Acceptor Derivatives Research Articles

Selective protein photocleavage by fluorescein derivatives

Modification of the structure of small molecular probe which can act as photocleavage reagent has become a considerable challenge to improve the ability to target specific sites on a large protein. These photoreagents can provide valuable information on the binding site recognition and the mechanism of the photocleavage reaction under photochemical control. In this study, site specific photocleavage of lysozyme and avidin by fluorescein derivatives, fluorescein sodium salt (F-1) and 5(6)-carboxyfluorescein diacetate (F-2) were reported here for the first time. Functional groups on the photoreagent have been proven to effect on the interaction with the protein. Cleavage of the proteins by fluorescein derivatives were successful under visible region when irradiating the solution mixture of protein, fluorescein derivative and electron acceptor, cobalt (III) hexamine trichloride, at 490–492 nm. N-terminal amino acid sequencing of the cleaved fragments of lysozyme indicated the cleavage site between Trp108 - Val 109 for both probes, whereas the cleavage of avidin by F-1 and F-2 were detected between Trp70 - Lys71. Binding interaction can be investigated using methods as simple as absorption and fluorescence spectroscopies. Absorption and fluorescence studies indicated the strong binding interactions between fluorescein derivatives and the target proteins. Computational modeling was used to gain a better insight of the protein-probe binding interaction and binding sites. Molecular docking studies indicated that F-1 and F-2 were located near the hydrophilic and hydrophobic sites of both proteins within 4 Å away from the cleavage site. The docking results clarified the binding sites of F-1 and F-2 on proteins, corresponding to the results obtained from the protein photocleavage studies.

Orbital Control and Coherent Charge Transport in Transition Metal Platinum(II)–Platinum(II) Lantern Complexes in Molecular Junctions

Platinum (II) dimers in organometallic complexes exhibit oscillatory vibrational charge transfer with optical excitation and whose nature depends strongly on the Pt-Pt distance. Yet the electronic transport of such devices has not been studied. We take a well-reported Pt(II) dimer complex that is ideal for transport in a molecular junction and subject it to a battery of electronic structure property calculations. With DFT, we find the orbital nature of the HOMO level to not be solely induced by the 5dz2 orbital as long thought, but rather a complex mixture with significant contributions from 6s orbital states from the Au electrodes that have not been considered before. We probe how the chemical tuning of the ligand affects the Pt-Pt bond length and thus conduction, by systematically modifying both the bridging ligands (BL) and cyclometallating ligands (CMLs) with donor (methyl) and acceptor (fluorine) derivatives. With nonequilibrium green’s functions (NEGF-DFT), we find patterns between the conductivity,...

Emphasizing the Operational Role of a Novel Graphene-Based Ink into High Performance Ternary Organic Solar Cells.

A novel solution-processed, graphene-based material was synthesized by treating graphene oxide (GO) with 2,5,7-trinitro-9-oxo-fluorenone-4-carboxylic acid (TNF-COOH) moieties, via simple synthetic routes. The yielded molecule N-[(carbamoyl-GO)ethyl]-N′-[(carbamoyl)-(2,5,7-trinitro-9-oxo-fluorene)] (GO-TNF) was thoroughly characterized and it was shown that it presents favorable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels to function as a bridge component between the polymeric donor poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl}) (PTB7) and the fullerene derivative acceptor [6,6]-phenyl-C71-butyric-acid-methylester (PC71BM). In this context, a GO-TNF based ink was prepared and directly incorporated within the binary photoactive layer, in different volume ratios (1%–3% ratio to the blend) for the effective realization of inverted ternary organic solar cells (OSCs) of the structure ITO/PFN/PTB7:GO-TNF:PC71BM/MoO3/Al. The addition of 2% v/v GO-TNF ink led to a champion power conversion efficiency (PCE) of 8.71% that was enhanced by ~13% as compared to the reference cell.

A computational study on boron dipyromethene ancillary acceptor-based dyes for dye-sensitized solar cells

A series of (D-π)2–An–A based organic dyes containing a boron dipyrromethene (BODIPY) moiety as an ancillary acceptor (An) derivative were chosen, and the effect of donor moieties (diarylamine, carbazole, azepine, and dibenzazepine) was investigated to understand their photophysical and photoelectrochemical properties by employing density functional theory.

