Crystalline hydrogen-bonded organic framework for air-tolerant triplet-triplet annihilation upconversion.

A hydrogen-bonded organic framework (HOF) consisting of a 9,10-diphenylanthracene carboxylic derivative, DPACOOH, was developed for solid state triplet-triplet annihilation upconversion (TTA-UC). The HOF sample shows a 70% increase in upconversion quantum yield and a lower threshold value of 126.0 mW cm-2 compared to those of the disordered powder sample, due to a 43% longer triplet diffusion length in HOF than that in the powder sample.

Multiple Force-Triggered Downconverted and Upconverted Emission in Polymers Containing Diels-Alder Adducts.

Fluorescent mechanophores can indicate the deformation or damage in polymers. The development of mechanophores with multi-triggered response is of great interest. Herein, Diels-Alder (DA) adducts are incorporated into linear poly(methyl acrylate) PMA-BA and network poly(hexyl methacrylate) (PHMA) as mechanophores to detect the stress caused by ultrasound, freezing, and compression. The DA mechanophores undergo retro-DA reaction to release 9-styrylanthracene chromophore upon applying force, resulting in cyan fluorescence. The dissociation ratio of the DA mechanophore after pulsed ultrasonication of PMA-BA solution for 240 minutes is estimated to be 52 % by absorption spectra and 1H NMR. Additionally, the rate constant of mechanical cleavage is calculated to be 1.2×10-4 min-1⋅kDa-1 with the decrease in molecular weight from 69 to 22 kDa measured by gel permeation chromatography. Freezing of PHMA gels as well as compression of PHMA bulk samples turn-on the DA mechanophores, revealing the microscale fracture. Photon upconversion responses toward various force stimuli are also achieved in both polymer solutions and bulk samples by doping platinum octaethylporphyrin (PtOEP) or palladium meso-tetraphenyltetrabenzoporphyrin (PdTPTBP) sensitizers with multiple excitation wavelengths.

A Single-Component Molecular Glass Resist Based on Tetraphenylsilane Derivatives for Electron Beam Lithography.

A novel molecular glass (TPSiS) with photoacid generator (sulfonium salt group) binding to tetraphenylsilane derivatives was synthesized and characterized. The physical properties such as solubility, film-forming ability, and thermal stability of TPSiS were examined to assess the suitability for application as a candidate for photoresist materials. The sulfonium salt unit underwent photolysis to effectively generate photoacid on UV irradiation, which catalyzed the deprotection of the t-butyloxycarbonyl groups. It demonstrates that the TPSiS can be used as a 'single-component' molecular resist without any additives. The lithographic performance of the TPSiS resist was evaluated by electron beam lithography. The TPSiS resist can resolve 25 nm dense line/space patterns and 16 nm L/4S semidense line/space patterns at a dose of 45 and 85 µC/cm2 for negative-tone development (NTD). The etching selectivity of the TPSiS resist to Si substrate is 8.6 under SF6/O2 plasma, indicating a potential application. Contrast analysis suggests that the significant solubility switch within a narrow exposure dose range (18-47 µC/cm2) by NTD is favorable for high-resolution patterns. This study supplies useful guidelines for the optimization and development of single-component molecular glass resists with high lithographic performance.

Dipyrene-Terminated Oligosilanes Enable Ratiometric Fluorescence Response in Polymers toward Mechano- and Thermo-Stimuli.

Developing fluorescent motifs capable of displaying mechano- and thermo-stimuli reversibly and ratiometrically is appealing for monitoring the deformation or temperature to which polymers are subjected. Here, a series of excimer-type chromophores Sin-Py (n = 1-3) consisting of two pyrenes linked with oligosilanes of one to three silicon atoms is developed as the fluorescent motif incorporated in a polymer. The fluorescence of Sin-Py is steered with the linker length where Si2-Py and Si3-Py with disilane and trisilane linkers display prominent excimer emission accompanied by pyrene monomer emission. Covalent incorporation of Si2-Py and Si3-Py in polyurethane gives fluorescent polymers PU-Si2-Py and PU-Si3-Py, respectively, where intramolecular pyrene excimers and corresponding combined emission of excimer and monomer are obtained. Polymer films of PU-Si2-Py and PU-Si3-Py display instant and reversible ratiometric fluorescence change during the uniaxial tensile test. The mechanochromic response arises from the reversible suppression of excimer formation during the mechanically induced separation of the pyrene moieties and relaxation. Furthermore, PU-Si2-Py and PU-Si3-Py show thermochromic response toward temperature, and the inflection point from the ratiometric emission as a function of temperature gives an indication of the glass transition temperature (Tg) of the polymers. The design of the excimer-based mechanophore with oligosilane provides a generally implementable way to develop mechano- and thermo-dual-responsive polymers.

