The photophysics of a luminescent ruthenium polypyridyl complex with pendant β-cylodextrin; pH modulation of lifetime and photoinduced electron transfer

At room temperature, [Ru(bpy)₂(phen-CD)][PF₆]₂, (phen-CD is 6 ^A -(5-amino-1, 10-phenanthroline)-6 ^A -deoxy- β-Cyclodextrin and bpy is 2,2'-bipyridine) exhibits an intense metal ligand charge transfer (MLCT) transition at 452 nm and a long lived luminescence, centred at 618 nm. We demonstrate, for the first time, that the luminescence quantum yield and lifetime of the Ru (II) polypyridyl centre depends markedly on the solution pH. The pH sensitive range extends from pH 3.9 to pH 13.2 and the luminescence quantum yield changes by more than 60% over this range. This pH sensitivity is attributed to protonation/deprotonation of the secondary amine group bridge between the phenanthroline unit and CD. The complex exhibits strong host-guest binding to anthraquinone and anthraquinone-2-carboxylic acid, with concomitant quenching of the [Ru(bpy)₂(phen-CD)]²⁺ excited state. This quenching arises from efficient intramolecular electron transfer. The sensitivity of this photoinduced process to the protonation state of the bridge is discussed.     

New tridentate cyclometalated platinum(II) and palladium(II) complexes of N,2-diphenyl-8-quinolinamine: syntheses, crystal structures, and photophysical properties

A new tridentate cyclometalated platinum(II) complex derived from N,2-diphenyl-8-quinolinamine, which consists of two crystallographic independent molecules with two intermolecular N-H-Cl-Pt hydrogen bonds forming a dimer, exhibited a low-energy luminescence at ca. 740 nm in a 1 × 10⁻³ M dichloromethane solution and a strong emission centered at 670 nm in a solid state, but the analogous palladium(II) complex was nonemissive at room temperature.     

Self-assembly of a double calix[6]arene pseudorotaxane in oriented channels

A synthetic study to disclose the more appropriate manner by which two calix[6]arene units could be connected for the construction of an extended tubular structure was undertaken. As a result, a head-to-tail double calix[6]arene having the structure of an oriented nanotube that is about 2.6 nm long and 1.6 nm wide was prepared and characterized. This molecule is able to act as a wheel-type host and forms a supramolecular complex with an axle-type molecule, derived from 4,4'-bipyridinium (viologen), through very efficient self-assembly in solution. The properties of such a pseudorotaxane-type complex, which is stabilized by a combination of noncovalent interactions, were investigated in solution by UV/Vis absorption spectroscopy and voltammetric methods. These observations provide a clue about the location of the bipyridinium unit along the nanotube. In the solid state, the complex undergoes a further stage of self-assembly, thereby initiating extended oriented tubular structures. Crystallographic studies revealed that the positioning of the viologen dication in this asymmetric wheel is addressed by a complicated pattern of cooperative noncovalent intermolecular interactions that involve only one half of the host, whereas the remaining (more polar) half of the host is exploited to create long-range structural order that leads to a "secondary" structure of extended supramolecular channels that, in turn, self-assemble in the lattice, thus giving rise to a "tertiary" structure of parallel sandwiches of nanotubes.     

Violet/deep-blue fluorescent organic light-emitting diode based on high-efficiency novel carbazole derivative with large torsion angle

A novel and highly efficient violet/deep-blue fluorescent carbazole and naphthalene-based compound (1) is designed and synthesized. The compound shows intensive violet/deep-blue fluorescence, high photoluminescence efficiency (0.72 in CH₂Cl₂, 0.65 in film) and narrow full width at half maximum (48 nm). The large torsion angles between carbazole and naphthalene guarantee the weak intermolecular interactions and suppress the π-π interactions in solid state, resulting in the highly efficient violet/deep-blue fluorescence. The maximum emission peak, luminance and external quantum efficiency for violet/deep-blue electroluminescence are 410 nm, 1326 cd/m² and ～2%, respectively.     

