Loss Of Excitation Energy Research Articles

A competitive trivalent-europium-activated phosphor: Achieving highly efficient red light emission in a sodium-rich garnet host

The reaction temperature is key factor for light-emitting phosphors synthesized by solid state method because it directly determines the crystallinity and further affects the luminescence property of the phosphors. While high temperature certainly benefits to the solid diffusion in reaction, it would waste enormous energy during long time heating. Herein, a novel Eu3+-activated and highly efficient red phosphor, NaGd2Ga3Ge2O12:Eu3+, is reported. By the reconstruction of the traditional Y3Al5O12 garnet host into the sodium-rich NaGd2Ga3Ge2O12 one, huge decrease of the synthesis temperature is successfully achieved. More importantly, such decrease of the synthesis temperature does not dissatisfy the luminescence property of the NaGd2Ga3Ge2O12:Eu3+ phosphors. Instead, the Eu3+ in the NaGd2Ga3Ge2O12 exhibits extremely high quantum yield up to 96.78% upon 394 nm excitation, showing great competitiveness among other iso-structral garnet hosts. This work indicates that the introduction of sodium in the eight-coordinated rare earth site of the garnet host can not only reduce the energy consumption during the stage of phosphor synthesis but also avoid the loss of excitation energy during the light converting stage of the Eu3+ to a large extent. By fabricating the as-synthesized red phosphor into a near-UV chip together with commercial green and blue phosphors, quality white light-emitting diodes with satisfactory color rendering index (as high as 90) and correlated color temperature (as low as 3986 K) can be easily obtained.

Effect of CF4 concentration on the discharge dynamics and reactive species distribution of atmospheric nanosecond pulsed He plasma jet

Based on a two dimensional self-consistent model, the effect of different CF4 concentrations on the discharge dynamics characteristics, F-containing species distribution and the distribution of the axial and radial ionization rates of He atmospheric pressure plasma jet (APPJ) has been investigated. In addition, the accuracy of the simulation is verified by comparing the experimental results. The ionization rate of He APPJ enhances with the increase of CF4 from 0% to 2% because of the Penning ionization of CF4 with metastable He while decreases in the case of 3% CF4 owing to the electronegativity and the electron excitation energy loss of CF4. The increase of CF4 concentration and the decrease of the electron density leads to the decrease of CF4 + density at 3% CF4. CF3 + density is determined by the Penning ionization rate of CF4 and the reaction rate of He+ + CF4 → CF3 + + F + He. As CF4 concentration increases from 2% to 3%, the decrease of metastable He and He+ concentration results in the significant decrease of CF3 + density. The densities of CF3 − and F− keep increasing from 1% to 3% CF4 due to the effect of the electron attachment reaction of CF4. With the addition of CF4, the ionization reaction of CF4 is gradually playing the major role in the streamer head, the Penning ionization of CF4 is the main source of electron ionization inside the jet and dominates in the formation of ionization wave tail. As the concentration of CF4 increases from 0% to 2%, the electron impact ionization rates of He and CF4 near the axis increase, resulting in the more uniform radial ionization rate distribution of He + 2% CF4 APPJ.

Bessel beam induced deep-penetrating bioimaging and self-monitored heating using Nd/Yb heavily doped nanocrystals

Biological probes facilitate optical imaging and disease diagnosis and treatment. However, the large absorption and scattering loss in the tissue highly limit the depth during the application. In the present research, an NIR-I bioprobing system, which utilizes the Bessel beam to excite heavily doping nanocrystals, has been developed for deep tissue applications. On the one hand, the capillary mode selection method generates the Bessel excitation beam, lowering the excitation energy loss. On the other hand, a strong energy harvest of NaYbF4:90%Nd nanocrystals enables effective fluorescence and heat generation upon 800 nm excitation. By considering the advantages of Bessel excitation and heavily doping nanocrystals, up to ∼3 cm penetration depth for ex vivo bioimaging and the potential self-monitored photothermal treatment are demonstrated. The resultant bioprobing system allows deep tissue imaging and photothermal therapy, showcasing broad prospects in medical research and clinical applications.

