Structured Emission Band Research Articles

Luminescent Diimine-Pt(IV) Complexes with Axial Phenyl Selenide Ligands

Luminescent diimine-Pt(IV) complexes [Pt(N^N)(Me)2(PhSe)2], (N^N = 2,2′-bipyridine (bpy, 1b), 1,10-phenanthroline (phen, 2b), and 4,4′-dimethyl-2,2′-bipyridine (Me2bpy, 3b), PhSe− = phenyl selenide were prepared and identified using multinuclear (1H, 13C{1H} and 77Se{1H}) NMR spectroscopy. The PhSe− ligands were introduced through oxidative addition of diphenyl diselenide to the non-luminescent Pt(II) precursors [Pt(N^N)(Me)2], N^N = (bpy, 1a), (phen, 2a), (Me2bpy, 3a), to give the luminescent Pt(IV) complexes 1b–3b. The UV-vis absorption spectra of 1b–3b are characterised by intense bands in the range 240–330 nm. We assigned them to transitions of essentially π−π* character with small metal and PhSe− ligand contributions with the help of TD-DFT (time-dependent density functional theory) calculations. The weak long-wavelength bands in the range 350–475 nm are of mixed ligand-to-metal charge transfer (L’MCT) (n(Se)→d(Pt)/intra-ligand charge transfer (IL’CT) (n(Se)→π*(Ph) or π(Ph)→π*(Ph))/ligand-to-ligand’ charge transfer (LL’CT) (L = N^N, L’ = PhSe−, M = Pt and n = lone pair) character. The Pt(IV) complexes showed broad emission bands in the solid state at 298 and 77 K, peaking at 560–595 nm with a blue shift upon cooling. Structured emission bands were obtained in the range 450–600 nm, with the maxima depending on the N^N ligands and the solvent polarity (CH2Cl2 vs. dimethyl sulfoxide (DMSO) and aqueous tris(hydroxymethyl)aminomethane hydrochloride (tris-HCl) buffer). The emissions originate from essentially ligand-centred triplet states (3LC) with mixed IL’CT/L’MCT contributions as concluded from the DFT calculation. Such dominating PhSe contributions to the emissive states are unprecedented in the world of luminescent diimine-Pt(IV) complexes.

Ionic liquids-based organo nano-fluorosensor for fast and selective detection of sarin gas surrogate, diethylchlorophosphate

This work intends to develop a sensitive and easily applicable ionic liquid (IL) based fluorimetric sensor for detecting sarin surrogate, diethylchlorophosphate (DCP) in solution and gas phases, respectively. We have designed and synthesized a pyrene butyrate anion-based IL (PBIL) from the sodium salt of pyrene butyrate and trihexyltetradecylphosphonium chloride (P66614Cl) by a simple ion exchange mechanism. By utilizing reprecipitation methods, PBIL-based nanoparticles, nPBIL, has been fabricated. Various conventional analytical techniques have confirmed the formations of PBIL and nPBIL. The as-prepared nPBIL shows a structured emission band from 300 to 420 nm along with an excimer-like emission range from 420 nm to 600 nm and displays bright cyan color photoluminescence because of the stacking of pyrene moieties in a nanocrystalline fashion. Interestingly, due to the introduction of DCP in the water-suspended nPBIL, there is a slight (6 nm) blue shift in the UV–visible absorption spectra with an immediate reduction in Mie-scattering. Simultaneously, there is a gradual decrease in excimer-like emission with a synchronized increase in monomeric emission with the steady introduction of DCP in the water-suspended solution of nPBIL due to the formation of a phosphorylated product. The limit of detection (LOD) utilizing our as-fabricated organo nanosensor, nPBIL, towards the detection of DCP is estimated to be 7.32 µM and found to be superior to many chemosensors available in the literature. An nPBIL-stained test kit experiment has also been demonstrated as a carriable and visible photonic device for the on-site detection of DCP within the assembly of other analogous harmful analytes. Also, a dip-stick analysis has been performed for selective recognization of DCP vapor. The effectiveness of nPBIL in identifying and quantifying DCP demonstrated its potential for usage as a photonic device for practical sample investigation.

