Electron-donating Triphenylamine Research Articles

Synthesis, Electrochemistry and Photochemistry of Hypervalent Phosphorus(V) Porphyrin and Antimony(V) Porphyrin Black Dyes

In the last few years, our focus has been on push-pull type hypervalent Group 15 porphyrins with intramolecular charge transfer (ICT) properties. Insertion of P(V) or Sb(V) ion in the porphyrin cavity results in a highly electron-deficient porphyrin center, under this condition the presence of electron-rich units in porphyrin meso-positions results in charge transfer within the molecules. Recently, we extended this strategy to 5,10,5,20-tetrakis(triphenylamine)porphyrin derivative where strong electron donor triphenylamine (TPA) units are in meso-positions. Upon insertion of the P(+5) and Sb(+5) ion, the resulting hypervalent Group 15 porphyrins manifested a strong ICT from the TPA units to the central porphyrin ring. The existence of ICT makes the absorption profiles cover the entire visible region with high molar extinction coefficients. Due to this reason, the studied hypervalent Group 15 porphyrins appear as black dyes. Here, I will present these porphyrins and discuss their structural, redox, and remarkable photophysical properties. Figure 1

Trident anchoring-lipid droplets strategy for fluorescence/super-resolution/lifetime imaging and diagnosis of fatty liver in vivo

Lipid droplets (LDs) are crucial dynamic organelles within cells that play an indispensable role in cellular energy supply, membrane formation, and signal transduction. Therefore, detecting and tracking LDs with high selectivity and resolution is particularly important. In this study, we describe a “trident” anchoring strategy (based on polarity, lipophilicity, and viscosity sensitivity) to achieve highly specific and dynamic imaging of LDs. A series of carbazole-substituted fluorescent protein (Car-FP) mimics conjugated with different electron-nature substituents (A–H) were synthesized and characterized. Spectroscopic properties indicate that the electron-donating triphenylamine (TPA)-conjugated H exhibits high sensitivity to polarity, viscosity response, and lipophilicity. Co-localization experiments in cells also demonstrate that H selectively localizes at LDs in living cells, displaying a bright yellow fluorescence signal (λex = 488 nm; λem = 577 nm) with a larger Stokes shift (89 nm) than the commercial LD dye bodipy 493/503 (10 nm). Super-resolution fluorescence imaging (SIM) and lifetime imaging (FLIM) are employed to visualize the distribution and aggregation in cell models of nonalcoholic fatty liver disease as well as zebrafish and mice models, demonstrating the potential applications of H in LD biology research and diagnosis of related diseases.

Multimodal phototherapy agents target lipid droplets for near-infrared imaging-guided type I photodynamic/photothermal therapy

The construction and optimization of a single phototherapeutic agent with photoluminescence, type I photodynamic therapy (PDT), and photothermal therapy (PTT) functions remain challenging. In this study, we aimed to design and synthesize four donor–acceptor (D-A) type aggregation-induced emission molecules: PSI, TPSI, PSSI, and TPSSI. We employed phenothiazine as an electron donor and 1,3-bis(dicyanomethylidene)indan as a strong electron acceptor in the synthesis process. Among them, TPSSI exhibited efficient type I reactive oxygen species generation, high photothermal conversion efficiency (45.44 %), and near-infrared emission. These observations can be attributed to the introduction of a triphenylamine electron donor group and a thiophene unit, which resulted in increased D–A strengths, a reduced singlet-triplet energy gap, and increased free intramolecular motion. TPSSI was loaded into bovine serum albumin to prepare biocompatible TPSSI nanoparticles (NPs). Our results have indicated that TPSSI NPs can target lipid droplets with negligible dark toxicity and can efficiently generate O2•− in hypoxic tumor environments. Moreover, TPSSI NPs selectively targeted 4T1 tumor tissues and exhibited a good PDT-PTT synergistic effect in vitro and in vivo. We believe that the successful preparation of multifunctional phototherapeutic agents will promote the development of efficient tumor diagnosis and treatment technologies. Statement of SignificanceThe construction of a single phototherapeutic agent with photoluminescence, type I photodynamic therapy, and photothermal therapy functions, and its optimization remain challenging. In this study, we construct four donor–acceptor aggregation-induced emission molecules using phenothiazine as an electron donor and 1,3-Bis(dicyanomethylidene)indan as a strong electron acceptor. By optimizing the molecular structure, an integrated phototherapy agent with fluorescence imaging ability and high photodynamic / photothermal therapy performance was prepared. We believe that the successful preparation of multifunctional phototherapeutic agents will promote the development of efficient tumor diagnosis and treatment technology.

