Solution Photoluminescence Research Articles

Intramolecular non-covalent interactions as a strategy towards controlled photoluminescence in copper(i) complexes

Easily accessible N-donor ligands enable tunable photoluminescence via steric modifications.

Possibility of adjusting the photoluminescence spectrum of Ca scheelites to the emission spectrum of incandescent lamps: [nCaWO4–(1–n)CaMoO4]: Eu3+ solid solutions

The specific features of the photoluminescence of [nCaWO4–(1–n)CaMoO4]:Eu3+ solid solutions with the scheelite structure are examined using X-ray phase analysis and photoluminescence, Raman scattering, and diffuse reflectance spectroscopy. The studied features are associated with a change in the long- and short-range orders of the crystal lattice upon variations in the composition of solutions in the range n = 0–1.0 (with a pitch of 0.2) at a concentration of red photoluminescence activator Eu3+ of 2 mol %. The mechanism of the modification of photoluminescence of solid solutions upon variations in their composition has been discussed. Anomalies in the variations in parameters of the crystal lattice, its short-range order, and luminescence spectra have been observed in the transition from pure compounds CaMoO4:Eu3+ and CaWO4:Eu3+ to solutions; the concentration of Eu3+ ions in the centrosymmetric localization increases (decreases) in the transition from the molybdate (tungstate). It has been demonstrated that the spectral radiant emittance of solid solution [0.4CaWO4–0.6CaMoO4]:Eu3+ (2 mol %) is the closest to that of an incandescent lamp.

Blue-Emitting Arylalkynyl Naphthalene Derivatives via a Hexadehydro-Diels-Alder Cascade Reaction.

We describe here three alkynyl substituted naphthalenes that display promising luminescence characteristics. Each compound is easily and efficiently synthesized in three steps by capitalizing on the hexadehydro-Diels-Alder (HDDA) cycloisomerization reaction in which an intermediate benzyne is captured by tetraphenylcyclopentadienone, a classical trap for benzyne itself. These compounds luminesce in the deep blue when stimulated either optically (i.e., photoluminescence in both solution and solid films) or electrically [in a light-emitting diode (LED)]. The photophysical properties are relatively insensitive to the electronic nature of the substituents (H, OMe, CO2Me) that define these otherwise identical compounds. Overall, our observations suggest that the twisted nature of the five adjacent aryl groups serves to minimize the intermolecular interaction between core naphthalene units in different sample morphologies. These compounds represent promising leads for the identification of others of value as the emissive component of organic LEDs (OLEDs).

Photo- and Electroluminescence of Substituted Divinyl Dibenzothiophene Sulfone

The spectral properties of two substituted divinyl dibenzothiophene sulfone in solutions of tetrahydrofuran, polyvinylcarbazole films, and films obtained by thermal vacuum deposition are investigated. The ability of these compounds in thin-layer ITO/PEDOT:PSS/NPD/L/Ca/Al and ITO/PEDOT:PSS/PVK+L/Ca/Al structures (L denotes the examined luminophore) to emit radiation at applied voltage is investigated. It is shown that the spectra of photo- and electroluminescence in the film have a strong red shift of ~100 nm compared to the photoluminescence in solutions. It is suggested that radiation belongs to excimers.

Two new hetero-dinuclear nickel(II)/zinc(II) complexes with compartmental Schiff bases: Synthesis, characterization and self assembly

Two compartmental Schiff bases, H2L1 [N,N′-bis(3-methoxysalicylidene)propane-1,3-diamine] and H2L2 [N,N′-bis(3-methoxysalicylidene)-2,2-dimethylpropane-1,3-diamine], have been utilized to prepare two hetero-dinuclear nickel(II)/zinc(II) complexes, [(DMSO)2NiL1Zn(NCS)2] (1) and [(DMSO)2NiL2Zn(NCS)2] (2). Both complexes have been characterized by elemental and spectral analysis. Single crystal X-ray diffraction analysis has confirmed their structures. The key step in the synthesis of these complexes is to use nickel(II) thiocyanate tetrahydrate and zinc(II) acetate dihydrate in a single pot. In each complex, octahedral nickel(II) is placed in the inner N2O2 compartment (with DMSO molecules being coordinated in the axial sites) and tetrahedral zinc(II) is placed in the outer O4 compartment of the Schiff bases. Supramolecular interactions in both complexes were explored. Both complexes show photoluminescence in DMSO solution at room temperature upon the irradiation of ultraviolet light. The life times of the excited states are in the range of 4–5ns.

