Electronic Energy Transfer Research Articles

Efficient wastewater disinfection by raised 1O2 yield through enhanced electron transfer and intersystem crossing via photocatalysis of peroxymonosulfate with CuS quantum dots modified MIL-101(Fe)

Peroxymonosulfate (PMS)-based photocatalysis is a promising alternative approach for wastewater disinfection. Singlet oxygen (1O2) is sensitive and efficient for bacterial inactivation. This study developed a 1O2-predominated PMS disinfection technique under visible light with CuS quantum dots (QDs) modified MIL-101(Fe) (CSQDs@MF). CuS QDs modification greatly enhanced the 1O2 quantum yield by 80% than that of MIL-101(Fe). Photoelectricity and photoluminescence tests demonstrated that both the enhanced electron transfer and energy transfer were responsible for improved 1O2 generation in Vis/PMS/CSQDs@MF system. The system took 60 min to inactivate 7.5-log E. coli, and it could be applied in a broad pH and dissolve oxygen range. Bacterial inactivation mechanism suggested that 1O2 attacked cell membrane first, then induced oxidative stress, up-regulated intracellular ROS level, eventually broke DNA strand. The system showed good disinfection performance on Gram-positive B. subtilis and fecal coliforms in practical wastewater, implying it is a promising alternative disinfection technology for wastewater treatment.

Energy Transfer in Aqueous Light Harvesting Antennae Based on Brush-like Inter-Conjugated Polyelectrolyte Complexes.

Conjugated polyelectrolytes (CPEs) have the potential to serve as building blocks of artificial light-harvesting systems. This is primarily due to their delocalized electronic states and potential for hierarchical self-assembly. We showed previously that inter-CPE complexes composed of oppositely charged exciton-donor and exciton-acceptor CPEs displayed efficient electronic energy transfer. However, near ionic charge equivalence, complexed CPE chains become net-neutral and thus experience a precipitous drop in aqueous solubility. To increase the stability and to rationally manipulate the phase behavior of inter-CPE complexes, we synthesized a series of highly water-soluble exciton-donor CPEs composed of alternating ionic and polar nonionic fluorene monomers. The nonionic monomer contained oligo(ethyleneglycol) sidechains of variable length. We then formed exciton donor-acceptor complexes and investigated their relative energy transfer efficiencies in the presence of a fixed exciton-acceptor CPE. We find that, even when the polar nonionic sidechains become quite long (nine ethyleneglycol units), the energy transfer efficiency is hardly affected so long as the inter-CPE network retains a net polyelectrolyte charge. However, near the onset of spontaneous phase separation, we observe a clear influence of the length of the oligo(ethyleneglycol) sidechains on the photophysics of the complex. Our results have implications for the use of polyelectrolyte phase separation to produce aqueous light-harvesting soft materials.

Bimolecular reactivity of 3d metal-centered excited states (Cr, Mn, Fe, Co)

Metal-centered (MC) excited states (ESs) of 3d transition metal complexes (TMCs) often possess rather low energies so that these represent the lowest energy ESs. Additionally, MC states are often strongly distorted, hence they efficiently decay non-radiatively to the ground state. As bimolecular photoinduced electron transfer (PET) and energy transfer (EnT) processes require contact to the substrate, the metal confinement of the ES wavefunction of MC states makes these processes challenging. Consequently, MC states are considered less useful as compared to long-lived charge transfer states of higher energy with wavefunctions extending onto the ligands. Despite these supposed drawbacks, some classes of TMCs can successfully engage in bimolecular PET and EnT processes with MC states being the photoactive states. We discuss these initial examples of MC ES reactivity covering chromium, manganese, iron, and cobalt complexes with the aim to gain a deeper understanding of these processes and to identify the decisive key parameters. Finally, we present catalytic photoredox and energy transfer processes using photosensitizers with suitable MC ESs.

