Conjugated Donor Acceptor Research Articles

A novel quinoxaline-based donor-acceptor type electrochromic polymer

We synthesize a quinoxaline-based novel conjugated donor–acceptor random copolymer containing benzodithiophene and 2,5-difluorophenylenedithiophene units as electron donors (coded r-PQ) and investigate the electrochromic properties of the material. Despite its high molecular weight, r-PQ is highly soluble in organic solvents owing to the side chain of alkoxy at the meta-position of the phenyl ring. The r-PQ film exhibits excellent redox-promoted blue to transmissive-state color switching with high coloration efficiency (>250cm2/C) and a fast response time (<0.5s). These results suggest that our quinoxaline-based random copolymer could be a promising candidate as an organic electrochromic material.

Random Copolymers Allow Control of Crystallization and Microphase Separation in Fully Conjugated Block Copolymers

Thin films of fully conjugated donor–acceptor block copolymers composed of an electron donating block and an electron accepting block can be used as single component photoactive layers in organic photovoltaic (OPV) devices. In order to realize their full potential, control over microphase separation and thin-film morphology are critical. In conjugated block copolymer systems where one or more blocks can crystallize, the morphological evolution is governed by the competition between microphase separation and crystallization. In this work, we control crystallization of fully conjugated block copolymers with a random copolymer block. We suppress the crystal packing of poly(3-hexylthiophene-2,5-diyl) (P3HT) through the insertion of a small number of 3-octylthiophene (3OT) units within the chains, yielding poly(3-hexylthiophene-2,5-diyl-random-3-octylthiophene-2,5-diyl) (P[3HT-r-3OT]). While crystallization of P3HT dominates the morphology and prevents microphase separation in poly(3-hexylthiophene-2,5-diyl)-b...

Investigation of the push–pull effects on β-functionalized zinc porphyrin coordinated to C60 donor–acceptor conjugates

Two novel β-functionalized push–pull zinc porphyrins with amine or phenyl push-groups and cyclic imide or carboxylic esters pull-groups have been newly synthesized for light energy harvesting applications. The ethynylphenyl spacers extended the conjugation of the porphyrin π-systems, as reflected by their red-shifted absorbance and fluorescence spectra. Computational studies performed at the B3LYP/6-31G* level indicated no steric hindrance between the porphyrin π-system and the substituents. The calculated HOMO and LUMO orbitals displayed significant delocalization in 1, where the electron density in the HOMO was localized over the push groups, whereas the LUMO was extended over the porphyrin π- and pull-groups. On the other hand, 2 did not display significant orbital segregation, which is attributed to its weaker push–pull character. Electrochemical studies revealed smaller HOMO–LUMO gaps for the push–pull zinc porphyrins. As a consequence of the push–pull effects, reduction in fluorescence intensity and lifetime was observed. Femtosecond transient absorption spectral studies revealed successful formation of singlet excited state in both of the push–pull porphyrins. Donor–acceptor conjugates were subsequently built and characterized by coordinating an electron acceptor, C60Im, via metal–ligand axial coordination. Efficient photo-induced charge separation in both donor–acceptor conjugates was witnessed wherein the charge-separated states persisted tens of nanoseconds prior returning to the ground state.

Aggregation and Solubility of a Model Conjugated Donor-Acceptor Polymer.

In conjugated polymers, solution-phase structure and aggregation exert a strong influence on device morphology and performance, making understanding solubility crucial for rational design. Using atomistic molecular dynamics (MD) and free-energy sampling algorithms, we examine the aggregation and solubility of the polymer PTB7, studying how side-chain structure can be modified to control aggregation. We demonstrate that free-energy sampling can be used to effectively screen polymer solubility in a variety of solvents but that solubility parameters derived from MD are not predictive. We then study the aggregation of variants of PTB7 including those with linear (octyl), branched (2-ethylhexyl), and cleaved (methyl) side chains, in a selection of explicit solvents and additives. Energetic analysis demonstrates that while side chains do disrupt polymer backbone stacking, solvent exclusion is a critical factor controlling polymer solubility.

