Modular synthesis of unsymmetrical [1]benzothieno[3,2-b][1]benzothiophene molecular semiconductors for organic transistors

A modular approach to underexplored, unsymmetrical [1]benzothieno[3,2-b][1]benzothiophene (BTBT) scaffolds delivers a library of BTBT materials from readily available coupling partners by combining a transition-metal free Pummerer CH-CH-type cross-coupling and a Newman-Kwart reaction. This effective approach to unsymmetrical BTBT materials has allowed their properties to be studied. In particular, tuning the functional groups on the BTBT scaffold allows the solid-state assembly and molecular orbital energy levels to be modulated. Investigation of the charge transport properties of BTBT-containing small-molecule:polymer blends revealed the importance of molecular ordering during phase segregation and matching the highest occupied molecular orbital energy level with that of the semiconducting polymer binder, polyindacenodithiophene-benzothiadiazole (PIDTBT). The hole mobilities extracted from transistors fabricated using blends of PIDTBT with phenyl or methoxy functionalized unsymmetrical BTBTs were double those measured for devices fabricated using pristine PIDTBT. This study underscores the value of the synthetic methodology in providing a platform from which to study structure-property relationships in an underrepresented family of unsymmetrical BTBT molecular semiconductors.

[1]Benzothieno[3,2-b][1]benzothiophene-Based Dyes: Effect of Ancillary Moiety on Mechanochromism and Aggregation-Induced Emission

It is an established fact that [1]benzothieno[3,2-b][1]benzothiophene (BTBT) is a champion molecule for high mobility OFETs devices. Recently it is also utilized in dye-sensitized solar cells (DSSCs) and organic photovoltaics...

Multifunctional Benzo[4,5]thieno[3,2-b]benzofuran Derivative with High Mobility and Luminescent Properties

Development of multifunctional materials and devices has garnered enormous attention in the field of organic optoelectronics; nevertheless, achieving high mobility together with strong luminescence in a single semiconductor remains a major bottleneck. Here, a new multifunctional semiconductor molecule, 2,7-diphenylbenzo[4,5]thieno[3,2-b]benzofuran (BTBF-DPh), that integrates high charge transporting [1]benzothieno[3,2-b][1]benzothiophene with a strongly emissive furan group, is synthesized and applied in three types of optoelectronic devices, including organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and organic phototransistors (OPTs). OLEDs based on BTBF-DPh as the emissive layer showed a blue emission with CIE coordinates of (0.151, 0.069) and a maximum current efficiency of 2.96 cd A^-1 with an external quantum efficiency of 4.23%. Meanwhile, OFETs fabricated with BTBF-DPh thin film manifested a carrier mobility of 0.181 cm² V^-1 s^-1, which is comparable to that of thiophene-based counterparts. Additionally, BTBF-DPh-based OPTs exhibited a maximum responsivity and detectivity of 2.07 × 10³ A W^-1 and of 5.6 × 10¹⁵ Jones, respectively. On the one hand, our rationally designed material, BTBF-DPh, has a dense and close-packed structure with an extended π-conjugation, facilitating charge transport through adjacent molecules. On the other hand, the weakened dipole-dipole interactions between BTBF-DPh molecules that resulted from the unambiguous J-aggregation and reduced spin-orbit coupling caused by replacing sulfur atom significantly suppress the exciton quenching, contributing to the improved photoluminescence performance. These results validate that our newly developed BTBF-DPh is a promising multifunctional organic semiconductor for optoelectronic devices.

Thienoisoindigo (TII)-Based Quinoidal Small Molecules for High-Performance n-Type Organic Field Effect Transistors

A novel quinoidal thienoisoindigo (TII)-containing small molecule family with dicyanomethylene end-capping units and various alkyl chains is synthesized as n-type organic small molecules for solution-processable organic field effect transistors (OFETs). The molecular structure of the 2-hexyldecyl substituted derivative, TIIQ-b16, is determined via single-crystal X-ray diffraction and shows that the TIIQ core is planar and exhibits molecular layers stacked in a "face-to-face" arrangement with short core intermolecular distances of 3.28 Å. The very planar core structure, shortest intermolecular N···H distance (2.52 Å), existence of an intramolecular non-bonded contact between sulfur and oxygen atom (S···O) of 2.80 Å, and a very low-lying LUMO energy level of -4.16 eV suggest that TIIQ molecules should be electron transporting semiconductors. The physical, thermal, and electrochemical properties as well as OFET performance and thin film morphologies of these new TIIQs are systematically studied. Thus, air-processed TIIQ-b16 OFETs exhibit an electron mobility up to 2.54 cm2 V-1 s-1 with a current ON/OFF ratio of 105-106, which is the first demonstration of TII-based small molecules exhibiting unipolar electron transport characteristics and enhanced ambient stability. These results indicate that construction of quinoidal molecule from TII moiety is a successful approach to enhance n-type charge transport characteristics.

Architecting layered molecular packing in substituted benzobisbenzothiophene (BBBT) semiconductor crystals

The construction of layered molecular packing structures in a non-layered crystalline material, benzobisbenzothiophene (BBBT), was achieved by employing long-alkyl and phenyl substituents, leading to high-performance organic thin-film transistors.

Di- and tetramethoxy benzothienobenzothiophenes: substitution position effects on the intermolecular interactions, crystal packing and transistor properties

The relationship between the structure and transistor properties of novel benzothienobenzothiophene (BTBT) derivatives with 2,3-dimethoxy and 2,3,7,8-tetramethoxy groups was investigated.

Investigating the Thermal Stability of Organic Thin-Film Transistors and Phototransistors Based on [1]-Benzothieno-[3,2-b]-[1]-benzothiophene Dimeric Derivatives

Two new highly thermally stable [1]benzothieno[3,2-b][1]benzothiophene (BTBT) dimeric derivatives, namely 1,4-bis([1]benzothieno[3,2-b][1]benzothiophene-2-yl)benzene (BTBT-Ph-BTBT) and 4,4'-bis([1]benzothieno[3,2-b][1]benzothiophene-2-yl)-1,1'-biphenyl (BTBT-DPh-BTBT), were synthesized by combining two simple fragment structures. Compared to the monomer compound 2-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT, μ_max =3.4×10^-2  cm²  V^-1  s^-1 ), the organic thin-film transistors (OTFTs) based on BTBT-Ph-BTBT and BTBT-DPh-BTBT showed significantly higher mobility (up to 2.5 and 3.6 cm²  V^-1  s^-1 for BTBT-Ph-BTBT and BTBT-DPh-BTBT, respectively). The mobility of OTFTs based on BTBT-Ph-BTBT was kept at a high value (2.4×10^-1  cm²  V^-1  s^-1 ) after the devices were thermally annealed at 350 °C. Furthermore, the organic phototransistors (OPTs) based on BTBT-Ph-BTBT and BTBT-DPh-BTBT displayed high photosensitivities in a range of 250-400 nm with a low intensity, making these materials potentially applicable for sensitive optoelectronic devices.