Generation and decay of N2(A3Σu +) molecules in reacting CO2 and CH4 plasmas

Time-resolved number densities of N2(A3Σu +, v = 0, 1) molecules in diffuse ns pulse discharge plasmas in N2, N2–H2, N2–CH4, N2–CO2, and N2–CO2–CH4 are measured by tunable diode laser absorption spectroscopy (TDLAS). The first series of measurements is made in the discharge pulse bursts at a relatively low pulse repetition rate (3 kHz), when the N2(A3Σu +) generation and decay after individual discharge pulses is fully resolved. The second set of data is taken during a sequence of two pulse bursts generated at a higher pulse repetition rate (100 kHz), for different delay times between the first and second bursts. This approach is used to determine the effect of accumulation and decay of reacting species generated in the plasma, including N, H, and O atoms, CO molecules, and C2 hydrocarbon product species, on the rate of N2(A3Σu +) production and quenching. The effect of these species can be isolated since the rates of N2(A3Σu +) quenching by the initial reactant species (H2, CH4, and CO2) are slow. Comparison of the measurement results with the kinetic modeling predictions is used to obtain insight into the plasma chemical reaction kinetics. The results complement the measurements of N, H, O, and CO in high-pressure reacting plasmas, and help quantify the plasma chemical processes driven by the electron impact dissociation, electronic excitation, and reactive quenching of the excited electronic states. The present results may be used for the development and validation of higher fidelity kinetic models of reacting plasmas, incorporating state-specific electronic and vibrational energy transfer and chemical reactions.

Multiple Interpenetrating Metal-Organic Frameworks with Channel-Size-Dependent Behavior for Selective Gossypol Detection and Perovskite Quantum Dot Encapsulation.

An interpenetrating structure endows metal-organic frameworks (MOFs) with many exciting applications, such as fluorescence detection and host-guest chemistry. Herein, two unique structure-interpenetrating In-MOFs (In-pdda-1 and In-pdda-2; H2pdda = 4,4'-(pyridine-2,5-diyl)dibenzoic acid) are constructed by different coordination configurations. The four-connected In3+ center shows a triangular-pyramidal configuration or a 2D rectangle, forming an unc topology for In-pdda-1 and a sql network for In-pdda-2, respectively. Two different interpenetrating modes created by linear rigid ligands and metal clusters are observed in the two MOFs (In-pdda-1, 8-fold interpenetrating mode; In-pdda-2, [2D + 2D] interpenetrating mode), which determine the channel-size-dependent properties in fluorescence applications. During the quantitative detection process of gossypol, the small rhombic channels divided by interpenetrating molecular planes of In-pdda-2 greatly limit the distance between the analyte and the probe, promoting electron transfer and energy transfer processes and thus resulting in a low detection limit (28.6 nM). In addition, the pore size effect of In-pdda-1 encouraged us to explore an in situ perovskite quantum dot encapsulation strategy to obtain a MAPbBr3@MOF material with tunable and stable luminescence properties. Both of the above channel-size-dependent fluorescence properties may provide inspiration for the structural design and specialized applications of MOF materials.

(Invited) Ultrafast Reducing Power of a Plasmonic Photocatalyst

Plasmonic nanomaterials are promising catalysts for selective, green, and efficient photo-driven processes, however currently the mechanisms involved in plasmon-driven catalysis are under debate. Contributions from processes such as vibrational and electronic energy transfer, electron transfer, or electromagnetic field enhancement could all lead to modified potential energy landscapes in the plasmon-molecule system. We have developed ultrafast and electrochemical surface-enhanced Raman spectroscopic (SERS) techniques to probe the contribution of these processes on the nanometer length scale and femtosecond timescale. This talk will highlight the use of these approaches in quantifying the rate, yield, and lifetime of plasmon-to-molecule charge transfer. We monitor changes in the vibrational spectra of adsorbed molecular species following plasmon excitation with picosecond time resolution, and quantify how many molecules are reduced and how quickly they undergo back electron transfer. Overall, these methods allow for quantification of the ultrafast reducing power of a plasmonic surface, and suggest routes for optimizing plasmonic systems for efficient and selective photochemistry.

Tunable Electronic Structure via DNA-Templated Heteroaggregates of Two Distinct Cyanine Dyes.

