Luminescence Color‐Tuning through Polymorph Doping: Preparation of a White‐Emitting Solid from a Single Gold(I)–Isocyanide Complex by Simple Precipitation

We report the luminescent color tuning of a new complex, 2‐benzothiophenyl(4‐methoxyphenyl isocyanide)gold(I) ( 1 ), by using a new “polymorph doping” approach. The slow crystallization of the complex 1 afforded three different pure polymorphic crystals with blue, green, and orange emission under UV‐light irradiation. The crystal structures of pure polymorphs of 1 were investigated in detail by means of single‐crystal X‐ray analyses. Theoretical calculations based on the single‐crystal structures provided qualitative explanation of the difference in the excited energy‐levels of the three polymorphs of 1 . In sharp contrast, the rapid precipitation of 1 , with the optimized conditions reproducibly afforded homogeneous powder materials showing solid‐state white‐emission with Commission Internationale de l’Éclairage (CIE) 1931 chromaticity coordinates of (0.33, 0.35), which is similar to pure white. New “polymorphic doping” has been revealed to be critical to this white emission through spectroscopic and X‐ray diffraction analyses. The coexistence of the multiple polymorphs of 1 within the homogeneous powder materials and the ideal mixing of multiple luminescent colors gave its white emission accompanied with energy transfer from the predominant green‐emitting polymorph to the minor orange‐emitting polymorph.     

A Unique Blend of 2‐Fluorenyl‐2‐anthracene and 2‐Anthryl‐2‐anthracence Showing White Emission and High Charge Mobility

White‐light‐emitting materials with high mobility are necessary for organic white‐light‐emitting transistors, which can be used for self‐driven OLED displays or OLED lighting. In this study, we combined two materials with similar structures—2‐fluorenyl‐2‐anthracene (FlAnt) with blue emission and 2‐anthryl‐2‐anthracence (2A) with greenish‐yellow emission—to fabricate OLED devices, which showed unusual solid‐state white‐light emission with the CIE coordinates (0.33, 0.34) at 10 V. The similar crystal structures ensured that the OTFTs based on mixed FlAnt and 2A showed high mobility of 1.56 cm² V⁻¹ s⁻¹. This simple method provides new insight into the design of high‐performance white‐emitting transistor materials and structures.     

Luminescent Tungsten(VI) Complexes: Photophysics and Applicability to Organic Light‐Emitting Diodes and Photocatalysis

The synthesis, excited‐state dynamics, and applications of two series of air‐stable luminescent tungsten(VI) complexes are described. These tungsten(VI) complexes show phosphorescence in the solid state and in solutions with emission quantum yields up to 22 % in thin film (5 % in mCP) at room temperature. Complex 2 c , containing a 5,7‐diphenyl‐8‐hydroxyquinolinate ligand, displays prompt fluorescence (blue–green) and phosphorescence (red) of comparable intensity, which could be used for ratiometric luminescent sensing. Solution‐processed organic light‐emitting diodes (OLEDs) based on 1 d showed a stable yellow emission with an external quantum efficiency (EQE) and luminance up to 4.79 % and 1400 cd m⁻² respectively. These tungsten(VI) complexes were also applied in light‐induced aerobic oxidation reactions.     

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.     

An Organic Molecule with Asymmetric Structure Exhibiting Aggregation‐Induced Emission,Delayed Fluorescence,and Mechanoluminescence

Compounds displaying delayed fluorescence (DF), from severe concentration quenching, have limited applications as nondoped organic light‐emitting diodes and material sciences. As a nondoped fluorescent emitter, aggregation‐induced emission (AIE) materials show high emission efficiency in their aggregated states. Reported herein is an AIE‐active, DF compound in which the molecular interaction is modulated, thereby promoting triplet harvesting in the solid state with a high photoluminescence quantum yield of 93.3 %, which is the highest quantum yield, to the best of our knowledge, for long‐lifetime emitters. Simultaneously, the compound with asymmetric molecular structure exhibited strong mechanoluminescence (ML) without pretreatment in the solid state, thus exploiting a design and synthetic strategy to integrate the features of DF, AIE, and ML into one compound.     

An Organic Molecule with Asymmetric Structure Exhibiting Aggregation‐Induced Emission,Delayed Fluorescence,and Mechanoluminescence

Compounds displaying delayed fluorescence (DF), from severe concentration quenching, have limited applications as nondoped organic light‐emitting diodes and material sciences. As a nondoped fluorescent emitter, aggregation‐induced emission (AIE) materials show high emission efficiency in their aggregated states. Reported herein is an AIE‐active, DF compound in which the molecular interaction is modulated, thereby promoting triplet harvesting in the solid state with a high photoluminescence quantum yield of 93.3 %, which is the highest quantum yield, to the best of our knowledge, for long‐lifetime emitters. Simultaneously, the compound with asymmetric molecular structure exhibited strong mechanoluminescence (ML) without pretreatment in the solid state, thus exploiting a design and synthetic strategy to integrate the features of DF, AIE, and ML into one compound.     

