Search results for "luminescence."
showing 10 items of 1568 documents
Impact of the use of sterically congested Ir(III) complexes on the performance of light-emitting electrochemical cells
2018
International audience; The synthesis, structural and optoelectronic characterization of a family of sterically congested cyclometalated cationic Ir(iii) complexes of the form [Ir(C^N)2(dtBubpy)]PF6 (with dtBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine and C^N = a cyclometalating ligand decorated at the 4-position of the pyridine ring and/or the 3-position of the phenyl ring with a range of sterically bulky substituents) are reported. This family of complexes is compared to the unsubstituted analogue complex R1 bearing 2-phenylpyridinato as cyclometalating ligand. The impact of sterically bulky substituents on the C^N ligands on both the solid state photophysics and light-emitting electrochemi…
Bulky, Dendronized Iridium Complexes and their Photoluminescence
2019
Solution-processed blue emitters are essential for low-cost organic light-emitting diodes (OLEDs) but still face challenges due to their poor color purity, low efficiency and limited operational stability. Herein, by extending the conjugation of ultraviolet-emissive, facial tris(diphenylbenzimidazolyl)iridium (Ir) (fac-(dpbic)3Ir), we introduce two new types of solution-processed emitters, i.e. triisopropylsilylethynyl(TIPSE)-substituted fac-(dpbic)3Ir (2) and fac-(dpbic)3Ir-based polyphenylene dendrimers D1 and D2. The emissions of Ir-complex 2 and the dendrimers were successfully pushed toward a pure and sky blue color, respectively, due to the dominant 3π–π* nature of their emissive exci…
Triphosphine-supported bimetallic Au(I)-M(I) (M = Ag, Cu) alkynyl clusters.
2014
The reactions of gold acetylides (AuC2R)n with triphosphine ligands PPh2-(CH2)n-PPh-(CH2)2-PPh2 (n = 1, dpmp; 2, dpep) in the presence of M(+) ions (M = Cu, Ag) lead to an assembly of the heterometallic clusters, the composition of which is determined by the steric bulkiness of the alkynyl groups and the flexibility of the phosphine motifs. For R = Ph, an unprecedented hexanuclear complex [Au5Cu(C2R)4(dpmp)2](2+) (1) was isolated, while for the aliphatic alkynes (R = 1-cyclohexanolyl, 2-borneolyl, 2,6-dimethyl-4-heptanolyl) a family of compounds based on a tetrametallic framework was prepared, [Au3Cu(C2R)3(dpmp)](+) (2, R = 1-cyclohexanolyl), [Au3M(C2R)3(dpep)]2(+2) (3, M = Cu, R = 1-cycloh…
Study of Confined 5-Aza[5]helicene in Ytterbium(III) Bis(2-ethylhexyl) Sulfosuccinate Reversed Micelles
2007
Some relevant physicochemical properties of 5-aza[5]helicene (H5) in solutions of ytterbium bis(2-ethylhexyl) sulfosuccinate (Yb(DEHSS)3) reversed micelles have been investigated by UV-vis-NIR, photoluminescence, and FT-IR techniques with the aim of emphasizing the role played by specific Yb(III)/H5 interactions and confinement effects as driving forces of its binding to reversed micelles, preferential solubilization site, and local photophysical properties. It has been found that the binding strength of 5-aza[5]helicene to reversed micelles, triggered by steric and orientational constrains as well as the water content, is mainly regulated by its interaction with the Yb(III) counterion. Mor…
Luminescence of localized states in silicon dioxide glass. A short review
2011
Abstract The target is the description of the properties of localized states in silica glass, which relate to aspects of short-to-intermediate-range order. It has been observed that laser light interaction with localized states of silica glass leads to the creation of luminescence centers. Created luminescence centers, excited with laser light, provide intra-center luminescence of oxygen deficient centers (ODC) comprising a blue band at 2.7 eV and a UV band at 4.4 eV. Structurally, these ODCs are understood to comprise twofold-coordinated silicons that are commonly part of some larger local structure, and their luminescence bands can be suppressed by reaction with chlorine or hydrogen. Besi…
