Unusual Luminescence Properties Research Articles

Unexpected Emission Behaviors of Rhodamine Derivatives in PVA After UV‒Green Light Excitation

AbstractRhodamine derivatives are a class of common fluorescent dyes and are usually co‐doped with room temperature phosphorescence (RTP) polymers for tuning colors; here, their unusual luminescence properties in polyvinyl alcohol are first disclosed. The doped polyvinyl alcohol (PVA) films are photo‐excited for 0.5‒1 min and emit orange and red afterglows with lifetimes of over 1 s at room temperature. More unexpectedly, the respective prompt and delayed room temperature emission colors and spectra are identical, and the red‐shifted afterglows are observed in liquid nitrogen, indicating that room temperature afterglow is thermally activated delayed fluorescence (TADF). Their molecular structure features and quantum chemical calculations support this inference. Impressively, the room temperature afterglows are visible light excitable up to 540 nm since the maximal and strong absorption bands are in green regions. Hence, this work discloses unknown excitation and emission properties of rhodamine derivatives and provides the really visible light excited yet intrinsic red TADF afterglows for the first time.

Giant Ln 30 -Cluster-Embedded Polyoxotungstate Nanoclusters with Exceptional Proton-Conducting and Luminescent Properties

Giant Ln ₃₀ -Cluster-Embedded Polyoxotungstate Nanoclusters with Exceptional Proton-Conducting and Luminescent Properties

Rotationally Assisted Spin-State Inversion in Carbene–Metal–Amides Is an Artifact

High-level quantum chemical calculations, presented in this Letter, show that the unusual luminescence properties of the high-performance thermally activated delayed fluorescence emitter CMA1, observed recently by Di et al. [ Science 2017, 356, 159-163 ], can be explained without resorting to the rotationally assisted spin-state inversion mechanism proposed by these authors. Multiconfiguration and relativistic effects lead to fast and efficient thermal equilibration of the excited singlet and triplet populations of this linear gold complex even for coplanar orientations of the ligands. The calculations predict S1 ⇝ T1 intersystem crossing outcompetes the submicrosecond fluorescence by 2 orders of magnitude, thus quenching prompt fluorescence. The significant time- and environment-dependent shifts of the CMA1 luminescence, observed in experiment, are attributed to effects of (hindered) solvent reorganization.

Unexpected Sole Enol‐Form Emission of 2‐(2′‐Hydroxyphenyl)oxazoles for Highly Efficient Deep‐Blue‐Emitting Organic Electroluminescent Devices

Considerable efforts have been devoted to the development of highly efficient blue light‐emitting materials. However, deep‐blue fluorescence materials that can satisfy the Commission Internationale de l'Eclairage (CIE) coordinates of (0.14, 0.08) of the National Television System Committee (NTSC) standard blue and, moreover, possess a high external quantum efficiency (EQE) over 5%, remain scarce. Here, the unusual luminescence properties of triphenylamine‐bearing 2‐(2′‐hydroxyphenyl)oxazoles (3a–3c) and their applications in organic light‐emitting diodes (OLEDs) are reported as highly efficient deep‐blue emitters. The 3a‐based device exhibits a high spectral stability and an excellent color purity with a narrow full‐width at half‐maximum of 53 nm and the CIE coordinates of (0.15, 0.08), which is very close to the NTSC standard blue. The exciton utilization of the device closes to 100%, exceeding the theoretical limit of 25% in conventional fluorescent OLEDs. Experimental data and theoretical calculations demonstrate that 3a possesses a highly hybridized local and charge‐transfer excited state character. In OLEDs, 3a exhibits a maximum luminance of 9054 cd m−2 and an EQE up to 7.1%, which is the first example of highly efficient blue OLEDs based on the sole enol‐form emission of 2‐(2′‐hydroxyphenyl)azoles.

Hybrid Perovskite Quantum Nanostructures Synthesized by Electrospray Antisolvent-Solvent Extraction and Intercalation.

