Forster Energy Transfer Research Articles

Development of InP-based polymer nanocomposites by wet route for optoelectronic devices

In this work, the effect of surface passivation of InP quantum dots (QDs) synthesized by the unconventional tri-n-octyl phosphine (TOP) route, on the structural and optoelectronic properties of their respective polymer nanocomposites, has been demonstrated by dispersing untreated and nascent hydrogen-treated InP QDs in P3HT polymer matrix, respectively. The surface passivation of InP QDs imparts photostability to its corresponding polymer–InP composite as a consequence of a better hydrogen passivation of defects acting as non-radiative recombination centres and can be achieved by employing a simple post-synthesis chemical treatment which is fast, reliable and reproducible. Here, with the distinctive usage of TOP both as a capping ligand and a source of phosphorus in conjunction with a novel chemical treatment, the quantum yield of InP QDs can be significantly enhanced and promotes charge transfer across donor (polymer)–acceptor (InP QDs) interface as supported by photoluminescence (PL) quenching studies as well. The increment in PL intensity upon incorporation of untreated InP QDs into the P3HT polymer matrix can be attributed to the dominance of Forster energy transfer between host P3HT polymer (donor) and guest InP nanocrystals (acceptors) in polymer/InP (untreated) composites. The mechanisms of energy and charge transfer in polymer–InP (u/t) based composites is depicted pictorally. The importance of these two different processes observed in polymer/InP (untreated) and polymer/InP (treated) composites is that it makes them useful for organic optoelectronic, i.e. electroluminescent and photovoltaic devices, respectively.

Fluorescence spectroscopic studies on the interaction between a new bismuth(III) Schiff base complex and bovine serum albumin

In this work, the binding interaction between a new bismuth(III) Schiff base complex |[Bi(valen)]Cl·2H2O}[H2valen=N,N'-bis(2-hydroxy-3-methoxyphenylmethylidene)-2,6-pyridinediamine, C21H19N3O4] and bovine serum albumin(BSA) was studied via fluorescence quenching method. The static quenching constant KLB and some thermodynamic parameters(e.g., ΔGθ, ΔHθ and ΔSθ) of the interaction were estimated. In particular, the binding site between the complex and BSA was explored by molecular docking. On the basis of the mechanism of Forster energy transfer, the binding distance between the bismuth(III) Schiff base complex and BSA(Trp.213) as well as the transfer efficiency was obtained. Furthermore, the effect of the bismuth(III) Schiff base complex on the con-formation of BSA was investigated using synchronous fluorescence spectroscopy.

Morphology-dependent exciton diffusion length in PPE-PPVs thin films as revealed by a Forster mechanism based-study

The effect of thickness and alkoxy side chains on the optical properties of poly(p-phenyleneethynylene)-alt-poly(p-phenylenevinylene)s (PPE–PPVs) have been investigated in parallel fashion. A Forster energy transfer mechanism has been invoked in order to infer the exciton diffusion length (LD). The latter parameter has been determined for six differently alkoxy-substituted PPE-PPVs for different thicknesses. The dependence of LD upon the donor-acceptor (D-A) distance (d) has been assessed as well. The results reveal an increase of LD up to 25nm, with the increase of the sample thickness and side chain length.

Enhancement of Förster energy transfer from thermally activated delayed fluorophores layer to ultrathin phosphor layer for high color stability in non-doped hybrid white organic light-emitting devices**Project supported by the National Natural Science Foundation of China (Grant Nos. 61675041 and 61605253), the Foundation for Innovation Research Groups of the National Natural Science Foundation of China (Grant No. 61421002), and the Science

