Electronic Energy Transfer Research Articles

The development of Friedländer heteroannulation through a single electron transfer and energy transfer pathway using methylene blue (MB+)

The radical Friedländer hetero-annulation of 2-aminoaryl ketone and -methylene carbonyl compound was used to develop a green tandem approach for the metal-free synthesis of polysubstitutedquinolines. At room temperature in an ethanol solvent, photo-excited state functions generated from MB+ were used as single-electron transfer (SET) and energy transfer (EnT) catalysts, utilizing visible light as a renewable energy source in the air atmosphere. The purpose of this research is to increase the use of a nonmetal cationic dye that is both inexpensive and widely available. High yields, energy-effectiveness, high atom economy, time-saving features of the reaction, and operational simplicity, and the least amount of a catalyst are the benefits of this study. As a result, a wide range of ecological and long-term chemical properties are obtained. Polysubstitutedquinolines' turnover number (TON) and turnover frequency (TOF) have been calculated. Surprisingly, such cyclization can be accomplished on a gram scale, indicating that the process has industrial potential.

Exploring the Potential of Water-Soluble Cu(II) Complexes with MPA–CdTe Quantum Dots for Photoinduced Electron Transfer

Three water-soluble copper complexes based on the amine/pyridine functionalities were investigated, along with quantum dots, as a catalyst–photosensitizer assembly, respectively, for fundamental understanding of photoinduced electron transfer. Luminescence quenching and lifetime measurements were performed to try and establish the actual process that leads to the quenching, such as electron transfer, energy transfer, or complex formation (static quenching). Cyclic voltammetry and dynamic light scattering experiments were also performed. Irrespective of the similar reduction potentials of the three complexes, very different photoluminescence properties were observed.

Tuning between Quenching and Energy Transfer in DNA-Templated Heterodimer Aggregates.

Molecular excitons, which propagate spatially via electronic energy transfer, are central to numerous applications including light harvesting, organic optoelectronics, and nanoscale computing; they may also benefit applications such as photothermal therapy and photoacoustic imaging through the local generation of heat via rapid excited-state quenching. Here we show how to tune between energy transfer and quenching for heterodimers of the same pair of cyanine dyes by altering their spatial configuration on a DNA template. We assemble “transverse” and “adjacent” heterodimers of Cy5 and Cy5.5 using DNA Holliday junctions. We find that the transverse heterodimers exhibit optical properties consistent with excitonically interacting dyes and fluorescence quenching, while the adjacent heterodimers exhibit optical properties consistent with nonexcitonically interacting dyes and disproportionately large Cy5.5 emission, suggestive of energy transfer between dyes. We use transient absorption spectroscopy to show that quenching in the transverse heterodimer occurs via rapid nonradiative decay to the ground state (∼31 ps) and that in the adjacent heterodimer rapid energy transfer from Cy5 to Cy5.5 (∼420 fs) is followed by Cy5.5 excited-state relaxation (∼700 ps). Accessing such drastically different photophysics, which may be tuned on demand for different target applications, highlights the utility of DNA as a template for dye aggregation.

Energy deposition on nuclear emulsion by slow recoil ions for directional dark matter searches

The electronic energy deposited on nuclear emulsions by C ions of 5--200 keV and Kr ions of 5--600 keV is evaluated and compared with those deposited by fast ions for designing and fabricating fine-grain nuclear emulsions for directional dark matter searches. The nuclear quenching factor and the electronic linear energy transfer, which refers to the specific electronic energy deposited along the ion track, are evaluated. The so-called core and penumbra of heavy-ion track structure is modified to understand the track caused by recoil ions produced by dark matter candidate, i.e., weakly interacting massive particles, striking a nucleus in the AgBr crystal of nuclear emulsion. Very heavy recoil ions, 100--180 keV Pb ions, produced in $\ensuremath{\alpha}$ decay are also studied. Furthermore, the track structures due to protons of 25--80 keV are evaluated to consider the influence of background neutrons in underground laboratories.

Light-Harvesting Crystals Formed from BODIPY-Proline Biohybrid Conjugates: Antenna Effects and Excitonic Coupling.

