Syntheses and Properties of Hole-Transporting Biindenofluorenes.

Described herein is a straightforward approach to synthesizing three biindenofluorene (BIF) derivatives, composed of antiaromatic indenofluorene units, which are the first non-alternant congeners of known bipentacene. Dimerization of indeno[1,2-b]fluorene and indeno[2,1-c]fluorene units by connecting carbons 3 and 3' and carbons 2 and 2', respectively, is shown to influence the highest occupied and lowest unoccupied molecular orbital energy levels of the resulting BIFs, affording band gaps (1.5-1.6 eV) that are smaller than that of a known indenofluorene polymer (2.3 eV). The hole mobilities of BIFs were determined to be ∼10-2 cm2 V-1 s-1.

Highly Soluble Ambipolar anti-Perylene-3,4 : 9,10-bis(benzimidazole)s Stabilize a Room-Temperature Columnar Hexagonal Phase.

A new series of highly soluble perylene anti-bis(4,5-dialkoxybenzimidazole)s bearing branched flexible chains stabilizing room temperature columnar hexagonal phase and with balanced ambipolar charge carrier mobility is reported for the first time. Only the anti isomer was successfully separated and characterized. These compounds have a high extinction coefficient, small optical band gap and wide absorption range, thus making them a promising class of ambipolar organic semiconductors capable of self-organizing.

First example of ambipolar naphthalene diimide exhibiting a room temperature columnar phase.

A self-assembled ambipolar organic semiconductor based on naphthalene diimide with low clearing temperature, solution processability, and high molar extinction coefficient, exhibiting a room temperature columnar hexagonal liquid crystalline phase is reported.

Ambipolar Columnar Self-assembled Organic Semiconductors based on Heteroatom bay-Annulated Perylene Bisimides.

Highly electron-deficient heteroatom (N, S, Se) bay-annulated PBIs exhibiting ordered columnar phase over a wide mesomorphic range including ambient temperature are reported in this manuscript. These compounds with six peripheral n-decyloxy chains exhibited absorption spectra with high molar extinction coefficients, electron-deficient nature and self-assembling behaviour. A detailed comparison with the PBIs bearing six peripheral n-decyl chains was also carried out to get the valuable insights on the structure-property relations in this important class of organic semiconductors. Both of the PBI series were tested for their charge carrier mobility by space charge limited current method and found that they exhibit ambipolar conductivity. This is in contrary to the vast body of literature, where most of the PBI based semiconductors exhibit electron transport behaviour. In general, PBIs derived from tri-n-alkyl anilines exhibit higher mobility values than the PBIs derived from tri-n-alkoxy anilines. Especially, the ambipolar S-annulated PBI derived from tri-n-alkyl aniline exhibited highest hole (8.39×10-3  cm2 /V.s) and electron (1.5×10-2  cm2 /V.s) mobility values and promising for the application in organic electronics.

High hole mobility in room temperature discotic liquid crystalline tetrathienoanthracenes.

Tetrathienoanthracene (TTA), a new discotic core fragment, is explored that shows a remarkably high hole mobility (µh) of 4.22 cm2 V-1 s-1 at room temperature when used in space-charge limited current (SCLC) devices. Strong co-facial interactions (π-π, SS) among TTA cores along with a high tendency of the derivative to align homeotropically in the columnar mesophase over a large area in SCLC cells contributed to the top-class charge carrier mobility.

High Hole Mobility and Efficient Ambipolar Charge Transport in Heterocoronene-Based Ordered Columnar Discotics.

Heterocoronene, a new redox-active core fragment, is utilized for the synthesis of room-temperature columnar discotic liquid crystals (DLCs). Three wedge-shaped side chains having different lengths of alkyl tails are introduced at the periphery of the heterocoronene core to prepare three kinds of discotic molecules, 1 (R = C10H21), 2 (R = C12H25), and 3 (R = C14H29). X-ray diffraction (XRD) analysis confirmed the packing variation in the columnar lattices regulated by alkyl chains of discrete length and steric bulk. When used in space charge limited current devices, compound 1 exhibits a high hole mobility value of 8.84 cm2/V s at ambient temperature, whereas compounds 2 and 3 show efficient ambipolar charge transport behavior with maximum hole (µh) and electron (µe) mobilities of 0.70 and 3.59 cm2/V s, respectively, for compound 3. The mobility values (µh = 8.84 cm2/V s for 1 and µe = 3.59 cm2/V s for 3) are remarkable and the highest ever disclosed for any DLC-based organic semiconductor, promising to deliver a good balance between mobility and processability in devices. The grazing incidence small- and wide-angle X-ray scattering experiments are employed to quantify the extent of alignment in the film state, which correlates with the observed trend of mobility values.

A New Approach to Compute the Porosity and Surface Roughness of Porous Coated Capillary-Assisted Low Pressure Evaporators.

The fundamental characteristics of metal coatings that influence heat transfer are porosity and surface roughness. It is a challenge to analyze the porosity and surface roughness due to the inadequate amount of copper per coated area. In this study, a new approach to non-invasively determine the porosity of metal films utilizing a helium pycnometer and computed micro-tomography (CMT) is presented. Furthermore, a telescope-goniometer is used to measure the surface roughness. Experiments are conducted on four varieties of thin film samples coated with copper powder using wire flame and plasma thermal spray coating methods. The porosities of the thin films were determined to be between 39 and 43%. The thermal spray coating increased the hydrophobicity of the surface and the plasma coating created super-hydrophobic surfaces. The new approach establishes that the porosity of thin films can be non-invasively determined and may also be applied to a wide variety of coated surfaces.