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Extrinsic heavy metal atom effect on the solid state room temperature phosphorescence of cyclic triimidazole
摘要： Four coordination compounds [Zn3(CH3COO)6(H2O)2](TT)2, [Cd(H2O)6](ClO4)2(TT)2, [Cd(H2O)6](BF4)2(TT)2, [Zn(H2O)6](BF4)2(TT)2 (1-4) accommodating triimidazo[1,2-a:1',2'-c:1'',2''-e][1,3,5]triazine (TT) as a guest in their crystal lattice are isolated and fully photophysically and structurally characterized. Their emission properties are compared with those of afterglow TT and interpreted taking into account the heavy atom effect and crystal packing similarities and differences. In the case of 1, due to the closeness of the TT H-aggregates arrangement with that of the phosphor's pure phase, the observed intensification of the phosphorescent emission at the expense of the prompt one is attributed to the extrinsic heavy atom effect of Zn. In 2 and 3, the heavier Cd atom is responsible for a decrease in the lifetimes of the afterglow emission, despite the presence of tightly overlapped H-dimers in the crystal structure. Finally for 4, isostructural with 3, the Zn atom reveals in RTUP lifetime comparable with that of 1.
关键词： extrinsic heavy atom effect,H aggregates,time resolved photoluminescence,room temperature ultralong phosphorescence,single crystal XRD
更新于2025-09-23 15:23:52
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Physico-chemical chlorophyll-a species in aqueous alcohol solutions determine the rate of its discoloration under UV light
摘要： Chlorophyll-a (Chl-a) discolors when it is exposed to light, and such discoloration decreases food quality. To elucidate the discoloration mechanism of Chl-a, we determined discoloration rate in di?erent Chl-a chemical species and assessed the size of Chl-a aggregates in mixed aqueous solutions of methanol and ethanol. Chl-a existed as monomer, J-aggregate, and random aggregate in solutions with di?erent alcohol concentrations. The predominant species depended on the alcohol concentration. Monomeric Chl-a and J-aggregates discolored quickly, whereas random aggregates discolored slowly. Particle sizes of J-aggregates were 319 and 2305 nm in diameter in aqueous solutions of methanol and ethanol, respectively. The sizes of random aggregates were 51 and 79 nm in 10% (v/v) aqueous solutions of methanol and ethanol, respectively. The size of Chl-a aggregates positively correlated with the rate of Chl-a discoloration under UV light. Based on the results obtained, we propose a mechanism of Chl-a discoloration.
关键词： Chlorophyll-a,Discoloration,Random aggregates,Particle size,J-aggregates
更新于2025-09-23 15:21:21
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Photo-Annealing of Merocyanine Aggregates
摘要： In this work we elucidate the fundamental difference between aggregate formation of donor-π-acceptor merocyanines in their electronic ground and excited states. While increasing the π-bridge size favors formation of π-stacked aggregates in the dark, irradiation with visible light causes reorientation of the dyes to form prototype H-aggregates with compensating dipole moments. This photo-annealing changes the supramolecular structure and its UV-vis spectroscopic properties dramatically, thus being of importance for the function of active layers composed of these dyes. Aggregates of the ground state dyes are bound cooperatively through ππ-London dispersion interactions and hydrogen bonds between the polar α-cyano-carboxylic acid groups. However, charge transfer upon photoexcitation leads to repulsion of the polar acid groups. Electronic excitation of the dyes approximately doubles the ground state dipole moment, thus driving molecular reorientation into prototype H-aggregate structures. We show that this photo-induced supramolecular rearrangement can disrupt the large polymeric aggregates formed in the dark. The photo-induced supramolecular structural changes reported in this work will influence the performance of optoelectronic devices composed of these structures and must be controlled to avoid morphological decomposition of active layers upon operation.
关键词： merocyanines,photo-annealing,H-aggregates,supramolecular structure,UV-vis spectroscopy,dipole moments,aggregate formation
更新于2025-09-23 15:21:21
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Synthesis and Photophysical Properties of Multichromic Nanocrystals of Polymethine Dyes
摘要： A unique method for the self-assembly of multilayer multichromic molecular crystals from three various polymethine dyes absorbing light in the broad spectral range has been developed. This method is based on the formation of an anionic platform of J-aggregates of magnesium complexes of thiamonomethinecyanines in an aqueous solution followed by the matrix synthesis of J-aggregates of two cationic trimethinecyanines on the surface of the platform. Spectral, luminescent, and photoelectric properties of the multichromic crystals of dyes have been studied. It has been shown that each multichromic organic crystal is a multilayer photoelement which possesses photoconductivity in three maxima of exciton absorption in the blue, green, and red spectral ranges with efficiency from 2.7 to 6.1%. The results form the basis for the technological development of high-organized molecular structures possessing unique optical and photoelectric properties with the aim of applying them in organic and hybrid organic/inorganic photonics and optoelectronics, including in the form of thin-film photoconverters in broad spectral ranges.