A boron dipyrromethene (BODIPY) derivative bearing a cis-proline residue at the meso-position crystallizes in the form of platelets with strong (i.e., ΦF = 0.34) red fluorescence, but the absorption and emission spectra differ markedly from those for dilute solutions. A key building block for the crystal is a pseudo-dimer where hydrogen bonding aligns the proline groups and separates the terminal chromophores by ca. 25 Å. Comparison with a covalently linked bichromophore suggests that one-dimensional (1D) excitonic coupling between the terminals is too small to perturb the optical properties. However, accretion of the pseudo-dimer forms narrow channels possessing a high density of chromophores. The resultant absorption spectrum exhibits strong excitonic splitting, which can be explained quantitatively using the extended dipole approach and allowing for coupling between ca. 30 BODIPY units. Fluorescence, which decays with a lifetime of 2.2 ns, is assigned to a delocalized and (slightly) super-radiant BODIPY dimer situated at the interface and populated via electronic energy transfer from the interior.

Deciphering CaO-induced peroxydisulfate activation for destruction of halogenated organic pollutants in a low energy vibrational mill

• CaO-PDS features high reactivity in low energy vibrational mill. • The CaO addition much enhances 2,4-DCP dechlorination and mineralization. • PDS is activated via electron transfer, base activation, and energy transfer. • CaO both activates PDS and transforms SO 4 •− surf to •OH surf. • CaO-PDS enables destruction of persistent halogenated organic pollutants. Mechanochemical (MC) treatment utilizing calcium oxide (CaO) and peroxydisulfate (PDS) for halogenated organic pollutants (HOPs) has been developed for pure substance degradation and contaminated soil remediation. However, the role of CaO and the mechanism of PDS activation in solid phase reaction remain unclear. This study was dedicated to decipher CaO-induced PDS activation for destruction of typical HOPs such as 2,4-dichlorophenol (2,4-DCP), in a low energy single-cylinder horizontal vibrational mill. With mass ratio of CaO:PDS:2,4-DCP = 6.3:6.7:1, CaO-PDS as co-milling agents destructs 2,4-DCP with much higher degradation and dechlorination rate than CaO (about 13.9- and 121.2-fold) or PDS (about 2.5- and 9.4-fold) only. According to detection of intermediates and measurement of total organic carbon, the CaO addition shifts the degradation pathway into dechlorination and ring-open routes, and increase mineralization efficiency from 64% (PDS only) to 96%. Quenching test suggests •OH surf is the dominant oxidative species with CaO-PDS as co-milling agents, which enables complete oxidative destruction. PDS in such MC system is activated mainly via electron transfer (∼50.6%), followed by base activation (∼40.5%) and energy transfer (＜ 8.9%). CaO plays a dual role in activating PDS and transforming SO 4 •− surf to •OH surf . Finally, CaO-PDS shows high reactivity in destructing persistent HOPs like polybrominated phenols and polychlorinated benzenes, which expands its potential in practical application. This study may guide the selection of effective oxidative co-milling agents for mineralization of solid HOPs by mechanochemistry, facilitating safe disposal of obsolete HOPs.

Photoluminescent carbon nanomaterials for sensing of illicit drugs: focus.

The growth of illicit drugs is a serious social problem, putting great pressure on law enforcement officers to screen numerous suspicious samples at crime scenes. Although commercial colorimetric kits are available, they are limited to common illicit drugs. With increasing numbers of new psychoactive substances in the market, accurate and rapid screening assays are highly demanded. Carbon dots (C-dots) are photoluminescent (PL) carbon nanomaterials with unique properties of excellent stability against salt and photo-irradiation, low blinking, and biocompatibility. They can be prepared easily through various routes from numerous precursors. This Focus provides examples of C-dots based PL assays for screening illicit drugs. The drugs induce PL changes of C-dots mostly through electron transfer and energy transfer. Liquid- and solid-phase PL assays of C-dots can be applied for in-field screening, with advantages of rapidity, low cost, selectivity, and minimum color interference, showing their great commercial potential.

