Enhanced Quantum Yield Research Articles

Halogen Effects-Induced Bright D-π-A Fluorophore as Scaffold for NIR Fluorogenic Probes with High Contrast.

Endowing fluorogenic probes with ultrahigh contrast is essential to increasing the accuracy of fluorescence sensing and imaging. Phenolate-based D-π-A fluorophores (A-DOH) belong to a big family of fluorophores and have attracted increasing attention in fluorogenic probe design. However, the intrinsic dilemma of weak intracellular emission of traditional A-DOH fluorophores resulted in low contrast during live cell imaging. Herein, we present a general and robust approach to preparing novel A-DOH fluorophores with bright NIR fluorescence in living cells based on the unique halogen effects. The reported chlorinated A-DOH fluorophore (A1-2ClOH) has an extremely strong fluorescence in an aqueous solution of pH 7.4 and living cells, which is 194 and 30 times higher than that of the traditional halogen-free analogue (A1-OH), respectively. We systematically investigated and demonstrated that the distinct -I and +M halogen effects, which led to a drastic decrease in the pKa value and a significant enhancement in the fluorescence quantum yield, respectively, should be responsible for the tremendous fluorescence enhancement. The flexible phenol caging chemistry allows one to prepare multiple NIR fluorogenic probes based on the A1-2ClOH scaffold with high contrast for live cell imaging of a variety of analytes by introducing a corresponding triggering moiety. Moreover, the conjugated azide group of A1-2ClOH enables the integration of more functions as desired through a facile click reaction. A fluorogenic probe (mitoProbe-PN) was synthesized as a paradigm by equipping the A1-2ClOH scaffold with a mitochondria-targeting moiety and a peroxynitrite-responsive triggering group and demonstrated specific high-contrast fluorescence imaging of endogenous OONO- in mitochondria of living macrophages.

Quantum yield enhancement of Mn-doped CsPbCl3 perovskite nanocrystals as luminescent down-shifting layer for CIGS solar cells

The emission and absorption properties of Mn doped CsPbCl3 NC make it ideal candidates as luminescent down shifting layer material for solar cells, However, effective Mn doping and further quantum yield improvement remains challenging. We present our modified hot injection route to obtain Mn doped CsPbCl3 nanocrystals with different morphologies and enhanced quantum yield. The samples presented were synthesized with precursor MnCl2 and PbCl2 with the ratio of 1:1, 1:2, 1:2.5 and 1:3. For samples with lower Mn doping level, the as prepared samples are uniform nanocubes with average size of 11 nm. When MnCl2 amount is increased beyond 2.5, large piece of nanosheets were found by TEM and AFM with ultrathin thickness and strong quantum confinement effect. CsPbCl3 nanocrystals with optimal Mn doping level show enhanced quantum yield of 69%. Luminescent down shifting layers prepared from Mn doped CsPbCl3 nanocrystals successfully increased short-circuit current (6.67%) and PCE (1.67%) of Cu(In,Ga)Se2 solar cell.

Self-trapped-induced energy funneling and broadband emission in the Mn2+ doped two-dimensional perovskite

The electronic structure modulations by metal cation doping and organic ligands modification are aroused great interests in perovskite community for spectrum tailoring and quantum yield (QY) enhancement. Herein, we synthesized the two-dimensional (2D) lead bromide perovskite with cyclohexenylethylamine as the organic ammonium ligands and divalent manganese as the doping ions by the combination of facile solution processes and low temperature solid-state method. Thanks to the synergy effects of the steric-hindrance induced self-trapped exciton (STE) by A-site engineering and the elevation of cascaded energy funneling among the FE, STE and the 4T1→6A1 transition of Mn2+. The emission spectrum of the Mn2+ doped 2D perovskite simultaneously covers both the blue and orange range with a QY of 47.01%, where the value is about twelve times of that of the un-doped one at room temperature. Our results indicate that the utilizing of soft organic ammonium and Mn2+ doping in 2D perovskite could not only adjust the energy level states and improve the QY remarkably, but also explore new opportunities in warm-white LEDs and other applications.