Molecular excitons are useful for applications in light harvesting, organic optoelectronics, and nanoscale computing. Electronic energy transfer (EET) is a process central to the function of devices based on molecular excitons. Achieving EET with a high quantum efficiency is a common obstacle to excitonic devices, often owing to the lack of donor and acceptor molecules that exhibit favorable spectral overlap. EET quantum efficiencies may be substantially improved through the use of heteroaggregates—aggregates of chemically distinct dyes—rather than individual dyes as energy relay units. However, controlling the assembly of heteroaggregates remains a significant challenge. Here, we use DNA Holliday junctions to assemble homo- and heterotetramer aggregates of the prototypical cyanine dyes Cy5 and Cy5.5. In addition to permitting control over the number of dyes within an aggregate, DNA-templated assembly confers control over aggregate composition, i.e., the ratio of constituent Cy5 and Cy5.5 dyes. By varying the ratio of Cy5 and Cy5.5, we show that the most intense absorption feature of the resulting tetramer can be shifted in energy over a range of almost 200 meV (1600 cm–1). All tetramers pack in the form of H-aggregates and exhibit quenched emission and drastically reduced excited-state lifetimes compared to the monomeric dyes. We apply a purely electronic exciton theory model to describe the observed progression of the absorption spectra. This model agrees with both the measured data and a more sophisticated vibronic model of the absorption and circular dichroism spectra, indicating that Cy5 and Cy5.5 heteroaggregates are largely described by molecular exciton theory. Finally, we extend the purely electronic exciton model to describe an idealized J-aggregate based on Förster resonance energy transfer (FRET) and discuss the potential advantages of such a device over traditional FRET relays.

Coherence and Efficient Energy Transfer in Molecular Wires: Insights from Surface Hopping Simulations.

Understanding the dynamics of electronic energy transfer through a molecular wire is essential to understand the working of natural processes like photosynthesis. We investigate simpler 2 and 3-site model Hamiltonians in this work to understand the importance of coherence to efficient energy transfer. We compare the results of surface hopping simulation with that of numerically exact results and rate theories. Different parameters are analyzed, motivated by a photosynthetic molecular wire - the FMO complex. A comparison of results from different theories shows that coherence can play an important role towards efficient energy transfer for certain parameters. When these coherences are important, even small couplings (of the order of 5 cm-1 ) in the Hamiltonian can significantly affect rates. Surface hopping simulations capture all the results correctly qualitatively. Rate theories, on the other hand, can differ significantly from numerically exact results when coherences become important. The results of this work should provide design guidelines for efficient energy transfer in molecular wires.

Allophycocyanin A is a carbon dioxide receptor in the cyanobacterial phycobilisome

Light harvesting is fundamental for production of ATP and reducing equivalents for CO2 fixation during photosynthesis. However, electronic energy transfer (EET) through a photosystem can harm the photosynthetic apparatus when not balanced with CO2. Here, we show that CO2 binding to the light-harvesting complex modulates EET in photosynthetic cyanobacteria. More specifically, CO2 binding to the allophycocyanin alpha subunit of the light-harvesting complex regulates EET and its fluorescence quantum yield in the cyanobacterium Synechocystis sp. PCC 6803. CO2 binding decreases the inter-chromophore distance in the allophycocyanin trimer. The result is enhanced EET in vitro and in live cells. Our work identifies a direct target for CO2 in the cyanobacterial light-harvesting apparatus and provides insights into photosynthesis regulation.

2D imaging of absolute methyl concentrations in nanosecond pulsed plasma by photo-fragmentation laser-induced fluorescence

