Asymmetric Donor-acceptor Research Articles

NIR-II Absorbed Dithienopyrrole-Benzobisthiadiazole Based Nanosystems for Autophagy Inhibition and Calcium Overload Enhanced Photothermal Therapy.

Although the current cancer photothermal therapy (PTT) can produce a powerful therapeutic effect, tumor cells have been proved a protective mechanism through autophagy. In this study, a novel hybrid theranostic nanoparticle (CaCO3@CQ@pDB NPs, CCD NPs) is designed and prepared by integrating a second near-infrared (NIR-II) absorbed conjugated polymer DTP-BBT (pDB), CaCO3, and autophagy inhibitor (chloroquine, CQ) into one nanosystem. The conjugated polymer pDB with asymmetric donor-acceptor structure shows strong NIR-II absorbing capacity, of which the optical properties and photothermal generation mechanism of pDB are systematically analyzed via molecular theoretical calculation. Under NIR-II laser irradiation, pDB-mediated PTT can produce powerful killing ability to tumor cells. At the same time, heat stimulates a large amount of Ca2+ inflow, causing calcium overload induced mitochondrial damage and enhancing the apoptosis of tumor cells. Besides, the released CQ blocks the self-protection mechanism of tumor cells and greatly enhances the attack of PTT and calcium overload therapy. Both in vitro and in vivo experiments confirm that CCD NPs possess excellent NIR-II theranostic capacity, which provides a new nanoplatform for anti-tumor therapy and builds great potential for future clinical research.

Piperazine appended naphthalimide-based organic scaffolds exhibiting efficient aggregation induced emission (AIE) and selective picric acid sensing

AIEgens (5a−5c &6a−6c) derived from piperazine-appended naphthalimide have been synthesized via strategic modifications following multi-step process. Resulting compounds have been thoroughly characterized by spectroscopic techniques (IR, NMR (1H &13C), HRMS, UV/Vis and fluorescence spectroscopy). The compounds under study represent an asymmetric donor-acceptor (D-A) system with a D-A′-π-A construct. Expectedly, these display efficient aggregation-induced emission (AIE) which has been followed by UV/Vis, fluorescence, fluorescence lifetime and morphological (SEM) studies. Morphological studies on these systems revealed spherical nanostructures in aggregated state. These compounds display solid-state emission and solvatochromism. It has been observed that the donor unit plays a crucial role in directing photophysical properties including AIE. Moreover, synthesized compounds exhibited selective sensing toward picric acid. Further, DFT studies have been performed to support and co-relate the physical properties.

Structure-enabled long-lived charge separation in single crystals of an asymmetric donor-acceptor perylenediimide cyclophane.

We report the synthesis and characterization of a covalently linked asymmetric cyclophane comprising a 1,7-di(pyrrolidin-1'-yl)perylene-3,4,9,10-bis(dicarboximide) (pyrPDI) and 1,6,7,12-tetra(4'-t-butylphenoxy)perylene-3,4,9,10-bis(dicarboximide) (tpPDI), which absorbs light from 400-750 nm. Single crystals of pyrPDI-tpPDI were analyzed by using X-ray diffraction and transient absorption microscopy. The crystal structure contains several types of intermolecular donor-acceptor interactions (pyrPDI-pyrPDI, tpPDI-tpPDI, and pyrPDI-tpPDI) in addition to the covalently installed intramolecular interaction. Following photoexcitation of the pyrPDI-tpPDI single crystal, the transient absorption data show that charge separation occurs in τ = 21 ps, which is about nine times faster than in toluene solution, while charge recombination occurs in τ > 2 μs, which is more than 400 times longer than in solution. The faster charge separation in the single crystals results from the intermolecular donor-acceptor pyrPDI-tpPDI interactions, while the greatly enhanced charge-separated state lifetime is a consequence of charge transport through the intermolecular π-stacks. These results demonstrate the utility of pre-organizing donor-acceptor structural motifs to elicit specific crystal morphologies that can lead to enhanced photogenerated charge carrier lifetimes for solar energy conversion.

Asymmetric donor–acceptor–host red thermally activated delayed fluorescent emitter for high-efficiency organic light emitting diodes

A new asymmetric D–A–H type TADF emitter, TPA-AQ-DCP, is designed to improve exciton utilization and restrict intermolecular interactions in OLEDs with red emission and efficiency of up to 17.60%.

