Quantum Lifetime Research Articles

Luminescent Ir(III) complexes with deprotonated 1-methyl-2-(2′-pyridyl)pyridinium ligand and 1,10-phenanthroline derivatives

A series of novel cationic [Ir(C^N)2(N^N)]3+ complexes bearing deprotonated 1-methyl-2-(2′-pyridyl)pyridinium (C^N) as cyclometalating ligand and 1,10-phenanthroline derivatives (N^N) as ancillary ligands have been prepared in the form of PF6− salts and identified by means of 1H and 31P NMR spectroscopy. Their luminescence properties have been studied in acetonitrile solutions at room temperature and in CH3OH/C2H5OH 1:1 glasses at 77 K. Depending on the α-diimine ligand coordinated, the room temperature values of emission wavelength λem, quantum yield ϕem and lifetime τem vary in the range of 535–630 nm, 0.12–0.60, and 0.06–840 μs, respectively. The complexes display the changes in the nature of the emissive states, their emission occurs either from the excited triplet states (3*C^N or 3*N^N) or from the excited singlet state (1*N^N).

Enhancement of the Photofunction of Phosphorescent Pt(II) Cyclometalated Complexes Driven by Substituents: Solid-State Luminescence and Circularly Polarized Luminescence.

Ligand functionalization is an attractive strategy for enhancing the performance of metal-based phosphorescent emitters. Here, we report the synthesis and characterization of cyclometalated Pt(II) complexes Pt3 and Pt4 containing organosilyl-substituted (2-(2-thienyl)pyridine) ligands and compare their properties with those of Pt1 (no substituent) and Pt2 (organocarbon substituent). The photophysical characteristics of these molecules, including their absorption and phosphorescence spectra, phosphorescence quantum yield and lifetime, were investigated. The molecular structures were revealed by X-ray diffraction analysis. Under UV light irradiation, Pt2-Pt4 emitted intense orange phosphorescence in the solid state because of the bulkiness of their side chains (up to ΦP: 0.49). Optically pure (-)-(S)Si-Pt4 and (+)-(R)Si-Pt4 were prepared using the optically active ligands (+)-L4 and (-)-L4, respectively. The chiroptical properties of (+)-(R)Si-Pt4, which has an asymmetric silicon atom, were investigated. Circular dichroism and circularly polarized luminescence measurements showed that these structural motifs are suitable for applications in chiroptical phosphorescent materials.

Enhanced stability of the optical responses from all-inorganic perovskite nanocrystals embedded in a synthetic opal matrix

Nanostructured luminescent materials based on perovskite nanocrystals (p-NCs) are attractive since their optical properties can be tuned in a wide spectral range with high luminescence quantum yields and lifetimes, however, they lack stability. In this work, the optical properties of highly luminescent colloidal p-NCs (CsPbX3, where X = Cl/Br, Br, I) embedded in porous opal matrices are presented. It is shown that the photoluminescence of the p-NCs embedded into opal matrices possess increased longtime stability of its spectral and kinetic parameters under ambient conditions. LEDs based on the developed materials show pure color p-NC emission with stability of its parameters. The results of this work may expand the knowledge of interactions between luminescent nanoparticles within multicomponent nanostructured materials for further photonic applications.

Impact of solvents on energy gap, photophysical, photometric properties for a new class of 4-HCM coumarin derivative: Nonlinear optical studies and optoelectronic applications

Now a day the derivatives of biscoumarins are receiving overwhelming importance due to their application in designing organic semiconductor materials for display application. Therefore, a new photostable, light emitting and highly efficient synthesized material to exhibit display property and nonlinear optical active materials with good band gap energy, we have synthesized 4-Hydroxy-3-[(4-hydroxy-2-oxo-2H-chromen-3-yl)(4-methoxyphenyl)methyl]-2H-chromen-2-one (4-HCM) molecule via the simple catalytic method. The photophysical property of studied molecule in various organic solvents having different polarity exhibited considerably acceptable results. The results of quantum yield, lifetime and large Stoke shift shows the compound is a good promising candidate for the laser dyes and light emitting diode color filters. The energy band gap was determined by both experimentally and theoretically which is found to be an average of 3.78 eV which is well matched to the semiconducting materials band gap. The nonlinear optical absorption properties of the synthesized 4-HCM molecule are investigated using Z-scan technique. Further, the optoelectronic properties were investigated the CIE, color rendering index, color purity and color correlated temperature results of the 4-HCM in all studied solvents revels that this compound exhibits blue color (CIE-co-ordinates x = 0.14, y = 0.08) and is suitable for optoelectronic device applications.

