Dipole-dipole Energy Transfer Research Articles

Gold Nanoparticle Based NSET For Monitoring Mg2+ Dependent RNA Folding

Understanding the mechanism of how RNA molecules fold into their native structures are vital to their functional properties. Here we report for the first time that gold nanoparticle based NSET can be used for probing the transition states of an RNA unfolding reaction. Our result shows that time-dependent NSET can clearly distinguish structural transitions between unfolded to folded states. Our experimental observation point out that NSET can be used for the design of an optical based molecular ruler to track RNA folding transition states at distances more than double the distances achievable using traditional dipole-dipole Coulombic energy transfer based methods.

Luminescence quenching kinetics upon diffusion-accelerated dipole-dipole energy transfer for a realistic condensed-matter model

The hard-sphere model is considered as a more realistic condensed-matter model. In this model, the radial distribution function of molecules in a medium, used for calculations of luminescence decay kinetics, takes into account the short-range order in fluids and has the shape of damped oscillations. It is assumed that the motion of donor and acceptor molecules in a solution for the lifetime of the excited state of the donor is described by the diffusion equation, while the luminescence quenching occurs due to the long-range dipole- dipole energy transfer. It is shown that, if diffusion coefficients are small, the kinetics determined in this study hardly differs at all from the traditional kinetics. At intermediate and large diffusion coefficients, this difference becomes significant and should be taken into account in estimating the Forster energy transfer radius and dif- fusion coefficients from experimental luminescence decay curves.

On the Quenching of Semiconductor Quantum Dot Photoluminescence by Proximal Gold Nanoparticles

Luminescent quantum dots (QDs) were proven to be very effective fluorescence resonance energy transfer donors with an array of organic dye acceptors, and several fluorescence resonance energy transfer based biosensing assemblies utilizing QDs have been demonstrated in the past few years. Conversely, gold nanoparticles (Au-NPs) are known for their capacity to induce strong fluorescence quenching of conventional dye donors. Using a rigid variable-length polypeptide as a bifunctional biological linker, we monitor the photoluminescence quenching of CdSe-ZnS QDs by Au-NP acceptors arrayed around the QD surface, where the center-to-center separation distance was varied over a broad range of values (approximately 50-200 Angstrom). We measure the Au-NP-induced quenching rates for such QD conjugates using steady-state and time-resolved fluorescence measurements and examine the results within the context of theoretical treatments based on the Förster dipole-dipole resonance energy transfer, dipole-metal particle energy transfer, and nanosurface energy transfer. Our results indicate that nonradiative quenching of the QD emission by proximal Au-NPs is due to long-distance dipole-metal interactions that extend significantly beyond the classical Förster range, in agreement with previous studies using organic dye-Au-NP donor-acceptor pairs.

Gold Nanoparticle Based FRET Asssay for the Detection of DNA Cleavage

We report gold nanoparticle based FRET assay to monitor the cleavage of DNA by nucleases. Fluorescence signal enhancement is observed by a factor of 120 after the cleavage reaction in the presence of S1 nuclease. The mechanism of distant dependent fluorescence quenching has been discussed. Our experimental results on distance dependent fluorescence quenching match quite well with theoretical findings obtained from the fluorescence quenching model by Gersten and Nitzan (Surf. Sci. 1985, 158, 165). Our experimental observation paradigm for the design of optical based molecular ruler strategies at distances more than double the distances achievable using traditional dipole-dipole Columbic energy transfer based methods.

Dipole Blockade at Förster Resonances in High Resolution Laser Excitation of Rydberg States of Cesium Atoms

High resolution laser excitation of np Rydberg states of cesium atoms shows a dipole blockade at Förster resonances corresponding to the resonant dipole-dipole energy transfer of the np+np --> ns+(n+1)s reaction. The dipole-dipole interaction can be tuned on and off by the Stark effect, and such a process, observed for relatively low n(25-41), is promising for quantum gate devices. Both Penning ionization and saturation in the laser excitation can limit the range of observation of the dipole blockade.