π-Hole···dz2[PtII] Interactions with Electron-Deficient Arenes Enhance the Phosphorescence of PtII-Based Luminophores.

Two phosphorescent PtII-based cyclometalated complexes were co-crystallized with perfluorinated arenes to give 1:1 co-crystals. The X-ray study revealed that each of the complexes is embraced by arenesF to give infinite reverse sandwich structures. In four out of six structures, a dz2 orbital of PtII is directed to the arenesF ring via π-hole···dz2[PtII] interactions, whereas in the other two structures, the filled dz2 orbital is directed toward the arene C atoms. Computed molecular electrostatic potential surfaces of the arenesF and the complexes, noncovalent interaction indexes for the co-crystals, and natural bond orbital calculations indicate that π-hole···dz2[PtII] contacts (and, generally, the stacking) are of electrostatic origin. The solid-state photophysical study revealed up to 3.5-fold luminescence quantum yield and 15-fold lifetime enhancements in the co-crystals. This increase is associated with the strength of the π-hole···dz2[PtII] contact that is dependent on the π-acidity of the areneF and its spatial characteristics.

Halogen Substitution in Zero‐Dimensional Mixed Metal Halides toward Photoluminescence Modulation and Enhanced Quantum Yield

AbstractZero‐dimensional (0D) organic−inorganic hybrid metal halides haveunprecedented degrees of freedom for structural tunability and photoluminescence modulation. Here, the 0D isomorphic hybrid metal mixed halides (C9NH20)9Pb3Zn2Br19(1−x)Cl19x (x = 0–1) with continuous halogen contents control, exhibiting tunable emission and enhancement of photoluminescence quantum yield (PLQY) are reported. The competitive bromine to chlorine substitution process in (C9NH20)9Pb3Zn2Br19(1−x)Cl19x occurs first in [ZnBr4−xClx]2− tetrahedron before the [Pb3Br11−xClx]5− trimer. The increasing Cl content in samples from x = 0 to 1 results in an expected blue shift of emission peak from 565 to 516 nm, and meanwhile a strikingly room temperature PL quantum yield increase from 8% to 91%. Combined experimental characterizations and theoretical calculations indicate that the blue shift of interband transition energy is responsible for the emission peak shift. Moreover, with the increasing Cl content, the enhanced electron−phonon interaction and the weakened thermal‐assisted nonradiative recombination result in more efficient radiative transition channels and ultimately enhanced PLQY. The impact of halogen substitution on electronic structures and optical properties in 0D hybrid metal halides is emphasized in this work as a new strategy to promote the future development of new luminescent materials.

Plasmonic quantum yield enhancement of a single molecule near a nanoegg

We investigate the impact of the dipole-active modes formed via the mode-mixing of the dipole mode with higher-order surface plasmon modes of a nanoegg on the radiative decay rate and quantum yield of an excited molecule near the nanoegg. The Purcell factor, rate of power dissipation by the emitter, and antenna efficiency of the nanoegg, as well as quantum yield enhancement of the emitter, were studied using the quasistatic approximation and the semiclassical theory of radiation, following the Gersten–Nitzan and Ford–Weber approaches. Compared to the concentric nanoshell, we show that the dielectric core–metallic shell nanoegg is a more efficient plasmonic nanoantenna for radiative decay rate enhancement of single emitters. The quantum yield of the emitter was found to be more enhanced near the nanoshell, while its emission rate was found to be more enhanced near the nanoegg.

Seaweed extract application and arbuscular mycorrhizal fungal inoculation: a tool for promoting growth and development of date palm (Phoenix dactylifera L.) cv «Boufgous»

