Dynamic Luminescence Research Articles

High-contrast flicker luminescence on dynamic covalent structure based nanoaggregates

In nanoscience, molecular switches have played a significant role to deliver different control abilities to practical functions, whereas high-contrast luminescence switchable manipulation at nanoscale is still limited. Since the tuning for emission behavior with high contrast ratio strongly connects to numerous visualized sensing and optoelectronic applications, we here report that autonomous pH control can be enrolled to address a high-contrast molecular emission change at the nanoaggregated level, for gaining a flicker luminescence performance in aqueous media. Employing a BODIPY contained dynamic covalent dye, we find its luminescent signal and nanoaggregate size can be spontaneously adjusted in water. On this basis, high-contrast luminescence switching of the material can be achieved upon the alternate introduction of base and acid into the aggregation state. Such a behavior can be attributed to a pH triggered photo-induced electron transfer regulation process. The dye aggregates can be well endocytosed for bioimaging and its luminescent variation can be autonomously displayed as a flicker effect. These results provide new visions for the design and development of smart materials with a dynamic luminescence behavior.

Band structure, photochemical properties and luminescence characteristics of (Ni,F)-doped α-Bi2O3 nanorods via facile hydrothermal synthesis

(Ni,F)-doped α-Bi2O3 nanomaterials were successfully prepared via a facile hydrothermal reaction route. The well-crystallized nanorods have a diameter of 50–150 nm and a length of 1–2.5 µm. The phase formations were studied via x-ray powder diffraction (XRD) together with structural Rietveld refinements. The incorporations of Ni2+ and F− ions in α-Bi2O3 lattices were discussed in relation to the energy dispersive x-ray analysis, x-ray photoelectron spectroscopy and XRD measurements. The band structure of α-Bi2O3 was greatly modified via Ni2+-, F−-codoping in the lattices, resulting in a red shift of the optical absorption edge and a narrowed band energy from 2.8 eV to 2.46 eV. Compared with the direct-allowed feature of pure α-Bi2O3, the indirect transition was shown in the (Ni,F)-doped sample. The valence band and conduction band of (Ni,F)-doped α-Bi2O3 were the hybridized (Bi6s+O2p+Ni3d) and (Bi6p+Ni3d), respectively. The photocatalytic activities on the photodegradation of rhodamine B were significantly improved in the (Ni,F)-doped sample. The effective photocatalysis was discussed in relation to the improved visible-light response, the modified band structure, and the longer dynamic luminescence decay. The longer recombination between the light-created electrons and holes was verified by the transition lifetimes in (Ni,F)-doped α-Bi2O3 nanorods. The reported hydrothermal synthesis was an advantageous approach to preparing α-Bi2O3; it is simple, has a low reaction temperature, no post-sintering is required, no template or surfactant is necessary, it suitable for large-scale production, it is low cost, etc.

Determination of deuterium oxide content in water based on luminescence quenching

Water molecules (H2O) often reduce luminescence lifetimes of various luminescence probes. The change of lifetime is usually caused by dynamic luminescence quenching induced by O-H oscillators which effectively take away energy from excited molecule. The process can be described by Stern-Volmer equation. We have studied selected luminescence systems where it is possible to detect considerable changes of lifetime in presence/absence of H2O and D2O in this work for analytical purposes. We have tested both, inorganic (Ln3+) and organic compounds using three different instrumentation in order to find the largest change between τH and τD. The Ln3+ containing systems have shown considerable increase/decrease of lifetimes in the presence/absence of D2O (Eu3+: τD/τH = 34.5) whereas organic systems gave significantly lower values of τD/τH (coumarin 123 lifetime ratio, τD/τH = 1.94). The calculated LOD varied from 0.04 mol l−1 (samarium nitrate) to 6.55 mol l−1 (riboflavin).

Platinum(II) Ring-Fused Chlorins as Near-Infrared Emitting Oxygen Sensors and Photodynamic Agents.

