Search

Abstract: In this paper we designed a kind of aggregation‐induced emission (AIE) chiral fluorescence emitters (R/S‐BINOL‐CN enantiomers) in the aggregate state. Chiral emissive nematic liquid crystals (N*‐LCs) prepared by doping this kind of AIE‐active R/S‐BINOL‐CN enantiomers into a common achiral nematic liquid crystal (N‐LC, E7) can self‐assemble as the regularly planar Grandjean texture leading to high luminescence dissymmetry factor (glum) of aggregation‐induced circularly polarized luminescence (AI‐CPL) signal up to 0.41, which can be attributed to dipolar interactions from polar cyano groups and π–π interactions between binaphthyl moiety of the dopant R/S‐BINOL‐CN and biphenyl group of the host molecules (E7). [ABSTRACT FROM AUTHOR]

Bis(dipyrrinato) ZnII complexes can have very high luminescent quantum yields upon judicious choice of the ligands. Although BODIPY (boron dipyrromethene) is still a front runner in the family of dipyrromethene compounds with their excellent photophysical properties, the authors show that zinc dipyrrins, exhibiting high fluorescence, are hot on its heels. The authors would like to thank the designer Vincenzo Pani for help in producing the graphical representation. More information can be found in the Full Paper by C. Bizzarri et al. on page 3816. [ABSTRACT FROM AUTHOR]

A novel enantiopure π‐allylruthenium(IV) precatalyst allowed the enantioselective and stereospecific allylations of indoles and gave access to indolin‐3‐ones, containing vicinal stereogenic centers. Facile separation of diastereoisomers exhibiting opposite circularly polarized luminescence (CPL) activities in diverse solvents, including water, demonstrated the potential of these sustainable transformations and of the newly prepared molecules. [ABSTRACT FROM AUTHOR]

Naphthalenediimides (NDIs) have been extensively studied due to their tunable luminescent properties. However, generally, the monomers or aggregates of non‐core substituted NDIs exhibit low fluorescence quantum yields (ΦFL<10 %) in the solid state, which limit their applications as light‐emitting materials and render their chiral species unsuitable for circularly polarized luminescence (CPL). Herein, a series of non‐core substituted chiral NDIs that exhibit high luminous efficiencies (ΦFL up to 56.8 % for racemate and 36.5 % for enantiomer) and a strong CPL behavior in the solid state is reported. These significant improvements are attributed to the unique molecular conformation of the chiral NDIs and the formation of distinctive discrete dimers. The structures of the NDIs were significantly simpler and more accessible than those of other NDIs. The findings evidence that non‐core substituted NDIs can exhibit strong fluorescence in the solid state and provide a new pathway to improve photophysical properties of NDIs. [ABSTRACT FROM AUTHOR]

A MOF ‐ based label ‐ free enzyme assay was designed in this work. To analyze polyphenol oxidase (PPO) activity, a luminescent MOF in which the emission could be selectively quenched by the o ‐ quinone product was synthesized. With it, the kinetics of PPO ‐ catalyzed oxidation could be reflected with the fluorescence signal. This method exhibits the advantages of high sensitivity, wide substrate adaptability, and minimal effects on the enzymatic reaction. More information can be found in the Full Paper by W. ‐ J. Ruan, et al. on page 6562 ff. [ABSTRACT FROM AUTHOR]

A series of isomorphic lanthanide metal-organic frameworks (MOFs) Ln(TATAB)⋅(DMF)4(H2O)(MeOH)0.5 (LnTATAB, Ln=Eu, Tb, Sm, Dy, Gd; H3TATAB=4,4′,4′′-s-triazine-1,3,5-triyltri- p-aminobenzoic acid) have been solvothermally synthesized and structurally characterized. Among these MOFs, TbTATAB exhibits good water stability and a high fluorescence quantum yield. Because mercury ions (Hg2+) have a high affinity to nitrogen atoms, and the space between multiple nitrogen atoms from triazine and imino groups is suitable for interacting with Hg2+ ions, TbTATAB shows highly selective and sensitive detection of Hg2+ in aqueous solution with a detection limit of 4.4 n m. Furthermore, it was successfully applied to detect Hg2+ ions in natural water samples. [ABSTRACT FROM AUTHOR]

The physicochemical properties of cationic dioxa ( 1), azaoxa ( 2), and diaza ( 3) [6]helicenes demonstrate a much higher chemical stability of the diaza adduct 3 (p KR +=20.4 [ABSTRACT FROM AUTHOR]

With our new home-built circularly polarized luminescence (CPL) instrument, we measured fluorescence and CPL spectra of the enantiomeric pairs of two quasi-isomeric BODIPY DYEmers 1 and 2, endowed with axial chirality. The electronic circular dichroism (ECD) and CPL spectra of these atropisomeric dimers are dominated by the exciton coupling between the main π-π* transitions (550-560 nm) of the two BODIPY rings. Compound 1 has strong ECD and CPL spectra ( glum=4×10−3) well reproduced by TD-DFT and SCS-CC2 (spin-component scaled second-order approximate coupled-cluster) calculations using DFT-optimized ground- and excited-state structures. Compound 2 has weaker ECD and CPL spectra ( glum=4×10−4), partly due to the mutual cancellation of electric-electric and electric-magnetic exciton couplings, and partly to its conformational freedom. This compound is computationally very challenging. Starting from the optimized excited-state geometries, we predicted the wrong sign for the CPL band of 2 using TD-DFT with the most recommended hybrid and range-separated functionals, whereas SCS-CC2 or a DFT functional with full exact exchange provided the correct sign. [ABSTRACT FROM AUTHOR]

