Synthesis and physical properties of the conjugated dendrons bearing twisted acenes used in solution processing of organic light-emitting diodes

π-Expanded [6]Helicene-Containing Nanographenes: Synthesis, Structures, and Chiroptical Properties

A family of chiral nanographenes bearing [6]helicene units has been synthesized via the classical Scholl reaction. Inserting the [6]helicene unit into the parent nanographene skeleton can result in different structural topologies and optoelectric properties. Moreover, the isolated enantiomers exhibit attractive chiroptical properties.

Self-Assembly of Functionalized Twistarenes into Supramolecular Assemblies with Chiroptical Property and Photoconductive Behavior

A pair of novel chiral 1-phenylethylamine-modified twistarenes (4 and 11; compound 4 = 9,14-di-tert-butyl-7,16-diphenyl-2-(1-phenylethyl)-1H-benzo[8',9']triphenyleno[2',3':6,7]fluoreno[2,1,9-def]isoquinoline-1,3(2H)-dione) have been synthesized and characterized, and how the solvent component affects the chirality transfer of their self-assembled processes is investigated in mixtures with THF and H2O. The ordered assembly of 11 exhibits circular dichroism response. In addition, both 11a and 11b display positive photoconducting behavior.

Synthesis and Ultrafast Broadband Optical Limiting Properties of a Two-Branched Twistacene

A novel two-branched twistacene (PyDN) has been designed and synthesized for application on ultrafast optical limiting. This twistacene exhibits excellent two photon absorption and two photon absorption-induced excited singlet state absorption, which was systematically investigated with a femtosecond Z-scan experiment, transient absorption spectrum, and two-photon excited fluorescence experiments. The admirable two photon absorption is attributed to the high degree of π electron delocalization in twistacene which is caused by introduction of two strong donors. The excited singlet state absorption cooperates with two-photon absorption to provide an excellent ultrafast optical limiting behavior with high linear transmittance, where the thresholds are 2.3-5.3 mJ/cm² in the spectral region of 532-800 nm of femtosecond laser and 133 mJ/cm² for picosecond pulse at 532 nm. These thresholds are lower than that of most of the optical limiters reported previously, which indicates PyDN is a promising candidate for ultrafast optical limiting.

Double π-Extended Helicene Derivatives Containing Pentagonal Rings: Synthesis, Crystal Analyses, and Photophysics

Two novel double π-extended [n]helicene (n = 5, 6) derivatives (7b and 9) including pentagonal rings have been synthesized and characterized. Both of them have three isomers containing two enantiomers (P₆), (M₆), and a diastereoisomer in a meso form (P,M). X-ray single crystal analyses suggest that molecules 7b and 9 exhibit offset packing models of (P₆,P₅)- and (M₆,M₅)-isomers. Optical resolution of the resultant compound 7b was finished, and their chiroptical properties, as well as the DFT calculations, were also examined.

Antioxidant and Organic Dye Removal Potential of Cu-Ni Bimetallic Nanoparticles Synthesized Using Gazania rigens Extract

Copper-nickel bimetallic nanoparticles (Cu-Ni BNPs) were fabricated using an eco-friendly green method of synthesis. An extract of synthesized Gazania rigens was used for the synthesis of BNPs followed by characterization employing different techniques including UV/Vis spectrophotometer, FTIR, XRD, and SEM. Spectrophotometric studies (UV-Vis and FTIR) confirmed the formation of bimetallic nanoparticles. The SEM studies indicated that the particle size ranged from 50 to 100 nm. Analysis of the BNPs by the XRD technique confirmed the presence of both Cu and Ni crystal structure. The synthesized nanoparticles were then tested for their catalytic potential for photoreduction of methylene blue dye in an aqueous medium and DPPH radical scavenging in a methanol medium. The BNPs were found to be efficient in the reduction of methylene blue dye as well as the scavenging of DPPH free radicals such that the MB dye was completely degraded in just 17 min at the maximum absorption of 660 nm. Therefore, it is concluded that Cu-Ni BNPs can be successfully synthesized using Gazania rigens extract with suitable size and potent catalytic and radical scavenging activities.

Borate-modified carbon dots as a probe for quercetin in plants

Schematic presentation of the PBA-CDs enhancing the fluorescence of quercetin in contrast to N-CDs.

