Self-assembly and charge transport properties of a benzobisthiazole end-capped with dihexylthienothiophene units

The synthesis of a new conjugated material is reported; BDHTT–BBT features a central electron-deficient benzobisthiazole capped with two 3,6-dihexyl-thieno[3,2-b]thiophenes. Cyclic voltammetry was used to determine the HOMO (−5.7 eV) and LUMO (−2.9 eV) levels. The solid-state properties of the compound were investigated by X-ray diffraction on single-crystal and thin-film samples. OFETs were constructed with vacuum deposited films of BDHTT–BBT. The films displayed phase transitions over a range of temperatures and the morphology of the films affected the charge transport properties of the films. The maximum hole mobility observed from bottom-contact, top-gate devices was 3 × 10−3 cm2 V−1 s−1, with an on/off ratio of 104–105 and a threshold voltage of −42 V. The morphological and self-assembly characteristics versus electronic properties are discussed for future improvement of OFET devices

Design and synthesis of next-generation organic semiconductors based on benzo[1,2-d:4,5-d′]bisoxazole

Benzobisazoles are a class of molecules that initially found their use in high-performance materials as high tensile strength fibers. Recent modifications to the syntheses of benzobisazoles have allowed for the materials to be studied as an n-type material to be used in organic semiconductors, more specifically organic light-emitting diodes (OLEDs). The high molecular stability required to produce blue light gives an opportunity for benzobisazoles to fulfill the requirement. Prior work on benzobisazoles, more specifically, the oxygen analog benzobisoxazole, has been used to try to achieve blue (<450 nm) but fell short in terms of efficiency due to molecular design choices. The following describes new design strategies such as utilizing single-bond linkage between the electron rich and deficient molecules, as well as transitioning from polymer to small molecules to fine-tune the properties of the materials for semiconductor applications. Utilizing a new design strategy, we demonstrate the ability to blue-shift the emission on two benzobisoxazole-based polymers by adopting single bond linkage between the benzobisoxazole and electron rich moieties fluorene and carbazole and achieve a usable brightness (> 1000 Cd/m2) when incorporated into OLEDs. With further modification of the benzobisoxazole core piece by adding dual conjugation along both axes to produce small molecules, we were able to achieve a deeper blue emission at higher efficiencies due to the reduced conjugation and aggregation than our previous systems experienced. Development of the small molecules led us to adopt a modular synthetic strategy for the high-efficiency material design of benzobisoxazole-based materials. In combination with Density Functional Theory calculations, we show the viability of performing computer-backed molecular design to develop materials to be used in all types of semiconductor applications. From calculations, we synthesize benzobisoxazole cruciforms that have both electron rich and electron deficient moieties. These products we then compared to experimental data to confirm the validity of computer-based rational design of molecules for not only blue OLEDs but for all semiconductor applications. The extremely high number of possible combinations of electron rich and electron deficient moieties allows for extensive future studies for the most optimal substituents for proper energy leveling tuning