Distance Dependence Of Energy Transfer Research Articles

Distance-Independent Efficiency of Triplet Energy Transfer from π-Conjugated Organic Ligands to Lanthanide-Doped Nanoparticles.

Lanthanide-doped nanoparticles (LnNPs) possess unique optical properties and are employed in various optoelectronic and bioimaging applications. One fundamental limitation of LnNPs is their low absorption cross-section. This hurdle can be overcome through surface modification with organic chromophores with large absorption cross-sections. Controlling energy transfer from organic molecules to LnNPs is crucial for creating optically bright systems, yet the mechanisms are not well understood. Using pump-probe spectroscopy, we follow singlet energy transfer (SET) and triplet energy transfer (TET) in systems comprising different length 9,10-bis(phenylethynyl)anthracene (BPEA) derivatives coordinated onto ytterbium and neodymium-doped nanoparticles. Photoexcitation of the ligands forms singlet excitons, some of which convert to triplet excitons via intersystem crossing when coordinated to the LnNPs. The triplet generation rate and yield are strongly distance-dependent. Following their generation, TET occurs from the ligands to the LnNPs, exhibiting an exponential distance dependence, independent of solvent polarity, suggesting a concerted Dexter-type process with a damping coefficient of 0.60 Å-1. Nevertheless, TET occurs with near-unity efficiency for all BPEA derivatives due to the lack of other triplet deactivation pathways and long intrinsic triplet lifetimes. Thus, we find that close coupling is primarily important to ensure efficient triplet generation rather than efficient TET. Although SET is faster, we find its efficiency to be lower and more strongly distance-dependent than the TET efficiency. Our results present the first direct distance-dependent energy transfer measurements in LnNP@organic nanohybrids and establish the advantage of using the triplet manifold to achieve the most efficient energy transfer and best sensitization of LnNPs with π-conjugated ligands.

Enhanced upconversion luminescence of NaYF4:Er nanocrystals based on the synergy between whispering gallery mode excitation and förster resonant energy transfer

The upconversion luminescence at the visible band was excited by the high power density whispering gallery mode (WGM) on the surface of the microsphere. Under the WGM excitation, Er3+ of NaYF4:Er3+ directly absorbed three photons at 1525 nm, followed by the generation of upconversion luminescence. We used WS2 quantum dots (QDs) as donors and NaYF4:Er3+ upconversion nanoparticles (UCNPs) as acceptors to enhance upconversion luminescence by Förster resonant energy transfer (FRET). The physical mixture composed of monolayer WS2 and NaYF4:Er3+ nanoparticles was coated on SiO2 microsphere by immersion method. Excited by high power density WGM, three photons were absorbed by WS2-QDs based on the quantum size effect to generate excited electrons as donors and UCNPs as acceptors based on FRET, subsequently, the energy of the electrons were transferred to the luminescence center Er3+ to improve the upconversion luminescence efficiency. The mechanism model of upconversion luminescence enhancement based on FRET of WS2–NaYF4:Er3+ was proposed, and the enhancement effect was experimentally studied and demonstrated. To study the distance dependence of energy transfer between QD and UCNP pairs, we covered the surface of the silica microsphere with a controlled concentration of WS2 mixed with NaYF4:Er3+ nano-particles. When the mixed concentration of WS2-QDs was 0.15%, the upconversion luminescence reached the highest efficiency. The results showed that a twofold upconversion luminescence enhancement can be experimentally achieved. The proposed approach for enhancing the upconversion luminescence could benefit the improvement of imaging signal-to-noise ratio (SNR) using UCNPs for fluorescent labels in life sciences.