Structure controlled solvatochromism and halochromic fluorescence switching of 2,2′-bipyridine based donor–acceptor derivatives

Simple donor–acceptor derivatives were prepared by substituting alicyclic amines into the 2,2′-bipyridine (Bpy) core unit and they exhibited substituent and structure dependent tunable and switchable fluorescence.

Effect of IT-M doping on charge transfer and ultrafast carrier dynamics of ternary organic solar cell materials

Using optical pump-terahertz (THz) time-domain spectroscopy measurements along with ab initio density functional theory (DFT) calculations, we studied the effect of 3,9-bis(2-methylene-(3-(1, 1-dicyanomethylene)-5-methylindanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno [1,2-b:5,6-b′]-dithiophene (IT-M) molecules on the ultrafast dynamics and photoconductivity of the active layers of ternary organic solar cells (OSCs), which are composed by the conjugated polymer donor and fullerene derivative acceptor. The THz photoconductivity measurements show that the introduction of IT-M molecule increases the photoconductivity of the ternary OSC and the maximum value of photoconductivity is obtained in the sample with IT-M weight ratio of 15%. To reveal the mechanism of IT-M doping on the photoconductivity of OSC material, ab initio DFT calculations were performed to identify the band structures of the ternary OSC heterostructures. Resonant charge transfers induced by the band alignment of IT-M with the conjugated polymer donor and fullerene derivative acceptor, which lead to an increase of photoconductivity with a reduction of electron–hole recombination rate, were obtained from DFT calculations. In addition to the resonant charge transfer process, defect scattering induced by the doping of IT-M molecules leads to a reduction of photoconductivity. By competing these two effects, maximum photoconductivity of ternary OSC materials is obtained with IT-M weight ratio of 15%. Moreover, the charge carrier densities and scattering times of ternary OSC materials were derived from the measured THz photoconductivity via the classical Drude–Smith model. With these material properties, we identified that the maximum value of photoconductivity in OSC material with IT-M weight ratio of 15% is induced by its long scattering time instead of high carrier density.

Photophysics, morphology and device performances correlation on non-fullerene acceptor based binary and ternary solar cells

Abstract Non-fullerene acceptor (NFA) based organic solar cells (OSCs) are of high efficiency and low energy loss and low recombination features, which is owing to the advantage of non-fullerene acceptors. The photophysics investigation of non-fullerene solar cells, in comparing to fullerene based analogue as well as mixed acceptor ternary blends could help to understand the working mechanism of NFA functioning mechanism. We choose PBDB-T donor, the fullerene derivative PC71BM acceptor, and the non-fullerene acceptor ITIC as the model system, to construct binary and ternary solar cells, which then subject to ultrafast spectroscopy investigation. The charge transfer pathway in binary and ternary blends is revealed. And it is seen that ITIC leads to a faster exciton separation and exciton diffusion. ITIC in blends suppresses the geminate recombination and shows smaller amount of charge transfer states, which is beneficial for the device performance. And the addition of ITIC enhances the crystallinity for both donor and acceptor leads to a morphology change of forming bicontinuous crystalline networks and phase separation. In a consequence, fill factor and JSC, increase dramatically for the related OSC.

Halogenation on terminal groups of ITIC based electron acceptors as an effective strategy for efficient polymer solar cells

Acceptor halogenation is an excellent modification method for modulating molecular energy levels, improving optical absorption, shortening the intermolecular packing distance thus ameliorating morphologies and achieving effective exciton dissociation and charge transfer of organic photovoltaic device. In this work, F, Cl and Br terminated ITIC small molecule acceptor (SMA) derivatives (IT-2F, IT-2Cl and IT-2Br) are designed and synthesized to compare the halogen substitution effect. Among these three acceptors, IT-2F based PSCs devices show the highest power conversion efficiencies (PCEs) around 12.08%, but Br terminated ITIC show downshifted LUMO energy level. Brominated ITIC show comparable PCEs with Cl and F terminated compound, and moreover chlorinated and brominated ITIC show low synthesis cost and easy purification than fluorinated materials, which may be favorable for future commercialization.

