Electron-donating Units Research Articles

Design new D-π-A materials for sensitizers for dye-sensitized solar cells: Quantum chemical study

Within this paper, we developed a new series of organic chromophores based on triphenyleamine (TPA) (AL1, AL-2, AL-11 and AL-22) by engineering the structure of the electron donor (D) unit via replacing a phenyle ring or inserting thiophene as a π-linkage. For the sake of scrutinizing the impact of the TPA donating ability and the spacer upon the photovoltaic, absorptional, energetic, and geometrical characteristic of these sensitizers, density functional theory (DFT) and time-dependent DFT (TD-DFT) have been utilized. According to structural characteristics, incorporating the acceptor, π-bridge and TPA does not result in a perfect coplanar conformation in AL-22. We computed EHOMO, ELUMO and bandgap (Eg) energies by performing frequency and ground-state calculations. Next, we performed TD-CAM-B3LYP calculations to compute oscillator strength (f) and the maximum adsorption wavelength (λmax). The absorption bands were extended up to ∼ 647 nm for AL-22. The findings demonstrated that AL-22 is the most promising dye among other dyes.

Rational Design of NIR-II AIEgens with Ultrahigh Quantum Yields for Photo- and Chemiluminescence Imaging.

Fluorescence imaging in the second near-infrared window (NIR-II, 1000-1700 nm) using small-molecule dyes has high potential for clinical use. However, many NIR-II dyes suffer from the emission quenching effect and extremely low quantum yields (QYs) in the practical usage forms. The AIE strategy has been successfully utilized to develop NIR-II dyes with donor-acceptor (D-A) structures with acceptable QYs in the aggregate state, but there is still large room for QY improvement. Here, we rationally designed a NIR-II emissive dye named TPE-BBT and its derivative (TPEO-BBT) by changing the electron-donating triphenylamine unit to tetraphenylethylene (TPE). Their nanoparticles exhibited ultrahigh relative QYs of 31.5% and 23.9% in water, respectively. By using an integrating sphere, the absolute QY of TPE-BBT nanoparticles was measured to be 1.8% in water. Its crystals showed an absolute QY of 10.4%, which is the highest value among organic small molecules reported so far. The optimized D-A interaction and the higher rigidity of TPE-BBT in the aggregate state are believed to be the two key factors for its ultrahigh QY. Finally, we utilized TPE-BBT for NIR-II photoluminescence (PL) and chemiluminescence (CL) bioimaging through successive CL resonance energy transfer and Förster resonance energy transfer processes. The ultrahigh QY of TPE-BBT realized an excellent PL imaging quality in mouse blood vessels and an excellent CL imaging quality in the local arthrosis inflammation in mice with a high signal-to-background ratio of 130. Thus, the design strategy presented here brings new possibilities for the development of bright NIR-II dyes and NIR-II bioimaging technologies.

Novel Donor-Acceptor Conjugated Polymer-Based Nanomicelles for Photothermal Therapy in the NIR Window.

In this study, a novel donor-acceptor conjugated polymer PDPPDTP was designed and synthesized by D-A polymerization using 2,6-di(trimethyltin)-N-dithieno[3,2-b:20,30-d]pyrrole as the electron-donating (D) unit and 3,6-bis(5-bromothiophen-2-yl)-2,5-dihexadecylpyrrolo[3,4-c]pyrrole-1,4-dione as the electron-accepting (A) unit. The prepared polymer has strong absorption in the near-infrared (NIR) range of 700-900 nm. Moreover, it shows excellent photothermal performance under irradiation at 808 nm. Next, the biodegradable amphiphilic polymer polyethylene glycol-polycaprolactone was used to encapsulate the new conjugated polymer into nanomicelles by the microemulsion method. The obtained PDPPDTP-loaded micelles exhibited a regular spherical structure, and their hydrodynamic diameter was about 78 nm, characterized by transmission electron microscopy and dynamic light scattering. Notably, the micelles exhibited good stability, and the encapsulation efficiency of the conjugated polymer in the micelles was ∼80%. In vitro cell experiments demonstrated that the nanomicelles not only showed good biocompatibility and low toxicity but also could effectively inhibit the proliferation of breast cancer cells 4T1 under the NIR light irradiation of 808 nm. Furthermore, in vivo studies of photothermal therapy (PTT) efficacy showed that the PDPPDTP-loaded micelles exhibited a remarkable tumor growth inhibition in a syngeneic murine tumor model, indicating that the nanomicelles loaded with this novel conjugated polymer could be further explored as a new type of theranostic agent and applied in the PTT of tumors.