Insights into the AIEE of 1,8‐Naphthalimides (NPIs): Inverse Effects of Intermolecular Interactions in Solution and Aggregates

Systematic structural perturbation has been used to fine‐tune and understand the luminescence properties of three new 1,8‐naphthalimides (NPIs) in solution and aggregates. The NPIs show blue emission in the solution state and their fluorescence quantum yields are dependent upon their molecular rigidity. In concentrated solutions of the NPIs, intermolecular interactions were found to quench the fluorescence due to the formation of excimers. In contrast, upon aggregation (in THF / H₂O mixtures), the NPIs show aggregation‐induced emission enhancement (AIEE). The NPIs also show moderately high solid‐state emission quantum yields (ca. 10–12.7 %). The AIEE behaviour of the NPIs depends on their molecular rigidity and the nature of their intermolecular interactions. The NPIs 1 – 3 show different extents of intermolecular (π–π and C?H???O) interactions in their solid‐state crystal structures depending on their substituents. Detailed photophysical, computational and structural investigations suggest that an optimal balance of structural flexibility and intermolecular communication is necessary for achieving AIEE characteristics in these NPIs.     

The effect of molecular imprinting on the pore size distribution of polymers

Molecular imprinting techniques are becoming an increasingly important domain of porous polymers generally, to achieve molecule specific recognition through morphology or stereochemistry of cavities. Imprinting is sought to increase both selectivity and sensitivity where the polymer may be present as particulate, membrane or thin film forms. Here, we detail mechanisms involved in the formation, stability and adsorption of binding sites, through the influence of polymerisation conditions and templates on the porosity of highly crosslinked molecularly imprinted polymers (MIPs). Environmental control represents an important area for porous polymers, here we focus on two template fungicides, iprodione and pyrimethanil, for ethylene glycol dimethacrylate (EGDMA) based polymers. In general, control of the pre-polymerisation interactions were able to vary the surface areas of polymers from 40–60 m² g⁻¹ to 300–436 m² g⁻¹ while pore sizes fell into distributions (a) close to the micropore region at ∼3.8 nm, (b) in the 10 to 20 nm mesopore region and (c) in the 20 to 50 nm mesopore region. The importance of intermolecular interactions and aggregation in the pre-polymerisation solution to the Brunauer, Emmett, Teller (BET) surface areas and pore size distribution of final polymers has been demonstrated by systematic variation of chemical functionality. These effects confirm recent molecular dynamic simulation studies of MIP formation and cavity stability.     

Co-Assembly of Chiral Amines and a Four-Armed Cyano-Substituted Luminophore through Hydrogen Bonds for Potential Development of Smart Chiroptical Materials

Chirality transfer from chiral molecules to assemblies is of vital importance to the design of functional chiral materials. In this work, selective co-assembly behaviors between chiral molecules and an achiral luminophore, potentially driven by the intermolecular salt-bridge type hydrogen bonds are reported. Cyano-substituted tetrakis(arylthio)benzene carboxylic acid ( TA ) served as the luminophore and hydrogen bond donors, which underwent co-assembly with different chiral amines. It was found that structures of chiral amines affect the chirality transfer and the properties of co-assemblies due to effects on hydrogen bonds and stacking pattern. Only in specific co-assemblies, the chiroptical properties occurred at both ground state and excited states based on the emerged Cotton effects and circularly polarized luminescence (CPL) signals, revealing that the chirality was successfully transferred from molecular level to supramolecular level. In addition, accurate quantitative examination of chiral amines was realized by circular dichroism (CD) spectra. This work demonstrates the characteristic chirality response and transfer through co-assembly, providing a potential method to develop smart chiroptical materials.     

Impact of metal cation complexation and protonation on tautomeric and resonance forms of the oxaalkyl Schiff bases derived from 5-substituted salicylaldehyde and 2-hydroxy-1-naphthlaldehyde

