Electron-deficient Moiety Research Articles

Solvatochromic covalent organic frameworks for the low-level determination of trace water in organic solvents

Here we report a rational design and preparation of luminescent COFs via the synergetic interaction of electron-rich and electron-deficient moieties. 4,4′,4′-(1,3,5-triazine-2,4,6-triyl) trianiline (TTA) with the electron-deficient unit and 2,6-diformyl-4-methylphenol (Dp) with the electron-rich moiety and −OH group were employed to synthesize the imine-linked DpTTA-COF. The intramolecular charge transfer enables DpTTA-COF to present a strong solvent polarity-dependent color change, based on which a solvatochromic sensor was successfully established. We demonstrate an emission wavelength and intensity dual-mode photoluminescent sensor for the detection of trace water in organic solvents with good sensitivity, reversibility and stability. In addition, the dual-signal solvatochromic sensor is also capable for organic solvents decoding. This work proposes a new strategy for the design and preparation of COFs with fascinating solvatochromic effect. This strategy could extend the application field of COFs by the integration of functional groups, affinity, and structural selectivity.

Aminoquinoxaline-Based Dual Colorimetric and Fluorescent Sensors for pH Measurement in Aqueous Media

This research is focused on the development of pH indicators based on the quinoxaline signaling group for acidic aqueous solutions (pH 1–5). A push–pull quinoxaline QC1 in which two electron-donating (3-aminopropyl)amino substituents are attached to positions 6 and 7 of the electron-deficient quinoxaline moiety was prepared using the palladium-catalyzed C–N cross-coupling reaction. The 3-aminopropyl residues are mostly protonated in aqueous solutions below pH 8, thus serving as hydrophilizing substituents that render quinoxaline derivative QC1 water-soluble in this range of acidities and useful for measurements in the pH range of 1–5. This chromophore is a dual optical chemosensor that exhibits shifts of both absorption and emission bands in response to external stimuli. The presence of naturally relevant metal cations (13 ions) does not interfere with spectrophotometric and fluorescence measurements of the optical response of aminoquinoxaline in the visible region. Moreover, these spectral changes are easily observed by the naked eye, allowing for rapid semi-quantitative analyses under “in-field” conditions.

Photocatalyzed difluoroalkylation of pyridine N-oxides

A photoredox catalytic strategy has been developed for the regioselective C2-, or C4-difluoroalkylation of pyridine N-oxides under mild conditions. This method provides an efficient protocol for the incorporation of electrophilic difluoroacetate radical (CF2CO2Et) into pyridine skeletons, based on the strategy of nitrogen-atom activation on electron-deficient pyridine moieties.

Dipyrido[3,2-a:2′,3′-c]phenazine acceptor based thermally activated delayed fluorescence emitters

A rigid π-conjugated and electron-deficient moiety, dipyrido[3,2-a:2′,3′-c]phenazine (DPPZ), was employed as the electron acceptor for thermally activated delayed fluorescence (TADF) emitters with a donor–acceptor structure. Two TADF emitters, DCz-DPPZ and DDPhCz-DPPZ, were prepared by adopting carbazole derivatives as the donor and DPPZ as the acceptor. Compared to DCz-DPPZ without substituents at the carbazole group, DDPhCz-DPPZ showed a narrower energy gap, a longer emission wavelength, and a higher photoluminescence quantum efficiency. The TADF organic light-emitting diodes based on DDPhCz-DPPZ exhibited a higher quantum efficiency of 12.4% than 4.6% of devices based on DCz-DPPZ. These results demonstrate that DPPZ is a suitable acceptor for constructing D–A type TADF emitters.

A Multifunctional Coordination Polymer Constructed by Viologen Derivatives: Photochromism, Chemochromism, and MnO4- Sensing.