Photophysical Study on the Rigid Pt(II) Complex [Pt(naphen)(Cl)] (Hnaphen = Naphtho[1,2-b][1,10]Phenanthroline and Derivatives.

The electrochemistry and photophysics of the Pt(II) complexes [Pt(naphen)(X)] (Hnaphen = naphtho[1,2-b][1,10]phenanthroline, X = Cl or C≡CPh) containing the rigid tridentate C^N^N-coordinating pericyclic naphen ligand was studied alongside the complexes of the tetrahydro-derivative [Pt(thnaphen)(X)] (Hthnaphen = 5,6,8,9-tetrahydro-naphtho[1,2-b][1,10]phenanthroline) and the N^C^N-coordinated complex [Pt(bdq)(Cl)] (Hbdq = benzo[1,2-h:5,4-h’]diquinoline. The cyclic voltammetry showed reversible reductions for the C^N^N complexes, with markedly fewer negative potentials (around −1.6 V vs. ferrocene) for the complexes containing the naphen ligand compared with the thnaphen derivatives (around −1.9 V). With irreversible oxidations at around +0.3 V for all of the complexes, the naphen made a difference in the electrochemical gap of about 0.3 eV (1.9 vs. 2.2 eV) compared with thnaphen. The bdq complex was completely different, with an irreversible reduction at around −2 V caused by the N^C^N coordination pattern, which lacked a good electron acceptor such as the phenanthroline unit in the C^N^N ligand naphen. Long-wavelength UV-Vis absorption bands were found around 520 to 530 nm for the C^N^N complexes with the C≡CPh coligand and were red-shifted when compared with the Cl derivatives. The N^C^N-coordinated bdq complex was markedly blue-shifted (493 nm). The steady-state photoluminescence spectra showed poorly structured emission bands peaking at around 630 nm for the two naphen complexes and 570 nm for the thnaphen derivatives. The bdq complex showed a pronounced vibrational structure and an emission maximum at 586 nm. Assuming mixed 3LC/3MLCT excited states, the vibronic progression for the N^C^N bdq complex indicated a higher LC character than assumed for the C^N^N-coordinated naphen and thnaphen complexes. The blue-shift was a result of the different N^C^N vs. C^N^N coordination. The photoluminescence lifetimes and quantum yields ΦL massively increased from solutions at 298 K (0.06 to 0.24) to glassy frozen matrices at 77 K (0.80 to 0.95). The nanosecond time-resolved study on [Pt(naphen)(Cl)] showed a phosphorescence emission signal originating from the mixed 3LC/3MLCT with an emission lifetime of around 3 µs.

Novel NIR-Phosphorescent Ir(III) Complexes: Synthesis, Characterization and Their Exploration as Lifetime-Based O2 Sensors in Living Cells.

A series of [Ir(N^C)2(N^N)]+ NIR-emitting orthometalated complexes (1–7) has been prepared and structurally characterized using elemental analysis, mass-spectrometry, and NMR spectroscopy. The complexes display intense phosphorescence with vibrationally structured emission bands exhibiting the maxima in the range 713–722 nm. The DFT and TD DFT calculations showed that the photophysical characteristics of these complexes are largely determined by the properties of the metalating N^C ligands, with their major contribution into formation of the lowest S1 and T1 excited states responsible for low energy absorption and emission, respectively. Emission lifetimes of 1–7 in degassed methanol solution vary from 1.76 to 5.39 µs and show strong quenching with molecular oxygen to provide an order of magnitude lifetime reduction in aerated solution. The photophysics of two complexes (1 and 7) were studied in model physiological media containing fetal bovine serum (FBS) and Dulbecco’s Modified Eagle Medium (DMEM) to give linear Stern-Volmer calibrations with substantially lower oxygen-quenching constants compared to those obtained in methanol solution. These observations were interpreted in terms of the sensors’ interaction with albumin, which is an abundant component of FBS and cell media. The studied complexes displayed acceptable cytotoxicity and preferential localization, either in mitochondria (1) or in lysosomes (7) of the CHO-K1 cell line. The results of the phosphorescence lifetime imaging (PLIM) experiments demonstrated considerable variations of the sensors’ lifetimes under normoxia and hypoxia conditions and indicated their applicability for semi-quantitative measurements of oxygen concentration in living cells. The complexes’ emission in the NIR domain and the excitation spectrum, extending down to ca. 600 nm, also showed that they are promising for use in in vivo studies.

