Efficient Intramolecular Charge Transfer Research Articles

Nanoporous and nonporous conjugated donor-acceptor polymer semiconductors for photocatalytic hydrogen production.

Conjugated polymers (CPs) as photocatalysts have evoked substantial interest. Their geometries and physical (e.g., chemical and thermal stability and solubility), optical (e.g., light absorption range), and electronic properties (e.g., charge carrier mobility, redox potential, and exciton binding energy) can be easily tuned via structural design. In addition, they are of light weight (i.e., mainly composed of C, N, O, and S). To improve the photocatalytic performance of CPs and better understand the catalytic mechanisms, many strategies with respect to material design have been proposed. These include tuning the bandgap, enlarging the surface area, enabling more efficient separation of electron–hole pairs, and enhancing the charge carrier mobility. In particular, donor–acceptor (D–A) polymers were demonstrated as a promising platform to develop high-performance photocatalysts due to their easily tunable bandgaps, high charge carrier mobility, and efficient intramolecular charge transfer. In this minireview, recent advances of D–A polymers in photocatalytic hydrogen evolution are summarized with a particular focus on modulating the optical and electronic properties of CPs by varying the acceptor units. The challenges and prospects associated with D–A polymer-based photocatalysts are described as well.

Comparative Studies on the Structure-Performance Relationships of Phenothiazine-Based Organic Dyes for Dye-Sensitized Solar Cells.

A D–A−π–A dye (PTZ-5) has been synthesized by introducing a benzothiadiazole (BTD) unit as an auxiliary acceptor in a phenothiazine-based D−π–A dye(PTZ-3) to broaden its spectral response range and improve the device performance. Photophysical properties indicate that the inclusion of BTD in the PTZ-5 effectively red-shifted the absorption spectra by reducing the Egap. However, the device measurements show that the open-circuit voltage (Voc) of PTZ-5 cell (640 mV) is obviously lower than that of the PTZ-3 cell (710 mV). This results in a poor photoelectric conversion efficiency (PCE) (4.43%) compared to that of PTZ-3 cell (5.53%). Through further comparative analysis, we found that the introduction of BTD increases the dihedral angle between the D and A unit, which can reduce the efficiency of intramolecular charge transfer (ICT), lead to a less qCT and lower molar extinction coefficient of PTZ-5. In addition, the ESI test found that the lifetime of the electrons in the PTZ-5 cell is shorter. These are the main factors for the above unexpected result of PCE. Our studies bring new insights into the development of phenothiazine-based highly efficient dye-sensitized solar cells (DSSCs).

A fluorescent tool for sensing the battery-pollution event in soil samples based on Zn2+-triggering ratiometric signals

The leakage of hazardous substances from batteries leads amount of pollution events for their high toxicity and universal use all over the world. Herein, a fluorescent sensor based on triphenylamine (TPAI) was designed to monitor the battery pollution in the real soil examples. Because Zn2+composes a large part of primary and secondary batteries, TPAI was constructed for high affinity of Zn2+ within an efficient intramolecular charge transfer process that could output an obvious green-to-red (510–600 nm) signal to avoid interference from the background substances. In this way, TPAI showed a low detection limit (4.16 × 10−9 M) and high binding constants towards Zn2+ (2.82 × 1012 M−1). Moreover, TPAI exhibited excellent selectivity for Zn2+ over other metal ions and several common compounds in soil. The sensing mechanism indicated that the selectivity might need to be further optimized through adjusting the bulk of donor segment of TPAI. Then, TPAI was used to discriminate the polluted and unpolluted soil samples through a feasible on-line detection proposal under the self-made mobile platform. Combining with the fluorescent sensors and our mobile platform, we believe this work can provide a practical tool for monitoring the pollution events in diverse environmental examples.

Donor-Acceptor Polymer Based on Planar Structure of Alkylidene-Fluorene Derivative: Correlation of Power Conversion Efficiency among Polymer and Various Acceptor Units.