A sensitive “off-on” electrochemiluminescence DNA sensor based on signal cascade amplification circuit and distance-dependent energy transfer

A sensitive “off-on” electrochemiluminescence (ECL) DNA sensor was constructed based on Exo III-assisted cascade amplification system. In the cascade amplification circuit, target DNA and Exo III cutting substrate were designed into an inverted T-shaped binding mode to form a stable DNA junction, thus effectively triggering Exo III digestion cycle. During the biosensor assembly process, ferrocene (Fc) and distance-dependent ECL resonance energy transfer (ECL-RET) and surface plasmon resonance (SPR) effects were introduced to regulate the ECL of semiconductor quantum dots (QDs). Carboxylated ZnCdSe/ZnS QDs were used as ECL signal probes and K2S2O8 was coreactant, and the initial cathodic ECL signal of QDs was efficiently quenched through electron and energy transfer with Fc and ECL-RET with Au NPs, leaving the system in “off” state. After the products of cascade amplification were introduced into the electrode surface, the single-stranded DNA modified with Fc was displaced, and the distance between Au NPs and QDs became farther, resulting in a transition from ECL-RET to SPR, and then a significant ECL signal boost was achieved, turning the system into “on” state. The combination of efficient cascade amplification system and sensitive “off-on” ECL signal change mode enabled the biosensing platform to detect target DNA with high selectivity (able to distinguish single-base mutated DNA) and ultra-high sensitivity (limit of detection was 31.67 aM, S/N = 3), providing a new perspective for designing highly sensitive and programmable ECL biosensors.

FRETing about the details: Case studies in the use of a genetically encoded fluorescent amino acid for distance-dependent energy transfer.

Förster resonance energy transfer (FRET) is a valuable method for monitoring protein conformation and biomolecular interactions. Intrinsically fluorescent amino acids that can be genetically encoded, such as acridonylalanine (Acd), are particularly useful for FRET studies. However, quantitative interpretation of FRET data to derive distance information requires careful use of controls and consideration of photophysical effects. Here we present two case studies illustrating how Acd can be used in FRET experiments to study small molecule induced conformational changes and multicomponent biomolecular complexes.

Interparticle energy transfer between NaNdF4 and NaYbF4 in self-assembled nanostructures

Förster resonance energy transfer (FRET) is a widely used spectroscopic technique. The development of donor–acceptor combinations is essential to advance this technique. To make the energy transfer efficiency independent of the external environment, we explored the potential of constructing donor–acceptor combinations with lanthanide ion-doped nanoparticles (LNPs), in which the 4f electrons of the lanthanide ions are shielded by the 5s and 6p electrons. Non-radiative energy transfer between LNPs was demonstrated in self-assembled nanostructures and core–shell structure of LNPs was used to control the distance between donor and acceptor in self-assembled nanostructures. The emission intensity ratio of donor and acceptor illustrates that the energy transfer efficiency decreases significantly with increasing distance and the effective energy transfer distance is 8.5 nm, showing the potential of using LNPs as donor–acceptor pairs in the construction of distance-dependent energy transfer system.

Distance-dependent resonance energy transfer in alkyl-terminated Si nanocrystal solids.

Understanding and controlling the energy transfer between silicon nanocrystals is of significant importance for the design of efficient optoelectronic devices. However, previous studies on silicon nanocrystal energy transfer were limited because of the strict requirements to precisely control the inter-dot distance and to perform all measurements in air-free environments to preclude the effect of ambient oxygen. Here, we systematically investigate the distance-dependent resonance energy transfer in alkyl-terminated silicon nanocrystals for the first time. Silicon nanocrystal solids with inter-dot distances varying from 3 to 5nm are fabricated by varying the length and surface coverage of alkyl ligands in solution-phase and gas-phase functionalized silicon nanocrystals. The inter-dot energy transfer rates are extracted from steady-state and time-resolved photoluminescence measurements, enabling a direct comparison to theoretical predictions. Our results reveal that the distance-dependent energy transfer rates in Si NCs decay faster than predicted by the Förster mechanism, suggesting higher-order multipole interactions.

Spatial and Temporal Resolution of Luminescence Quenching in Small Upconversion Nanocrystals.

