Electronic Excitation Energy Transfer Research Articles

Processes of electronic excitation energy transfer between luminescent dye molecules in microheterogeneous systems based on polymer micellar solutions

The processes of electronic excitation energy transfer (EEET) between different-type dye molecules in polymer micellar solutions with different polyelectrolyte concentration have been analyzed. The possibility of regulating the EEET efficiency between dye molecules due to change of the structure of polymer micellar complexes has been established. The results presented are explained from the viewpoint of the fractal character of distribution of interacting particles. The experimental dependence of the fractal dimension of the distribution of dye molecules in polymer micellar solutions on the polyelectrolyte concentration has been obtained.

Sensitized anti-Stokes luminescence centers in microcrystals of Zn0.6Cd0.4S solid solutions with adsorbed dye molecules and few-atomic silver clusters

The sensitized anti-Stokes luminescence excited by radiation with wavelengths from 610 to 750 nm and flux densities of 1014–1015 quanta/(cm2·s) is detected for microcrystals of Zn 0.6 Cd 0.4 S solid solutions with adsorbed organic malachite green and methylene blue dye molecules. The position of its excitation spectra coincides with that of the absorption spectra of adsorbed dye molecules, which suggests the cooperative mechanism of its occurrence. The possibility of amplification of the anti-Stokes luminescence by means of adsorption of silver atoms and few-atomic silver clusters, in addition to the dye molecules, on the Zn 0.6 Cd 0.4 S surface is investigated. It is assumed that in the latter case, the anti-Stokes luminescence is excited as a result of two-quantum optical transitions with electron or electron excitation energy transfer from the dye molecules adsorbed on the Zn 0.6 Cd 0.4 S surface to silver atoms and few-atomic silver clusters creating deep local states with photoionization energies of 1.8–2.0 eV in the gap.

Exciton energy transfer between adsorbates

The electron excitation energy transfer between adsorbed molecules on a solid surface via virtual and real surface excitons is considered. The rate of energy transfer via virtual excitons is calculated analytically. The nonradiative energy transfer to surface impurity centers is considered in the case of rapid migration of virtual or real excitons leading to repeatedly changed distances between centers of excitation localization. A theoretical model of the kinetics of “surface exciton-T-center” cross annihilation is constructed as a mirror image of the theory of cross annihilation of oxygen-containing objects adapted to a system of quasiparticles.

Theoretical investigation of electronic excitation energy transfer in bichromophoric assemblies

Electronic excitation energy transfer (EET) rates in rylene diimide dyads are calculated using second-order approximate coupled-cluster theory and time-dependent density functional theory. We investigate the dependence of the EET rates on the interchromophoric distance and the relative orientation and show that Forster theory works quantitatively only for donor-acceptor separations larger than roughly 5 nm. For smaller distances the EET rates are over- or underestimated by Forster theory depending on the respective orientation of the transition dipole moments of the chromophores. In addition to the direct transfer rates we consider bridge-mediated transfer originating from oligophenylene units placed between the chromophores. We find that the polarizability of the bridge significantly enhances the effective interaction. We compare our calculations to single molecule experiments on two types of dyads and find reasonable agreement between theory and experiment.

Specific features of dissipation of electronic excitation energy in coupled molecular solid systems based on silicon nanocrystals on intense optical pumping

A phenomenological model of transfer and dissipation of electronic excitation energy in the case of intense optical pumping of coupled systems based on arrays of silicon nanocrystals is developed. The calculated dependences of the relative concentrations of donors of energy and acceptors of energy on the intensity of optical pumping are compared with the experimental data on photoluminescence of structures containing silicon nanocrystals surrounded by oxygen molecules and erbium ions. From the comparison between the calculated and experimental dependences, the parameter of coupling of excitons in the silicon nanocrystals with the surrounding acceptors of energy is estimated.