The methyl radical plays a central role in plasma-assisted hydrocarbon chemistry but is challenging to detect due to its high reactivity and strongly pre-dissociative electronically excited states. We report the development of a photo-fragmentation laser-induced fluorescence (PF-LIF) diagnostic for quantitative 2D imaging of methyl profiles in a plasma. This technique provides temporally and spatially resolved measurements of local methyl distributions, including in near-surface regions that are important for plasma-surface interactions such as plasma-assisted catalysis. The technique relies on photo-dissociation of methyl by the fifth harmonic of a Nd:YAG laser at 212.8 nm to produce CH fragments. These photofragments are then detected with LIF imaging by exciting a transition in the B-X(0, 0) band of CH with a second laser at 390 nm. Fluorescence from the overlapping A-X(0, 0), A-X(1, 1), and B-X(0, 1) bands of CH is detected near 430 nm with the A-state populated by collisional B-A electronic energy transfer. This non-resonant detection scheme enables interrogation close to a surface. The PF-LIF diagnostic is calibrated by producing a known amount of methyl through photo-dissociation of acetone vapor in a calibration gas mixture. We demonstrate PF-LIF imaging of methyl production in methane-containing nanosecond pulsed plasmas impinging on dielectric surfaces. Absolute calibration of the diagnostic is demonstrated in a diffuse, plane-to-plane discharge. Measured profiles show a relatively uniform distribution of up to 30 ppm of methyl. Relative methyl measurements in a filamentary plane-to-plane discharge and a plasma jet reveal highly localized intense production of methyl. The utility of the PF-LIF technique is further demonstrated by combining methyl measurements with formaldehyde LIF imaging to capture spatiotemporal correlations between methyl and formaldehyde, which is an important intermediate species in plasma-assisted oxidative coupling of methane.

Organophotocatalytic oxidation of alcohols to carboxylic acids

AbstractA sustainable photochemical protocol for the oxidation of alcohols to ketones and carboxylic acids has been developed by using 2,4,6‐triphenylpyrylium tetrafluoroborate (TPPT) as organophotocatalyst and molecular oxygen as oxidant under visible light irradiation. The key reactive oxygen species, superoxide (O2•−) for the first oxidation step from alcohol to aldehyde and singlet oxygen (1O2) for the second oxidation step from aldehyde to carboxylic acid, were generated successfully by electron transfer and energy transfer pathways, respectively. A range of primary and secondary alcohols were converted to the corresponding carboxylic acids or ketones, and the optimized reaction conditions were applied to the synthesis of benzocoumarin.

The pathways of electronic excitation back energy transfer processes (BET) in novel Eu3+ heterocyclic 1,3-diketonates bearing a perfluorinated moiety

A series of novel brightly emitting Eu3+ coordination compounds with 1,3-diketones bearing a thiophene moiety and a linear CnF2n+1 chain (n = 1–8) were synthesized and fully characterized. The dependence of back energy transfer (BET) processes on the fluorinated chain length of the ligand environment was investigated in detail. The rates of radiative, non-radiative, and BET processes were estimated by a complete set of spectroscopic methods, including temperature stimulated luminescence measurements. It was demonstrated that fluorination provided a remarkable increase in the photoluminescence quantum yield up to 58% along with an increase in sensitization efficiency from 45 to 86%. It was explained by the reduction of non-radiative relaxation on molecular oscillators. The probability of the BET process has a trend to decrease from 500 to 100 s−1 upon an extension of the diketone fluorinated chain. Moreover, the back energy transfer process occurs from the resonant level of Eu3+ ion to ligand triplet state T1 through activation energy barrier ΔEA between potential energy surfaces of T1 and 5D0 states. It was found that extension of the fluorinated chain in ligand alter the activation energy and frequency factor of BET. The influence of the both parameters on BET was studied. The results obtained give a fundamental basis for further rational design of highly efficient luminescent compounds of Eu3+ ions.

Hybridization-Sensitive Fluorescent Probes for DNA and RNA by a Modular "Click" Approach.