The Lone-Pair Stereochemistry and Its Effect on Supramolecular Interaction of Dinuclear Pb(II) Dicarboxylate Compound With 2,6-Bis(benzimidazolyl)pyridine

A dinuclear Pb(II) dicarboxylate compound with 2,6-bis(benzimidazolyl)pyridine has been synthesized under hydrothermal condition. Single-crystal X-ray diffraction analysis shows that the arrangement of the half deprotonated H2bbp ligand and carboxylate groups displays a coordination gap around the Pb(II) ion, occupied possibly by a stereoactive lone pair of electrons on Pb(II) ion, the coordination environment around the lead atoms being hemidirected. The coordination sphere of a unique dinuclear Pb(II) complex is controlled by lone pair activity, weak Pb···O interactions, π-π interaction, and the hydrogen bond. Strong bathochromic shift effect on the solution and solid-state photoluminescence of complex is influenced by the above weak interactions. CCDC: 841895.

Effect of pH of Synthesis on CdS/L-cys Colloidal Solutions Optical Properties

Using the measurements of absorption spectra and photoluminescence, as well as electron microscopic studies, the limits of concentrations of cadmium and sulfur ions and the stabilizer L-cysteine, suitable for obtaining stable colloidal solutions of quantum dots (size 1 - 5 nm) with CdS and high quantum yield. The influence of the initial pH values ​​of the reaction system within 7 - 11 on the absorption edge, photoluminescence and quantum yield of colloidal solutions of CdS / L-cis nanoparticles is shown. The results were systematized using the simplex lattice design of the Chefe method.

Peripheral halo-functionalization in [Cu(N^N)(P^P)]+ emitters: influence on the performances of light-emitting electrochemical cells.

A series of heteroleptic [Cu(N^N)(P^P)][PF6] complexes is described in which P^P = bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) and N^N = 4,4'-diphenyl-6,6'-dimethyl-2,2'-bipyridine substituted in the 4-position of the phenyl groups with atom X (N^N = 1 has X = F, 2 has X = Cl, 3 has X = Br, 4 has X = I; the benchmark N^N ligand with X = H is 5). These complexes have been characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses and cyclic voltammetry; representative single crystal structures are also reported. The solution absorption spectra are characterized by high energy bands (arising from ligand-centred transitions) which are red-shifted on going from X = H to X = I, and a broad metal-to-ligand charge transfer band with λmax in the range 387-395 nm. The ten complexes are yellow emitters in solution and yellow or yellow-orange emitters in the solid-state. For a given N^N ligand, the solution photoluminescence (PL) spectra show no significant change on going from [Cu(N^N)(POP)]+ to [Cu(N^N)(xantphos)]+; introducing the iodo-functionality into the N^N domain leads to a red-shift in λ compared to the complexes with the benchmark N^N ligand 5. In the solid state, [Cu(1)(POP)][PF6] and [Cu(1)(xantphos)][PF6] (fluoro-substituent) exhibit the highest PL quantum yields (74 and 25%, respectively) with values of τ1/2 = 11.1 and 5.8 μs, respectively. Light-emitting electrochemical cells (LECs) with [Cu(N^N)(P^P)][PF6] complexes in the emissive layer have been tested. Using a block-wave pulsed current driving mode, the best performing device employed [Cu(1)(xantphos)]+ and this showed a maximum luminance (Lummax) of 129 cd m-2 and a device lifetime (t1/2) of 54 h; however, the turn-on time (time to reach Lummax) was 4.1 h. Trends in performance data reveal that the introduction of fluoro-groups is beneficial, but that the incorporation of heavier halo-substituents leads to poor devices, probably due to a detrimental effect on charge transport; LECs with the iodo-functionalized N^N ligand 4 failed to show any electroluminescence after 50 h.

Dual Stimulus-responsive Fluorescence Behavior and Mechanism of P(NIPAM-co-RhBHA)-NP