Novel conjugated polymers based on cyclopenta[c]thiophene-4,6(5H)-dione for efficient polymer solar cells

A series of polymers based on indandione derivatives, TIND-HT-BDT, TIND-HT-BDTF, TIND-DHT-BDT, and TIND-DHT-BDTF, were synthesized as donor materials for polymer solar cells (PSCs). The polymers have a typical donor-acceptor configuration, where TIND-HT (5-((5-hexylthiophen-2-yl)methylene)-4H-cyclopenta[c]thiophene-4,6(5H)-dione) and TIND-DHT (5-((4,5-dihexylthiophen-2-yl)methylene)-4H-cyclopenta[c]thiophene-4,6(5H)-dione) are the electron acceptor units, while benzodithiophene (BDT) or fluorinated benzodithiophene (BDTF) are the electron donor units. Non-fullerene inverted-type PSCs with a configuration of ITO/ZnO/polymer:Y6BO/MoO3/Ag devices based on polymers as the donor and Y6BO as the acceptor were fabricated. The best power conversion efficiency (PCE) of 11.1% was achieved using the inverted-type PSCs based on TIND-DHT-BDTF with an open-circuit voltage (Voc) of 0.82 V and short-circuit current density (Jsc) of 22.6 mA/cm2. This study provides insights into novel donor materials for non-fullerene PSCs.

An Efficient Electron Donor for Conjugated Microporous Polymer Photocatalysts with High Photocatalytic Hydrogen Evolution Activity.

Conjugated microporous polymers (CMPs) with donor-acceptor (D-A) molecular structure show high photocatalytic activity for hydrogen evolution due to the efficient light-induced electron/hole separation, which is mostly determined by the nature of electron donor and acceptor units. Therefore, the selection of electron donor and acceptor holds the key point to construct high performance polymer photocatalysts. Herein, two dibenzo[b,d]thiophene-S,S-dioxide (BTDO) containing CMP photocatalysts using tetraphenylethylene (TPE) or dibenzo[g,p]chrysene (DBC) as the electron donor to investigate the influence of the geometry of electron donor on the photocatalytic activity are design and synthesized. Compared with the twisted TPE donor, DBC has a planar molecular structure with extended π-conjugation, which promotes the charges transmission and light-induced electron/hole separation. As a result, the polymer DBC-BTDO produced from DBC donor shows a remarkable photocatalytic hydrogen evolution rate (HER) of 104.86mmolh-1 g-1 under full arc light (λ>300nm), which is much higher than that of the polymer TPE-BTDO (1.80mmolh-1 g-1 ), demonstrating that DBC can be an efficient electron donor for constructing D-A polymer photocatalysts with high photocatalytic activity for hydrogen evolution.

A Thiazole-Based Polymer Donor for Efficient Organic Solar Cells

The development of new materials plays a critical role in improving the efficiency of organic solar cells (OSCs). At present, the relatively high-lying highest occupied molecular orbital (HOMO) level of the high-efficiency polymer donor is regarded as one of the main reasons for the low open-circuit voltage (Voc). In this work, we introduced the strong electron-withdrawing thiazole unit into the construction of a polymer donor. We designed and prepared an alternating donor–acceptor material, namely PSZ, by copolymerizing 4-methyl thiazole with an electron-donating benzodithiophene unit and studied its application in high-efficiency OSCs. The optical and electrical properties of the new material were characterized by UV–Vis absorption spectroscopy and electrochemical cyclic voltammetry. Results show that PSZ is a typical wide-bandgap material with a high optical bandgap of 2.0 eV and a deep HOMO level of − 5.70 eV. When a non-fullerene BTP-eC9 was selected as the acceptor material, Voc reached 0.88 V in the resulting device, and the corresponding power conversion efficiency (PCE) was 8.15%. In addition, when PSZ was added as the third component to the binary photoactive combination with PBDB-TF as the donor and BTP-eC9 as the acceptor, Voc of the cell device could be increased, thereby obtaining a high PCE of 17.4%. These results indicated that introducing thiazole units into polymer donors can remarkably reduce the HOMO levels and improve Voc and PCE in OSCs.

