Donor Acceptor Concentration Research Articles

Im-SCC-FRET: improved single-cell-based calibration of a FRET system.

We recently developed a SCC-FRET (single-cell-based calibration of a FRET system) method to quantify spectral crosstalk correction parameters (β and δ) and system calibration parameters (G and k) of a Förster resonance energy transfer (FRET) system by imaging a single cell expressing a standard FRET plasmid with known FRET efficiency (E) and donor-acceptor concentration ratio (RC) (Liu et al., Opt. Express30, 29063 (2022)10.1364/OE.459861). Here we improved the SCC-FRET method (named as Im-SCC-FRET) to simultaneously obtain β, δ, G, k and the acceptor-to-donor extinction coefficient ratio (ε A ε D), which is a key parameter to calculate the acceptor-centric FRET efficiency (EA), of a FRET system when the range of β and δ values is set as 0-1. In Im-SCC-FRET, the target function is changed from the sum of absolute values to the sum of squares according to the least squares method, and the initial value of β and δ estimated by the integral but not the maximum value spectral overlap between fluorophore and filter. Compared with SCC-FRET, the experimental results demonstrate that Im-SCC-FRET can obtain more accurate and stable results for β, δ, G, and k, and add the ratio ε A ε D, which is necessary for the FRET hybrid assay. Im-SCC-FRET reduces the complexity of experiment preparation and opens up a promising avenue for developing an intelligent FRET correction system.

Vertical Phase Regulation with 1,3,5-Tribromobenzene Leads to 18.5% Efficiency Binary Organic Solar Cells.

The sequential deposition method assists the vertical phase distribution in the photoactive layer of organic solar cells, enhancing power conversion efficiencies. With this film coating approach, the morphology of both layers can be fine-tuned with high boiling solvent additives, as frequently applied in one-step casting films. However, introducing liquid additives can compromise the morphological stability of the devices due to the solvent residuals. Herein, 1,3,5-tribromobenzene (TBB) with high volatility and low cost, is used as a solid additive in the acceptor solution and combined thermal annealing to regulate the vertical phase in organic solar cells composed of D18-Cl/L8-BO. Compared to the control cells, the devices treated with TBB and those that underwent additional thermal processing exhibit increased exciton generation rate, charge carrier mobility, charge carrier lifetime, and reduced bimolecular charge recombination. As a result, the TBB-treated organic solar cells achieve a champion power conversion efficiency of 18.5% (18.1% averaged), one of the highest efficiencies in binary organic solar cells with open circuit voltage exceeding 900mV. This study ascribes the advanced device performance to the gradient-distributed donor-acceptor concentrations in the vertical direction. The findings provide guidelines for optimizing the morphology of the sequentially deposited top layer to achieve high-performance organic solar cells.

Bevel Structure Based XPS Analysis as a Non-Destructive Chemical Probe for Complex Interfacial Structures of Organic Semiconductors.

The bevel structure of organic multilayers produced by finely controlled Ar gas cluster ion beam sputtering preserves both the molecular distribution and chemical states. Nevertheless, there is still an important question of whether this method can be applicable to organic multilayer structures composed of complex or ambiguous interfaces used in real organic optoelectronic devices. Herein, various bevel structures are fabricated from different types of organic semiconductors using a solution-based deposition technique: complicatedly intermixed electron-donor and electron-acceptor bulk heterojunction structure, thin film structure with an internal donor-acceptor concentration gradient, and multi-layered structure with more than three layers. For these organic material combinations listed above, the bevel structure is fabricated with finely tuned Ar gas cluster ion beam sputtering. The location-dependent X-ray photoelectron spectroscopy (XPS) results obtained for each bevel structure exactly correspond to the XPS depth profiles. This result demonstrates that the bevel structure analysis is a powerful method to distinguish subtle differences in chemical component distributions and chemical states of organic semiconductors even with complex or ambiguous interfaces. Ultimately, due to its reliability as verified by this study, the proposed bevel structure analysis is expected to greatly expand other analytical techniques with a limited spatial or depth resolution.