Novel near-infrared luminescent compounds based on platinum(II) 4,5,6,7-tetrahydropyrazolo[1,5-a]pyridine-fused chlorins are described. These compounds have high photostability and display light emission, in particular simultaneous fluorescence and phosphorescence emission in solution at room temperature, in the biologically relevant 700-850 nm red and near-infrared (NIR) spectral region, making them excellent materials for biological imaging. The simultaneous presence of fluorescence and phosphorescence emission at room temperature, with the phosphorescence strongly quenched by oxygen whereas fluorescence remains unaffected, allows these compounds to be used as ratiometric oxygen sensors in chemical and biological media. Both steady-state (fluorescence vs phosphorescence intensities) and dynamic (dependence of phosphorescence lifetimes upon oxygen concentration) luminescence approaches can be used. Photocytotoxicity studies against human melanocytic melanoma cells (A375) indicate that these compounds display potential as photosensitizers in photodynamic therapy.

Supramolecular Agent–Simulant Correlations for the Luminescence Based Detection of V‐Series Chemical Warfare Agents with Trivalent Lanthanide Complexes

AbstractSolution spectroscopic investigations into the interactions of eight potential bidentate V‐series organophosphorus chemical warfare agent (OP CWA) simulants with [Eu(phen)2(NO3)3]·2H2O demonstrated that the chemical and structural composition of the secondary binding site within the simulant was of paramount importance. Only simulants containing both phosphoryl/phosphonyl and amine moieties generated analogous spectroscopic behaviours to V‐series OP CWAs seen in previous studies. The results demonstrated that the bidentate chelation mechanism was driven by the phosphoryl/phosphonyl moieties and that the presence of the amine moieties induced a significant secondary dynamic luminescence quenching mechanism. The binding modes of the simulants VO and TEEP to trivalent lanthanides (Eu and La) were further investigated using 1H and 31P NMR spectroscopic titrations and kinetic IR experiments. VO, with both the phosphonyl and amine binding sites was found to be the most appropriate simulant for V‐series OP CWAs in supramolecular studies with trivalent lanthanide ions and we recommend VO for use in supramolecular studies of this type.

Electronic Energy Transfer Modulation in a Dynamic Foldaxane: Proof‐of‐Principle of a Lifetime‐Based Conformation Probe

AbstractAbiotic aromatic oligoamide foldamers are shown to self‐assemble in solution to form a double helix, which can accommodate a bichromophoric thread in its central void. While in solution reversible electronic energy transfer is instilled between chromophoric termini of the free, flexible thread as evidenced through delayed luminescence, upon rigidification of the rod the chromophores are mutually distanced and effectively decoupled. Consequently, the chromophores display their individual photophysical characteristics. The observed conformation‐dependent changes of dynamic luminescence properties, which are particularly sensitive to distance, offers a new strategy for lifetime‐based detection of geometry on the molecular scale as demonstrated through real‐time luminescence detection of molecular complexation leading to foldaxane formation.

Electronic Energy Transfer Modulation in a Dynamic Foldaxane: Proof-of-Principle of a Lifetime-Based Conformation Probe.

Abiotic aromatic oligoamide foldamers are shown to self-assemble in solution to form a double helix, which can accommodate a bichromophoric thread in its central void. While in solution reversible electronic energy transfer is instilled between chromophoric termini of the free, flexible thread as evidenced through delayed luminescence, upon rigidification of the rod the chromophores are mutually distanced and effectively decoupled. Consequently, the chromophores display their individual photophysical characteristics. The observed conformation-dependent changes of dynamic luminescence properties, which are particularly sensitive to distance, offers a new strategy for lifetime-based detection of geometry on the molecular scale as demonstrated through real-time luminescence detection of molecular complexation leading to foldaxane formation.

Broadband 27 μm amplified spontaneous emission of Er^3+ doped tellurite fibers for mid-infrared laser applications

Er3+ doped tellurite fibers have been fabricated using a convenient suction technique. Different scanning calorimetry (DSC), Electro-probe micro-analyzer (EPMA), Raman, steady and dynamic luminescence spectra were performed to investigate their thermal, structure, and luminescent properties. Broadband 2.7 μm amplified spontaneous emission (ASE) emission with concurrent 1.5 μm and visible up-conversion emissions have been achieved in fibers with various lengths upon the excitation of 980 nm laser diode (LD). A quantitative study of the spectroscopic properties has been further analyzed in detail according to the Jude-Ofelt model, rate equation, and Dexter’s theory to evaluate the competitive relationship among them. The desirable spectroscopic characteristics associated with excellent thermal stability and mechanical properties indicate that the Er3+ doped tellurite fibers are excellent host matrices for 2.7 μm lasing and may provide applications in mid-infrared fiber lasers and amplifiers.