Enhancing the photovoltaic performance of chlorobenzene-cored unfused electron acceptors by introducing S⋯O noncovalent interaction

The chlorination strategy has been proven an effective approach for designing efficient conjugated electron donor (ED) or acceptor (EA) units for organic solar cells (OSCs). However, up to now, the chlorination strategy has only been used in the design of unfused electron acceptors (UFAs) by modifying the terminal 2-(3-oxo-2,3-dihydroinden-1-ylidene (IC) groups. Due to the steric hindrance of Cl atom, the chlorobenzene (CB)-centered UFAs have not been reported. Herein, two novel CB cored UFAs named 2Cl-4F and Cl-4F were designed and synthesized, the steric effect drawbacks of Cl-atoms was successfully overcome by involving S···O noncovalent interaction. The C-shape Cl-4F based OSCs with PM6 as donor, yields a power conversion efficiency (PCE) of 11.71%, significantly higher than that of the S-shape 2Cl-4F-based device (3.95%). This work reveals that appropriate central-core chlorine engineering is a simple and effective approach to develop novel efficient UFAs.

Aminopeptidase N Activatable Nanoprobe for Tracking Lymphatic Metastasis and Guiding Tumor Resection Surgery via Optoacoustic/NIR-II Fluorescence Dual-Mode Imaging

Lymphatic metastasis is a crucial mechanism by which the cancer cells break away from the primary (original) tumor and travel to the closest regional lymph node(s) and ultimately to other organs or parts of the body, which is closely associated with tumor recurrence and reduced survival. Thus, tracking tumor lymphatic metastasis and realizing imaging-guided lymphoma resection surgery is of great significance. In this study, an activatable nanoprobe is developed for precisely tracking lymphatic metastasis of tumors and imaging-guided resection of the primary tumor and metastatic lymphoma. The molecular probe contains tricyanofuran as the electron-accepting unit (electron acceptor), xanthene as the electron-donating unit (electron donor), and alanine as the responsive unit (recognition moiety) for aminopeptidase N, and the probe molecules form the nanoprobe with bovine serum albumin as the matrix. The nanoprobe can respond specifically to aminopeptidase N overproduced in the tumor, thereby transmuting the alanine into an amino group, and correspondingly the nanoprobe is activated. Strong optoacoustic and NIR-II fluorescence signals emitted by the activated nanoprobe can be utilized for visualizing the lymphatic metastasis of tumors. Moreover, the nanoprobe with the aid of three-dimensional multispectral optoacoustic tomography (3D MSOT) imaging can accurately locate the tumor site of lymphatic metastasis, and ultimately, both the primary tumor and the metastatic lymphoma can be excised with resection surgery under the guidance of NIR-II fluorescence imaging.

An Orange‐Emitting Phosphorescent Iridium(III) Complex Featuring Three Strong Electron‐Donating N‐Embedded π‐Conjugation Units

A new facial phosphorescent iridium complex fac-Ir(NO)3 with three strong electron-donating N-embedded π-conjugation units has been prepared. It can display a distinct orange phosphorescence emission with a narrow half-peak width. In addition, it also shows both distinct intraligand charge transfer (ILCT) and partial unusual ligand-to-metal charge transfer (LMCT) excited state properties due to strong electron-donating capacity of three N-embedded π-conjugation units.

Unity Makes Strength: Constructing Polymeric Catalyst for Selective Synthesis of CO 2 /Epoxide Copolymer

Unity Makes Strength: Constructing Polymeric Catalyst for Selective Synthesis of CO ₂ /Epoxide Copolymer

NIR-II Fluorescent Probe for Detecting Trimethylamine Based on Intermolecular Charge Transfer.

