials (2007, 19, 3008-3011)  (VIP and “Advanced in Advance” paper)

Titanyl-phthalocyanine (TiOPc) is known as one of the most efficient organic photoconductors widely used in more than 90% laser printers. In its triclinic a-structure, TiOPc molecules form concave and convex pairs with significant molecular overlaps and very short intermolecular distances, N6-N6 (3.145 Å) in the convex pair and C9-C28 (3.211 Å) in the concave pair. These surprisingly close p-p molecular contacts indicate a-TiOPc can be a very promising organic semiconductor for organic field-effect transistors. And over 90% selected devices exhibited hole mobility over 1.0 cm² V^-1 s^-1 with on/off ratio over 10⁶.

Figure 2 Molecular structure of TiOPc and densely packed a-TiOPc.

Advanced Materials (2007, 19, 2613-2617 ) (VIP paper)

Single crystals can not only reveal the intrinsic properties of organic semiconductor, but also fabricate high performance devices, which have attracted attention recently. We have been concentrating on organic single crystals and devices for some time (Adv. Mater. 2006, 18, 65－68, Adv. Mater. 2006, 18, 3010－3014, J. Am. Chem. Soc. 2006, 128, 14634-14639). On the basis here we studied the photo switches and phototransistors of organic single crystals for the first time, by using sub-micro/nanometer ribbons of a remarkable air-stable, n-type organic semiconductor, F16CuPc. After this study we demonstrated: (1) High quality photo switchers of F₁₆CuPc single crystals could be fabricated, which were capable to switch reversible and fast. (2) Single crystal field-effect phototransistors of F₁₆CuPc individual submicro/ nanoribbon exhibited strong photo dependence, i.e., the light can act as an independent variable to control the output current of the single crystalline transistors. (3) The maximum on/off ratio of the phototransistor was at 4.5×10⁴ (at V_G=-6.0 V), which was probably due to the gate applied bias providing an efficient way for the dissociation of the photo generated excitons, and which was beneficial for the formation of the conducting channel of the phototransistors. (4) The high light sensitivity, large on/off ratio of the phototransistors suggested their potential applications in optoisolators, optical switches, retro sensors and circuits etc., which opened a new way to realize the light detection and signal magnification in a single organic device, indicating a future for low cost, ultrahigh density organic photoelectric integration.

Figure 3 Organic single crystalline photo switches and transistors

Advanced Materials (2007, 19, 2624-2628)