Fluorescent DNA probes were prepared in a modular approach using the “click” post-synthetic modification strategy. The new glycol-based module and DNA building block place just two carbons between the phosphodiester bridges and anchor the dye by an additional alkyne group. This creates a stereocenter in the middle of this artificial nucleoside substitute. Both enantiomers and a variety of photostable cyanine–styryl dyes as well as thiazole orange derivatives were screened as “clicked” conjugates in different surrounding DNA sequences. The combination of the (S)-configured DNA anchor and the cyanylated cyanine–styryl dye shows the highest fluorescence light-up effect of 9.2 and a brightness of approximately 11,000 M–1 cm–1. This hybridization sensitivity and fluorescence readout were further developed utilizing electron transfer and energy transfer processes. The combination of the hybridization-sensitive DNA building block with the nucleotide of 5-nitroindole as an electron acceptor and a quencher increases the light-up effect to 20 with the DNA target and to 15 with the RNA target. The fluorescence readout could significantly be enhanced to values between 50 and 360 by the use of energy transfer to a second DNA probe with commercially available dyes, like Cy3.5, Cy5, and Atto590, as energy acceptors at the 5′-end. The latter binary probes shift the fluorescent readout from the range of 500–550 nm to the range of 610–670 nm. The optical properties make these fluorescent DNA probes potentially useful for RNA imaging. Due to the strong light-up effect, they will not require washing procedures and will thus be suitable for live-cell imaging.

Challenges in temperature measurements in gas-phase photothermal catalysis

Luca Mascaretti completed his PhD in 2018 at Politecnico di Milano, Italy. Afterwards, he has worked as a postdoc researcher at the Regional Centre of Advanced Technologies and Materials, Palacký University in Olomouc (Czech Republic). His research activity is related to titanium oxide/nitride-based nanostructured materials for solar energy conversion processes. Andrea Schirato is currently a physics PhD candidate across Politecnico di Milano and the Italian Institute of Technology (Genoa) under the supervision of Profs. G. Della Valle and R. Proietti Zaccaria. His research activities focus on the theoretical study and numerical modeling of ultrafast nonlinear phenomena driven by hot carriers, including non-equilibrium electronic and phononic energy transfer in nanostructured materials and metasurfaces. Tiziano Montini is associate professor at the University of Trieste in Italy. He received his PhD in chemistry from the University of Trieste in 2006, followed by a postdoc fellowship. His research activity concerns on nanomaterials as catalysts for renewable energy production and environmental protection. Alessandro Alabastri is currently an assistant professor in the Electrical and Computer Engineering Department at Rice University. He received his PhD in nanosciences in 2014 from the Italian Institute of Technology and the University of Genoa. In 2015, he was visiting researcher in the Molecular Foundry at the Lawrence Berkeley National Laboratory. He worked on several aspects of light-to-heat conversion, photothermal effects in nanostructures, and heat recovery in light-powered thermofluidic devices. Alberto Naldoni is currently an associate professor at University of Turin, Italy. Since 2017, he is the co-leader of the photoelectrochemistry group at the Regional Centre of Advanced Technologies and Materials, Palacký University Olomouc (Czech Republic). He obtained his PhD in chemical sciences from University of Milan (2010). From 2014 to 2017, he was visiting research faculty at the Birck Nanotechnology Center of Purdue University. His group focuses on nanomaterials for plasmonics, photocatalysis, and photoelectrochemistry. Paolo Fornasiero is a professor at the University of Trieste in Italy. He received his PhD in chemistry from the University of Trieste in 1997, followed by a postdoc fellowship at Reading University (UK). His group currently focuses on research into nanomaterials for environmental and energy-related applications.

Dextran-graft-PNIPAM / Au nanoparticles / perylenediimide hybrid system as thermosensitive optical switches and fluorescent labels for potential use in nanophotonics and biomedical applications

A triple thermosensitive polymer Dextran-g-Poly(N-isopropylacrylamide)/Au nanoparticles/Perylenediimide (D-g-PNIPAM/AuNPs/PDI) hybrid nanosystem was formulated in aqueous solution for potential use as thermoresponsive fluorescent optical switch and label. The completely reversible effect of sharp enhancement-quenching of the photoluminescence of D-g-PNIPAM/AuNPs/PDI nanosystem was revealed during the heating-cooling cycle in the narrow temperature range of 25–47 °C, containing the temperature point of the LCST phase transition of the thermosensitive polymer. The sharp change in the intensity of photoluminescence was shown to result from the competing effects of plasmonic enhancement and non-radiative FRET transfer of electronic excitation energy during thermo-induced LCST transition of the D-g-PNIPAM macromolecule. The observed effect allows to carry out the temperature control of the photoluminescence intensity, which appears to be particularly important for potential applications of D-g-PNIPAM/AuNPs/PDI hybrid nanosystem in photonics, biology and medicine, such as thermosensitive fluorescent optical switch and label or intracellular fluorescent thermometer.