High-Efficiency Organic Solar Cells With Solution Processable Non-Fullerene Acceptor as an Interlayer

Interlayers and interface engineering plays a pivotal role in achieving efficient charge extraction necessary for realizing high power conversion efficiency (PCE) in bulk heterojunction organic solar cells. In this study, we report a novel strategy of combining advantages of both fullerene derivative and non-fullerene acceptor materials by employing solution processable non-fullerene acceptor 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indan-one))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2’,3’-d’]-s-indaceno[1,2-b:5,6-b’]dithiophene (ITIC) to modify the interface between ZnO-based electron transport layer and poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl) benzo [1,2-b;4,5-b'] dithiophe-ne-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carb-oxylate-2-6-diyl)] (PTB7-Th): phenyl-C71-butyric acid methyl ester-based photoactive layer. An improvement in PCE from ∼ 7.5% to ∼ 9% has been achieved for the devices with ITIC modified interlayer. Time resolved photoluminescence (PL) via time correlated single photon counting and photo-electrochemical impedance spectroscopy (photo-EIS) measurements were carried out to investigate the causes for improved PCE for the devices with ITIC modified interlayer.

Triazine-Acceptor-Based Green Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes.

High-efficiency thermally activated delayed fluorescence (TADF) is leading the third-generation technology of organic light-emitting diodes (OLEDs). TADF emitters are designed and synthesized using inexpensive organic donor and acceptor derivatives. TADF emitters are a potential candidate for next-generation display technology when compared with metal-complex-based phosphorescent dopants. Many studies are being conducted to enhance the external quantum efficiencies (EQEs) and photoluminescent quantum yield of green TADF devices. Blue TADF reached an EQE of over 35% with the support of suitable donor and acceptor moieties based on a suitable molecular design. The efficiencies of green TADF emitters can be improved when an appropriate molecular design is applied with an efficient device structure. The triazine acceptor has been identified as a worthy building block for green TADF emitters. Hence, we present here a review of triazine with various donor molecules and their device performances. This will help to design more suitable and efficient green TADF emitters for OLEDs.

Theoretical study of diphenylsulfone derivatives for blue thermally activated delayed fluorescence emitters

Novel thermally activated delayed fluorescence (TADF) emitters were designed with diphenylsulfone (DPS) as an electron acceptor and carbazole derivatives as electron donors and their electronic and optical properties were investigated theoretically for applications to blue organic light-emitting diodes (OLEDs). By using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations, we obtained the electron distributions of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) as well as the energy of the lowest singlet (S1) and lowest triplet (T1) excited states. We show that 2mDTC-DPS would be a suitable blue OLED emitter because it has sufficiently small ΔEST value, which is favorable for a reverse intersystem crossing (RISC) process from T1 to S1 states and an emission wavelength of 429 nm with sufficiently large F values.

Protons venture into the inverted region

Physical Chemistry One of the most counterintuitive features of electron transfer kinetics is the inverted region. As Marcus theory predicts and experiments have borne out, electron transfer slows down once the driving force for it becomes especially favorable. Parada et al. now offer evidence for such inverted behavior in proton-coupled electron transfer (see the Perspective by Dempsey). Specifically, they examined a series of compounds with phenol bridging anthracene (electron acceptor) and pyridine (proton acceptor) derivatives. Time-resolved spectroscopy and accompanying theory revealed slower rates at higher driving forces in the back reaction that follows light-induced intramolecular proton and electron transfer. Science , this issue p. [471][1]; see also p. [436][2] [1]: /lookup/doi/10.1126/science.aaw4675 [2]: /lookup/doi/10.1126/science.aaw9900

An Updated Strategy for Designing Non-Fullerene Acceptors by the Lowest Singlet and Triplet States Excitation: Influence of Periodical Substitution from O, S, and Se to Te for BAE Derivatives

