n-Type Thin-Film Transistors Based on Diketopyrrolopyrrole Derivatives: Role of Siloxane Side Chains and Electron-Withdrawing Substituents.

The physical properties, packing, morphology, and semiconducting performance of a planar π-conjugated system can be effectively modified by introducing side chains and substituent groups, both of which can be complementary to the π framework in changing the intermolecular association, frontier molecular orbital energy, optical band gap, and others. We herein show that installation of end-capped electron-withdrawing groups (EWGs), such as dicyanovinyl (-DCV), 3-ethylrhodanine (-RD), and 2-(3-oxo-indan-1-ylidene)-malononitrile (-INCN), together with siloxane side chains to the backbones of dithienyldiketopyrrolopyrrole (DPPT), such as , , and , can greatly improve its solubility, air stability, and film morphology to serve as an n-channel in thin-film transistor fabrication. The EWGs attached to the DPPT core narrowed the optical band gap () and changed the highest occupied molecular orbital and the lowest unoccupied molecular orbital energies ( and ), making them suitable for n-channel field-effect transistor (FET) applications.

Influences of Conjugation Length on Organic Field-Effect Transistor Performances and Thin Film Structures of Diketopyrrolopyrrole-Oligomers.

Here, two diketopyrrolopyrrole (DPP)-based oligomers, DPP-4T and DPP-6T, are studied to reveal the influences of conjugation length on thin-film morphology and organic field-effect transistor (OFET) performances. PDMS-assisted crystallization in a solvent-annealing chamber is applied to prepare crystal arrays of DPP-4T and DPP-6T to optimize the quality of charge channels for OFET characterizations. To deliver insights into microstructure and morphology of thin films, a characterization procedure for determining molecular packing in thin film and crystallinity of the crystal arrays is presented via grazing incidence wide-angle X-ray scattering, electron diffraction, and lattice simulation software package (Cerius2).

Roles of 3-Ethylrhodanine in Attaining Highly Ordered Crystal Arrays of Ambipolar Diketopyrrolopyrrole Oligomers.

Until now, only limited DPP oligomers delivered ambipolar semiconductor characteristics. To develop a facile strategy of preparing ambipolar mono-DPP oligomers, two dithienyl diketopyrrolopyrrole (DPPT) based-conjugated molecules, DPPT-RD and DPPT-DCV, which contain 3-ethylrhodanine (RD) and dicyano-2-vinyl (DCV) end substituents were synthesized. The influences of the -RD end substituents on the molecular properties, solid-state morphology, and OFET performances of the DPPT oligomer were investigated.

Conformational Preferences and the Phase Stability of Fullerene Hexa-adducts.

Molecular conformation and the assembly structure determine the spatial arrangements of the constituent units and the functions of a molecule. Although, fullerene hexa-adducts (FHAs) have been known as functional materials with great versatility, their conformational preferences and phase stability remain a complicate issue. By choosing bithiophene (T2 ) and dodecyl bithiophene (C12 T2 ) as the peripheral units of FHA, and using microscopic, scattering and diffraction characterizations, our study reveals how the intramolecular interaction and environmental stimulus affects the conformational preferences and phase stability of FHAs.

Flat-on ambipolar triphenylamine/C nano-stacks formed from the self-organization of a pyramid-sphere-shaped amphiphile.

A giant amphiphile, which is constructed with an amorphous nano-pyramid (triphenylamine, TPA) and a crystalline nano-sphere (C), was synthesized. Structural characterization indicates that this pyramid-sphere-shaped amphiphile ( ) forms a solvent-induced ordered phase, in which the two constituent units self-assemble into alternating stacks of two-dimensional (2D) TPA and C nano-sheets. Due to the complexity of the molecular structure and the amorphous nature of the nano-pyramid, phase formation was driven by intermolecular C-C interactions and the ordered phase could not be reformed from the melt.