Natural Acceptor of Coumarin-Isomerized Red-Emissive BioAIEgen for Monitoring Cu2+ Concentration in Live Cells via FLIM.

Artificial aggregation-induced emission luminogens (AIEgens) have flourished in bio-applications with the development of synthetic chemistry, which however are plagued by issues like singularity in structures and non-renewability. The unique structures and renewability of biomass moieties can compensate for these drawbacks, but their properties are hard to design and regulate due to their confined structures. Therefore, it appears to be a reasonable approach to derive AIEgens from abundant biomass (BioAIEgens), integrating the bilateral advantages of both synthetic and natural AIEgens. In this work, the blue-violet emissive coumarin with its lactone structure serving as a rare natural acceptor, is utilized to construct donor-π-acceptor typed BioAIE isomers incorporating the propeller-like and electron-donating triphenylamine (TPA) unit. The results show that Cm-p-TPA undergoes charge transfer with its keto form, emitting red light at 600nm, which can be applied to monitor Cu2+ concentration during mitophagy using fluorescence lifetime imaging microscopy because of the excellent biocompatibility, photostability, and specific recognition to Cu2+ . This work not only demonstrates the feasibility of utilizing positional isomerization to modulate excited-state evolutions and resultant optical properties, but also provides evidence for the rationality of constructing biologically-active BioAIEgens via a biomass-derivatization concept.

Mitochondria-targeted pentacyclic triterpene NIR-AIE derivatives for enhanced chemotherapeutic and chemo-photodynamic combined therapy

Complexes formed by combining pentacyclic triterpenes (PTs) with Aggregation-Induced Emission luminogens (AIEgens), termed pentacyclic triterpene-aggregation induced emission (PT-AIEgen) complexes, merge the chemotherapeutic properties of PTs with the photocytotoxicity of AIEgens. In this study, we synthesized derivatives by connecting three types of triphenylamine (TPA) pyridinium derivatives with three common pentacyclic triterpenes. Altering the connecting group between the electron donor TPA and the electron acceptor pyridinium resulted in increased production of reactive oxygen species (ROS) by PT-AIEgens and a red-shift in their fluorescence emission spectra. Importantly, the fluorescence emission spectra of BA-3, OA-3, and UA-3 extended into the near-infrared (NIR) range, enabling NIR-AIE imaging of the sites where the derivatives aggregated. The incorporation of the pyridinium structure improved the mitochondrial targeting of PT-AIEgens, enhancing mitochondrial pathway-mediated cell apoptosis and improving the efficiency of chemotherapy (CT) and chemo-photodynamic combined therapy (CPCT) both in vivo and in vitro. Cellular fluorescence imaging demonstrated rapid cellular uptake and mitochondrial accumulation of BA-1 (−2, −3). Cell viability experiments revealed that BA-1 (−2), OA-1 (−2), and UA-1 (−2) exhibited superior CT cytotoxicity compared to their parent drugs, with BA-1 showing the most potent inhibitory effect on HeLa cells (IC50 = 1.19 μM). Furthermore, HeLa cells treated with BA-1 (1 μM), BA-2 (1.25 μM), and BA-3 (1 μM) exhibited survival rates of 2.99 % ± 0.05 % μM, 5.92 % ± 2.04 % μM, and 2.53 % ± 0.73 % μM, respectively, under white light irradiation. Mechanistic experiments revealed that derivatives induced cell apoptosis via the mitochondrial apoptosis pathway during both CT and CPCT. Remarkably, BA-1 and BA-3 in CPCT inhibited cancer cell proliferation in an in vivo melanoma mouse xenograft model. These results collectively encourage further research of PT-AIEgens as potential anticancer agents.