A multifunctional Cd-based coordination polymer based on a viologen derivative and a secondary carboxylic ligand, namely, {[Cd2(bcbp)(pta)2 (H2O)]·2H2O}n (1, H2bcbpCl2 = 1,1'-bis(4-carboxyphenyl)-(4,4'-bipyridinium) dichloride, H2pta = p-phthalic acid), has been solvothermally synthesized and structurally characterized. Compound 1 is a 3D framework built on {Cd2(pta)2 (H2O)}n net with square channels which intalls bcbp ligands at the diagonal position of the two adjacent square channels. Notably, compound 1 exhibits a reversible photochromic transformation between yellowish gray and dark green under xenon light irradiation, which should be attributed to the formation of free viologen radicals. Furthermore, compound 1 also displays a chemochromic phenomenon from yellowish gray to dark green after exposure to ammonia and hydrazine, which could be ascribed to the generation of viologen radicals and charge-transfer complexes triggered by nucleophilic attack of electron-rich ammonia and hydrazine molecules to the electron-deficient viologen moiety in the bcbp ligand. Moreover, compound 1 is capable of quickly and selectively detecting MnO4- with a high quenching coefficient and a low limit of detection via a luminescent quenching process caused by the competitive absorption of excitation energy.

Porphyrindiene-Based Tandem Diels–Alder Reaction for Preparing Low-Symmetry π-Extended Porphyrins with Push–Pull Skeletons

Tandem Diels-Alder reactions of masked porphyrindienes (i.e., sulfolenoporphyrins) with benzoquinones and stilbenes, followed by aromatization, have been developed to load porphyrin with mixed annulation units (i.e., terphenyl and naphthoquinone), furnishing the low-symmetry π-extended porphyrins (DxAy) with push-pull skeletons. All low-symmetrical chromophores display panchromatic absorption spectra, which look like a spectral combination of symmetrical congeners (D4/A4) in a certain ratio. Among them, tD2A2 with trans-arrangement of push/pull units possesses the largest maximum centered at 766 nm with the onset around 900 nm. The fusion of the electron-deficient naphthoquinone moiety on the porphyrin core results in the approximately quantitative regulation of the Eox1 and HOMOs (i.e., 0.10-0.13 V increase for the Eox1 and 0.14-0.16 eV decrease for the HOMOs per naphthoquinone unit). In brief, this work provides a new way to construct low-symmetry π-extended porphyrins with tunable properties resorting to the ratios and locations of the annulated push-pull units.

Synthesis, Photophysical, Electrochemical, and Non-linear Optical Properties of Triaryl Pyrazole-based B-N Coordinated Boron Compounds.

We report here a set of triaryl pyrazole based B-N coordinated boron compounds (11-17) synthesized by electrophilic aromatic borylation strategy. All the pyrazole boron compounds were thoroughly characterized using multinuclear NMR spectroscopy, LC-MS, and single crystal X-ray diffraction analysis (for 12-17). The photoluminescence measurements of 11-17 revealed that the emission peak maxima were tuned based on the substitution on N-phenyl. The photophysical and electrochemical properties were further supported by theoretical calculations. Z-scan based investigations at 515 nm pump wavelength showed that B-N coordination led to enhancement of nonlinear absorption (two-photon absorption (TPA)) in these compounds if an electron deficient moiety is attached. It has also been observed that an appropriate choice of moiety allows to optimally maneuver the molecular polarizability of the π-system and consequently, assists in controlling the third-order nonlinear optical response.

A unique small molecule class of fluorophores with large Stokes shift based on the electron deficient 9-methoxypyrroloisoquinolinetrione core

A novel fluorescent core based on electron-deficient 9-methoxypyrroloisoquinolinetrione moiety with a condensed imide cycle is developed. The new class of dyes show large Stokes shift up to 6519 cm-1 (Δλ up to 130 nm), however, unlike parent 5-hydroxyisoquinolones, 9-methoxypyrroloisoquinolinetrione are not superphotoacidic which could be responsible for the large Stokes shifts. At the same time methylation of 5-hydroxyisoquinolones reduces Stokes shift from 5086 to 4689 cm-1. The increase in Stokes shift upon the formation of an imide cycle was shown to be due to unusual bond-lengths relaxation involving the imide ring.