Hybrid Inorganic/Organic Semiconductor Heterostructures with Efficient Non‐Radiative Energy Transfer

An inorganic/organic hybrid semiconductor heterostructure is reported, in which an InGaN quantum well is non-radiatively coupled to a semiconducting polymer overlayer (see Figure). This architecture has the potential to take advantage of the complementary attributes of the two types of semiconductor that it contains, and may lead to devices with highly efficient emission across the entire visible spectrum.

Back and Forth Transfer and Coherent Coupling in a Cold Rydberg Dipole Gas

Coupling by the resonant dipole-dipole energy transfer between cold cesium Rydberg atoms is investigated using time-resolved narrow-band deexcitation spectroscopy. This technique combines the advantage of efficient Rydberg excitation with high-resolution spectroscopy at variable interaction times. Dipole-dipole interaction is observed spectroscopically as avoided level crossing. The coherent character of the process is linked to back and forth transfer in the np + np <--> ns + (n + 1)s reaction. Decoherence in the ensemble has two different origins: the atom motion induced by dipole-dipole interaction and the migration of the s-Rydberg excitation in the environment of p-Rydberg atoms.

Energy transfer studies in Eu3+-doped lead–niobium–germanate glasses

The spectral migration of energy among Eu 3+ ions in lead-niobium-germanate glass (60GeO 2 -25PbO-15Nb205) with different Eu 3+ concentrations (0.5, 1, 3, and 5 mol%) has been investigated at low temperature by using time-resolved fluorescence line narrowing (TRFLN) spectroscopy. The spectral features of the time-resolved fluorescence line-narrowed 5 D 0 → 7 F 0 emission spectra under resonant excitation at different wavelengths along the 7 F 0 → 5 D 0 transition as a function of time, excitation wavelength, and concentration reveal the existence of energy migration between discrete regions of the inhomogeneous broadened spectral profile. The analysis of the time evolution of the 5 D 0 → 7 F 0 emission shows that the electronic mechanism responsible for the ion-ion interaction can be identified as a dipole-dipole energy transfer process.

Intramolecular Energy Transfer in Molecular Dyads Comprising Free-base Porphyrin and Ruthenium(II) Bis(2,2‘:6‘,2‘ ‘-terpyridine) Termini

A molecular dyad has been synthesized in which free-base porphyrin and ruthenium(II) bis(2,2':6',2-terpyridine) subunits are linked via a meso-phenylene group. The distal terpyridine ligand bears a single phenylethynylene group. Selective illumination into the metal complex is followed by rapid intramolecular triplet-triplet energy transfer from the metal-to-ligand charge-transfer (MLCT) triplet to the lowest-energy π,π* triplet state localized on the porphyrin. This process is characterized by a reorganization energy of 0.14 eV and an electronic coupling matrix element of 76 cm - 1 . Because of the alkynylene substituent, the initially produced MLCT state is centered on the distal terpyridine. Therefore, triplet energy transfer must cross the proximal terpyridine ligand. At low temperature, nuclear tunneling renders the rate of triplet energy transfer activationless. Upon selective illumination into the lowest-energy singlet (S 1 ) state localized on the porphyrin, fast singlet-triplet energy transfer occurs, to populate the MLCT triplet with high efficiency. This process happens by way of Dexter-type electron exchange at room temperature, and the MLCT triplet can be identified as a reaction intermediate at low temperature. The activation energy for singlet-triplet energy transfer is only 0.05 eV, because of the smaller energy gap, and the electronic coupling matrix element is decreased to 11 cm - 1 , because energy transfer is spin-forbidden. At low temperature, dipole-dipole energy transfer becomes the main mechanism for decay of the porphyrin S 1 state. Excitation into the Soret band of the porphyrin is followed by rapid internal conversion to S 1 without energy or electron transfer to the appended metal complex.