Synthesis, photophysical, quantum chemical investigation, linear and non-linear optical properties of coumarin derivative: Optoelectronic and optical limiting application.

In order to develop a new photostable, light emitting and highly efficient synthesized material to exhibit display property and non-linear optical active materials with good band gap energy, we have synthesized molecule via simple catalytic method. The photophysical property of studied molecule in various organic solvents having different polarity exhibited considerably acceptable results. The results of quantum yield, lifetime and large Stoke shift shows the compound is a good promising candidate for the laser dyes and light emitting diode color filters. The energy band gap was determined by both experimentally and theoretically which is found to be an average of 3.2 eV which is well matched to the semiconducting materials band gap. The non-linear optical absorption properties of the synthesized molecule are dissolved in suitable solvents had been investigated using Z-scan technique. We have determined the sign and magnitude of nonlinear absorption coefficient by the method of open aperture Z-scan setup using an Nd: YAG continuous wave laser at 532 nm. The open aperture Z-scan profiles clearly demonstrate the presence of reverse saturable absorption kind nonlinearity in the investigated compound and are due to the two-photon absorption. Results of the non-linear optical studies confirm that the studied compound is more latent applications for optical limiting in continuous wave regime. Further, the optoelectronic properties were investigated the international commission on illumination, color rendering index, color purity, and correlated color temperature is results of the studied molecule in all studied solvents revels that this compound exhibits blue to cyan color and is suitable for organic light emitting diode which can be preferably used for daylight applications.

Water-soluble norsquaraine dyes for protein labeling and pH-sensing applications

Novel pH-sensitive, water-soluble, long-wavelength fluorescent norsquaraine dyes and their barbituric and dicyanomethylene derivatives were synthesized and investigated. Some of these dyes contain a carboxylic functionality that was converted into an NHS ester to facilitate bio-conjugation. The absorption and emission spectra, fluorescence quantum yields, lifetimes, polarization, and photostabilities were measured free in solution and after binding to bovine serum albumin (BSA) and compared to those of conventional squaraines and the norcyanine dye CypHer5. Contrary to squaraines, norsquaraines are pH-sensitive but almost unaffected by the interaction with proteins. These dyes can potentially be used as fluorescent labels for biomedical applications, in particular for protein labeling, polarization-based assays, cell-based and pH-sensing measurements.

Solvent dependent spectroscopic properties of fingerprint reagent - 1,8-Diazafluoren-9-one

The photophysical and photochemical properties of fingerprint reagent - 1,8-diazafluoren-9-one (DFO) - were studied using steady-state, time-resolved spectroscopic techniques and semiempirical quantum-chemical calculations. In order to understand how microenvironment influences the excited-state properties of DFO, fluorescence quantum yields, lifetimes and rate constants were determined. Spectroscopic studies and theoretical calculations indicate that the energy-level disposition of close-lying nπ* and ππ* states of DFO is significantly modified by solvent polarity. The multiple linear regression analyses proposed by Kamlet-Taft and Catalán reveal that DFO solvation is mainly determined by dipolar solute-solvent interactions, whereas the specific interactions play a less significant role. Finally, the difference in the ground and excited state dipole moments of investigated dye was obtained using solvatochromic shift methods based on the Onsager's description of general solute-solvent interactions.

Selective Detection of Trinitrophenol by Amphiphilic Dimethylaminopyridine-Appended Zn(II)phthalocyanines at the Near-Infrared Region.