Numerical study of the influence of O2 admixture on the propagation and F-containing species distribution of He/CF4 atmospheric pressure plasma jet

O2 impurity in the working gas of an He/CF4 atmospheric pressure plasma jet (APPJ) can affect the discharge dynamics and the density of reactive species. Therefore, a two-dimensional (2D) fluid model is built in order to explore the influence of an O2 admixture on the propagation and F-containing species distribution of He/CF4 APPJ. The addition of 0.1% O2 accelerates the ionization rates of APPJ due to the increase of Penning ionization reactions of O2, resulting in the increases of axial speed and F-containing reactive species (CF4+, CF3+, CF2+, CF+, F+, CF3, F, CF3−) when APPJ approaches the dielectric surface. The addition of O2 has the inhibitory effect on the rise of some F-containing reactive species (CF3+ and F). As O2 concentration increases to 2%, the concentration of F-containing reactive species shows a downward trend due to the increase of excitation energy loss and an electron attachment reaction of O2. Different from the axial speed, the radial speed decreases continuously with the increase of O2 because of the high O2 concentration on the dielectric surface when APPJ propagates radially. This also results in a reduced distribution of reactive species fluxes. The excitation energy loss and electronegativity of O2 and CF4 in the case of He + 0.5% CF4 + 0.5% O2 have been presented in this paper. It is discovered that excitation energy loss of O2 is stronger than that of CF4, but the electronegativity of CF4 is stronger than that of O2.

Remarkably Enhanced Red Upconversion Emission in β-NaLuF4:Er,Tm Microcrystals via Ion Exchange.

Internal OH- defects always cause significant depletion of excitation energy for low upconversion efficiency; however, preventing the incorporation of OH- into the crystal lattice is very difficult during the synthesis of upconversion crystals. In this work, red upconversion emission is dramatically enhanced in Er3+-sensitized hexagonal NaLuF4 (β-NaLuF4) microcrystals through a collaborative effect of ion exchange and Tm3+ doping. The ion exchange can not only maintain the morphology very well but also strongly reduce the internal OH- defects, which can enhance the upconversion luminescence due to improved excitation energy harvesting and red to green (R/G) ratio due to intense cross-relaxation. Doping of Tm3+ as an energy trapping center not only regulates the red emission output but also reduces the excitation energy loss. β-NaLuF4:Er,Tm microcrystals after ion exchange exhibit stronger red upconversion emission compared with β-NaYF4:Er,Tm and β-NaGdF4:Er,Tm counterparts. Moreover, fluorescent labeling of the fingerprint pattern printed from β-NaLuF4:Er,Tm microcrystals with stable and intense red fluorescence has been demonstrated under 980 nm excitation.

Influence of different O2/H2O ratios on He atmospheric pressure plasma jet impinging on a dielectric surface

A two-dimensional (2D) axisymmetric fluid model is built to investigate the effect of different O2 and H2O admixture on the plasma dynamics and the distribution of reactive species in He atmospheric pressure plasma jet (APPJ). The increase of O2:H2O ratio slows down both the intensity and the propagation speed of the ionization wave. Due to the decrease of both H2O ionization rate and H2O Penning ionization as well as the stronger electronegativity of O2, the increase of O2:H2O ratio results in a significant reduction of electron density in the APPJ, which restricts the occurrence of electron collision ionization reactions and inhibits the propagation of plasma. The excitation energy loss of O2 is not the reason for the weakening of the plasma ionization wave. The densities of O2 +, O− and O2 − increase with the rise of O2 admixture while H2O+ decreases due to the decrease of electron density and H2O concentration. OH− density is affected by both the increase of O− and the decrease of H2O so it shows a peak in the case of O2:H2O = 7:3. O is mainly produced by the excitation reactions and the electron recombination reaction (e + O2 + → 2O), which is directly related to the O2 concentration. OH is mainly produced by e + H2O → e + H + OH so the OH density decreases due to the decrease of electron density and H2O concentration with the increase of O2:H2O ratio. On the dielectric surface, when the propagation of the streamer extinguishes, O flux shows an upward trend while the OH flux decreases, and the propagation distance of O and OH decreases with the increase of O2:H2O ratio.