Photoluminescence of Ni(II), Pd(II), and Pt(II) Complexes [M(Me2dpb)Cl] Obtained from C‒H Activation of 1,5-Di(2-pyridyl)-2,4-dimethylbenzene (Me2dpbH).

The three complexes [M(Me2dpb)Cl] (M = Ni, Pd, Pt) containing the tridentate N,C,N-cyclometalating 3,5-dimethyl-1,5-dipyridyl-phenide ligand (Me2dpb−) were synthesised using a base-assisted C‒H activation method. Oxidation potentials from cyclic voltammetry increased along the series Pt < Ni < Pd from 0.15 to 0.74 V. DFT calculations confirmed the essentially ligand-centred π*-type character of the lowest unoccupied molecular orbital (LUMO) for all three complexes in agreement with the invariant reduction processes. For the highest occupied molecular orbitals (HOMO), contributions from metal dyz, phenyl C4, C2, C1, and C6, and Cl pz orbitals were found. As expected, the dz2 (HOMO-1 for Ni) is stabilised for the Pd and Pt derivatives, while the antibonding dx2−y2 orbital is de-stabilised for Pt and Pd compared with Ni. The long-wavelength UV-vis absorption band energies increase along the series Ni < Pt < Pd. The lowest-energy TD-DFT-calculated state for the Ni complex has a pronounced dz2-type contribution to the overall metal-to-ligand charge transfer (MLCT) character. For Pt and Pd, the dz2 orbital is energetically not available and a strongly mixed Cl-to-π*/phenyl-to-π*/M(dyz)-to-π* (XLCT/ILCT/MLCT) character is found. The complex [Pd(Me2dpb)Cl] showed a structured emission band in a frozen glassy matrix at 77 K, peaking at 468 nm with a quantum yield of almost unity as observed for the previously reported Pt derivative. No emission was observed from the Ni complex at 77 or 298 K. The TD-DFT-calculated states using the TPSSh functional were in excellent agreement with the observed absorption energies and also clearly assessed the nature of the so-called “dark”, i.e., d‒d*, excited configurations to lie low for the Ni complex (≥3.18 eV), promoting rapid radiationless relaxation. For the Pd(II) and Pt(II) derivatives, the “dark” states are markedly higher in energy with ≥4.41 eV (Pd) and ≥4.86 eV (Pt), which is in perfect agreement with the similar photophysical behaviour of the two complexes at low temperatures.

Melt Growth and Physical Properties of Bulk LaInO3 Single Crystals

Large bulk LaInO3 single crystals are grown from the melt contained within iridium crucibles by the vertical gradient freeze (VGF) method. The obtained crystals are undoped or intentionally doped with Ba or Ce, and enabled wafer fabrication of size 10 × 10 mm2. High melting point of LaInO3 (≈1880 °C) and thermal instability at high temperatures require specific conditions for bulk crystal growth. The crystals do not undergo any phase transition up to 1300 °C, above which a noticeable thermal decomposition takes place. The good structural quality of the crystals makes them suitable for epitaxy. The onset of strong optical absorption shows orientation‐dependent behavior due to the orthorhombic symmetry of the LaInO3 crystals. Assuming direct transitions, optical bandgaps of 4.35 and 4.39 eV are obtained for polarizations along the [010] and the [100], [001] crystallographic directions, respectively. There is an additional weak absorption in the range between 2.8 and 4 eV due to oxygen vacancies. Density‐functional‐theory calculations support the interpretation of the optical absorption data. Cathodoluminescence spectra show a broad, structured emission band peaking at ≈2.2 eV. All bulk crystals are electrically insulating. The relative static dielectric constant is determined at a value of 24.6 along the [001] direction.

A Single-Component Supramolecular Organic Framework with Efficient Ultralong Phosphorescence

Supramolecular organic frameworks (SOFs), due to the atomically precise integration of the repeated building units, exhibit intriguing properties and consequently potential applications in chemical...