Three-coordinated mononuclear Cu(I) complexes with crystallization-enhanced thermally activated delayed fluorescence characteristics

Triangular three-coordinated copper(I) halide complexes (1 (I), 2 (Br)) were developed based on a rigid bidentate P-donor ligand functionalized with electron-deficient pyridoimidazole moiety. The results of the temperature-dependent spectroscopic properties reveal that both Cu(I) complexes in crystalline powder at 298 K achieve orange thermally activated delayed fluorescence (TADF) with high photoluminescence quantum yields of 77% for 1 and 56% for 2, and microsecond lifetimes of 55.1 μs (1) and 73.5 μs (2), respectively. Additionally, aromatic CH···π interactions in molecular packing structures constitute an appealing class of crystallization-induced emission enhancement (CIEE) complexes. The results suggest that such highly efficient copper-based stimuli-responsive materials are beneficial for a broad range of applications.

Spontaneous Isomerization of a Hydroxynaphthalene-Containing Spiropyran in Polar Solvents Enhanced by Hydrogen Bonding Interactions.

The synthesis of spiropyran dyes exhibiting solvent-driven isomerization even in the dark condition is an important subject for the design of optical materials. A conventional synthesis strategy involves the conjugation of indoline moieties with electron-deficient aromatic moieties. Herein, we report that a spiropyran conjugated with a hydroxynaphthalene moiety (1) is a new member exhibiting solvent-driven isomerization, even bearing an electron-donating −OH moiety. The dye exists as a colorless spirocyclic (SP) form in nonpolar media. It, however, shows a blue color in polar media, especially in aqueous media, due to the formation of ring-opened merocyanine (MC) forms, where the isomerization terminates in 10 s even at room temperature. The spontaneous SP → MC isomerization originates from the MC forms stabilized by the highly delocalized π-electrons on the hydroxynaphthalene moiety. The solvation in polar media and the hydrogen bonding interaction with water molecules decrease the ground-state energy of the MC forms, triggering spontaneous isomerization. The dye exhibits two MC absorption bands assigned to the trans–trans–cis (TTC) and cis–trans–cis (CTC) isomers. The absorbance of the CTC band increases more significantly with an increase in the water content, and the increase exhibits a linear relationship with a hydrogen-bond donor acidity of solvents. The phenolate oxygen of the CTC form has larger hydrogen-bond acceptor basicity, resulting in stronger stabilization by the water molecule.

Reversible photochromism and photoresponsive luminescence in naphthalene diimide-based framework with Lindqvist-type polyoxometalate template

Metal-organic frameworks that contain photoactive organic ligands or photoactive inorganic components are an emerging class of multifunctional hybrid materials that in recent years has gradually become an ideal platform for building photochromic complexes. In this paper, a metal-organic framework based on naphthalene diimide (NDI) ligand with Lindqvist-type W6O192– polyanions, [Ce2(BINDI) (DMF)8]·[W6O19] (1), (H4BINDI = N, N'-bis(5-isophthalic acid)-1,4,5,8-naphthalene diimide) was synthesized and systematically characterized. It displays a cationic two-dimensional grid coordination network, featuring anion–π interactions between W6O192– and expanded π–electron deficient naphthalene diimide (NDI) moieties. Moreover, because of the presence of electron-deficient NDI moieties and photoactive W6O192–, this complex exhibits fast responsive reversible photochromism and photoresponsive tunable luminescence. UV–Vis, IR, PXRD, EPR, and XPS spectral studies indicate that the obviously photochromic phenomenon of complex 1 is derived from photoinduced electron-transfer form NDI radicals and W5+ species.

Temperature-sensitive emission of dialkylaminostyrylhetarene dyes and their incorporation into phospholipid aggregates: Applicability for thermal sensing and cellular uptake behavior