How the π bridge in donor-π-acceptor type covalent triazine frameworks influenced their photocatalytic hydrogen evolution performance

Covalent triazine frameworks (CTFs) have recently emerged as promising organic semiconductor materials for use in hydrogen evolution reactions (HERs) under visible light radiations. Nevertheless, how to favorably tune the CTF structure and optimize the photo-induced electron transfer pathway for highly efficient HERs still remains a challenge. Herein, we designed a thiophene-bridged electron-donating triphenylamine moiety-based donor-π-acceptor (D-π-A) type CTF, SCTF, which is found to be a more feasible photocatalyst for HER in comparison with the benzene-bridged one, BCTF. The HER rate by using SCTF could reach 977.1 μmol h−1, which is 6.81 times that by BCTF. Further studies on the thermodynamics and kinetics of charge separation in resulted CTFs suggested that the employment of thiophene π bridge in SCTF rather than benzene in BCTF could lead to the broader light absorption, optimize charge transfer pathway in crystalline CTFs and enhance the built-in electric field to dramatically accelerate charge separation and transfer. The in-depth exploration of the photocatalytic process has further revealed the role of thiophene bridge in promoting the photocatalytic HER efficiency for D-π-A type CTFs. Overall, we have offered a promising strategy to finely tune CTF structure and the photogenerated carriers transfer pathway for efficient CTF-based photocatalytic HER catalysts.

Effects of the change of isomers on room-temperature phosphorescence, thermally activated delayed fluorescence, and long persistent luminescence of organic hole-transporting materials with the selective potential for the application in electronic devices and optical sensors of oxygen

Competition of room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) was investigated on the example of four newly synthesised organic isomeric compounds containing two electron-donating triphenylamine moieties and single electron-accepting dibenzothiophene-2-yl(phenyl)methanone unit by numerous theoretical and experimental approaches. The different emission origin (RTP or TADF) of the isomeric compounds was caused by the different energy gaps between the lowest singlet and triplet states locally exited and charge transfer in nature. Very different external quantum efficiencies ranging from 2.8 to 13.9% were observed for green phosphorescent organic light-emitting diodes fabricated using the isomeric compounds as the hosts. Such device efficiency differences were related to the different hole mobility values. The hole mobilities of ca. 1 × 10−3 cm2V−1s−1 were observed at an electric field of 6.4 × 105 V/cm for the derivatives having triphenylamine moieties at C-2, C-4, and at C-3, C-5 positions of the central benzene ring. Considerably lower hole mobilities of ca. 1 × 10−5 cm2 V−1 s−1 were recorded at the same electric field for the compounds with triphenylamine groups at C-2, C-3, and at C-2, C-6 positions. Depending to the great extent on RTP and TADF processes, different efficiencies of long persistent luminescence (LPL) of the exciplex-forming solid-state mixtures of the isomers and bis[2-(diphenylphosphine)phenyl] ether oxide (DPEPO) were detected. The compound with triphenylamine groups at C-3, and C-5 positions as RTP emitter and its molecular mixture with DPEPO as LPL emitter the active layers of optical sensors of oxygen were prepared. They showed the Stern–Volmer constant of 4.55 × 10−4 ppm in the range of oxygen concentrations up to 10000 ppm.

Suppressing Excess Lead Iodide Aggregation and Reducing N-Type Doping at Perovskite/HTL Interface for Efficient Perovskite Solar Cells.