Structures of the main resonance and tautomeric forms of three Schiff bases of 2-hydroxy-1-naphthaldehyde (1OXA), 5-bromosalicylaldehyde (2OXA) and 5-nitrosalicylaldehyde (3OXA) with 1,8-diamine-3,6-dioxaoctane, before and after protonation and complexation of monovalent metal cations, have been studied by FTIR, ¹H, ¹³C and ¹⁵N NMR methods. The spectroscopic investigations provided clear evidence that the Schiff bases exist in acetonitrile solution as three different tautomers: 1OXA in enamine-oxo, 2OXA in imine-hydroxy and 3OXA in a low-barrier O···H···N imine-oxo forms. It was found on the basis of multinuclear NMR studies, that in solid state, the enamine-oxo and imine-hydroxy tautomers are formed exclusively, but not the untypical imine-oxo tautomer, which requires strong stabilisation by solvent molecules in solution. MOG-PM6 calculations of the different tautomers allowed visualisation of their energetically the most favourable structures. Protonation of 1OXA–3OXA Schiff bases leads to formation of common forms, i.e. protonated imine-hydroxy structure, irrespectively of the structure of tautomer before protonation. In turn, coordination of monovalent metal cations implies common formation of zwitterionic forms within all studied ligands in solution. Application of FT-IR and NMR titrations in combination with ESI MS spectrometry revealed the nature and the structure of OXA complexes, whose formation is impeded by the intra- and intermolecular interactions. MOG-PM6 calculations allowed visualisation of Li⁺ and Na⁺ metal coordination sphere geometries within structure of all investigated complexes, stabilised by intermolecular interactions with solvent molecules.     

A highly emissive AIE-active luminophore exhibiting deep-red to near-infrared piezochromism and high-quality lasing

Further development of high-efficiency and low-cost organic fluorescent materials is intrinsically hampered by the energy gap law and spin statistics, especially in the near-infrared (NIR) region. Here we design a novel building block with aggregation-induced emission (AIE) activity for realizing highly efficient luminophores covering the deep-red and NIR region, which originates from an increase in the orbital overlap and electron-withdrawing ability. An organic donor–acceptor molecule (BPMT) with the building block is prepared and can readily form J-type molecular columns with multiple C–H⋯N/O interactions. Notably, such synthesized materials can emit fluorescence centered at 701 nm with extremely high photoluminescence quantum yields (PLQYs) of 48.7%. Experimental and theoretical investigations reveal that the formation of the hybridized local and charge-transfer (HLCT) state and substantial C–H⋯N/O interactions contribute to a fast radiative decay rate and a slow nonradiative decay rate, respectively, resulting in high PLQYs in the solid state covering the NIR range. Remarkably, such BPMT crystals, as a first example, reveal strong-penetrability piezochromism along with a distinct PL change from the deep-red (λ_max = 704 nm) to NIR (λ_max = 821 nm) region. Moreover, such typical AIE-active luminophores are demonstrated to be a good candidate as a lasing medium. Together with epoxy resin by a self-assembly method, a microlaser is successfully illustrated with a lasing wavelength of 735.2 nm at a threshold of 22.3 kW cm⁻². These results provide a promising approach to extend the contents of deep-red/NIR luminophores and open a new avenue to enable applications ranging from chemical sensing to lasing.

A HLCT-type luminophore is prepared with bright deep-red fluorescence, showing high-performance piezochromism and lasing.     

Acid/Base Switching of the Tautomerism and Conformation of a Dioxoporphyrin for Integrated Binary Subtraction

Compared with most of the reported logic devices based on the supramolecular approach, systems based on individual molecules can avoid challenging construction requirements. Herein, a novel dioxoporphyrin DPH₂₂ was synthesized and two of its tautomers were characterized by single‐crystal X‐ray diffraction studies. Compound DPH₂₂ exhibits multichannel controllable stepwise tautomerization, protonation, and deprotonation processes through interactions with H⁺ and F^? ions. By using the addition of H⁺ and F^? ions as inputs and UV/Vis absorption values at λ=412, 510, 562, and 603 nm as outputs, the controlled tautomerism of DPH₂₂ has been successfully used for the construction of an integrated molecular level half‐subtractor and comparator. In addition, this acid/base‐switched tautomerism is reversible, thus endowing the system with ease of reset and recycling; consequently, there is no need to modulate complicated intermolecular interactions and electron‐/charge‐transfer processes.     