In the present study, based on spectral overlap between 1,8-naphthalimide and N-acrylyl-N'-rhodamine B acylhy- drazine thiourea (RhBHA), reversible on-off ring reaction of RhBHA at various pH values, and thermosensitive property of poly(N-isopropyl acrylamide) (PNIPAM), a novel linear polymer P(NIPAM-co-RhBHA)-NP was prepared via a series of chemical reactions. Firstly, 4-(2-aminoethyl)amino-N-aminopropane-1,8-naphthalimide (NP-NH2) and RhBHA were prepared respectively, and they were used as the donor and acceptor to construct a fluorescence resonance energy transfer (FRET) system. Secondly, incorporating RhBHA into PNIPAM by reversible addition-fragmentation chain transfer polymerization (RAFT), P(NIPAM-co-RhBHA) was synthesized. Finally, P(NIPAM-co-RhBHA)-NP was fabricated by amide condensation between NP-NH2 and the as-prepared P(NIPAM-co-RhBHA). The structure of P(NIPAM-co-RhBHA)-NP was characterized via 1 H NMR, FTIR, UV-vis and GPC. The fluorescence responsive behavior of the polymer to environmental temperature and pH value was investigated by photoluminescence (PL) in buffer solutions, and the mechanism was discussed in detail. The results indicate that, in an acidic solution, energy can be transferred from NP-NH2 moieties to RhBHA moieties via FRET mechanism, either pH values or environmental temperatures play important roles to affect the fluorescence emission of P(NIPAM-co-RhBHA)-NP. Keywords 1,8-naphthalimide; N-acrylyl-N'-rhodamine B acylhydrazine thiourea; poly(N-isopropyl acrylamide); fluores- cence resonance energy transfer; stimulus-responsive polymer

Emission properties and Cu(i)-Cu(i) interaction in 2-coordinate dicopper(i)-bis(N-heterocyclic)carbene complexes.

The synthesis, characterization, and emission properties of 2-coordinate dicopper(i) complexes bearing two trimethylene-bridged bis-NHC ligands, [Cu2(L3Me)2](PF6)2 (1), [Cu2(L3Et)2](PF6)2 (2), [Cu2(L3Bu)2](PF6)2 (3), [Cu2(L3MeOPh)2](PF6)2 (4) and [Cu2(L3Mes)2](PF6)2 (5), where L3R denotes trimethylene-bridged bis(N-heterocyclic)carbene (NHC) ligand substituted by two R groups at the nitrogen atoms of NHC, have been investigated. The quantum yield, Φ, and the lifetime, τ, of the emission of 2, are 0.21 and 25 μs, respectively in methanol, which is a well-known solvent for quenching the luminescence of many copper(i) complexes. The 8-shaped geometry of the dicopper(i) complexes brings a considerable copper(i)-copper(i) interaction which affects the luminescent properties. Additionally, we find that methoxyphenyl and mesityl groups substituted at the nitrogen atom of the NHC moiety drastically stabilize the bis(NHC) copper(i) complexes even in air-saturated acetone-d6.

Solid-state and solution photoluminescence of platinum(ii) complexes with 4′-substituted terpyridine ligands – structural, spectroscopic and electrochemical studies

Platinum(II) complexes with the formula [PtCl(L)]CF3O3S (where L = 4′-(4-chlorophenyl)-2,2′:6′,2′′-terpyridine (L1), 4′-(4-bromophenyl)-2,2′:6′,2′′-terpyridine (L2), and 4′-(benzothiophene-2-yl)-2,2′:6′,2′′-terpyridine (L3)) were synthesized from precursor [Pt(PhCN)2Cl2] and characterized by FT-IR, NMR, UV-vis spectroscopy, X-ray crystallography and electrochemical studies. The emission properties of the coordination compounds were studied in solution and in the solid state at ambient temperature and in methanol : ethanol frozen glass matrices at 77 K. The quantum yields of fluorescence, lifetimes and the nature of the excited states were described on the basis of the molecular properties of the compounds. To elucidate the structural, spectroscopic and bonding properties of the obtained compounds, calculations at the DFT level were undertaken. Coordination compounds are emissive in both solution and solid states. Emission energies and the character of excited states in solution are governed by the donor–acceptor properties of the 4′ substituent of the terpyridine core. The emission properties in the solid state are attributed to the aggregation induced phenomenon. Moreover, the compounds [PtCl(L1)]CF3O3S and [PtCl(L2)]CF3O3S display a bathochromic shifted emission corresponding to J-aggregation (head-to-head Pt⋯Pt interactions), while in the case of compound [PtCl(L3)]CF3O3S a hypsochromic shifted emission compared to that in solution is characteristic of the H-aggregation process (head-to-tail Pt⋯π interaction). The coordination compounds display a strong rigidochromic effect with decay times changing from the ps/ns scale at ambient conditions to the μs domain in frozen glass matrices.