Investigation of extreme ultraviolet spectra from highly charged holmium ions in 1 μ m laser-produced plasmas

Absolute intensity calibrated extreme ultraviolet spectra radiated by highly charged holmium (Ho) ions from 1 μm Nd:YAG laser generated plasmas in the 1–8 nm wavelength spectral range were measured and investigated. The spectral features show a broad structured continuum-like emission band, most prominent in the wavelength range 6–8 nm, which accounts for more than half of the emitted power. Assuming local thermodynamic equilibrium (LTE) in the laser produced plasmas and using the flexible atomic code and Cowan suite of codes, the wavelengths and LTE-gA values of unresolved transition arrays (UTAs) from E 1-contributing transition arrays 4p–4d, 4d–4f and super transition arrays such as 4p64d k−14f + 4p54d k+1–4p64d k−24f2 + 4p44d k+2 + 4p54d k 4f and 4d10(5s5p) k 4f m−k –4d9(5s5p) k 4f m−k+1 were calculated and shown to be responsible for the strongest observed spectral structure. Transitions between these excited to excited states are considered, since even if only weakly present, they will not be influenced by opacity effects unlike resonance transitions involving ground configurations. Another two intense continuous emission bands at 3–6 nm and 2–3 nm that dominate the spectra in the shorter wavelength range mainly arise from 4d–5p, 4d5s–4d5s5p, 4f–5g, 4f5s–4f5s5g and 4d–5f, 4d5s–4d5s5f, 4p–5s transitions. Spectral line shape parameters of Gaussian fits to the LTE-gA weighted radiation spectra of each Ho ion were given, enabling direct explanation of recorded spectra. Based on the LTE-gA UTAs formalism parameters, reasonable agreement is obtained between the synthetic spectrum and experimental result enabling some of the observed spectral features to be identified.

Aromatic β‐Diketone as a Novel Anchoring Ligand in Iridium(III) Complexes for Dye‐Sensitized Solar Cells

A novel β‐diketone ligand bearing a thiophene moiety and an anchoring Ph‐COOCH3 unit has been designed, prepared and used in synthesis of cyclometalated benzimidazole‐based iridium(III) complexes for application in dye‐sensitized solar cells (DSSC). The replacement of traditional 4,4'‐dicarboxy‐2,2'‐bipyridine by this aromatic β‐diketone results in excellent tuning the redox potentials and excited state properties of these IrIII complexes, one of which exhibits good efficiency when used as a dye in DSSC. All the complexes demonstrate reversible redox behavior, with oxidation potentials (Ir4+/Ir3+) strongly depending on the electron‐donor/withdrawing nature of the substituents in the cyclometalated ligands. Surprisingly, the latter has just a little effect on their luminescence spectra, in which structured emission bands are observed. Time‐resolved spectroscopic studies in combination with DFT calculations show that the complexes emit light by mixed 3MLCT–3LC excited states predominantly composed of the diketone ligand‐centered triplet state.

Quinolone Complexes with Lanthanide Ions: An Insight into their Analytical Applications and Biological Activity.

Quinolones comprise a series of synthetic bactericidal agents with a broad spectrum of activity and good bioavailability. An important feature of these molecules is their capacity to bind metal ions in complexes with relevant biological and analytical applications. Interestingly, lanthanide ions possess extremely attractive properties that result from the behavior of the internal 4f electrons, behavior which is not lost upon ionization, nor after coordination. Subsequently, a more detailed discussion about metal complexes of quinolones with lanthanide ions in terms of chemical and biological properties is made. These complexes present a series of characteristics, such as narrow and highly structured emission bands; large gaps between absorption and emission wavelengths (Stokes shifts); and long excited-state lifetimes, which render them suitable for highly sensitive and selective analytical methods of quantitation. Moreover, quinolones have been widely prescribed in both human and animal treatments, which has led to an increase in their impact on the environment, and therefore to a growing interest in the development of new methods for their quantitative determination. Therefore, analytical applications for the quantitative determination of quinolones, lanthanide and miscellaneous ions and nucleic acids, along with other applications, are reviewed here.

A double rollover cycloplatinated(ii) skeleton: a versatile platform for tuning emission by chelating and non-chelating ancillary ligand systems.