This study synthesized a novel polymer, poly(alkylidene fluorene-alt-diphenylquinoxaline) (PAFDQ), based on a planar alkylidene-fluorene and a highly soluble quinoxaline derivative through the Suzuki coupling reaction. We designed a novel molecular structure based on alkylidene fluorene and quinoxaline derivatives due to compact packing property by the planar structure of alkyidene fluorene and efficient intra-molecular charge transfer by quinoxaline derivatives. The polymer was largely dissolved in organic solvents, with a number average molecular weight and polydispersity index of 13.2 kg/mol and 2.74, respectively. PAFDQ showed higher thermal stability compared with the general fluorene structure owing to its rigid alkylidene-fluorene structure. The highest occupied and lowest unoccupied molecular orbital levels of PAFDQ were −5.37 eV and −3.42 eV, respectively. According to X-ray diffraction measurements, PAFDQ exhibited the formation of an ordered lamellar structure and conventional edge-on π-stacking. The device based on PAFDQ/Y6-BO-4Cl showed the best performance in terms of short circuit current (9.86 mA/cm2), open-circuit voltage (0.76 V), fill factor (44.23%), and power conversion efficiency (3.32%). Moreover, in the PAFDQ/Y6-BO-4Cl-based film, the phase separation of donor-rich and acceptor-rich phases, and the connected dark domains, was observed.

Replacing aromatic π-system with cycloalkyl in triphenylamine dyes to impact intramolecular charge transfer in dyes pertaining to dye-sensitized solar cells application

In this study, five dyes comprising different donor moieties were proposed with a new design approach. In the triphenylamine (TPA) moiety, the lone pair electron on N takes part in resonance with three phenyl rings. As a result, the donating ability of TPA decreases in TPA-based dyes and hence the intramolecular charge transfer (ICT). We have proposed cycloalkyl moieties in place of phenyl moieties to stop the participation in the resonance of the lone pair with the other two phenyl rings so that the available lone pair on N will be pumped towards acceptor to achieve an efficient ICT. All dyes were subjected to density functional theory (DFT) and time-dependent DFT to evaluate their ground and excited-state properties. The projected density of state and natural bond orbital analyses were carried out to confirm the ICT from the donor to the acceptor moiety and also to comprehend the donating ability of the newly proposed donor moieties. The reorganization energy of the dyes was calculated to find out the conformational changes that occurred during photoexcitation. The dyes were attached to (1 0 1) anatase surface of TiO2 to understand the electron transfer from the excited-state of the dye to the conduction band of the TiO2. The adsorption energy of the dyes onto the (1 0 1) anatase surface of the TiO2 was also evaluated. The absence of defect states in the density of states spectrum indicated the smooth electron transfer at the dye/TiO2 interfaces.

Exploring the impact of central core modifications among several push-pull configurations to enhance nonlinear optical response

The present study explores a series of novel donor-π-acceptor (D-π-A) molecules containing 4,4′-dimethyldiphenylamine moiety as donor, 4,4′-dinitrodiphenylborane as acceptor while different π-bridges as efficient linkers between them, which comprises of (−HCCH−)n, (−Ph−)n and (−Ph ̶ HCCH−)n combinations for compounds in series 1, 2 and 3, respectively. Quantum chemical computations are applied to calculate the linear polarizability (α), first (β) and second (γ) hyperpolarizabilities. A comparative analysis is performed considering an increase of NLO polarizabilities as a function of different π-linkers. Among the investigated compounds, 3c shows the largest first and second hyperpolarizabilities of 1378 × 10−30 and 34971 × 10−36 esu, respectively. Interestingly, an increase in NLO polarizability is observed by modifying the π-conjugated bridges and the largest NLO polarizability is observed for series 3 possessing (Ph ̶ HCCH−)n π-linker which is found due to its lower transition energy and higher oscillator strengths. Furthermore, TD-DFT investigations, frontier molecular orbitals (FMOs) and electron density difference (EDD) maps analysis have shown a more efficient intramolecular charge transfer character from donor to acceptor moieties through (Ph ̶ HCCH−)n π-linkers. The density of states (DOS) maps are showing explicit contributions of electronic states from different fragments of a molecular system where the partial contributions of (Ph ̶ HCCH−)n π-linkers is seen significant in HOMO-LUMO orbitals of all the systems in series number 3. Thus, we believe that our study will highlight the importance of different D-π-A chromophores having variant types of π-conjugation cores as discussed in the present investigation.