A guest-dependent dynamic fivefold interpenetrated 3D porous metal-organic framework (MOF) of ZnII ions has been synthesized that exhibits selective carbon dioxide adsorption. Furthermore, the MOF shows excellent luminescence behavior, which is supported by a systematic study on the guest-responsive multicolor emission of a suspension of the MOF. The dual-emission behavior arises from the excited-state intramolecular proton transfer (ESIPT), and the compound also shows remarkable potential to detect traces of water in various organic solvents. The experimental observations were also painstakingly authenticated by using time-dependent density-functional-theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

Two new acceptors containing platinum-carbazole ( 1) and platinum-triphenylamine ( 2) backbones with bite angles of 90° and 120°, respectively, have been synthesised and characterised. Reactions of the rigid acceptor 1 with linear dipyridyl-based donors ( 3 and 4) generated [4+4] self-assembled molecular squares ( 5 and 6), and similar treatments with acceptor 2 instead of 1 yielded [6+6] self-assembled molecular hexagons ( 7 and 8). The metallacycles were characterised by multinuclear NMR spectroscopy (1H and 31P) and ESI-MS. The geometries of the metallacycles were optimised by using the PM6 method. When aggregates of the metallacycles were formed by adding hexane solutions in dichloromethane, aggregation-induced emission was observed for metallacycles 5 and 7, and aggregation-caused quenching was observed for metallacycles 6 and 8. The formation of aggregates was verified by dynamic light scattering and TEM analyses. Macrocycles 5 and 7 are white-light emitters in THF. Moreover, their high luminescence in both solution and the solid state was utilised for the recognition of nitroaromatic explosives. [ABSTRACT FROM AUTHOR]

Photoinduced intramolecular direct arylation allows structurally unique compounds containing phenanthro[9′,10′:4,5]imidazo[1,2- f]phenanthridine and imidazo[1,2- f]phenanthridine skeletons, which mediate excited-state intramolecular proton transfer (ESIPT), to be efficiently synthesized. The developed polycyclic aromatics demonstrate that the combination of five-membered ring structures with a rigid arrangement between a proton donor and a proton acceptor provides a means for attaining large fluorescence quantum yields, exceeding 0.5, even in protic solvents. Steady-state and time-resolved UV/Vis spectroscopy reveals that, upon photoexcitation, the prepared protic heteroaromatics undergo ESIPT, converting them efficiently into their excited-state keto tautomers, which have lifetimes ranging from about 5 to 10 ns. The rigidity of their structures, which suppresses nonradiative decay pathways, is believed to be the underlying reason for the nanosecond lifetimes of these singlet excited states and the observed high fluorescence quantum yields. Hydrogen bonding with protic solvents does not interfere with the excited-state dynamics and, as a result, there is no difference between the occurrences of ESIPT processes in MeOH versus cyclohexane. Acidic media has a more dramatic effect on suppressing ESIPT by protonating the proton acceptor. As a result, in the presence of an acid, a larger proportion of the fluorescence of ESIPT-capable compounds originates from their enol excited states. [ABSTRACT FROM AUTHOR]

Tetracyclic heterocycles that exhibit high photoluminescence quantum yields were synthesized by anellation reactions of mono-, di-, and trifunctionalized 2,3-dichloroquinoxalines. Thus, treatment of 2,3-dichloroquinoxaline with TMPLi (TMP=2,2,6,6-tetramethylpiperidyl) allows a regioselective lithiation in position 5. Quenching with various electrophiles (iodine, (BrCl2C)2, allylic bromide, acid chloride, aryl iodide) leads to 5-functionalized 2,3-dichloroquinoxalines. Further functionalization in positions 6 and 8 can be achieved by using TMPLi or TMPMgCl ⋅LiCl furnishing a range of new di- and tri-functionalized 2,3-dichloroquinoxalines. The chlorine atoms are readily substituted by anellation with 1,2-diphenols or 1,2-dithiophenols leading to a series of new tetracyclic compounds. These materials exhibit strong, tunable optical absorption and emission in the blue and green spectral region. The substituted O-heterocyclic compounds exhibit particularly high photoluminescence quantum yields of up to 90 %, which renders them interesting candidates for fluorescence imaging applications. [ABSTRACT FROM AUTHOR]

Highly photoluminescent carbon nanodots (CNDs) were synthesized for the first time from metal-organic framework (MOF, ZIF-8) nanoparticles. Coupled with fluorescence and non-toxic characteristics, these carbon nanodots could potentially be used in biosafe color patterning. [ABSTRACT FROM AUTHOR]

A family of cyclic phosphine‐disiloxane featuring peri‐substituted naphthyl(Nap)/acenaphthyl(Ace) scaffolds has been prepared and fully characterized including X‐ray structure, which enables a detailed structural analysis. This straightforward synthesis takes advantage of both ortho‐ and peri‐substitution of Nap/Ace‐substituted phosphine oxides. The synthetic method allows diversifying the polycyclic aromatic platform (Nap and Ace) as well as the Si substituents (Me and Ph). Despite a strong steric congestion, the P‐atom remains reactive toward oxidation or coordination. In particular, Au(I) complex could be prepared. All the compounds display absorption/luminescence in the UV‐Vis range. Surprisingly, the P‐trivalent derivatives display unexpected luminescence in the green in solid‐state. [ABSTRACT FROM AUTHOR]

