A series of cycloalkyl-substituted naphthalene tetracarboxylic diimides (Cyn-NTCDIs, n ¼ 3-8) are prepared and the transistor properties and molecular packings are systematically investigated. Cy5-Cy8-NTCDIs have similar brickwork structures, where two molecules are located on the top of a molecule with large displacement along the molecular short axis. The intermolecular overlap is maximized when the small slipping along the molecular long axis makes the molecules nearly perpendicular to the substrate.Consequently, the mobility decreases exactly in the same order as the interlayer d-spacings.

We have investigated trap density of states (trap DOS) in n-channel organic field-effect transistors based on N,N ’-bis(cyclohexyl)naphthalene diimide (Cy-NDI) and dimethyldicyanoquinonediimine (DMDCNQI). A new method is proposed to extract trap DOS from the Arrhenius plot of the temperature-dependent transconductance. Double exponential trap DOS are observed, in which Cy-NDI has considerable deep states, by contrast, DMDCNQI has substantial tail states. In addition, numerical simulation of the transistor characteristics has been conducted by assuming an exponential trap distribution and the interface approximation. Temperature dependence of transfer characteristics are well reproduced only using several parameters, and the trap DOS obtained from the simulated characteristics are in good agreement with the assumed trap DOS, indicating that our analysis is self-consistent. Although the experimentally obtained Meyer-Neldel temperature is related to the trap distribution width, the simulation satisfies the Meyer-Neldel rule only very phenomenologically. The simulation also reveals that the subthreshold swing is not always a good indicator of the total trap amount, because it also largely depends on the trap distribution width. Finally, band transport is explored from the simulation having a small number of traps. A crossing point of the transfer curves and negative activation energy above a certain gate voltage are observed in the simulated characteristics, where the critical VG above which band transport is realized is determined by the sum of the trapped and free charge states below the conduction band edge

Thienyl-substituted tetrathiafulvalene (DTh-TTF, 1a) and a t-butyl derivative (1b) are prepared, and the remarkable photoresponse and memory effect in the transistors are investigated. Upon irradiation of light with a wavelength shorter than the absorption edge (535 nm), the threshold voltage of 1b shifts by as large as 57 V, and the drain current increases by 10 3 times. The photo generated conducting state is maintained for several tens of minutes but erased by the application of a large negative gate voltage. Results and discussionSynthesis 1a and 1b were synthesized starting from unsubstituted and t-butyl substituted thiophene 2 according to Scheme 2 Scheme 1 Chemical structures of TTF, DTTTF, HMTTF, and quaterthiophene.Scheme 2 Synthesis of 1a and 1b.

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