Fluorescence/phosphorescence hybrid white organic light-emitting devices (WOLEDs) based on double emitting layers (EMLs) with high color stability are fabricated. The simplified EMLs consist of a non-doped blue thermally activated delayed fluorescence (TADF) layer using 9,9-dimethyl-9,10-dihydroacridine-diphenylsulfone (DMAC-DPS) and an ultrathin non-doped yellow phosphorescence layer employing bis[2-(4-tertbutylphenyl)benzothiazolato-N, C2’] iridium (acetylacetonate) ((tbt)2Ir(acac)). Two kinds of materials of 4,7-diphenyl-1,10-phenanthroline (Bphen) and 1,3,5-tris(2-N-phenylbenzimidazolyl) benzene (TPBi) are selected as the electron transporting layer (ETL), and the thickness of yellow EML is adjusted to optimize device performance. The device based on a 0.3-nm-thick yellow EML and Bphen exhibits high color stability with a slight Commission International de l’Eclairage (CIE) coordinates variation of (0.017, 0.009) at a luminance ranging from 52 cd/m2 to 6998 cd/m2. The TPBi-based device yields a high efficiency with a maximum external quantum efficiency (EQE), current efficiency, and power efficiency of 10%, 21.1 cd/A, and 21.3 lm/W, respectively. The ultrathin yellow EML suppresses hole trapping and short-radius Dexter energy transfer, so that Förster energy transfer (FRET) from DMAC-DPS to (tbt)2Ir(acac) is dominant, which is beneficial to keep the color stable. The employment of TPBi with higher triplet excited state effectively alleviates the triplet exciton quenching by ETL to improve device efficiency.

Systematic study of the hybrid plasmonic-photonic band structure underlying lasing action of diffractive plasmon particle lattices

We study lasing in distributed feedback lasers made from square lattices of silver particles in a dye-doped waveguide. We present a systematic analysis and experimental study of the band structure underlying the lasing process as a function of the detuning between the particle plasmon resonance and the lattice Bragg diffraction condition. To this end, as gain medium we use either a polymer doped with Rh6G only, or polymer doped with a pair of dyes (Rh6G and Rh700) that act as a F\orster energy transfer (FRET) pair. This allows for gain, respectively, at 590 or 700 nm when pumped at 532 nm, compatible with the achievable size tunability of silver particles embedded in the polymer. By polarization-resolved spectroscopic Fourier microscopy, we are able to observe the plasmonic/photonic band structure of the array, unraveling both the stop gap width, as well as the loss properties of the four involved bands at fixed lattice Bragg diffraction condition and as a function of detuning of the plasmon resonance. To explain the measurements we derive an analytical model that sheds insights on the lasing process in plasmonic lattices, highlighting the interaction between two competing resonant processes, one localized at the particle level around the plasmon resonance, and one distributed across the lattice. Both are shown to contribute to the lasing threshold and the overall emission properties of the array.

How to Open a Nucleosome

DNA accessibility in the cell nucleus depends on its packaging. The stability of the basic compaction unit, the nucleosome, is regulated through the interactions between DNA and histones. Natural sequence variation along the DNA strongly modulates nucleosome stability. Histone variations, mutations and posttranslational modifications alter intra- and internucleosomal interactions. We are investigating interactions which hold nucleosomes together by measuring distances in reconstituted samples using single molecule Forster energy transfer.

Fabrication and Characterization of PCBM: P3HT-based Thin-film Organic Solar Cells with Zinc Phthalocyanine and 1,8-Diiodooctane

[6,6]-phenyl C61-butyric acid methyl ester (PCBM) and poly(3-hexylthiophene) (P3HT) bulk heterojunction solar cells added with zinc-tetra-tertiary-butyl-phthalocyanine (ZnPc) and 1,8-diiodooctane (DIO) were fabricated and characterized. Incident photon-to-current conversion efficiencies in the range of 400-650 nm were increased by the ZnPc addition, and the absorption range of ZnPc overlapped with the photoluminescence range of P3HT. Photovoltaic properties of the solar cells with an inverted structure were improved by the ZnPc and DIO addition. Microstructures of the thin films were analyzed by X-ray diffraction. The improvement would be due to the Forster energy transfer mechanism the direct charge transfer from ZnPc to PCBM, and the phase separation of PCBM and P3HT by the DIO addition would also contribute the improvement.