Synthesis, crystal structure, polymorphism and microscopic luminescence properties of anthracene derivative compounds

Anthracene derivative compounds are currently investigated because of their unique physical properties (e.g. bright luminescence and emission tunability), which make them ideal candidates for advanced optoelectronic devices. Intermolecular interactions are the basis of the tunability of the optical and electronic properties of these compounds, whose prediction and exploitation benefit from knowledge of the crystal structure and the packing architecture. Polymorphism can occur due to the weak intermolecular interactions, requiring detailed structural analysis to clarify the origin of observed material property modifications. Here, two silylethyne-substituted anthracene compounds are characterized by single-crystal synchrotron X-ray diffraction, identifying a new polymorph in the process. Additionally, laser confocal microscopy and fluorescence lifetime imaging microscopy confirm the results obtained by the X-ray diffraction characterization, i.e. shifting the substituents towards the external benzene rings of the anthracene unit favours π-π interactions, impacting on both the morphology and the microscopic optical properties of the crystals. The compounds with more isolated anthracene units feature shorter lifetime and emission spectra, more similar to those of isolated molecules. The crystallographic study, supported by the optical investigation, sheds light on the influence of non-covalent interactions on the crystal packing and luminescence properties of anthracene derivatives, providing a further step towards their efficient use as building blocks in active components of light sources and photonic networks.

Facile and versatile access to substituted hexabenzoovalene derivatives: characterization and optoelectronic properties

We describe the design and modular synthesis of a library of substituted hexabenzoovalene derivatives (SHBO), along with the key precursor dinaphthopyrenes (3), highlighting the influence of a wide array of substituent variation on the photophysical properties via UV-vis absorption, fluorescence spectra and electrochemical methods. The results show that the cyclized hexabenzoovalenes present a stronger spectroscopic red-shift than the corresponding dinaphthopyrenes. X-ray diffraction analysis suggests that intermediate 3hx containing two nitro groups forms a trans-configuration with twisted structures. Our systematic investigation might provide a realistic design strategy to construct large one-dimensional and two-dimensional materials via bottom-up approaches.

Synthesis, Crystal Analysis, and Optoelectronic Properties of Diazole-Functionalized Acenes and Azaacenes

Doping heteroatoms into the skeletons of parent acenes can provide more opportunities to construct novel thermally and photostable organic π-conjugated semiconductors. Herein, a family of diazole-decorated acenes (APyS and APySe) and azaacenes (PyP, PyTh, PyPy, PyPh, and PyAP) have been successfully synthesized through the classical reactions. Single-crystal X-ray analyses showed that these as-formed diazole-modified derivatives adopted a twisted topology configuration, whereas the azaacenes display reclining-chair architectures, besides a twisted structure. All these compounds displayed yellow or red light in solution. Moreover, their electrochemical behaviors were also examined. We also found that the azaacenes exhibited a positive spectroscopic response to acid.

Deep insights into the viscosity of small molecular solutions for organic light-emitting diodes

The viscosities of small molecular solutions and the surface morphologies of the corresponding thin films are investigated, toward high-performance devices (length–width ratio = 2 : 1).

Pyridine-Based Electron-Transport Materials with High Solubility, Excellent Film-Forming Ability, and Wettability for Inkjet-Printed OLEDs

Film morphology has predominant influence on the performance of multilayered organic light-emitting diodes (OLEDs), whereas there is little reported literature from the angle of the molecular level to investigate the impact on film-forming ability and device performance. In this work, four isomeric cross-linkable electron-transport materials constructed with pyridine, 1,2,4-triazole, and vinylbenzyl ether groups were developed for inkjet-printed OLEDs. Their lowest unoccupied molecular orbital (∼3.20 eV) and highest occupied molecular orbital (∼6.50 eV) levels are similar, which are mainly determined by the 1,2,4-triazole groups. The triplet energies of these compounds can be tuned from 2.51 to 2.82 eV by different coupling modes with the core of pyridine, where the 2,6-pyridine-based compound has the highest value of 2.82 eV. Film formation and solubility of the compounds were investigated. It was found that the 2,6-pyridine-based compound outperformed the 2,4-pyridine, 2,5-pyridine, and 3,5-pyridine-based compounds. The spin-coated blue OLEDs based on the four compounds have achieved over 14.0% external quantum efficiencies (EQEs) at the luminance of 100 cd m^-2, and a maximum EQE of 12.1% was obtained for the inkjet-printed device with 2,6-pyridine-based compound.

Versatile Donor-π-Acceptor-Type Aggregation-Enhanced Emission Active Fluorophores as Both Highly Efficient Nondoped Emitter and Excellent Host