Sustained wash-resistant receptor activation responses of GPR119 agonists

G protein-coupled receptor 119 (GPR119) is involved in regulating metabolic homoeostasis, with GPR119 agonists targeted for the treatment of type-2 diabetes and obesity. Using the endogenous agonist oleoylethanolamide and a number of small molecule synthetic agonists we have investigated the temporal dynamics of receptor signalling. Using both a dynamic luminescence biosensor-based assay and an endpoint cAMP accumulation assay we show that agonist-driven desensitization is not a major regulatory mechanism for GPR119 despite robust activation responses, regardless of the agonist used. Temporal analysis of the cAMP responses demonstrated sustained signalling resistant to washout for some, but not all of the agonists tested. Further analysis indicated that the sustained effects of one synthetic agonist AR-231,453 were consistent with a role for slow dissociation kinetics. In contrast, the sustained responses to MBX-2982 and AZ1 appeared to involve membrane deposition. We also detect wash-resistant responses to AR-231,453 at the level of physiologically relevant responses in an endogenous expression system (GLP-1 secretion in GLUTag cells). In conclusion, our findings indicate that in a recombinant expression system GPR119 activation is sustained, with little evidence of pronounced receptor desensitization, and for some ligands persistent agonist responses continue despite removal of excess agonist. This provides novel understanding of the temporal responses profiles of potential drug candidates targetting GPR119, and highlights the importance of carefully examining the the mechanisms through which GPCRs generate sustained responses.

Enhanced broadband 18 μm emission in Bi/Tm^3+ co-doped fluorogermanate glasses

Enhanced broadband 1.8 μm emission has been demonstrated in Bi/Tm3+ co-doped fluorogermanate glasses under a selectable pumping scheme. Detailed studies based on structure analysis, absorption spectra, excitation and emission spectra, and dynamic luminescence decay curves indicate that the enhanced broadband 1.8 μm luminescence originates from extremely efficient energy transfer process from Bi to Tm3+. Furthermore, the detailed energy transfer mechanism between Bi and Tm3+ is rationally analyzed. This novel pumping scheme and sensitizing mechanism of Bi/Tm3+ co-doping could provide the experimental basis for ~2.0 μm laser flexibly pumped by visible lasers, optical parametric oscillators, commercial 808 and 980 nm laser diodes.

Spectroscopic properties and energy transfer parameters of Yb3 +/Tm3 + co-doped fluorogermanate glasses

Yb3+/Tm3+ co-doped fluorogermanate glasses have been prepared by the melt-quenching method. Their luminescent properties were investigated by absorption spectra, excitation and emission spectra, and dynamic luminescence decay curves. The energy transfer parameters were analyzed by the phonon sideband theory and the energy transfer mechanism between Yb3+ and Tm3+ was proposed. An efficient 1.8μm luminescence with reduced up-conversion emission is achieved under excitation of 980nm laser diode. It is found that the emission at 800nm is the main path of energy loss in the up-conversion process and it can be lowered at a higher Tm3+ doping level. In addition, the forward energy transfer parameter from Yb3+ to Tm3+ is approximately two orders of magnitude greater than the backward one, supporting efficient 1.8μm emission.

Detection of NAD(P)H-dependent enzyme activity with dynamic luminescence quenching of terbium complexes.

We discovered that positively charged terbium complexes bearing 1,4,7,10-tetraazacyclododecane functionalized with amide ligands are highly sensitive to dynamic luminescence quenching by NAD(P)H. We exploited this phenomenon to establish a general time-resolved luminescence-based assay platform for sensitive detection of NAD(P)H-dependent enzyme activities.