Wavelike electronic energy transfer in donor-acceptor molecular systems through quantum coherence.

Quantum-coherent intermolecular energy transfer is believed to play a key role in light harvesting in photosynthesis and photovoltaics. So far, a direct, real-space demonstration of quantum coherence in donor-acceptor systems has been lacking because of the fragile quantum coherence in lossy molecular systems. Here, we precisely control the separations in well-defined donor-acceptor model systems and unveil a transition from incoherent to coherent electronic energy transfer. We monitor the fluorescence from the heterodimers with subnanometre resolution through scanning tunnelling microscopy induced luminescence. With decreasing intermolecular distance, the dipole coupling strength increases and two new emission peaks emerge: a low-intensity peak blueshifted from the donor emission, and an intense peak redshifted from the acceptor emission. Spatially resolved spectroscopic images of the redshifted emission exhibit a σ antibonding-like pattern and thus indicate a delocalized nature of the excitonic state over the whole heterodimer due to the in-phase superposition of molecular excited states. These observations suggest that the exciton can travel coherently through the whole heterodimer as a quantum-mechanical wavepacket. In our model system, the wavelike quantum-coherent transfer channel is three times more efficient than the incoherent channel.

POSS‐based fluorescence sensor for rapid analysis of β‐carotene in health products

In recent years, fluorescent organic-inorganic hybrid nanomaterials have received much interest as potential fluorescent sensor materials. In this study, fluorescent organic-inorganic hybrid nanomaterials (POSS@ANT) were created using polyhedral oligomeric silsesquioxane as the precursor and 9,10-bromoanthracene as the monomer. The morphology and composition of POSS@ANT, as well as its pore characteristics and fluorescence properties were studied. POSS@ANT displayed steady fluorescence emission at an excitation wavelength of 374 nm. Next, a β-carotene fluorescence sensor was developed using the capacity of β-carotene to quench the fluorescence of POSS@ANT. The quenching process is linked to acceptor electron transfer and energy transfer, and the sensor has a high selectivity for β-carotene. This β-carotene fluorescence analysis method that we established has a linear range of 0.2-4.3mg/L and a detection limit of 0.081 mg/L. Finally, it was used to quantify β-carotene in health products, the recovery rate was 91.1-109.9%, the relative standard deviation (RSD) was 2.2-4.3%, and the results were comparable with the results of high-performance liquid chromatography. The approach is reliable and can be used to determine β-carotene in health products.

Inner-sphere and outer-sphere charge-transfer quenching of the uranyl UO22+(VI) luminescence, and kinetics for the tertiary and secondary alcohols activated uranyl emission

For the uranyl UO22+(VI) luminescence, the quenching constants (Kq: mM−1) of various σ–donors and π–donors, which have been shown to form electron-donor–acceptor (EDA) complexes with UO22+, were found directly related to the ionization energies (IE: eV) of the electron donors, such that the common logarithm logKq = –0.0932(IE) + 1.671 (R2 = 0.945). The relationship has revealed an inner-sphere mechanism for the quenching resulting from the charge-transfer (a single-electron transfer) from the HOMO of the quenching substance (Q) to a SOMO of the excited state (UO22+)* that takes place in an EDA [Q, (UO22+)*] complex. For some weak electron donors which do not form EDA complexes with UO22+, their Kq values for the quenching of UO22+ luminescence were found significantly much smaller than expected from the logKq versus IE relationship established for the inner-sphere charge-transfer quenching. The observations have indicated an outer-sphere charge-transfer quenching mechanism possibly resulting from the simple collision between the quenching substance and UO22+ without the formation of an EDA complex between them. In the presence of tertiary butyl alcohol (tBuOH) at 0 – 0.015 M (15 mM), the intensity (I) of the emission of UO22+ (0.01 M) at 508 nm (with Ex = 340 nm) in acetone was found to increase linearly as a function of the tBuOH millimolar concentration (mM) (I = 34.2[tBuOH] + 1802, R2 = 0.992). Kinetic analysis has revealed an electronic energy transfer from the excited state of tBuOH (A*), identified by luminescence spectroscopy, to the ground state of UO22+ (U) to promote it to the excited state (U*) (A* + U → A + U*), enhancing the UO22+ luminescence. The excitation energy transfer is believed to follow a Dexter mechanism, with the overall spin of the energy donor and acceptor conserved, followed by an intersystem crossing ([1A*, 1U] → [1A, 1U*] → [1A, 3U*]).

