Non-conjugated Linker Research Articles

Molecular Junctions for Terahertz Switches and Detectors.

Molecular electronics targets tiny devices exploiting the electronic properties of the molecular orbitals, which can be tailored and controlled by the chemical structure and configuration of the molecules. Many functional devices have been experimentally demonstrated; however, these devices were operated in the low-frequency domain (mainly dc to MHz). This represents a serious limitation for electronic applications, although molecular devices working in the THz regime have been theoretically predicted. Here, we experimentally demonstrate molecular THz switches at room temperature. The devices consist of self-assembled monolayers of molecules bearing two conjugated moieties coupled through a nonconjugated linker. These devices exhibit clear negative differential conductance behaviors (peaks in the current-voltage curves), as confirmed by ab initio simulations, which were reversibly suppressed under illumination with a 30 THz wave. We analyze how the THz switching behavior depends on the THz wave properties (power and frequency), and we benchmark that these molecular devices would outperform actual THz detectors.

Non-conjugated linkage enabling a quinone-based cathode material with long cycle life and high energy density for aqueous zinc batteries

A phenyl cross-linked tri-p-benzoquinone cathode realizes 150 000 cycle life with 143 mA h g−1 capacity retained at 100 A g−1.

Efficient Intramolecular Singlet Fission in Spiro-Linked Heterodimers.

We investigate intramolecular singlet fission (iSF) of spiro-linked azaacene heterodimers by time-resolved spectroscopy and quantum chemical calculations. Combining two different azaacenes through a nonconjugated linker using condensation chemistry furnishes azaacene heterodimers. Compared to their homodimers, iSF quantum yields are improved at an extended absorption range. The driving force of iSF, the energy difference ΔEiSF between the S1 state and the correlated triplet pair 1(TT), is tuned by the nature of the heterodimers. iSF is exothermic in all of the herein studied molecules. The overall quantum yield for triplet exciton formation reaches approximately 174%. This novel concept exploits large energy differences between singlet electronic states in combination with spatially fixed chromophores, which achieves efficient heterogeneous iSF, if the through-space interaction between the chromophores is minimal.

Electrochromic and energy storage properties of novel terpyridine-Fe(II) coordination polymers: Improving performance by molecular engineering of nonconjugated linkers from linear to three-arm star configuration

In this work, two novel terpyridine-Fe(II) coordination polymers ( DTP-Fe and TTP-Fe ) with nonconjugated linkers were developed for electrochromism and energy storage. Both coordination polymers exhibited efficient electrochromic switch between purple and pale yellow with optical contrast over 60%, short coloring time around 2 s, high coloration efficiency over 440 cm 2 C −1 , and good cycle stability. Moreover, the electrodes based on polymers DTP-Fe and TTP-Fe showed a specific capacitance of 21.42 and 35.84 mAh·g −1 at 1 A g −1 , respectively. More important, we demonstrated that the three-arm star configuration may be superior to the conventional linear configuration for efficient electrochemical process, which resulted in the improved performance of the coordination polymer TTP-Fe . An asymmetric electrochromic supercapacitor based on TTP-Fe thin film and Prussian blue thin film was fabricated and possessed potential application in energy saving smart windows. • Two terpyridine-Fe(II) coordination polymers were developed for electrochromism and supercapacitor. • TTP-Fe with a three-arm star configuration showed superior performance. • An asymmetric electrochromic supercapacitor based on TTP-Fe was fabricated.