AIE active quinazoline based probes for selective detection of Fe3+ and acidochromism

Synthesis and thorough characterizations of two A-D-π-A’ type asymmetric donor–acceptor constructs 6-(4-(4-(pyridin-2-yl)piperazin-1-yl)-phenyl)-5,6-dihydrobenzo-[4,5]-imidazo[1,2–c]-quinazoline (P1) and 6-(4-(4-(pyrimidin-2-yl)-piperazin-1-yl)phenyl)-5,6-dihydro-benzo[4,5]-imidazo[1,2–c] quinazoline (P2) have been described. The formation and composition of these compounds have been ascertained by spectroscopic studies (IR, 1H, 13C, ESI–MS, UV/Vis and fluorescence). Quinazoline unit in P1 and P2 acts as acceptor whereas piperazine as donor moiety and their properties has further been tuned by incorporating pyridyl and pyrimidyl group. AIE behaviour of P1 and P2 have been studied in THF/water by absorption and emission spectroscopy by varrying water fraction. Prominent role of the restriction of intra-molecular rotation on (RIR) in AIE for these compounds has been supported by viscosity measurements. Photophysical behaviour and morphology of the aggregates have been investigated by UV/Vis, fluorescence, and scanning electron microscopy (SEM). Owing to asymmetric donor–acceptor (A-D- π -A’) nature these display (twisted intramolecular charge transfer) TICT via D-A unit. In addition, P1 and P2 serve as highly selective and sensitive fluorescence sensor for Fe3+ and Job’s plot analysis suggested 2:1 binding stoichiometry between the metal centre Fe3+ and probes. As well, P1 and P2 display promising reversible acidochromism.

D-A-D’ type phenothiazine modified bisarylic methanone derivatives exhibiting fluorescent response to mechanical force and reversible tricolor switching

Two D-A-D′ type bisarylic methanone derivatives PTZ-BZ-Cz and PTZ-BZ-TPA, which consisted of two different electron donors and the same electron acceptor were designed and synthesized. Theoretical calculations revealed that both possessed asymmetric donor-acceptor structures and highly distorted spatial conformations. Optical researches illustrated that both exhibited an evident intramolecular charge transfer (ICT) characteristics and effective emission in the solid state. Interestingly, the mechanochromic behaviors were found. The XRD indicated that the reason for the mechanochromic phenomenon was crystalline-to-amorphous transition. It should be noted that PTZ-BZ-Cz exhibited high contrast and tricolor switching mechanochromic properties under external force stimuli. This novel phenomenon is very interesting for the development of mechanochromic materials that can simultaneously achieve high-contrast and multicolor switching. The current work provided a basis for the design of organic molecules featuring both high contrast and multicolor switching.

Competitive ICT in asymmetric D−A Scaffolds showing visible solvatochromism, temperature-induced emission enhancement and AIE based acidochromism

Meticulous attention to details of intramolecular charge transfer (ICT) has proved to be an effective strategy to design donor-acceptor fluorophores equipped with multichromic behaviour. Herein, we report three asymmetric donor-acceptor fluorophores bearing A′−D−A−D−A′ and D′−D−A−D−D′ scaffolds. The D−A−D core has been modified by appending pyridine/pyrimidine as additional acceptor and phenyl as additional donor and piperazine as flexible spacers. The asymmetric scaffold has equipped them with naked-eye solvatochromism even under daylight which further authenticated the effective charge separation in ground as well as excited state. The comparative account of photophysical behaviour displays the varying extent of twisted intramolecular charge transfer (TICT) owing to asymmetry. The interplay of restricted intramolecular rotation (RIR) and TICT leads to AIE induced H+ sensing and reversible acidochromism in PC1 which can be visualized by a comparatively uncommon acid induced emission enhancement. The activation of vibrational bands at higher temperature leads to a rare temperature induced emission enhancement in PC1−PC3. PC1 has been developed as the very first ‘turn-on’ thermochromic sensor based on β-diketone-boron difluoride (BF2bdk) complexes.

Liver injury long-term monitoring and fluorescent image-guided tumor surgery using self-assembly amphiphilic donor-acceptor NIR-II dyes

Real-time monitoring of liver dysfunction represents a significant unmet demand in clinical and preclinical research. The second near-infrared window (NIR-II, 1000–1700 nm) fluorescent imaging is an attractive method for biomedical imaging and may be a promising approach for liver dysfunction monitoring. Herein, we designed and synthesized a small-molecule NIR-II dye TQT 1009 with an asymmetric donor-acceptor (D-A) core. By introducing four kinds of polyethylene glycol (PEG) with different length and molecular weights (nK, n = 0.5, 2, 5, 10) to TQT1009, the dye was self-assembled into different nanoparticles named as TQP nK with regulated size and controllable circulation lifetime in vivo. In general, TQP nK showed a super high contrast ratio for blood vessels, bones, intestines, lymph, and tumor imaging. The best-selected probe, TQP 10K, exhibited ultralong in vivo circulation time (>96 h) which was suitable for long-term quantitative monitoring of liver and vessel function at a single dose, implying the excellent prospects compared with ICG, which was quickly eliminated in blood within a few minutes. Meanwhile, TQP 10K also achieved NIR-II surgical navigation of tumor in an extended time window (>7 d). Overall, our results demonstrate the self-assembly PEGylated amphiphilic TQP nK provide a new probe design strategy for liver function monitoring and image-guided tumor surgery in a prolonged time window.

