Polymorphism in new thienothiophene-thiazolothiazole organic semiconductors.

The front cover artwork is provided by J. A. Schneider from D. Perepichka's group (McGill University). The image shows two packing motifs of the same organic semiconductor, which either hinder or facilitate charge transport. In the foreground the crystal polymorphs and a single crystal field-effect transistor are pictured. Read the full text of the article at 10.1002/cphc.201500066.

Pentacenobis(thiadiazole)dione, an n-type semiconductor for field-effect transistors.

A new heteroacenequinone, pentaceno[2,3-c:9,10-c']bis([1,2,5]thiadiazole)-6,13-dione (PBTDQ), with two peripheral thiadiazole rings was synthesized, and its solid-state properties were characterized. The fused planar structure with a low-lying LUMO and low reorganization energy facilitates electron transport, affording µe values of up to 0.11 cm(2) V(-1) s(-1) in field-effect transistor devices.

Crystal engineering of dual channel p/n organic semiconductors by complementary hydrogen†bonding.

The supramolecular arrangement of organic semiconductors in the solid state is as critical for their device properties as the molecular structure, but is much more difficult to control. To enable supramolecular design of semiconducting materials, we introduced dipyrrolopyridine as a new donor semiconductor capable of complementary hydogen bonding with naphthalenediimide acceptors. Through a combination of solution, crystallographic, and device studies, we show that the self-assembly driven by H bonding a) modulates the charge-transfer interactions between the donor and acceptor, b) allows for precise control over the solid-state packing, and c) leads to a combination of the charge-transport properties of the individual components. The predictive power of this approach was demonstrated in the synthesis of three new coassembled materials which show both hole and electron transport in single-crystal field-effect transistors. These studies provide a foundation for advanced solid-state engineering in organic electronics, capitalizing on the complementary H bonding.

Comprehensive investigation of self-assembled monolayer formation on ferromagnetic thin film surfaces.

We report a simple, universal method for forming high surface coverage SAMs on ferromagnetic thin (< or =100 nm) films of Ni, Co, and Fe. Unlike previous reports, our technique is broadly applicable to different types of SAMs and surface types. Our data constitutes the first comprehensive examination of SAM formation on three different ferromagnetic surface types using two different surface-binding chemistries (thiol and isocyanide) under three different preparation conditions: (1) SAM formation on electroreduced films using a newly developed electroreduction approach, (2) SAM formation on freshly evaporated surfaces in the glovebox, and (3) SAM formation on films exposed to atmospheric conditions beforehand. The extent of SAM formation for all three conditions was probed by cyclic voltammetry for surfaces functionalized with either (11-thiolundecyl)ferrocene (Fc-(CH2) 11-SH) or (11-isocyanoundecyl)ferrocene (Fc-(CH2) 11-NC). SAM formation was also probed for straight-chain molecules, hexadecanethiol and hexadecaneisocyanide, with contact angle measurements, X-ray photoelectron spectroscopy, and reflection-absorption infrared spectroscopy (RAIRS). The results show that high surface coverage SAMs with low surface-oxide content can be achieved for thin, evaporated Ni and Co films using our electroreduction process with thiols. The extent of SAM formation on electroreduced films is comparable to what has been observed for SAMs/Au and to what we observe for SAMs/Ni, Co, and Fe samples prepared in the glovebox.

Halochromism and protonation-induced assembly of a benzo[g]indolo[2,3-b]quinoxaline derivative.

A new halochromic compound is reported with pronounced UV/Vis spectral responses that depend on the extent of protonation and on the counter-ion structure. The absorption can be controlled over the entire visible spectrum and into the near-IR via a protonation-induced assembly mechanism. Thin-films were used for colorimetric detection of acid vapors.

Synthesis and Divergent Electronic Properties of Two Ring-Fused Derivatives of 9,10-Diphenylanthracene.

Two new contorted polycyclic aromatic hydrocarbons (PAHs) 1 and 2 were synthesized by acid-catalyzed benzannulation of a substituted anthracene. The isomers reveal dissimilar photophysical and redox properties with 2 having a much smaller HOMO-LUMO gap than 1. In the solid state, 2 packs in a unique two-dimensional herringbone motif that gives rise to efficient ambipolar charge transport in OFET devices, a feature not previously observed in contorted PAHs. On the other hand, 1 packs in one-dimensional dimerized π-stacks and displays insulating properties.

Supramolecular control of organic p/n-heterojunctions by complementary hydrogen bonding.

The supramolecular structure of organic semiconductors (OSCs) is the key parameter controlling their performance in organic electronic devices, and thus methods for controlling their self-assembly in the solid state are of the upmost importance. Recently, we have demonstrated the co-assembly of p- and n-type organic semiconductors through a three-point hydrogen-bonding interaction, utilizing an electron-rich dipyrrolopyridine (P2P) heterocycle which is complementary to naphthalenediimides (NDIs) both in its electronic structure and H bonding motif. The hydrogen-bonding-mediated co-assembly between P2P donor and NDI acceptor leads to ambipolar co-crystals and provides unique structural control over their solid-state packing characteristics. In this paper we expand our discussion on the crystal engineering aspects of H bonded donor-acceptor assemblies, reporting three new single co-crystal X-ray diffraction structures and analyzing the different packing characteristics that arise from the molecular structures employed. Particular attention is given toward understanding the formation of the two general motifs observed, segregated and mixed stacks. Co-assembly of the donor and acceptor components into a single, crystalline material, allows the creation of ambipolar semiconductors where the mutual arrangement of p- and n-conductive channels is engineered by supramolecular design based on complementary H bonding.

Synthesis, crystal structures, and electronic properties of nonlinear fused thienoacene semiconductors.

Two fused thienoacene compounds with two-dimensional ring connectivity were synthesized, and their semiconducting properties were characterized. Both compounds have a crystal structure comprised of herringbone arrays of tight π-π stacks. Strong π-π interactions lead to self-assembly into well-defined crystalline thin films from the vapor phase for both compounds. Field effect transistors were fabricated, affording identical hole mobilities of 3.0 × 10(-3) cm(2)/(V s) and I(on/off) > 10(5).