Novel amphiphilic Zn(II)phthalocyanines (ZnPcs) peripherally substituted with four and eight dimethylaminopyridinium units (ZnPc1 and ZnPc2) were synthesized by cyclotetramerization of the corresponding phthalonitriles. The effect of aggregation and photophysical (fluorescence quantum yields and lifetimes) and photochemical (singlet oxygen generation and photodegradation under light irradiation) properties was investigated. The chemosensing ability of ZnPcs toward explosive nitroaromatic compounds was explored in aqueous medium. This study demonstrates that ZnPc1 and ZnPc2 show fluorescence quenching behavior upon interaction with different nitro analytes and show unprecedented selectivity toward 2,4,6-trinitrophenol with a limit of detection (LOD) of 0.7–1.1 ppm with a high quenching rate constant (Ksv) of 1.6–2.02 × 105. The near-infrared (NIR) fluorescence in thin films was quenched efficiently because of the photoinduced electron-transfer process through strong intermolecular π–π and electrostatic interactions. The sensing process is highly reversible and free from the interference of other commonly encountered nitro analytes. Further, experiments were performed to demonstrate the use of ZnPcs as efficient heterogeneous photocatalysts in the reduction of nitro explosives. The smart dual performance of multicharged ZnPcs in aqueous media quantifies them as attractive candidates in developing sensor materials at the NIR region and to possibly convert the toxic explosives into useful scaffolds. These results provide an interesting perspective toward elaboration of stable fluorescent systems for the selective sensing behavior of nitro explosives and their facile heterogeneous catalytic behavior in the reduction reactions.

Mechanofluorochromic Properties of an AIEE‐Active 2‐Phenylbenzoxazole Derivative: More than Meets the Eye?

AbstractThe presence of a dicyanovinyl group on the robust 2‐phenylbenzoxazole framework led to the emergence of aggregation‐induced emission enhancement (AIEE) characteristics. A mechanofluorochromic (MFC) behaviour was observed. The pristine microcrystals emitted yellow‐green light, which became golden yellow upon grinding, with the reverse process observed upon heating or solvent fuming. This phenomenon was accompanied by a reversible evolution of the photoluminescence quantum yields and lifetimes. These variations were attributed to the formation of different types of emissive species in the crystalline phases and in the ground material, which is a mixture of very small microcrystals and amorphous matter. Remarkably, evidence was also given for other spectroscopic effects, which depend on the size, compactness and heterogeneity of the solid samples. These effects are presumably linked to the generation of regions rich in low‐energy exciton traps in polycrystalline and pressed samples, and to light reabsorption. They are enhanced by the fact that the pristine platelets exhibit self‐waveguided edge emission, and they are all the more significant as the MFC effect is rather weak.

Recent Progress of the Lifetime of Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescent Material.

Recently, the external quantum efficiency and lifetime of organic light-emitting diodes (OLEDs) have been dramatically upgraded due to development of organic materials and device structure. In particular, an intramolecular or intermolecular complex based on thermally activated delayed fluorescent (TADF) materials has greatly contributed to improving OLED device performance. Although high external quantum efficiency has been the main objective of the development of TADF materials as hosts and emitters, recent interest has been directed towards the lifetime of TADF-material-based OLEDs. For the past several years, remarkable advances in the lifetime of phosphorescent and TADF OLEDs have been made using TADF materials as hosts or emitters in the emitting layer. Therefore, since TADF materials are useful as both hosts and emitters for a long lifetime, this work discusses the recent progress made in developing TADF materials for long-lifetime OLEDs.

Cytotoxicity, cellular uptake, and subcellular localization of a nitrogen oxide and aminopropyl-β-lactose derivative ruthenium complex used as nitric oxide delivery agent

This work investigates how the luminescent ruthenium-nitrite complexes cis-[Ru(py-bodipy)(dcbpy)2(NO2)](PF6) (I) and cis-[Ru(py-bodipy)(dcbpy-aminopropyl-β-lactose)2(NO2)](PF6) (II) behave toward the melanoma cancer cell line B16F10. The chemical structure and purity of the synthesized complexes were analyzed by UV-Visible and FTIR spectroscopy, MALDI, HPLC, and 1H NMR. Spectrofluorescence helped to determine the fluorescence quantum yields and lifetimes of each of these complexes. In vitro MTT cell viability assay on B16F10 cancer cells revealed that the complexes possibly have a tumoricidal role. The metal-nitrite complexes evidenced the dichotomous NO nature: at high concentration, NO exerted a tumoricidal effect, whereas cancer cells grew at low NO concentration. Flow cytometry or fluorescence microscopy aided cellular uptake calculation. Cell staining followed by fluorescence microscopy associated with organelle markers such as DAPI and Rhodamine 123 detected preferential intracellular localization of the ruthenium-nitrite py-bodipy and aminopropyl lactose derivative ruthenium complex in mitochondria. Thus, the cytotoxicity of compounds (I) and (II) against B16F10 cancer cell line show concentration-dependent results. The present studies suggest that nitric oxide ruthenium derivative compounds could be new potential chemotherapeutic agents against cytotoxic cells.

