Chlorine‐Free Red‐Burning Pyrotechnics

The development of a red, chlorine‐free pyrotechnic illuminant of high luminosity and spectral purity was investigated. Red‐light emission based solely on transient SrOH_(g) has been achieved by using either 5‐amino‐1H‐tetrazole or hexamine to deoxidize the combustion flame of a Mg/Sr(NO₃)₂/Epon‐binder composition and reduce the amount of both condensed and gaseous SrO, which emits undesirable orange‐red light. The new formulations were found to possess high thermal onset temperatures. Avoiding chlorine in these formulations eliminates the risk of the formation of PCBs, PCDDs, and PCDFs. This finding, hence, will have a great impact on both military pyrotechnics and commercial firework sectors.     

High‐Nitrogen‐Based Pyrotechnics: Perchlorate‐Free Red‐ and Green‐Light Illuminants Based on 5‐Aminotetrazole

Prototype testing of perchlorate‐free hand‐held signal illuminants for the US Army’s M126 A1 red‐star and M195 green‐star parachute illuminants are described. Although previous perchlorate‐free variants for these items have been developed based on high‐nitrogen compounds that are not readily available, the new formulations consist of anhydrous 5‐aminotetrazole as the suitable perchlorate replacement. Compared to the perchlorate‐containing control, the disclosed illuminants exhibited excellent stabilities toward various ignition stimuli and had excellent pyrotechnic performance. The illuminants are important from both military and civil fireworks perspectives, as the perchlorate‐free nature of the illuminants adequately address environmental concerns associated with perchlorate‐containing red‐ and green‐light‐emitting illuminants.     

Brighter‐ and Longer‐Burning Barium‐Free Illuminants for Military and Civilian Pyrotechnics

The development of barium‐free pyrotechnic illuminants is described. Heavy metal barium nitrate oxidizer and strontium nitrate oxidizer were replaced with sodium nitrate to adequately address environmental concerns while providing the brightest possible illuminant. The new formulations further address environmental concerns and mitigate single‐point‐of‐failure through the replacement of polyester‐based Laminac 4116/Lupersol binder system with the epoxy‐based Epon 813/Versamid 140 binder system. The new formulations were found to burn longer and brighter than the control with a low sensitivity to various ignition stimuli.     

Chlorine‐Free Pyrotechnics: Copper(I) Iodide as a “Green” Blue‐Light Emitter

The generation of blue‐light‐emitting pyrotechnic formulations without the use of chlorine‐containing compounds is reported. Suitable blue‐light emission has been achieved through the generation of molecular emitting copper(I) iodide. The most optimal copper(I) iodide based blue‐light‐emitting formulation was found to have performances exceeding those of chlorine‐containing compositions, and was found to be insensitive to various ignition stimuli.     

"Green" pyrotechnics: a chemists' challenge

Fireworks are probably the application of chemistry which resonates best with the general public. However, fireworks and (civil and military) pyrotechnic applications cause environmental pollution and thus have given rise to the development of new, environmentally friendly pyrotechnic compounds and formulations. Nitrogen-rich energetic materials, such as the derivatives of tetrazoles and tetrazines, are about to revolutionize traditional pyrotechnic compositions. This Review summarizes the sources of pollution in current formulations and recent efforts toward "green" pyrotechnics.     

DFT/TDDFT Studies on the Electronic Structures and Spectral Properties of Carbazole‐based Blue Light‐emitting Dendrimers

The purpose of this paper is to provide an in‐depth investigation of the electronic and optical properties of two series of carbazole‐based blue light‐emitting dendrimers, including 1 – 6 six oligomers. These materials show great potential for application in organic light‐emitting diodes as efficient blue‐light and red‐light emitting materials due to the tuning of the optical and electronic properties by the use of different electron donors (D) and electron acceptors (A). The geometric and electronic structures of these compounds in the ground state are calculated using density functional theory (DFT) and the ab initio HF, whereas the lowest singlet excited states were optimized by ab initio single excitation configuration interaction (CIS). All DFT calculations are performed using the B3LYP functional on 6‐31G* basis set. The outcomes show that the highest occupied molecular orbitals (HOMOs), lowest occupied molecular orbitals (LUMOs), energies gaps, ionization potentials, electron affinities and reorganization energies of each molecular are affected by different D and A moieties and different substitute positions.     