Room temperature phosphorescence, thermally activated delayed fluorescence and multicolor mechanochromic luminescence of emitters through molecular interaction and conformational modulations

Two novel heavy atom-free pure organic pyrimidine-based asymmetric donor-acceptor type emitters were designed and synthesized. The twisted D-A conformation was favored to produce small ΔEst and effective ISC. Excitingly, PMBT and CzPMBT showed precious fluorescence-RTP-TADF triple emission. Furthermore, PMBT responded to external stimuli of volatile solvents fumigation and different intensity grinding to generate a multicolor switching system, which included charming white light due to the dual emission of fluorescence and phosphorescence. Crystallographic analysis was conducted to explain the reasons for the differences in photophysical properties produced by the two compounds. This research provides insight into the mechanism of action of RTP, TADF and multicolor MCL through intermolecular interactions and conformational modulation.

Asymmetric donor-acceptor molecule-regulated core-shell-solvation electrolyte for high-voltage aqueous batteries

<h2>Summary</h2> Salt-concentrated aqueous electrolytes show a wider electrochemical window than conventional aqueous electrolytes, yet still suffer from significant hydrogen evolution reaction (HER) at <1.9 V versus Li⁺/Li. Introducing organic compounds was reported to alleviate HER, but all reported organic additives are flammable, inevitably compromising the safety property. Here, we report a new all-nonflammable-ingredient aqueous electrolyte via hybridizing with nonflammable methylurea. The structurally asymmetric methylurea molecules possessing both donor and acceptor functional groups regulate the hydrogen bonding network, resulting in peculiar nanoscale core-shell-like clusters. Such unique solution structure allows localized super-high salt concentration in the electrolyte and suppresses HER at 0.5 V versus Li⁺/Li, achieving a 4.5 V electrochemical window. Under a harsh testing condition with low electrolyte loading, no excess Li resource, no electrode precoating, and conventional aluminum current collectors, this electrolyte realizes a stable cycling of a rocking-chair NbO₂|LiMn₂O₄ full cell (∼175 Wh kg^–1) without compromising the safety property.

Nanosecond-time-scale delayed fluorescence towards fast triplet-singlet spin conversion for efficient orange-red OLEDs with negligible efficiency roll-off

Efficient thermally activated delayed fluorescence (TADF) relies on fast reverse intersystem crossing (RISC) that promotes triplet-singlet spin conversion to shorter excited state lifetime, which is a decisive factor to achieve high electroluminescence performance. In this study, two new TADF emitters BenCN-PXZ and BDCN-PXZ employing an asymmetric donor-acceptor framework are designed and synthesized by combining different CN-modified acceptor units with phenoxazine (PXZ) as a strong electron donor unit. The influence of CN-group with different substituting sites is systematically compared to highlight the structure-property relationship. BenCN-PXZ and BDCN-PXZ exhibit red emission with emission peak over 600 nm and short delayed lifetime within 0.6 µs in the neat film. Surprisingly, the delayed lifetime of BDCN-PXZ is still shorter than 1 µs even being doped into CBP host, implying their promising application in organic light-emitting devices (OLEDs). Both Non-doped and doped OLEDs are fabricated for comparison, among which, doped device based on BDCN-PXZ: CBP presented superior device performances and negligible efficiency roll-off (2.8%) at 1000 cd m−2, which is almost the best results for orange-red TADF-based OLEDs.

Electron Push-Pull Effects on Intramolecular Charge Transfer in Perylene-Based Donor-Acceptor Compounds.