Surface Chemistry-Mediated Near-Infrared Emission of Small Coinage Metal Nanoparticles.

From size-dependent luminescence to localized surface plasmon resonances, the optical properties that emerge from common materials with nanoscale dimensions have been revolutionary. As nanomaterials get smaller, they approach molecular electronic structures, and this transition from bulk to molecular electronic propertiesis a subject of far-reaching impact. One class of nanomaterials that exhibit particularly interesting optoelectronic features at this size transition are coinage metal (i.e., group 11 elements copper, silver, and gold) nanoparticles with core diameters between approximately 1 to 3 nm (∼25-200 atoms). Coinage metal nanoparticles can exhibit red or near-infrared photoluminescence features that are not seen in either their molecular or larger nanoscale counterparts. This emission has been exploited both as a probe of electronic behavior at the nanoscale as well as in critical applications such as biological imaging and chemical sensing. Interestingly, it has been demonstrated that theirphotoluminescence figures of merit such as emission quantum yield, energy, and lifetimeare largely independent of particle diameter. Instead, emission from particles at this size range depends heavily on the particle surface chemistry, which includes both its metallic composition and the capping ligand architecture. The strong influence of surface chemistry on these emergent optoelectronic phenomena has powerful implications for both the study and use of these particles, primarily due to the theoretically limitlesspossible surface ligand architectures and metallic compositions. In this Account, we highlight recent work that studies and uses surface chemistry-mediated photoluminescence from coinage metal nanoparticles. Specifically, we emphasize the distinct, as well as synergistic, roles of the nanoparticle capping ligand and the nanoparticle corefor controlling and/or enhancing theirnear-infrared photoluminescence. We then discuss the implications of surface chemistry-mediated photoluminescence as it relates to downstream applications such as energy transfer, sensing, and biological imaging. We conclude by discussing current challenges that remain in the field, including opportunities to develop new particle synthetic routes, analytical tools, and physical frameworks with which to understand small nanoparticle emission. Taken together, we anticipate that these materials will be foundational both in understanding the unique transition from molecular to bulk electronic structures and in the development of nanomaterials that leverage this transition.

Thermally Induced Disorder-Order Phase Transition of Gd2Hf2O7:Eu3+ Nanoparticles and Its Implication on Photo- and Radioluminescence.

Crystal structure has a strong influence on the luminescence properties of lanthanide-doped materials. In this work, we have investigated the thermally induced structural transition in Gd2Hf2O7 (GHO) using Eu3+ ions as the spectroscopic probe. It was found that complete phase transition from the disordered fluorite phase (DFP) to the ordered pyrochlore phase (OPP) can be achieved in GHO with the increase of annealing temperature from 650 → 1100 → 1300 °C. OPP is the more stable structural form for the GHOE nanoparticles (NPs) annealed at a higher temperature based on the energy calculation by density functional theory (DFT). The asymmetry ratio of the GHOE-650 NPs was the highest, whereas the quantum yield, luminescence intensity, and lifetime values of the GHOE-1300 NPs were the highest. Emission intensity of Eu3+ ions increases significantly with the phase transition from the DFP to OPP phase and is attributed to the higher radiative transition rate (281 s–1) of the 5D0 level of the Eu3+ ion in the environment with relatively lower symmetry (C2v) because of the increase of crystal size. As the structure changes from DFP to OPP, radioluminescence showed tunable color change from red to orange. The Eu3+ local structure obtained from DFT calculation confirmed the absence of inversion symmetry in the DFP structure, which is consistent with the experimental emission spectra and Stark components. We also elucidated the host to dopant optical energy transfer through density of states calculations. Overall, our current studies present important observations for the GHOE NPs: (i) thermally induced order–disorder phase transition, (ii) change of point group symmetry around Eu3+ ions in the two phases, (iii) high thermal stability, and (iv) tunability of radioluminescent color. This work provides fundamental understanding of the relationship between the crystal structure and photophysical properties of lanthanide-doped materials and helps design a strategy for advanced optoelectronic materials.