DNA tetrahedral scaffolds-based platform for the construction of electrochemiluminescence biosensor

Proximal metallic nanoparticles (NPs) could quench the electrochemiluminescence (ECL) emission of semiconductor quantum dots (QDs) due to Förster energy transfer (FRET), but at a certain distance, the coupling of light-emission with surface plasmon resonance (SPR) result in enhanced ECL. Thus, the modification strategies and distances control between QDs and metallic NPs are critical for the ECL intensity of QDs. In this strategy, a SPR enhanced ECL sensor based on DNA tetrahedral scaffolds modified platform was reported for the detection of telomerase activity. Due to the rigid three-dimensional structure, DNA tetrahedral scaffolds grafting on the electrode surface could accurately modulate the distance between CdS QDs and luminol labelled gold nanoparticles (L-Au NPs), meanwhile provide an enhanced spatial dimension and accessibility for the assembly of multiple L-Au NPs. The ECL intensities of both CdS QDs (−1.25V vs. SCE) and luminol (+0.33V vs. SCE) gradually increased along with the formation of multiple L-Au NPs at the vertex of DNA tetrahedral scaffolds induced by telomerase, bringing in a dual-potential ECL analysis. The proposed method showed high sensitivity for the identification of telomerase and was successfully applied for the differentiation of cancer cells from normal cells. This work suggests that DNA tetrahedral scaffolds could serve as an excellent choice for the construction of SPR-ECL system.

Comment on the article “Investigation of Fluorescence Resonance Energy Transfer between Fluorescein and Rhodamine 6G”

In this comment we, report the missing of relevant literature regarding Forster energy transfer (FRET) between fluorescein and rhodamine 6G in a recent paper (Spectrochim. Acta A, 149 (2015) 143–149). In this paper, the authors claim that “a new FRET pair” has been identified, which is absolutely incorrect. In fact, studies on FRET in this dye pair under different conditions have been done earlier. Further, the estimated critical transfer distance may have uncertainty because of donor quantum yield which is not clarified in the paper.

High-efficiency blue fluorescent devices with simple structure

Thermally activated delayed fluorescence (TADF) materials can harvest both singlet and triplet excitons for light emission without the utilization of heavy metal elements such as iridium and platinum and become the third generation organic optoelectronic materials after fluorescent and phosphorescent materials. TADF material bis[4-(9,9-dimethyl-9, 10-dihydroacridine)phenyl]sulfone (DMAC-DPS) shows high photoluminescence quantum yield in solid films, rendering it as a suitable emitter for non-doped organic light emitting diodes. We optimize the hole transport layer, electron transport layer and emission layer thickness for the none-doped DMAC-DPS devices to pursuit high luminance efficiency. We compare the properties of the devices using indium tin oxide (ITO)/MoO3 hole injection contact with either a 40 nm mCP or 30 nm NPB/10 nm mCP hole transport layer and the results indicate (1) the former devices show larger current than the latter devices for there is a large energy barrier of ca. 0.7 eV for hole injection from NPB into mCP in the latter devices; (2) Both of the devices show similar luminance efficiency and the underlying reason is that the small modulation of the dominant hole current slightly affects the device efficiency. In order to investigate the influence of different electron transport layers on the device performance, we have prepared the devices with either 10 nm DPEPO/40 nm TmPyPB, 50 nm TmPyPB or 50 nm SPPO13 electron transport layer and find out (1) the devices with DPEPO electron transport layer show the highest EQE of 16.2% due to the fact that DPEPO with triplet energy of 3.3 eV can confine excitons inside the emisson layer effectively; (2) The devices with SPPO13 possess the highest current density at certain voltage among the devices and the maximum external quantum efficiency and power efficiency for the SPPO13 based devices are 14.3% and 26.8 lm W - 1, which are higher than 13.8% and 22.2 lm W - 1 for the TmPyPB based devices. The possible reason is that highly polarized phosphorus oxygen groups of SPPO13 greatly improve the electron injection and as a result improve the carrier balance in the devices. Moreover, we compare the properties of the devices with a 15 and 30 nm emission layer and find that the devices with a 30 nm emission layer have slightly better luminance efficiency. High efficiency of the DMAC-DPS devices can be attributed to the effective conversion of triplet excited states to singlet excited states via reverse intersystem crossing (RISC) process. TADF sensitized fluorescence devices can achieve high luminance efficiency by using the well-established fluorescent materials with the advantages such as the superior stability, versatility and abundance. We report highly efficient blue TADF sensitized devices using DMAC-DPS as the host material and the traditional fluorescence blue-emitting material 2,5,8,11-tetra-tert-butylperylene (TBPe) as the guest material. The devices with 1.0% TBPe show the maximum external quantum efficiency and power efficiency of 12.7% and 22.9 lm W - 1, which are about 3 times higher than those of the conventional 2-methyl-9,10-bis(naphthalen- 2-yl)anthracene (MADN): TPBe devices. This can be attributed to the effective use of triplet excited states for light emission via RISC process and highly efficient Forster energy transfer process from DMAC-DPS to TBPe. Utilization of a TADF material as host material and sensitizer and a traditional fluorescence material as emitting dopant serves as a novel approach to achieve high-efficiency organic light emitting diodes.