The Lithium Salts of Bis(azolyl)borates as Strontium- and Chlorine-free Red Pyrotechnic Colorants

After concerns regarding the use of chlorinated material for pyrotechnic items had reinforced, the action of the U.S. Environmental Protection Agency on health concerns about strontium ushered in a new era in the production of red light. Lithium was shown to impart red color to a pyrotechnic flame, however only a very narrow selection of such formulations can be found in the literature. Dihydrobis(azolyl)borates are a well investigated, easily accessible class of materials which have been proven to be suitable as pyrotechnic coloring agents. With their high nitrogen contents such moieties should also meet the requirements of a low combustion temperature and a reducing flame atmosphere for a lithium-based red-burning composition. This work evaluates the capability of the lithium salts of dihydrobis(pyrazol-1-yl)borate, dihydrobis(1,2,4-triazol-1-yl)borate, and dihydrobis(tetrazol-1-yl)borate to serve as red color imparters. The latter compounds were characterized by multinuclear NMR experiments, IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction and were investigated with respect to their thermal stabilities as well as sensitivities toward various ignition stimuli.     

Bipolar Host Materials for Organic Light‐Emitting Diodes

It is important to balance holes and electrons in the emitting layer of organic light‐emitting diodes to maximize recombination efficiency and the accompanying external quantum efficiency. Therefore, the host materials of the emitting layer should transport both holes and electrons for the charge balance. From this perspective, bipolar hosts have been popular as the host materials of thermally activated delayed fluorescent devices and phosphorescent organic light‐emitting diodes. In this review, we have summarized recent developments of bipolar hosts and suggested perspectives of host materials for organic light‐emitting diodes.     

Aggregation‐Induced Delayed Fluorescence Based on Donor/Acceptor‐Tethered Janus Carborane Triads: Unique Photophysical Properties of Nondoped OLEDs

Luminescent materials consisting of boron clusters, such as carboranes, have attracted immense interest in recent years. In this study, luminescent organic–inorganic conjugated systems based on o‐carboranes directly bonded to electron‐donating and electron‐accepting π‐conjugated units were elaborated as novel optoelectronic materials. These o‐carborane derivatives simultaneously possessed aggregation‐induced emission (AIE) and thermally activated delayed fluorescence (TADF) capabilities, and showed strong yellow‐to‐red emissions with high photoluminescence quantum efficiencies of up to 97 % in their aggregated states or in solid neat films. Organic light‐emitting diodes utilizing these o‐carborane derivatives as a nondoped emission layer exhibited maximum external electroluminescence quantum efficiencies as high as 11 %, originating from TADF.     

Guanidinium 5,5′‐Azotetrazolate: A Colorful Chameleon for Halogen‐Free Smoke Signals

A progressive halogen‐free multicolored smoke system to obtain white, red, violet, yellow, green, and blue smoke color is presented. The nitrogen‐rich salt guanidinium 5,5′‐azotetrazolate (GZT), which is usually applied as a gas generator or propellant ingredient, was combined with different smoke dyes (Solvent Red 1, Solvent Violet 47, Solvent Green 3, Solvent Yellow 33). These two‐component smoke mixtures offer a convenient and safe multicolor approach without the need for potassium chlorate or any other hazardous material. The common smoke characteristics with respect to burn time/burn rate, yield factor, transfer rate, as well as energetic properties were determined and compared with classic chlorate‐based formulations currently used. To the best of our knowledge, nothing comparable is known in the literature and a completely new research area in modern pyrotechnics is opened.     

Luminescent copolymers for applications in multicolor‐light‐emitting devices

Light‐emitting diodes based on organic materials [organic light‐emitting diodes (OLEDs)] have attracted much interest over the past decade. Several different attempts have been made to realize multicolor OLEDs. This article describes a new approach based on energy transfer in a donor/acceptor system. A copolymer containing both donor and acceptor compounds as comonomer units is prepared. The polymer consists of a derivative of a luminescent dye [4‐dicyanmethylene‐2‐methyl‐6‐4H‐pyran (DCM); acceptor compound], which is copolymerized with fluorene (donor compound) to combine the properties of an electroactive polymer with a highly luminescent dye. Photochemical processing is achieved by UV irradiation of this copolymer in the presence of gaseous trialkylsilanes. This reagent selectively saturates the C?C bonds in the DCM comonomer units while leaving the fluorene units essentially unaffected. As a result of the photochemical process, the red electroluminescence of the acceptor compound vanishes, and the blue‐green electroluminescence from the polyfluorene units is recovered. Compared with previous approaches based on polymer blends, this copolymer approach avoids problems associated with phase‐separation phenomena in the active layer of OLEDs. © 2006Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4317–4327, 2006     