Paddle-Wheel BODIPY-Hexaoxatriphenylene Conjugates: Participation of Redox-Active Hexaoxatriphenylene in Excited-State Charge Separation to Yield High-Energy Charge-Separated States.

Hexaoxatriphenylene, a scaffold linker often utilized in building covalent organic frameworks, is shown to be electroactive and a useful entity to build light energy-harvesting donor-acceptor systems. To demonstrate this, new donor-acceptor conjugates have been synthesized by employing BODIPY as a sensitizer. Excited-state electron transfer leading to high-energy charge-separated states, useful to drive energy-demanding photocatalytic reactions, from the electron-rich hexaoxatriphenylene to 1BODIPY*, in the synthesized tri-BODIPY-hexaoxatriphenylene "paddle-wheel" conjugates, has been successfully demonstrated using femtosecond transient absorption spectroscopy. The measured rate of charge separation was in the range of ∼3-10 × 1011 s-1, revealing ultrafast charge separation.

Naphthalene Diimide Copolymers by Direct Arylation Polycondensation as Highly Stable Supercapacitor Electrode Materials

Conjugated donor–acceptor copolymers based on naphthalene diimide (NDI) as acceptor and thiophene-terminated oligophenylenevinylene as donor moieties (P1 and P2, respectively) were synthesized using the direct (hetero) arylation (DHAP) polymerization route. Nitrile groups were introduced at the vinylene linkage in one copolymer (P2) to fine-tune its electrochemical properties. Both polymers show π–π* transition in the 300–480 nm region and intramolecular charge transfer (ICT) from thiophene to NDI in the 500–800 nm region in the absorption spectra. P2 exhibits a blue-shifted intramolecular charge transfer (ICT) band in the absorption spectrum as well as a lower reduction potential in the cyclic voltammogram compared to the analogous polymer without the nitrile substitution (P1). The two polymers were evaluated as type III supercapacitor materials by preparing composite electrodes with carbon nanotubes (CNTs) and employing 0.5 M H2SO4 as the electrolyte. Their performance was compared with that of P(NDI2OD...

A DFT analysis of the ground and charge-transfer excited states of Sc3N@Ih-C80 fullerene coupled with metal-free and zinc-phthalocyanine.

Endohedral metallofullerenes and phthalocyanine derivatives are recognized as excellent active materials in organic photovoltaics (OPVs). The tri-metallic nitride endohedral C80 fullerenes have greater absorption coefficients in the visible region and electron-accepting abilities similar to C60, which can allow for higher efficiencies in OPV devices. In this work, we have investigated the ground and charge transfer excited states of two co-facial donor-acceptor (D-A) molecular conjugates formed by the non-covalent coupling of trimetallic nitride endohedral fullerene (Sc3N@Ih-C80) with metal-free (H2Pc) and zinc-phthalocyanine (ZnPc) chromophores using DFT calculations. The charge transfer (CT) excitation energies are calculated using the perturbative delta-SCF method that enforces orthogonality between the ground and excited states. The binding energies calculated using the PBE and DFT-D3 methods indicate that the dispersion effects play an important role in the stabilization of these complexes. The ground state dipole moment of the Sc3N@C80-H2Pc dyad is much larger than that of Sc3N@C80-ZnPc, but this is reversed in the excited state where the dipole moment of Sc3N@C80-ZnPc increases significantly. The lowest few excitation energies in the gas phase for the two complexes are very close, in the range of 1.51-2.66 eV for Sc3N@C80-ZnPc and 1.51-2.71 eV for the Sc3N@C80-H2Pc complex. However, the lower ionization potential and lower exciton binding energy make the Sc3N@C80-ZnPc dyad a better candidate for OPVs as compared to the Sc3N@C80-H2Pc dyad.

Triplet electron transfer and spin polarization in a palladium porphyrin-fullerene conjugate.