Design, characterization, optical and photophysical properties of novel thiophene monomers and polymers containing pyrene moieties linked via rigid and flexible spacers

Herein, we report the synthesis of three novel thiophene monomers connected to pyrene moieties via a flexible oligo(ethylene glycol) (OEG) spacer with an oxygen α-to-pyrene (T1), a flexible OEG spacer with an oxygen β-to-pyrene (T2), and a rigid acetylene spacer (T3). These monomers were prepared in an easy manner from commercially available 3-bromo-4-methylthiophene and further characterized by NMR spectroscopy and mass spectrometry. Monomer T2 exhibited the absorption band at 344 nm and a strong “monomer” emission band at 375 nm typical of a 1-pyrenemethyl derivative. Moreover, T1 and T3 showed red shifted absorption bands at 352 and 384 nm arising from the pyrene substituents, namely the electron-donating oxygen α−to-pyrene and the extended conjugation length, respectively. These compounds exhibited a broad “monomer” emission band between 360˜480 nm without excimers. Homopolymers (OHP1, OHP2, and OHP3) obtained from these monomers were partially soluble and their photophysical properties such as quantum yield and lifetime were characterized. Emission spectra of the oligomers OHP1 and OHP3 exhibited an emission band at ˜500 nm, which is due to the conjugated polythiophene backbone and does not arise from intramolecular pyrene-pyrene interactions.

The Catalytic Cycle of Water Oxidation in Crystallized Photosystem II Complexes: Performance and Requirements for Formation of Intermediates

Crystals of photosystem II (PSII) contain the most homogeneous copies of the water-oxidizing reaction center where O2 is evolved (WOC). However, few functional studies of PSII operation in crystals have been carried out, despite their widespread use in structural studies. Here we apply oximetric methods to determine the quantum efficiency and lifetimes of intermediates of the WOC cycle as a function of added electron acceptors (quinones and ferricyanide), both aerobically and anaerobically. PSII crystals exhibit the highest quantum yield of O2 production yet observed of any native or isolated PSII (61.6%, theoretically 59 000 μmol O2/mg Chl/h). WOC cycling can be sustained for thousands of turnovers only using an electron acceptor (quinones, ferricyanide, etc.). Simulations of the catalytic cycle identify four distinct photochemical inefficiencies in both PSII crystals and dissolved PSII cores that are nearly the same magnitude. The exogenous acceptors equilibrate with the native plastoquinone acceptor at...

Recent Developments in Tandem White Organic Light-Emitting Diodes.

Tandem white organic light-emitting diodes (WOLEDs) are promising for the lighting and displays field since their current efficiency, external quantum efficiency and lifetime can be strikingly enhanced compared with single-unit devices. In this invited review, we have firstly described fundamental concepts of tandem device architectures and their use in WOLEDs. Then, we have summarized the state-of-the-art strategies to achieve high-performance tandem WOLEDs in recent years. Specifically, we have highlighted the developments in the four types of tandem WOLEDs (i.e., tandem fluorescent WOLEDs, tandem phosphorescent WOLEDs, tandem thermally activated delayed fluorescent WOLEDs, and tandem hybrid WOLEDs). Furthermore, we have introduced doping-free tandem WOLEDs. In the end, we have given an outlook for the future development of tandem WOLEDs.

A novel molecular design employing a backbone freezing linker for improved efficiency, sharpened emission and long lifetime in thermally activated delayed fluorescence emitters

A novel molecular design employing a backbone structure freezing linker was developed to improve the external quantum efficiency, lifetime and emission profile of thermally activated delayed fluorescence (TADF) emitters.

Platinum(ii) and palladium(ii) complexes with electron-deficient meso-diethoxyphosphorylporphyrins: synthesis, structure and tuning of photophysical properties by varying peripheral substituents.