In oases ecosystems, date palm (Phoenix dactylifera L.) is a plant that has several socio-economic and environmental roles. During the last decades, the cultivation of date palm and its development are threatened by several constraints, in particular, organic and mineral matter depletion. The main objective of this study was to evaluate the effects of a seaweed extract (SWE) derived from the brown algae Fucus spiralis and an arbuscular mycorrhizal fungus (AMF) strain (Rhizophagus irregularis DAOM 197198) as well as their combination on the growth and development of the date palm (P. dactylifera L.). Growth, physiological, and histological parameters were evaluated. The results show that AMF combined with SWE induced the greatest effect. Indeed this treatment significantly increased the total dry weight, leaf area, stomatal conductance, and nitrogen (N) and phosphorus (P) levels by 27, 36, 48, 377, and 94%, respectively, compared to the control. Potassium (K) and calcium (Ca) contents were highly increased by AMF compared to other treatments. The results also show an enhancement in quantum yield of the photochemistry of PSII (Fv/Fm) by the AMF, SWE, and AMF+SWE treatments. The number of sclerenchyma fibers in AMF+SWE, SWE, and AMF treatments was increased by 681, 164 and 154% respectively, while, the number of vascular bundles was improved by 24% in the SWE treatment compared to the control. Lastly, the results indicated the positive effect of SWE or AMF and, especially, their combination as an efficient practice to improve growth and development of date palm.

Hydrophilic Polymer-Brush Functional Fluorescent Nanoparticles to Suppress Nonspecific Interactions and Enhance Quantum Yield for Targeted Cell Imaging

Hydrophilic poly(glyceryl monomethacrylate) (PGMMA) brush-functional nanoparticles were prepared via macromolecular chain-transfer-agent-adjusted reversible addition–fragmentation chain-transfer pr...

Deep ultraviolet surface-enhanced fluorescence spectroscopy using aluminum nanospheres dimer

The electromagnetic enhancement mechanism of deep ultraviolet surface-enhanced fluorescence (DUV-SEF) was systematically studied theoretically for a molecule placed at the center of the aluminum (Al) nanospheres dimer. The enhanced local excitation field, fluorescence quantum yield and corresponding fluorescence enhancement were calculated in detail with finite element method (FEM). The simulation results reveal that Al nanospheres dimer can provide the strong hotspot for SEF detection in the DUV region. The excitation filed enhancement, quantum yield and fluorescence enhancement are sensitive to the dimer distance at the nanogap of two nanospheres. It was found that the stronger excitation filed enhancement with a small Al to Al distance can significantly compensate the decrease to the quantum yield, and thus lead to the larger fluorescence enhancement at smaller distance. The maximum fluorescence enhancement factor can reach as high as 4 orders at the distance of 1 nm under the excitation wavelength of 200 nm. Our studies can improve the understanding of underlying enhancement mechanism in DUV-SEF effect and further expand its applications in the DUV region.

Discovery of Novel Pseudomonas putida Flavin-Binding Fluorescent Protein Variants with Significantly Improved Quantum Yield.

Oxygen-independent, flavin-binding fluorescent proteins (FbFPs) are emerging as alternatives to green fluorescent protein (GFP), which has limited applicability in studying anaerobic microorganisms, such as human gastrointestinal bacteria, which grow in oxygen-deficient environments. However, the utility of these FbFPs has been compromised because of their poor fluorescence emission. To overcome this limitation, we have employed a high-throughput library screening strategy and engineered an FbFP derived from Pseudomonas putida (SB2) for enhanced quantum yield. Of the resulting SB2 variants, KOFP-7 exhibited a significantly improved quantum yield (0.61) compared to other reported engineered FbFPs, which was even higher than that of enhanced GFP (EGFP, 0.60), with significantly enhanced tolerance against a strong reducing agent.

Giant enhancement of white light emission from Ca9Ln(PO4)7:Eu2+,Mn2+ (Ln = La, Lu, Gd) phosphors achieved by remote aluminum reduction

A series of single-phase Ca9Ln(PO4)7:Eu2+,Mn2+ (Ln = Gd, La, Lu) phosphors with enhanced quantum yields were successfully developed through a topochemical reduction reaction strategy by using elemental aluminum as the reducing agent. Changes were observed both in the spectral shapes and photoluminescence intensities. New broadband emission covering the whole red region and centered at 630 nm from the remote Al reduced Ca9Ln(PO4)7:Eu2+ phosphors was observed, and their PL intensity was found to be greatly enhanced. The remote Al reduced Ca9Gd(PO4)7:Eu2+ reaches 4.3 times higher PL than the phosphors prepared by the traditional reduction method under CO atmosphere with the optimal Eu2+ dopant content. Finally, enhanced white-light emissions were gradually obtained by co-doping Eu2+ and Mn2+ in Ca9Ln(PO4)7, and the PLQY value is raised from extremely low to 61.6%. The mechanism for the changes of luminescence behavior was studied and discussed. This research also provides an enlightening reference for the preparation and development of high efficiency single-phase white light emitting phosphors.