Seven three dimensional (3D) uranyl organic frameworks (UOFs), formulated as [NH4][(UO2)3(HTTDS)(H2O)] (1), [(UO2)4(HTTDS)2](HIM)6 (2, IM=imidazole), [(UO2)4(TTDS)(H2O)2(Phen)2] (3, Phen=1,10‐phenanthroline), [Zn(H2O)4]0.5[(UO2)3(HTTDS)(H2O)4] (4), and {(UO2)2[Zn(H2O)3]2(TTDS)} (5), {Zn(UO2)2(H2O)(Dib)0.5(HDib)(HTTDS)} (6, Dib=1,4‐di(1H‐imidazol‐1‐yl)benzene) and [Na]{(UO2)4[Cu3(u3‐OH)(H2O)7](TTDS)2} (7) have been hydrothermally prepared using a rigid octadentate carboxylate ligand, tetrakis(3,5‐dicarboxyphenyl)silicon(H8TTDS). These UOFs have different 3D self‐assembled structures as a function of co‐ligands, structure‐directing agents and transition metals. The structure of 1 has an infinite ribbon formed by the UO7 pentagonal bipyramid bridged by carboxylate groups. With further introduction of auxiliary N‐donor ligands, different structure of 2 and 3 are formed, in 2 the imidazole serves as space filler, while in 3 the Phen are bound to [UO2]2+ units as co‐ligands. The second metal centers were introduced in the syntheses of 4–7, and in all cases, they are part of the final structures, either as a counterion (4) or as a component of framework (5−7). Interesting, in 7, a rare polyoxometalate [Cu3(μ3‐OH)O7(O2CR)4] cluster was found in the structure. It acts as an inorganic building unit together with the dimer [(UO2)2(O2CR)4] unit. Those uranyl carboxylates were sufficiently determined by single crystal X‐ray diffraction, and their topological structures and luminescence properties were analyzed in detail. [ABSTRACT FROM AUTHOR]

Keywords: boron complexes; crystallization-induced emission; fluorescence; vapochromism; crystal transition EN boron complexes crystallization-induced emission fluorescence vapochromism crystal transition 9194 9194 1 06/30/21 20210625 NES 210625 B A vapochromic luminescent crystal b consisting of boron diiminate has been discovered. Cover Feature: Reversible Vapochromic Luminescence Accompanied by Planar Half-Chair Conformational Change of a Propeller-Shaped Boron -Diketiminate Complex (Chem. Eur. J. 36/2021) Boron complexes, crystallization-induced emission, fluorescence, vapochromism, crystal transition. [Extracted from the article]

Leakage of volatile organic compounds (VOCs) is one of the most severe industrial problems, because it can cause environmental pollution, global warming, fire, and explosion. Hence, the visualization of leakage is an essential technology to detect it at an early stage. Molecular crystals, fluorescence color of which can be changed by the exposure to VOCs could potentially serve as the sensing materials for realizing rapid and facile VOC detection. However, these materials usually require harsh conditions, such as heating or a vacuum, to recover their initial phases for reuse. Therefore, it remains a challenge to obtain completely reversible sensing systems without such energy‐consuming recycling processes. Herein, the reversible color change of fluorescence from the crystals of a propeller‐shaped boron β‐diketiminate complex is reported. The complex was crystallized in distinct crystalline phases having different luminescent colors. Importantly, these phases were interconverted very rapidly (time constant <60 s) and repeatedly upon exposure to the vapors of the appropriate VOCs. The small energy differences between conformers of the complex could lead to this pseudopolymorphic behavior. This finding could be applied for the development of further eco‐friendly reversible sensing materials based on four‐coordinated boron complexes. [ABSTRACT FROM AUTHOR]

Through a dual‐ligand synthetic approach, five isoreticular primitive cubic (pcu)‐type pillared‐layer metal–organic frameworks (MOFs), [Zn2(dicarboxylate)2(NI‐bpy‐44)]⋅x DMF⋅y H2O, in which dicarboxylate=1,4‐bdc (1), Br‐1,4‐bdc (2), NH2‐1,4‐bdc (3), 2,6‐ndc (4), and bpdc (5), have been engineered. MOFs 1–5 feature twofold degrees of interpenetration and have open pores of 27.0, 33.6, 36.8, 52.5, and 62.1 %, respectively. Nitrogen adsorption isotherms of activated MOFs 1′–5′ at 77 K all displayed type I adsorption behavior, suggesting their microporous nature. Although 1′ and 3′–5′ exhibited type I adsorption isotherms of CO2 at 195 K, MOF 2′ showed a two‐step gate‐opening sorption isotherm of CO2. Furthermore, MOF 3′ also had a significant influence of amine functions on CO2 uptake at high temperature due to the CO2–framework interactions. MOFs 1–5 revealed solvent‐dependent fluorescence properties; their strong blue‐light emissions in aqueous suspensions were efficiently quenched by trace amounts of nitrobenzene (NB), with limits of detection of 4.54, 5.73, 1.88, 2.30, and 2.26 μm, respectively, and Stern–Volmer quenching constants (Ksv) of 2.93×103, 1.79×103, 3.78×103, 4.04×103, and 3.21×103 m−1, respectively. Of particular note, the NB‐included framework, NB@3, provided direct evidence of the binding sites, which showed strong host–guest π–π and hydrogen‐bonding interactions beneficial for donor–acceptor electron transfer and resulting in fluorescence quenching. [ABSTRACT FROM AUTHOR]