Planar D-σ-A type thermally activated delayed fluorescence material with Intra- and intermolecular charge transfer characteristics

Intramolecular charge transfer (intra-CT) and intermolecular charge transfer (inter-CT) are two general molecular design strategies of thermally activated delayed fluorescence (TADF) materials for organic light-emitting diodes (OLEDs). Herein, a diphenylamine (DPA) donor and a 2,4-diphenyl-1,3,5-triazine (TRZ) acceptor are connected by two planar units, non-conjugated 9,9-dimethyl-9H-xanthene (XA) and conjugated dibenzo[b,d]furan (FR), to give D-σ-A type emitter DPA-XA-TRZ and D-π-A type emitter DPA-FR-TRZ. Coexistence of intra- and inter-CT is found for DPA-XA-TRZ and is readily tuned by various doping concentrations owing to the non-conjugated linkage. In contrast, DPA-FR-TRZ shows a dominant intra-CT characteristic due to the strong molecular conjugation. The planar molecular skeleton of DPA-XA-TRZ could not only enhance intramolecular electronic coupling, but also reduce steric hindrance and shorten intermolecular distance to enhance inter-CT process. A maximum external quantum efficiency (EQEmax) of 21.9 % is achieved for the OLED device based on DPA-XA-TRZ, which is 2.5 times higher than that of DPA-FR-TRZ (8.4 %). DPA-XA-TRZ can also be utilized as an assistant host to sensitize multiple resonance TADF emitter DMAc-BN, and an EQEmax of 31.7 % is realized owing to its dual CT processes and high reverse intersystem crossing rate (kRISC), which is significantly superior to the conventional mCBP host and mCBP:PO-T2T exciplex cohost.

Enhanced blue thermally activated delayed fluorescence with rigid adamantane as non-conjugated linker for space-confined donor-acceptor charge transfer: a theoretical study

A lack of control over the relative orientation of donor and acceptor moieties in solid films is the main reason for poor electroluminescence efficiency found in most D-σ-A patterns. In this study, adamantane was introduced as the linker for the construction of a D-σ-A system since its rigid but non-conjugated nature. For a systematic study, the same donor (9,9-dimethyl-10-phenyl-9,10-dihydroacridine, DMTPA) and acceptor (2,4,6-triphenyl-1,3,5-triazine, TPZ) block were attached at different sites of the adamantine molecule, forming three kinds of configuration including face-to-face (FF), head-to-tail (HT), and chair (CH) style. DFT/TD-DFT simulation was carried out to investigate the electronic structures, optical characteristics, and charge transfer (ICT) properties of these three designed molecules. Attributed to a non-conjugated adamantane linker, the conjugation between donor and acceptor was disrupted for either of these molecules, resulting in high triplet energy of 2.79, 2.99, and 3.10 eV, respectively. Among them, the face-to-face style molecule presents the smallest ΔEST and greatest charge transfer excitation from donor to acceptor, suggesting an excellent potential for thermal activated delayed fluorescence (TADF). Face-to-face type molecule is a good option for a high-performance blue organic light-emitting diode (OLED) host material based on these results. Our investigation may open a door for designing new host molecule with other donor and acceptor groups to further enhance the efficiency and longevity of OLEDs.

Conjugated/nonconjugated alternating copolymers for enhanced NIR-II fluorescence imaging and NIR-II photothermal-ferrotherapy.

Conjugated polymers hold great promise for NIR-II fluorescence imaging (FI)-guided NIR-II photothermal therapy (PTT) due to the advantages of easy modification of chemical structures and adjustable NIR absorption. However, to make use of these advantages, it is of paramount importance to formulate conjugated polymers with excellent solubility in organic solution, great NIR-II photothermal conversion efficiency, and high NIR-II fluorescence quantum yield. Herein, a new class of conjugated/nonconjugated alternating copolymers (CNACPs) is reported by introducing nonconjugated linkers into a conjugated backbone to modulate the extinction coefficient at 1064 nm and NIR-II fluorescence quantum yield. The NIR-II absorption, NIR-II emission, and NIR-II photothermal properties of the new CNACPs were studied. Interestingly, it is observed that longer nonconjugated linkers in CNACPs result in higher NIR-II fluorescence intensity with sufficient NIR-II absorption and NIR-II photothermal ability. With these newly developed CNACPs (BBT-C6), phototheranostic nanoparticles (BBTD6/Fe@PMA) are prepared through facile nanoprecipitation using PMA-AD-PEG as an iron ion chelator for NIR-II FI-guided NIR-II PTT/ferrotherapy synergistic therapy. In vitro and in vivo, BBTD6/Fe@PMA effectively inhibited 4T1 cells and tumor progression under 1064 nm laser irradiation. Consequently, this work provides new CNACPs by incorporating nonconjugated linkers into a conjugated backbone to design more effective NIR-II fluorescence imaging and NIR-II photothermal therapy agents.