Solid-state fluorescent 1,2,4-triazole zinc(II) complexes: Self-organization via bifurcated (N[sbnd]H)2⋯Cl contacts

Five bis-triazole zinc(II) chloride complexes exhibiting solid-state fluorescence were prepared in 58–99% isolated yields and fully characterized by HRESI-MS, IR, 1H- and CP-MASTOSS 13C{1H} NMR. Results of single-crystal XRD indicate that their crystal structures include the rare bifurcated NH⋯Cl noncovalent contacts. The estimated energy of these interactions is 1.3–1.9 kcal/mol (5.2–7.6 kcal/mol per each associate) as verified by DFT calculations at the ωB97XD/6-31G(d) level of theory and by QTAIM method. The complexes exhibit emission maxima in the range 372–422 nm and nanosecond lifetimes of the fluorescence. In the case of the 3-pheny-1-dimethylamino-1,2,4-triazole complex, a significant enhancement of quantum yield (ca. 20-fold) and blue shift of the emission maximum (33 nm) were observed relatively to the uncomplexed 1,2,4-triazole.

An HBT-based fluorescent dye with enhanced quantum yield in water system and its application for constructing NQO1 fluorescent probe

A novel HBT-based fluorescent dye HBTM, which exhibited long wavelength emission (~600 nm) and large Stokes shift (~203 nm) due to the intrinsic mechanism of ESIPT coupled ICT process, was reasonably designed and synthesized by conjugating neutral pyrimidine moiety as the electron acceptor to 2-(benzo[d]thiazol-2-yl)-4-methylphenol scaffold. Fluorescence emission of HBTM showed less significant spectral dependency on solvents nature, delivering excellent anti-hypochromatic properties, and notably enhanced quantum yield (Φ = 25.5%) in water system was obtained. Furthermore, a “Turn-On” fluorescent probe HBTMP was developed for the detection of NQO1 by masking the hydroxyl group of HBTM with quinone propionic acid (QPA) as the sensing group. Probe HBTMP displayed a highly sensitive and selective response to NQO1 with a linear relationship in the range of 60–180 ng/mL and low detection limit of 1.6 ng/mL, and was successfully applied in detecting endogenous NQO1 in living cancer cells.

Quantitative Detection of G‐Quadruplex DNA in Live Cells Based on Photon Counts and Complex Structure Discrimination

AbstractG‐quadruplex DNA show structural polymorphism, leading to challenges in the use of selective recognition probes for the accurate detection of G‐quadruplexes in vivo. Herein, we present a tripodal cationic fluorescent probe, NBTE, which showed distinguishable fluorescence lifetime responses between G‐quadruplexes and other DNA topologies, and fluorescence quantum yield (Φf) enhancement upon G‐quadruplex binding. We determined two NBTE‐G‐quadruplex complex structures with high Φf values by NMR spectroscopy. The structures indicated NBTE interacted with G‐quadruplexes using three arms through π–π stacking, differing from that with duplex DNA using two arms, which rationalized the higher Φf values and lifetime response of NBTE upon G‐quadruplex binding. Based on photon counts of FLIM, we detected the percentage of G‐quadruplex DNA in live cells with NBTE and found G‐quadruplex DNA content in cancer cells is 4‐fold that in normal cells, suggesting the potential applications of this probe in cancer cell detection.

Quantitative Detection of G-Quadruplex DNA in Live Cells Based on Photon Counts and Complex Structure Discrimination.