Small robust organic molecules showing solid‐state luminescence are promising candidates for optoelectronic materials. Herein, we investigate a series of diphenylphosphanyl anthracenes [9‐PPh2‐10‐R‐(C14H8)] and their sulfur oxidised analogues. The oxidation causes drastic changes in the molecular structure as the new orientation of the bulky (S)PPh2 substituent induces a strong butterfly bent structure of the anthracene core, which triggers a strong bathochromic shift resulting in a green solid‐state fluorescence. As the emission properties change only slightly upon aggregation the origin of the emission is attributed to a typical monomer fluorescence. The host–guest complexes of [9‐(S)PPh2‐10‐Ethyl‐(C14H8)] with four basic arenes reveal an emission enhancement up to five‐times higher quantum yields compared to the pure host. Less interchromophoric interactions and a restriction of intramolecular motion within the host molecules due to fixation by weak C−H⋅⋅⋅π interactions with the co‐crystallised arene are responsible for that emission enhancement. [ABSTRACT FROM AUTHOR]

This study describes the synthesis, structure, and photophysical properties of a new luminescent polyaromatic boronic acid scaffold, diazaboryl‐naphthyl‐ketones (DNKs). These stable compounds display extremely bright fluorescence, aggregation‐induced emission, positive solvatochromism, and solid‐state fluorescence. DFT calculations and X‐ray crystallographic study revealed notable electronic and structural differences between these compounds and the parent diaminonaphthalene (DAN) adducts. Acylation of the DAN system causes a localization of both HOMO and LUMO onto the DNK unit, which validates the negligible influence of the B‐aryl substituent. The LUMO energy is lowered, and its shape significantly altered. Photophysical data in solution and the solid state revealed blue‐shifted, narrowed, and intense emissions for DNKs (up to 89 % quantum yield). The potential utility of the fluorogenic DNK system was demonstrated with a proof‐of‐concept for the determination of trace boronic acid contaminants in solid samples, down to one‐ppm level, using HPLC with fluorescence detection. This method could be useful in pharmaceutical development for the quantitation of difficult‐to‐detect and potentially mutagenic residual boronic acid from late cross‐coupling reactions in drug syntheses. [ABSTRACT FROM AUTHOR]

Different molecular strategies have been carefully evaluated to produce solid‐state luminescence enhancement (SLE) in compounds that show dark states in solution. A set of α‐phenylstyrylarene derivatives with a butterfly shape have been designed and synthesised, for the first time, with the aim of improving the solid‐state fluorescence emission of their parent styrylarene compounds. Although these butterfly molecules are not fluorescent in solution, one of them (1,2,4,5‐tetra(α‐phenylstyryl)benzene) exhibits a fluorescence quantum yield as high as 68 % in a drop‐cast sample and 31 % in its crystalline form. In contrast, 1,3,5‐tris(α‐phenylstyryl)benzene and 4,6‐bis(α‐phenylstyryl)pyrimidine do not show SLE. A range of fluorescence spectroscopy experiments and DFT calculations were carried out to unravel the origin of different photophysical behaviour of these compounds in the solid state. The results indicate that a rational strategy to control the SLE effect in luminogens depends on a delicate balance between molecular properties and inter‐/intramolecular interactions in the solid state. [ABSTRACT FROM AUTHOR]

A variety of carbazolyl‐appended Schiff bases were readily synthesized from 1‐formylcarbazoles and aniline derivatives. Boron complexation of the resulting ligands allowed for facile preparation of new carbazole‐based BODIPY analogues showing solid‐state fluorescence. Furthermore, some dyes were converted into chiral compounds through the Et2AlCl‐mediated incorporation of a binaphthyl unit. The chiral dyes showed aggregation‐induced fluorescence and circularly polarized luminescence (CPL) with the ΦF and glum of up to 0.22 and −3.5×10−3, respectively, in the solid state. The solid‐state fluorescence and CPL were well characterized by the crystal packing analyses and DFT calculations. [ABSTRACT FROM AUTHOR]

The influence of the chemical substitution, crystal packing, and aurophilic interactions of the gold(I) acetylide complexes of the type (ArCOC≡C)nAuPEt3 (n=1,2) on their luminescent properties were examined. All described complexes undergo ligand scrambling in solution, which results in the formation of stable, easily isolated crystals that contain [ArCO(C≡C)n]2Au−(Et3P)2Au+ homoleptic species. In particular, we observed that the (benzoylacetylide)gold(I) complex yields three crystal forms with strikingly different luminescence properties. We monitored the conversion pathway for these forms: an orange luminescent form of homoleptic complex upon drying undergoes spontaneous transformation to bright green fluorescent form and finally to the weakly blue emissive one. In addition, we report a rare example of a helical arrangement of Au⋅Au⋅Au chains that are observed for the first time in acetylide gold(I) complexes in the case of heteroleptic (benzoylacetylide)gold(I) complex. This is a very rare case in which crystal structures and ensuing electronic properties of the heteroleptic and AuI complexes could be directly compared. [ABSTRACT FROM AUTHOR]