Excess lead iodide (PbI2 ) aggregation at the charge carrier transport interface leads to energy loss and acts as unstable origins in perovskite solar cells (PSCs). Here, a strategy is reported to modulate the interfacial excess PbI2 by introducing π-conjugated small-molecule semiconductors 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline] (TAPC) into perovskite films through an antisolvent addition method. The coordination of TAPC to PbI units through the electron-donating triphenylamine groups and π-Pb2+ interactions allows for a compact perovskite film with reduced excess PbI2 aggregates. Besides, preferred energy level alignment is achieved due to the suppressed n-type doping effect at the hole transport layer (HTL) interfaces. As a result, the TAPC-modified PSC based on Cs0.05 (FA0.85 MA0.15 )0.95 Pb(I0.85 Br0.15 )3 triple-cation perovskite achieved an improved PCE from 18.37% to 20.68% and retained ≈90% of the initial efficiency after 30 days of aging under ambient conditions. Moreover, the TAPC-modified device based on FA0.95 MA0.05 PbI2.85 Br0.15 perovskite produced an improved efficiency of 23.15% compared to the control (21.19%). These results provide an effective strategy for improving the performance of PbI2 -rich PSCs.

Novel hole transporting materials based on cyclopentadithiophene for perovskite solar cells

We have demonstrated three LY-HTMs for perovskite solar cells in this report. These LY-HTMs embed cyclopentadithiophene (CPT) core that incorporates 2∼4 triphenylamine electron donor units. Designing LY-HTMs with Lewis-basic property of carbonyl or imine, can effectively passivate the defects of insufficiently coordinated Pb2+ in the perovskite layer. The LY-HTMs have good thermal stability and enhanced intermolecular interaction, thereby dense packing, due to the sulfur-sulfur interaction in the dithiophene structure. Moreover, the sulfur-sulfur interaction achieves a deeper HOMO energy level that can be well-matched to perovskite solar cells (PSCs). It also improves the charge mobility to enhance Voc and Jsc values. The best performance using LY-1 as a HTM in PSCs exhibited a Jsc of 23.1 mA∙cm−2, a Voc of 1.06 V, and a fill factor of 0.78, corresponding to an overall conversion efficiency of 19.12% (the control device of spiro-OMeTAD, 17.69%). In addition, the PCEs of the LY-1 PSC devices underwent decays of only 90% and 74.8% of their original values after 10 and 30 days, respectively, under an Ar atmosphere.

Turning the energy channel of side-chain TADF polymers by monomer optimization for high-efficiency solution-processed white OLEDs

Suppressing non-radiative channel in luminescent polymer is the key factor for high device efficiency of organic light-emitting diodes (OLEDs). In this paper, we synthesized three side-chain TADF polymers, PTRZ-TRZ, PTRZ-TPA and PTRZ-Cz, to deeply investigate the relationship between energy transfer and molecular structure. The photophysical measurements show that the copolymerized monomer has significant effect on the exciton deexcitation process of TADF fragment. The rigid carbazole unit can efficiently separate the TADF units to inhibit the aggregation-caused quenching (ACQ) of polymer, while electron-donating triphenylamine unit will induce the severe charge transfer state to form low energy exciplex, which lead to severe energy leakage of the excited TADF. Moreover, according to the single-charge devices test, the ideal separation unit also can improve the capability of charge injection and carrier balance. As a result, the solution-processed OLEDs host with PTRZ-Cz achieved the external quantum efficiency (EQEmax) of 14.2%, which was much higher than that of PTRZ-TPA and PTRZ-TRZ. By doping red phosphorescent emitter Ir(MDQ)2(acac), the hybrid white OLED devices (T-P WOLEDs) based on PTRZ-Cz achieved the maximum current efficiency (CEmax), power efficiency (PEmax) and EQEmax of 46.8 cd/A, 32.6 lm/W and 20.7%, respectively, with a high CRI of 80.6. The outcomes obtained in this study can provide useful insights into the structure−property relationship for further development of efficient TADF polymer hosts for solution-processable OLEDs.