Unique Luminescence of Hexagonal Dominant Colloidal Copper Indium Sulphide Quantum Dots in Dispersed Solutions

Luminescent hexagonal dominant copper indium sulphide (h-dominant CIS) quantum dots (QDs) by precursor-injection of mixed metal-dialkyldithiocarbamate precursors. Owing to the different reactivity of the precursors, this method allowed the CIS QDs to grow while retaining the crystallinity of the hexagonal nucleus. The photoluminescence (PL) spectra exhibited dual emission (600–700 nm red emission and 700–800 nm NIR emission) resulting from the combined contributions of the hexagonal (wurtzite) h-CIS and tetragonal (chalcopyrite) t-CIS QDs, i.e. the NIR and red emissions were due to the h-CIS QDs and coexisting t-CIS QDs (weight ratio of h-CIS/t-CIS ~ 10), respectively. The PL intensities of the h-CIS as well as t-CIS QDs were enhanced by post-synthetic heat treatment; the t-CIS QDs were particularly sensitive to the heat treatment. By separating h-CIS and t-CIS successfully, it was demonstrated that this phenomenon was not affected by size and composition but by the donor-acceptor pair states and defect concentration originating from their crystal structure. The h-dominant CIS QDs in this work provide a new technique to control the optical property of Cu-In-S ternary NCs.

Donor-acceptor preassociation, excited state solvation threshold, and optical energy cost as challenges in chemical applications of photobases.

Photobases are molecules with increased pKa in the excited state that can serve to transduce light energy into proton removal capability. They can be used to control chemical reactions using light, such as removing protons from a catalytic site in reactions that are rate-limited by proton transfer. We identify and explore several major challenges toward their practical applications. Two important challenges are the need for pre-association (or ground state hydrogen bonding) between the proton donor and the photobase, and the need for excited state solvation of the photogenerated products. We investigate these two challenges with the photobase 5-methoxyquinoline as the proton acceptor and a low-pKa alcohol, 2,2,2-trifluoroethanol, as the proton donor. We vary the concentration of the donor in a background non-hydrogen-bonding solvent. Using absorption spectroscopy, we have identified that the donor-acceptor concentration ratio must exceed 100 : 1 to achieve appreciable ground state hydrogen bonding. Interestingly, emission spectroscopy reveals that the onset of ground state hydrogen bonding does not guarantee successful excited state proton transfer. It takes an additional order of magnitude increase in donor-acceptor ratio to achieve that goal, revealing that it is necessary to have excess donor molecules to reach the solvation threshold for the photogenerated products. The next challenge is reducing the large ground-excited state energy gap, which often requires UV photons to drive proton transfer. We show experimental and computational data comparing the photobasicity and optical energy gap for a few N-aromatic heterocyclic photobases. In general, we find that reducing the energy gap by increasing the conjugation size necessarily reduces photobasicity, while adding substituents of varying electron-withdrawing strength allows some fine-tuning of this effect. The combination of these two factors provide a preliminary design space for creating new photobasic molecules.

Identification of carbon‐hydrogen complexes in n‐ and p‐type silicon

AbstractThe origin of several deep traps E42, E90, E262, and H180 in hydrogenated n ‐type and p ‐type FZ and CZ Si is investigated. Comparing the depth profiles of these defects in samples with different C, O, H, and shallow donor (acceptor) concentrations we conclude that they belong to carbon‐hydrogen‐related defects consisting of one C and one H atom. The similar annealing behavior and identical depth profiles of E42 and E262 correlate them with two different charge states of the same defect. From a comparison with earlier calculations we attribute E42 to the double acceptor and E262 to the single acceptor state of the CH1AB complex. In good agreement with the results of previous studies E90 is assigned to the acceptor state of the CH1BC complex. Our preliminary Laplace DLTS studies on SiGe with a Ge content <5% show different local Ge environments for E90 and H180 in the nearest and second‐nearest neighborhood. We interpret this as an indication for a different origin of these defects. After annealing the samples under reverse bias at 320 K another CH‐related defect (CHB) can be detected by Laplace DLTS in n ‐type Si. Previously, this defect was often wrongly assigned to the single donor state of CH1BC. The field dependence of the emission rate of CHB identifies the level as a single donor state. However, the depth distribution of CHB differs clearly from that of E90. Our results on the carbon‐hydrogen complex give a conclusive explanation of previously reported controversial experimental data. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Engineering vertical morphology with nanoparticulate organic photovoltaic devices

Sequential deposition of monolayers, composed of nanoparticles with varied donor-acceptor concentration ratios, has allowed the fabrication of organic photovoltaic (OPV) active layers with engineered vertical morphology. The performance of polymer-polymer poly(9,9-dioctylfluorene-co-bis-N,N-phenyl-1,4-phenylenediamine):poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (PFB:F8BT) and polymer-fullerene poly(3-hexylthiophene):phenyl C61 butyric acid methyl ester (P3HT:PCBM) nanoparticulate (NP), graded nanoparticulate (GNP) and bulk heterojunction (BHJ) OPV devices have been studied. For both material systems the highest device VOC is observed for the graded structure. Furthermore, thermal treatments can be used to alleviate parasitic series resistance in the GNP devices, thus improving device JSC and efficiency. Overall, this work shows that the nanoparticle approach provides a new experimental lever for morphology control in OPV devices.