Described here is the synthesis and characterization of heteroleptic binuclear platinum(ii) complexes of the type [Pt2(μ-bpy-2H)(S^S)2] and [Pt2(μ-bpy-2H)(L)2(X)2], containing a 2,2'-bipyridine-based double rollover cycloplatinated core (Pt(μ-bpy-2H)Pt), in combination with the anionic S^S- chelate ligands di(ethyl)dithiocarbamate (dedtc) and O,O'-di(cyclohexyl)dithiophosphate (dcdtp) or non-chelating L/X ancillary ligands (PPh3/Me, t-BuNC/Me, PPh3/SCN and PPh3/N3). The new complexes were characterized using multinuclear (1H, 31P and 195Pt) NMR spectroscopy and some of them additionally using single crystal X-ray diffraction. The absorption and photoluminescence of the complexes show a strong dependence on the ancillary ligands. Upon excitation at 365 nm, in a CH2Cl2 rigid matrix (77 K), the complexes exhibit structured emission bands with λmax between 488 nm and 525 nm and vibrational spacing around 1350 cm-1, indicating the excited states centered on the cyclometalated ligand (3ILCT) with some mixing 3MLCT characteristics. In the case of the PPh3/N3 complex, a dual emission band (orange color) is observed in the solid state at 298 K for which the low energy band arises from an aggregation-induced emission (AIE). Upon lowering the temperature (77 K), thermochromism is observed (orange to yellow) which is accompanied by the intensification of the high energy band (ligand-centered structured band). Finally, in order to rationalize the obtained photophysical data, complete DFT (density functional theory) and TD-DFT (time-dependent DFT) calculations were performed on the selected complexes.

Metalated Ir(III) Complexes Based on the Luminescent Diimine Ligands: Synthesis and Photophysical Study.

A series of novel diimine (N∧N) ligands containing developed aromatic [2,1- a]pyrrolo[3,2- c]isoquinoline system have been prepared and used in the synthesis of Ir(III) luminescent complexes. In organic solvents, the ligands display fluorescence which depends strongly on the nature of solvents to give moderate to strong orange emission in aprotic solvents and shows a considerable blue shift and substantial increase in emission intensity in methanol. Insertion of electron-withdrawing and -donating substituents into peripheral phenyl fragment has nearly no effect onto emission parameters. The ligands were successfully used to prepare the metalated [Ir(N∧C)2(N∧N)]+ complexes (where N∧C = phenylpyridine (N∧C-1), p-tolylpyridine (N∧C-2), 2-(benzo[ b]thiophen-2-yl)pyridine (N∧C-3), 2-benzo[ b]thiophen-3-yl)pyridine (N∧C-4), and methyl 2-phenylquinoline-4-carboxylate (N∧C-5)) using standard synthetic procedures. The complexes obtained display moderate to strong phosphorescence in organic solvents; the emission characteristics is determined by the nature of emissive triplet state, which varies substantially with the variations in the structure and donor properties of the C- and N-coordinating functions in metalating ligands. TD-DFT calculations show that for complexes 1, 2, and 4 the emission originates from the mixed 3MLCT/3LLCT excited states with the major contribution from the aromatic moiety of the diimine ligand, whereas in 3 the emissive triplet manifold is mainly located at the N∧C ligand to give structured emission band typical for the ligand centered (LC) excited state. In the case of 5, the phosphorescence may be also assigned to the mixed 3MLCT/3LLCT excited state; however, the major contribution is attributed to the aromatic moiety of the metalating N∧C ligand.

Highly Stable and Efficient Light-Emitting Electrochemical Cells Based on Cationic Iridium Complexes Bearing Arylazole Ancillary Ligands.