Type-I organic photosensitizers with two complementary reactive oxygen species based on donor-acceptor (D-A) molecules

Type-I photosensitizers (PSs) are considered to be a better choice for photodynamic therapy (PDT) because they can efficiently generate reactive oxygen species (ROS) in the hypoxia condition of tumor, showing less oxygen dependence. However, there are relatively few reported highly efficient type-I organic PSs, especially those simultaneously generated two or more species of type-I ROS. Herein, based on electron-acceptor of 9,10-phenanthrenequinone (PQ), a D-A-D structural type-I PS of PPQ constructed from electron-donor of 9-phenyl-carbazole (PCZ) was firstly developed and could simultaneously produce two type-I ROS under white light irradiation. As the generated ROS of hydroxyl radical (•OH) and superoxide anion radical (O2•−) possessed complementary oxidizing ability and radical lifetime, PPQ showed excellent PDT effects for tumor cells under normoxia or hypoxia. The ability of ROS generation and PDT performance of PPQ were better than those of another PQ derivative (TPQ) constructed with common electron-donor triphenylamine (TPA). More importantly, experiments in aqueous solution and vitro both revealed that •OH generated not only from the well-known transformation of O2•− but also direct electron transition from water to triplet excited PS, which demonstrated the oxygen dependence of type-I PSs more clearly. This new type-I PS offers an opportunity to obtain deep insights of the mechanism of type-I PSs, and provides a new strategy for development of type-I PSs.

Bioimaging and detecting endogenous and exogenous cyanide in foods, living cells and mice based on a turn-on mitochondria-targeted fluorescent probe

A novel fluorescent probe, with advanced features including “turn-on” fluorescence response, high sensitivity, good compatibility, and mitochondria-targeting function, has been synthesized based on structural design for detecting and visualizing cyanide in foods and biological systems. An electron-donating triphenylamine group (TPA) was employed as the fluorescent and an electron-accepting 4-methyl-N-methyl-pyridinium iodide (Py) moiety was used as a mitochondria-targeted localization unit, which formed intramolecular charge transfer (ICT) system. The “turn-on” fluorescence response of the probe (TPA-BTD-Py, TBP) toward cyanide is attributed two reasons, one is the insertion of an electron-deficient benzothiadiazole (BTD) group into the conjugated system between TPA and Py, and the other is the inhibition of ICT induced by the nucleophilic addition of CN–. Two active sites for reacting with CN− were involved in TBP molecule and high response sensitivity were observed in tetrahydrofuran solvent containing 3 % H2O. The response time could be reduced to 150 s, the linear range was 0.25–50 μM, and the limit of detection was 0.046 μM for CN− analysis. The TBP probe was successfully applied to the detection of cyanide in food samples prepared in aqueous solution, including the sprouting potato, bitter almond, cassava, and apple seeds. Furthermore, TBP exhibited low cytotoxicity, clear mitochondria-localizing capability in HeLa cells and excellent fluorescence imaging of exogenous and endogenous CN– in living PC12 cells. Moreover, exogenous CN– with intraperitoneal injection in nude mice could be well monitored visually by the “turn-on” fluorescence. Therefore, the strategy based on structural design provided good prospects for optimizing fluorescent probes.

An AIE-active fluorescent probe with near-infrared (NIR) emission for selectively monitoring and bioimaging Cys in living cells

Cysteine (Cys), as a kind of essential bio-thiols, plays a pivotal role in modulating cell metabolism, maintaining intracellular redox balance and facilitating protein synthesis. In order to investigate its role in these physiological processes, fluorescent probe was selected as an important method for selectively detecting Cys. However, most of the probes possess ACQ effect, which limits their applications in the field of biosensing and bioimaging. Herein, an AIE-active fluorescent probe TCF-TPA was synthesized for specifically detecting Cys in HeLa cells. TCF-TPA, consisted of a tricyanofuran (TCF) fluorophore, was modified with an acrylate group for distinguish Cys from other bio-thiols, and the incorporation of electron-donating triphenylamine endowed the probe with AIE property and strong intramolecular charge transfer effect, thereby enabling the probe to have near-infrared (NIR) emission length (666 nm). Meanwhile, TCF-TPA possessed low detection limit for Cys (73.0 nM) and was successfully performed bioimaging of Cys in HeLa cells.