Solid state and solution photoluminescence properties of a novel meso–meso-linked porphyrin dimer Schiff base ligand and its metal complexes

We prepared novel meso-meso linked 4-bromo-2,6-bis[5-(4-iminophenyl)-10,15,20-triphenylporphyrin]phenol (HL) and its Cu(II), Fe(III), Mn(III), Pt(II) and Zn(II) transition metal complexes. Structural characterizations of the ligand (HL) and its metal complexes were done by the spectroscopic and analytical methods. The electronic absorption and photoluminescence spectra of the ligand, its metal complexes and the metal salts used for preparing of the complexes were investigated in the solid and solution state. The emission and excitation data of the CuCl2·2H2O in both solid and the solution state were obsrved in the longest wavelenght. On the other hand, the emission value of the ZnCl2 salt was shown at the shortest wavelenght. The emission values of the [LCu4Cl3(H2O)2]H2O and LPt4Cl3 complexes in the solid state are bigger than the other metal salts. The ligand and its metal complexes show the very interesting absorption spectral properties in the solid state. Metal complexes have less number Q bands in the solid state. The electrochemical properties of the ligand and its metal complexes were investigated and found that they show the reversible or irreversible redox processes at the different scan rates. Thermal properties of the compopunds were investigated in the 20–900°C temperature range.

Structure, luminescence and antimicrobial properties of mononuclear silver(I) complexes of pyridine 2-carboxamide

Two Ag(I) complexes, [Ag(HL)2]ClO4 (1) and [Ag(HL)2]NO3⋅H2O (2), where HL is pyridine 2–carboxamide, have been synthesized and characterized by various spectroscopic techniques. The X-ray crystal structural analyses indicate that both the complexes consist of slightly distorted square planar silver(I) ions and ligand-supported weak Ag ⋯⋅Ag metallophilic interactions. Both the complexes show photoluminescence in solid state and acetonitrile solution at room temperature. Antimicrobial studies have been performed with these silver(I) complexes against various gram + ve, gram −ve bacterial and fungal species.

Preparation of concentrated monodisperse colloidal solutions of CdTe nanocrystals

Processes of preparation of concentrated colloidal solutions of CdTe nanocrystals (NCs) stabilized by thioglycolic acid (TGA) and of subsequent sedimentation precipitation of monodisperse fractions from the initial polydisperse solutions have been studied. Spectra of optical absorption and of photoluminescence of colloidal solutions of CdTe NCs have been studied experimentally immediately after the completion of synthesis and after postsynthesis treatment.

Highly efficient microwave-assisted synthesis of photoactive polyamides bearing 5-(3-acetoxynaphthoylamino)benzamide moieties

A novel aromatic dicarboxylic acid monomer, 5-[4-(3-acetoxynaphthoylamino)benzoylamino]isophthalic acid, was prepared in five steps. The direct polycondensation of this dicarboxylic acid with several aromatic diamines was performed under microwave irradiation and conventional heating in the presence of triphenyl phosphite/pyridine/ N-methyl-2-pyrrolidone/calcium chloride. The polymerization reactions were effectively preceded, and the resulting novel photoactive polyamides (PAs) were obtained in high yields and moderate inherent viscosities in the range of 0.32–0.58 dL g−1. Thermogravimetric analysis results showed that polymers were thermally stable, 10% weight loss temperatures were in excess of 430°C and 488°C, and char yields at 800°C under nitrogen atmosphere were higher than 62%. The resulting polymers exhibited ultraviolet–visible absorption bands at 268 and 312 nm in N,N-dimethylformamide (DMF) solution. Their photoluminescence in DMF solution demonstrated fluorescence emission bands maxima around 367 and 429 nm for all of the PAs.

Polymeric nanocomposites loaded with fluoridated hydroxyapatite Ln(3+) (Ln = Eu or Tb)/iron oxide for magnetic targeted cellular imaging.

ObjectiveTo fabricate polymeric nanocomposites with excellent photoluminescence, magnetic properties, and stability in aqueous solutions, in order to improve specificity and sensitivity of cellular imaging under a magnetic field.MethodsFluoridated Ln3+-doped HAP (Ln3+-HAP) NPs and iron oxides (IOs) can be encapsulated with biocompatible polymers via a modified solvent exaction/evaporation technique to prepare polymeric nanocomposites with fluoridated Ln3+-HAP/iron oxide. The nanocomposites were characterized for surface morphology, fluorescence spectra, magnetic properties and in vitro cytotoxicity. Magnetic targeted cellular imaging of such nanocomposites was also evaluated with confocal laser scanning microscope using A549 cells with or without magnetic field.ResultsThe fabricated nanocomposites showed good stability and excellent luminescent properties, as well as low in vitro cytotoxicity, indicating that the nanocomposites are suitable for biological applications. Nanocomposites under magnetic field achieved much higher cellular uptake via an energy-dependent pathway than those without magnetic field.ConclusionThe nanocomposites fabricated in this study will be a promising tool for magnetic targeted cellular imaging with improved specificity and enhanced selection.