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.     

Synthesis,Structure, Properties,and Application of a Carbazole‐Based Diaza[7]helicene in a Deep‐Blue‐Emitting OLED

A carbazole‐based diaza[7]helicene, 2,12‐dihexyl‐2,12‐diaza[7]helicene ( 1 ), was synthesized by a photochemical synthesis and its use as a deep‐blue dopant emitter in an organic light‐emitting diode (OLED) was examined. Compound 1 exhibited good solubility and excellent thermal stability with a high decomposition temperature (T_d=372.1 °C) and a high glass‐transition temperature (T_g, up to 203.0 °C). Single‐crystal structural analysis of the crystalline clathrate ( 1 )₂ ? cyclohexane along with a theoretical investigation revealed a non‐planar‐fused structure of compound 1 , which prevented the close‐packing of molecules in the solid state and kept the molecule in a good amorphous state, which allowed the optimization of the properties of the OLED. A device with a structure of ITO/NPB (50 nm)/CBP:5 % 1 (30 nm)/BCP (20 nm)/Mg:Ag (100 nm)/Ag (50 nm) showed saturated blue light with Commission Internationale de L’Eclairage (CIE) coordinates of (0.15, 0.10); the maximum luminance efficiency and brightness were 0.22 cd A^?1 (0.09 Lm W^?1) and 2365 cd m^?2, respectively. This new class of helicenes, based on carbazole frameworks, not only opens new possibilities for utilizing helicene derivatives in deep‐blue‐emitting OLEDs but may also have potential applications in many other fields, such as molecular recognition and organic nonlinear optical materials.     

Synthesis and molecular structure of 2,4,6‐tri[bis(diisopropylamino)boryl(methylamino)]borazine, [(NiPr2)2B(Me)N]3B3N3H3

Reaction of bis(diisopropylamino)(methylamino)borane, (NHⁱPr)₂B(NHMe), with 2,4,6‐trichloroborazine (ClBNH)₃ affords 2,4,6‐tri[bis(diisopropylamino)boryl(methylamino)]borazine, 2,4,6‐[(NⁱPr₂)₂B(Me)N]₃B₃N₃H₃, which is the first boryl‐borazine structurally characterized. According to the X‐ray single crystal structure and the chemical shifts of ¹¹B NMR resonances of boron atoms, compared with the aminoborane and borazine analogs, the borazine and boryl π‐systems are not coplanar either in the solid state or in organic solution. Copyright © 2002 John Wiley & Sons, Ltd.     

Simple synthesis,photophysics, and electroluminescent properties of poly[2,7‐bis(4‐tert‐butylstyryl)fluorene‐9, 9‐diyl‐alt‐alkane‐α,ω‐diyl]

A simple synthetic route was used for the synthesis of a novel series of alternating copolymers based on substituted 2,7‐distyrylfluorene bridged through alkylene chains. First, 2,7‐dibromofluorene was reacted with 2 equiv of butyllithium, and this was followed by a treatment with 1 equiv of α,ω‐dibromoalkane to yield the intermediate, poly(2,7‐dibromofluorene‐9,9‐diyl‐alt‐alkane‐α,ω‐diyl). ( 1 ) Heck coupling of the latter with 1‐tert‐butyl‐4‐vinylbenzene afforded the target, poly[2,7‐bis(4‐tert‐butylstyryl)fluorene‐9,9‐diyl‐alt‐alkane‐α,ω‐diyl] ( 2 ). The two versions of 2 ( 2a and 2b which have hexane and decane, respectively, as alkane groups) were readily soluble in common organic solvents. Their glass‐transition temperature was relatively low (52 and 87 °C). An intense blue photoluminescence emission with maxima at about 408 and 409 nm was observed in tetrahydrofuran solutions, whereas thin films exhibited an orange emission with maxima at 569 and 588 nm. Very large redshifts of the photoluminescence maxima and Stokes shifts in thin films indicated strong aggregation in the solid state. Both polymers oxidized and reduced irreversibly. Single‐layer light‐emitting diodes with hole‐injecting indium tin oxide and electron‐injecting aluminum electrodes were fabricated. They emitted orange light with external electroluminescence efficiencies of 0.52 and 0.36% photon/electron, as determined in light‐emitting diodes made of 2a and 2b , with alkylenes of (CH₂)₆ and (CH₂)₁₀, respectively. An increase in the external electroluminescence efficiency up to 1.5% was reached in light‐emitting diodes made of polymer blends consisting of 2a and poly(9,9‐dihexadecylfluorene‐2,7‐diyl), which emitted blue‐white light. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 809–821, 2007.     