When one is trying to maintain original advantageous properties of molecule without increasing the difficulty of synthesis and processing, simultaneously, adding more predictable properties is a preferred choice for designing promising molecules. Here, we report the photovoltaic performance of bistricyclic aromatic enes (BAE) derivative acceptors as a function of heteroatom substitutions (O, S, Se, Te), and the range they can maintain. Beyond that, by combining singlet–triplet exciton conversion with singlet fission (SF), an additional perspective to characterize molecules performance is predicted by employing T1-excitation. Theoretical calculation results showed that for small molecules (BAEs), heavy atom substitution of the same group could increase conformation stability, electron acceptability, and spin–orbit coupling. After expansion of the molecular size (DPP-BAE-DPP), the difference in molecular properties is mainly due to the conformation type for singlet states excitation. For triplet states excitation, the degree of negative correlation between SF and singlet–triplet exciton conversion decreases, which is conducive to obtaining more T1 excitons, thus improving the organic photovoltaic performances. As a result, A-S-DPP, A-Te-DPP, T-S-DPP, T-Se-DPP and T-Te-DPP not only have superior single-excitation performance but also potential triple-excitation possibilities; they are promising acceptors. These results provided some new evidence for designing nonfullerene acceptors and demonstrating the role of heavy atoms substitution in photovoltaic performance.

Theoretical study of thermally activated delayed fluorescence from benzofuro[2,3-b]pyridine based emitters

Novel thermally activated delayed fluorescence (TADF) materials with 6-position modified benzofuro[2,3-b]pyridine (6BFP) as an electron acceptor and phenylcarbazole derivatives [9-phenyl-1,8-diamethyl-9H-carbazole (PmCz), and 9,9',9''-(benzene-1,2,3-triyl)tris(9H-carbazole) (BtCz)] as electron donors were designed, and a theoretical study of their electronic and optical properties was conducted to determine their utility for blue organic light-emitting diodes (OLEDs). Using density functional theory (DFT) and time-dependent DFT calculations, we obtained the electron distribution of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) and the energy of the lowest singlet (S1) and the lowest triplet (T1) excited states. We show that BtCz-6BFP would be a suitable sky-blue TADF emitter because it has a sufficiently small energy difference between the S1 state and the T1 state (ΔEST) value (0.353 eV), which is favorable for a reverse intersystem crossing process from T1 to S1 states, and an emission wavelength of 467.4 nm with a sufficiently large oscillator strength (F) value (0.1109).

Highly-efficient semi-transparent organic solar cells utilising non-fullerene acceptors with optimised multilayer MoO3/Ag/MoO3 electrodes

We report the optimisation of a semi-transparent solar cell based on a blend of a recently reported high performance donor polymer (PFBDB-T) with a non-fullerene acceptor derivative (C8-ITIC).

Effective Molecular Engineering Approach for Employing a Halogen-Free Solvent for the Fabrication of Solution-Processed Small-Molecule Solar Cells.

To utilize the potential of small-molecule-based organic solar cells, proper designs of the photoactive materials which result in reasonable performance in a halogen-free solvent system and thickness tolerance over a range are required. One of the best approaches to achieve these requirements is via the molecular engineering ofsmall-molecule electron donors. Here, we have modified a previously reported dithienobenzodithiophene (DTBDT)-based small molecule (SM1) via the dimerization approach, that is, the insertion of an additional DTBDT into the main backbone of the small molecule (SM2). An SM1-based photoactive film showed severe pinhole formation throughout the film when processed with a halogen-free o-xylene solvent. On the other hand, the modified small-molecule SM2 formed an excellent pinhole-free film when processed with the o-xylene solvent. Because of the dimerization of the DTBDT in the SM2 core, highly crystalline films with compact lamellae and an enhanced donor/acceptor interdigitation were formed, and all of these factors led to a high efficiency of 8.64% with chloroform and 8.37% with the o-xylene solvent systems. To the best of our knowledge, this study represents one of the best results with the SM donor and fullerene derivative acceptor materials that have shown the device performance with halogen-free solvents.

Efficient heterojunction solar cells based on the synergy between planarity and dipole moment in fluorinated-thienothiophenes-based donor-acceptor polymers

Polymers consisting of benzodithiophene, dithienopyrrole derivative donor monomers and thiophene derivative acceptor units are synthesized. The effects of F on optical performance for several Donor-Acceptor conjugated polymer systems are investigated. The introduction of F is conducive to increasing the dipole moment of the molecule for effective intramolecular charge transmission. The incorporation of F in acceptor unit improves molecular planarity simultaneously. It is found that dipole moment and molecular planarity play a synergistic role in photovoltaic performance. Under the premise of ensuring the planarity, the dipole moment is enhanced, the charge transfer within the molecule can also be strengthened, thus, the short-circuit current is greatly increased. The theoretical calculations show and explain the effect of the F on the dipole moment. Finally, a PCE of 4% is achieved with a large short-circuit current density of 14.36 mA cm−2. These results represent a synergy between planarity and dipole moment for improving the PCE.

