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A DNA-Encapsulated Silver Cluster and the Roles of Its Nucleobase Ligands
摘要： Silver clusters consisting of ~10 atoms are readily bound by and encapsulated within DNA strands to yield strong absorption and emission. The coordination environments, however, are poorly understood, so cluster adducts can only be empirically tuned. This work describes the C4AC4TC3G strand that templates a particular cluster adduct. Its sequence has three types of nucleobases with distinct roles – tracts of cytosines that collectively coordinate the cluster, thymine acting as a junction in the overall strand, and the adenine/guanine pair that exclusively forms the cluster. In relation to the native oligonucleotide, the DNA-silver cluster complex diffuses faster and is more compact, thus suggesting that the strands folds because of the cluster. The Ag10 6+ adduct emits with λex/λem = 490/540 nm, a 19% quantum yield, and a biexponential 1.1/2.1 ns lifetime. The electronic environment for the cluster is controlled by the heteroatoms in the adenine and guanine. Most significantly, the N7 and the N2 in the guanine change the fluorescence quantum yield by 60-fold and shift the fluorescence lifetime by ~3.8 ns. Thus, our studies discern distinct spectroscopic and structural roles for the nucleobase ligands in C4AC4TC3G, and these finding may help develop new DNA templates for other silver cluster adducts.
关键词： Nucleobase ligands,DNA,Silver clusters,Lifetime,Fluorescence,Quantum yield
更新于2025-09-23 15:21:21
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Plasmonic Enhancement of Dye Fluorescence in Polymer/Metal Nanocomposites
摘要： The effect of the plasmonic enhancement of dye fluorescence in poly(vinyl butyral) films containing Ag/SiO2 core-shell nanoparticles has been thoroughly studied. It has been shown that the magnitude of this effect can be quite large (up to 5 times) even for a dye having a very high quantum yield (coumarin 7). Therewith, it substantially depends on the size and concentration of Ag/SiO2 particles and the quantum yield of a dye. The results obtained are discussed with involvement of mechanisms reported in the literature for plasmonic enhancement of fluorescence of dyes characterized by high and low quantum yields.
关键词： plasmonic enhancement,dye fluorescence,quantum yield,polymer/metal nanocomposites,Ag/SiO2 core-shell nanoparticles
更新于2025-09-23 15:19:57
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Photoluminescence in <i>m</i> -carborane–anthracene triads: a combined experimental and computational study
摘要： New hybrids synthesized by linking two anthracenyl units to the Ccluster atoms of a non- (4), a mono- (5) and a di-iodinated (6) m-carborane fragment through CH2 spacers, along with their full characterization, are reported. Noticeably, bonding the m-carborane fragment to the anthracene moieties produces a significant increase of more than two-fold in the intrinsic fluorescence quantum yield (fF) of the anthracene itself, with values of fF 4 60% in THF and fF 4 48% in toluene, although it does not alter the absorption and emission patterns of the fluorophore in solution. A red-shift of the emission maximum with respect to the solution is observed in the aggregate state (THF/H2O, 1 : 99 v/v), along with moderate quantum yields; compounds 4 and 5 show fF = 22 and 19%, respectively, whereas 6 has a lower value (fF = 8%). The di?erence between the fF values in the aggregate state has been attributed to the arrangement of dimers for each compound in the solid state structures. X-ray crystal structures of compounds 4 and 5 show the anthracene units to be roughly parallel, whereas such an arrangement is clearly disrupted in compound 6. Such di?erences have been analyzed by Hirshfeld surfaces, decomposed fingerprint plots for the three compounds and DFT calculations. The combined results from the supramolecular analyses and DFT studies support the idea that a less delocalized system in the case of 6 can be explained by the di?erent packing in the aggregate or solid state for this di-iodo-derivative. The observed arrangement of molecules of 6 seems to be related to a larger number of H(cid:2) (cid:2) (cid:2)I contacts, with respect to the non-iodinated or mono-iodinated compounds, 4 or 5. According to this assumption, there is a direct relationship between the structure in the solid state and the PL properties; in the m-carborane derivatives, small changes in their structures have caused variations in the photophysical properties, especially in the quantum e?ciency.