A series of bis-cyclometalated iridium(III) complexes of general formula [Ir(ppy)2(N∧N)][PF6] (ppy- = 2-phenylpyridinate; N∧N = 2-(1H-imidazol-2-yl)pyridine (1), 2-(2-pyridyl)benzimidazole (2), 1-methyl-2-pyridin-2-yl-1H-benzimidazole (3), 2-(4'-thiazolyl)benzimidazole (4), 1-methyl-2-(4'-thiazolyl)benzimidazole (5)) is reported, and their use as electroluminescent materials in light-emitting electrochemical cell (LEC) devices is investigated. [2][PF6] and [3][PF6] are orange emitters with intense unstructured emission around 590 nm in acetonitrile solution. [1][PF6], [4][PF6], and [5][PF6] are green weak emitters with structured emission bands peaking around 500 nm. The different photophysical properties are due to the effect that the chemical structure of the ancillary ligand has on the nature of the emitting triplet state. Whereas the benzimidazole unit stabilizes the LUMO and gives rise to a 3MLCT/3LLCT emitting triplet in [2][PF6] and [3][PF6], the presence of the thiazolyl ring produces the opposite effect in [4][PF6] and [5][PF6] and the emitting state has a predominant 3LC character. Complexes with 3MLCT/3LLCT emitting triplets give rise to LEC devices with luminance values 1 order higher than those of complexes with 3LC emitting states. Protecting the imidazole N-H bond with a methyl group, as in complexes [3][PF6] and [5][PF6], shows that the emissive properties become more stable. [3][PF6] leads to outstanding LECs with simultaneously high luminance (904 cd m-2), efficiency (9.15 cd A-1), and stability (lifetime over 2500 h).

New fluorescent metal receptors based on 4,4′-carbonyl bis(carbamoylbenzoic) acid analogues with naphthalene fluorophore

In this manuscript is described a research related with two ditopic receptors based on 4,4′-carbonyl bis(carbamoylbenzoic) acids bearing a naphthyl (2a) and naphthylmethyl fluorophores (2b), which interact with metal ions. The fluorescence properties of both receptors were influenced by the connectivity with the amide group. The non-spaced receptor 2a presents an electron delocalisation from the amide to the naphthyl group having a broad red-shifted emission band and high quantum yield. The spaced receptor 2b presented a photo-induced electron transfer (PET) process from the amide to the naphthyl group, and a structured emission band is present at the UV region with low quantum yield. The different chemical structure influenced the fluorescent response used to analyse the coordination with metallic ions. The 2a receptor has an ON–OFF response because of the inhibition of the ICT process. The 2b receptor shows an OFF–ON response because of the inhibition of the PET process. Additional analytical studies by 1H-NMR and FTIR demonstrated the strong interaction of the amide and carboxylic functional groups with the metallic ions. Competitive experiments with EDTA showed that a very stable complexes are obtained between metallic ions and the new receptors.

Solvatochromism and turn-off fluorescence sensing property of N,N′-bis(3-pentyl)perylene-3, 4, 9, 10-bis(dicarboximide) towards nitroaromatics and photophysical study of its microstructures

Here, we report solvatochromic effect of N,N′-bis(3-pentyl)perylene-3, 4, 9, 10-bis(dicarboximide) [EP-PDI] in THF-DMF mixture. Fibroid like microstructure of EP-PDI has been synthesized by re-precipitation method using SDS as morphology directing soft template. Morphology of the particles is characterized using optical and scanning electronic microcopy (SEM). Photophysical properties of the aggregated hydrosol and also the solvatochromic effect of EP-PDI are carried out using UV–vis, steady state and time-resolved fluorescence study. The fluorescence spectra of EP-PDI in THF show structured emission band and aggregated hydrosol exhibits E-type and Y-type excimer emission. The intense fluorescence emission property of EP-PDI is used for sensing the presence of nitroaromatics in the medium. Among the different nitroaromatics, picric acid (PA) strongly quenches the fluorescence emission intensity of EP-PDI and this quenching property of PA is being used to detect PA in THF having concentration as low as 3.0μM. The mechanism of this quenching has been explained due to ground state complexation between EP-PDI and PA.

Binuclear Complexes and Extended Chains Featuring Pt(II)-Tl(I) Bonds: Influence of the Pyridine-2-Thiolate and Cyclometalated Ligands on the Self-Assembly and Luminescent Behavior.