Polarization of phosphorescence transitions and probabilities of intramolecular nonradiative deactivation of the lowest triplet state of aromatic molecules

This study continues the experimental testing of the validity of the inductive resonance theory of dipole-dipole energy transfer from the T 1→S 0 transition dipole to stretching vibrations of intramolecular CH bonds of naphthalene and its hydroxy derivatives. To this end, in the series of compounds under study, the range of variation of the geometrical parameter [Φ(CH)]2 of the Forster theory, which accounts for the mutual orientation of the energy donor and acceptor, is estimated. Preliminarily, the angles between the transition dipole moments of the radiative and absorptive electronic transitions (T 1→S 0 and S 0→S 1; T 1→S 0 and S 0→S 2; S 1→S 0 and S 0 →S 1; and S 1→S 0 and S 0→S 2) are measured at 77 K by the method of polarization photoselection. From the polarization measurements, the angles between the phosphorescence transition dipole moment and the plane of a molecule are determined. It was found that, upon passage from naphthalene to its β derivatives, the orientation of the dipole moment of the radiative T 1→S 0 transition relative to the plane of a molecule markedly changes, with the in-plane component of the dipole moment being increased by an order of magnitude. The experimentally determined rate constants of nonradiative deactivation of the T 1 state averaged over the CH groups of the naphthalene ring system, k nr(CH), are compared with the rate constants [Φ(CH)]2 of the inductive resonance energy transfer from the dipole of the T 1→S 0 transition to the dipole of the CH vibrations polarized in the plane of a molecule, calculated with regard to the orientational factor [Φ(CH)]2. This comparison showed that, in the series of compounds under study, a change in the orientation of the dipole moment of the radiative T 1→S 0 transition relative to the plane of a molecule does not affect the rate of the nonradiative T 1⇝S 0 transition. This inference is confirmed by the absence of a correlation between the rate constants k dd(CH) calculated by us (with regard to [Φ(CH)]2) and the well-known rate constants k nr(CH) of individual sublevels of the T 1 state measured at T≤1.35 K for a number of organic molecules. The possible sources of discrepancy between the experimental data that k nr(CH) is independent of [Φ(CH)]2 and the predictions of the theory are considered. A conclusion is made that the electronic-vibrational energy transfer between electric dipoles is the most probable mechanism of the T 1⇝S 0 transitions, but the rate constant of the dipole-dipole energy transfer upon interaction of the electronic and vibrational dipoles in a molecule does not depend on their orientations.

Dephasing of resonant energy transfer in a cold Rydberg gas

When the dipole-dipole energy transfer, $\mathrm{Rb} {25s}_{1/2}+\mathrm{Rb} {33s}_{1/2}\ensuremath{\rightarrow}\mathrm{Rb} {24p}_{1/2}+\mathrm{Rb} {34p}_{3/2},$ resonant at fields of 3.0 and 3.4 V/cm, is observed in a cold Rydberg gas, the resonances are broader than expected for this dipole-dipole interaction alone. Using a variant of the Ramsey interference method, in which the system is detuned from the resonance, we observe a density-dependent dephasing which we attribute to the inhomogeneities in the always resonant dipole-dipole excitation exchange interactions $\mathrm{Rb} {25s}_{1/2}+\mathrm{Rb} {24p}_{1/2}\ensuremath{\rightarrow}\mathrm{Rb} {24p}_{1/2}+\mathrm{Rb} {25s}_{1/2}$ and $\mathrm{Rb} {33s}_{1/2}+\mathrm{Rb} {34p}_{3/2}\ensuremath{\rightarrow}\mathrm{Rb} {34p}_{3/2}+\mathrm{Rb} {33s}_{1/2}.$ Since the dephasing rate is comparable to the observed widths, it appears that all of these interactions contribute to the observed linewidths.

Energy Back-Transfer and other Nonradiative Energy-Transfer Processes in Yb3 + , Er3 + : Y 3Al5 O 12

Experimental data from two yttrium aluminum garnet (YAG) crystal samples with different doping concentrations were analyzed through the calculation of the exact solution of the general nonradiative energy-transfer master equations. Besides the dipole-dipole direct energy transfer and the dipole-dipole migration processes assumed by other authors to predict the -fluorescence decay, it is shown that a quadrupole-quadrupole direct energy transfer and a dipole-dipole back-transfer process are also present. The used free parameter values predicted our experimental data as well as other experimental data reported in the literature. Further, our modeling also calculates the acceptor transients which were also compared to experimental data. Therefore, the used modeling can be applied to analyze complicated nonradiative energy-transfer processes where traditional models fail. © 2002 The Electrochemical Society. All rights reserved.