A series of asymmetric donor-acceptor (D-A) perylene-based compounds, 3-(N,N-bis(4'-(R)-phenyl)amino)perylene (Peri-DPA(R)), were successfully prepared to explore their intramolecular charge transfer (ICT) properties. To induce ICT between the donor and acceptor, diphenylamine (DPA) derivatives (electron donor units) with the same functional groups (R = CN, F, H, Me, or OMe) at both para positions were linked to the C-3 position of perylene to produce five Peri-DPA derivatives. A steady-state spectroscopy study on Peri-DPA(R)s exhibited a progressively regulated ICT trend consistent with the substituent effect as it progressed from the electron-withdrawing group to the electron-donating group. In particular, a comparative study using a D-A-D (donor-acceptor-donor) system demonstrated that not only the electron push-pull substituent effect but also subunit combinations influence photophysical and electrochemical properties. The different ICT characters observed in Lippert-Mataga plots of D-A(CN) and D-A-D(CN) (CN-substituted D-A and D-A-D) led to the investigation on whether ICT emission of two systems with differences in subunit combinations is of the same type or of a different type. The femtosecond transient absorption (fs-TA) spectroscopic results provided direct evidence of ICT origin and confirmed that D-A(CN) and D-A-D(CN) exhibited the same transition mix of ICT (from donor to acceptor) and reverse ICT (rICT, from arylamine to CN unit). Density functional theory (DFT)/TD-DFT calculations support the presence of ICT for all five compounds, and the experimental observations of rICT presented only for CN-substituted compounds.

Asymmetric-donor (D2D2′)–acceptor (A) conjugates for simultaneously accessing intrinsic blue-RTP and blue-TADF

Asymmetric-donor–acceptor (D2D2′–A) conjugates for simultaneously accessing blue room-temperature phosphorescence (BRTP) and blue thermally activated delayed fluorescence (BTADF).

Asymmetric Color‐Changeable Luminophore with Donor–Acceptor–Donor Structure for Solvent and Temperature Sensitive Properties

AbstractAn asymmetric donor–acceptor–donor (D–A–D) type organic luminophore is reported for solvent and temperature sensors. The electronic absorption and luminescence properties of the luminophore were assessed from its electronic absorption and luminescence spectra, which depended on the external environment. The D–A–D luminophore showed environment‐sensitive charge transfer fluorescence based on structural transformation through excited singlet states. Characteristic D–A–D phosphorescence was also observed at 494 nm, which was shorter than that of the D–A–D fluorescence (502 nm). In this study, the novel photophysical properties of a D–A–D‐type luminophore induced by its asymmetric electronic structure are described.

Star-Shaped Boron-Containing Asymmetric Host Materials for Solution-Processable Phosphorescent Organic Light-Emitting Diodes.

Boron‐containing compounds have attracted considerable attention because of their electron‐accepting properties, and they are widely used in a variety of fields. However, due to the essential requirement to protect the empty pz‐orbital of the boron atom using large steric hindrance or rigid groups, borane derivatives generally show poor solubility and are rarely reported as acceptor units to construct bipolar host materials for phosphorescent organic light‐emitting diodes (PhOLEDs). Here, a combined star‐shaped and asymmetric donor–acceptor molecular design strategy to improve the solubility and fine tune the optical and electronic properties of boron‐containing materials is presented. High thermal stability, solvent solubility, solution processability, and triplet energy are achieved simultaneously. With the thus‐designed boron‐containing bipolar molecules as host materials, the solution‐processed PhOLEDs exhibit high device performances, which are comparable to the vacuum‐processed counterparts, showing high external quantum efficiencies up to 18.5% and 14.5% in blue and white PhOLEDs, respectively. These results demonstrate the great potential of the star‐shaped and symmetry‐breaking borane derivatives in solution‐processable organic optoelectronic devices.

Strategies for the Molecular Design of Donor–Acceptor-type Fluorescent Emitters for Efficient Deep Blue Organic Light Emitting Diodes

We describe several strategies for the molecular design of high-efficiency blue fluorescent emitters. Asymmetric donor–acceptor (D–A) and symmetric A–D–A-type fluorescent emitters were designed with spiroacridine donors and diphenyltriazine acceptors. Substituting a toluene or xylene moiety for the phenyl group connecting the donor and acceptor and replacing the diphenylsilane group with a fluorene moiety resulted in a deeper blue emission without any losses in luminescence efficiency. On the basis of these substitutions, deep blue organic light emitting diodes (OLEDs) with Commission Internationale de L’Eclairage (CIE) coordinates of (0.149, 0.082) and an external quantum efficiency (EQE) of 7.7% were fabricated using a D–A-type emitter. Symmetrizing the D–A structure to an A–D–A structure increased the proportion of horizontally oriented emission dipoles in the organic film from 70 to 90%. OLEDs incorporating symmetric A–D–A-type emitters had EQEs as high as 8.5% due to increased outcoupling efficiencie...