Conjugated polyelectrolyte-based ternary exciton funnels via liposome scaffolds

We used a vesicle scaffold to form a ternary, quasi-panchromatic funnel for electronic excited states oriented from the outer surface towards the membrane. We did so via electronic energy transfer (EET) from two conjugated polyelectrolytes to a phthalocyanine.

Плазмон-активированный фёрстеровский перенос энергии в молекулярных системах

To explain the experimentally observed effect of silver nanoparticles on the fluorescence of organic dyes and the nonradiative intermolecular transfer of electronic excitation energy in multilayer nanostructures, the previously proposed theoretical model of plasmon resonance in spherical nanoparticles of metals was used. The rates of radiative and nonradiative (FRET) processes in film structures with Ag nanoparticles were calculated for fluorescein and rhodamine B molecules, as well as for two-component systems fluorescein–nile red (NR) and rhodamine B–NR. A version of the model was used that takes into account the effect of NPs on FRET between molecules, the radiative decay of donor and acceptor molecules, and the energy transfer from the dye to plasmonic nanoparticles. The calculation of the UDA rate for pairs with different energy transfer efficiency showed a greater increase in the UDA parameter for the fluorescein–nile red pair than for the rhodamine B–nile red pair. Estimation of the fluorescence enhancement factor of donor and energy acceptor molecules and the rate of energy transfer from the dye to silver NPs showed their insignificant contribution to the formation of the resulting energy transfer efficiency enhancement in the presence of plasmonic NPs.

Plasmon-activated Forster energy transfer in molecular systems

To explain the experimentally observed effect of silver nanoparticles on the fluorescence of organic dyes and the nonradiative intermolecular transfer of electronic excitation energy in multilayer nanostructures, the previously proposed theoretical model of plasmon resonance in spherical nanoparticles of metals was used. The rates of radiative and nonradiative (FRET) processes in film structures with Ag nanoparticles were calculated for fluorescein and rhodamine B molecules, as well as for two-component systems fluorescein-nile red (NR) and rhodamine B-NR. A version of the model was used that takes into account the effect of NPs on FRET between molecules, the radiative decay of donor and acceptor molecules, and the energy transfer from the dye to plasmonic nanoparticles. The calculation of the UDA rate for pairs with different energy transfer efficiency showed a greater increase in the UDA parameter for the fluorescein-nile red pair than for the rhodamine B-nile red pair. Estimation of the fluorescence enhancement factor of donor and energy acceptor molecules and the rate of energy transfer from the dye to silver NPs showed their insignificant contribution to the formation of the resulting energy transfer efficiency enhancement in the presence of plasmonic NPs. Keywords: energy transfer, silver nanoparticles, plasmon, model

Recent progress in organophotoredox reaction.

In the past decade, visible light photoredox catalysis has been established as a gentle and powerful strategy for the activation of organic molecules. As an important part of this, organic photocatalysts are widely used in chemical synthesis due to their attributes, such as cheapness and relatively high redox potential. In this article, we review the related organic reactions promoted by visible light in the presence of various organic photocatalysts over the past 5 years. The reaction mechanisms involving single electron transfer, energy transfer and proton-coupled electron transfer are also discussed. The recovery and reuse of some supported organic photocatalysts are highlighted. Moreover, prospects for the development of organic photocatalysts are emphasized.

Ruthenium(II) complexes with phosphonate-substituted phenanthroline ligands: synthesis, characterization and use in organic photocatalysis.