A series of dialkylaminostyrylhetarene dyes constructed from electron-rich and electron-deficient moieties of various structures connected via vinylene π-bridges are introduced as temperature-sensitive luminophores. The temperature dependent emission of the dyes in the acidified dichloromethane solutions derives from temperature-induced shift of the equilibrium between neutral and protonated forms of the dyes. The heating-induced blue shift and intensification of emission of neutral form of the dyes make them a promising basis for development of nanoparticles exhibiting temperature-sensitivity in aqueous solutions at pH typical of biological liquids. Hydrophobicity-driven incorporation of the water insoluble dyes into L-α-phosphatidylcholine(PC)-based bilayers allows to obtain water dispersible dye-PC aggregates, and to follow their emission in the aqueous solutions. Structure of the dyes has strong impact on the efficacy of the dyes incorporation into the PC-based bilayers, temperature sensitivity of emission of the dye-PC aggregates and its reversibility under the heating/cooling cycles. This enables structural optimization of the dyes in order to obtain the dye-PC species demonstrating maximal temperature dependence and reversibility of their luminescence in aqueous solutions. The selected leader exhibits low cytotoxicity exemplified for M−HeLa and Chang Liver cell lines, while the efficient cell internalization of the dye, manifested in the staining of the cell cytoplasm, opens further opportunities for biosensing applications.

Physical and Electrochemical Properties of Soluble 3,4-Ethylenedioxythiophene (EDOT)-Based Copolymers Synthesized via Direct (Hetero)Arylation Polymerization.

Over the past decades, π-conjugated polymers (CPs) have drawn more and more attention and been essential materials for applications in various organic electronic devices. Thereinto, conjugated polymers based on the 3,4-ethylenedioxythiophene (EDOT) backbone are among the high-performance materials. In order to investigate the structure–property relationships of EDOT-based polymers and further improve their electrochemical properties, a series of organic solvent–soluble EDOT-based alternative copolymers consisting of electron-rich fragments (fluorene P1, carbazole P2, and 3,4-alkoxythiophene P3) or electron-deficient moieties (benzotriazole P4 and thieno[3,4-c]pyrrole-4,6-dione P5) were synthesized via direct C–H (hetero)arylation polymerization (DHAP) in moderate to excellent yields (60–98%) with medium to high molecular weights (M n = 3,100–94,000 Da). Owing to their various electronic and structural properties, different absorption spectra (λ max = 476, 380, 558, 563, and 603 nm) as well as different specific capacitances of 70, 68, 75, 51, and 25 F/g with 19, 10, 21, 26, and 69% of capacity retention after 1,000 cycles were observed for P1–P5, respectively. After careful study through multiple experimental measurements and theoretical calculation, appropriate electronic characteristics, small molecular conformation differences between different oxidative states, and well-ordered molecular stacking could improve the electrochemical performance of CPs.

Protein stabilized polymeric nanoparticles inspired relay drug delivery for tackling post-chemotherapeutic metastasis

The pro-metastatic potential of chemotherapy limits its therapeutic benefits against invasive cancer. Herein, a protein stabilized polymeric nanoparticle inspired relay drug delivery platform was developed to address post-chemotherapeutic metastasis. An ROS-responsive Phenylboronic acid (PBA)-Rich cationic polymer (RPP) bridges Doxorubicin (Dox) coordination and Snail-targeted siRNA (siSnail) compression, and natural apolipoprotein A-I (apoA-I) is attracted by surface electron-deficient PBA moieties for nanoparticle shaping, drug biostability, and tumour-penetration. The spatially-separated structure enables a timing-controlled relay drug delivery in tumour cells, where Dox gives a prior release phase by acidity, and RPP polymer is subsequently disintegrated by concentrated ROS for rapid siSnail liberation. In dual therapy, Dox pre-treatment upregulated pro-metastatic factors and aggravated metastasis, but subsequent liberation by siSnail silenced the central metastatic regulator of Epithelial-mesenchymal transition (EMT). The terminal nanoparticles exhibited advanced therapeutic efficacy, achieving primary tumour shrinkage (tumour weight inhibition, TWI of ~86.15%) and complete metastatic nodule elimination. This work promises to improve the clinical benefits of chemotherapy against invasive cancer.

Ni-Catalyzed Borylation of Aryl Sulfoxides.