Distributed-Feedback Solid-State Polymeric-Dye Lasers Based on Excitation-Energy Transfer

Using Q-switched Nd:YAG laser excitation, we investigate both theoretically and experimentally the energy transfer between dyes Pyronin-Y (PY) and cresyl violet (CV) incorporated in a methyl methacrylate (MMA) matrix. From the absorption and fluorescence spectral data of PY and CV dyes, we calculate the absorption and emission cross-section of donor and acceptor dye molecules, the critical transfer radius R0, the critical concentration C0, the half-quenching concentration C1/2, and the Foster-type transfer rate kf . We study the influence of donor–acceptor concentration and pump power on the energy transfer and its mechanism. Both energy transfer phenomenon and the self-absorption mechanism play a role in laser tunability. We achieve a tuning of the output wavelength (between 580 and 670 nm) by varying the periodic gain modulation generated by a Q-switched Nd:YAG laser.

Formation of vertical concentration gradients in poly(3-hexylthiophene-2,5-diyl): Phenyl-C61-butyric acid methyl ester-graded bilayer solar cells

In the present work, we demonstrate that graded bilayer solar cells provide a very interesting alternative to the bulk heterojunction active layers commonly used in organic photovoltaic cells. One of the main advantages of this type of active layers is the possibility to optimize independently both donor and acceptor layers. Using various process methods, we obtain active layers that demonstrate a donor–acceptor vertical concentration gradient. These devices exhibit not only a high fill factor but also a remarkable increase in open-circuit voltage (Voc). In order to understand the influence of the film morphology over the device parameters, we provide a complete study using energy-dispersive x-ray spectroscopy elemental mapping of the device cross sections, showing evidence that ideal donor–acceptor concentration gradient are required to obtain high fill factors. Furthermore, we use a simple equivalent electrical model to extrapolate device parameters such as reverse saturation current for a clearer understanding of the origin of the Voc increase.

The band energy diagram of PCBM–DH6T bulk heterojunction solar cells: synchrotron-induced photoelectron spectroscopy on solution processed DH6T:PCBM blends and in situ prepared PCBM/DH6T interfaces

Applying high resolution synchrotron-induced photoelectron spectroscopy (SXPS), the electronic properties of a bulk heterojunction (BHJ) model solar cell consisting of phenyl-C61-butyric-acid-methyl-ester (PCBM) as an acceptor and α,ω-dihexylsexithiophene (DH6T) as a donor are investigated. This donor material can be prepared via UHV thermal evaporation and solution based techniques. Samples prepared by either technique show identical core levels and valence band spectra proving the equivalency of the resulting electronic properties. The formation of the PCBM/DH6T interface is studied in an in situ experiment based on stepwise evaporation of DH6T onto PCBM. The deposition of donor–acceptor mixed solutions leads to phase separated bulk heterojunction layers with a donor cap. The combination of SXPS measurements on a series of ex situ prepared blend films from solutions with varying donor–acceptor concentrations with in situ interface formation experiments enables deriving the band diagram across the bulk heterojunction and into the donor cap. Band bending of up to 0.3 eV is induced in the DH6T cap layer and a dipole of 0.26 eV forms at the PCBM:DH6T bulk heterojunction. The direction of the band bending leads to hole accumulation on the donor side of the interface, which may increase recombination with transferred electrons in the acceptor and thereby negatively affects the device performance.

Hollow fiber‐based liquid membrane microextraction combined with high‐performance liquid chromatography for extraction and determination of trimetazidine in human plasma

A hollow fiber-based liquid phase microextraction strategy combined with high-performance liquid chromatography was evaluated for the quantitative determination of trimetazidine in human plasma. Trimetazidine was extracted from a 2.1 mL basified plasma sample (donor phase) into the organic solvent (n-octanol) impregnated in the pores of a hollow fiber and then extracted into an acidic solution (acceptor phase) inside the lumen of the hollow fiber. The result showed that transport of drugs from alkaline sample solution into 0.5 m HCl occurred efficiently when 25 μL of 250 mm sodium 1-octanesulfonate was added into the donor phase. Several parameters influencing the efficiency of the method, such as the nature of organic solvent used to impregnate the membrane, compositions of donor phase and acceptor phase, type and concentration of carrier, extraction time, stirring rate and salt concentration, were investigated and optimized. Under the optimal conditions, the calibration curves were obtained in the range of 5-200 ng/mL with reasonable linearity (r > 0.9980). The method was successfully applied to determine the concentration of trimetazidine in human plasma.