Luminescence studies on varied concentration of Eu3+ doped SrO-ZnO-PbO-P2O5 glasses for photonic applications

Optical and structural properties of concentration variation of Eu3+ doped SrO-ZnO-PbO-P2O5 glasses have been reported. The structural properties are analysed from XRD and FTIR spectra. The oscillator strength and Judd-Ofelt intensity parameters are determined from the absorption. The strongest emission peak is obtained at 612 nm (red) for 5D0→7F2 transition. The luminescence emission waning is observed for more than 2 mol% Eu3+ concentration due to loss of excitation energy by cross-relaxation and migration process. Different radiative parameters are calculated using the Judd-Ofelt parameters. Effect of concentration quenching on the radiative parameters has been highlighted. The decay profiles are fitted with single-exponential curves. The CIE chromaticity coordinates are located in the reddish-orange region. The present EuSrZnLP glasses could be potentially used for LED and photonic devices.

Effect of CF4 ratio on the interaction of atmospheric nanosecond pulsed He plasma jet with a dielectric material

In this paper, a two dimensional (2D) axisymmetric fluid model is built to study the effect of the ratio of CF4 admixture on the plasma dynamics and F-containing species concentration in He atmospheric pressure plasma jet. The steady mole fraction distribution of He and CF4 is first studied, which presents that the mole fractions of CF4 show peaks at 5 mm from the symmetry axis on the dielectric surface due to the dual influences of the boundary layer effect and air mixing. The CF4 admixture enhances the propagation speed of ionization wave, and the axial velocity reaches the peak value in the case of He + 1.5% CF4. The conversion from the ring-shaped plasma–surface interaction to a solid-disk one results from the addition of CF4. The Penning ionization of CF4 accelerates the plasma jet propagation within 1.5% CF4. However, the excitation energy loss and electron attachment caused by the addition of CF4 also quench the propagation of plasma jet, which become obvious in the case of 2% CF4. F-containing groups (CF4+, CF3+, CF3−, F−, CF3, and F), mainly produced by the Penning ionization reaction, electron attachment reaction, and He+ + CF4 → He + CF3+ + F, also show peaks for He + 1.5% CF4. On the dielectric surface, as the radial distance increases, the ratio of F-containing neutral species (CF3 and F) to O atom at 200 ns decreases due to the increase of O atom concentration and then increases at the streamer head because the surface flux of CF3 reaches the maximum value. The maximum surface flux radial distribution distance for ratio of F-containing species to O atom, CF3 and F appear in the case of 1.5% CF4.

The distribution of OH radicals in a pulsed DC He + H2O plasma jet with the presence of a dielectric material

The distribution and density of OH radicals in a pulsed DC He + H2O plasma jet are studied by a two-dimensional (2D) plasma jet model. This article shows the effect of adding H2O to the pure He plasma jet on the OH density distribution and the changes of the OH density under different H2O contents. The process of streamer propagation toward the dielectric surface and development of the streamer on the dielectric surface are discussed in this article. The total OH radicals are generated from two parts in a He + H2O atmospheric pressure plasma jet (APPJ). The first part is produced with the water in ambient air outside the tube, and the other part is generated with the water in the helium flow. At the time when the streamer approaches the dielectric surface, it is found that electron-impact dissociation of H2O and electron neutralization of H2O+ are the main reactions to generate OH species and three-body combination of OH and OH with He is the main reaction to consume OH species. The OH density shows a donut shape in a pure He APPJ, while the density distribution of OH radicals under the nozzle gradually becomes uniform with the increase in the H2O content added to the helium flow, but the maximum value is at the both ends of the streamer outside the tube. The electron density initially increases with the increase in the proportion of H2O added to the He plasma jet and then gradually decreases with the H2O ratio greater than 0.5%. The enhancement of Penning ionization with the increasing H2O content is the main reason for the increase in electron density, while the increasing consumption of electrons by the excitation energy loss causes the decrease in the electron density with the H2O ratio more than 0.5%. The increase in the H2O content will bring both positive and negative effects. On the one hand, the increase in the H2O content added to the He gas flow will promote the generation of OH species. On the other hand, the decrease in the electron density caused by the increasing excitation energy loss slows the rapid growth of the reaction rates of the two main reactions related to the production of OH species. Eventually, OH density reaches saturation with the H2O ratio at 1.5% under the combined effect mentioned above.