A new kind of small organic NIR-II fluorophore molecule (ZS-1010) based on intermolecular charge transfer was developed as a NIR-II fluorescent probe for trimethylamine (TMA) detection, which is important for the diagnosis of cardiovascular disease, chronic kidney disease and diabetes. ZS-1010 has a strong push-pull electron system composed of electron donor unit and electron acceptor unit, exhibiting strong absorption and emission in the NIR-II region. When mixed with TMA which possesses strong electron-donating characteristics, the push-pull system of ZS-1010 will be affected along with the dipole moment change, leading to the quenching of fluorescence. This is the first example of TMA fluorescent probe in the NIR-II window showing deep penetration, fast response speed, high selectivity and pH stability.

A straightforward synthetic strategy towards conjugated donor-acceptor naphthylimido-azomethines with tunable films morphologies and opto-electronic properties

An important challenge in organic electronic applications is to control the molecular assembly pathway towards organic coatings with desired morphologies. Here, new donor-acceptor napththylimido-azomethine oligomers with triphenylamine or carbazole as electron-donor unit are synthesized and investigated for their opto-electronic properties, with focus on the effect induced by morphological features. A novel structural pattern is approached, with naphthylimide and azomethine directly linked through NN bond. When oligomer films are prepared from different solvents by drop-casting and spin-coating techniques, rectangular sheets, worm-, island- or granular-like morphologies evolve, in conjunction with the molecular structure and processing conditions. Besides high thermal stability, the oligomers display overlapped localized and intramolecular charge transfer transitions involving main and degenerated molecular orbitals, which enable fluorescence modulation in dependence on solvent polarity. With the energy band gap sensitively tailored by the structural elements and solid state molecular packing, the coatings sustain ambipolar charge transport and can be used as n- or p-type active layers in opto-electronic applications. These results confirm that the molecular design is a powerful tool to fine-tune the molecular assembly of organic donor–acceptor molecules and their corresponding opto-electronic features.

Zinc Donor–Acceptor Schiff Base Complexes as Thermally Activated Delayed Fluorescence Emitters

Four new zinc(II) Schiff base complexes with carbazole electron donor units and either a 2,3-pyrazinedicarbonitrile or a phthalonitrile acceptor unit were synthesized. The donor units are equipped with two bulky 2-ethylhexyl alkyl chains to increase the solubility of the complexes in organic solvents. Furthermore, the effect of an additional phenyl linker between donor and acceptor unit on the photophysical properties was investigated. Apart from prompt fluorescence, the Schiff base complexes show thermally activated delayed fluorescence (TADF) with quantum yields up to 47%. The dyes bearing a phthalonitrile acceptor emit in the green–yellow part of the electromagnetic spectrum and those with the stronger 2,3-pyrazinedicarbonitrile acceptor—in the orange–red part of the spectrum. The emission quantum yields decrease upon substitution of phthalonitrile with 2,3-pyrazinedicarbonitrile and upon introduction of the phenyl spacer. The TADF decay times vary between 130 µs and 3.5 ms at ambient temperature. The weaker phthalonitrile acceptor and the additional phenyl linker favor longer TADF decay times. All the complexes show highly temperature-dependent TADF decay time (temperature coefficients above −3%/K at ambient conditions) which makes them potentially suitable for application as molecular thermometers. Immobilized into cell-penetrating RL-100 nanoparticles, the best representative shows temperature coefficients of −5.4%/K at 25 °C that makes the material interesting for further application in intracellular imaging.