Donor–acceptor copolymers for red‐ and near‐infrared‐emitting polymer light‐emitting diodes

We report a comparative study of two organic soluble, vinylene‐based, alternating donor–acceptor copolymers with 1,4‐(2,5‐dihexadecyloxyphenylene) as the donor; the acceptor is either a 2,5‐linked pyridine or a 5,8‐linked 2,3‐diphenylpyrido[3,4‐b]pyrazine. The polymers are synthesized via a Heck coupling methodology from a dihalo monomer and a divinyl monomer to yield number‐average molecular weights of 16,000 g/mol for the pyridine polymer (PPyrPV) and 6500 g/mol for the pyridopyrazine polymer (PPyrPyrPV), with high solubility in common chlorinated solvents and lower solubility in less polar solvents (e.g., tetrahydrofuran). Thin‐film measurements show band gaps of 2.2 and 1.8 eV for PPyrPV and PPyrPyrPV, respectively. Both polymers exhibit photoluminescence in solution and in the solid state and exhibit electroluminescence when incorporated into light‐emitting diodes. In this case, a broad red emission centered at 690 nm for PPyrPV and a near‐infrared emission centered at 800 nm for PPyrPyrPV have been observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1417–1431, 2005     

Highly Efficient Near‐Infrared Organic Light‐Emitting Diode Based on a Butterfly‐Shaped Donor–Acceptor Chromophore with Strong Solid‐State Fluorescence and a Large Proportion of Radiative Excitons

The development of near‐infrared (NIR) organic light‐emitting diodes (OLEDs) is of growing interest. Donor–acceptor (D–A) chromophores have served as an important class of NIR materials for NIR OLED applications. However, the external quantum efficiencies (EQEs) of NIR OLEDs based on conventional D–A chromophores are typically below 1 %. Reported herein is a butterfly‐shaped D–A compound, PTZ‐BZP. A PTZ‐BZP film displayed strong NIR fluorescence with an emission peak at 700 nm, and the corresponding quantum efficiency reached 16 %. Remarkably, the EQE of the NIR OLED based on PTZ‐BZP was 1.54 %, and a low efficiency roll‐off was observed, as well as a high radiative exciton ratio of 48 %, which breaks through the limit of 25 % in conventional fluorescent OLEDs. Experimental and theoretical investigations were carried out to understand the excited‐state properties of PTZ‐BZP.     

Bright White‐Light Emission from a Single Organic Compound in the Solid State

White‐light‐emitting materials and devices have attracted enormous interest because of their great potential for various lighting applications. We herein describe the light‐emitting properties of a series of new difunctional organic molecules of remarkably simple structure consisting of two terminal 4‐pyridone push–pull subunits separated by a polymethylene chain. They were found to emit almost “pure” white light as a single organic compound in the solid state, as well as when incorporated in a polymer film. To the best of our knowledge, they are the simplest white‐light‐emitting organic molecules reported to date.     

Characteristics of a single‐layered organic electroluminescent device using a carrier‐transporting copolymer and a nonconjugated light‐emitting polymer

We have synthesized a novel carrier‐transporting copolymer and a nonconjugated light‐emitting polymer. The carrier‐transporting copolymer has a triphenylamine moiety as a hole‐transporting unit and a triazine moiety as an electron‐transporting unit, both of which are located in the polymer side chain. The nonconjugated light‐emitting polymer has a perylene moiety, which acts as an emitting unit in the polymer side chain. These polymers are very soluble in most organic solvents, such as monochlorobenzene, tetrahydrofuran, chloroform, and benzene. A single‐layered electroluminescent device consisting of ITO/copolymer and emitting‐material 4‐(dicyanomethylene)‐2‐methyl‐6‐(4‐dimethylaminostyryl)‐4H‐pyran (DCM) or light‐emitting polymer)/Al mixtures exhibits maximum external quantum efficiency when the concentration of the emitting material is 30 wt %. The device emits red or blue light according to the emitting material. When CsF is used as the electron‐injecting material, the drive voltage decreases drastically to 7 V, and the highest quantum efficiency is 0.5%. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2733–2743, 2003     

Luminescent Ionic Transition‐Metal Complexes for Light‐Emitting Electrochemical Cells