Syntheses, structures, and photophysical properties of mono- and dinuclear sulfur-rich gold(I) complexes

The dinuclear gold complexes [{Au(PPh 3)} 2(mu- dmid)] ( 1) ( dmid = 1,3-dithiole-2-one-4,5-dithiolate) and [{Au(PPh 3)} 2(mu- dddt)] ( 2) ( dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) were synthesized and characterized by X-ray crystallography. Both complexes exhibit intramolecular aurophilic interactions with Au...Au distances of 3.1984(10) A for 1 and 3.1295(11) A for 2. A self-assembly reaction between 4,5-bis(2-hydroxyethylthio)-1,3-dithiole-2-thione ( (HOCH 2 CH 2 ) 2 dmit) and [AuCl(tht)] affords the complex [AuCl{ (HOCH 2 CH 2 ) 2 dmit}] 2 ( 4), which possesses an antiparallel dimeric arrangement resulting from a short aurophilic contact of 3.078(6) A. This motif is extended into two dimensions due to intra- and intermolecular hydrogen bonds via the hydroxyethyl groups, giving rise to a supramolecular network. Three compounds were investigated for their rich photophysical properties at 298 and 77 K in 2-MeTHF and in the solid state; [Au 2(mu- dmid)(PPh 3) 2] ( 1), [Au 2(mu- dddt)(PPh 3) 2] ( 2), and [AuCl{( HOCH 2 CH 2 ) 2 dmit}] ( 4). 1 exhibits relatively long-lived LMCT (ligand-to-metal charge transfer) emissions at 298 K in solution (370 nm; tau e approximately 17 ns, where M is a single gold not interacting with the other gold atom; i.e., the fluxional C-SAuPPh 3 units are away from each other) and in the solid state (410 nm; tau e approximately 70 mus). At 77 K, a new emission band is observed at 685 nm (tau e = 132 mus) and assigned to a LMCT emission where M is representative for two gold atoms interacting together consistent with the presence of Au...Au contacts as found in the crystal structure. In solution at 77 K, the LMCT emission is also red-shifted to 550 nm (tau e approximately 139 mus). It is believed to be associated to a given rotamer. 2 also exhibits LMCT emissions at 380 nm at 298 K in solution and at 470 nm in the solid state. 4 exhibits X/MLCT emission (halide/metal to ligand charge transfer) where M is a dimer in the solid state with obvious Au...Au interactions, resulting in red-shifted emission band, and is a monomer in solution in the 10 (-5) M concentration (i.e., no Au...Au interactions) resulting in blue-shifted luminescence. Both fluorescence and phosphorescence are observed for 4.     

Supramolecular assembly and solvochromic luminescence of a Au(I) complex containing di(4-pyridylmethyl)aminedithiocarbamate

The di(4-pyridylmethyl)aminedithiocarbamate (DPMACS₂) ligand was used to react with (Me₂S)AuCl to give a dinuclear complex, [Au(DPMACS₂)]₂, which shows both intramolecular Au(I)⋅⋅⋅Au(I) distances of 2.741(9)–2.788(1) Å and intermolecular Au(I)···Au(I) contacts of 2.917(5)–3.047(7) Å, leading to 1-D Au(I) chains in the solid state. In addition, complex [Au(DPMACS₂)]₂ shows the luminescence at 555 nm at room temperature while excited, and almost no energy shift for the luminescence at 553 nm upon grinding has been observed. In this regard, we further examined the solvochromic luminescence upon grinding with various solvents, and the luminescence is within 549–572 nm. It is noted that the solvochromic luminescence for dichloromethane (566 nm) and 1,2-dichloroethane (572 nm) has been observed, and the original luminescence at 555 nm can be restored upon solvent loss. Indeed, such red-shifts for the solvochromic luminescence are most likely due to a decrease in intermolecular Au(I)⋅⋅⋅Au(I) contacts while solvents entering into crystal lattices upon grinding and it is a reversible process upon solvent loss.     

Experimental and Theoretical Insights into the Optical Properties and Intermolecular Interactions in Push-Pull Bromide Salts

Experimental and theoretical insights into the nature of intermolecular interactions and their effect on optical properties of 1-allyl-4-(1-cyano-2-(4-dialkylaminophenyl)vinyl)pyridin-1-ium bromide salts ( I and II ) are reported. A comparison of optical properties in solution and in the solid-state of the salts ( I and II ) with their precursors ( Ia and IIa ) is made. The experimental absorption maxima (λ_max) in CHCl₃ is at 528 nm for I and at 542 nm for II , and a strong bathochromic shift of ∼110 nm is observed for salts I and II compared with their precursors. The absorption bands in solid-state at ∼627 nm for I and at ∼615 nm for II that are assigned to charge transfer (CT) effect. The optical properties and single crystal structural features of I and II are explored by experimental and computational tools. The calculated λ_max and the CT are in good agreement with the experimental results. The intermolecular interactions existing in the crystal structures and their energies are quantified for various dimers by PIXEL, QTAIM and DFT approaches. Three types of interactions, (i) the cation⋅⋅⋅cation interactions, (ii) cation⋅⋅⋅anion interactions and (iii) anion⋅⋅⋅anion interactions are observed. The cationic moiety is mainly destabilized by C−H⋅⋅⋅N/π and π⋅⋅⋅π interactions whereas the cation and anion moiety is predominantly stabilized by strong C−H⋅⋅⋅Br⁻ interactions in both structures. The existence of charge transfer between cation and anion moieties in these structures is established through NBO analysis.     