Uncovering Structure–Property Relationships in Push–Pull Chromophores: A Promising Route to Large Hyperpolarizability and Two-Photon Absorption

In this investigation, we report the first hyperpolarizabilities and two-photon absorption cross sections of a large series of 12 push–pull cationic chromophores. All of these dyes show a dipolar acceptor+–π–donor structure, where the nature of the donor and acceptor units and π-bridge was synthetically tuned to allow insightful comparisons among the molecules. The hyperpolarizability was obtained through a solvatochromic method, by exploiting the rare negative solvatochromism exhibited by the investigated compounds. The two-photon absorption cross sections were determined through two-photon excited fluorescence measurements by means of a tunable nanosecond laser system for sample excitation. The nonlinear optical properties were discussed relatively to the photoinduced intramolecular charge transfer occurring in these donor–acceptor systems, investigated by femtosecond transient absorption experiments. We found a strong increase in hyperpolarizability upon increasing the molecular conjugation. Unexpectedly, the hyperpolarizability is almost unaffected by an increase in donor/acceptor strength and intramolecular charge transfer degree. Differently, the two-photon absorption cross sections of these dyes are enhanced by an increase in both molecular conjugation and intramolecular charge transfer efficiency. Several recent literature works have reported at the same time scattered information about the hyperpolarizability and two-photon absorption of small organic molecules. Our investigation is, to the best of our knowledge, the first attempt to uncover detailed structure–property relationships for these two nonlinear optical properties. Our results represent a promising route to achieve large hyperpolarizability and two-photon absorption in push–pull dyes and may drive the design of new efficient nonlinear optical materials.

Intramolecular charge transfer-based spirobifluorene-coupled heteroaromatic moieties as efficient hole transport layer and host in phosphorescent organic light-emitting diodes

In this study, we report two efficient intramolecular charge transfer (ICT) compounds with versatile functionality as hole transporting layers (HTL) and hosts in emission layer (EML) of phosphorescent organic light emitting diodes (Ph-OLEDs) with donor-acceptor-donor structures. In both molecules, 9,9′-spirobifluorene (SBF) was employed as a common electron acceptor, while phenoxazine (PXZ) or phenothiazine (PTZ) were used as donors. The molecules 2,7-di(10H-phenoxazin-10-yl)-9,9′-spirobi[fluorene] (SBF-PXZ) and 2,7-di(10H-phenothiazin-10-yl)-9,9′-spirobi[fluorene] (SBF-PTZ) were synthesized via a Buckwald-Hartwig cross-coupling reaction in a single step that exhibited typical ICT phenomena. The extremely twisted geometrical configurations of SBF-PXZ and SBF-PTZ may allow for effective intramolecular charge-transfer. Both molecules exhibited strong absorption and emission characteristics in the visible region in solution as well as in the thin film form; significant positive solvatochromism was also observed for both compounds. The replacement of PTZ donor with the PXZ donor caused a bandgap reduction together with an improved ionization potential (IP). The deeper IP (>5.1 eV), greater glass transition temperature, and higher hole mobility extracted from the hole only devices of both molecules revealed them as superior candidates for HTL applications (with/without exciton blocking layers) in Ph-OLEDs. It is further corroborated by the enhanced half-life time of Ph-OLEDs with SBF-PXZ/SBF-PTZ HTLs. Moreover, the OLED performances with SBF-PTZ and SBF-PXZ as EMLs and hosts for phosphorescent dopant OLEDs have exemplified the versatility of the proposed ICT compounds.