Luminescent upconversion nanocrystals (UCNCs) have become one of the most promising nanomaterials for biosensing, imaging, and theranostics. However, their ultimate translation into robust luminescent probes for daily use in biological and medical laboratories requires comprehension and control of the many possible deactivation pathways that cause upconversion luminescence (UCL) quenching. Here, we demonstrate that thorough modeling of UCL rise and decay kinetics using a freely accessible software can identify the UCL quenching mechanisms in small (<40 nm) UCNCs with spatial and temporal resolution. Applied to the most relevant β-NaYF4:Yb3+,Er3+ UCNCs, our model showed that only a few distinct nonradiative low-energy transitions were deactivated via specific solvent and ligand vibrations with a strong downstream effect on the population and depopulation dynamics of the emitting states. UCL quenching could penetrate ca. 4 nm inside the UCNC, which resulted in significant size-dependent changes of UCL intensities and spectra. Despite the large surface-to-volume ratios and UCL quenching via the UCNC surface, we found strong contributions of the outer layers to the overall UCL, which will be highly important for the design of UCNPs to investigate biomolecular interactions via distance-dependent energy transfer methods. Our advanced kinetic model is easily scalable to different UCNC architectures, environments, and energy transfer interactions such that relatively simple modeling of UCL kinetics can be used for efficiently optimizing UCNCs for their final application as practical luminescent probes.

Distance dependent energy transfer dynamics from a molecular donor to a zeolitic imidazolate framework acceptor.

Zeolitic Imidazolate frameworks (ZIFs) have been demonstrated as promising light harvesting and photocatalytic materials for solar energy conversion. To facilitate their application in photocatalysis, it is essential to develop a fundamental understanding of their light absorption properties and energy transfer dynamics. In this work, we report distance-dependent energy transfer dynamics from a molecular photosensitizer (RuN3) to ZIF-67, where the distance between RuN3 and ZIF-67 is finely tuned by depositing an ultrathin Al2O3 layer on the ZIF-67 surface using an atomic layer deposition (ALD) method. We show that energy transfer time decreases with increasing distance between RuN3 and ZIF-67 and the Förster radius is estimated to be 14.4 nm.

In-situ tailoring upconversion processes from lanthanide ions doped ferroelectric films through piezoelectric strain

The ability to manipulate the upconversion processes in lanthanide doped phosphors is of great significance for both scientific research and practical applications. In this regards, we have demonstrated in-situ tailoring the upconversion processes in Yb3+, Er3+ and Tm3+ tri-doped BaTiO3 thin films through piezoelectric strain. In contrast to conventional chemical routes, the physical approach can eliminate the persisted sample-to-sample inherent inhomogeneities, and identify the lattice deformation impact on the intra-configurational 4f transitions of dopant ions, as well as inter-lanthanide ions energy transfers. Herein, the reduced photoluminescence intensities and the elongated lifetimes for the multi-color emissions mainly arise from strain-induced improved lattice symmetry, which contributes to the reduction of radiative probabilities of dopant Er3+ and Tm3+ ions. While the reduced distances between the dopant ions enhance the energy transfer. These two mechanisms are entangled and act simultaneously. The observed phenomena indicate that the influence of the variation of crystal-field effect on the upconversion emissions suppresses that of the interionic distance-dependent energy transfer under 0.2% biaxial strain imposed by PMN-PT substrates. Our work has unambiguously provided new opportunities to render the upconversion processes. More intriguingly, integrating lanthanide-doped ferroelectric films with giant piezoelectric actuators provide an in-situ and dynamic modulation of the upconversion emissions.

Active Mediation of Plasmon Enhanced Localized Exciton Generation, Carrier Diffusion and Enhanced Photon Emission

Understanding the enhancement of charge carrier generation and their diffusion is imperative for improving the efficiency of optoelectronic devices particularly infrared photodetectors that are less developed than their visible counterpart. Here, using gold nanorods as model plasmonic systems, InAs quantum dots (QDs) embedded in an InGaAs quantum well as an emitter, and GaAs as an active mediator of surface plasmons for enhancing carrier generation and photon emission, the distance dependence of energy transfer and carrier diffusion have been investigated both experimentally and theoretically. Analysis of the QD emission enhancement as a function of distance reveals a Förster radius of 3.85 ± 0.15 nm, a near-field decay length of 4.8 ± 0.1 nm and an effective carrier diffusion length of 64.0 ± 3.0 nm. Theoretical study of the temporal-evolution of the electron-hole occupation number of the excited states of the QDs indicates that the emission enhancement trend is determined by the carrier diffusion and capture rates.

Novel Double-Potential Electrochemiluminescence Ratiometric Strategy in Enzyme-Based Inhibition Biosensing for Sensitive Detection of Organophosphorus Pesticides.