New semi-conducting rotaxane based on β-cyclodextrin and anthracene moieties

A new rotaxane (BPAAn/β-CD), consisting of an anthracene-based semi-conducting material (BPAAn) encapsulated into β-cyclodextrin (β-CD), has been synthesized via the Williamson reaction in solvent-free conditions. The supramolecular structure of the compound was confirmed by NMR and FT-IR spectroscopies. The optical and morphological properties of this organic material were investigated by UV–visible absorption, photoluminescence spectroscopy and atomic force microscopy. BPAAn/β-CD film has an optical gap of 2.9eV and exhibits green photoluminescence. An optical gap of 2.9eV was estimated from the absorption edge of the rotaxane thin film. The BPAAn/β-CD exhibits a blue photoluminescence in dilute solution; whereas, a green emission was observed in the solid state, due to the π–π interaction in the anthracene moieties. The rotaxane shows a significantly enhanced PL quantum yield and improved film quality in comparison with the free BPAAn. The HOMO and LUMO levels were estimated using cyclic voltammetry analysis, and show enhanced electron affinity of the BPAAn in its complexed form. A single-layer device with the configuration [ITO/rotaxane/Aluminum] has been elaborated and showed low turn-on voltage of 5V.

High efficiency and optical anisotropy in double-heterojunction nanorod light-emitting diodes.

Recent advances in colloidal quantum dot light-emitting diodes (QD-LEDs) have led to efficiencies and brightness that rival the best organic LEDs. Nearly ideal internal quantum efficiency being achieved leaves light outcoupling as the only remaining means to improve external quantum efficiency (EQE) but that might require radically different device design and reoptimization. However, the current state-of-the-art QD-LEDs are based on spherical core/shell QDs, and the effects of shape and optical anisotropy remain essentially unexplored. Here, we demonstrate solution-processed, red-emitting double-heterojunction nanorod (DHNR)-LEDs with efficient hole transport exhibiting low threshold voltage and high brightness (76,000 cd m(-2)) and efficiencies (EQE = 12%, current efficiency = 27.5 cd A(-1), and power efficiency = 34.6 lm W(-1)). EQE exceeding the expected upper limit of ∼ 8% (based on ∼ 20% light outcoupling and solution photoluminescence quantum yield of ∼ 40%) suggests shape anisotropy and directional band offsets designed into DHNRs play an important role in enhancing light outcoupling.

A green light emitting polymer in a PMMA matrix: oligo(azomethine-ether) \newlinewith benzothiazole moieties

This study aimed to synthesize an oligo(azomethine-ether) with benzothiazole moiety in organic medium by means of chemical oxidative polycondensation (OP). Optical properties were examined by photoluminescence (PL) and UV-Vis measurements both in solutions and solid film involved a poly (methyl methacrylate) (PMMA) matrix. Oligomer film in the PMMA matrix emitted a fine green light with a fluorescence quantum yield (QY) of 3.30%. Spectral and thermal observations showed a high rate of C--O--C coupling (cross-linking) for the oligomer. SEC results indicated low molecular weight (\sim3200--4650 g mol^{-1}) and the oligomer was soluble in organic solvents with high polarity. Electrochemical behavior was characterized by cyclic voltammetry (CV), morphological properties by scanning electron microscopy (SEM), and thermal characteristics by TG-DTA and DSC techniques.

Functional carbazole liquid-crystal block codendrimers with optical and electronic properties.

The synthesis and characterisation of a family of block codendrimers consisting of highly versatile mesogenic and carbazole-containing 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) dendrons are reported. The liquid-crystal behaviour was investigated by means of differential scanning calorimetry, polarised-light optical microscopy and X-ray diffraction. Depending on the chemical structure of the constituent dendrons, the codendrimers show lamellar or columnar mesophases. On the basis of the experimental results, models both at the molecular level and in the mesophase are proposed. The physical properties of the block codendrimers derived from the presence of the carbazole moiety in their structure were investigated: photoluminescence in solution and in the mesophase, electrochemical behaviour and hole transport. Electrodeposition of carbazole dendrons afforded a globular supramolecular conformation in which the mesogenic molecular side plays a key role.