Performances of two side-chain modified medium-bandgap alternating polymers with main-chain twisted non-fullerene acceptor

Two alternating polymers (P3 and P4) based on side-chain modified benzo[1,2-b:4,5-b′]dithiophene as the electron-donating unit and fluorinated benzothiadiazole derivatives as the electron-withdrawing segment were adopted as donor materials to blend with a main-chain twisted non-fullerene acceptor (i-IEICO-4 F) for bulk heterojunction polymer solar cells (PSCs). The effects of the two types of side-chain substitutions on the UV-Vis absorptive characteristics, frontier molecular orbitals, and photovoltaic performances of the polymers were systematically probed. Both two polymers have medium-bandgaps, 1.75 eV for P3 and 1.71 eV for P4, respectively, guaranteeing the complementary absorption with i-IEICO-4 F. Among these polymers, the device of polymer P3, which has 2,3-octylthienyl side-chain, shows enhanced dielectric constant, suppressed trap-assisted recombination, promoted hole mobility with more balanced carrier mobility, and suitable phase separation, thus successfully achieving an efficiency of 10.67%. While the alkoxylphenyl substituted polymer P4 has slightly deepened molecular energy level and bathochromic-shifted absorption spectrum and achieved enhanced open-circuit voltage, improved electron mobility, and inhibitive bimolecular recombination in the device, thus acquiring a slightly reduced efficiency of 10.19%. This work not only elaborates the applicability of benzothiadiazole-based medium bandgap polymer donors with main-chain twisted acceptors but also reveals the importance of the side-chain modification of the polymer donors on the performances of the fabricated PSCs.

Two-Photon Absorption Cooperative Effects within Multi-Dipolar Ruthenium Complexes: The Decisive Influence of Charge Transfers.

One- and two-photon characterizations of a series of hetero- and homoleptic [RuL3-n(bpy)n]2+ (n = 0, 1, 2) complexes carrying bipyridine π-extended ligands (L), have been carried out. These π-extended D−π−A−A−π−D-type ligands (L), where the electron donor units (D) are based on diphenylamine, carbazolyl, or fluorenyl units, have been designed to modulate the conjugation extension and the donating effect. Density functional theory calculations were performed in order to rationalize the observed spectra. Calculations show that the electronic structure of the π-extended ligands has a pronounced effect on the composition of HOMO and LUMO and on the metallic contribution to frontier MOs, resulting in strikingly different nonlinear properties. This work demonstrates that ILCT transitions are the keystone of one- and two-photon absorption bands in the studied systems and reveals how much MLCT and LLCT charge transfers play a decisive role on the two-photon properties of both hetero- and homoleptic ruthenium complexes through cooperative or suppressive effects.

Effect of the Aza-N-Bridge and Push-Pull Moieties: A Comparative Study between BODIPYs and Aza-BODIPYs.

In the field of fluorescent dyes, difluoroboron-dipyrromethenes (BODIPY) have a highly respected position. To predict their photophysical properties prior to synthesis and therefore to successfully design molecules specifically for one’s needs, a solid structure–function understanding based on experimental observations is vital. This work delivers a photophysical evaluation of BODIPY and aza-BODIPY derivatives equipped with different electron-withdrawing/-donating substituents. Using combinatorial chemistry, pyrroles substituted with electron-donating/-withdrawing substituents were condensed together in two different manners, thus providing two sets of molecules. The only difference between the two sets is the bridging unit providing a so far lacking comparison between BODIPYs and aza-BODIPYs structural homologues. Replacing the meso-methine bridge with an aza-N bridge results in a red-shifted transition and considerably different, temperature-activated, excited-state relaxation pathways. The effect of electron-donating units on the absorption but not emission for BODIPYs was suppressed compared to aza-BODIPYs. This result could be evident in a substitution pattern-dependent Stokes shift. The outlook of this study is a deeper understanding of the structure–optics relationship of the (aza)-BODIPY-dye class, leading to an improvement in the de novo design of tailor-made molecules for future applications.

Highly stable bulk heterojunction organic solar cells based on asymmetric benzoselenadiazole‐oriented organic chromophores