Synthesis and optoelectronic properties of a dinuclear iridium (III) complex containing a picolinic acid derivative by nonconjugated linkage with a D-A-D core

A novel dinuclear iridium (Ⅲ) complex containing a non- conjugated bridging picolinic acid ligand of (C8TPAPhOC2FIrpic)2BT with a D-A-D core was synthesized and characterized, in which the D-A-D core consists of benzo[c][1,2,5]thiadiazole (BT) and triphenylamino (TPA) units. Its optophysical, electrochemical and electroluminescent characteristics were primarily studied. It is found this dinuclear iridium (Ⅲ) complex exhibited similar photoluminescent and electroluminescent profiles, but higher brightness and efficiency in compared with the picolinic acid ligand in the single-emissive-layer organic light-emitting devices. The maximum luminance of 7404 cd/m2 and current efficiency of 0.81 cd/A was obtained in the (C8TPAPhOC2FIrpic)2BT-based devices. The efficient energy transfer is observed from the terminal iridium complex unit to the picolinic acid ligand. This work demonstrates that the picolinic acid ligand with a D-A-D core can facilitate dinuclear iridium (III) complex to exhibit the ancillary ligand-based red emission.

Molecular engineering by σ-linkers enables delayed fluorescence emitters for high-efficiency sky-blue solution-processed OLEDs

Two novel thermally activated delayed fluorescence (TADF) emitters, namely Me2AcBO and F2AcBO, based on the 9,9-dimethrylacridine donor and a rigid oxygen-bridged cyclized boron acceptor, were designed and synthesized for highly efficient blue solution-processed organic light-emitting diodes (OLEDs). Me2AcBO and F2AcBO feature a twin structure derived by coupling two individual TADF monomers through non-conjugated linkers. The two new emitters exhibit 3D molecular structures, excellent thermal/morphological properties, high photoluminescence quantum yields over 97%, and high reverse intersystem crossing rates on the order of 106 s−1, which greatly benefit the high device efficiency. Solution-processed sky-blue TADF OLEDs based on Me2AcBO and F2AcBO achieved the maximum external quantum efficiency of 11.0% and 10.9%, respectively, with Commission Internationale de L’Eclairage (CIE) coordinates of (0.14, 0.25). Interestingly, relatively low efficiency roll-offs of 33% and 34% at the luminance of 1000 cd/m2 were demonstrated for Me2AcBO and F2AcBO based devices, respectively. This study presents a novel strategy to realize highly efficient sky-blue TADF emitters for solution-processed OLEDs.

Self-assembly monomolecular engineering towards efficient and stable inverted perovskite solar cells

Perovskite solar cells (PSCs) with monolayer-modified anodes are promising for high efficiency and stability devices with simplified configuration. Though preliminary studies on modified anodes by small organic molecules were reported, the goal-directed design and regulation of such compounds have been sparsely reported so far, thus limiting device performances. Herein, D-o-D type triphenylamine derivatives with non-conjugated linkage of sp3 oxygen are proposed to finely tune the energy level alignment and enhance the defect passivation at the ITO/perovskite interface, thus facilitating the efficient charge extraction at the anodes. The optimized molecules considerably ameliorate the photovoltaic performances of the corresponding inverted PSCs, engendering a preeminent power-conversion-efficiency (PCE) of 20.57% with negligible hysteresis. Remarkably, a good long-term stability is recorded for the unencapsulated device with over 94% of the initial PCE maintained after 180 days storage in N2 condition. Those improved performances validate the feasibility of the D-o-D molecules for cost-effective PSCs with high-efficiency, and excellent long-term stability.

