As a first step in structure-based design of highly selective and potent Cdk4 inhibitors, we performed structure-based generation of a novel series of Cdk4 inhibitors. A Cdk4 homology model was constructed according to X-ray analysis of an activated form of Cdk2. Using this model, we applied a new de novo design strategy which combined the de novo design program LEGEND with our in-house structure selection supporting system SEEDS to generate new scaffold candidates. In this way, four classes of scaffold candidates including diarylurea were identified. By constructing diarylurea informer libraries based on the structural requirements of Cdk inhibitors in the ATP binding pocket of the Cdk4 model, we were able to identify a potent Cdk4 inhibitor N-(9-oxo-9H-fluoren-4-yl)-N'-pyridin-2-ylurea 15 (IC(50) = 0.10 microM), together with preliminary SAR. We performed a docking study between 15 and the Cdk4 model and selected a reasonable binding mode which is consistent with the SAR. Further modification based on the proposed binding mode provided a more potent compound, N-[(9bR)-5-oxo-2,3,5,9b-tetrahydro-1H-pyrrolo[2,1-a]isoindol-9-yl]-N'-pyridin-2-ylurea 26a (IC(50) = 0.042 microM), X-ray analysis of which was accomplished by the soaking method. The predicted binding mode of 15 in Cdk4 was validated by X-ray analysis of the Cdk2-26a complex.

High-performance non-volatile memory that can operate under various mechanical deformations such as bending and folding is in great demand for the future smart wearable and foldable electronics. Here we demonstrate non-volatile solution-processed ferroelectric organic field-effect transistor memories operating in p-and n-type dual mode, with excellent mechanical flexibility. Our devices contain a ferroelectric poly(vinylidene fluoride-cotrifluoroethylene) thin insulator layer and use a quinoidal oligothiophene derivative (QQT(CN)4) as organic semiconductor. Our dual-mode field-effect devices are highly reliable with data retention and endurance of 46,000 s and 100 cycles, respectively, even after 1,000 bending cycles at both extreme bending radii as low as 500 mm and with sharp folding involving inelastic deformation of the device. Nano-indentation and nano scratch studies are performed to characterize the mechanical properties of organic layers and understand the crucial role played by QQT(CN)4 on the mechanical flexibility of our devices.

Fabrication of p-n structures is a key issue in a number of electronic devices, including rectifying diodes, solar cells, and bipolar transistors. Complementary metal oxide semiconductor (CMOS) technology based on the integration of discrete p-and n-channel field-effect transistors (FETs) on a same substrate has been widely used in a variety of electronic applications and enables the fabrication of integrated circuits with low-power dissipation and high operational stability. In the growing field of organic electronics, efficient large-scale organic CMOS integrated circuits [1,2] as well as lateral p-n diodes [3] have already been realized by thermally evaporating p-and n-type semiconducting organic molecules separately through shadow masks. Alternatively, fabrication of organic inverters by inkjet printing, self-assembly, or spin-coating has also been reported and has demonstrated the enormous potential of solution processing for low-cost, large-area, flexible electronics. [4][5][6][7][8][9][10] However, in spite of remarkable recent advances in high-mobility organic FET materials [11][12][13][14] and nanostructuration techniques, [15] there has still been no reliable approach for effectively patterning p-n bipolar and CMOS microstructures made from solutionprocessible organic semiconductors. We have addressed this issue by exploiting the unique charge-transport properties of the solution-processible dicyanomethylene-substituted quinoidal quaterthiophene [QQT(CN)4], which can be converted from an ambipolar p-type-dominant to n-type semiconductor by either thermal annealing or direct laser writing.The chemical structure of the QQT(CN)4 oligomer is shown in the inset of Figure 1a. Quinoidal oligothiophene derivatives generally show a low highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy bandgap and are very promising candidates for n-type or single-component ambipolar organic FETs. [16][17][18][19][20][21] We have fabricated top-contact bottom-gate organic FETs under ambient conditions by spin-coating a QQT(CN)4 thin film on top of a polyimide gate-dielectric layer and using chromium drain/source electrodes. The transfer and output characteristics displayed in Figure 1 show that the device based on as-prepared QQT(CN)4 thin film exhibits an ambipolar behavior with a predominant hole-transport character. The charge-carrier field-effect mobilities were extracted from the transfer characteristics in the saturated regions. Hole and electron mobilities were measured to be 2 AE 1 Â 10 À3 and 4 AE 1 Â 10 À4 cm 2 V À1 s À1 , respectively. Compared to the QQT(CN)4-based device performance obtained using octadecyltrichlorosilane-treated SiO 2 as gate-dielectric layer and gold top-contact electrodes, [16] these mobility values are substantially lower. However, the use of a polyimide gate dielectric presents the significant advantage of strongly reducing COMMUNICATION www.advmat.de www.MaterialsViews.com

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We report on the realization of high performance solution-processed ambipolar organic transistors based on a quinoidal oligothiophene derivative. The devices show hole and electron field-effect mobilities in air as high as 0.1 and 0.006 cm2 V−1 s−1, respectively, and can be converted from ambipolar p-type dominant to n-type transistors by thermal annealing. The conversion of the majority carrier type is assigned to strong variations in molecular packing. The demonstration of complementary flexible inverters suggests an effective strategy for patterning lateral pn-bipolar structures in solution-processed thin films made from a monolithic ambipolar organic semiconductor.