Search

A combined experimental and theoretical study was carried out to investigate the ambipolar charge transport properties of a series of N-heteropentacenes in organic field-effect transistors (OFETs). Introduction of nitrogen atoms in the core and halogen atoms around the periphery of the pentacene framework can efficiently tune the highest occupied molecular orbitals (HOMOs) of the N-heteropentacenes from −5.18 eV to −5.53 eV and the lowest unoccupied molecular orbitals (LUMOs) from −3.08 eV to −3.69 eV. By lowering their HOMO and LUMO energy levels with respect to the Fermi level of the gold electrode, the transistors of these molecules exhibited a transition from hole-dominant bipolar, to balanced ambipolar, and to electron-dominant bipolar transport characteristics. Meanwhile, with the lowering of the frontier molecular orbital energy levels, the transistors also exhibited a decrease of the electron threshold voltage and an increase of the hole threshold voltage. Charge carrier mobility calculations based on Marcus theory and first principle molecular dynamics were conducted to simulate the carrier transport dynamics. The comparison between experimental and theoretical results revealed that for the given device structure, the ratio of electron and hole mobilities of the ambipolar OFETs was strongly affected by the charge injection barrier. This result provides useful guidelines for future molecular design of ambipolar OFETs.

Highly efficient organic reactions in water are important for designing environmental-friendly and low cost synthetic processes. Herein, we demonstrate an intermediate-in-water strategy for the heterogeneous synthesis of benzofurans in aqueous media. The cyclization reaction of 2-(phenylethynyl)phenol to 2-phenylbenzofuran cannot proceed in pure water. However, this reaction can be efficiently promoted by the formation of sparingly soluble intermediate in the presence of alkaline. Quantitative conversion of a variety of substrates to benzofuran derivatives has been achieved in the absence of noble metal catalyst. Other remarkable features including easy-isolation and purification of product, along with wide range of functional group tolerance render the methodology promising in the realm of green-synthesis.

By changing the packing motif of the conjugated cores and the thin-film microstructures, unipolar organic semiconductors may be converted into ambipolar materials. A combined experimental and theoretical investigation is conducted on the thin-film organic field-effect transistors (OFETs) of three organic semiconductors that have the same conjugated core structure of s-indaceno[1,2-b: 5,6-b'] dithiophene-4,9-dione but with different n-alkyl groups. The optical and electrochemical measurements suggest that the three organic semiconductors have very similar energy levels; however, their OFETs exhibit dramatically different transport characteristics. Transistors based on compound 1a or 1c show ambipolar transport properties, while those based on compound 1b show p-type unipolar behavior. Specifically, compound 1c is characterized as a good ambipolar semiconductor with the highest electron mobility of 0.22 cm 2 V-1 s(-1) and the highest hole mobility of 0.03 cm 2 V-1 s(-1). Complementary metal oxide semiconductor (CMOS) inverters incorporated with compound 1c show sharp inversions with high gains above 50. Theoretical investigations reveal that the drastic difference in the transport properties of the three materials is due to the difference in their molecular packing and film microstructures.

The reactions can be performed without microwave irradiation providing the corresponding products after significantly longer reaction times in lower yields.