Ultra-pH-sensitive sensor for visualization of lysosomal autophagy, drug-induced pH alteration and malignant tumors microenvironment

The acidity of lysosome is essential to complete its own physiological activities. The abnormal fluctuation of pH in lysosome can cause many serious diseases, such as cancer and Alzheimer's disease. Therefore, it is particularly important to develop a tool for visualizing detection the pH fluctuations of lysosome. Herein, a new ratiometric fluorescent probe (SN-Lyso) with (ICT-FRET) dual mechanism for detecting pH fluctuations of lysosomes was proposed, which was the combination of the 2-(2-morpholinoethyl)-1,8-naphthalic anhydride and spiropyran by a nonconjugated linker. SN-Lyso responded to acid and alkali pH changes with red and green emissions, respectively. Meanwhile, SN-Lyso was successfully applied in fluorescence imaging in living cells. It was found that cells undergoing autophagy could cause lysosomal pH to decrease, and chloroquine-stimulated result in lysosomal pH to increase. In addition, SN-Lyso was sensitive to pH and could specifically identify tumor in mice. We expect that SN-Lyso will provide an efficient method for studying the mechanism of lysosomal pathology and visualizing the treatment of tumor sites.

A smart TP-FRET-based ratiometric fluorescent sensor for bisulfite/formaldehyde detection and its imaging application

Bisulfite (HSO3−) and formaldehyde (FA) are hazardous environmental pollutants that pose serious risks to human health. Herein, we report for the first time a novel TP-FRET-based TP-ratiometric reversible fluorescence sensor NPXH, which is based on combining TP naphthalimide fluorophore with a deep red-emitting xanthene fluorophore via a nonconjugated linker, for reversible detection of bisulfite/formaldehyde. In presence of HSO3−, NPXH shows a significant ratio enhancement (∼6-fold) in I535/I630, ultra-fast response (less than 8 s) and super low detection limit (7.48 nM). In addition, the fluorescence signal of NPXH is easily and rapidly recovered by FA within 1 min. More impressively, NPXH has shown excellent detection capability in food and water samples and has been successfully applied to HSO3−/FA detection in liver tissue, zebrafish and mice.

Molecular engineering of head-tail terpyridine-Fe(II) coordination polymers employing alkyl chain linkers toward enhanced electrochromic performance

For the first time, we demonstrated that employing long alkyl chains as a nonconjugated linker in ditopic ligands is a promising strategy to construct Fe(II) coordination polymers for efficient electrochromics. Three new Fe(II) coordination polymers with ditopic organic ligands, in which two terpyridine moieties were connected by nonconjugated alkylchain linkers were synthesized. The morphology and hydrophobicity of the thin film made from the Fe(II) coordination polymers can be adjusted by changing the length of alkylchain linker. Benefiting from the longer length of the linker, the ditopic terpyridine-Fe coordination polymer FeL2 performed superior electrochromic performance as compared to FeL1 in the same condition, including shorter switch time, lower operation potential, higher optical contrast and coloration efficiency. Remarkably, the elaborate coordination polymer FeL2 exhibited the highest optical contrast up to 76% among the reported electrochromic materials based on Fe-complexes up to date. Due to the hydrophobic property of FeL3 probably benefit from its longer alkyl chain linkers, we carried out the electrochromic switch based on ionic Fe(II) coordination polymers using aqueous electrolyte for the first time.