Ru(II) complexes with polypyridyl ligands play a central role in the development of photocatalytic organic reactions. This work is aimed at the structural modification of such complexes to increase their photocatalytic efficiency and adapt them for the preparation of reusable photocatalytic systems. Nine [Ru(phen)(bpy)2]2+-type complexes (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline) (Ru-Pcat) bearing the P(O)(OEt)2 substituent attached to the phen core directly or through a 1,4-phenylene linker were synthesized and characterized by spectroscopic and electrochemical techniques. The coordination mode of phen ligands was confirmed by single crystal X-ray analysis. The (spectro)electrochemical data show that the first electron transfer in Ru-Pcat takes place on the phen ligand. The emission maxima and quantum yields are strongly affected by the substitution pattern, reaching the far-red region (697 nm) for Ru-3,8P2. The singlet oxygen quantum yields of Ru-Pcat were evaluated using the chemical trapping method. Finally, the photocatalytic performance of Ru-Pcat in the oxidation of sulfides with molecular oxygen was investigated. Both dialkyl and alkyl aryl sulfides were quantitatively transformed into sulfoxides under irradiation with a blue LED in the acetonitrile-water mixture (10 : 1) using a low loading of 0.005-0.05 mol% Ru(II) photocatalysts. To rationalize the effect of phosphonate substituents on the photocatalytic efficiency, comparative kinetic studies of (1) 4-nitrothioanisole oxidation proceeding predominantly via the electron transfer pathway and (2) oxidation of dibutyl sulfide wherein singlet oxygen serves as an oxidant have been performed. It was demonstrated that complexes with the P(O)(OEt)2 substituent at positions 4 and 7 outperform the benchmark photocatalyst Ru-(bpy)3 and the parent complex Ru-phen in the reactions proceeding through electron transfer (reductive quenching photocatalytic cycle). The TON in the oxidation of 4-methoxythioanisole was found to be as high as 1 000 000 that is, to our knowledge, the highest among previously reported photocatalysts. In contrast, upon separating the P(O)(OEt)2 group and the phen core with the 1,4-phenylene linker, singlet oxygen quantum yields significantly increase that favors reactions proceeding through energy transfer (the oxidation of dibutyl sulfide in our case). Thus, both series of Ru(II) complexes prepared in this work are promising for the improvement of known photocatalytic reactions and the development of new transformations.

Comparative analysis of lanthanide excited state quenching by electronic energy and electron transfer processes.

The relative sensitivities of structurally related Eu(III) complexes to quenching by electron and energy transfer processes have been compared. In two sets of 9-coordinate complexes based on 1,4,7-triazacyclononane, the Eu emission lifetime decreased as the number of conjugated sensitising groups and the number of unbound ligand N atoms increased, consistent with photoinduced electron transfer to the excited Eu(III) ion that is suppressed by N-protonation. Quenching of the Eu 5D0 excited state may also occur by electronic energy transfer, and the quenching of a variety of 9-coordinate complexes by a cyanine dye with optimal spectral overlap occurs by an efficient FRET process, defined by a Förster radius (R0) value of 68 Å and characterised by second rate constants in the order of 109 M-1 s-1; these values were insensitive to changes in the ligand structure and to the overall complex hydrophilicity. Quenching of the Eu and Tb excited states by energy transfer to Mn(II) and Cu(II) aqua ions occurred over much shorter distances, with rate constants of around 106 M-1 s-1, owing to the much lower spectral overlap integral. The calculated R0 values were estimated to be between 2.5 to 4 Å in the former case, suggesting the presence of a Dexter energy transfer mechanism that requires much closer contact, consistent with the enhanced sensitivity of the rate of quenching to the degree of steric shielding of the lanthanide ion provided by the ligand.

Review on LSPR assisted photocatalysis: effects of physical fields and opportunities in multifield decoupling.

Since nano scale local surface plasmon resonance (LSPR) can broaden the visible absorption region, enhance the local electromagnetic field and produce a thermal effect simultaneously, the appropriate utilization of the LSPR effect is a noteworthy research direction towards visible light driven photocatalysts with high efficiency and low cost. In this study, the influence mechanism of the optical, electric, magnetic, and thermal physical fields on the photocatalytic efficiency of the LSPR system is for the first time reviewed, based on which the research bottlenecks of this method including the accurate predesign and regulation of the photocatalyst, the interpretation of electron movement and energy transfer mechanism, are specifically analyzed. Due to the micro-nano localization of LSPR, auxiliary methods are needed to reflect the micro electromagnetic and temperature field distribution which are otherwise formidable to measure experimentally. Alternatively, numerical methods with decoupling calculations of nano-scale physical fields are necessary to develop. Therefore, the development potential of different numerical simulation methods including mainstream FDTD, FEM and DDA is subsequently expounded, providing opportunities in resolving the bottleneck issues associated with photocatalysis. It is worth mentioning that although many important advances have been achieved in the preparation and application of LSPR assisted photocatalysts, the convincing function mechanism of LSPR is still lacking due to its multifield synergistic enhancement effect.