Perovskites based on organometal lead halides have attracted great deal of scientific attention recently in the context of solar cells and optoelectronic devices due to their unique and tunable electronic and optical properties. Herein, we show that the use of electrospray technique in conjunction with the antisolvent-solvent extraction leads to novel low-dimensional quantum structures (especially 2-D nanosheets) of CH3NH3PbI3- and CH3NH3PbBr3-based layered perovskites with unusual luminescence properties. We also show that the optical bandgaps and emission characteristics of these colloidal nanomaterials can be tuned over a broad range of visible spectral region by compositional tailoring of mixed-halide (I- and Br-based) perovskites.

Alkaline Earth Metal Ion/Dihydroxy-Terephthalate MOFs: Structural Diversity and Unusual Luminescent Properties.

Alkaline earth (group 2) metal ion organic frameworks (AEMOFs) represent an important subcategory of MOFs with interesting structures and physical properties. Five MOFs, namely, [Mg2(H2dhtp)2(μ-H2O)(NMP)4] (AEMOF-2), [Mg2(H2dhtp)1.5(DMAc)4]Cl·DMAc (AEMOF-3), [Ca(H2dhtp)(DMAc)2] (AEMOF-4), [Sr3(H2dhtp)3(DMAc)6]·H2O (AEMOF-5), and [Ba(H2dhtp)(DMAc)] (AEMOF-6) (H4dhtp = 2,5-dihydroxy-terepthalic acid; DMAc = N,N-dimethylacetamide; NMP = N-methylpyrrolidone), are presented herein. The reported MOFs display structural variety with diverse topologies and new structural features. Interestingly, AEMOF-6 is the first example of a Ba(2+)-H2dhtp(2-) MOF, and AEMOF-5 is only the second known Sr(2+)-H2dhtp(2-) MOF. Detailed photoluminescence studies revealed alkaline earth metal ion-dependent fluorescence properties of the materials, with the heavier alkaline earth metal ions exhibiting red-shifted emission with respect to the lighter ions at room temperature. A bathochromic shift of the emission was observed for the MOFs (mostly for AEMOF-3 and AEMOF-4) at 77 K as a result of excited state proton transfer (ESIPT), which involves an intramolecular proton transfer from a hydroxyl to an adjacent carboxylic group of the H2dhtp(2-) ligand. Remarkably, AEMOF-6 displays rare yellow fluorescence at room temperature, which is attractive for solid state lighting applications. To probe whether the alkaline earth metal ions are responsible for the unusual luminescence properties of the reported MOFs, the potential energy surfaces (PESs) of the ground, S0, and lowest energy excited singlet, S1, states of model complexes along the intramolecular proton transfer coordinate were calculated by DFT and TD-DFT methods.

Unusual Ce3+ luminescence and Ce3+ → Tb3+ energy transfer behavior in strontium lithium borate SrLiB9O15

Ce3+ and Tb3+ ions are important activators for various phosphors, but no detailed study has been performed on SrLiB9O15 crystal. Ce3+- and Ce3+/Tb3+-doped SrLiB9O15 phosphors were synthesized by using a standard high temperature solid-state technique. The phase purity and optical properties of the prepared samples are investigated by XRD, excitation and emission spectra. The unusual luminescence properties of Ce3+ activator, the Ce3+ site occupying and Ce3+→Tb3+ energy transfer behavior are discussed.

Towards near-IR emissive rhenium tricarbonyl complexes: Synthesis and characterisation of unusual 2,2′-biquinoline complexes

Diethyl-2,2′-biquinoline-4,4′-dicarboxylate (debq) reacts with pentacarbonylbromorhenium in toluene to give fac-[Re(CO)3(debq)Br]; subsequent reaction with AgOTf in MeCN affords the cationic complex fac-[Re(CO)3(debq)(MeCN)]OTf. X-ray crystallographic data on fac-[Re(CO)3(debq)Br] show that the debq ligand is coordinated in a bidentate fashion at an angle of 32° from the equatorial plane of the complex: DFT calculations confirm this as the lowest energy conformation. fac-[Re(CO)3(debq)Br] and fac-[Re(CO)3(debq)(MeCN)]OTf both possess 1MLCT absorptions in the visible region, the former most red-shifted to ca. 465 nm. Both complexes demonstrated unusual luminescent properties: in solution, emission appears to be dominated by ligand-centred processes, whereas only 3MLCT emission, tailing into the near-IR, was observed in the solid state at 671 (τ = 59 ns) and 711 nm (τ = 19 ns) for fac-[Re(CO)3(debq)(MeCN)]OTf and fac-[Re(CO)3(debq)Br], respectively. However, the debq ligand is not labile in these complexes, which are robust to competing ligands and coordinating solvents.