Importance of weak interactions in developing 1,3-bis(4,6-dimethyl-1H-nicotinonitrile-1-yl)1,3-dioxy propane polymorphs

The structure of 1,3-bis(4,6-dimethyl-1H-nicotinonitrile-1-yl)1,3-dioxy propane polymorphs has been characterized by X-ray diffraction, FT-IR, 1H and 13C NMR spectroscopies. The influence of intra and intermolecular weak interactions is thoroughly studied in solid state using single crystal X-ray diffraction and FT-IR. These polymorphs belong to monoclinic space group 'P2(1/n)' and 'P2(1/c)'. These polymorphs have C-H?n (lone pair), hydrogen bonds, C-N?π, C-H?π and π?π intermolecular non-covalent interactions. These polymorphs are the result of weak interactions and solvent used in crystallization. The FT-IR spectra have been recorded in the solid phase and NMR has been recorded in solvent. The optimized geometry has been calculated by B3LYP methods using different basis sets. The FT-IR and NMR spectra of 1st polymorphs has been calculated at B3LYP/6-31G (d) level. The scaled theoretical wave number showed good agreement with the experimental values. These two polymorphs as well as other stereomers are studied by DFT calculations.     

New poly(p‐phenylene vinylene) derivatives with two oxadiazole rings per repeat unit: Synthesis,photophysical properties,electroluminescence, and metal ion recognition

Two new poly(p‐phenylene vinylene) derivatives OX1‐PPV and OX2‐PPV bearing two 1,3,4‐oxadiazole rings per repeat unit and a fully conjugated backbone with solubilizing dodecyloxy side groups were synthesized and investigated. The amorphous conjugated polymers had glass‐transition temperature values of 60–75 °C and emitted intense blue or greenish‐blue light in solution with photoluminescence (PL) emission maxima at 379–492 nm and PL quantum yields of 0.41–0.52. In the solid state they emitted yellowish‐green light with PL emission maxima at 533–555 nm. Cyclic voltammetry showed that both conjugated polymers had reversible reduction and irreversible oxidation, making them n‐type materials. The electron affinity of OX2‐PPV was estimated as 2.85 eV whereas that of OX1‐PPV was 2.75 eV. Yellow electroluminescence (EL) was achieved from single‐layer light‐emitting diodes of OX2‐PPV with an EL emission maximum at 555 nm and a brightness of 70 cd/m². Polymer OX2‐PPV, which was functionalized with 2,6‐bis(1,3,4‐oxadiazole‐2‐yl)pyridine, demonstrated sensitivity to various metal ions as a fluorescence‐mode chemosensor. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2112–2123, 2004     

Synthesis,Electronic Properties and WOLED Devices of Planar Phosphorus‐Containing Polycyclic Aromatic Hydrocarbons

We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs).     

Highly efficient and stable blue‐light‐emitting copolyfluorene consisting of carbazole,oxadiazole, and charge‐trapping anthracene groups

This article presents the synthesis and electroluminescent (EL) properties of a stable blue‐light‐emitting copolyfluorene ( P1 ) consisting of carbazole, oxadiazole and charge‐trapping anthracene groups by Suzuki coupling reaction. The hole‐transporting carbazole and electron‐transporting oxadiazole improve charges injection and transporting properties, whereas the anthracene is the ultimate emitting chromophore. The thermal, photophysical, electrochemical, and EL properties of P1 were investigated by thermogravimetric analysis, differential scanning calorimeter, optical spectroscopy, cyclic voltammetry, and EL devices fabrication and characterization. P1 demonstrated high‐thermal stability with thermal decomposition and glass tranistion temperatures above 400 and 145°C, respectively. In film state, P1 showed blue emission at 451 nm attributed to anthracene chromophore. Photophysical and electrochemical investigations demonstrate that effective energy transfer from fluorene to anthracene segments and charges trapping on anthracene segments leads to efficient and stable blue emission originating from anthracence. Polymer light‐emitting diodes using P1 as the emitting layer (ITO/PEDOT:PSS/ P1 /Ca/Al) exhibited excellent current efficiency (5.1 cd/A) with the CIE coordinate being (0.16, 0.11). The results indicate that copolyfluorene is a promising candidate for the blue‐emitting layer in the fabrication of efficient PLEDs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Designing,Describing and Disseminating New Materials by using the Network Topology Approach

This Concept article describes how network topology analysis is applied to different fields of solid‐state chemistry. Its usefulness is demonstrated by examples from metal–organic frameworks, group 14 allotropes and related compounds, ice polymorphs, zeolites, supramolecular (organic) solid‐state chemistry, Zintl phases, and cathode materials for Li‐ion batteries.     