Enhanced Vertical Concentration Gradient in Rubbed P3HT:PCBM Graded Bilayer Solar Cells.

Graded bilayer solar cells have proven to be at least as efficient as the bulk heterojunctions when it comes to the Poly(3-hexylthiophene) (P3HT) - [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) donor-acceptor system. However, control of the vertical concentration gradient using simple techniques has never been reported. We demonstrate that rubbing the P3HT layer prior to PCBM deposition induces major morphological changes in the active layer. Using the newly introduced energy-dispersive X-ray spectroscopy element mapping technique, we found that rubbing P3HT induces the formation of an ideal vertical donor-acceptor concentration gradient. Furthermore, the P3HT crystallites undergo a molecular reorientation from edge-on to face-on configuration inducing a better charge transport in the vertical direction. The combination of these two major morphological changes leads to the fabrication of high-performance solar cells that exhibit, to date, the record efficiencies for spin-coated graded bilayers solar cells.

Organic position sensitive photodetectors based on lateral donor-acceptor concentration gradients

We report on an organic photodiode configuration based on a donor/acceptor bilayer with opposed complementary thickness gradients. We rely on the strong dependence of the optical field on thickness to achieve spatially dependent spectral responses, a proof-of-concept for position sensitive detection. Ratiometric photocurrent values at two wavelengths allow for position determination independently of the light intensity with a spatial resolution below 600 μm.

Modeling and Performance Analysis of a Quad Detector

In this paper we are interested in modeling, performance evaluation, and measurement of a quadrant detector. Photodiode is modeled using its differential equations then implemented and solved using ORCAD -pspise. The model validation was performed by comparing the model results with the experimental measurements using a proposed setup. The model was used to investigate the effect of the photodiode donor concentrations, acceptor concentrations and intrinsic region concentrations. The simulation results showed that the donor concentrations should be kept as small as possible in order to improve the photodiode performance, the acceptor concentrations has a small effect on the performance, and as the intrinsic region concentration increases the photocurrent increases and the junction capacitance decreases with a small increase in the dark current.

Spectroscopy characterization of the interaction between brevifolin carboxylic acid and bovine serum albumin

Themechanism of binding of the antivirus drug, brevifolin carboxylic acid (BCA) with bovine serum albumin (BSA) was investigated by steady-state and time-resolved fluorescence, circular dichroism (CD), Fourier transform infrared (FT-IR) and Raman spectroscopy under pseudo-physiological conditions for the first time. A strong fluorescence quenching was observed and the quenching mechanism was considered as static quenching. Various binding parameters were evaluated. The quantitative analysis of CD spectral data revealed that the a-helical content of BSA increased from 48.91% (in free BSA) to 52.46% (in bound form) in the presence of BCA. Based on the Förster's theory of non-radiation energy transfer, the relation of the binding average distance r between the donor (BSA) and acceptor (BCA) and acceptor concentration was determined. The changes in association constants of BCA-BSA in the presence of the common ions are also discussed. From the CD, FT-IR, time-resolved fluorescence and Raman spectroscopic results, it is apparent that the interaction of BCA with BSA causes a conformational change in the protein, and the Trp and Tyr residues are buried in more hydrophobic surroundings. BCA mainly binds to residue Trp 212 located in domain II of BSA by hydrophobic interaction and hydrogen bond.

Effect of donor-acceptor concentration ratios on nonradiative energy transfer in closely packed CdTe quantum dots

This study investigates the dependence of Förster resonance energy transfer (FRET) on donor-acceptor (D/A) concentration ratios in mixed-size CdTe quantum dots (QDs) films by using photoluminescence (PL) and time-resolved PL spectroscopy. Experimental results indicate that an increasing donor concentration significantly quenches the emission intensity and lifetime in donor QDs and enhances that in acceptor QDs, providing clear evidence of increased FRET efficiency. When D/A ratio exceeds 6, however, the emission intensity and the lifetime of acceptors start to decline, reflecting a decreasing FRET efficiency because of a markedly declining availability of acceptor QDs.