(Invited) Inverted Planar Perovskite Solar Cells Using Coordination Fullerene Polymers As Acceptor Layer

Perovskite solar cells can be composed of thin film of perovskite donor and fullerene derivative acceptor sandwiched between a PEDOT:PSS coated ITO positive electrode and a low work function metal negative electrode. So far, [6,6]-phenyl-C61-butrilic acid methyl ester (PC60BM) and its corresponding C70 derivative (PC70BM) have been dominantly used as the acceptors in these solar cells.1 Fullerenes and fullerene derivatives can be incorporated into polymeric structure with transition metal atoms (Pd, Pt) or metal complexes units (-Ir(CO)2-, -Rh(CF3CO2)2-, -Ni[P(CH3)3]-).2 They can be formed under chemical and electrochemical conditions. Coordination polymers of fullerene and palladium, C60Pdx (x = 1-3), have been investigated most intensively. The chemical synthesis of this material is carried out in benzene solution containing fullerene and zero-valent palladium complex as precursors for polymerization process. The same procedure has been applied for the formation of coordination polymers of fullerene derivatives, PC60BM and PC70BM. These polymers formed regularly sized spherical particles with diameter of about 120 nm (Fig. 1). They also exhibit electrochemical activity in the potential range of fullerene cage reduction (Fig. 2). Electron transfer on the polymeric backbone results in the significant increase of the conductivity of the polymeric material.3 Coordination polymers containing PC60BM and PC70BM can be used as an acceptor layer in perovskite solar cells. We anticipate an improvement in power conversion efficiency and stability of the devices in comparison to the solar cells based on tin crystalline films of PC60BM and PC70BM. Meng, L.; You, J.; Guo, T.F.; Yang, Y. Chem. Res. 2016, 49, 155-165.Balch, A.L.; Winkler, K. Chem. Rev. 2016, 116, 3812-3882.Gradzka, E.; Wysocka-Zolopa, M.; Winkler, K. Phys. Chem. C 2014, 118, 14061-14072. Figure 1

Rational Design of Dithienopicenocarbazole-Based Dyes and a Prediction of Their Energy-Conversion Efficiency Characteristics for Dye-Sensitized Solar Cells

A series of metal-free organic donor–acceptor (D–A) derivatives (ME01–ME06) of the known dye C281 were designed using first-principles calculations in order to evaluate their potential for applications in dye-sensitized solar cells (DSSCs). Their physical and electronic properties were calculated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). These include molecular properties that are required to assess the feasibility of a dye to function in DSSCs: UV–vis absorption spectra, light-harvesting efficiency (LHE), and driving forces of electron injection (ΔGinj). ME01, ME02, and ME04 are predicted to exhibit broad absorption optical spectra that cover the entire visible range, rendering these three dyes promising DSSC prospects. Device-relevant calculations on these three short-listed dyes and the parent dye C281 were then performed, whereupon the dye molecules were adsorbed onto anatase TiO2 surfaces to form the DSSC working electrode. Associated DSSC device cha...

Dithieno[3,2-b:2',3'-d]pyrrol Fused Nonfullerene Acceptors Enabling Over 13% Efficiency for Organic Solar Cells.

A new electron-rich central building block, 5,5,12,12-tetrakis(4-hexylphenyl)-indacenobis-(dithieno[3,2-b:2',3'-d]pyrrol) (INP), and two derivative nonfullerene acceptors (INPIC and INPIC-4F) are designed and synthesized. The two molecules reveal broad (600-900 nm) and strong absorption due to the satisfactory electron-donating ability of INP. Compared with its counterpart INPIC, fluorinated nonfullerene acceptor INPIC-4F exhibits a stronger near-infrared absorption with a narrower optical bandgap of 1.39 eV, an improved crystallinity with higher electron mobility, and down-shifted highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels. Organic solar cells (OSCs) based on INPIC-4F exhibit a high power conversion efficiency (PCE) of 13.13% and a relatively low energy loss of 0.54 eV, which is among the highest efficiencies reported for binary OSCs in the literature. The results demonstrate the great potential of the new INP as an electron-donating building block for constructing high-performance nonfullerene acceptors for OSCs.