By employing triphenylamine (TPA) and/or carbazole as donor and cyano group as acceptor, three donor-π-acceptor (D-π-A)-type fluorophores, 4,6-di(4-(diphenylamino)phenyl)isophthalonitrile (DTPAIPN), 4-(4-(diphenylamino)phenyl)-6-(3,5-(9,9'-dicarbazolyl)phenyl)isophthalonitrile (TPAmCPIPN), and 4,6-di(3,5-(9,9'-dicarbazolyl)phenyl)isophthalonitrile (DmCPIPN), were designed, synthesized, and characterized for their thermal, photophysical, electrochemical, and electroluminescent properties. All three compounds exhibited excellent thermal and morphological stabilities with thermal decomposition (T_d) and glass transition temperature (T_g) values ranging from 396 to 516 °C and from 114 to 211 °C, respectively. The investigation into the photophysical properties revealed the aggregation-enhanced emission (AEE) feature of these chromophores. The performances of the nondoped devices were significantly improved as compared to those of the doped devices, further confirming the AEE nature. In particular, DmCPIPN-based nondoped device rendered the maximum current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) values of 26.6 cd A^-1, 22.4 lm W^-1, and 8.3%, respectively, in comparison with 9.1 cd A^-1, 4.9 lm W^-1, and 4.2% for the doped device. The versatility of these new luminogens was demonstrated through the utilization of them as host for highly efficient red phosphorescent organic light-emitting diodes (PHOLEDs). The EQE of the DmCPIPN-hosted device reached as high as 19.3% with a reduced efficiency roll-off of 10.3% at 1000 cd m^-2. These results demonstrate that the new luminogens of this work can be used as both nondoped emitter and host for high-performance OLEDs, which facilitates the development of multifunctional materials for OLEDs applications.

Controlling the Growth of Molecular Crystal Aggregates with Distinct Linear and Nonlinear Optical Properties

Two novel donor-acceptor molecules, 2,7-diphenylbenzo[1,2-b:4,3-b']difuran-4,5-dicarbonitrile and 2,7-bis(4-methoxyphenyl)benzo[1,2-b:4,3-b']difuran-4,5-dicarbonitrile containing cyano group as the electron acceptor, were synthesized. Their single-crystal structures, molecular packing, and self-assembly behaviors were also investigated. By simple solvent evaporation techniques, these compounds self-assemble into various low-dimensional microstructures that demonstrate distinctive nonlinear optical properties depending on the orientations of their transition dipoles. This study highlights the importance of the transition dipole moment in the construction of low-dimensional molecular materials with highly efficient nonlinear optical properties.

Synthesis, Optoelectronic and Self-Assembly Properties of Diazadioxaacene Derivatives

Two novel diazadioxaacene derivatives (ADOP and ADOQ) have been successfully synthesized and characterized. Their single crystal analyses disclose that molecule ADOP forms a twisted topology configuration, whereas ADOQ adopts reclining-chair architecture. Both of them emit strong blue fluorescence in organic solvents. Moreover, they can self-assemble to form regular nanobelts and nanowires, respectively, via a simple surfactant-assisted method.

Synthesis, Physical Properties and Memory Device Application of a Twelve-Ring Fused Twistheteroacene

Developing new organic conjugated materials for high density memory devices is highly desirable. In this research, a novel donor-acceptor-type twelve-ring fused twistheteroacene, 2,7,19,24-tetra-tert-butyl-13,30-didodecyl-9,17,26,34-tetraphenyl benzo[8',9']triphenyleno[2',3':7,8]dibenzo[b,e][1,4]dioxino[1,2,3,4-lmn]dibenzo[6',7':10',11']tetraceno[2',3':5,6][1,4]dioxino[2,3-f][3,8]phenanthroline-12,14,29,31(13H,30H)-tetraone (DPyN) has been synthesized and characterized. It displays high thermal stability, possesses a broad absorption band centered at 510 and 538 nm, and emits red fluorescence in organic solvents. A solution-processed memory device with DPyN as an active element shows an excellent memory performance with an ON/OFF current ratio of 10^3.46 :1 and a threshold voltage of -2.44 V.

Synthesis and physical properties of triphenylamine-functionalized twistacenes: blue-emitting fluorophores

Two novel triphenylamine-decorated twistacenes SNPy and DNPy have been synthesized and characterized.

Synthesis, Crystal Analyses, Physical Properties, and Electroluminescent Behavior of Unsymmetrical Heterotwistacenes

Four novel unsymmetrical heteroacenes containing five-membered heterocycles (OPyN, TPyN, TPyC, TPyO) have been synthesized and characterized. The formed molecules exhibited twisted structures, determined by crystal analysis and showed blue/green fluorescence in dichloromethane and in thin film. Compounds OPyN and TPyN were selectively used as active ingredients, and the fabricated devices displayed promising electroluminescent performance.

Enhanced electron affinity and charge balance property of a bipolar material: highly efficient solution-processed deep blue electrofluorescent and green electrophosphorescent devices

The slight move in the ratio of the donor and acceptor group can slightly affect the optoelectronic property as a whole, and consequently modulate the electron affinity, charge balance property and exciton recombination efficiency.

Synthesis and Physical Properties of Hyperbranched Polymers Containing Twisted Acenes

Novel hyperbranched co-polymers HP1–HP4 with twisted acene units and truxene groups have been synthesised through Suzuki coupling reaction and characterised. Single crystal analyses showed that the model compounds 3 and 5 had twisted structures with torsion angles of 40.73° and 28.65°, respectively. The polymers show blue light emission in organic solvents and thin films, as well as high stability, which might be utilised as potential candidates for organic electronic materials.