Tunable photoluminescence properties of [Ru(bpy)2(tatp)]2+ bound to a BSA–SWCNTs film upon incorporation of [Co(phen)3]3+

Abstract Photoluminescence properties of [Ru(bpy)2(tatp)]2+ (bpy = 2,2′-bipyridine and tatp = 1,4,8,9-tetra-aza-triphenylene) bound to a BSA–SWCNTs film (BSA = bovine serum albumin and SWCNTs = single-walled carbon nanotubes) upon incorporation of [Co(phen)3]3+ (phen = 1,10-phenanthroline) are first investigated by means of steady-state and time-resolved fluorescence spectroscopy. The BSA-bound [Ru(bpy)2(tatp)]2+ shows tunable luminescence properties by [Co(phen)3]3+, where an increasing amount of BSA is found to increase the emission intensity of [Ru(bpy)2(tatp)]2+–BSA dyad with binding constant of 1.9 × 102 M−1, and however decrease the luminescence of [Ru(bpy)2(tatp)]2+–BSA–[Co(phen)3]3+ triad with quenching constant of 2.4 × 103 M−1. Moreover, BSA is combined with SWCNTs to construct BSA–SWCNTs bio-nanohybrids, which mediate the photo-induced electron transfer (PET) between [Ru(bpy)2(tatp)]2+ and [Co(phen)3]3+, representing a dynamic luminescence quenching process. On basis of such a PET, [Ru(bpy)2(tatp)]2+ and [Co(phen)3]3+ are assembled on the surfaces of BSA–SWCNTs to fabricate a photoanode and a cathode, respectively, showing detectable photovoltaic response. The present study could provide a versatile platform for the fabrication and evaluation of nanoscale optoelectronic devices.

Efficient 20 μm fluorescence in Ho^3+-doped fluorogermanate glass sensitized by Cr^3+

A comprehensive investigation on Cr3+ → Ho3+ energy transfer has been comparatively carried out in Ho3+-doped, Cr3+-doped and Cr3+/Ho3+ co-doped fluorogermanate glasses. Steady and dynamic luminescence spectra of the glass samples are detected under excitation of static/microsecond-pulsed xenon lamps and an 808 nm laser diode, respectively. Through strong sensitization of Cr3+, the 2.0 μm emission of Ho3+: 5I7 → 5I8 can be efficiently achieved in an extremely extended excitation band of 325-830 nm. The energy transfer mechanisms involved are rationally discussed in detail for Cr3+/Ho3+ co-doping. On the basis of theoretical and experimental data, the energy transfer efficiency of Cr3+ → Ho3+ is appropriately calculated to be 26.2%. This novel Cr3+/Ho3+ codoping system could provide the experimental basis for obtaining 2.0 μm laser flexibly pumped by the xenon lamp or the 808 nm laser diode.

ChemInform Abstract: Role of Heteroaromatic Cycles in the Inter‐ and Intra‐Molecular Dynamics of Excited Aryl Ketones

AbstractReview: 217 refs.

Ce3+-Sensitized GdPO4:Tb3+ Nanorods: An Investigation on Energy Transfer, Luminescence Switching, and Quantum Yield

Herein we report the enhanced green emission from Tb3+-doped GdPO4 nanorods sensitized with Ce3+. The increase in the rate of nonradiative transition processes in sensitizer due to efficient energy transfer to activator is realized from steady-state and dynamic luminescence studies. Luminescence quenching due to cross relaxation is least significant up to 20 at. % Ce3+ and 7 at. % Tb3+ concentration. The quantum yield of the sample with maximum luminescence, i.e., GdPO4:Tb3+ (5 at. %)/Ce3+ (7 at. %), is found to be 28%. Also, samples are readily redispersible in water and could be easily incorporated in polymer-based films that show strong green light emission under UV excitation. The luminescence switching (ON and OFF) behavior is examined using alternately an oxidizing agent (KMnO4) and then a reducing agent (ascorbic acid) through a redox reaction (Ce3+/Ce4+). Both GdPO4:Tb3+ and GdPO4:Tb3+/Ce3+ are observed to be paramagnetic.