关键词： X-ray diffraction,anthracene,m-carborane,Hirshfeld surfaces,photoluminescence,DFT calculations,fluorescence quantum yield
更新于2025-09-19 17:15:36
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Relation between Fluorescence Quantum Yield and Opena??Circuit Voltage in Complete Perovskite Solar Cells
摘要： Bringing the Voc of a perovskite solar cell toward its radiative value, corresponding to a 100% external fluorescence quantum yield (QY) of the cell, has been pursued to reach the highest performance photovoltaic devices. Striving for it, many works have focused on maximizing the QY of the active layer isolated from the rest of the cell layers. However, such quantity does often not correlate with Voc following the ideal diode relation. Herein, the QYs of complete FA0.8MA0.2PbI3-yBry solar cells are reported, ranging from 0.1 to 3%, and compare them with their Vocs, ranging from 1 to 1.13 V. By combining these measurements with electromagnetic simulations based on a full-wavevector detailed balance and a fluorescence power loss model, it is demonstrated that a non-optimal Voc in mixed-cation lead halide perovskite cells is not only due to non-radiative photocarrier recombination at traps. Besides the expected parasitic absorption of the emitted photons in the electrode layers, discrepancies appear between Voc and QY. These discrepancies are attributed to the rise of energy barriers, a side-effect of trap removal. Indeed, although surface passivation may enhance the QY, its beneficial effect may be counterbalanced by the emergence of such barriers between active and charge transporting layers.
关键词： perovskite solar cells,radiative limit,open-circuit voltage,fluorescence quantum yield,detailed balance theory
更新于2025-09-19 17:13:59
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Dibenzo[ <i>hi</i> , <i>st</i> ]ovalene as Highly Luminescent Nanographene: Efficient Synthesis via Photochemical Cyclodehydroiodination, Optoelectronic Properties, and Single-Molecule Spectroscopy
摘要： Dibenzo[hi,st]ovalene (DBOV), as a new nanographene, has demonstrated promising optical properties, such as red emission with a high fluorescence quantum yield of 79% and stimulated emission, as well as high thermal stability and photostability, which indicated its promise as a light-emitting and optical gain material. However, the previous synthetic routes required at least 12 steps. This obstructed access to different derivatives, e.g., to obtain crystals suitable for X-ray diffraction analysis and to tune the optoelectronic properties. Here, we report an efficient synthetic pathway to DBOV based on a sequential iodination-benzannulation of bi(naphthylphenyl)diyne, followed by photochemical cyclodehydroiodination (PCDHI). This protocol included a fused bischrysene as a key intermediate and furnished scalable amounts of meso-substituted DBOV derivatives with different substituents. DBOV with 2,6-dimethylphenyl groups could be used for single-crystal X-ray analysis, revealing the precise structure of the DBOV core. The optoelectronic properties of the DBOV derivatives were investigated by UV?vis absorption and fluorescence spectroscopy, cyclic voltammetry, and density functional theory calculations. Single-molecule spectroscopy at room and low temperatures provided novel insights into the photophysics of DBOV embedded in a polymer film. As a result of weak coupling of the optical transitions to the matrix, single-molecule emission spectra at 4.5 K showed narrow vibronic lines. The fluorescence autocorrelation function covering 9 orders of magnitude in time displayed high contrast photon antibunching and bunching, from which the fluorescence decay rate and the triplet population and depopulation rates could be retrieved. Remarkably, the intersystem crossing rate into the triplet state decreased by more than an order of magnitude at low temperature, demonstrating that temperature can be a crucial parameter to boost single photon emission of an aromatic hydrocarbon.