Effect of donor groups on the photovoltaic performance of benzothiadiazole-core substituted small molecules for fullerene-based bulk heterojunction organic solar cells

Herein, two symmetric donor-π-acceptor-π-donor-type π-conjugated small molecule donors (BTM and BTP), based on a benzothiadiazole central acceptor core unit and end-capped with electron-donating triphenylamine and 3,5-dimethoxyphenyl)vinyl, are synthesized via a multistep coupling reaction. The structural, thermal, optical, and electrochemical properties of the small molecules are systematically analyzed; subsequently, the molecules are applied as electron donor materials for bulk heterojunction organic solar cell fabrication. Compared with BTM, BTP exhibits a strong absorption spectrum with a precisely tuned optical bandgap (approximately 1.87 eV), desired morphology, and improved interfacial properties. The solar devices fabricated with BTP:PC71BM (1:2.5, w/w) exhibit a higher power conversion efficiency (PCE) of approximately 7.08% with an enhanced current density (JSC) of approximately 12.90 mA/cm2, high open-circuit voltage (VOC) of approximately 0.989 V, and fill factor (FF) of approximately 55.5% compared with BTM-based devices (approximately 4.86%). Notably, the high VOC achieved for the BTP:PC71BM (1:2.5, w/w) devices is a result of the deep-lying HOMO energy level and low LUMO energy offset (approximately 0.51 eV) between the BTP donor and PC71BM acceptor. The high hydrophobicity and stable surface morphology of BTP:PC71BM (1:2.5, w/w) exhibits a high room temperature stability approximately > 94% and retain 6.70% of PCE of its original PCE (7.08%) after 288 hr.

Triphenylamine-based N,O-bidentate BF2 complexes: synthesis and photophysical properties

N,O-bidentate BF2 dyes (TTBKI-1 and TTBKI-2) with D–π–A structures were designed and synthesized by combining an electron-donating triphenylamine unit, a π-conjugated thiophene unit, and an electron-accepting NBF2O moiety.

Push-Pull Effect of Terpyridine Substituted by Triphenylamine Motive-Impact of Viscosity, Polarity and Protonation on Molecular Optical Properties.

The introduction of an electron-donating triphenylamine motive into a 2,2′,6′,2′′-terpyridine (terpy) moiety, a cornerstone molecular unit in coordination chemistry, opens new ways for a rational design of photophysical properties of organic and inorganic compounds. A push-pull compound, 4′-(4-(di(4-tert-butylphenyl)amine)phenyl)-2,2′,6′,2′′-terpyridine (tBuTPAterpy), was thoroughly investigated with the use of steady-state and time-resolved spectroscopies and Density Functional Theory (DFT) calculations. Our results demonstrate that solvent parameters have an enormous influence on the optical properties of this molecule, acting as knobs for external control of its photophysics. The Intramolecular Charge Transfer (ICT) process introduces a remarkable solvent polarity effect on the emission spectra without affecting the lowest absorption band, as confirmed by DFT simulations, including solvation effects. The calculations ascribe the lowest absorption transitions to two singlet ICT excited states, S1 and S2, with S1 having several orders of magnitude higher oscillator strength than the “dark” S2 state. Temperature and viscosity investigations suggest the existence of two emitting excited states with different structural conformations. The phosphorescence emission band observed at 77 K is assigned to a localized 3terpy state. Finally, protonation studies show that tBuTPAterpy undergoes a reversible process, making it a promising probe of the pH level in the context of acidity determination.