Lewis Acidic Behavior of Fluorinated Organomercurials

Owing to their unusual Lewis acidic properties, the coordination chemistry of fluorinated organomercurials is attracting increasing interest. In this review, the authors focus on the synthesis, structures, and properties of neutral Lewis adducts involving fluorinated organomercurials such as (CF3)2Hg, (C6F5)HgCl, (C6F5)2Hg, and [(o-C6F4)Hg]3. While most of these organomercurials form adducts with common Lewis basic organic substrates, [(o-C6F4)Hg]3 also interacts with aromatic hydrocarbons, alkynes, N-heterocycles, and metallocenes to form π-complexes. In some cases, this complexation mode results in the formation of supramolecules with unusual luminescence properties or microporosity.

Selected-Control Hydrothermal Synthesis and Formation Mechanism of Monazite- and Zircon-Type LaVO4 Nanocrystals

Selective-controlled structure and shape of LaVO(4) nanocrystals were successfully synthesized by a simple hydrothermal method without the presence of catalysts or templates. It was found that tuning the pH of the growth solution was a crucial step for the control of the structure transformation, that is, from monoclinic (m-) to tetragonal (t-) phase, and morphology evolution of LaVO(4) nanocrystals. Further studies demonstrated that the morphology of the product had a strong dependence on the initial lanthanum sources. In the La(NO(3))(3) or LaCl(3) reaction system, pure t-LaVO(4) nanorods with uniform diameters about 10 nm could be obtained. But when using La(2)(SO(4))(3) as the lanthanum source, we can get t-LaVO(4) nanowiskers with broomlike morphology. The detailed systematic study had shown that a special dissolution-recrystallization transformation mechanism as well as an Ostwald ripening process was responsible for the phase control and anisotropic morphology evolution of the LaVO(4) nanocrystals. As a result, the controlled synthesis of m- and t-LaVO(4) not only has great theoretical significance in studying the polymorph control and selective synthesis of inorganic materials but also benefits the potential applications based on LaVO(4) nanocrystals owing to the unusual luminescent properties induced by structural transformation.

Pi-complexation of biphenyl, naphthalene, and triphenylene to trimeric perfluoro-ortho-phenylene mercury. Formation of extended binary stacks with unusual luminescent properties.

Trimeric perfluoro-ortho-phenylene mercury (1) crystallizes from CS(2) as a pure compound. In the crystal, 1 forms staggered cofacial dimers (centroid distance of 3.38 A). In the dimer, the individual components are associated via long mercury-pi interactions (3.443 < Hg...C < 3.650 A). Interestingly, this arrangement leads to the existence of relatively short intermolecular mercury-mercury distances (3.811 < Hg...Hg < 4.093 A). In this form, compound 1 is photoluminescent and exhibits a broad emission band with a maximum at 440 nm and a shoulder at 530 nm. Compound 1 interacts with biphenyl, naphthalene, or triphenylene to form 1.biphenyl (2), 1.naphthalene (3), and 1.triphenylene (4), respectively. These adducts have been characterized by elemental analysis and X-ray crystallography. Their structure reveals the existence of stacks in which molecules of 1 and molecules of arenes alternate. In each stack, secondary pi-interactions occur between the arene and the mercury centers of 1. The resulting Hg...C distances range from 3.25 to 3.55 A and are within the sum of the van der Waals radii. They reflect the presence of secondary polyhapto-pi interactions occurring between the electron-rich aromatic molecules and the acidic mercury centers. In the case of the triphenylene adduct 4, a arene-fluoroarene interaction is also observed (centroid distance of 3.605 A). Compounds 2-4 are photoluminescent. The emission observed for 2 and 3 corresponds to the phosphorescence of the aromatic substrate and suggests the occurrence of a mercury heavy atom effect. In the case of 4, the emission appears at longer wavelengths than those typically observed for triphenylene.