A new asymmetrically designed D-A-D organic chromophore 4-(7-(5′-hexyl-[2,2′-bithiophen]-5-yl)benzo[c][1,2,5]selenadiazol-4-yl)-N,N-diphenylaniline (RSeT) with benzoselenadiazole acceptor unit has been synthesized using two different electron donor materials of triphenylamine (TPA) and n-hexyl bithiophene unit. Attachment of nonplanar electron-donating TPA unit subsequently heightened the optoelectronic properties and altered the solubility in organic solvents. RSeT of the optical bandgap of ~1.95 eV with the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of −5.31 and −3.36 eV was applied as an electron donor material for stable bulk heterojunction organic solar cells. In this work, two different buffer layers of poly (3, 4-ethylenedioxythiophene):polystyrene sulfonate acid (PEDOT:PSS) and compact titanium oxide (c-TiO2) were used and their influences on the device performance were investigated. Buffer layer of c-TiO2 with RSeT:PC61BM (1:3, w/w) active layer achieved a high open-circuit voltage (Voc) of ~0.985 V, short-circuit current density (Jsc) of ~11.26 mA/cm2 and improved fill factor of ~0.62 which resulted in a high power conversion efficiency (PCE) of ~6.88%. After 30 days, interestingly, RSeT:PC61BM (1:3, w/w) devices with a c-TiO2 buffer layer demonstrated good stability with the PCE value remaining at 85% of its initial value.

Synthesis, photoluminescence and electroluminescence properties of a new blue emitter containing carbazole, acridine and diphenyl sulfone units

The development of luminescent materials with both thermally activated delayed fluorescence (TADF) and aggregation-induced emission (AIE) characteristics is conducive to the preparation of high-efficiency organic light-emitting diodes (OLEDs). Herein, a new emitter, namely 10-(4-((3,5-di(9 H -carbazol-9-yl)phenyl)sulfonyl)phenyl)-9,9-dimethyl-9, 10-dihydroacridine ( CZ-DPS-DMAC ), bearing carbazole as the skeleton, 9,9-dimethyl-9,10-dihydroacridine as the electron donor unit and diphenyl sulfone as the electron acceptor group was designed and synthesized. The structure was characterized by 1 H NMR, 13 C NMR and mass spectrometry. The optical, electrical, and thermal properties were studied comprehensively. The results show that CZ-DPS-DMAC excellent thermal stabilities, stable redox properties, obvious AIE and TADF characteristics. It also exhibits high photoluminescence quantum yield of 54% in powder. On this basis, non-doped (A) and doped (B, C) OLEDs with CZ-DPS-DMAC and different concentrations doped into the DPEPO host as light-emitting layers were manufactured. Electroluminescence investigation shows that device A displays a blue emission with maximum emission peak ( λ max ) of 483 nm, a maximum current efficiency ( CE max ) of 25.42 cd A −1 , a maximum power efficiency ( PE max ) of 30.70 lm W −1 , a maximum luminance ( L max ) of 2322 cd m −2 and a maximum external quantum efficiency ( EQE max ) of 12.00%. The device B in which the guest doped with 10% concentration in the host material is the light-emitting layer exhibits good performance with a λ max of 477 nm, a CE max of 23.40 cd A −1 , a PE max of 20.28 lm W −1 , a L max of 1753 cd m −2 and an EQE max of 14.27%. The excellent performance demonstrated by CZ-DPS-DMAC suggests that it is a promising candidate for fabricating OLEDs with high efficiency. • A new blue emitter containing carbazole and acridine as donors and diphenyl sulfone as acceptor was designed and synthesized • The compound exhibits obvious thermally activated delayed fluorescence and aggregation-induced emission characteristics • The non-doped OLED based on the emitter displays good blue electroluminescence performance with EQE max of 12.00%.

Cover Feature: Resist or Oxidize: Identifying Molecular Structure–Photostability Relationships for Conjugated Polymers Used in Organic Solar Cells (ChemSusChem 3/2022)

The Cover Feature shows that the photostability of conjugated polymers used as absorber materials for organic solar cells strongly depends on the chemical structure and properties of the used building blocks. Using electron-rich moieties facilitates photooxidation, whereas polymers composed of weak electron donor and acceptor units exhibit high electrochemical oxidation potentials and show excellent stability towards the light-induced degradation. More information can be found in the Full Paper by I. V. Martynov et al.

Molecular engineering of covalent triazine frameworks for highly enhanced photocatalytic aerobic oxidation of sulfides

By integrating various electron-donating units into CTFs, their photophysical and photochemical properties can be facilely modulated to achieve an enhanced performance for photocatalytic selective oxidation of sulfides to sulfoxides.