Organic luminescent materials with high quantum yields and/or white‐light‐emitting properties in particular play a crucial role in labeling and optoelectronic devices. In this work we have synthesized a new 2,3,6,7‐tetramethoxy‐9,10‐di‐p‐tolylanthracene‐bridged pillar[5]arene dimer with persistent mazarine blue fluorescent emission and much higher quantum yields in both solution and the solid state in comparison with its corresponding emissive linker without pillarene units, which exhibits typical aggregation‐caused quenching. According to the fluorescence data and single‐crystal analyses, their contrasting fluorescent performances can be rationally ascribed to their different stacking structures and intermolecular interactions. Three fluorescent guests containing different chromophores and/or terminal binding sites have also been synthesized to interact with the pillar[5]arene dimer to construct supramolecular ensembles with highly controllable luminescence, taking advantage of the stimuli‐responsive properties of the supramolecular host–guest interactions. Intriguingly, multicolor fluorescence, including white‐light emission (0.31, 0.35), which is in high demand, has been achieved by tuning the molar ratio of the host and guest and/or by changing the solvent system. This strategy holds great potential for the design and development of fluorescent materials with high quantum yields, controllable emission wavelength, and good stimuli‐responsiveness. [ABSTRACT FROM AUTHOR]

The fabrication of carbon dots and their doped forms by top‐down chemical cleavage has attracted considerable attention in the efforts to meet the increasing demands for optoelectronic applications ranging from biosensing to electro‐ and photocatalysis. However, due to strong quantum confinement effects, the size decrease often leads to an increase in the band gap, even in the emission of deep‐ultraviolet (DUV) light, which greatly limits their applications. Here, we report a facile hot‐tailoring strategy for fabricating carbon nitride nanodots (CNDs) with redshifted intrinsic photoluminescent (PL) emission, compared with the pristine bulk precursor. It has been found that the different leaving abilities of the C,N‐containing groups during the pyrolysis stage and the chemical passivation during the liquid‐collection stage played vital roles. Due to the redshifted photoluminescence and other attractive features, the as‐obtained CNDs were successfully applied in visual double text encryption with higher security and also in bioimaging with photostability superior to traditional dyes. This work highlights the great potential of the hot‐tailoring method in modulating carbon‐based nanostructures and offsetting band‐gap widening as the size decreases. [ABSTRACT FROM AUTHOR]

The mechanoresponsive behavior and photochemical response of a new bis(cyanostyryl)benzene fluorophore (CSB‐5) were investigated. Green fluorescence with λem,max of 507 nm was found for CSB‐5 in chloroform solution, mirroring the behavior of a previously reported similar dye (CSB‐6). Alternatively, crystalline samples of CSB‐5 exhibited orange fluorescence with λem,max of 620 nm, attributable to excimer emission. Although the emission color change was not clearly noticeable by naked eye, CSB‐5 exhibited mechanochromic luminescence, due to transformation into the amorphous state upon grinding the crystalline powder. Interestingly, rubbed films of CSB‐5 prepared on glass substrates exhibited a pronounced emission color change from orange to green when exposed to UV light. This response is the result of a photochemical reaction that occurs in the amorphous state and which causes a decrease of the excimer emission sites so that the emission color changes from excimer to monomer. The crystalline material did not display such a photoinduced emission color change and the difference in photochemical reactivity between crystalline and amorphous states was exploited to pattern the emission color of rubbed films. [ABSTRACT FROM AUTHOR]

With the aim of developing all‐organic bipolar semiconductors with high charge mobility and efficient E‐type fluorescence (so‐called TADF) as environmentally friendly light‐emitting materials for optoelectronic applications, four noble metals‐free dyes with linear and V‐shapes were designed using accepting pyridine‐3,5‐dicarbonitrile and donating carbazole units. By exploiting a donor‐acceptor design strategy and using moieties with different donating and accepting abilities, TADF emitters with a wide variety of molecular weights were synthesized to achieve the optimum combination of charge‐transporting and fluorescent properties in one TADF molecule. Depending on molecule structures, different TADF emitters capable of emitting in the range from 453 to 550 nm with photoluminescence quantum yields up to 98 % for the solutions in oxygen‐free toluene were obtained. All compounds showed bipolar charge‐transport. Hole mobility of 2.8×10−3 cm2/Vs at 7×105 V cm−1 was observed for the compound containing two di‐tert‐butyl‐substituted carbazole moieties. The compounds were tested in both non‐doped and doped organic light‐emitting diodes using different hosts. It was shown that the developed TADF emitters are suitable for different color devices with electroluminescence ranging from blue to yellow and with brightness, maximum current and external quantum efficiencies exceeding 10 000 cd m−2, 15 cd/A, and 7 %, respectively. Metal‐free shine: Four noble metals‐free dyes with linear and V‐shapes were designed using accepting pyridine‐3,5‐dicarbonitrile and donating carbazole units (see figure). The TADF emitters are suitable for color devices with blue to yellow electroluminescence. [ABSTRACT FROM AUTHOR]

A new metal–organic framework (MOF), [Zn6L4(Me2NH2+)4⋅3 H2O] (1) was constructed based on [9, 9′‐biscarbazole]‐3, 3′, 6, 6′‐tetracarboxylic acid (H4L) and Zn2+ ions. The porous framework and intense blue fluorescence of the MOF based on the biscarbazole moiety of the ligand could facilitate efficient host to guest energy transfer, which makes it an ideal platform for the tuning of luminescence. When the MOFs go blue: A metal organic framework (MOF) was constructed based on a novel biscarbazole tetracarboxylic acid ligand. This blue fluorescent MOF serves as an ideal platform for host–guest energy transfer. [ABSTRACT FROM AUTHOR]