The effect of Mg introduction on structural and luminescence properties of Zn2SiO4:Mn phosphor

The effect of magnesium on the structural and luminescent properties of Zn2SiO4:Mn phosphor has been considered on the example of the Zn1.92-2xMn2xMg0.08SiO4 solid solutions. It is demonstrated that the introduction of magnesium ions into the cationic sublattice of Zn2-2xMn2xSiO4 increases the isomorphic capacity of the willemite structure from x = 0.13 to x = 0.20 and stabilizes manganese in a doubly charged state. It is shown that at x ≤ 0.1 doping with magnesium increases the luminescence intensity of crystal phosphor. A crystal-chemical mechanism of the influence of co-doping on the luminescence intensity has been proposed: the addition of magnesium reduces the local distortion regions of the crystal structure around Mn2+ activator-ion and reduces the excitation energy losses on these distortions.

Efficient Long-Range, Directional Energy Transfer through DNA-Templated Dye Aggregates.

The benzothiazole cyanine dye K21 forms dye aggregates on double-stranded DNA (dsDNA) templates. These aggregates exhibit a red-shifted absorption band, enhanced fluorescence emission, and an increased fluorescence lifetime, all indicating strong excitonic coupling among the dye molecules. K21 aggregate formation on dsDNA is only weakly sequence dependent, providing a flexible approach that is adaptable to many different DNA nanostructures. Donor (D)-bridge (B)-acceptor (A) complexes consisting of Alexa Fluor 350 as the donor, a 30 bp (9.7 nm) DNA templated K21 aggregate as the bridge, and Alexa Fluor 555 as the acceptor show an overall donor to acceptor energy transfer efficiency of ∼60%, with the loss of excitation energy being almost exclusively at the donor-bridge junction (63%). There was almost no excitation energy loss due to transfer through the aggregate bridge, and the transfer efficiency from the aggregate to the acceptor was about 96%. By comparing the energy transfer in templated aggregates at several lengths up to 32 nm, the loss of energy per nanometer through the K21 aggregate bridge was determined to be <1%, suggesting that it should be possible to construct structures that use much longer energy transfer "wires" for light-harvesting applications in photonic systems.

Effect of oxygen as additive on an atmospheric nanosecond pulsed helium plasma jet impinging on a dielectric surface

Based on a 2D axisymmetric plasma fluid model, the effect of the levels of O2 admixtures on the plasma dynamics of an atmospheric pressure He plasma jet incident on a dielectric surface situated normal to the jet axis has been studied. The introduction of O2 admixture in the feedstock gas changes the shape of the discharge ionization rate that approaches the target surface from a ring to a solid disk. As the streamer extinguishes radial propagation along the dielectric surface, comparatively larger plasma-surface contact areas were obtained for O2 additions to the He plasma of less than 0.5% relative to that for the discharge in pure He, while in the case of 2% O2, the radial propagation distance dropped off significantly. The propagation of an ionization wave peaked in the range 0.2%–1% for the O2 admixture. The enhanced ionization reactions are considered to predominate for small concentrations of O2 as additive, and the negative role played by the excitation energy loss and the attachment of electrons to O2 is more important with the addition of 2% O2. There was a remarkable incremental gain in the flux intensity of O on the surface center, while the flux of N was mainly concentrated on the streamer head. The magnitude of the O flux on the surface showed a peak at the 0.5% O2 admixture level, and the flux of O3 on the surface was directly proportional to the O2 concentration.

Conformational Impact on Energy Storage Efficiency of Subphthalocyanine-Fullerene Hybrids.

Hybrid molecules involving subphthalocyanine and Buckminsterfullerene derivatives are interesting candidates as heavy metal free triplet sensitizers. Subphthalocyanine efficiently absorbs visible photons and transfer the singlet excited state energy to the Buckminsterfullerene where intersystem crossing produces triplet states in high yield. Thus, far the efficiency of the triplet-generating photophysics in these systems has been hampered by back energy transfer to the subphthalocyanine triplet state resulting in loss of excitation energy. Herein an efficient strategy is realized to avoid loss of triplet energy by back energy transfer. A hybrid molecule based on subphthalocyanine and Buckminsterfullerene is presented in which dispersion-induced π-π interactions result in a molecular geometry where highly efficient through-space singlet excited state energy transfer takes place in one direction, whereas energy flow in the opposite direction via the triplet manifold is blocked by lack of orbital overlap. The approach opens for a new class of heavy-metal-free triplet sensitizers of particular relevance to the fields of photodynamic therapy and noncoherent photon upconversion.

Theoretical rationalization for reduced charge recombination in bulky carbazole-based sensitizers in solar cells.