关键词： multichromic nanocrystals,polymethine dyes,nanophotonics,photoelectric properties,J-aggregates
更新于2025-09-23 15:21:21
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Excitation Transfer in Hybrid Nanostructures of Colloidal Ag2S/TGA Quantum Dots and Indocyanine Green J-Aggregates
摘要： The regularities of the electron excitations exchange in hybrid associates of colloidal Ag2S quantum dots, passivated with thioglycolic acid (Ag2S/TGA QDs) with an average size of 2.2 and 3.7 nm with Indocyanine Green J-aggregates (ICG) were studied in this work by methods of absorption and luminescence spectroscopy. It was shown that IR luminescence sensitization of Ag2S/TGA QDs with an average size of 3.7 nm in the region of 1040 nm is possible due to non-radiative resonance energy transfer from Ag2S/TGA QDs with an average size of 2.2 nm and luminescence peak at 900 nm using ICG J-aggregate as an exciton bridge. The sensitization efficiency is 0.33. This technique provides a transition from the first therapeutic window (NIR-I, 700-950 nm) to the second (NIR-II, 1000-1700 nm). It can allow high to increase the imaging in vivo resolution.
关键词： Non-radiative resonance energy transfer (FRET),Indocyanine green,Hybrid associate,Luminescence properties,Silver sulfide quantum dots,J-aggregates
更新于2025-09-23 15:21:01
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Highly Efficient Energy Transfer from Water Soluble Zinc Silver Indium Sulphide Quantum Dot to Organic J-Aggregates
摘要： The present work has been carried out with an aim to design and develop an efficient light harvesting inorganic-organic hybrid nanoscale material by employing less toxic, environment friendly inorganic substance and also to understand the mechanism of inter-particle electronic interaction between the inorganic and organic components of the nanomaterial. Specifically, the inorganic-organic hybrid associate has been made by integrating water soluble semiconductor QDs (Zinc-silver-indium-sulfide (ZAIS)) and organic J-aggregates of a cyanine dye (S2165). The fabrication of present nano-hybrid system has been achieved via electrostatically driven self-assembly of organic dyes over ZAIS QDs. The interaction between QD and J-aggregates have been investigated by steady state and time resolved fluorescence measurements. Zeta potential measurements have also been performed to understand the role of electrostatic interaction and thermodynamic feasibility of the association process. The investigations have revealed that energy transfer (ET) process between QD and J-aggregates mediated through dipole-dipole mechanism. Interestingly, data analysis based on F?rster theory has further revealed that the ET from QD to J-aggregates is very high indicating efficient electronic coupling between the inorganic QD and the organic J-aggregates. Zeta potential measurements and thermodynamic calculations have demonstrated that the interaction between QD and organic dye is electrostatically driven and the association of organic dyes over QD is thermodynamically feasible. The outcome of the present study is expected to be helpful in designing efficient nanoscale light harvesting devices. Additionally, fluorescence microscopy and toxicity studies on the QDs have also shown its suitability for biological applications.
关键词： energy transfer,fluorescence microscopy,electrostatic interaction,J-aggregates,inorganic-organic hybrid,toxicity studies,quantum dots
更新于2025-09-23 15:21:01
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MALDI MS Imaging at Acquisition Rates Exceeding 100 Pixels per Second
摘要： The practicality of matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) applied to molecular imaging of biological tissues is limited by the analysis speed. Typically, a relatively low speed of stop-and-go micromotion of XY stages is considered as a factor substantially reducing the rate with which fresh sample material can be supplied to the laser spot. The sample scan rate in our laboratory-built high-throughput imaging TOF mass spectrometer was significantly improved through the use of a galvanometer-based optical scanner performing fast laser spot repositioning on a target plate. The optical system incorporated into the ion source of our MALDI TOF mass spectrometer allowed focusing the laser beam via a modified grid into a 10-μm round spot. This permitted the acquisition of high-resolution MS images with a well-defined pixel size at acquisition rates exceeding 100 pixel/s. The influence of selected parameters on the total MS imaging time is discussed. The new scanning technique was employed to display the distribution of an antitumor agent in 3D colorectal adenocarcinoma cell aggregates; a single MS image comprising 100 × 100 pixels with 10-μm lateral resolution was recorded in approximately 70 s.