Peripheral carbazole or cyano substitutents in poly (aryl ether) based bipolar polymeric hosts: Increase the hole or electron injection properties for blue phosphorescent polymer light emitting diodes

AbstractA series of poly (aryl ether) based bipolar polymer hosts, PCzOPOC8, PCzOPOCz, and PCzOPOCN with a peripheral carbazole or cyano unit which joins the main chain by a nonconjugated linker of a hexyl group, were synthesized and characterized. They depicted high triplet level (ET) (>2.80 eV), which was probably attributed to oxygen‐interrupted nonconjugated main chains of polymers as well as carbazole and phosphine oxide groups with high ET. While doped with a 10 wt% typical blue phosphor {iridium(III)[bis(4,6‐difluoro phenyl)pyridinato‐N, C2]picolinate, FIrpic)}, compared with those of nonsubstituted PCzOPOC8 and peripheral cyano‐substituted PCzOPOCN, PCzOPOCz with carbazole moiety gave better performances due to balance of carrier flux from carbazole moiety with good hole transport ability.

A novel fluorescent probe for ratiometric detection of formaldehyde in real food samples, living tissues and zebrafish.

Herein, a two-photon (TP) ratiometric fluorescent probe (NpFA) was developed for detecting formaldehyde (FA) in real food samples, living onion tissues and zebrafish by fluorescence resonance energy transfer (FRET) strategy. Specifically, a TP fluorophore as the donor and a FA turn-on naphthalimide fluorophore as the acceptor were connected by a non-conjugated linker to construct the TP-FRET-based NpFA, which exhibited a target-modulated ratiometric fluorescence response to FA rapidly with high selectivity and sensitivity during 65s, and a large ratio ~5-fold enhancement at I550/I410 after addition of FA, displaying ~60-fold enhancement at 550nm and a quite low DOC of 5.8±0.2nM. Moreover, NpFA has a good imaging resolution and depth of deep tissue penetration. Therefore, based on the above results, NpFA has the capability to be a useful tool for investigating FA in real samples application, and we also hope NpFA will further study of the physiological and pathological function of FA.

TP-FRET-Based Fluorescent Sensor for Ratiometric Detection of Formaldehyde in Real Food Samples, Living Cells, Tissues, and Zebrafish.

Formaldehyde (FA, HCHO) is a highly reactive carbonyl species, which is very harmful to humans and the environment as a tissue fixative and preservative. Therefore, developing some highly sensitive, selective, and rapid detection methods is significant for human health in food safety and environmental protection. Herein, a two-photon (TP) ratiometric sensor, CmNp-CHO, has been constructed by conjugating a TP donor (Π-push-pull-structure) with a FA off-on acceptor (functioned with hydrazide moiety) via a nonconjugated linker through the fluorescence resonance energy transfer mechanism. Such a scaffold affords CmNp-CHO a reliable and specific probe for detecting FA with two well-resolved emission peaks separated by 124 nm. Also, it responds to FA rapidly with high selectivity and sensitivity during 1.0 min and a large ratio enhancement at I550/I426 with addition of 0-20μM FA, exhibiting ∼4-fold ratio increase and a fairly low LOD of 8.3 ± 0.3 nM. Moreover, CmNp-CHO has been successfully employed for detecting FA in live cells, onion tissues, and zebrafish, exhibiting that CmNp-CHO can serve as a useful tool for investigating FA in real food application and offering strong theoretical support and technical means for investigation of physiological and pathological functions of FA.

Rational Design of Carbazole- and Carboline-Based Polymeric Host Materials for Realizing High-Efficiency Solution-Processed Thermally Activated Delayed Fluorescence Organic Light-Emitting Diode.