Generally, electrochemiluminescence (ECL) ratiometric assays were based on the energy transfer (ET) between an emitter and a metal nanomaterial or between two different emitters. The choice of suitable energy donor-acceptor pair and the distance dependence of ET would greatly limit the practical application of ratiometric assays. This work explored a novel double-potential ECL ratiometry without the ET for organophosphorus pesticides (OPs) analysis, in which, reduced graphene oxide-CdTe quantum dots (RGO-CdTe QDs) and carboxyl-conjugated polymer dots (PFO dots) were chosen as cathodic and anodic ECL emitters, and the reactant (dissolved O2) and the product (H2O2) in enzymatic reactions served as their coreactants, respectively. With the occurrence of the enzymatic reactions induced by the acetylcholinesterase (AChE) and choline oxidase (ChOx), the cathodic ECL signal from RGO-CdTe QDs was at "signal off" state due to the consumption of dissolved O2. Meanwhile, the anodic ECL signal from PFO dots was at "signal on" state due to the in situ generation of H2O2. In the presence of OPs, the cathodic ECL signal would increase while the anodic ECL signal would decline correspondingly due to the inhibition of OPs on the activity of AChE. Using the reactant and the product in enzymatic reactions as the coreactants of two different ECL emitters, we conveniently achieved the opposite change trend in two ECL signals for the ratiometric detection of OPs, which exhibited a greatly improved accuracy, reliability and sensitivity, thus, showing a great attraction for developing ECL ratiometric systems for the bioanalysis.

Distance-dependent energy transfer between CdSe/CdS quantum dots and a two-dimensional semiconductor

Atomically thin semiconductors, such as the transition metal dichalcogenides, show great potential for nanoscale photodetection, energy harvesting, and nanophotonics. Here, we investigate the efficiency of energy transfer between colloidal quantum dots with a cadmium selenide core and cadmium sulfide shell and monolayer molybdenum diselenide (MoSe2). We show that MoSe2 effectively quenches the fluorescence of quantum dots when the two materials are in contact. We then separate the MoSe2 and quantum dots by inserting variable thickness hexagonal boron nitride (h-BN) spacers and show that the efficiency at which the MoSe2 quenches fluorescence decreases as the h-BN thickness is increased. For distances d, this trend can be modeled by a 1/d4 decay, in agreement with theory and recent studies involving graphene.

Spectroscopic and Structural Studies of a Surface Active Porphyrin in Solution and in Langmuir-Blodgett Films.

Controlling aggregation of the dual sensitizer-emitter (S-E) zinc tetraphenylporphyrin (ZnTPP) is an important consideration in solid state noncoherent photon upconversion (NCPU) applications. The Langmuir-Blodgett (LB) technique is a facile means of preparing ordered assemblies in thin films to study distance-dependent energy transfer processes in S-E systems and was used in this report to control the aggregation of a functionalized ZnTPP on solid substrates. This was achieved by synthetic addition of a short polar tail to one of the pendant phenyl rings in ZnTPP in order to make it surface active. The surface active ZnTPP derivative formed rigid films at the air-water interface and exhibited mean molecular areas consistent with approximately vertically oriented molecules under appropriate film compression. A red shift in the UV-vis spectra as well as unquenched fluorescence emission of the LB films indicated formation of well-ordered aggregates. However, NCPU, present in the solution phase, was not observed in the LB films, suggesting that NCPU from ZnTPP as a dual S-E required not just a controlled aggregation but a specific orientation of the molecules with respect to each other.

Distance-Dependent Energy Transfer between Ga2O3 Nanocrystal Defect States and Conjugated Organic Fluorophores in Hybrid White-Light-Emitting Nanophosphors

We report a quantitative analysis and development of hybrid white-light-emitting nanoconjugates, prepared by functionalizing colloidal γ-Ga2O3 nanocrystals with selected organic fluorophores. Using the Forster resonance energy transfer (FRET) formalism, we studied the coupling of native defect states in Ga2O3 nanocrystals, as energy donors, with different orange-red-emitting fluorophores bound to nanocrystal surfaces, as energy acceptors. Variations in the average nanocrystal size and dye surface coverage were used to characterize the efficiency of the energy transfer process and the corresponding donor–acceptor separations. The results show that for approximately three rhodamine B molecules per nanocrystal the energy transfer efficiency increases from 23% to 49% by decreasing the NC size from 5.3 to 3.6 nm. These FRET efficiencies correspond to the estimated donor–acceptor distances of 3.55 ± 0.02 and 2.99 ± 0.03 nm, respectively. Similar trends were observed for ATTO 590-conjugated Ga2O3 nanocrystals, a...