关键词： fluorescence quantum yield,nanographene,single-molecule spectroscopy,optoelectronic properties,photochemical cyclodehydroiodination
更新于2025-09-16 10:30:52
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A Facile One Step Hydrothermal Synthesis of Carbon Quantum Dots For Label -Free Fluorescence Sensing Approach to Detect Picric Acid in Aqueous Solution
摘要： In this work, a facile one step approach has been applied for the synthesis of nitrogen and sulphur co-doped water soluble carbon quantum dots (NS-CQDs) through hydrothermal treatment of L-Lysine and thiourea. The obtained NS-CQDs have a high quantum yield (QY) of 53.19 % and emit strong blue fluorescence under UV light excitation of wavelength 365 nm. The morphology of NS-CQDs is spherical in shape and their sizes are distributed in the range 5-8 nm with average diameter 6.86 nm. Moreover the NS-CQDs show excitation dependent emission behavior due to quantum confinement effect. Additionally, NS-CQDs serve as a fluorescent probe for the selective and sensitive detection of picric acid (PA) in aqueous solution. A good linear response to PA in the concentration range 1-10 μM with a detection limit 0.24 μM has been obtained. The high selectivity of PA by NS-CQDs is suggested to be arises from fluorescence resonance energy transfer (FRET) mechanism. Finally these NS-CQDs fluorescent probes have been examined in real water sample by measuring the concentration of PA in tap water.
关键词： Fluorescence,quantum yield,Picric acid,Carbon quantum dots
更新于2025-09-11 14:15:04
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Facile preparation of high fluorescent carbon quantum dots from orange waste peels for nonlinear optical applications
摘要： A facile and eco‐friendly hydrothermal method was used to prepare carbon quantum dots (CQDs) using orange waste peels. The synthesized CQDs were well dispersed and the average diameter was 2.9 ± 0.5 nm. Functional group identification of the CQDs was confirmed by Fourier transform infrared spectrum analysis. Fluorescence properties of the synthesized CQDs exhibited blue emission. The fluorescence quantum yield of the CQDs was around 11.37% at an excitation wavelength of 330 nm. The higher order nonlinear optical properties were examined using a Z‐scan technique and a continuous wave laser that was operated at a wavelength of 532 nm. Results demonstrated that the synthesis of CQDs can be considered as promising for optical switching devices, bio‐scanning, and bio‐imaging for optoelectronic applications.
关键词： Z‐scan analysis,fluorescence quantum yield,CQDs,HR‐TEM,hydrothermal method
更新于2025-09-11 14:15:04
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Fluorescence quantum yield of CDOM in coastal zones of the Arctic seas
摘要： Along with traditional optical indices, calculated from absorption and ?uorescence spectra to describe chromophoric dissolved organic matter (CDOM) naturally occurring in water, the ?uorescence quantum yield (FQY) becomes signi?cant. Knowledge of CDOM optical properties is important for satellite remote sensing as well as for lidar ground-true measurements. The FQY as a function of excitation wavelength within 240–500 nm range for a variety of the Arctic shelf waters was determined for the ?rst time in order to identify the characteristic chromophores peculiar to di?erent regions of the Arctic basin a?ected by freshwater runo?. The surface water samples were collected during several cruises in 2015–2017 in the following sites: the mouth areas of the Khatanga and Lena Rivers (the Laptev Sea), the delta area of the Northern Dvina River (the White Sea), desalinated waters of the Kara Sea (in?uenced by freshwater of the Ob and Yenisei Rivers) and the East Siberian Sea (in?uenced by freshwaters of the Indigirka and Kolyma Rivers), as well the shelf areas of those seas not a?ected by terrigenous runo?. To characterize DOM, conventional optical indices SR, HIX, and BIX were calculated. In most cases, important humic character of DOM was established, while the contribution of autochthonous organic matter varied from low to intermediate level. For the samples with terrestrial impact, the FQY decreased from excitation at 240 nm to 270–280 nm and then increased, demonstrating two peaks at 340 and 380 nm, with constant decrease towards longer excitation wavelengths; at λex = 380 nm FQY varied from 1.4% to 3.1%. In some cases, additional maximum at 270 nm of FQY-excitation dependency was observed as an indicator of autochthonous nature of biological material. Minimal FQY was measured for the White Sea surface waters, the maximal for the Laptev and East Siberian seas.
关键词： optical properties,fluorescence quantum yield,CDOM,Arctic seas,remote sensing
更新于2025-09-04 15:30:14