Using single donor–acceptor pairs to study the conformational dynamics of macromolecules

It is shown that in the presence of triplet levels of donor and acceptor molecules, the formula for function E(R) describing the dependence of efficiency E of Forster energy transfer on donor–acceptor distance R differs considerably from the one commonly used in experimental works.

Simple Model for Gold Nano Particles Concentration Dependence of Resonance Energy Transfer Intensity

Gold nano particles (GNPs) concentration dependence of the energy transfer occurs between the fluorophores and GNPs is investigated. In the case of theses pairs, GNPs can enhance or quench the fluorescence of fluorophores depending upon the relative magnitudes of two energy transfer mechanisms: i) the plasmonic field enhancement at the fluorophores emission frequencies (plasmon coupled fluorescence enhancement) and ii) the localized plasmon coupled Forster energy transfer from fluorescent particles to gold particles, which quenches the fluorescence. The competition of these mechanisms is depending on the spectral overlap of fluorophores and GNPs, their relative concentration, excitation wavelength. Simple two branches surface plasmon polariton model for GNPs concentration dependence of the energy transfer is proposed. The experimental data and theoretical results confirm our findings.

Spectral and photochemical properties of covalently linked dyads based on 2-styrylquinoline and 6-hydroxy-2-naphthoic acid

Photophysical and photochemical properties of bichromophoric covalently linked SnN dyads (n = 3, 5, 9), in which the 2-styrylquinoline (SQ) and 6-hydroxy-2-naphthoic acid (Np) moieties are linked by the dioxypolymethylene bridge–O–(CH2) n –O–have been studied. The properties of the dyads have been compared with those of the model compounds 2-(4-methoxystyryl)quinoline and methyl 6-hydroxy-2-naphthoate. Inductive-resonance (Forster) energy transfer (FRET) from the Np to the SQ unit with an efficiency up to 99.6% is observed in the S 1 state of the dyads. The Np unit in the neutral form does not affect the photoisomerization of the SQ unit regardless of the form of the latter, neutral or protonated (cationic). The Np moiety in the anionic (deprotonated) form hinders the photoisomerization of the SQ moiety, presumably, as a result to a combined action of several factors.

A high-order external distributed feedback polymer laser with low working threshold

In this paper, we report a high-order distributed feedback (DFB) polymer laser with low working threshold. Using the high-order grating increases the lithographic tolerances, providing coherent light sources that are more amenable to mass-manufacturing techniques, such as laser direct writing lithography and roll-to-roll processing. To enable high-order DFB lasing, an unconventional working configuration is designed in which the grating is situated on top of the uniform conjugated polymer film. In addition, a novel Forster energy transfer blend of two conjugated polymers is used as the gain medium. Upon pumping, the device emits lasing around 603.6 nm with a bandwidth of 0.5 nm. The threshold is around 20.5 μJ cm−2 (~2.56 kW cm−2), about to enter the regime of inexpensive LED pumping. A further increase in pump energy results in simultaneous oscillations at the 29th and 30th Bragg orders. Operating principles of the high-order DFB polymer laser, including spectral performance and threshold dependence on pump length, are investigated. This approach represents a step towards low-cost, even ‘disposable’ polymer lasers.

Nonradiative and radiative Förster energy transfer between quantum dots

We theoretically study nonradiative and radiative energy transfer between two localized quantum emitters, a donor (initially excited) and an acceptor (receiving the excitation). The rates of nonradiative and radiative processes are calculated depending on the spatial and spectral separation between the donor and acceptor states and for different donor and acceptor lifetimes for typical parameters of semiconductor quantum dots. We find that the donor lifetime can be significantly modified only due to the nonradiative Forster energy transfer process at donor–acceptor separations of approximately 10 nm (depending on the acceptor radiative lifetime) and for the energy detuning not larger than 1–2 meV. The efficiency of the nonradiative Forster energy transfer process under these conditions is close to unity and decreases rapidly with an increase in the donor–acceptor distance or energy detuning. At large donor–acceptor separations greater than 40 nm, the radiative corrections to the donor lifetime are comparable with nonradiative ones but are relatively weak.