A series of electron-deficient platinum(ii) and palladium(ii) meso-(diethoxyphosphoryl)porphyrins, namely [10-(diethoxyphosphoryl)-5,15-bis(p-tolyl)porphyrinato]palladium(ii) (PdDTolPP), {10-(diethoxyphosphoryl)-5,15-bis[p-(methoxycarbonyl)phenyl]porphyrinato}palladium(ii) [PdD(CMP)PP], [10-(diethoxyphosphoryl)-5,15-dimesitylporphyrinato]palladium(ii) (PdDMesPP), [5-(diethoxyphosphoryl)-10,15,20-trimesitylporphyrinato]palladium(ii) (PdTMesPP) and the corresponding platinum(ii) compounds, were synthesized and structurally characterized in solution by means of 1H, 13C, 31P NMR spectroscopies and in the solid state by single crystal X-ray diffraction [PdDTolPP, PdD(CMP)PP and PtD(CMP)PP]. Their optical and photophysical properties (UV-vis absorption, luminescence and excitation spectra, phosphorescence quantum yields and lifetimes) were also determined. The complexes under investigation emit at room temperature in the near-infrared region (670-770 nm). Phosphorescence quantum yields of the palladium(ii) meso-phosphorylated porphyrins lie in the range of 3.4 to 5.8%, with lifetimes of 633 to 858 μs in deoxygenated toluene solutions at room temperature. The corresponding platinum(ii) complexes exhibit phosphorescence quantum yields in the range of 9.2 to 11%, with luminescence decay times of 56 to 69 μs. Moreover, effective homogeneous oxygen quenching and good sensitivity in toluene (∼155 Pa-1 s-1) were observed for the platinum(ii) complexes with phosphorylporphyrins in solution. Investigations of the photostability of porphyrinylposphonates and related complexes lacking a phosphoryl group in DMF under irradiation in air using a 400 W vis-NIR lamp demonstrated that photobleaching is strongly dependent on the substituents at the periphery of the macrocycle. Platinum and palladium trimesitylphosphorylporphyrins PdTMesPP and PtTMesPP exhibit high photostability in DMF solution and seem to be the most potentially interesting derivatives of the series for oxygen sensing in biological samples and the covalent immobilization on solid supports to prepare sensing devices including optic fibers.

Fluorescence Behavior of Bis(cyanostyryl)pyrrole Derivatives Depending on the Substituent Position of Cyano Groups in Solution and in Solid State.

We synthesized a novel fluorophore of distyrylpyrrole derivatives possessing cyano groups at different positions on olefin. Their fluorescence properties in solution and solid state were investigated by photoluminescence quantum yield and lifetime measurements, which provided a radiative decay constant ( kf) and nonradiative decay constant ( knr). The derivative with cyano groups at the inner position of the molecule, inner isomer, shows a high fluorescence quantum yield (Φf = 0.43) in solution, while another derivative with a cyano group at the outer position, outer isomer, hardly shows fluorescence (Φf < 0.01) due to the large nonradiative decay ( knr > 10 ns-1). Upon formation of a single crystal or nanoparticles, these difference were inverted; the quantum yield of the outer and inner isomer was enhanced and diminished, respectively. We explained these differences between in solution and solid state by means of analysis of a single X-ray structure and computation study.

Luminescence and anion recognition performance of mononuclear Eu(III) complexes with N- and O- donor pyridine derivatives

A series of Eu(III) complexes with pyridine-2-carboxamide (PCA), pyridine-2-carboxaldoxime (PCAO), pyridine-2,3-dicarboxylic anhydride (PDCA) or pyridine-2-methanol (PM) as primary ligands and 4,4′-dimethoxy-2,2′-bipyridine (DMBP) as ancillary ligand were synthesized. The interaction between the ligands and complexes were confirmed by FT-IR study. The complexes were abbreviated as [Eu(PCA)3DMBP].Cl3 (C1), [Eu(PCAO)3DMBP].Cl3 (C2), [Eu(PDCA)3DMBP].Cl3 (C3) and [Eu(PM)3DMBP].Cl3 (C4). Optical studies were done by UV–vis spectroscopy and PL spectroscopy. The highest intrinsic luminescent quantum yield (53.42%) and lifetime value (1456 μs) were found for C3. Lowest quantum yield was exhibited by C2. Anion sensing studies of all the complexes were done by UV–vis and PL spectroscopy and it was observed that complex C1 showed remarkable change in optical properties upon addition of F− and HSO4− ions. Thus C1 can be used as optical sensor for F− and HSO4− ions. The FQD for F− and HSO4− ions were found to be 6.55 and 3.58 respectively for C1.