Theoretical study of T shaped phenothiazine/carbazole based organic dyes with naphthalimide as π-spacer for DSSCs.

Eight novel T shaped phenothiazine/carbazole based organic dyes with naphthalimide as π-spacer were designed, and the geometries, electronic structures, and optical features of these isolated dyes and dye-(TiO2)9 systems were investigated with density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations. Some quantify factors influencing the energy conversion efficiency (PCE) such as the light harvesting efficiency (LHE), electron injection driving force (ΔGinject) and dye regeneration driving force (ΔGreg) were also calculated for dye-sensitized solar cells (DSSCs) applications. It is found that these dyes show a good performance of electron injection and dye regeneration owing to the proper value of ΔGinject and ΔGreg. The optimized geometries of the non-planar molecular configuration of donor and the planar structure of the naphthalimide conjugated bridge are beneficial to efficient intramolecular charge transfer and the suppression of molecular aggregation. The properties about the electronic structure and absorption spectra indicate that replacement of benzene with thiophene unit near to cyanoacetic acid acceptor can generate more efficient conjugation effect and achieve red shift of absorption spectra, resulting a higher Jsc and Voc in DSSCs device. The theoretical results reveal that DTPH2, DTPH4, DTCA2 and DTCA4 would be used as potential sensitizers for DSSCs applications.

Near-Infrared Fluorescent pH Responsive Probe for Targeted Photodynamic Cancer Therapy

We developed a pH dependent amino heptamethine cyanine based theranostic probe (I2-IR783-Mpip) that can be activated by near infrared light. I2-IR783-Mpip, in acidic condition, exhibited an intense, broad NIR absorption band (820–950 nm) with high singlet oxygen generation upon exposure to NIR light (~850 nm). Theoretical calculations showed that the protonation of the probe in an acidic environment decreased the molecular orbital energy gaps and increased the intramolecular charge transfer efficiency. I2-IR783-Mpip exhibited good photodynamic efficiency towards liver hepatocellular carcinoma cells under physiological and slightly acidic conditions while normal human embryonic kidney cells remained alive under the same conditions. Detection of intracellular reactive oxygen species (ROS) in cells treated with I2-IR783-Mpip after NIR light exposure confirmed PDT efficiency of the probe in acidic environment. Moreover, I2-IR783-Mpip also demonstrated efficient phototoxicity under deep-seated tumour cell system. We believed this is the first PDT agent that possesses intrinsic tumour binding and selectively eradicate tumour in acidic environment under 850 nm NIR lamp.

Structure-property relationships in multi-stimuli responsive BODIPY-biphenyl-benzodithiophene TICT rigidochromic rotors exhibiting (pseudo-)Stokes shifts up to 221 nm.

Structure-property relationships of donor-π-acceptor (D-π-A) type molecular dyad (pp-AD) and triads (pp-ADA and Me-pp-ADA) based on benzodithiophene and BODIPY with biphenyl spacers have been reported. Rotors pp-AD and pp-ADA showed efficient twisted intramolecular charge transfer (TICT) with near infrared (NIR) emissions at ∼712 nm and ∼725 nm with (pseudo-)Stokes shifts of ∼208 nm and ∼221 nm, respectively, and prominent solvatochromism. A structurally similar triad, Me-pp-ADA, with tetramethyl substituents on the BODIPY core instead was TICT inactive and exhibited excitation energy transfer with a transfer efficiency of ∼88% as revealed using steady state emission and transient absorption measurements. Rotors pp-AD and pp-ADA showed NIR emission with an enhancement in intensity with the addition of water in THF solution as well as a pronounced change in emission intensity with temperature and viscosity variations, which justify their utility as temperature and viscosity sensors. Furthermore, the linear correlation of lifetime with fluorescence intensity ratios of the donor and acceptor justifies the rigidochromic behaviour of these rotors.