Energy Transfer Directly to Bilayer Interfaces to Improve Exciton Collection in Organic Photovoltaics

Ternary blends and energy cascades are gaining popularity as ways to engineer absorption as well as exciton and charge collection in organic solar cells. Here, we use kinetic Monte Carlo simulations to investigate energy cascade designs for improving exciton collection in bilayer solar cells via a Forster energy transfer mechanism. We determine that an interfacial monolayer (C) between the donor and acceptor with a D → A → C energy cascade will lead to good exciton collection, allowing for >90% collection, even for energy donor layers up to 75 nm thick. We further examine how roughening the interface, increasing the exciton diffusion length, and using other energy cascade designs affect the enhancement from the energy transfer. We also propose using the inherent charge transfer states at the interfaces as energy acceptors and estimate that the Forster radius could be as large as 3.4 nm, leading to nearly 70% improvement in exciton collection, without the need for a third material.

Effect of the length of ligands passivating quantum dots on the electrooptical characteristics of organic light-emitting diodes

The electrooptical characteristics of organic light-emitting diodes with quantum dots passivated with organic ligands of different lengths as emitting centers are investigated. It is established that the thickness of the ligand coating covering the quantum dots has little effect on the Forster energy transfer in the diodes, but significantly affects the direct injection of charge carriers into the quantum-dot layer. It is shown that the thickness of the passivation coating covering the quantum dots in a close-packed nanoparticle layer is deter- mined both by the length of passivating ligands and the degree of quantum-dot coverage with ligands.

ChemInform Abstract: Metal—Organic Framework Materials for Light‐Harvesting and Energy Transfer

AbstractReview: 74 refs.

Programming Nanophotonic Materials with DNA

DNA is a unique nanoscale material that enables the design and synthesis of nanoscale structures of prescribed shape and functionality via programmable self-assembly. Angstrom-level control over the location and orientation of programmed Watson-Crick basepairs offers the ability to scaffold and spatially organize optically active materials to yield novel optical and photonic properties. Here, we present two distinct strategies for designing and synthesizing DNA-based photonic materials, and emphasize the roles of computational modeling in this process. First, we use computational modeling to design mechanically stiff nanoscale DNA “molds” that have user-specified three-dimensional cavity with a nucleating gold seed, which grows in solution to fill and replicate the cavity. We demonstrate the capability of producing nanoparticles of various shapes and materials that exhibit plasmonic properties that are consistent with electromagnetism simulations. In silico design of stiff molds of nearly arbitrary geometric cavities with resulting optical properties that are prescribed a priori enable a property-by-design framework for producing inorganic particles with prescribed functional properties. Second, we use DNA to program the scaffolding of chromophores into complex three-dimensional assemblies, enabling controlled energy transfer at the nanoscale. This strategy is inspired by nature, where cells use organized assemblies of chromophores to capture photons and funnel the resulting excitons toward the reaction center where they are converted to chemical energy. In particular, the close-packing of chromophores results in the emergence of quantum coherence that can strongly affect exciton transport across the structure. Using Forster energy transfer modeling, as well as a hybrid molecular dynamics and quantum mechanical approach, we demonstrate how emergent excitonic and light-harvesting properties of diverse DNA-dye assemblies can be elucidated.

On the quantitative absorption and Stokes shift in PbSe quantum dots embedded in glasses

The synthesis of PbSe quantum dots (QDs) in silicate glasses was achieved by a simple melt-annealing technique. Transmission electron microscopy analysis proves the formation of PbSe QDs in glasses. The absorption spectra show that the light absorption originates from the PbSe QDs in glasses mostly, and the energy-integrated molar extinction coefficient for the first exciton transition was deemed to be only about 1/10 of those from colloidal PbSe QDs. The photoluminescence analysis reveals that the Forster energy transfer is responsible for the shape of the PL peak. For the sample with PbSe QDs in a small radius of 5.2 nm, a pronounced Stokes shift of 70 meV was found, and the Huang–Rhys factor was calculated to be 2.1.