Regioisomerism in cationic sulfonyl-substituted [Ir(C^N)2(N^N)]+ complexes: its influence on photophysical properties and LEC performance
2016
A series of regioisomeric cationic iridium complexes of the type [Ir(C^N)2(bpy)][PF6] (bpy = 2,2'-bipyridine) is reported. The complexes contain 2-phenylpyridine-based cyclometallating ligands with a methylsulfonyl group in either the 3-, 4- or 5-position of the phenyl ring. All the complexes have been fully characterized, including their crystal structures. In acetonitrile solution, all the compounds are green emitters with emission maxima between 493 and 517 nm. Whereas substitution meta to the Ir-C bond leads to vibrationally structured emission profiles and photoluminescence quantum yields of 74 and 77%, placing a sulfone substituent in a para position results in a broad, featureless em…
Multiscale Investigation of the Structural, Electrical and Photoluminescence Properties of MoS2 Obtained by MoO3 Sulfurization
2022
In this paper, we report a multiscale investigation of the compositional, morphological, structural, electrical, and optical emission properties of 2H-MoS2 obtained by sulfurization at 800 °C of very thin MoO3 films (with thickness ranging from ~2.8 nm to ~4.2 nm) on a SiO2/Si substrate. XPS analyses confirmed that the sulfurization was very effective in the reduction of the oxide to MoS2, with only a small percentage of residual MoO3 present in the final film. High-resolution TEM/STEM analyses revealed the formation of few (i.e., 2–3 layers) of MoS2 nearly aligned with the SiO2 surface in the case of the thinnest (~2.8 nm) MoO3 film, whereas multilayers of MoS2 partially standing up with r…
Micrometer-size crystalline monolayer MoS2 domains obtained by sulfurization of molybdenum oxide ultrathin films
2023
In this work, the formation of micrometer-size crystalline monolayer (1L) MoS2 flakes with triangular shape and a central multilayer core is obtained by the sulfurization at 800 °C of pre-deposited ultrathin MoOx films (1.2–1.8 nm) on c-sapphire substrates. The thickness uniformity, crystalline quality, doping and strain distribution in the MoS2 flakes as a function of the initial MoOx thickness was evaluated by micro-Raman (μR) mapping. The excellent crystalline quality of the triangular 1L-MoS2 flakes was confirmed by micro-photoluminescence (μPL) maps, showing a very intense peak at ∼1.85 eV, that decreases in the central part, as expected for multilayers MoS2. A biaxial strain of ∼0.38–…
Strong Emission Enhancement in pH‐Responsive 2:2 Cucurbit[8]uril Complexes
2019
Organic fluorophores, particularly stimuli-responsive molecules, are very interesting for biological and material sciences applications, but frequently limited by aggregation- and rotation-caused photoluminescence quenching. A series of easily accessible bipyridinium fluorophores, whose emission is quenched by a twisted intramolecular charge-transfer (TICT) mechanism, is reported. Encapsulation in a cucurbit[7]uril host gave a 1:1 complex exhibiting a moderate emission increase due to destabilization of the TICT state inside the apolar cucurbituril cavity. A much stronger fluorescence enhancement is observed in 2:2 complexes with the larger cucurbit[8]uril, which is caused by additional con…
Luminescence from nearly isolated surface defects in silica nanoparticles
2015
A structured emission/excitation pattern, proper of isolated defects, arises in a vacuum from silica nanoparticles. The luminescence, centered around 3.0-3.5 eV, is characterised by a vibronic progression due to the phonon coupling with two localised modes of frequency ∼1370 cm(-1) and ∼360 cm(-1), and decays in about 300 ns at 10 K. On increasing the temperature, the intensity and the lifetime decrease due to the activation of a non-radiative rate from the excited state. Concurrently, the temperature dependence of the lineshape evidences the low coupling with non-localised modes of the matrix (Huang-Rhys factor S ~ 0.2) and the poor influence of the inhomogeneous broadening. These findin…