Recently, various host materials have been developed for solution-processed thermally activated delayed fluorescent organic light-emitting diodes (TADF-OLEDs). Compared with small-molecule hosts, polymeric hosts are advantageous for inducing a uniform distribution and segregation of dopant molecules in the emissive layer without undesired large-scale phase separation. In this study, new polymer hosts were demonstrated, in which a bipolar conjugative moiety consisting of a carbazole (Cz) donor and an α-carboline (α-Cb) acceptor was bound to the polystyrene backbone through a non-conjugated linker. They exhibited high triplet energies of >2.8 eV, and their emission spectra overlapped with the absorption spectrum of a green TADF emitter, which allowed facile energy transfer from the polymeric host to the small-molecule dopants. High device performance was observed, with external quantum efficiencies (EQEs) of 13.65, 17.09, and 17.48% for solution-processed green TADF-OLEDs using PSCzCz, PSCzCb, and PSCbCz, respectively, as hosts for the EML. The EQEs of bipolar host (PSCzCb and PSCbCz)-based devices were higher than those of unipolar host (poly(N-vinylcarbazole) and PSCzCz)-based devices owing to the well-balanced charge-carrier transport. According to these results, the polymeric host bearing a bipolar Cz and α-Cb coupled moiety is a promising material for solution-processable TADF-OLEDs.

A TP-FRET-based fluorescent sensor for ratiometric visualization of selenocysteine derivatives in living cells, tissues and zebrafish

Selenium is a biologically essential micronutrient element serving as an essential building block for selenoproteins (SePs), which is playing a key role in various cellular functions. Hence, it is of great significance to developing a reliable and rapid method for detection of Sec in biosystems. Compared with the previously reported probes that have been developed for selective detection of Sec, two-photon (TP) ratiometric Sec-specific probes would be advantageous for the NIR excitation and built-in correction of the dual emission bands. To quantitatively and selectively detect Sec over biothiols with rapid and sensitive response, we for the first time report a new fluorescence resonance energy transfer (FRET)-based TP ratiometric fluorescence probe CmNp-Sec, which was constructed by conjugating a TP fluorophore 6 (coumarin derivative with a D-π-A-structure) with a naphthalimide fluorophore 9 via a non-conjugated linker, and employed a 4-dinitrobenzene-ether (DNB) with a strong ICT effect as Sec responsive moiety. It exhibits quantitatively detect Sec in a wide range (0-50 μM) with a limit of detection of 7.88 nM within 10 min. More impressively, this probe can be conveniently used to detect Sec in living cells, tissues and zebrafish, demonstrating it has the latent capability in further biological applications.

Luminescent Rhenium(I)-Polypyridine Complexes Appended with a Perylene Diimide or Benzoperylene Monoimide Moiety: Photophysics, Intracellular Sensing, and Photocytotoxic Activity.

This communication reports novel luminescent rhenium(I)-polypyridine complexes appended with a perylene diimide (PDI) or benzoperylene monoimide (BPMI) moiety through a non-conjugated linker. The photophysical and photochemical properties originating from the interactions of the metal polypyridine and perylene units were exploited to afford new cellular reagents with thiol-sensing capability and excellent photocytotoxic activity.

A dual-site modulated FRET-based two-photon ratiometric fluorescent probe for tracking lysosomal pH changes in living cells, tissues and zebrafish

Lysosomal pH plays an essential role in mediating various biological processes such as immunization, cell metabolism and enzyme activity. Herein, by utilizing the fluorescence resonance energy transfer (FRET) strategy, a two-photon (TP) ratiometric fluorescent probe (NpLys-pH) has been developed for tracking of lysosomal pH changes in living cells, tissues, and zebrafish. NpLys-pH was constructed by conjugating a pH turn-on TP fluorophore 1 (D-π-A-structured naphthalene derivative) with a pH turn-off naphthalimide fluorophore 2via a non-conjugated linker. Meanwhile, NpLys-pH has two potential pH response sites that modulate the fluorescence signal by ICT and PET, respectively. The FRET process exists between the TP fluorophore 1 and naphthalimide fluorophore 2. In addition, NpLys-pH respond to pH rapidly and reversibly with high selectivity and sensitivity and has been applied for tracking lysosomal pH changes in living cells, tissues and zebrafish. We expect that the new probe present here can prompt the development of a wide variety of TP ratiometric fluorescent probes which can find application in detecting other important analytes in biological systems.