Disparity between solution-phase equilibria and charge state distributions in positive-ion electrospray mass spectrometry

Two peptides, bradykinin and gramicidin S, were used to investigate the relationship between protonation in the solution phase and charge state distribution observed in electrospray ionization (ES) mass spectra. The degree of protonation in solution was estimated using acid-base equilibrium calculations where possible. Protonation in solution was varied by adjusting pH, solvent composition and peptide concentration. Major disparities were observed between calculated solution-phase peptide protonation and the charge state distributions observed in ES mass spectra. The [(M + 2H)²⁺]/[(M + H)⁺] ratio calculated in solution was larger than the abundance ratio (M + 2H)²⁺ /(M + H)⁺ in the ES mass spectra of all acidic aqueous (pH < 6.5) and non-aqueous solutions; in basic aqueous solutions (pH > 9.5) the opposite was true. At high pH, electrophoretic droplet charging may reduce the activity of OH^? in positively charged droplets. The results at low pH imply the existence of supplementary factors in the ES ionization process which largely attenuate the degree of charging in the gas phase as compared with solution. Factors such as the increasing intra- and intermolecular coulombic repulsion between charge carriers (protons) and increasing attractive forces between protonated sites and counterions at progressively later stages of charged droplet evaporation were hypothesized to be chiefly responsible for this effect. Non-aqueous solvents of high basicity compete with analytes to some extent for available protons, forming protonated solvent molecules while decreasing the sensitivity and the degree of multiple charging of peptides.     

Unveiling the Hidden,Dark, and Short Life of a Vibronic State in a Boron Difluoride Formazanate Dye

Boron difluoride (BF₂) formazanate dyes are contenders for molecular species that exhibit a large Stokes shift and bright red emission. Excitation of 3‐cyanoformazanate complexes with 10 μs wide pulses of specific wavelengths resulted in strong luminescence at 663 nm at both room temperature in solution and at 77 K in a frozen solution. Analysis of the short‐lived excitation spectrum from this luminescence shows that it arises from a vibronic manifold of a higher‐lying excited state. This dark state relaxes to the emitting state over 10 μs. TD‐DFT calculations of the two lowest‐energy excited states show that the relaxed geometries are planar for S₁ but highly distorted in S₂. The specific time‐ and wavelength‐dependence of the excitation profile provides a unique optical encryption capability through the comparison of emission intensities between adjacent vibronic bands only accessible in the 0–12 μs time domain.     

Water-induced luminescence improvement in a lanthanide β-diketone complex for monitoring water purity

Water-caused luminescence quenching is a well-known and intractable issue for luminescence lanthanide complexes, greatly confining their broad application as sensing and displaying devices in water system.Herein, an anionic and coordination-saturated lanthanide complex with a nanosheet-like structure has been prepared. It exhibits excellent photophysical properties both in solid state and in aqueous suspension. Noteworthily, a 13% improvement for sensitization efficiency from organic ligand to c...     

Unveiling the Hidden,Dark, and Short Life of a Vibronic State in a Boron Difluoride Formazanate Dye

Boron difluoride (BF₂) formazanate dyes are contenders for molecular species that exhibit a large Stokes shift and bright red emission. Excitation of 3‐cyanoformazanate complexes with 10 μs wide pulses of specific wavelengths resulted in strong luminescence at 663 nm at both room temperature in solution and at 77 K in a frozen solution. Analysis of the short‐lived excitation spectrum from this luminescence shows that it arises from a vibronic manifold of a higher‐lying excited state. This dark state relaxes to the emitting state over 10 μs. TD‐DFT calculations of the two lowest‐energy excited states show that the relaxed geometries are planar for S₁ but highly distorted in S₂. The specific time‐ and wavelength‐dependence of the excitation profile provides a unique optical encryption capability through the comparison of emission intensities between adjacent vibronic bands only accessible in the 0–12 μs time domain.     