Abstract: Luminescent lanthanide‐containing compounds have a lot of stimulating applications. However, the fine‐tuning of the optical properties of multi‐nuclear lanthanide edifices is still a big challenge. We report here the coordination self‐assembly of a group of bright luminescent lanthanide organic polyhedra (LOPs) with record high emission quantum yields, by using two fully‐conjugated ligands featuring the triazole‐pyridine‐amido (tpa) chelating moiety, easily‐accessible from the “Click” reaction. The self‐assembled LOPs are characterized by NMR spectroscopy, high‐resolution ESI‐TOF‐MS, and X‐ray crystallography. Interestingly, inter‐metal energy transfer (ET) is confirmed on the mixed‐lanthanide polyhedral molecules, though the metal centers are separated nearly 2 nm apart. A feasible ratiometric luminescent thermometer, with work range from cryogenic to physiological temperatures, has been demonstrated with the mixed Eu/Tb LOPs. We envisage these molecular‐level bright luminescent LOPs have great application potential in displaying, labelling/imaging, up‐conversion materials etc. [ABSTRACT FROM AUTHOR]

Abstract: Dibenzo[7]helicenes were synthesized with up to 99 % ee by rhodium(I)/binap‐catalyzed enantioselective intramolecular [2+2+2] cycloaddition of 2‐phenylnaphthalene‐linked triynes. Additionally, [2+1+2+1] cycloaddition products, that is, twisted anthracenes, were also synthesized by using difluorphos as ligand. Although these compounds are not configurationally stable at elevated temperature, their Scholl reactions afforded configurationally stable double dibenzo[6]helicenes. The thus‐obtained dibenzo[7]helicene exhibited good circularly polarized luminescence property and the double dibenzo[6]helicene showed high fluorescence quantum yield. [ABSTRACT FROM AUTHOR]

Abstract: The study of molecules that self‐assemble through noncovalent interactions is one of the most attractive topics in supramolecular chemistry. The use of short peptides or modified nucleotides as building blocks for the aggregates is particularly intriguing because these are very easy to synthesize; moreover, subtle changes in the chemical structure of such building blocks may drastically affect the properties of the aggregates. The ability of peptide nucleic acids (PNA) to aggregate has been very little explored, despite its practical applications. In this work we investigated the self‐assembling properties of a PNA dimer, conjugated at the N‐terminus to a fluorenylmethoxycarbonyl group. This PNA dimer forms nano‐aggregates at low concentration in CHCl3/CH3OH mixtures. The aggregates retain very interesting fluorescent properties (high quantum yield in the visible region with lifetimes on the nanosecond scale), which make them promising materials for applications in optoelectronics. [ABSTRACT FROM AUTHOR]

A series of terpyridine/acridine conjugates exhibits strong blue‐to‐green emission and thermally activated delayed fluorescence (TADF) character in the solid state. An organic light‐emitting device with a green emissive terpyridine/acridine conjugate showed an external quantum efficiency of approximately 25%, a power efficiency of over 80 lm W−1, and an exceptionally low‐efficiency roll‐off. More information can be found in the Full Paper by H. Sasabe and J. Kido et al. on page 114 ff. [ABSTRACT FROM AUTHOR]

A chiral cationic [6]helicene, which is depicted in the image, has been found to be a powerful dye and fluorophore that emits circularly polarized light in the red to far‐red region. More information can be found in the Full Paper by E. Vauthey, J. Lacour et al. on page 18394 ff. [ABSTRACT FROM AUTHOR]

Copper and gold halide and pseudo-halide complexes stabilised by methyl-, ethyl- and adamantyl-substituted cyclic (alkyl)(amino)carbene (CAAC) ligands are mostly linear monomers in the solid state, without aurophilic Au⋅⋅⋅Au interactions. (Et2L)CuCl shows the highest photoluminescence quantum yield (PLQY) in the series, 70 %. The photoemissions of Me2L and Et2L copper halide complexes show S1→S0 fluorescence on the ns time scale, in agreement with theory, as well as a long-lived emission. Monomeric (Me2L)CuNCS is a white emitter, whereas dimeric [(Et2L)Cu(μ-NCS)]2 shows intense yellow emission with a photoluminescence (PL) quantum yield of 49 %. The reaction of (AdL)MCl (M=Cu or Au) with phenols ArOH (Ar=Ph, 2,6-F2C6H3, 2,6-Me2C6H3, 3,5- tBu2C6H3, 2- tBu-5-MeC6H3, 2-pyridyl), thiophenol, or aromatic amines H2NAr′′ (Ar′=Ph, 3,5-(CF3)2C6H3, C6F5, 2-py) afforded the corresponding phenolato, thiophenolato and amido complexes. Although the emission wavelengths are only marginally affected by the ring substitution pattern, the PL intensities respond sensitively to the presence of substituents in the ortho or meta positions. In gold aryloxides, PL is controlled by steric factors, with strong luminescence in compounds with Au- O-C-C torsion angles <50°. Calculations confirm the dependence of oscillator strength on the torsion angle, as well as the inter-ligand charge transfer nature of the emission. The HOMO/LUMO energy levels were estimated based on first reduction and oxidation potentials. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of four new tetracyanobutadiene (TCBD) derivatives (1-3 and 2') incorporating 2- or 2,7-fluorenyl and diphenylamino moieties are reported. The electroactivity of 1-3 and 2' was studied by cyclic voltammetry (CV), while the linear optical and (thirdorder) nonlinear optical (NLO) properties were investigated by electronic spectroscopy and Z-scan studies, respectively. All experimental investigations were rationalized by DFT computations, providing an insight into the electronic structure of these derivatives and on their application potential. We show that these derivatives are nonluminescent in solution at ambient temperatures, but become fluorescent in solvent glasses. This finding constitutes an unprecedented observation for TCBD derivatives. Also, we show by Z-scan studies that these derivatives behave as two-photon absorbers in the near-IR range (800-1050 nm). These third-order NLO properties are discussed and compared with those of their alkynyl precursors (4-6), which have been investigated by two-photon excited fluorescence (TPEF). [ABSTRACT FROM AUTHOR]