N‐Ethyl Carbazole Derived D‐π‐A‐π‐D Based Fluorophores: Consolidated Spectroscopic, Viscosity and DFT Studies

AbstractThis article reports design and synthesis of three new fluorophores (5 a‐c) with the donor‐π‐acceptor‐π‐donor motif, where dicyano vinylene group is the central acceptor, N‐ethyl carbazole group is a fixed donor and varying the N‐substituted secondary donors so as to study their photophysical behavior. Based on the systematic photophysical and theoretical reconnaissances, the fluorophores structure‐property relationships are defined. Their spectral and photophysical behaviors are affected by the solvent polarity, with a significant bathochromic shift in emission and large Stoke shifts being observed in polar solvents. Contrary to dipolar asymmetric analogue this system shows an efficient intramolecular charge transfer as observed from various solvent polarity plots. For 5 a, 5 b, and 5 c, the viscosity induced emission studies show respectively 3.78, 6.53, and 6.82 times enhancement in their fluorescence intensity and hence act as a fluorescent molecular rotor (FMR). The structure and electronic properties of these fluorophores were evaluated using density functional theory computations using B3LYP/6‐311++G(d,p). The frontier molecular orbitals and the optimized geometry reveal that secondary donors in each fluorophore donate the electron and not the N‐ethyl carbazole group which is more twisted. The non‐linear and linear optical properties were determined employing solvatochromic and computational methods in solvents of varying polarities with results falling within the expected limiting values. The linear and non‐linear optical properties of the fluorophores change with the strength of different secondary donors used and solvent polarity. The two photon absorption cross‐section described using two level approximation is highest for 5 b (115‐172 GM).

Structural Effect on the Cellular Selectivity of an NIR-Emitting Cyanine Probe: From Lysosome to Simultaneous Nucleus and Mitochondria Selectivity with Potential for Monitoring Mitochondria Dysfunction in Cells.

Bright red to NIR emitting cyanine probes 2-3 were synthesized in very good yields. Probes 2-3 exhibited excellent fluorescent quantum yields (ϕfl ≈ 0.1-0.4) and large Stokes shift (Δλ > 150 nm) due to efficient intramolecular charge transfer (ICT) in the conjugated π system. Organelle specificity of these probes was investigated by live cell fluorescence confocal microscopy studies. Probe 3 exhibited the ability to visualize the cell nucleus and mitochondria simultaneously in live cell samples during imaging experiments. However, in structurally modified probe 2 with different substituents (i.e., benzothiazolium vs benzothiazole), the selectivity of the probe switched entirely toward cellular lysosomes. Spectrometric DNA titration experiments were conducted to confirm the DNA/nucleus selectivity of probe 3. The study further evaluates the role of the substituent toward DNA selectivity. Probe 3 was identified as a valuable fluorescent marker to visually identify and study mitochondrial dysfunction in live cells via fluorescent confocal microscopy.

Porphyrin sensitizers involving a fluorine-substituted benzothiadiazole as auxiliary acceptor and thiophene as π bridge for use in dye-sensitized solar cells (DSSCs)

Three ‘donor–acceptor–π bridge–acceptor’ (D–A–π–A) type zinc porphyrin sensitizers TH-0F, TH-1F and TH-2F with a benzothiadiazole (BTD) unit bearing no fluorine, one fluorine and two fluorine atoms, respectively, as the auxiliary acceptor and thiophene as the π bridge were designed and synthesized for use in dye-sensitized solar cells (DSSCs). The influence of fluorine atom and thiophene unit on the photophysical and photochemical properties of the sensitizers was investigated. It was shown that the photon to current conversion efficiencies (PCE) of three sensitizer-based devices increased in the order of TH-2F > TH-1F > TH-0F, with the highest PCE of 6.98% achieved for the TH-2F-based device. To further understand the molecular structure of the TH series of dyes, a density functional (DFT) calculation was performed. The result suggests that the strong electron-withdrawing ability of the fluorine atom, along with the intramolecular interaction between the auxiliary acceptor and thiophene, optimized the electronic configuration, thereby facilitating the intramolecular charge transfer efficiency and ultimately improving the performance of the corresponding device.