Copper(I) Donor–Chromophore–Acceptor Assembly for Light-Driven Oxidation on a Zinc Oxide Nanowire Electrode

Dye-sensitized photoelectrochemical cells have emerged as a potential candidate for solar-to-fuel conversion. Herein, we report a Cu(I)-based donor–chromophore–acceptor triad comprising a triphenylamine electron donor and a dipyrido[3,2-a:2′,3′-c]phenazine electron acceptor as the active material for photoanodes. Energy levels of this triad are carefully aligned for thermodynamically favorable photoinduced electron transfer. Once this triad is surface-grafted onto zinc oxide nanowires, photoelectrochemical studies confirm the utility of this architecture for oxidative processes such as alcohol oxidation with modest yields.

Polynaphthylimide-Azomethines Containing Triphenylamine or Carbazole Moieties with Tuned Optoelectronic Properties through Molecular Design.

Polyazomethines containing electron-donor triphenylamine (TPA) or carbazole (Cbz) and electron-acceptor naphthyl(di)imide were synthesized and investigated with regard to thermal, optical and electronic features, with a focus on their modulation by molecular design. The polycondesation of an imido-based diamine with a Cbz- or TPA-based dialdehyde led to donor-acceptor polymers with good thermostability, up to 318 °C. These displayed good solubility in organic solvents, which enabled easy polymer processability in thin films with different molecular assemblies. The molecular order improved the charge carrier’s mobility, with a direct impact on the bandgap energy. The optical properties studied by UV–Vis absorption and fluorescence experiments showed solvent-dependence, characteristic for donor-acceptor systems. The structural parameters exerted a strong influence on the light-emissive behavior, with the prevalence of intrinsic or intramolecular charge transfer fluorescence contingent on the donor-acceptor strength and polymer geometry. All polymers showed good electroactivity, supporting both electrons and holes transport. The exchange of Cbz with TPA proved to be an efficient tool with which to decrease the bandgap energy, while that of naphthyl(di)imide with bis(naphthylimide) was beneficial for fluorescence enhancement. This study may contribute to a deeper understanding of the physico-chemistry of electronic materials so as to make them more competitive in the newest energy-related or other optoelectronic devices.

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.

Development of new thiocyanate-free Ruthenium(II) dyes bearing isoquinoline chromophores for hydrogen production via water splitting

Four thiocyanate-free ruthenium(II) dyes, [RuII(4, 4-dicarboxylic acid-2,2-bipyridine)2(L1 or L2)](PF6)] and [RuII(tetraethyl[2,2′-bipyridine]-4,4′-diylbis(phosphonate))2(L1 or L2)](PF6)] with different anchoring groups, coded as Ru1–Ru4, were synthesized and characterized by NMR spectroscopy and mass spectrometry, and their electrochemical and photophysical properties were investigated. Density functional theory (DFT) calculation was used to gain insight into the factors responsible for photocatalytic properties of Ru1–Ru4 as effective photosensitizers. Relative to common ruthenium dyes, such as [Ru(bpy)3]2+ and N719, the absorption spectra of our dyes with triphenylamine moiety are broader with enhanced molar absorptivities (ε), especially, in the region between 400 nm and 650 nm. This is attributed to the extended π-conjugation system by inserting electron-donating triphenylamine to isoquinoline through thiophene moiety in their cyclometalating (C∧N) ligands, in which strong intramolecular charge transfer (ICT) ability was induced. All the new ruthenium(II) complexes were used as photosensitizers for visible-light driven hydrogen production reactions by attaching to platinized TiO2 nanoparticles (Pt–TiO2) in the presence of sacrificial electron donor (SED) ascorbic acid (AA) in purely aqueous solution. A H2 turnover number (TON) up to 14232 was demonstrated after 236 h irradiation. Complexes with tetraethyl[2,2′-bipyridine]-4,4′-diylbis(phosphonate) anchoring groups were found to be outperform to those with classical 4, 4-dicarboxylic acid-2,2-bipyridine, which may be one of the crucial steps in designing superior ruthenium(II) photosensitizers for hydrogen generation from water.