Determination of carrier effective mass, impurity energy levels, and compensation ratio in Ga4Se3S layered crystals by Hall effect measurements

AbstractIn this work, the dark electrical resistivity, charge carriers density and Hall mobility of Ga4Se3S single crystals have been measured and analyzed in the temperature region of 200–350 K. The data analyses have shown that this crystal exhibits an extrinsic n‐type of conduction. The temperature‐dependent dark electrical resistivity analysis reflected the existence of energy level as 0.31 eV. The temperature dependence of carrier density was analyzed by using the single donor‐single acceptor model. The latter analysis allowed the determination of electron effective mass as 0.38m0, hole effective mass as 0.42m0, donor impurity energy level as 0.45 eV, acceptor–donor concentration ratio (Na/Nd) as 0.97 and a donor–acceptor concentration difference as Nd – Na = 1.5 × 1011 cm–3. The Hall mobility of Ga4Se3S is found to increase with decreasing temperature following a power law of slope of ∼(–6.3). The abnormal behavior of mobility was attributed to the domination of phonon scattering and/or crystals anisotropy. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Estimating protein-protein interaction affinity in living cells using quantitative Förster resonance energy transfer measurements

We have previously demonstrated that Forster resonance energy transfer (FRET) efficiency and the relative concentration of donor and acceptor fluorophores can be determined in living cells using three-cube wide-field fluorescence microscopy. Here, we extend the methodology to estimate the effective equilibrium dissociation constant (Kd) and the intrinsic FRET efficiency (Emax) of an interacting donor-acceptor pair. Assuming bimolecular interaction, the predicted FRET efficiency is a function of donor concentration, acceptor concentration, Kd, and Emax. We estimate Kd and Emax by minimizing the sum of the squared error (SSE) between the predicted and measured FRET efficiency. This is accomplished by examining the topology of SSE values for a matrix of hypothetical Kd and Emax values. Applying an F-test, the 95% confidence contour of Kd and Emax is calculated. We test the method by expressing an inducible FRET fusion pair consisting of FKBP12-Cerulean and Frb-Venus in HeLa cells. As the Kd for FKBP12-rapamycin and Frb has been analytically determined, the relative Kd (in fluorescence units) could be calibrated with a value based on protein concentration. The described methodology should be useful for comparing protein-protein interaction affinities in living cells.

Photoacoustic study on the photostability of polymethyl methacrylate films doped with Rhodamine 6G–Rhodamine B dye mixture system

The photosensitivity of dye mixture-doped polymethyl methacrylate (PMMA) films are investigated as a function of laser power, concentration of the dyes, modulation frequency and the irradiation wavelength. Energy transfer from a donor molecule to an acceptor molecule affects the emission output of the dye mixture system. Photosensitivity is found to change with changes in donor–acceptor concentrations. PMMA samples doped with the dye mixture are found to be more photosensitive when the dyes are mixed in the same proportion.

Kinetic analysis of a Golgi UDP-GlcNAc:polypeptide-Thr/Ser N-acetyl-α-glucosaminyltransferase from Dictyostelium

Mucin-type O-glycosylation in Dictyostelium is initiated in the Golgi by a UDP-GlcNAc:polypeptide-Thr/Ser N-acetyl-alpha-glucosaminyltransferase (Dd-pp alphaGlcNAcT2) whose sequence is distantly related to the sequences of animal polypeptide-Thr/Ser N-acetyl-alpha-galactosaminyltransferases, such as murine Mm-pp alphaGalNAcT1. To evaluate the significance of this similarity, highly purified Dd-pp alphaGlcNAcT2 was assayed using synthetic peptides derived from known substrates. Dd-pp alphaGlcNAcT2 strongly prefers UDP-GlcNAc over UDP-GalNAc, preferentially modifies the central region of the peptide, and modifies Ser in addition to Thr residues. Initial velocity measurements performed over a matrix of UDP-GlcNAc donor and peptide acceptor concentrations indicate that the substrates bind to the enzyme in ordered fashion before the chemical conversion. Substrate inhibition exerted by a second peptide, and the pattern of product inhibition exerted by UDP, suggest that UDP-GlcNAc binds first and the peptide binds second, consistent with data reported for Mm-pp alphaGalNAcT1. Two selective competitive inhibitors of Mm-pp alphaGalNAcT1, retrieved from a screen of neutral-charge uridine derivatives, also inhibit Dd-pp alphaGlcNAcT1 competitively with only slightly less efficacy. Inhibition is specific for Dd-pp alphaGlcNAcT2 relative to two other Dictyostelium retaining glycosyltransferases. These data support a phylogenetic model in which the alphaGlcNAcT function in unicellular eukaryotes converted to an alphaGalNAcT function in the metazoan ortholog while conserving a similar reaction mechanism and active site architecture.