A set of eight helical diamines were designed and synthesized to demonstrate their relevance as all-in-one materials for multifarious applications in organic light-emitting diodes (OLEDs), that is, as hole-transporting materials (HTMs), EMs, bifunctional hole transporting + emissive materials, and host materials. Azahelical diamines function very well as HTMs. Indeed, with high Tg values (127-214 °C), they are superior alternatives to popular N, N′-di(1-naphthyl)- N, N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB). All the helical diamines exhibit emissive properties when employed in nondoped as well as doped devices, the performance characteristics being superior in the latter. One of the carbohelical diamines (CHTPA) serves the dual function of hole transport as well as emission in simple double-layer devices; the efficiencies observed were better by quite some margin than those of other emissive helicenes reported. The twisting endows helical diamines with significantly high triplet energies such that they also function as host materials for red and green phosphors, that is, [Ir(btp)2acac] (btp=2-(2′-benzothienyl)pyridine; acac=acetylacetonate) and [Ir(ppy)3] (ppy=2-phenylpyridine), respectively. The results of device fabrications demonstrate how helicity/ helical scaffold may be diligently exploited to create molecular systems for maneuvering diverse applications in OLEDs. [ABSTRACT FROM AUTHOR]

A series of fluorescent 'push-pull' tetrathia[9]helicenes based on quinoxaline (acceptor) fused with tetrathia[9]helicene (donor) derivatives was synthesized for control of the excited-state dynamics and circularly polarized luminescence (CPL) properties. In this work, introduction of a quinoxaline onto the tetrathia[9]helicene skeleton induced the 'push-pull' character, which was enhanced by further introduction of an electron-releasing Me2N group or an electron-withdrawing NC group onto the quinoxaline unit (denoted as Me2N-QTTH and NC-QTTH, respectively). These trends were successfully discussed in terms of by electrochemical measurements and density functional theory (DFT) calculations. As a consequence, significant enhancements in the fluorescence quantum yields ( ΦFL) were achieved. In particular, the maximum ΦFL of Me2N-QTTH was 0.43 in benzene (NC-QTTH: ΦFL=0.30), which is more than 20 times larger than that of a pristine tetrathia[9]helicene (denoted as TTH; ΦFL=0.02). These enhancements were also explained by kinetic discussion of the excited-state dynamics such as fluorescence and intersystem crossing (ISC) pathways. Such significant enhancements of the ΦFL values thus enabled us to show the excellent CPL properties. The value of anisotropy factor gCPL (normalized difference in emission of right-handed and left-handed circularly polarized light) was estimated to be 3.0×10−3 for NC-QTTH. [ABSTRACT FROM AUTHOR]

New bis- and tris(iminopyrrole)-functionalized linear (1,2-(HNC4H3-C(H)N)2-C6H4 ( 2), 1,3-(HNC4H3-C(H)N)2-C6H4 ( 3), 1,4-(HNC4H3-C(H)N)2-C6H4 ( 4), 4,4′-(HNC4H3-C(H)N)2-(C6H4-C6H4) ( 5), 1,5-(HNC4H3C-(H)N)2-C10H6 ( 6), 2,6-(HNC4H3C-(H)N)2-C10H6 ( 7), 2,6-(HNC4H3C-(H)N)2-C14H8 ( 8)) and star-shaped (1,3,5-(HNC4H3-C(H)N-1,4-C6H4)3-C6H3 ( 9)) π-conjugated molecules were synthesized by the condensation reactions of 2-formylpyrrole ( 1) with several aromatic di- and triamines. The corresponding linear diboron chelate complexes (Ph2B[1,3-bis(iminopyrrolyl)-phenyl]BPh2 ( 10), Ph2B[1,4-bis(iminopyrrolyl)-phenyl]BPh2 ( 11), Ph2B[4,4′-bis(iminopyrrolyl)-biphenyl]BPh2 ( 12), Ph2B[1,5-bis(iminopyrrolyl)-naphthyl]BPh2 ( 13), Ph2B[2,6-bis(iminopyrrolyl)-naphthyl]BPh2 ( 14), Ph2B[2,6-bis(iminopyrrolyl)-anthracenyl]BPh2 ( 15)) and the star-shaped triboron complex ([4′,4′′,4′′′-tris(iminopyrrolyl)-1,3,5-triphenylbenzene](BPh2)3 ( 16)) were obtained in moderate to good yields, by the treatment of 3- 9 with B(C6H5)3. The ligand precursors are non-emissive, whereas most of their boron complexes are highly fluorescent; their emission color depends on the π-conjugation length. The photophysical properties of the luminescent polyboron compounds were measured, showing good solution fluorescence quantum yields ranging from 0.15 to 0.69. DFT and time-dependent DFT calculations confirmed that molecules 10 and 16 are blue emitters, because only one of the iminopyrrolyl groups becomes planar in the singlet excited state, whereas the second (and third) keeps the same geometry. Compound 13, in which planarity is not achieved in any of the groups, is poorly emissive. In the other examples ( 11, 12, 14, and 15), the LUMO is stabilized, narrowing the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO), and the two iminopyrrolyl groups become planar, extending the size of the π-system, to afford green to yellow emissions. Organic light-emitting diodes (OLEDs) were fabricated by using the new polyboron complexes and their luminance was found to be in the order of 2400 cd m−2, for single layer devices, increasing to 4400 cd m−2 when a hole-transporting layer is used. [ABSTRACT FROM AUTHOR]