Dependence of cooperative luminescence intensity onYb3+spatial distribution in crystals and glasses

Cooperative emission has been recorded in several ${\mathrm{Yb}}^{3+}$ stoichiometric crystals. Its intensity, normalized by the square of the ${}^{2}{F}_{5/2}$ excited level population, is shown to depend only on the ${\mathrm{Yb}}^{3+}$ ions spatial distribution. In most cases, other material dependent parameters do not need to be taken into account, as confirmed by a theoretical analysis. Cooperative luminescence (CL) is therefore an easy way to probe ${\mathrm{Yb}}^{3+}$ clustering in crystals and glasses. This measurement has been carried out in aluminosilicate and phosphate glasses for which CL intensity strongly varies with the glass composition. Two models of Yb distribution are proposed to relate CL and glass structure or to allow easy comparison between samples. Finally, the extension of these results to other rare-earth ions and energy transfer processes is examined. It is found that dipole-dipole energy transfer and CL interaction coefficients vary in the same way but with reduced amplitude for the former. This results from the CL dependence on a quadrupole-dipole process at short distances.

Förster energy transfer from a fluorescent dye to a phosphorescent dopant: a concentration and intensity study

We report on the long-range dipole-dipole Forster energy transfer between a fluorescent dye and a phosphorescent dopant in solid thin films. For our study we used 4,4′-N,N′-dicarbazole-biphenyl as a host and the organometallic complex fac tris(2-phenylpyridine) iridium(III) as a guest. By studying the photoluminescence efficiency of films with various host and guest concentrations and by comparing these results with those obtained from a numerical model, we determine a Forster radius of R0 ∼ 3 nm.

Kinetics of Triplet-Triplet Annihilation of Mg-Phthalocyanine in Methanol and Deuteromethanol

Using the method of flash photolysis, the effect of deuteration of a solvent on the kinetics of triplet-triplet annihilation is studied on the example of Mg-phthalocyanine (Mg-Phc) in methanol-h 4 and methanol-d 4 at ∼298 K. The time and concentration kinetic dependences are different in different solvents, which cannot be explained only by the difference in the viscosity of the latter. The experimental data are analyzed based on consideration of the triplet-triplet annihilation mechanism via the formation of triplet-triplet complexes from molecules in a triplet state. It is established that in methanol-d 4 the constants of the rates of monomolecular deactivation of the triplet state and of the decomposition of the complexes is 1.5–2 times smaller than in methanol-h 4. The effect of deuteration is explained by the decrease in the rate of dipole-dipole energy transfer from the triplet state of the pigment to the solvent molecules in deuteration.

Mono- and dinuclear ruthenium(II) and osmium(II) polypyridine complexes built around spiro-bridged bis(phenanthroline) ligands: synthesis, electrochemistry, and photophysics.

Two new dyads have been synthesized in which terminal Ru(II) and Os(II) polypyridine complexes are separated by sterically constrained spiro bridges. The photophysical properties of the corresponding mononuclear complexes indicate the importance of the decay of the lowest-energy triplet states localized on the metallo fragments through the higher-energy metal-centered excited states. This effect is minimized at 77 K, where triplet lifetimes are relatively long, and for the Os(II)-based systems relative to their Ru(II)-based counterparts. Intramolecular triplet energy transfer takes place from the Ru(II)-based fragment to the appended Os(II)-based unit, the rate constant being dependent on the molecular structure and on temperature. In all cases, the experimental rate constant matches surprisingly well with the rate constant calculated for Förster-type dipole-dipole energy transfer. As such, the disparate rates shown by the two compounds can be attributed to stereochemical factors. It is further concluded that the spiro bridging unit does not favor through-bond electron exchange interactions, a situation confirmed by cyclic voltammetry.