Molecular Engineering of a Donor-Acceptor Polymer To Realize Single Band Absorption toward a Red-Selective Thin-Film Organic Photodiode.

Herein, we explore the strategy of realizing a red-selective thin-film organic photodiode (OPD) by synthesizing a new copolymer with a highly selective red-absorption feature. PCZ-Th-DPP, with phenanthrocarbazole (PCZ) and diketopyrrolopyrrole (DPP) as donor and acceptor units, respectively, was strategically designed/synthesized based on a time-dependent density functional theory calculation, which predicted the significant suppression of the band II absorption of PCZ-Th-DPP due to the extremely efficient intramolecular charge transfer. We demonstrate that the synthesized PCZ-Th-DPP exhibits not only a high absorption coefficient within the red-selective band I region, as theoretically predicted, but also a preferential face-on intermolecular structure in the thin-film state, which is beneficial for vertical charge extraction as an outcome of a glancing incidence X-ray diffraction study. By employing PCZ-Th-DPP as a photoactive layer of Schottky OPD, to fully match its absorption characteristic to the spectral response of the red-selective OPD, we demonstrate a genuine red-selective specific detectivity in the order of 1012 Jones while maintaining a thin active layer thickness of ∼300 nm. This work demonstrates the possibility of realizing a full color image sensor with a synthetic approach to the constituting active layers without optical manipulation.

Revealing high hydrogen evolution activity in zinc porphyrin sensitized hierarchical porous TiO2 photocatalysts

In this work, a dye/TiO2 system for hydrogen generation via the reduction of water has been investigated. The use of simple and template free synthesis process for hierarchical porous architecture of TiO2 (HPT) with a panchromatic Zinc-porphyrin (LG5) sensitizer has been identified as the potential material in photoinduced hydrogen production. The effect of the dye absorbed by the Pt-HPT has been tested for the hydrogen production under visible light irradiation in presence of triethanolamine (TEOA) or Glycerol (Gly) as sacrificial electron donor (SED). The enhanced activity and effective charge transfer from the dye to the TiO2 molecule is significant in the PHPT-LG5 composite. The PHPT-LG5 catalyst exhibited higher photocatalytic activity of 4196 μmol g−1 h−1 with an impressive turnover numbers (TON) of 8392 and apparent quantum yield (AQY) of 7.43% of light irradiation using 450 W Xe lamp when compared to the corresponding simple semiconductor as well as the N719 dye loaded catalysts. The acrylic group present in the dye molecule helps in binding the semiconductor with the dye molecule and leads to superior photocatalytic activity. The diffuse reflectance spectroscopy (DRS), and computational studies of the dye molecule and the composite suggests the better photocatalytic performance of the composite. The Fourier Transform Infra-Red Spectroscopy (FTIR) studies reveals the strong attachment of the dye molecule with the semiconductor hierarchical porous TiO2 (HPT) results in the enhancement in hydrogen production, the stability tests of the photocatalyst shows higher reproducibility at neutral pH in TEOA. A systematic study of LG5 with sacrificial electron donors and pH were performed and are correlated with the photocatalytic activity of N719 dye. The presence of the cyanoacrylic group as an anchoring group in the LG5 leads to red shift in S and Q bands suggesting the efficient intramolecular charge transfer behavior (CT) and possess strategies for broadening the light harvesting properties. The present work opens up a new window toward solar energy conversion with extended light harvesting capacity and enhanced photocatalytic activity.