G-quadruplex DNA show structural polymorphism, leading to challenges in the use of selective recognition probes for the accurate detection of G-quadruplexes in vivo. Herein, we present a tripodal cationic fluorescent probe, NBTE, which showed distinguishable fluorescence lifetime responses between G-quadruplexes and other DNA topologies, and fluorescence quantum yield (Φf ) enhancement upon G-quadruplex binding. We determined two NBTE-G-quadruplex complex structures with high Φf values by NMR spectroscopy. The structures indicated NBTE interacted with G-quadruplexes using three arms through π-π stacking, differing from that with duplex DNA using two arms, which rationalized the higher Φf values and lifetime response of NBTE upon G-quadruplex binding. Based on photon counts of FLIM, we detected the percentage of G-quadruplex DNA in live cells with NBTE and found G-quadruplex DNA content in cancer cells is 4-fold that in normal cells, suggesting the potential applications of this probe in cancer cell detection.

Achieving ACQ-AIE modulation using isostructural organic fluorophores

Design and synthesis of molecular assemblies which exhibit aggregation-induced emission (AIE) have attracted persistent attention in recent years. However, studies on the impact of the substitution position in isostructural molecules to regulate aggregation-induced emission (AIE) or convert aggregation-caused quenching (ACQ) to AIE have not been reported to date. In the present study, aggregation properties of two isostructural fluorophores viz. (E)-4-(2-(anthracen-9-yl)vinyl)benzonitrile (p-AnCN) and (E)-3-(2-(anthracen-9-yl)vinyl)benzonitrile (m-AnCN), with different substitution positions have been evaluated. It was observed that m-AnCN exhibits an ACQ behavior, whereas, p-AnCN exhibits enhanced emission upon aggregation. Upon aggregation, c.a. 1.4-fold decrease in luminescence quantum yield has been observed for m-AnCN, whereas, c.a. 11-fold enhancement in luminescence quantum yield has been achieved for p-AnCN. Results from the study indicate that absence of interplay between the excited states from a dark Intramolecular Charge Transfer (ICT) state to Locally Excited state (LE) in m-AnCN is the primary reason behind the observed difference in the emission properties of the aggregates. Thus, modulation of ACQ-AIE properties has been achieved using isostructural organic fluorophores, which in turn can be used as a versatile strategy to achieve AIE-luminophores. Further, the AIE active p-AnCN aggregates have been utilized to generate three-component white light emission with CIE coordinates of (0.33, 0.33).

Pattern recognition of amino acids based on highly fluorescent SDS modified pyridyl thiazole derivative

Selective and sensitive detection of amino acids is extremely significant as they play a key role in many biological processes. Herein, a pyridyl-thiazole based fluorophore (PTCN), modified with sodium dodecyl sulphate (SDS) assemblies, has been employed for the sensing of AA in aqueous solution. PTCN molecule exhibited excellent pH response due to the protonation of pyridyl nitrogen followed by the intramolecular charge transfer. PTCN showed dual emission along with enhanced quantum yield in SDS micellar assemblies. This improved the sensitivity of the PTCN –SDS system (PS), not only by lowering the limit of detection but also by detecting basic AA along with acidic AA. A fluorescence turn on response of PS system with acidic AA i.e. Asp and Glu has been observed. However, the PS system exhibited a ratiometric sensing pattern for basic AA i.e. Arg, Lys and Hys. Protonation and deprotonation of the fluorophore in presence of different types of AA are responsible for the changes observed in fluorescence spectra. The detection limits for Asp and Glu were found to be 0.47 μM and 0.64 μM respectively. Arg, Lys and Hys showed a detection limit of 8.36 μM, 26.6 μM and 51.9 μM respectively. Principal component analysis (PCA) effectively demonstrated discrimination of acidic, basic and neutral AA clusters. This study demonstrates the efficiency of the PS ensemble for selective, sensitive and discriminative sensing of AA.