Radiative and Non-Radiative Decay Pathways in Carbon Nanodots toward Bioimaging and Photodynamic Therapy.

The origin and classification of energy states, as well as the electronic transitions and energy transfers associated with them, have been recognized as critical factors for understanding the optical properties of carbon nanodots (CNDs). Herein, we report the synthesis of CNDs in an optimized process that allows low-temperature carbonization using ethanolamine as the major precursor and citric acid as an additive. The results obtained herein suggest that the energy states in our CNDs can be classified into four different types based on their chemical origin: carbogenic core states, surface defective states, molecular emissive states, and non-radiative trap states. Each energy state is associated with the occurrence of different types of emissions in the visible to near-infrared (NIR) range and the generation of reactive oxygen species (ROS). The potential pathways of radiative/non-radiative transitions in CNDs have been systematically studied using visible-to-NIR emission spectroscopy and fluorescence decay measurements. Furthermore, the bright photoluminescence and ROS generation of these CNDs render them suitable for in vitro imaging and photodynamic therapy applications. We believe that these new insights into the energy states of CNDs will result in significant improvements in other applications, such as photocatalysis and optoelectronics.

Tailoring Bi2MoO6 by Eu3+ incorporation for enhanced photoluminescence emissions

Here, an experimental study is presented on the structural, electronic, and optical properties of Bi2-xMoO6:xEu3+ (x = 0, 0.5, 1.0, 2.0, and 4.0 mol%) materials, synthesized by means of the microwave-assisted solvothermal method using ethylene glycol as a solvent. Different characterization techniques (X-ray diffraction measurements with Rietveld refinements, Raman and ultraviolet–visible diffuse reflectance spectroscopy, field emission scanning electron microscopy, and photoluminescence emissions) have been employed to examine the structural and electronic properties, energy transfer and defect evolution which control the performance of the as-synthetized materials. Present findings provide deep insights into the substitution of Eu3+ cations in Bi2MoO6, with focus on their influence on process that dictate the superior optical properties.

Cuprous Cluster-Based Coordination Sheets as Photocatalytic Regulators to Activate Oxygen, Benzoquinone, and Thianthrenium Salts.

Cuprous clusters are well known for their important fluorescent properties and tunable redox behavior, but the coordinated protecting groups restrict their application in photocatalysis, in particular, the inner-sphere activation of substrates. By modifying fluorescent cuprous clusters with terminal iodides into two-dimensional coordination sheets, we report a photocatalytic regulator to synergistically combine electron transfer and energy transfer for the oxidative coupling of benzoquinone and terminal alkynes. Under visible light irradiation, the well-modified excited state of the cuprous clusters in the coordination sheets reduces benzoquinones to generate aoxy radicals through electron transfer and activates oxygen through energy transfer. The aoxy radicals interact with copper-coordinated phenylacetylene to form an active intermediate, which is further oxidized by the in situ formed active oxygen species and aryl ketones are obtained. The warranted potential of the excited coordination sheets enables the reductive activation of thianthrenium salts as radical precursors, facilitating radical capture and further C-N coupling via an inner-sphere activation mechanism. The new catalytic approach optimizes the redox properties and excited-state lifetime, shortens the electron transfer steps, and promotes the potential collision of a low concentration of active species in tandem catalytic cycles, thus paving a new way to develop ecologically benign, cost-effective, multipurpose, and flexible catalytic systems.