关键词： MSI,TOF,Mass spectrometry imaging,High throughput,Laser beam scanning,Colorectal adenocarcinoma,3D cell aggregates,Spheroids,Grid ion source,MALDI
更新于2025-09-23 15:21:01
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Photochemical dynamics under incoherent illumination: Light harvesting in self-assembled molecular J-aggregates
摘要： Transport phenomena in organic, self-assembled molecular J-aggregates have long attracted a great deal of attention due to their potential role in designing novel organic photovoltaic devices. A large number of theoretical and experimental studies have been carried out describing excitonic energy transfer in J-aggregates under the assumption that excitons are induced by a coherent laser-light source or initialized by a localized excitation on a particular chromophore. However, these assumptions may not provide an accurate description to assess the efficiency of J-aggregates, particularly as building blocks of organic solar cells. Under natural conditions, J-aggregates would be subjected to an incoherent source of light (as is sunlight), which would illuminate the whole photosynthetic complex rather than a single molecule. In this work, we present the first study of the efficiency of photosynthetic energy transport in self-assembled molecular aggregates under incoherent sunlight illumination. By making use of a minimalistic model of a cyanine dye J-aggregate, we demonstrate that long-range transport efficiency is enhanced when exciting the aggregate with incoherent light. Our results thus support the conclusion that J-aggregates are, indeed, excellent candidates for devices where efficient long-range incoherently induced exciton transport is desired, such as in highly efficient organic solar cells.
关键词： incoherent illumination,exciton transport,organic solar cells,J-aggregates,photosynthetic energy transport
更新于2025-09-23 15:19:57
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Numerical study of microscale laser bulging based on crystal plasticity
摘要： Microscale laser bulging is an innovative and promising micro metal forming technology and is widely used in the micro electronics industry. With the image-based Voronoi tessellations, the three-dimensional finite element models of disk-shaped polycrystalline aggregates with different initial grain sizes were established to simulate the processes of microscale laser bulging of pure copper foil. The temporal-spatial-distributed laser shock wave pressure was employed to deform the polycrystalline aggregates of pure copper foil. A size-dependent unified constitutive model of crystal plasticity, incorporating the thermally-activated and viscous drag-dominated stages of dislocation motion, was developed and implemented into the finite element codes to describe the plastic deformation behavior at a wide range of strain rates. In the cases of different laser shock wave pressures and initial grain sizes, the predicted maximum bulging heights of pure copper foil are in good agreement with the experimental data, and the resultant thickness and surface roughness also correlate well with the corresponding experiment observations. The simulated equivalent plastic strains and Mises stresses of residual stress components were analyzed by the cross comparisons, and the effect of grain boundary on laser shock wave was further discussed in detail.
关键词： laser shock wave,numerical simulation,polycrystalline aggregates,crystal plasticity,microscale laser bulging
更新于2025-09-23 15:19:57
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Photophysical Impact of Diacetylenic Conjugation on Classical Donor-Acceptor Electronic Energy Pair
摘要： Organic fluorophores with extended π-conjugation are important for their wide-spread applications. The present work provides photophysical insights of a diacetylene bridged classical donor-acceptor electronic energy pair, naphthalene-pyrene, in comparison with its part molecular structures, naphthyl and pyrenyl acetylenes as well as parent naphthalene and pyrene chromophores. The diacetylenic dye loses individual spectral identities of the donor and acceptor fluorophores exhibiting a locally excited (LE) emission (~411 nm) from the overall molecular entity with high fluorescence quantum yields (0.55–0.84) in non-aqueous media. In contrast to parent pyrene, the hybrid derivative shows strongly allowed S0→S1 transition. In mixed-aqueous media, the dye forms J-aggregates displaying a new red-shifted absorption (~425 nm) as well as emission (~510 nm) band. Unlike the hybrid dye, the naphthyl and pyrenyl acetylenes do not form aggregates. In the aggregate state of the hybrid fluorophore, electronic energy transfer takes place from the naphthyl moiety to pyrenyl ring. The excited state photophysical properties of the dye is exploited to vapor sensing in solid state.
关键词： vapor sensing,Organic fluorophores,donor-acceptor electronic energy pair,diacetylene bridged,naphthalene-pyrene,locally excited emission,J-aggregates,electronic energy transfer,π-conjugation,fluorescence quantum yields
更新于2025-09-23 15:19:57