Photostimulated formation of sensitized anti-Stokes luminescence centers in AgCl(I) microcrystals

The low-temperature photostimulated activation of sensitized anti-Stokes luminescence in heterogeneous systems based on AgCl(I) microcrystals with adsorbed organic dye molecules and their aggregates is investigated. It is shown that the observed considerable (by more than an order of magnitude) enhancement of the intensity of this luminescence is caused by the formation of silver atoms and few-atom clusters on the surface of AgCl(I) microcrystals, which increase the efficiency of a two-quantum excitation of sensitized anti-Stokes luminescence by optical radiation in the range 630–730 nm with the flux density 1013–1015 quantum cm−2s−1. Analysis of all the experimental results indicates that the excitation mechanism of anti-Stokes luminescence is based on successive electron transfer or electron-excitation energy transfer from a dye molecule to an atomic-molecular dispersive silver center.

Resonance energy transfer from a fluorescent dye molecule to plasmon and electron-hole excitations of a metal nanoparticle

The authors study the distance dependence of the rate of electronic excitation energy transfer from a dye molecule to a metal nanoparticle. Using the spherical jellium model, they evaluate the rates corresponding to the excitation of l=1, 2, and 3 modes of the nanoparticle. The calculation takes into account both the electron-hole pair and the plasmon excitations of the nanoparticle. The rate follows conventional R(-6) dependence at large distances while small deviations from this behavior are observed at shorter distances. Within the framework of the jellium model, it is not possible to attribute the experimentally observed d(-4) dependence of the rate to energy transfer to plasmons or electron-hole pair excitations.

Electronic Excitation Energy Transfer in DNA. Nature of Triplet Excitations Capturing Centers

Spectral properties, energy structure, and electronic processes in DNA, poly(dAdT)2, d(CCCGGGTTTAAA), d(ATC), d(AT), dGMP, dAMP, dCMP, dTMP were studied. The DNA lowest excited electronic singlet and triplet levels are connected with guanine and adenine bases, correspondingly. The DNA fluorescence is close to a linear combination of the guanine and cytidine emissions and connected, to a greater extent, with the singlet energy transfer to these bases. The origin of the DNA phosphorescence is associated with AT-sequences that are traps of triplet excitations in DNA. The triplet energy transfer to these centers and adenine bases (that are most photostable) leads to the DNA self-protection against a damage induced by electronic excitations of DNA.

Nonradiative energy transfer as a method for investigation of self-assembling nanostructures of lanthanide complexes in solutions

Works concerning the application of nonradiative transfer of electronic excitation energy to investigation into nanostructures of lanthanide complexes in aqueous solutions are surveyed. The effect of the formation of nanosized structures on the quenching of energy donors Ln(III) ions by acceptor ions in concentrated chloride solutions of structuring ions (Li(I), Ca(II)) was discussed. The columinescence phenomenon observed in aqueous solutions of lanthanide chelates was considered. It was shown that the enhancement of luminescence Eu(III) and Tb(III) complexes in water in the presence of excess β-diketones with an admixture of other Ln(III) ions, primarily Gd(III), (columinescence) is due to sensitization via energy transfer over triplet levels of the ligands in the nanostructures formed under these conditions and to the weakening of deactivation of excited luminescent ions by the formation of nanostructures. The influence of the solution preparation procedure on the formation of nanostructures of chelates with different lanthanide ions was revealed, which manifest itself as a variation in the enhancement and quenching of luminescence in the presence of ions from the cerium and yttrium subgroups. Possible applications of the columinescence phenomenon to chemical and medical analysis are briefly discussed.

Self‐Assembled Hybrid Oligo(p‐phenylenevinylene)–Gold Nanoparticle Tapes

Taped energy transfer: A hybrid gel consisting of π-conjugated oligo(p-phenylenevinylene) tapes (OPV1 and OPV2) and gold nanoparticles has been constructed in toluene through noncovalent interactions (see picture). The proximity of the metal particles to the π-conjugated molecules results in transfer of electronic excitation energy from the molecules to the metal in the gel state.