Higher efficiency in the end‐use of energy requires substantial progress in lighting concepts. All the technologies under development are based on solid‐state electroluminescent materials and belong to the general area of solid‐state lighting (SSL). The two main technologies being developed in SSL are light‐emitting diodes (LEDs) and organic light‐emitting diodes (OLEDs), but in recent years, light‐emitting electrochemical cells (LECs) have emerged as an alternative option. The luminescent materials in LECs are either luminescent polymers together with ionic salts or ionic species, such as ionic transition‐metal complexes (iTMCs). Cyclometalated complexes of Ir^III are by far the most utilized class of iTMCs in LECs. Herein, we show how these complexes can be prepared and discuss their unique electronic, photophysical, and photochemical properties. Finally, the progress in the performance of iTMCs based LECs, in terms of turn‐on time, stability, efficiency, and color is presented.     

Deep‐Red to Near‐Infrared Thermally Activated Delayed Fluorescence in Organic Solid Films and Electroluminescent Devices

The design and synthesis of highly efficient deep red (DR) and near‐infrared (NIR) organic emitting materials with characteristic of thermally activated delayed fluorescence (TADF) still remains a great challenge. A strategy was developed to construct TADF organic solid films with strong DR or NIR emission feature. The triphenylamine (TPA) and quinoxaline‐6,7‐dicarbonitrile (QCN) were employed as electron donor (D) and acceptor (A), respectively, to synthesize a TADF compound, TPA‐QCN. The TPA‐QCN molecule with orange‐red emission in solution was employed as a dopant to prepare DR and NIR luminescent solid thin films. The high doped concentration and neat films exhibited efficient DR and NIR emissions, respectively. The highly efficient DR and NIR organic light‐emitting devices (OLEDs) were fabricated by regulating TPA‐QCN dopant concentration in the emitting layers.     

Red‐Tuned Mn d–d Emission in Doped Semiconductor Nanocrystals

Light‐emitting Mn‐doped semiconductor nanocrystals have been extensively studied for the last three decades for their intense and stable Mn d–d emission. In principle, this emission should be fixed at 585 nm (yellow), but recent studies have shown that the emission can be widely tuned even to 650 nm (red). This is a spectacular achievement as this would make Mn‐doped nanocrystals efficient and tunable light emitters. Keeping these developments in view, the chemistry of the synthesis of these materials, their photophysical processes and the expected origins of their red emission are summarized in this Minireview. All the related important studies from 1992 onwards are chronologically discussed, and one particular case is elaborated on in detail. As these materials are potentially important for biology, and photovoltaic, sensing and light‐emitting devices, this Minireview is expected to help researchers investigating the chemistry, physics and applications of these materials.     

Saturated Red‐Light‐Emitting Gold(III) Triphenylamine Dendrimers for Solution‐Processable Organic Light‐Emitting Devices

A novel isoquinoline‐containing C^N^C ligand and its phosphorescent triphenylamine‐based alkynylgold(III) dendrimers have been synthesized. These alkynylgold(III) dendrimers serve as phosphorescent dopants in the fabrication of efficient solution‐processable organic light‐emitting devices (OLEDs). The photophysical, electrochemical, and electroluminescence properties were studied. A saturated red emission with CIE coordinates of (0.64, 0.36) and a high EQE value of 3.62 % were achieved. Unlike other red‐light‐emitting iridium(III) dendrimers, a low turn‐on voltage of less than 3 V and a reduced efficiency roll‐off at high current densities were observed; this can be accounted for by the enhanced carrier transporting ability and the relatively short lifetimes in the high‐generation dendrimers. This class of alkynylgold(III) dendrimers are promising candidates as phosphorescent dopants in the fabrication of solution‐processable OLEDs.     

Efficient Blue Electroluminescence from a Single‐layer Organic Device Composed Solely of Hydrocarbons

An interesting physical phenomenon, electroluminescence, that was originally observed with a hydrocarbon molecule has recently been developed into highly efficient organic light‐emitting devices. These modern devices have evolved through the development of multi‐element molecular materials for specific roles, and hydrocarbon devices have been left unexplored. In this study, we report an efficient organic light‐emitting device composed solely of hydrocarbon materials. The electroluminescence was achieved in the blue region by efficient fluorescence and charge recombination within a simple single‐layer architecture of macrocyclic aromatic hydrocarbons. This study may stimulate further studies on hydrocarbons to uncover their full potential as electronic materials.