Transient electron paramagnetic resonance (TREPR) spectroscopy is used to investigate the pathway and dynamics of electron transfer in a palladium porphyrin-fullerene donor-acceptor conjugate. The heavy Pd atom in the porphyrin greatly enhances the rate of intersystem crossing and as a result, electron transfer from the porphyrin to fullerene occurs via the porphyrin triplet state. The sign of the polarization pattern of the radical pair generated by the electron transfer is opposite in benzonitrile and the liquid crystal 5CB. This difference is the result of a change in sign of the spin-spin coupling, which allows the values of the dipolar and exchange couplings between the electrons in the charge-separated state to be estimated. In addition to the radical pair, signals from the fullerene triplet state are also observed. The polarization of the fullerene triplet state inverts with time, while the radical pair signal decays to a multiplet pattern that persists for times longer than the spin-lattice relaxation time. A kinetic model, developed to explain these effects, reveals that forward and reverse electron transfer between the charge-separated state and the fullerene takes place. This process, combined with singlet recombination of the radical pair accounts for the inversion of the fullerene triplet state polarization and the long-lived multiplet polarization of the radical pair.

Exploring Tetrathiafulvalene–Carbon Nanodot Conjugates in Charge Transfer Reactions

AbstractCarbon nanodots (CNDs) were synthesized using low‐cost and biocompatible starting materials such as citric acid/urea, under microwave irradiation, and constant pressure conditions. The obtained pressure‐synthesized CNDs (pCNDs) were covalently modified with photo‐ and electroactive π‐extended tetrathiafulvalene (exTTF) by means of a two‐step esterification reaction, affording pCND‐exTTF. The electronic interactions between the pCNDs and exTTF were investigated in the ground and excited states. Ultrafast pump–probe experiments assisted in corroborating that charge separation governs the deactivation of photoexcited pCND‐exTTF. These size‐regular structures, as revealed by AFM, are stable electron donor–acceptor conjugates of interest for a better understanding of basic processes such as artificial photosynthesis, catalysis, and photovoltaics, involving readily available fluorescent nanodots.

Exploring Tetrathiafulvalene-Carbon Nanodot Conjugates in Charge Transfer Reactions.

Carbon nanodots (CNDs) were synthesized using low-cost and biocompatible starting materials such as citric acid/urea, under microwave irradiation, and constant pressure conditions. The obtained pressure-synthesized CNDs (pCNDs) were covalently modified with photo- and electroactive π-extended tetrathiafulvalene (exTTF) by means of a two-step esterification reaction, affording pCND-exTTF. The electronic interactions between the pCNDs and exTTF were investigated in the ground and excited states. Ultrafast pump-probe experiments assisted in corroborating that charge separation governs the deactivation of photoexcited pCND-exTTF. These size-regular structures, as revealed by AFM, are stable electron donor-acceptor conjugates of interest for a better understanding of basic processes such as artificial photosynthesis, catalysis, and photovoltaics, involving readily available fluorescent nanodots.

Bidirectional Solvatofluorochromism of a Pyrrolo[3,2-b]pyrrole–Diketopyrrolopyrrole Hybrid

Hybridization of electron donors and acceptors provides routes to long-wavelength absorbing and fluorescing dyes. Varying the coupling of low-lying charge-transfer (CT) states with the ground and different locally excited states profoundly affects the photophysics of such donor–acceptor conjugates. Herein, we hybridize an electron-deficient diketopyrrolopyrrole (DPP) moiety with an electron-rich pyrrolopyrrole (PP) that is symmetrically N-arylated with 4-nitrophenyl substituents. The lowest Franck–Condon state is located on the DPP ring structure and dominates the photophysics of the hybrid. Similar to the DPP moiety, the hybrid exhibits optical absorption that is invariant to the solvent media. The PP donor considerably modulates its fluorescence by undergoing electron transfer to the locally excited DPP to form a CT state. For nonpolar media, an increase in solvent polarity causes a bathochromic shift of the fluorescence reaching the longest wavelengths for chloroform and DCM. A further increase in the ...