Photochemical behavior of luminescent compositions based on antimony(III) and europium(III) complexes in high-pressure polyethylene

Luminescent and photochemical properties of polymer compositions based on the Eu(NO3)3(Phen)2 complex and complexes of antimony(III) halides with diphenylguanidine are investigated. It is found that high-pressure polyethylene (HPPE) containing europium(III) and antimony(III) complexes in combination exhibits efficient transfer of electronic excitation energy from antimony(III) levels to europium(III) levels and photosensitization of europium(III) luminescence. It is shown that the europium(III) and antimony(III) complexes increase the stability of HPPE to UV radiation.

Electronic Excitation Energy Transfer between Two Single Molecules Embedded in a Polymer Host

Unidirectional electronic excitation energy transfer from a photoexcited donor chromophore to a ground state acceptor chromophore - both linked by a rigid bridge - has been investigated by low temperature high-resolution single molecule spectroscopy. Our approach allows for accurately accessing static disorder in the donor and acceptor electronic transitions and to calculate the spectral overlap for each couple. By plotting the experimentally determined transfer rates against the spectral overlap, we can distinguish and quantify Förster- and non-Förster-type contributions to the energy transfer.

Photoinduced Electron Transfer and Excitation Energy Transfer in Directly Linked Zinc Porphyrin/Zinc Phthalocyanine Composite

Photoinduced electron transfer (ET) and excitation energy transfer (ENT) reactions in monomer and slipped-cofacial dimer systems of a directly linked Zn porphyrin (Por)-Zn phthalocyanine (Pc) heterodyad, ZnPc-ZnPor, were investigated by means of the picosecond and femtosecond transient absorption spectroscopies. In the dimer dyad system of two heterodyads connected through the coordination bond between two imidazolyl-substituted ZnPor bearing ZnPc, ZnPc-ZnPor(D), the rapid ENT from the ZnPor to ZnPc in the subpicosecond time region was followed by photoinduced charge separation (CS) and charge recombination (CR) with time constants of 47 and 510 ps, respectively. On the other hand in the monomer dyad system, no clear charge-separated state was observed although the CS with a time constant of 200 ps and CR with < or =70 ps were estimated. These results indicated that the dimer slipped-cofacial arrangement of pair porphyrins is advantageous for the effective production of the CS state. This advantage was discussed from the viewpoint of a decrease in the reorganization energy of the dimer relative to that of the monomer system. In addition, the electrochemical measurements indicated that the strong interaction between ZnPc and ZnPor moieties also contributed to the fast CS process despite the marginal driving force for the CS process. The dimer dyad of ZnPc-ZnPor provides full advantages in efficiencies of the light harvesting and the CS state production.

Enhancement of electronic excitation energy transfer in the colloidal crystals of colloidal silica suspensions doped with fluorescent dyes

The efficiency of electronic excitation energy transfer from photo-excited rhodamine 110 (Rh110, energy donor) to rhodamine B (RhB, energy acceptor) in an exhaustively deionized colloidal silica suspension has been studied. This colloidal suspension shows Bragg reflection due to the formation of colloidal crystals and the Bragg-peak wavelength is controllable by the volume fraction of the silica spheres. When the Bragg-peak wavelength matches with the fluorescence band of Rh110, a depletion was observed in the Rh110 fluorescence spectrum. This means the fluorescence of Rh110 is partially trapped due to the Bragg reflection inside the crystal lattice. In the coexistence of RhB, the enhancement of RhB fluorescence intensity was observed. These facts clearly indicate the trapped photon energy of Rh110 is efficiently transferred to RhB within the colloidal crystals. The quantitative measurements showed that the enhancement of the transfer efficiency is 20% (or slightly more) in the present experimental conditions.

Nonradiative energy transfer in carbocyanine dye compositions inside surfactant micelles

Utilizing forced concentration of carbocyanine dye molecules DiI and DiD within a surfactant micelle, we have detected nonradiative transfer of electronic excitation energy for low initial dye concentrations in the aqueous micellar solution. Luminescence and fluorescence anisotropy decay studies allowed us to establish that in the micelles, the hydrophilic head of the dye is in contact with the water while the C18H37 groups are located in the hydrocarbon core of the micelle. We show that due to the structural features of the DiD acceptor molecule, rotational diffusion of the acceptor in the micelle is more free than for the donor DiI, the motion of which is constrained in the micelle.