Reversible reconfiguration of DNA origami nanochambers monitored by single-molecule FRET.

Today, DNA nanotechnology is one of the methods of choice to achieve spatiotemporal control of matter at the nanoscale. By combining the peculiar spatial addressability of DNA origami structures with the switchable mechanical movement of small DNA motifs, we constructed reconfigurable DNA nanochambers as dynamic compartmentalization systems. The reversible extension and contraction of the inner cavity of the structures was used to control the distance-dependent energy transfer between two preloaded fluorophores. Interestingly, single-molecule FRET studies revealed that the kinetics of the process are strongly affected by the choice of the switchable motifs and/or actuator sequences, thus offering a valid method for fine-tuning the dynamic properties of large DNA nanostructures. We envisage that the proposed DNA nanochambers may function as model structures for artificial biomimetic compartments and transport systems.

Hybrid ZnO-Based Nanoconjugate for Efficient and Sustainable White Light Generation

Developing new ways of generating white light is of paramount importance for the design of the next generation of smart, energy-efficient lighting sources. Here we report tunable white light emission of hybrid organic–inorganic nanostructures based on colloidal ZnO nanocrystals conjugated with organic fluorophores. These materials act as single nanophosphors owing to the distance-dependent energy transfer between the two components. The defect-based size-tunable ZnO nanocrystal blue-green emission coupled with complementary color emission from different fluorophores allows for the generation of white light with targeted chromaticity, color temperature, and color rendering index. We further show that silane layer-protected nanoconjugates result in increased stability of white light emission over a long period of time. The results of this work demonstrate an inexpensive, green, and sustainable approach to general solid-state lighting, without the use of rare earth or heavy metals. Colloidal form of the repo...

Distance dependence of energy transfer from InGaN quantum wells to graphene oxide

We report the distance-dependent energy transfer from an InGaN quantum well to graphene oxide (GO) by time-resolved photoluminescence (PL). A pronounced shortening of the PL decay time in the InGaN quantum well was observed when interacting with GO. The nature of the energy-transfer process has been analyzed, and we find the energy-transfer efficiency depends on the 1/d² separation distance, which is dominated by the layer-to-layer dipole coupling.

Distance Dependence of Intrahelix RuII* to OsII Polypyridyl Excited-State Energy Transfer in Oligoproline Assemblies