Peripheral phenothiazine induced suppression of charge separation from the singlet excited zinc phthalocyanine to coordinated C60 in supramolecular donor–acceptor conjugates

Self-assembled donor–acceptor conjugates featuring zinc phthalocyanine carrying four entities of peripheral phenothiazine entities, (PTZ)[Formula: see text]ZnPc, axially coordinated to either phenyl imidazole or pyridine functionalized fulleropyrrolidine (C[Formula: see text]Im or C[Formula: see text]Py) has been newly designed, synthesized and characterized. Due to the direct connectivity of the phenothiazine entities to the ZnPc [Formula: see text]-system, efficient charge transfer type interactions suppressing fluorescence of ZnPc in (PTZ)[Formula: see text]ZnPc was observed. Axial coordination of C[Formula: see text]Im or C[Formula: see text]Py to the metal center of (PTZ)[Formula: see text]ZnPc served as an electron acceptor in the conjugates. Optical absorption studies revealed stable complex formation wherein the evaluated binding constants [Formula: see text] were found to be 3.9 × 10[Formula: see text] M[Formula: see text] for (PTZ)[Formula: see text]ZnPc:ImC[Formula: see text] and 3.3 × 10[Formula: see text] M[Formula: see text] for (PTZ)[Formula: see text]ZnPc:PyC[Formula: see text] conjugates with 1:1 molecular stoichiometry. Computational studies performed at the HF/[6-311G(d,p) for H, C, and N, and 6-311G(2df) for S and Zn] level revealed stable structures of the conjugates. The evaluated center-to-center and edge-to-edge distances for the (PTZ)[Formula: see text]ZnPc:ImC[Formula: see text] were 13.6 and 10.4 Å, while for the (PTZ)[Formula: see text]ZnPc:PyC[Formula: see text] conjugate these distances were 10.2 and 7.3 Å. That is, the C[Formula: see text] was about 3̃ Å closer to ZnPc in the latter conjugate. From the free-energy calculations, photoinduced electron transfer from the [Formula: see text]ZnPc* to fullerene within the conjugates was established to be an exothermic process, however, a hole transfer from ZnPc[Formula: see text] to peripheral PTZ was found to be energetically an uphill process. From femtosecond transient absorbance studies, occurrence of photoinduced charge separation in (PTZ)[Formula: see text]ZnPc:ImC[Formula: see text] was found to be weak due to the competing charge transfer interactions within the (PTZ)[Formula: see text]ZnPc and longer donor–acceptor distance while in the case of the (PTZ)[Formula: see text]ZnPc:PyC[Formula: see text] conjugate, electron transfer occurred competitively to yield radical ion-pairs. From nanosecond transient spectroscopy, lifetime of the (PTZ)[Formula: see text]ZnPc[Formula: see text]:PyC[Formula: see text] charge separated state was found to be in the 200 ns range, revealing charge stabilization to some extent.

Effect of molecular architecture on morphology in the nanostructures and its applications in superhydrophobicity and organic photovoltaics

Morphological structures with respect to the effect of carbazole derivatization, which are based on conjugated donor–acceptor moieties, are presently explored. In this work, light management studies, organic photovoltaics devices and surface properties are systematically investigated. Two carbazole derivatives Cz–Bt (carbazole–benzothiadiazole) and Cz–Bt–BT (carbazole–benzothiadiazole–bithiophene) are electrosprayed, resulting in triangle and spike (2-D and 3-D pyramids) structures, respectively. These 2-D and 3-D pyramids differ due to an additional bithiophene unit at the molecular level, which has imparted a higher degree of rotational freedom. The effects of derivatives, solution concentrations and solvents vapor pressure on morphology are studied. Further, these submicron-size pyramids are characterized by enhancement in light absorption due to scattering and multi-reflection. It is observed that 2-D pyramids enhance up to 44.4%, whereas 3-D pyramids enhance up to 18.7% of light absorption. Subsequently, these structures are characterized in organic photovoltaics architecture, using various layer design strategies, and, thus, we able to obtain insights about layer addition, with respect to structures size and morphology. In addition, the effect of fabrication procedure assisting in an increase in hydrophobicity is also demonstrated.

Charge Transport and Rectification in Donor–Acceptor Dyads

Organic, conjugated donor–acceptor (D–A) systems are essential components of photovoltaic devices. Design and optimization of D–A systems is typically based on trial-and-error experimentation methods that would benefit from fundamental physical insights on structure–function relationships at the molecular level. Here, we implement a nonequilibrium Green’s function methodology at the density functional theory (DFT) level and examine charge-transport and rectification properties of a series of conjugated D–A systems. We investigate 42 molecular junctions formed by D–A dyads bridging model gold electrodes, showing clearly how transport properties are determined by chemical composition, symmetry of frontier orbitals, and molecular conformation. Key properties are compared to experimental data. Notably, an inverse correlation between conductance and rectification is found, with relatively large rectification ratios caused by the asymmetry of frontier orbitals near the Fermi level. We discuss design principles ...