Direct arylation synthesis of thienoisoindigo‐based low‐band‐gap polymer from asymmetric donor–acceptor monomer

ABSTRACTThienoisoindigo (TIG) moiety has been paid numerous attentions as an excellent acceptor building block in low‐band‐gap polymers. Herein, a new TIG‐dithiophene alternating copolymer (PTIG2T) was successfully synthesized from an asymmetric TIG‐based donor–acceptor (D‐A) monomer via the self‐condensation‐type direct arylation polymerization. PTIG2T exhibited the light absorption over 1000 nm owing to the intramolecular charge transfer in the thin film state, which corresponded to an optical band gap of 1.24 eV. The HOMO and LUMO levels of PTIG2T were determined to be −5.08 and −3.60 eV, respectively. Furthermore, the organic photovoltaic (OPV) with a PTIG2T/PC61BM active layer achieved a power conversion efficiency (PCE) of 3.19%, which is one of the highest PEC achieved by OPVs with TIG‐based materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 430–436

Theoretical perspective for internal quantum efficiency of thermally activated delayed fluorescence emitter in solid phase: A QM/MM study

Abstract Excited state dynamics and charge transfer property of an orange-red thermally activated delayed fluorescence (TADF) emitter are theoretically investigated by a quantum mechanics/molecular mechanics (QM/MM) method and kinetic Monte Carlo simulation. The factors that influence internal quantum efficiency of the organic light-emitting diode (OLED) based on an asymmetric donor–acceptor (D–A) type molecule 10-(7-fluoro-2,3-diphenylquinoxalin-6-yl)-10H-phenoxazine (FDQPXZ) are analyzed. The results show that the intramolecular rotation of donor unit is restricted because of the enhanced intermolecular interaction in solid phase, which hinders the non-radiative consumption of the excited state energy. The decreased reorganization energy in solid phase is mainly contributed by dihedral angle in low-frequency (

Photophysics of an Asymmetric Donor–Acceptor–Donor′ TADF Molecule and Reinterpretation of Aggregation-Induced TADF Emission in These Materials

We report an in-depth photophysical investigation of an asymmetric donor–acceptor–donor′ (D–A–D′) thermally activated delayed fluorescence (TADF) molecule (4-(9H-carbazol-9-yl)phenyl)(4-(10H-phenothiazin-10-yl)phenyl)sulfone and compare its photophysical properties to the parent symmetric D–A–D and D′–A–D′ molecules. These D–A–D type small molecules all show strong TADF. The work reveals how the relative orientations of D–A (D′–A) moieties favor reverse intersystem crossing (rISC) by forming stable charge transfer (CT) states. The key requirement for the efficient TADF emitters is to achieve a very small CT-local triplet state energy splitting, which is shown to be complex in the asymmetric molecule. Throughout the investigations, we show that in the asymmetric D–A–D′ system, even though ECT (D–A) > ECT (D′–A), no evidence of energy transfer from D–A to A–D′ is observed, nor from excited D to D′. This is ascribed to the near orthogonality of the D and D′ units and the very strong decoupling of the electro...

Exquisite 1D Assemblies Arising from Rationally Designed Asymmetric Donor-Acceptor Architectures Exhibiting Aggregation-Induced Emission as a Function of Auxiliary Acceptor Strength.

One-dimensional nanostructures with aggregation-induced emission (AIE) properties have been fabricated to keep the pace with growing demand from optoelectronics applications. The compounds 2-[4-(4-methylpiperazin-1-yl)benzylidene]malononitrile (PM1), 2-{4-[4-(pyridin-2-yl)piperazin-1-yl]-benzylidene}malononitrile (PM2), and 2-{4-[4-(pyrimidin-2-yl)piperazin-1-yl]benzylidene}malononitrile (PM3) have been designed and synthesized by melding piperazine and dicyanovinylene to investigate AIE in an asymmetric donor-acceptor (D-A) construct of A'-D-π-A- topology. The synthetic route has been simplified by using phenylpiperazine as a weak donor (D), dicyanovinylene as an acceptor (A), and pyridyl/pyrimidyl groups (PM2/PM3) as auxiliary acceptors (A'). It has been established that A' plays a vital role in triggering AIE in these compounds because the same D-A construct led to aggregation-caused quenching upon replacing A' with an electron-donating ethyl group (PM1). Moreover, the effect of restricted intramolecular rotation and twisted intramolecular charge transfer on the mechanism of AIE has also been investigated. Furthermore, it has been clearly shown that the optical disparities of these A'-D-π-A architectures are a direct consequence of comparative A' strength. Single-crystal X-ray analyses provided justification for role of intermolecular interactions in aggregate morphology. Electrochemical and theoretical studies affirmed the effect of the A' strength on the overall properties of the A'-D-π-A system.