Ultrafast excited state dynamics of biliverdin dimethyl ester coordinate with zinc ions

As one of the biological endogenous pigments, biliverdin (BV) and its dimethyl ester (BVE) have extremely weak fluorescence in solution with quantum yield less than 0.01%. However, the situation reverses with the addition of zinc ions. The strength for fluorescence of BVE-Zn2+ complex is greatly enhanced and fluorescence quantum yield can increase to 5%. Herein, we studied ultrafast excited state dynamics of BVE-Zn2+ complex in ethanol, n-propanol, and DMSO solutions in order to reveal the mechanism of fluorescence quantum yield enhancement. The results show that BVE can form a stable coordination complex with zinc with 1:1 stoichiometry in solution. BVE is structurally and energetically more stable in the complex. Using picosecond time-resolve fluorescence and femtosecond transient absorption spectroscopy, we show that smaller non-radiative rate constant of BVE-Zn2+ complex in DMSO is the key to increasing its fluorescence quantum yield and the excited state decay mechanism is also revealed. These results provide valuable information about the fluorescence property change after BVE binding to metal ions and may provide a guidance for the study of phytochromes or other fluorescence proteins in which BV/BVE acts as chromophores.

Enhancing Quantum Yield in Strained MoS2 Bilayers by Morphology-Controlled Plasmonic Nanostructures toward Superior Photodetectors

Recently, extracting hot electrons from plasmonic nanostructures and utilizing them to enhance the optical quantum yield of two-dimensional transition-metal dichalcogenides (TMDs) have been topics of interest in the field of optoelectronic device applications, such as solar cells, light-emitting diodes, photodetectors, and so on. The coupling of plasmonic nanostructures with nanolayers of TMDs depends on the optical properties of the plasmonic materials, including radiation pattern, resonance strength, and hot electron injection efficiency. Herein, we demonstrate the augmented photodetection of a large-scale, transfer-free bilayer MoS2 by decorating this TMD with four different morphology-controlled plasmonic nanoparticles. This approach allows engineering the band gap of the bilayer MoS2 due to localized strain that stems up from plasmonic nanoparticles. In particular, the plasmonic strain blue shifts the band gap of bilayer MoS2 with 32 times enhanced photoresponse demonstrating immense hot electron injection. Besides, we observed the varied photoresponse of MoS2 bilayer hybridized with different morphology-controlled plasmonic nanostructures. Although hot electron injection was a substantial factor for photocurrent enhancement in hybrid plasmonic semiconductor devices, our investigations further show that other key factors such as highly directional plasmonic modes, high-aspect-ratio plasmonic nanostructures, and plasmonic strain-induced beneficial band structure modifications were crucial parameters for effective coupling of plasmons with excitons. As a result, our study sheds light on designing highly tailorable plasmonic nanoparticle-integrated transition-metal dichalcogenide-based optoelectronic devices.

Visible Light Photodegradation of Formaldehyde over TiO2 Nanotubes Synthesized via Electrochemical Anodization of Titanium Foil.

In this study, a series of TiO2 nanotubes (NTs) were synthesized employing electrochemical anodization of titanium foil in an ionic liquid solution containing a mixture of glycerol and choline chloride, acting as electrolyte. The as-synthesized TiO2 NTs were calcined at 350, 450, or 550 °C for a 2 h duration to investigate the influence of calcination temperature on NTs formation, morphology, surface properties, crystallinity, and subsequent photocatalytic activity for visible light photodegradation of gaseous formaldehyde (HCHO). Results showed that the calcination temperature has a significant effect on the structure and coverage of TiO2 NTs on the surface. Freshly synthesized TiO2 NTs showed better-ordered structure compared to calcined samples. There was significant pore rupture with increasing calcination temperature. The transformation from anatase to rutile phase appeared after calcination at 450 °C and the weight fraction of the rutile phase increased from 19% to 36% upon increasing the calcination temperature to 550 °C. The band gaps of the TiO2 NTs were in the range from 2.80 to 2.74 eV, shifting the active region of the materials to visible light. The presence of mixed anatase–rutile TiO2 phases in the sample calcined at 450 °C showed enhanced photoactivity, which was confirmed by the 21.56 mg∙L−1∙g−1 removal of gaseous formaldehyde under 120 min of visible light irradiation and displayed enhanced quantum yield, ∅HCHO of 17%.