"Two-Point" Self-Assembly and Photoinduced Electron Transfer in meso-Donor-Carrying Bis(styryl crown ether)-BODIPY-Bis(alkylammonium)fullerene Donor-Acceptor Conjugates.

BF2 -chelated dipyrromethene, BODIPY, was functionalized to carry two styryl crown ether tails and a secondary electron donor at the meso position. By using a "two-point" self-assembly strategy, a bis-alkylammonium-functionalized fullerene (C60 ) was allowed to self-assemble the crown ether voids of BODIPY to obtain multimodular donor-acceptor conjugates. As a consequence of the two-point binding, the 1:1 stoichiometric complexes formed yielded complexes of higher stability in which fluorescence of BODIPY was found to be quenched; this suggested the occurrence of excited-state processes. The geometry and electronic structure of the self-assembled complexes were derived from B3LYP/3-21G(*) methods in which no steric constraints between the entities was observed. An energy-level diagram was established by using spectral, electrochemical, and computational results to help understand the mechanistic details of excited-state processes originating from 1 bis-styryl-BODIPY*. Femtosecond transient absorbance studies were indicative of the formation of an exciplex state prior to the charge-separation process to yield a bis-styryl-BODIPY.+ -C60.- radical ion pair. The time constants for charge separation were generally lower than charge-recombination processes. The present studies bring out the importance of multimode binding strategies to obtain stable self-assembled donor-acceptor conjugates capable of undergoing photoinduced charge separation needed in artificial photosynthetic applications.

Coumarin-indole conjugate donor–acceptor system: Synthesis and biological activity studies of two coumarin-indole based push–pull dyes

Classical techniques employed to determine the amount of extractable poly(hydroxyalkanoate)s (PHAs) from cells, are laborious and destructive. Sudan black staining is commonly used in the laboratory to investigate the presence of intracellular PHA. The aim of the present study was to develop a low-cost alternative technique to achieve a quick determination of extractable intracellular PHA. This methodology employs a basic laboratory spectroscopy equipment and Sudan black dye for spectra determination. The correlation between the content of PHA in cell samples taken directly from the culture flask and its spectra was determined using partial least square regression analysis and simple linear regression analysis. The best fit obtained for calibration correlation analysis (R2 = 0.944, RSE: 1.24%), together with the good extractable PHA predictions (RSE = 0.51%) demonstrate that the proposed methodology constitutes a fast way with high potential for the determination of extractable PHA. Based on its simplicity and flexibility, its application would be suitable in routine monitoring and rapid quantification in large-scale processes involving PHA metabolism.

Ambipolar charge transport in a donor–acceptor–donor‐type conjugated block copolymer and its gate‐voltage‐controlled thin film transistor memory

ABSTRACTWe demonstrate a fully conjugated donor–acceptor–donor (D–A–D) triblock copolymer, PBDTT–PNDIBT–PBDTT, which contains PBDTT as the donor block and PNDIBT as the acceptor block. The polymer was synthesized by end‐capping each block with a reactive unit, followed by condensation copolymerization between the two blocks. The physical, optical, and electrochemical properties of the polymer were investigated by comparing those of donor‐ and acceptor‐homopolymers (i.e., PBDTT and PNDIBT), which are the oligomeric monomers, and their blends. On using the newly synthesized block copolymer, ambipolar charge transport behavior was observed in the corresponding thin‐film transistor, and the behavior was compared to that of blend film of donor‐ and acceptor‐homopolymers. Owing to the presence of donor and acceptor blocks in a single polymer chain, it was found that the triblock copolymer can store two‐level information; the ability to store this information is one of the most intriguing challenges in memory applications. In this study, we confirmed the potential of the triblock copolymer in achieving distinct two‐stage data storage by utilizing the ambipolar charge trapping phenomenon, which is expected in donor and acceptor containing random and block copolymers in a thin‐film transistor. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3223–3235