Platinum solvate complexes [Pt(C6F5)(C^N)(S)] [C^N = phenylpyridinyl (ppy), S = dimethyl sulfoxide (DMSO) (A); C^N = benzoquinolinyl (bzq), S = CH3COCH3 (B)] react with [Tl(Spy)] (Spy = 2-pyridinethiolate) to afford binuclear [{Pt(C6F5)(C^N)}Tl(Spy)] [C^N = ppy (1) and bzq (2)] species containing a Pt-Tl bonding interaction, supported by a μ-Spy-κN,S bridging ligand, as confirmed by X-ray diffraction. However, the related reactions with [Tl(SpyCF3-5)] [SpyCF3-5 = 5-(trifluoromethyl)-2-pyridinethiolate] give neutral extended chains [{Pt(C6F5)(C^N)}Tl(SpyCF3-5)]n [C^N = ppy (3) and bzq (4)]. 3 features a zigzag -Pt-Tl···S-Pt- chain, generated by Pt-Tl and Tl···S bonds, with the SpyCF3 acting as a μ-κN:κ(2)S bridging ligand, whereas 4 displays an unsupported ···Tl-Pt···Tl-Pt··· backbone (angle of ca. 158.7°). The lowest-energy absorption bands in the UV-vis spectra in CH2Cl2, associated with (1)L'LCT transitions with minor (1)LC/(1)MLCT (L' = Spy or SpyCF3-5; L = C^N) character, are similar for all complexes 1-4, demonstrating that for 3 and 4 the chains break down in solution to yield similar bimetallic Pt-Tl units. For 2, two different forms, 2-o (orange) and 2-y (yellow), exhibiting different colors and emissions were found depending on the isolation conditions. Slow crystallization favors formation of the thermodynamically more stable yellow form (2-y), which exhibits a high-energy (HE) structured emission band, whereas fast crystallization gives rise to the orange form (2-o), with a remarkably lower energy structureless emission. Complexes 1 and 3 exhibit dual luminescence in the solid state at 298 K: an unstructured low-energy band associated with (3)ππ* excimeric emission due to π···π (C^N) interactions and a more structured HE band, assigned, with support of density functional theory calculations, to an intraligand (3)LC (C^N) excited state mixed with some ligand (SPy)/platinum-to-ligand (C^N)(3)[(L' + M)LCT] charge transfer. Chain 4 only shows a HE band at 298 K, attributed to a (3)L'LCT (SpyCF3 → bzq) excited state mixed with a minor (3)MLCT/(3)MM'CT (M = Pt; M' = Tl) contribution. At 77 K, the ππ*-stacking emission is predominant in all complexes, except in the form 2-y. Interestingly, 2-4 exhibit reversible mechanochromic color and luminescence changes, with remarkable red shift and increased quantum yields, and upon exposure to solvents, they are restored to their original color and emission. On the basis of powder X-ray diffraction studies, a plausible mechanism of the mechanochromic processes is proposed, involving reversible crystalline-to-amorphous phase transitions.

Newly designed luminescent di- and tetra-nuclear double rollover cycloplatinated(II) complexes

The known binuclear complex [Pt2(μ-bpy-2H)(Me)2(DMSO)2], 1, in which bpy = 2,2′-bipyridine and DMSO = dimethyl sulfoxide, was reacted with 2 equiv bis(diphenylphosphino)methane, dppm, to give the new double rollover cycloplatinated(II) complex [Pt2(μ-bpy-2H)(Me)2(κ1-dppm)2], 2, in which each metallic center bears a monodentate dppm ligand. The reaction of 2 with 2 equiv of the known monomeric cycloplatinated (II) complex [Pt(Me)(bhq-H)(SMe2)], in which bhq = 7,8-benzo[h]quinoline, gave the new unsymmetrical tetranuclear complex [{(bhq-H)(Me)Pt(μ-dppm)Pt(Me)}2(μ-bpy-2H)], 3. The complexes were fully characterized using multinuclear (1H and 31P{1H}) NMR spectroscopy and elemental analysis. Photophysical properties of the synthesized complexes were investigated and the results were confirmed by DFT calculations. The complexes 1–3 are brightly luminescent in solution and solid state. The complex 1 exhibits structured emission band, complying with the cyclometalated ligand being the centered emissive state. The complexes 2 and 3, however, exhibit unstructured emission bands, confirming a large amount of MLCT in their emissive states.