Multicolor Amplified Spontaneous Emissions Based on Organic Polymorphs That Undergo Excited‐State Intramolecular Proton Transfer

Two polymorphs emitting near‐infrared ( 1 R form: α phase, λ_em=702 nm, Φ_f=0.41) and orange‐red fluorescence ( 1 O form: β phase, λ_em=618 nm, Φ_f=0.05) were synthesized by finely controlling the crystallization conditions of compound 1 , a structurally simple excited‐state intramolecular proton transfer (ESIPT)‐active molecule. Multicolor amplified spontaneous emissions (ASEs) were realized, for the first time, based on these polymorphs. Notably, the 1 O crystal underwent heating‐induced phase transformation from the β phase to the α form in a single‐crystal to single‐crystal (SCSC) manner accompanied with an unprecedented ASE changing. The ASE behavior of polymorphs 1 R , 1 O as well as the ASE changing during SCSC was investigated. The feasibility of multicolor lasing based on the present organic polymorphs was confirmed, which may provide a new development strategy for organic laser science and technology.     

Multifunctional Organic Emitters for High‐Performance and Low‐Cost Organic Light‐Emitting Didoes

Organic light‐emitting diodes (OLEDs) have great potential applications in display and solid‐state lighting. Stability, cost and high operational efficiency are key issues governing the future commercial application of OLEDs. In this context, searching for multifunctional emitting materials with acceptable light‐emitting and charge‐transporting characteristics has gained increasing attention. For achieving high‐performance and low‐cost OLEDs, the suitable molecular design featured with different electronic and optical nature should be incorporated by combining the advantages of both functional units into the same molecules. This review highlights recent and current advances in developing bifunctional or multifunctional molecules, with the focus on structures, properties, and applications in OLEDs and organic laser.     

Polymorphism of N,N'-diacetylbiuret studied by solid-state 13C and 15N NMR spectroscopy, DFT calculations, and X-ray diffraction

The molecular configuration and crystal structure of solid polycrystalline N,N′′‐diacetylbiuret (DAB), a potential nitrogen‐rich fertilizer, have been analyzed by a combination of solid‐ and liquid‐state NMR spectroscopy, X‐ray diffraction, and DFT calculations. Initially a pure NMR study (“NMR crystallography”) was performed as available single crystals of DAB were not suitable for X‐ray diffraction. Solid‐state ¹³C NMR spectra revealed the unexpected existence of two polymorphic modifications (α‐ and β‐DAB) obtained from different chemical procedures. Several NMR techniques were applied for a thorough characterization of the molecular system, revealing chemical shift anisotropy (CSA) tensors of selected nuclei in the solid state, chemical shifts in the liquid state, and molecular dynamics in the solid state. Dynamic NMR spectroscopy of DAB in solution revealed exchange between two different configurations, which raised the question, is there a correlation between the two different configurations found in solution and the two polymorphic modifications found in the solid state? By using this knowledge, a new crystallization protocol was devised which led to the growth of single crystals suitable for X‐ray diffraction. The X‐ray data showed that the same symmetric configuration is present in both polymorphic modifications, but the packing patterns in the crystals are different. In both cases hydrogen bonds lead to the formation of planes of DAB molecules. Additional symmetry elements, a two‐fold screw in the case of α‐DAB and a c‐glide plane in the case of β‐DAB, lead to a more symmetric (α‐DAB) or asymmetric (β‐DAB) intermolecular hydrogen‐bonding pattern for each molecule.     

Synthesis,characterization, and electroluminescence of fluorene and carbazole‐based blue light‐emitting polymers with different noncoplanar molecular architectures

In order to investigate the explicit optoelectronic variations of the photoluminescent polymer with sterically hindered side chains, three novel alternate polymers (P0, P1, and P2) based on fluorene and carbazole moieties were successfully synthesized through Suzuki coupling reaction. The molecular structures of the polymers were fully characterized by ¹H‐NMR, ¹³C‐NMR, elemental analysis, and gel permeation chromatograph, respectively. The photophysical properties, thermal stability, and energy band gaps of polymers P0, P1, and P2 were further examined through UV–vis absorption, photoluminescent spectra, differential scanning calorimetry, thermogravimetric analysis, and cyclic voltammetry. The experimental results indicated that the polymers took on wide band gaps of about 3.50 eV with deep blue emission in thin solid films. These polymers were found to show a high thermal stability with decomposition temperatures at 5% weight loss of the compounds in the range of 353–416 °C. Blue light‐emitting electroluminescent devices of the most branched polymer P2 with highest light‐emitting efficiency as emitting layers were characterized, which showed obviously improved spectral stabilities with respect to the parent polyfluorene materials. In conclusion, we have established an effective method to improve the spectral stabilities of polyfluorene material by synthesizing the zigzag‐shaped copolymer of fluorene and carbazole with sterically hindered pendant moieties of different molecular sizes. Copyright © 2014 John Wiley & Sons, Ltd.     

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.