Red Photoluminescence from Bi3+and the Influence of the Oxygen-Vacancy Perturbation in ScVO4: A Combined Experimental and Theoretical Study

We report on a red-emitting ScVO4:Bi3+ phosphor which does not show excitation at energies below 2.88 eV (430 nm). X-ray diffraction, time-resolved, and quantitative photoluminescence (PL) spectroscopy were employed to characterize relations between crystal structure and luminescence properties of the material. Results show that incorporation of Bi3+ renders the blue photoemission of blank ScVO4 to red. Dynamic luminescence analysis between 10 and 300 K reveals a complicated dependence of energy transfer from VO43– groups to Bi3+ ions and population redistribution of 3P1 and 3P0 of Bi3+ on temperature. This reflects in distinct changes in the luminescence decay functions. That is, a dramatic decrease of Bi3+ luminescence lifetime occurs from hundreds to only several microseconds. Density functional theory is employed to reveal how the unusual red Bi3+ luminescence comes, and results indicate that the perturbation of oxygen vacancies which is generated readily when bismuth precipitates into ScVO4 is the re...

Broadly Tunable Emission from CaMoO4:Bi Phosphor Based on Locally Modifying the Microenvironment Around Bi3+ Ions

AbstractThe trivalent green element of bismuth, when doped into different compounds, can produce multiple emissions in ultraviolet, blue, green or even yellow spectral regimes. The emission adjustability comes from the susceptibility of bismuth naked 6s electrons to the crystal field particularly surrounding Bi3+. However, this has never been observed in a single compound. In this work, we report that broadly tunable bismuth emission indeed occurs even within the same host (CaMoO4) when the local microenvironment around Bi3+ is modified by intentional introduction of alkali ions. As the radius of the selected alkali ion decreases, the emission regularly blue‐shifts from 586 to 554 nm, and its intensity is enhanced greatly. For instance, the integrated intensity for the Li+ and Bi3+ codoped sample is 4.46 times stronger than the Bi3+ single‐doped sample upon excitation at 300 nm. Low‐temperature photoluminescence spectra surprisingly reveal that energy transfer can partially take place from the MoO42– group to Bi3+ at lower temperature when excited into the charge transfer state of the MoO42– group, however, this does not occur at higher temperature. The mechanism needs further study. Dynamic luminescence analysis between 10 and 300 K implies a population dependence of the excited states 3P0 and 3P1 on temperature that is responsible for the evolution of the Bi3+ emission lifetime with temperature.

Software for simulation of luminescence quenching mechanism: the stern-volmer kinetic model.

A software that includes both Stochastic and Molecular Dynamics procedures has been developed with the aim of visualizing the Stern-Volmer kinetic mechanism of dynamic luminescence quenching. The software allows the student to easily simulate and graphically visualize the molecular collisions, the molecular speed distributions, the luminescence decay curves, and the Stern-Volmer graphs. The software named SternVolmer is written for the FreeBASIC compiler and can be applied to dynamic systems where luminescent molecules, during their excited state lifetimes, are able to collide with quenching molecules (collisional quenching). The good agreement found between the simulations and the expected results shows that this software can be used as an effective teaching aid for the study of luminescence and kinetic decay of excited states.

Molecular crystalline materials with tunable luminescent properties: from polymorphs to multi-component solids

Tuning and controlling the luminescent properties of molecular materials by changing the orientation and arrangement of the fluorophores within a solid has played an important role in realizing multi-color emission. The formation of polymorphs and multi-component molecular solids have attracted considerable interest as new ways of achieving controllable luminescence and other photophysical properties for application in the next generation of photofunctional materials. In this article, recent advances in the synthesis of fluorescent polymorphs and multi-component materials and potential photo-related applications of the resulting materials are described. We first review the methods of preparation of polymorphs with tunable static luminescence, and the switching of the dynamic luminescence between polymorphs for potential sensor applications is also introduced. Attention is then focused on the supramolecular design (making use of hydrogen bonding and halogen bonding interactions) and methods of fabrication of multi-component molecular solids, and their color-tunable fluorescence and phosphorescence together with their stimuli-responsive properties for use as sensors. The use of density functional theory to study intramolecular and intermolecular energy transfer as well as the electronic structures of multi-component molecular solids is also outlined. Finally, we briefly discuss perspectives for the further development of these luminescent molecular solid-state materials.