Zinc phthalocyanine carrying sulfenyl and sulfydryl functionalized sulfur vacancies MoS2 for enhancement of the third order nonlinear optical property

Zinc phthalocyanine carrying sulfenyl and 6-sulfydryl linkers was firstly used to functionalize with sulfur vacancies MoS2. The synthesized MoS2/ZnPc composite was further prepared to be PVA (polyvinyl alcohol) thin films by a drop coating method. The microscopic structures and photophysical properties of novel MoS2/ZnPc composite were characterized. A series of analysis results indicate that zinc phthalocyanine with sulfenyl and 6-sulfydryl linkers is loaded to sulfur vacancies of MoS2 by ligand conjugation. The third order nonlinear optical properties of MoS2/ZnPc composite were studied by an open aperture Z-scan technique at 532 nm with 4 ns laser pulses width. In comparison with individual MoS2 or ZnPc, whether MoS2/ZnPc solution or MoS2/ZnPc/PVA film sample possesses larger third order nonlinear absorption coefficients (β) and lower limiting thresholds (F50). It can be ascribed to a combination of different NLO absorption mechanisms for MoS2/ZnPc composite, including one-photon absorption, two photon absorptions and nonlinear scattering of MoS2, triplet excited state absorption of ZnPc, nonlinear scattering of MoS2/ZnPc and the photo-induced electron transfer or energy transfer (PET/ET) process between MoS2 and ZnPc moieties.

O2 and Other High-Energy Molecules in Photosynthesis: Why Plants Need Two Photosystems.

The energetics of photosynthesis in plants have been re-analyzed in a framework that represents the relatively high energy of O2 correctly. Starting with the photon energy exciting P680 and “loosening an electron”, the energy transfer and electron transport are represented in a comprehensive, self-explanatory sequence of redox energy transfer and release diagrams. The resulting expanded Z-scheme explicitly shows charge separation as well as important high-energy species such as O2, TyrZ˙, and P680+˙, whose energies are not apparent in the classical Z-scheme of photosynthesis. Crucially, the energetics of the three important forms of P680 and of P700 are clarified. The relative free energies of oxidized and reduced species are shown explicitly in kJ/mol, not encrypted in volts. Of the chemical energy produced in photosynthesis, more is stored in O2 than in glucose. The expanded Z-scheme introduced here provides explanatory power lacking in the classical scheme. It shows that P680* is energetically boosted to P680+˙ by the favorable electron affinity of pheophytin and that Photosystem I (PSI) has insufficient energy to split H2O and produce O2 because P700* is too easily ionized. It also avoids the Z-scheme’s bewildering implication, according to the “electron waterfall” concept, that H2O gives off electrons that spontaneously flow to chlorophyll while releasing energy. The new analysis explains convincingly why plants need two different photosystems in tandem: (i) PSII mostly extracts hydrogen from H2O, producing PQH2 (plastoquinol), and generates the energetically expensive product O2; this step provides little energy directly to the plant; (ii) PSI produces chemical energy for the organism, by pumping protons against a concentration gradient and producing less reluctant hydrogen donors. It also documents that electron transport and energy transfer occur in opposite directions and do not involve redox voltages. The analysis makes it clear that the high-energy species in photosynthesis are unstable, electron-deficient species such as P680+˙ and TyrZ˙, not putative high-energy electrons.

Ion\u2013electron energy transfer in kinetic and fluid modelling of the tokamak scrape-off layer

Using the 1D kinetic electron code SOL-KiT, simulations of the divertor tokamak scrape-off layer were carried out to explore the presence of kinetic effects in energy transfer between the ions and electrons. During steady-state conditions, it was found that the ion–electron energy transfer is well described by a fluid model, with only minimal differences seen when electrons are treated kinetically. During transient regimes (featuring a burst of energy into the scrape-off layer), we see evidence of enhanced energy exchange when calculated kinetically as compared to a fluid model. The kinetic correction represents an additional 8–55% ion–electron energy transfer across the domain, depending on the pre-transient plasma collisionality. Compared to the total energy going into the plasma during the transient, the correction is less than 1%, so its impact on plasma profiles may be small. The effect is seen to increase in strength along the domain, peaking in front of the divertor target. The overall discrepancy (integrated along the domain) increases during the transient energy burst and disappears on a similar timescale. However, at the target the effect peaks later and takes several multiples of the transient duration to relax. This effect may be only partially explained by an additional population of cold electrons arising from neutral ionization.