Copyright of Chemistry - A European Journal is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chemistry - A European Journal is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Three boradiazaindacene (BODIPY) dyes with different-coloured (greenish-yellow, orange and red) fluorescence and good Stokes shifts were synthesised starting from the greenish-yellow BODIPY dye PM546. The high Stokes shifts of the dyes are due to the release of the steric strain in their excited states relative to that in the highly twisted ground states. One of these compounds might be a useful water-soluble fluorophore, whereas the other two are promising H+ sensors. [ABSTRACT FROM AUTHOR]

Star-shaped charge-transporting materials with a triphenylamine (TPA) core and various phenylethenyl side arm(s) were obtained in a one-step synthetic procedure from commercially available and relatively inexpensive starting materials. Crystallinity, glass-transition temperature, size of the π-conjugated system, energy levels, and the way molecules pack in the solid state can be significantly influenced by variation of the structure of these side arm(s). An increase in the number of phenylethenyl side arms was found to hinder intramolecular motions of the TPA core, and thereby provide significant enhancement of the fluorescence quantum yield of the TPA derivatives in solution. On the other hand, a larger number of side arms facilitated exciton migration through the dense side-arm network formed in the solid state and, thus, considerably reduces fluorescence efficiency by migration-assisted nonradiative relaxation. This dense network enables charges to move more rapidly through the hole-transport material layer, which results in very good charge drift mobility ( μ up to 0.017 cm2 V −1 s−1). [ABSTRACT FROM AUTHOR]

Chlorophyll breakdown is a visual phenomenon of leaf senescence and fruit ripening. It leads to the formation of colorless chlorophyll catabolites, a group of (chlorophyll-derived bilin-type) linear tetrapyrroles. Here, analysis and structure elucidation of the chlorophyll breakdown products in leaves of banana ( Musa acuminata) is reported. In senescent leaves of this monocot all chlorophyll catabolites identified were hypermodified fluorescent chlorophyll catabolites ( hmFCCs). Surprisingly, nonfluorescent chlorophyll catabolites (NCCs) were not found, the often abundant and apparently typical final chlorophyll breakdown products in senescent leaves. As a rule, FCCs exist only fleetingly, and they isomerize rapidly to NCCs in the senescent plant cell. Amazingly, in the leaves of banana plants, persistent hmFCCs were identified that accounted for about 80 % of the chlorophyll broken down, and yellow leaves of M. acuminata display a strong blue luminescence. The structures of eight hmFCCs from banana leaves were analyzed by spectroscopic means. The massive accumulation of the hmFCCs in banana leaves, and their functional group characteristics, indicate a chlorophyll breakdown path, the downstream transformations of which are entirely reprogrammed towards the generation of persistent and blue fluorescent FCCs. As expressed earlier in related studies, the present findings call for attention, as to still elusive biological roles of these linear tetrapyrroles. [ABSTRACT FROM AUTHOR]

A series of nonplanar tetraphenylethene (TPE)-hexaphenylbenzene (HPB) adducts was designed and synthesized by Diels-Alder reaction of the acetylene precursors and tetraphenylcyclopentadienone. All of the adducts showed aggregation-induced emission features. The twisting amplitude and steric hindrance of the TPE and HPB units were found to play a crucial role in their fluorescence behaviors in the aggregated state. [ABSTRACT FROM AUTHOR]

Heteronuclear complexes {[Hg(R)2][Au(R′)(PMe3)]2} n (R=R′=C6Cl2F3 ( 3); R=R′=C6F5 ( 4); R=C6Cl2F3, R′=C6F5 ( 5); R=C6F5, R′=C6Cl2F3 ( 6)) were prepared by the treatment of the corresponding organomercury compounds, [Hg(C6X5)2], with two equivalents of [Au(C6X5)(PMe3)]. Their crystal structures, as determined by using X-ray diffraction methods, display Au⋅⋅⋅Hg interactions. Although only compound 4 and 5 show luminescence in the solid state, all of these compounds quench the fluorescence of naphthalene in solution. Solution studies of these derivatives suggest a cooperative effect of the gold(I) center in switching on the quenching capabilities of the [Hg(C6X5)2] synthon with naphthalene. Theoretical studies confirmed the quenching ability of the organomercury species in the presence of gold. [ABSTRACT FROM AUTHOR]