Förster Resonance Energy Transfer between Fluorescent Organic Semiconductors: Poly(9,9-dioctylfluorene-alt-benzothiadiazole) and 6,13-Bis(triisopropylsilylethynyl)pentacene

In the present study, an investigation of the electronic excitation energy transfer between two p-type fluorescent semiconductors, F8BT [poly(9,9-dioctylfluorene-alcohol-benzothiadiazole] and TIPS-P [6,13-bis(triisopropylsilylethynyl)pentacene], has been carried out in a chloroform solution using steady-state and time-domain fluorescence techniques. The spectral overlap integral between donor (F8BT) emission and acceptor (TIPS-P) absorption is 2.04 × 1015 nm4/(M cm), and the corresponding critical transfer distance is 53.12 Å. In donor decay dynamics, at the lower acceptor concentrations, the observed results deviate from the Förster theory due to the combined effect of diffusion and energy migration. However, it does not exhibit energy migration and distribution for higher acceptor concentrations, and the system follows the Förster model of resonance excitation energy transfer (FRET). The higher value of the donor-acceptor interaction strength than self-interaction (donor-donor interaction) appears to be responsible for this behavior. Further, in acceptor decay, the appearance of the rise time and its decrease with the acceptor concentration confirms FRET from F8BT to TIPS-P.

Molecular Spatiomics by Proximity Labeling.

ConspectusProximity labeling can be defined as an enzymatic “in-cell” chemical reaction that catalyzes the proximity-dependent modification of biomolecules in live cells. Since the modified proteins can be isolated and identified via mass spectrometry, this method has been successfully utilized for the characterization of local proteomes such as the sub-mitochondrial proteome and the proteome at membrane contact sites, or spatiotemporal interactome information in live cells, which are not “accessible” via conventional methods. Currently, proximity labeling techniques can be applied not only for local proteome mapping but also for profiling local RNA and DNA, in addition to showing great potential for elucidating spatial cell–cell interaction networks in live animal models. We believe that proximity labeling has emerged as an essential tool in “spatiomics,” that is, for the extraction of spatially distributed biological information in a cell or organism.Proximity labeling is a multidisciplinary chemical technique. For a decade, we and other groups have engineered it for multiple applications based on the modulation of enzyme chemistry, chemical probe design, and mass analysis techniques that enable superior mapping results. The technique has been adopted in biology and chemistry. This “in-cell” reaction has been widely adopted by biologists who modified it into an in vivo reaction in animal models. In our laboratory, we conducted in vivo proximity labeling reactions in mouse models and could successfully obtain the liver-specific secretome and muscle-specific mitochondrial matrix proteome. We expect that proximity reaction can further contribute to revealing tissue-specific localized molecular information in live animal models.Simultaneously, chemists have also adopted the concept and employed chemical “photocatalysts” as artificial enzymes to develop new proximity labeling reactions. Under light activation, photocatalysts can convert the precursor molecules to the reactive species via electron transfer or energy transfer and the reactive molecules can react with proximal biomolecules within a definite lifetime in an aqueous solution. To identify the modified biomolecules by proximity labeling, the modified biomolecules should be enriched after lysis and sequenced using sequencing tools. In this analysis step, the direct detection of modified residue(s) on the modified proteins or nucleic acids can be the proof of their labeling event by proximal enzymes or catalysts in the cell. In this Account, we introduce the basic concept of proximity labeling and the multidirectional advances in the development of this method. We believe that this Account may facilitate further utilization and modification of the method in both biological and chemical research communities, thereby revealing unknown spatially distributed molecular or cellular information or spatiome.