The search for greater efficiency in organic dye-sensitized solar cells (DSCs) and in their perovskite cousins is greatly aided by a more complete understanding of the spectral and morphological properties of the photoactive layer. This investigation resolves a discrepancy in the observed photoconversion efficiency (PCE) of two closely related DSCs based on carbazole-containing D-π-A organic sensitizers. Detailed theoretical characterization of the absorption spectra, dye adsorption on TiO2 , and electronic couplings for charge separation and recombination permit a systematic determination of the origin of the difference in PCE. Although the two dyes produce similar spectral features, ground- and excited-state density functional theory (DFT) simulations reveal that the dye with the bulkier donor group adsorbs more strongly to TiO2 , experiences limited π-π aggregation, and is more resistant to loss of excitation energy via charge recombination on the dye. The effects of conformational flexibility on absorption spectra and on the electronic coupling between the bright exciton and charge-transfer states are revealed to be substantial and are characterized through density-functional tight-binding (DFTB) molecular dynamics sampling. These simulations offer a mechanistic explanation for the superior open-circuit voltage and short-circuit current of the bulky-donor dye sensitizer and provide theoretical justification of an important design feature for the pursuit of greater photocurrent efficiency in DSCs. © 2017 Wiley Periodicals, Inc.

Allocation of Absorbed Light Energy in Photosystem II in NPQ Mutants of Arabidopsis.

To analyze changes of energy allocation in PSII at non-steady state photosynthesis, the induction and relaxation of non-photochemical quenching of Chl fluorescence was re-evaluated with the use of Arabidopsis thaliana mutants in which the ability to induce non-photochemical quenching was either enhanced (npq2) or suppressed (npq1 and npq4). When dark-treated leaves of the wild type (WT) were illuminated, very high Φf,D, which represents the loss of excitation energy via non-regulated dissipation, at the beginning of light illumination was gradually decreased to the steady-state level. In contrast, ΦNPQ, representing regulated energy dissipation in PSII, was relatively constant after a significant change in the first 10 min. In npq1 and npq4 mutants, lower ΦNPQ resulted in much higher Φf,D than in the WT. Comparison of npq1 and npq4 mutants showed a kinetic difference of two types of non-photochemical quenching. Because non-photochemical quenching calculated as NPQ = Fm - Fm')/Fm' was determined by the interplay between ΦNPQ and Φf,D, NPQ and ΦNPQ, both of which represent regulatory heat dissipation, were not linearly correlated. We showed that the kinetics of NPQ formation in the light and relaxation in the dark were affected by drastic changes in Φf,D We discuss the nature of a high level of Φf,D at the dark-light transition. We also point out an unavoidable problem of applying the energy allocation model when the Fv/Fm value changes during a photoinhibiotry illumination.

Steady-state and time-resolved luminescence of Ru(II) polypyridine complexes attached to Ag nanoparticles: Effect of chemisorption in comparison with electrostatic bonding

Steady state and nanosecond time resolved luminescence (namely, 3MLCT phosphorescence) of [Ru(bpy)3]2+ and of [Ru(bpy)2(dcbpy)]2+/bpy=2,2′-bipyridine; dcbpy=2,2′-bipyridyl-4,4′-dicarboxylic acid/attached to Ag NPs (the former by the electrostatic bonding, the latter by chemisorption) in non-aggregated Ag NP hydrosol systems has been investigated, and compared to the luminescence characteristics of the complexes in aqueous solutions. The intensity decrease of the 452nm (and/or 455nm, respectively) main band and elimination of the short wavelength shoulders in the excitation spectra and the intensity decrease of the emission spectra observed for both complexes upon their attachment to Ag NPs is attributed to the overlap of the excitation spectra with the surface plasmon extinction (SPE) of Ag NPs. The overlap leads to a loss of excitation energy by SPE as well as to a decrease of the 1MLCT to 3MLCT intersystem crossing efficiency. The time-resolved luminescence study shows that the 3MLCT phosphorescence lifetimes of both complexes are markedly (by 3 and 4 orders of magnitude, respectively) shortened upon their attachment to Ag NPs. Nevertheless, the 3MLCT lifetime of the chemisorbed [Ru(bpy)2(dcbpy)]2+ is by at least one order of magnitude shorter than that of the electrostatically bonded [Ru(bpy)3]2+, which indicates, that the phosphorescence lifetimes of these luminophores are strongly affected by the type of Ag NP surface–luminophore bonding.