Tuning Solid-State Luminescence in Conjugated Organic Materials: Control of Excitonic and Excimeric Contributions through π Stacking and Halogen Bond Driven Self-Assembly

Two polymorphs with distinctly different fluorescence emission (green and yellow; G, Y) emanating from excitonic and excimeric contributions were prepared from solution as well as by using physical vapour transport. Based on crystal structure investigations, the vibrationally-resolved excitonic emission is found to originate from a β-Sheet arrangement (G), whereas a sandwich herringbone structure is responsible for the excimer emission (Y). The intermolecular interactions and energies were quantified to have a complete picture of the decisive factors that controls the self-assembly. Halogen-bond directed self-assembly was explored to fine-tune the intermolecular interactions through co-crystallization as well as a commercially viable liquid assisted grinding method. A smooth fluorescence shift from G to Y was achieved by co-assembly due to substantial differences in the π orbital overlap in the molecular packing. Our investigation provides a comprehensive understanding of the origin of excitonic and excimeric contributions of emission behaviour in conjunction with the molecular packing and π–π orbital overlap, and might provide a directive towards the engineering of fluorescent functional molecular materials.     

Binuclear Copper(I) Complexes for Near-Infrared Light-Emitting Electrochemical Cells

Two binuclear heteroleptic Cu^I complexes, namely Cu−NIR1 and Cu−NIR2, bearing rigid chelating diphosphines and π-conjugated 2,5-di(pyridin-2-yl)thiazolo[5,4-d]thiazole as the bis-bidentate ligand are presented. The proposed dinuclearization strategy yields a large bathochromic shift of the emission when compared to the mononuclear counterparts (M1–M2) and enables shifting luminescence into the near-infrared (NIR) region in both solution and solid state, showing emission maximum at ca. 750 and 712 nm, respectively. The radiative process is assigned to an excited state with triplet metal-to-ligand charge transfer (³MLCT) character as demonstrated by in-depth photophysical and computational investigation. Noteworthy, X-ray analysis of the binuclear complexes unravels two interligand π–π-stacking interactions yielding a doubly locked structure that disfavours flattening of the tetrahedral coordination around the Cu^I centre in the excited state and maintain enhanced NIR luminescence. No such interaction is present in M1–M2. These findings prompt the successful use of Cu−NIR1 and Cu−NIR2 in NIR light-emitting electrochemical cells (LECs), which display electroluminescence maximum up to 756 nm and peak external quantum efficiency (EQE) of 0.43 %. Their suitability for the fabrication of white-emitting LECs is also demonstrated. To the best of our knowledge, these are the first examples of NIR electroluminescent devices based on earth-abundant Cu^I emitters.     

1,2,5-Triphenylpyrrole Derivatives with Dual Intense Photoluminescence in Both Solution and the Solid State: Solvatochromism and Polymorphic Luminescence Properties

Five organic luminophores, 1,2,5-triphenylpyrrole (TPP) derivatives 3 a – e bearing electron-withdrawing or electron-donating groups, have been synthesized by Pd-catalyzed Suzuki coupling of 1-phenyl-2,5-di(4′-bromophenyl)pyrrole and para-substituted phenylboronic acid derivatives. They possess good thermal stabilities with high decomposition temperatures above 310 °C. Investigation of the photophysical properties of the luminogens 3 a – e indicated that they exhibited dual intense photoluminescence in both solution and the solid state due to their twisted conformations, and their fluorescence quantum yields (Φ_F) were determined as 68.7–94.9 % in THF solution and 19.1–52.0 % in solid powder form. Compounds 3 a – c bearing electron-accepting groups exhibited remarkable solvatochromism with large Stokes shifts, attributable to their D-π-A structure and intramolecular charge-transfer effect. In particular, 3 a , bearing aldehyde groups, displayed an obvious red-shift of the emission band from 445 to 564 nm with increasing solvent polarity. However, no obvious solvatochromic behavior was observed for compounds 3 d , e bearing electron-donating groups. The luminophore 3 a exhibited polymorphic luminescence properties and crystallization-induced emission enhancement.