Disordered superlattices

A disordered superlattice (d-SL) is a kind of disordered crystalline semiconductor in which atomic alignment is disordered in some directions but ordered in other directions. The d-Sl exhibits remarkable luminescence capability and artificial disordering along one direction. (AlGaAs)(AlGaAs), (AlP)(GaP) and (SiGe)Si d-SLs are grown. The temperature dependence of (AlGaAs)(AlGaAs) photoluminescence (PL) is described. The disordered effect appears most strongly in the (AlAs)(GaAs) d-SL. The (AlP)(GaP) d-SL emits electroluminescence 4.5 times more strongly than the bulk alloy and the ordered sublattice. The (SiGe) Si d-SL also emits enhanced luminescence. For further improvement, increases in the band offset and in the total number of monolayers in the superlattice are required. The physical mechanism for the unusual luminescence properties of a d-SL is discussed in terms of carrier localization and confinement. A d-SL can be suggested to be a promising material for the enhancement of the luminescence capability.

One-dimensional migration of 3MLCT (metal-to-ligand charge transfer) excitation energy in chloro(6-phenyl-2,2'-bipyridine)palladium(+)

Unusual luminescence properties below 80 K are reported for Pd{sup II}(phbpy)Cl (phbpy = 6-phenyl-2,2{prime}-bipyridine). Interpretation of the luminescent data indicated that the nature of the luminescent state is triplet metal-to-ligand charge transfer as in Ru(bpy){sup 2+}{sub 3}. The luminescence spectrum is shown to be dependent on the wavelength of excitation, and the decay rate of the excited species increased considerably between 5 and 41 K. 11 refs., 3 figs.

Unusual luminescent properties of odd‐ and even‐substituted naphthyl‐derivatized dioxetanes

With the advent of enzymatically induced chemiluminescence and improved instrumentation for luminometry, ultrasensitive detection of a wide variety of analytes is now possible using standard immunoassay and DNA probe formats. Model molecular orbital calculations and literature precedent suggest that the singlet efficiencies observed upon decomposition of dioxetanes appended with donor substituted aromatic moieties are dependent on substitution pattern. We have recently discovered, in a series of 3-(2'-spiroadamantane)-4-methoxy-4-acetoxynaphth-2'-yl-1,2-+ ++dioxetanes, that enzymatic generation of a non-conjugated, charge transfer excited state results in luminescence of markedly different properties than that observed from an isomeric, conjugated excited state. An example of the former type, 3-(2'-spiroadamantane)-4-methoxy-4-(7"-acetoxy)naphth-2'-yl- 1,2- dioxetane (1) emitting at 550 nm, not only provides an increase in phi CL, but exhibits a dramatic bathochromic shift of 80-110 nm from the 460 nm emission of the conjugated isomer 3-(2'-spiroadamantane)-4-methoxy-4-(6"-acetoxy)naphth-2'-yl- 1,2-dioxetane (2). These developments, along with the attendant glow-type luminescence kinetics displayed during the enzymatic decomposition of the new 'odd-pattern' dioxetane, allow the design of simple protocols capable of simultaneous or 'multichannel' detection of several analytes.

The nature of the long-wave bands in the emission spectra of aromatic o-hydroxycarboxylic acids and their derivatives

The reasons for the simultaneous presence of two emission bands, blue and red, in the fluorescence spectra of certain aromatic o-hydroxycarboxylic acids and their derivatives have been examined. It was shown that the unusual luminescence properties of these compounds were determined by the large differences in energy of the intramolecular hydrogen bonds in the normal and excited electronic states. The long-wave luminescence bands in similar cases are the result of optical transitions in the high frequency sublevels of the ground electronic state (sometimes in the dissociaton region of the hydrogen bond).