Effect of additional phenothiazine donor and thiophene π-bridge on photovoltaic performance of quinoxaline cored photosensitizers

A series of quinoxaline-based sensitizers were designed through the elongation of π-conjugation length based on the sense of directional electron transport from donor to acceptor. To facilitate an efficient intramolecular charge transfer, we introduced additional donor moieties and thiophene unit as light-absorbing chromophore and π-bridge. The photophysical and electrochemical properties of the synthesized dyes were investigated, and photovoltaic performances of the solar cells based on the sensitizers were also explored. Under AM 1.5 G simulated solar illumination, the dye with a pair of dimeric phenothiazine donors gave the best overall power conversion efficiency of 5.41% owing to its intense and broad visible light absorption. The insertion of a thiophene bridge between the phenothiazine and the quinoxaline ring improved the photovoltaic efficiency by impeding charge recombination and increasing electron lifetime. Optimization of the photovoltaic performance condition gave an overall efficiency of 6.48% for NQX8. The results led us to conclude that proper π-conjugation length, location of π-spacer, and molecular conformation should be considered when designing novel sensitizer structures for dye-sensitized solar cells (DSSCs).

Modulation of the emission behavior and mechanofluorochromism by electron-donating moiety of D-π-A type quinoxaline derivatives

New donor-π-acceptor (D-π-A) type quinoxaline derivatives with carbazole (ECVQ), triphenylamine (TPVQ) and phenothiazine (EPVQ) moieties as electron-donating groups were synthesized by standard Knoevenagel condensation reactions with good yields. Their fluorescent emission spectra in both solution and the solid state and mechanofluorochromic behavior was compared and studied. The results indicated that these D-π-A type molecules showed unique intramolecular charge transfer (ICT) properties. The extent of the ICT of the three compounds increased with the sequence of ECVQ < TPVQ < EPVQ. It is interesting that TPVQ and EPVQ exhibited reversible mechanofluorochromism upon the treatment of grinding and fuming. TPVQ showed low emission color change (a spectral shift of 12 nm), and EPVQ revealed high contrast MFC with a large spectral change of 53 nm, which might be originated from bending configuration of EPVQ with phenothiazine group and efficient ICT progress. By sharp contrast, ECVQ did not exhibit MFC behavior. The reason was that the planar molecular conformation and weak ICT degree of ECVQ. This work demonstrated dynamic control of the fluorescent emission and mechanofluorochromic behavior by using different electron donating moieties of D-π-A type quinoxaline derivatives.

Direct Solar‐to‐Electrochemical Energy Storage in a Functionalized Covalent Organic Framework

AbstractA covalent organic framework integrating naphthalenediimide and triphenylamine units (NT‐COF) is presented. Two‐dimensional porous nanosheets are packed with a high specific surface area of 1276 m2 g−1. Photo/electrochemical measurements reveal the ultrahigh efficient intramolecular charge transfer from the TPA to the NDI and the highly reversible electrochemical reaction in NT‐COF. There is a synergetic effect in NT‐COF between the reversible electrochemical reaction and intramolecular charge transfer with enhanced solar energy efficiency and an accelerated electrochemical reaction. This synergetic mechanism provides the key basis for direct solar‐to‐electrochemical energy conversion/storage. With the NT‐COF as the cathode materials, a solar Li‐ion battery is realized with decreased charge voltage (by 0.5 V), increased discharge voltage (by 0.5 V), and extra 38.7 % battery efficiency.

Direct Solar‐to‐Electrochemical Energy Storage in a Functionalized Covalent Organic Framework

A covalent organic framework integrating naphthalenediimide and triphenylamine units (NT-COF) is presented. Two-dimensional porous nanosheets are packed with a high specific surface area of 1276 m2 g-1 . Photo/electrochemical measurements reveal the ultrahigh efficient intramolecular charge transfer from the TPA to the NDI and the highly reversible electrochemical reaction in NT-COF. There is a synergetic effect in NT-COF between the reversible electrochemical reaction and intramolecular charge transfer with enhanced solar energy efficiency and an accelerated electrochemical reaction. This synergetic mechanism provides the key basis for direct solar-to-electrochemical energy conversion/storage. With the NT-COF as the cathode materials, a solar Li-ion battery is realized with decreased charge voltage (by 0.5 V), increased discharge voltage (by 0.5 V), and extra 38.7 % battery efficiency.