Transfer of Electronic Excitation Energy between Randomly Mixed Dye Molecules in the Channels of Zeolite L

Host-guest materials containing strongly fluorescent donor and acceptor molecules have been prepared. Fine-tuning of the donor to acceptor distance in this material allows beautiful visible and quantitative observation of electronic excitation energy transfer phenomena. Oxonine and pyronine have been used as guest molecules and zeolite L as host. The dyes have been inserted by ion exchange. Stationary state and time-resolved experiments have been carried out with zeolite crystals of 300 and 700 nm size in the dye concentration range of 10(-4) mol/L up to 0.042 mol/L. The fluorescence decay of the donor and the pumping of the acceptor via energy transfer, which can be well observed, became faster with increasing loading. The behavior of the system follows requirements expected for Förster energy transfer material.

Taking into account the conformational dynamics of macromolecules when analyzing luminescent probe signals

A mathematical model is proposed that takes into account the specific features of electronic excitation energy transfer between the molecular probes sorbed on a polymeric chain in a liquid solution. The kinetics of the process is described from the standpoint of the stochastic changes in macromolecular conformations. The results of numerical solution of the problem are described, as well as the analytical expressions obtained in the context of perturbation theory for a low transfer rate and/or fast conformational dynamics of the macrochain. A channel of nonlinear (with respect to excitation) deactivation resulting from binary annihilation of closely spaced excited centers is considered. Expressions for the efficient rate of mutual quenching and delayed annihilation fluorescence of the probe are obtained. The time dependences of characteristic luminescent signals and the parametric curves of relative fluorescence quantum yield are given.

Time-Resolved Measurements of Intramolecular Energy Transfer in Single Donor/Acceptor Dyads

We have investigated electronic excitation energy transfer in a specifically designed bichromophoric donor/acceptor dyad in which the donor (perylenediimide) and acceptor (terrylenediimide) are linked by a rigid heptaphenyl-spacer. Because of the choice of the bridge, which defines the distance and orientation of the two chromophores, donor as well as acceptor emission is observed. The significantly smaller photostability of the donor allows for time-resolved measurements of the acceptor emission at the single-molecule level with and without energy transfer from the donor. By analyzing the differences of the rise/decay profiles for both pathways, we could determine time constants of energy transfer with high accuracy for single dyads. The results show that the experimental approach presented here works even for situations in which the energy transfer times are smaller than the temporal resolution of the detection system.

Electronic Excitation Energy Transfer between Different Types of Dye Molecules in a Porous Glass Matrix

The processes of electronic excitation energy transfer (EEET) between different types of dye molecules inserted into the matrix of a porous glass have been investigated. An extreme character of the dependence of the EEET efficiency on the size of pores has been revealed. The dependence of the fractal dimensionality of the distribution of dye molecules on the sizes of the pores has been determined.

Intermolecular Processes in Excited Electronic States in the Gas Phase (Review)

A brief review of works on the temperature dependences of the rate constants kq of the intermolecular processes proceeding in the excited electronic states in the gas phase is given. The dependences kq(T) for such biomolecular processes as intermolecular vibrational energy transfer in the triplet state vibrational quasi-continuum, triplet-triplet electron excitation energy transfer, and intermolecular photoinduced electron transfer have been compared. The experimental data have shown that in the gas phase for all analyzed intermolecular processes both an increase and a decrease in kq with increasing temperature (T) is observed, which is not associated with the specific intermolecular interactions leading to the formation of long-lived components. The change in the type of temperature dependence is due to the change in the mechanisms of the radiationless transitions with increasing density of vibrational levels in the final electronic state. The applicability of the known models based on the theory of radiationless transitions for predicting the temperature dependences kq(T) is discussed.