B←N-Incorporated Dibenzo-azaacene with Selective Near-Infrared Absorption and Visible Transparency

Colorless Near-Infrared Absorbing Dyes Based on B-N Fused Donor-Acceptor-Donor π-Conjugated Molecules for Organic Phototransistors

The introduction of a colorless function to organic electronic devices allows responses to light in the near-infrared (NIR) region and is expected to broaden the applications of these devices. However, the development of a colorless NIR dye remains a challenge due to the lack of a rational molecular design for controlling electronic transitions. In this study, to suppress the π-π* transitions in the visible region, polycyclic donor-acceptor-donor π-conjugated molecules with boron bridges (Py-FNTz-B and IP-FNTz-B) are designed and synthesized, which contain pyrrole or indenopyrrole as donor units with fluorinated naphthobisthiadiazole (FNTz) as an acceptor unit. The pyrrole end-capped Py-FNTz-B shows an absorption band in the NIR region without distinct visible-light absorption, which has led to the establishment of colorless characteristics. The indenopyrrole end-capped IP-FNTz-B shows a narrow optical energy gap of 0.87 eV in films. Time-resolved microwave conductance and field-effect transistors demonstrate the semiconducting characteristics of these molecules, and Py-FNTz-B-based devices function as NIR phototransistors. Theoretical analyses indicate that the combination of a polyene-like electronic structure with orbital symmetry is important to obtain NIR wavelength-selective absorption. This study suggests that a molecular design based on electronic structures can be effective in the development of colorless NIR-absorbing dyes for organic electronics.

Recent Research Progress of Organic Small-Molecule Semiconductors with High Electron Mobilities

Organic electronics has made great progress in the past decades, which is inseparable from the innovative development of organic electronic devices and the diversity of organic semiconductor materials. It is worth mentioning that both of these great advances are inextricably linked to the development of organic high-performance semiconductor materials, especially the representative n-type organic small-molecule semiconductor materials with high electron mobilities. The n-type organic small molecules have the advantages of simple synthesis process, strong intermolecular stacking, tunable molecular structure, and easy to functionalize structures. Furthermore, the n-type semiconductor is a remarkable and important component for constructing complementary logic circuits and p-n heterojunction structures. Therefore, n-type organic semiconductors play an extremely important role in the field of organic electronic materials and are the basis for the industrialization of organic electronic functional devices. This review focuses on the modification strategies of organic small molecules with high electron mobility at molecular level, and discusses in detail the applications of n-type small-molecule semiconductor materials with high mobility in organic field-effect transistors, organic light-emitting transistors, organic photodetectors, and gas sensors.

An Amorphous n-Type Conjugated Polymer with an Ultra-Rigid Planar Backbone

High charge carrier mobility polymer semiconductors are always semi-crystalline. Amorphous conjugated polymers represent another kind of polymer semiconductors with different charge transporting mechanism. Here we report the first near-amorphous n-type conjugated polymer with decent electron mobility, which features a remarkably rigid, straight and planar polymer backbone. The molecular design strategy is to copolymerize two fused-ring building blocks which are both electron-accepting, centrosymmetrical and planar. The polymer is the alternating copolymer of double B←N bridged bipyridine (BNBP) unit and benzobisthiazole (BBTz) unit. It shows a decent electron mobility of 0.34 cm²  V^-1  s^-1 in organic field-effect transistors. The excellent electron transporting property of the polymer is possibly due to the ultrahigh backbone stiffness, small π-π stacking distance, and high molecular weight.

Novel Synthetic Approach to Heteroatom Doped Polycyclic Aromatic Hydrocarbons: Optimizing the Bottom-Up Approach to Atomically Precise Doped Nanographenes

The success of the rational bottom-up approach to nanostructured carbon materials and the discovery of the importance of their doping with heteroatoms puts under the spotlight all synthetic organic approaches to polycyclic aromatic hydrocarbons. The construction of atomically precise heteroatom doped nanographenes has evidenced the importance of controlling its geometry and the position of the doping heteroatoms, since these parameters influence their chemical-physical properties and their applications. The growing interest towards this research topic is testified by the large number of works published in this area, which have transformed a once "fundamental research" into applied research at the cutting edge of technology. This review analyzes the most recent synthetic approaches to this class of compounds.

B←N-Incorporated Dibenzo-azaacenes as n-Type Thermoelectric Materials

Organic thermoelectric materials play a vital role in flexible power generating applications, such as wearable electronics and sensor networks. While there is a wealth of research on p-type organic thermoelectric materials, developments on n-type counterparts as complementary are comparatively limited. Herein, we report a new kind of n-type small-molecule thermoelectric materials based on B←N-incorporated dibenzo-azaacenes 1,2-DBNA-2 and 1,2-DBNA-5. Because of the low-lying lowest unoccupied molecular orbital (LUMO) energy levels, 1,2-DBNA-2 and 1,2-DBNA-5 could be efficiently n-doped, and the rigid and almost planar skeleton could ensure good carrier transfer. When doped with a typical n-dopant (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine (N-DMBI), 1,2-DBNA-5 exhibits a moderate conductivity of 0.01 S cm^-1 and a power factor of 0.06 μW m^-1 K^-2 with a Seebeck coefficient of -244.4 μV K^-1 in thermoelectric devices. These results not only demonstrate that B←N-incorporated dibenzo-azaacenes are a novel class of n-type thermoelectric materials but also highlight a new strategy to develop n-type organic thermoelectric materials.

Mono- and Dinitro-BN-Naphthalenes: Formation and Characterization

Mono- and dinitro-BN-naphthalenes, i.e., 1-nitro-, 3-nitro-, 1,6-dinitro-, 3,6-dinitro-, and 1,8-dinitro-BNN, were generated in the nitration of 9,10-BN-naphthalene (BNN), a boron–nitrogen (BN) bond-embedded naphthalene, with AcONO₂ and NO₂BF₄ in acetonitrile. The nitrated products were isolated and characterized by NMR, GC-MS, IR, and X-ray single crystallography. The effects of the nitration on the electron density and aromaticity of BNN were evaluated by B-11 NMR analysis and HOMA calculations.

Bandgap Engineering of an Aryl-Fused Tetrathianaphthalene for Visible-Blind Organic Field-Effect Transistors

Stability problem of organic semiconductors (OSCs) because of photoabsorption has become a major barrier to large scale applications in organic field-effect transistors (OFETs). It is imperative to design OSCs which are insensitive to visible and near-infrared (VNIR) light to obtain both environmental and operational stability. Herein, taking a 2,3,8,9-tetramethoxy [1,4]benzodithiino[2,3-b][1,4]benzodithiine (TTN2) as an example, we show that controlling molecular configuration is an effective strategy to tune the bandgaps of OSCs for visible-blind OFETs. TTN2 adopts an armchair-like configuration, which is different from the prevailing planar structure of common OSCs. Because of the large bandgap, TTN2 exhibits no photoabsorption in the VNIR region and OFETs based on TTN2 show high environmental stability. The devices worked well after being stored in ambient air, (i.e. in the presence of oxygen and water) and light for over two years. Moreover, the OFETs show no observable response to light irradiation from 405–1,020 nm, which is also favorable for high operational stability.