Laser spectroscopy ofNd3+ions inGeO2−PbO−Bi2O3glasses

The optical properties of ${\mathrm{Nd}}^{3+}$ ions in six different compositions of glasses based on ${\mathrm{GeO}}_{2},$ PbO, and ${\mathrm{Bi}}_{2}{\mathrm{O}}_{3}$ have been investigated by using steady-state and time-resolved laser spectroscopy. Judd-Ofelt parameters were derived from the absorption spectra and used to calculate the ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{F}_{3/2}}}^{4}{I}_{11/2}$ stimulated emission cross section and the ${}^{4}{F}_{3/2}$ radiative lifetime. Site-selective spectroscopy and time resolved fluorescence line narrowing experiments were performed in the ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{F}_{3/2}}}^{4}{I}_{9/2}{,}^{4}{I}_{11/2}$ transitions. For all samples studied a line narrowing of the ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{F}_{3/2}}}^{4}{I}_{11/2}$ emission has been observed when exciting at the long wave side of the ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{I}_{9/2}}}^{4}{F}_{3/2}$ transition. The lifetimes of the ${}^{4}{F}_{3/2}$ state do not show a monotonic variation with the excitation wavelength indicating large site-to-site variations in the local crystal field. Spectral migration of excitation among the ${\mathrm{Nd}}^{3+}$ ions has been studied from the time evolution of the ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{F}_{3/2}}}^{4}{I}_{9/2}$ spectra under resonant excitation. The results can be interpreted in terms of a dipole-dipole energy transfer mechanism. Visible upconversion has been observed in these glasses under infrared laser excitation.

希土類イオンの有機媒体発光 ネオジム錯体の配位子設計とその展開

The relatively low efficiency of Nd (III) emission in organic media has been improved by 1) suppression of the radiationless transition process via vibrational excitation of the surrounding medium, 2) prevention of dipole-dipole nonradiative energy transfer processes via energy migration, 3) suppression of radiationless transition of D2O molecules in the vicinity of Nd (III) complexes (formation of twelve-coordinate Nd (III) complex with DMSO-d6), 4) allowance of electron transitions of Nd (III) by the introduction of asymmetric ligand field, 5) photosensitization by use of energy transfer from organic ligands. The luminescence of NMI) was observed for the first time in undeuterated acetone when Nd (III) was complexed with bis-perfluorooctylsulfonylamine (pos). As to the applications of luminescent Nd (III) complexes, developments of luminescent lanthanide polymers and EL device were successful.

Near-field optical excitation as a dipole-dipole energy transfer process.

The process of fluorescence excitation in the scanning near-field optical microscope (SNOM) is considered as a dipole-dipole resonance energy transfer process between a molecule under study and a SNOM aperture, which can be treated as a magnetic-type point dipole. It is shown that such an approach satisfactorily describes the conditions of the usual SNOM fluorescence experiments. Fluorescence excitation dependence on the polarization of the incident light and medium refraction index have been obtained. The equation to calculate the resonance dipole-dipole energy transfer radius (which is a natural unit of a SNOM's longitudinal resolution) is derived. Those cases where such a radius is of the order of the SNOM aperture, and thus single dipole, can strongly influence the radiation conditions are discussed briefly.

Laser spectroscopy ofPr3+ions inLiKY1−xPrxF5single crystals

The visible luminescence of ${\mathrm{Pr}}^{3+}$-doped fluoride ${\mathrm{LiKY}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{F}}_{5}$ crystals $(x=0.001,$ 0.01, 0.02, 0.03, 0.05, and 0.1) has been investigated as a function of concentration and temperature by using time-resolved laser spectroscopy. The temperature-dependent concentration quenching of the ${}^{3}{P}_{0}$ fluorescence in the 10--77 K temperature range can be described in the framework of a thermally activated cross-relaxation process involving the ${}^{1}{D}_{2}$ and ${}^{3}{H}_{6}$ states. However, the single exponential character of the decays at all concentrations and temperatures suggests that energy migration is also present in this system. The fluorescence from the ${}^{1}{D}_{2}$ level shows a strong concentration quenching for ${\mathrm{Pr}}^{3+}$ concentrations higher than $x=0.001$ even at 4.2 K. The time evolution of the decays from the ${}^{1}{D}_{2}$ state for concentrations higher than $x=0.001$ is consistent with a dipole-dipole energy transfer mechanism. Anti-Stokes emission from the ${}^{3}{P}_{0}$ level following excitation of the ${}^{1}{D}_{2}$ state is also studied for different ${\mathrm{Pr}}^{3+}$ concentrations. Analysis of the upconverted fluorescence decays supports that the mechanism responsible for the upconvertion process is energy transfer. However, this process seems to be complex enough to allow for the use of a single model which could explain the behavior observed.