New Iridium Complex Coordinated with Tetrathiafulvalene Substituted Triazole-pyridine Ligand: Synthesis, Photophysical and Electrochemical Properties.

A new iridium(III) complex based on the triazole-pyridine ligand with tetrathiafulvalene unit, [Ir(ppy)2(L)]PF6 (1), has been synthesized and structurally characterized. The absorption spectra, luminescent spectra and electrochemical behaviors of L and 1 have been investigated. Complex 1 is found to be emissive at room temperature with maxima at 481 and 510 nm. The broad and structured emission bands are suggested a mixing of 3LC (3π-π*) and 3CT (3MLCT) excited states. The influence of iridium ion coordination on the redox properties of the TTF has also been investigated by cyclic voltammetry.

Thienylpyridine-based cyclometallated iridium(iii) complexes and their use in solid state light-emitting electrochemical cells

The synthesis and characterization of four iridium(iii) complexes [Ir(thpy)2(N^N)][PF6] where Hthpy = 2-(2'-thienyl)pyridine and N^N are 6-phenyl-2,2'-bipyridine (1), 4,4'-di-(t)butyl-2,2'-bipyridine (2), 4,4'-di-(t)butyl-6-phenyl-2,2'-bipyridine (3) or 4,4'-dimethylthio-2,2'-bipyridine (4) are described. The single crystal structures of ligand 4 and the complexes containing the [Ir(thpy)2(1)](+) and [Ir(thpy)2(4)](+) cations have been determined. In [Ir(thpy)2(1)](+), the pendant phenyl ring engages in an intra-cation π-stacking interaction with one of the thienyl rings in the solid state, and undergoes hindered rotation on the NMR timescale in [Ir(thpy)2(1)](+) and [Ir(thpy)2(3)](+). The solution spectra of [Ir(thpy)2(1)][PF6] and [Ir(thpy)2(4)][PF6] show emission maxima around 640 nm and are significantly red-shifted compared with [Ir(thpy)2(2)][PF6] and [Ir(thpy)2(3)][PF6] which have structured emission bands with maxima around 550 and 590 nm. In thin films, the emission spectra of the four complexes are similar with emission peaks around 550 and 590 nm and a shoulder around 640 nm that are reminiscent of the features observed in solution. In solution, quantum yields are low, but in thin films, values range from 29% for [Ir(thpy)2(1)][PF6] to 51% for [Ir(thpy)2(4)][PF6]. Density functional theory calculations rationalize the structured emission observed for the four complexes in terms of the (3)LC nature predicted for the lowest-energy triplet states that mainly involve the cyclometallated [thpy](-) ligands. Support for this theoretical result comes from the observed features of the low temperature (in frozen MeCN) photoluminescence spectra of the complexes. Photoluminescence and electroluminescence spectra of the complexes in a light-emitting electrochemical cell (LEC) device configuration have been investigated. The electroluminescence spectra are similar for all [Ir(thpy)2(N^N)][PF6] complexes with emission maxima at ≈600 nm, but device performances are relatively poor probably due to the poor charge-transporting properties of the complexes.

Analysis of the quasicontinuum band emitted by highly ionised tungsten atoms in the 4–7 nm range

Spectra emitted by highly ionized tungsten atoms from magnetically confined plasmas show a common feature: a narrow structured quasi-continuum emission band most prominent in the range 4−7 nm, which accounts for 40−80% of the radiated power. This band has been fairly well explained by unresolved transitions from groups 4d-4p, 4f-4d (Δn = 0) and 5d-4f, 5g-4f and 5p-4d (Δn = 1). In this work we use a Multi-Configuration Dirac-Fock code in Breit self-consistent field mode to compute level energies and transition probabilities for W27+ to W37+ ions contributing to this emission band. Intra-shell correlation was introduced in the calculation for both initial and final states and all dipole and quadrupole radiative transitions have been considered. The wavefunctions in the initial and final states are optimized separately and the resulting non-orthogonality effect is fully taken into account. The importance of some satellite lines was assessed. Together with the ionic distributions obtained by using the FLYCHK application and assuming that the initial states population depends statistically on the temperature we were able to synthesize plasma emission spectrum profiles for several electron temperatures.