A nickel/N‐heterocyclic carbene (NHC) catalytic system has been developed for the borylation of aryl sulfoxides with B2(neop)2 (neop=neopentyl glycolato). A wide range of aryl sulfoxides with different electronic and steric properties were converted into the corresponding arylboronic esters in good yields. The regioselective borylation of unsymmetric diaryl sulfoxides was also feasible leading to borylation of the sterically less encumbered aryl substituent. Competition experiments demonstrated that an electron‐deficient aryl moiety reacts preferentially. The origin of the selectivity in the Ni‐catalyzed borylation of electronically biased unsymmetrical diaryl sulfoxide lies in the oxidative addition step of the catalytic cycle, as oxidative addition of methoxyphenyl 4‐(trifluoromethyl)phenyl sulfoxide to the Ni(0) complex occurs selectively to give the structurally characterized complex trans‐[Ni(ICy)2(4‐CF3‐C6H4){(SO)‐4‐MeO‐C6H4}] 4. For complex 5, the isomer trans‐[Ni(ICy)2(C6H5)(OSC6H5)] 5‐I was structurally characterized in which the phenyl sulfinyl ligand is bound via the oxygen atom to nickel. In solution, the complex trans‐[Ni(ICy)2(C6H5)(OSC6H5)] 5‐I is in equilibrium with the S‐bonded isomer trans‐[Ni(ICy)2(C6H5)(SOC6H5)] 5, as shown by NMR spectroscopy. DFT calculations reveal that these isomers are separated by a mere 0.3 kJ/mol (M06/def2‐TZVP‐level of theory) and connected via a transition state trans‐[Ni(ICy)2(C6H5)(η2‐{SO}‐C6H5)], which lies only 10.8 kcal/mol above 5.

Investigating the effect of diverse structural variation of conjugated polymer electrolytes as the interlayer on photovoltaic properties

The effect of the diverse structural variation of conjugated polymer electrolytes (CPEs) as an interlayer on the photovoltaic properties was investigated. We found that the CPE with a strong electronegative BT group in the backbone and OH salt group in the side chain offers the highest PCEs among CPEs. • Diverse structural variation of conjugated polymer electrolytes (CPEs). • Step-by-step improvement in efficiency of solar cells based on diverse CPEs as interlayer. • Optical simulations of solar cells using transfer matrix formalism. A series of conjugated polymer electrolytes (CPEs) based on dimethylamino propyl fluorene (FN), thiophene (T), benzothiadiazole (BT), and dithienyl benzothiadiazole (TBT) were synthesized by the Suzuki coupling reaction. Quaternarized polyelectrolytes were obtained from the post-polymerization treatment of the amino-terminal group. The incorporation of electron-rich (T), electron-deficient moiety (BT), and their combination (TBT) in the polymer backbone represent the different effects of polarity. Conjugated backbones are substantially strengthened by varying their electron affinity and conjugated planarity. We systematically investigated the effect of applying CPEs with different backbones and functionalities in the side chain. Different backbones produce different molecular dipoles, and the side chain functionality induces an interfacial dipole. Inverted polymer solar cells (iPSCs) based on a bulk heterojunction (BHJ) were fabricated with the ITO/ZnO/CPE/PTB7-Th:PC 71 BM/MoO 3 /Ag structure. The device performance enhancement was achieved by inserting CPEs as the interlayer. Modifying the polymer backbone leads to improved efficiency and modifying the side chain functionality improves the performance compared with that of the interlayered neutral polymer.

A series of multi-responsive viologen-based alkaline-earth metal coordination complexes: Thermochromism, photochromism, and vapochromism

Due to their external stimuli responsive properties, chromic materials have attracted considerable interest in various fields. In this work, a series of alkaline-earth metal based coordination complexes constructed from viologen derivative, [Mg(H2O)6·(bdpbpy)·H2O] (1), [Ca(bdpbpy)(H2O)4] (2), [Sr(bdpbpy)(H2O)4] (3), [Ba(bdpbpy)(H2O)4] (4), (H4bdpbpy·2Cl = 1,1-bis(3,5-dicarboxyphenyl)-4,4-bipyridinium chloride) have been synthesized and characterized by elemental analyses, FT-IR spectroscopy, single-crystal X-ray diffraction, and thermogravimetric analysis. Because of electron transfer between the oxygen atom of carboxylate and bipyridinium moieties, compounds 1–4 exhibit reversible thermochromic and photochromic properties upon thermo treatment or Uv-vis irradiation. Due to presence of electron-deficient bipyridinium moieties (Lewis acidic sites), these compounds can be used as potential colorimetric sensor for ethanediamine vapor detection. The multi-responsive performances of compounds 1–4 can widen their applications in some particular systems that call for color changing properties of external stimuli.