Light Harvesting and Blue-Green Light Induced Non-Photochemical Quenching in Two Different C-Phycocyanin Mutants of Synechocystis PCC 6803

Cyanobacteria are oxygen-evolving photosynthetic organisms that harvest sunlight and convert excitation energy into chemical energy. Most of the light is absorbed by large light harvesting complexes called phycobilisomes (PBs). In high-light conditions, cyanobacteria switch on a photoprotective mechanism called non-photochemical quenching (NPQ): During this process, absorption of blue-green light transforms the inactive orange form of the orange carotenoid protein OCP (OCP(o)) into the red active form OCP(r) that subsequently binds to the PB, resulting in a substantial loss of excitation energy and corresponding decrease of the fluorescence. In wild-type cells, the quenching site is a bilin chomophore that fluoresces at 660 nm and which is called APC(Q)(660). In the present work, we studied NPQ in two different types of mutant cells (CB and CK) that possess significantly truncated PBs, using spectrally resolved picosecond fluorescence spectroscopy. The results are in very good agreement with earlier in vitro experiments on quenched and unquenched PBs, although the fraction of quenched PBs is far lower in vivo. It is also lower than the fraction of PBs that is quenched in wild-type cells, but the site, rate, and location of quenching appear to be very similar.

Critical Shell Thickness of Core/Shell Upconversion Luminescence Nanoplatform for FRET Application

Almost all the luminescence upconversion nanoparticles used for Forster resonant energy transfer (FRET) applications are bare cores based on the consideration that the energy transfer efficiency is optimized because the distance between energy donors and acceptors is minimized. On the other hand, it is well proved that core/shell structure is efficient in minimizing the nonradiative loss of excitation energy of the luminescence donors. In this work we use core/shell upconversion NaYF4:Yb3+,Er3+@NaYF4 nanoparticles and rose bengal photosensitizer to construct a FRET conjugate. From the photophysics and singlet oxygen generation we have determined that the core/shell structured nanoparticles are better than bare cores for FRET applications. More importantly, we have found that there exists a critical shell thickness for the best FRET performance. In the model we have established, the critical shell thickness is a trade-off between the opposing optimal conditions for upconversion and FRET efficiency. This wo...

Optical properties of aluminophosphate glasses containing silver, tin, and dysprosium

The spectroscopic properties of a Dy3+-doped aluminophosphate glass containing silver and tin were reported. Different oxidation and aggregation states of silver were obtained by varying silver concentration and glass thermal history. The addition of silver and tin at the lowest concentration studied results in Dy3+ ions emission under nonresonant UV excitation in connection with the appearance of an excitation band around 270 nm, which is associated to isolated Ag+ ions and twofold-coordinated Sn centers. The increase in silver and tin concentration leads to a broadening of aforementioned band and to the presence of charged silver dimers as evidenced by the appearance of an excitation band around 330 nm. The data indicated that light absorption might take place at ionic silver species and twofold-coordinated Sn centers, followed by energy transfer to Dy3+ ions. After heat treatment, ionic silver species were reduced to atomic Ag by tin with the subsequent formation of Ag nanoparticles (NPs) inside the dielectric host. A quenching effect in Dy3+ ions luminescence was shown with the presence of the Ag NPs, most notably for excitation of 6H15/2 → 4F9/2, 4I15/2, 4G11/2 transitions, which were in resonance with the dipole absorption mode of the particles. The silver NPs were believed to provide radiationless pathways for excitation energy loss in Dy3+ ions.

Development of bioinspired artificial photosynthetic systems

The specific objective of this review is to describe recent development of bioinspired artificial photosynthetic systems and their applications. First, multi-step electron-transfer systems composed of electron donor-acceptor ensembles are presented, mimicking functions of the photosynthetic reaction center. However, a significant amount of energy is lost during the multi-step electron-transfer processes. Then, as an alternative to conventional charge-separation functional molecular models based on multi-step long-range electron transfer within redox cascades, simple electron donor-acceptor dyads linked by covalent or non-covalent bonding have been developed to attain a long-lived and high-energy charge-separated state without significant loss of excitation energy. Such simple molecular dyads, capable of fast charge separation but extremely slow charge recombination, have significant advantages with regard to synthetic feasibility, providing a variety of applications including construction of organic solar cells and development of efficient photocatalytic systems for the solar energy conversion.