Ke Jie Tan

Synthesis, characterization, self-assembly, and physical properties of 11-methylbenzo[d]pyreno[4,5-b]furan.

Synthesis, structure, and physical properties of a novel 11-methylbenzo[d]pyreno[4,5-b]furan (BPF) and its self-assembly in water have been reported. The performance of nanowire-based films in organic light-emitting diodes is much better than that of the thin film deposited by directly drop-coating BPF molecules in THF solution. SEM study indicates that the well-organized structure (nanowires) is an important factor in enhancing the performance of OLED devices.

Crystal structure and phototransistor behavior of N-substituted heptacence.

6,8,15,17-Tetraaza-1.18,4.5,9.10,13.14-tetrabenzoheptacene (TTH, 1) has been prepared and characterized by single-crystal X-ray structure analysis. A phototransistor device based on TTH single crystal demonstrated that TTH showed a good performance in signal amplification under the photoconductive effect as well as photocontrolled switches.

Ultrathin organic single crystals: fabrication, field-effect transistors and thickness dependence of charge carrier mobility

Organic single crystals with thickness ranging from a few monolayers to micrometres were fabricated by an “Organic Crystal Cleavage” method. The mobility slightly increased with decreased thickness and rose sharply when the crystal thickness was below some critical thickness. The gate induced charges in the field-effect transistor (FET) channel and in the vicinity of the metal–semiconductor interface reducing the contact barrier. The values of mobility measured on very thin crystals without the contact barrier precisely reflect the transport properties of organic semiconductors.

Influence of Vibronic Coupling on Band Structure and Exciton Self-Trapping in α-Perylene

Exciton sizes influence transport processes and spectroscopic phenomena in molecular aggregates and crystals. Thermally driven nuclear motion generally localizes electronic states in equilibrium systems. Exciton sizes also undergo dynamic changes caused by nonequilibrium relaxation in the lattice structure local to the photoexcitations (i.e., self-trapping). The α-phase of crystalline perylene is particularly well-suited for fundamental studies of exciton self-trapping mechanisms. It is generally agreed that a subpicosecond self-trapping process in α-perylene localizes photoexcited excitons onto pairs of closely spaced molecules (i.e., dimers), which then relax through excimer emission. Here, electronic relaxation dynamics in α-perylene single crystals are investigated using a variety of nonlinear optical spectroscopies in conjunction with a Frenkel exciton model. Linear absorption and photon echo spectroscopies suggest that excitons are delocalized over less than four unit cells (16 molecules) at 78 K prior to self-trapping. Stimulated Raman spectroscopies conducted on and off electronic resonance reveal significant vibronic coupling in a mode at 104 cm(-1), which corresponds to the displacement between perylene molecules comprising a dimer. Strong vibronic coupling in this mode suggests that motion along the interdimer axis is instrumental in driving the self-trapping process. The results are discussed in the context of our recent study of tetracene and rubrene single crystals in which similar experiments and models were employed.

Synthesis, Structure, Physical Properties, and Displacement Current Measurement of an n-Type Organic Semiconductor: 2:3,5:6-Bis(1,1-dicyanoethylene-2,2-dithiolate)-quinone

An n-type organic semiconductor 2:3,5:6-bis(1,1-dicyanoethylene-2,2-dithiolate)-quinone (BDQ) has been successfully synthesised and characterised. The single crystal structure of BDQ, determined by single-crystal X-ray crystallography, indicated that BDQ is a planar molecule with strong face-to-face π-π stacking (3.40 A) and S···S interactions (3.66 A) between neighbouring molecules, which might be in favour of the effective charge transport. The UV-vis spectrum shows that BDQ has shoulder absorption up to 550 nm (2.25 eV). The electrochemical property displays that the HOMO-LUMO gap of BDQ obtained from the half-wave redox potential is 1.92 eV. The displacement current measurement of BDQ-based devices is demonstrated and discussed.

Control of Electronic Properties of Organic Semiconductor

The electronic properties of organic field effect transistors limit the efficiency of integrated circuits build on basis of printed organic semiconductors. In order to control the mobility of high efficient semiconductors, like rubrene, tetracene, tetracyanoquinodimethane (TCNQ), copper phthalocyanine and many others, single-crystal field-effect transistors have been prepared on surfaces of single crystals and characteristics have been measured. The highest mobility has been measured on rubrene single crystals. The mobility of as-grown crystals measured by air-gap field effect transistor is in the range of 10 cm2/Vs but falls below 1 cm2/Vs during reduction. It was observed that the measured mobility depends on the dielectric used for field effect transistors.