Benzo/Naphthodifuranone-Based Polymers: Effect of Perpendicular-Extended Main Chain π-Conjugation on Organic Field-Effect Transistor Performances.

For polymer semiconductors, the backbone structure plays an essential role in determining their physicochemical properties and charge transport behaviors. In this work, two donor-acceptor-type polymers (P-BDF and P-NDF) based on benzodifuranone (BDF) and naphthodifunarone (NDF) as electron-deficient moieties and indaceno-dithiophene as electron-rich groups are designed, synthesized and, for the first time, applied in organic field-effect transistor. P-BDF and P-NDF differ from their backbone structures while P-BDF has a more planar backbone conformation due to its smaller conjugated core size and P-NDF features a perpendicular-extended main chain structure. As a result, P-BDF polymer exhibits bathochromic optical absorption, deeper molecular orbital energy levels, and more importantly, closer π-stacking and stronger aggregation in the solid state and thus affords a more promising hole mobility of up to 0.85 cm2 V-1 s-1 in OFET devices, while that of the P-NDF-based devices is only 0.55 cm2 V-1 s-1 . The results suggest the great potential of BDF/NDF-type chromophores in constructing novel organic semiconductors and also indicate that the main chain coplanarity of polymer semiconductors is more essential than the sole extension of π-conjugations (especially at the perpendicular direction of polymer main chains) for the design of high-performance OFET materials.

Defined Poly(borosiloxane) as an Artificial Solid Electrolyte Interphase Layer for Thin-Film Silicon Anodes

Solid electrolyte interphase (SEI) formation in Li-ion batteries is essential for good long-term performance of the cell. However, for electrodes exhibiting high volume expansion (like Si and Sn), continuous SEI formation can not only deplete electrolyte content but also increase cell impedance and hence mediocre performance. This is particularly detrimental in the case of thin-film electrodes where there is a minute amount of active materials loading. In the current work, defined poly(borosiloxane) (PBS) as an artificial polymeric SEI having self-healing, anion-trapping properties, and electron-deficient boron moiety is investigated. Studies on thin-film Si electrodes show excellent enhancement with polymeric coating in terms of cycling stability. These improvements are attributed to a combination of factors including the anion-trapping effect of tricoordinate boron, self-healing ability of PBS, and adherence to the electrode surface.

Exploring the effect of the spacer structure in the heterocyclic ring-fused isoindigo-based conjugated polymer on the charge-transporting property

Isoindigo (IID) has been developed as an electron deficient moiety for high-performance conjugated organic materials, especially for constituting donor–acceptor (D-A) type conjugated polymers. To further enhance the planarity of IID unit to promote the associated intramolecular charge transfer (ICT) effect of the derived polymers, various of structural modifications have been performed in recent years. Herein, two heterocyclic ring-fused IID core structures, tetrafluorobenzene-centered IID (FBIID) and pyrazine-centered IID (PzIID), were developed and copolymerized with two common electron-rich moieties, 2,2′-bithiophene (2 T) and (E)-1,2-bis(thiophen-2-yl)ethene (TVT). The properties and structure-mobility relationship of the prepared four D-A type polymers, PFBIID-2 T, PFBIID-TVT, PPzIID-2 T, and PPzIID-TVT are systematically studied to elucidate the effect of the spacer structure in the heterocyclic ring-fused IID units. Both the simulation results and experimental analyses show that the PzIID-based polymers possess much higher planarity and mobility than the FBIID-based ones because of the less substituents on the pyrazine spacer, which reduces the steric hindrance within the structure. Finally, we show that the distinctly different planarity between FBIID and PzIID results in significantly different field-effect transistor (FET) mobility. Owing to the higher planarity and improved stacking and crystallinity of the polymer chains, the PzIID-derived polymers deliver much higher hole mobilities (μhs) of > 3 × 10 −4 (cm2 V−1 s−1) than the FBIID-derived polymers that show no conspicuous charge-transporting properties. This result clearly highlights the crucial role of the spacer structure in designing the heterocyclic ring-fused IID core structures.