Coumarin-indole conjugate donor-acceptor system: Synthesis, photophysical properties, anion sensing ability, theoretical and biological activity studies of two coumarin-indole based push-pull dyes

Two coumarin-indole conjugate fluorescent dyes having donor-acceptor-donor (D-A-D) (CI-1 and CI-2) were synthesized, and characterized using IR, 1H/13C NMR and HRMS. The absorption and emission properties of the dyes were determined in different solvents. The anion sensitivity and selectivity of the dyes were studied with some anions (CN−, F−, AcO−, Cl−, Br−, I−, HSO4− and H2PO4−) in DMSO, and their interaction mechanisms were evaluated by spectrophotometric and 1H NMR titration techniques. In addition, the molecular and electronic structures of CI-1, as well as the molecular complexes of CI-1, formed with the anions (F− and AcO−), were obtained theoretically and confirmed by DFT and TD-DFT calculations. CI-1 behaves as a colorimetric chemosensor for selective and sensitive detection of CN− in DMSO/H2O (9:1) over other competing anions such as F− and AcO−. However, only CN− interacts with chromophore CI-2 via Michael addition and the main absorption maxima shifts hypsochromically with an observed distinctive color change from orange to yellow. For using as a optic dye, the thermal stability properties of the dyes was determined by TGA (Thermal Gravimetric Analysis). Antimicrobial, antifungal and DNA-ligand interaction studies of the dyes were also examined. The dyes cause conformational changes on DNA and selectively bind to nucleotides of A/A and G/G.

Diketopyrrolopyrrole-Based Conjugated Polymer Entailing Triethylene Glycols as Side Chains with High Thin-Film Charge Mobility without Post-Treatments.

Side chain engineering of conjugated donor–acceptor polymers is a new way to manipulate their optoelectronic properties. Two new diketopyrrolopyrrole (DPP)‐terthiophene‐based conjugated polymers PDPP3T‐1 and PDPP3T‐2, with both hydrophilic triethylene glycol (TEG) and hydrophobic alkyl chains, are reported. It is demonstrated that the incorporation of TEG chains has a significant effect on the interchain packing and thin‐film morphology with noticeable effect on charge transport. Polymer chains of PDPP3T‐1 in which TEG chains are uniformly distributed can self‐assemble spontaneously into a more ordered thin film. As a result, the thin film of PDPP3T‐1 exhibits high saturated hole mobility up to 2.6 cm2 V−1 s−1 without any post‐treatment. This is superior to those of PDPP3T with just alkyl chains and PDPP3T‐2. Moreover, the respective field effect transistors made of PDPP3T‐1 can be utilized for sensing ethanol vapor with high sensitivity (down to 100 ppb) and good selectivity.

(Invited) Axially Assembled Photosynthetic Antenna-Reaction Center Mimics

A series of porphyrin based donor-acceptor conjugates in which the arrangement of various components are in perpendicular orientation to the porphyrin plane have been constructed and used to study the pathways of electron and energy transfer processes. The employed aluminum(III) porphyrin in these studies is found to be synthetically more advantageous as it provides reaction site on both faces of the porphyrin plane. The axial hydroxyl group on one side of the aluminum(III) porphyrin plane is able to form a covalent ester or ether bond with an energy harvester or electron acceptor while Lewis bases such as pyridine or an imidazole group form a metal-ligand axial coordination on other side of the plane hosting an electron donor or acceptor. The advantage of this configuration of the conjugates is that the donor and acceptor sides of the complex are located on opposite faces of the porphyrin which minimizes the rate of charge recombination. Moreover, the excited state \U0001d70b* orbital of porphyrin and axially coordinated ligand lie in the same space which causes an increase in the electronic coupling thus facilitating the electron/energy transfer processes. The distance dependence of sequential electron transfer in vertical, linear supramolecular triads constructed using tetrathiafulvalene (TTF), aluminum(III) porphyrin (AlPor) and fullerene (C60) entities will be discussed. Further, results of photoinduced energy transfer followed by electron transfer in antenna-reaction center mimicking BODIPY-AlPor-C60 supramolecular triads will be highlighted. Figure 1