Energy transfer between the metal-to-ligand charge transfer (MLCT) excited states of [Pra [M(II)(bpy)2(4-Me-4'(-N(H)CO)bpy)](PF6)2 units ([Pra(M(II)bpy2(mbpy)](2+): M(II) = Ru(II) or Os(II), bpy = 2,2'-bipyridine, mbpy = 4'-methyl-2,2'-bipyridine-4-carboxamido, Pra = 4-M(II)-L-proline) linked covalently to oligoproline assemblies in room temperature acetonitrile occurs on the picosecond-nanosecond time scale and has been time-resolved by transient emission measurements. Three derivatized oligoprolines, [CH3-CO-Pro6-Pra[Os(II)(bpy)2(mbpy)](2+)-Pro2-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro2-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro6-Glu-NH2](6+) (ORR-2, Pro = L-proline and Glu = glutamic acid); [CH3-CO-Pro6-Pra[Os(II)(bpy)2(mbpy)](2+)-Pro3-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro3-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro6-Glu-NH2](6+) (ORR-3); and CH3-CO-Pro6-Pra[Os(II)(bpy)2(mbpy)](2+)-Pro5-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro5-Pra[Ru(II)(bpy)2(mbpy)](2+)Pro6-Glu2-NH2](6+) (ORR-5), were prepared by using solid-phase peptide synthesis. Given the helical nature of the resulting assemblies and the nature of the synthesis, composition, length, and loading pattern are precisely controlled in the assemblies. In acetonitrile, they adopt a proline I helical secondary structure, confirmed by circular dichroism, in which the appended chromophores are ordered in well-defined orientations and internuclear separation distances although helix formation for ORR-2 is incomplete. Quantitative comparison of oligoproline ground-state absorption and steady-state emission spectra to those for the constituents, [Boc-Pra[M(II)(bpy)2(mbpy)](2+)-OH](PF6)2 (Boc = N(α)-(1,1-dimethylethoxycarbonyl), shows that following Ru(II) light absorption, Ru(II)* undergoes facile energy transfer resulting in sensitization of Os(II). Sensitization efficiencies are 93% for ORR-2, 77% for ORR-3, and 73% for ORR-5. Picosecond-resolved emission measurements reveal complex, coupled dynamics that arise from excited-state decay and kinetically competitive -Ru(II)*-Ru(II)- → -Ru(II)-Ru(II)*- energy transfer migration/exchange and downhill -Ru(II)*-Os(II) → -Ru(II)-Os(II)* energy transfer. These processes were modeled simultaneously to extract rate constants for Ru(II)* → Ru(II) energy-transfer migration, k(Ru*-Ru), and Ru(II)* → Os(II) energy transfer, k(Ru*-Os). For ORR-2, k(Ru*-Ru) = 2.9 × 10(7) s(-1) and k(Ru*-Os) = 3.4 × 10(8) s(-1). For ORR-3, k(Ru*-Ru) = 1.2 × 10(7) s(-1) and k(Ru*-Os) = 1.3 × 10(8) s(-1). For ORR-5, k(Ru*-Ru) = 3.6 × 10(6) s(-1) and k(Ru*-Os) = 5.8 × 10(7) s(-1), all in acetonitrile at 22 °C. The data were analyzed by assuming Dexter energy transfer with the Franck-Condon factors arising from intramolecular structural and medium changes evaluated by use of an emission spectral fitting procedure. Fits of the data to the Dexter mechanism were consistent with the predicted distance dependence of energy transfer.

Thermal lens probing of distant dependent fluorescence quenching of Rhodamine 6G by silver nanoparticles

Manipulation of the characteristics of laser dyes using metal nanoparticles is one of the rapidly growing areas in nanotechnology due to their promising applications in diverse fields, ranging from biomedical imaging to green energy. The energy transfer behavior of a silver nanoparticle (Ag NP) with a dye molecule, Rhodamine 6G (Rh 6G), is interrogated using static photoluminescence as well as a laser based dual beam thermal lens technique. Spherical Ag NPs of various concentrations are prepared using chemical reduction method and is mixed with a fixed concentration of Rh 6G. It is observed that the intrinsic fluorescence of Rh 6G (1×10−6M) is quenched in proximity of the Ag NPs and the quenching efficiency increases with an increase in Ag NP concentration (2.5×10−4▒–▒10×10−4M). The dye–NP distance is evaluated by varying the concentrations of Ag NPs and it is found to decrease with an increase in the NP concentration in the mixture from 92 to 69Å (1Å=10−10m). The distance dependent energy transfer efficiency showed that dye–NP mixture follows R−4 dependence, where R is the dye–NP distance.

Sensitization of ultra-long-range excited-state electron transfer by energy transfer in a polymerized film

Distance-dependent energy transfer occurs from the Metal-to-Ligand Charge Transfer (MLCT) excited state Ru(bpy)3(2+*) to an anthracene-acrylate derivative (Acr-An) incorporated into the polymer network of a semirigid poly(ethyleneglycol)dimethacrylate monolith. Following excitation, Ru(bpy)3(2+*) to Acr-An triplet energy transfer occurs followed by long-range, Acr-(3)An-Acr-An → Acr-An-Acr-(3)An, energy migration. With methyl viologen dication (MV(2+)) added as a trap, Acr-(3)An + MV(2+) → Acr-An(+) + MV(+) electron transfer results in sensitized electron transfer quenching over a distance of approximately 90 Å.