Sulfonium-Functionalized Polystyrene-Based Nonchemically Amplified Resists Enabling Sub-13 nm Nanolithography.

Nonchemically amplified resists based on triphenyl sulfonium triflate-modified polystyrene (PSTS) were prepared by a facile method of modification of polystyrene with sulfonium groups. The uploading of the sulfonium group can be well-controlled by changing the feed ratio of raw materials, resulting in PSTS0.5 and PSTS0.7 resists with sulfonium ratios of 50 and 70%, respectively. The optimum developer (methyl isobutyl ketone/ethanol = 1:7) is obtained by analyzing contrast curves of electron beam lithography (EBL). PSTS0.7 exhibits a better resolution (18 nm half-pitch (HP)) than the PSTS0.5 resist (20 nm HP) at the same developing conditions for EBL. This novel resist platform was further evaluated by extreme ultraviolet lithography, and patterning performance down to 13 nm HP at a dose of 186 mJ cm-2 with a line edge roughness of 2.8 nm was achieved. Our detailed study of the reaction and patterning mechanism suggests that the decomposition of the polar triflate and triphenyl sulfonium groups into nonpolar sulfide or polystyrene plays an important role in the solubility switch.

Molecular Glass Resists Based on Tetraphenylsilane Derivatives: Effect of Protecting Ratios on Advanced Lithography.

A series of t-butyloxycarbonyl (t-Boc) protected tetraphenylsilane derivatives (TPSi-Boc x , x = 60, 70, 85, 100%) were synthesized and used as resist materials to investigate the effect of t-Boc protecting ratio on advanced lithography. The physical properties such as solubility, film-forming ability, and thermal stability of TPSi-Boc x were examined to assess the suitability for application as candidates for positive-tone molecular glass resist materials. The effects of t-Boc protecting ratio had been studied in detail by electron beam lithography. The results suggest that the TPSi-Boc x resist with different t-Boc protecting ratios exhibit a significant change in contrast, pattern blur, and the density of bridge defect. The TPSi-Boc70% resist achieves the most excellent patterning capability. The extreme ultraviolet (EUV) lithography performance on TPSi-Boc70% was evaluated by using the soft X-ray interference lithography. The results demonstrate that the TPSi-Boc70% resist can achieve excellent patterning capability down to 20 nm isolated lines at 8.7 mJ/cm2 and 25 nm dense lines at 14.5 mJ/cm2. This study will help us to understand the relationship between the t-Boc protecting ratio and the patterning ability and supply useful guidelines for designing molecular resists.

Coupling Red-to-blue Upconversion Organic Microcrystals with Cd0.5 Zn0.5 S for Efficient and Durable Photocatalytic Hydrogen Production.

For semiconductor photocatalysts with excellent performance in solar H2 production, broadening the utilization of solar irradiation is highly necessary to further improve the solar conversion efficiency. Herein, we combined a Cd0.5 Zn0.5 S photocatalyst with DPA/PdTPTBP microcrystals capable of red-to-blue photon upconversion, realizing substantial performance enhancement and an apparent quantum yield of 0.16% for H2 production driven by sub-bandgap photons (600∼650 nm). Meanwhile, this system could smoothly work with H2 production rate of 1.40 mmol g-1 h-1 for as long as 40 hours under 200 mW/cm2 irradiation with only 3% attenuation of photocatalytic activity. Moreover, the O2 -barrier property of DPA/PdTPTBP microcrystals assures that photocatalytic H2 production remains effective in the presence of 10% O2 by volume, which offers an opportunity for the photocatalytic application in O2 -enriched environments. The combination of O2 -resistant upconversion microcrystals and semiconductor catalysts is the most successful solution for the construction of TTA-UC-based photocatalytic H2 production system so far. The present study provides a clear guideline for designing new TTA-UC-based photocatalytic systems.

An enzyme cascade fluorescence-based assay for the quantification of phenylalanine in serum.

The quantification of phenylalanine in clinical samples is essential for the diagnosis and treatment of neonatal phenylketonuria. In this report, an enzyme cascade strategy was proposed and a high-efficiency fluorescence assay was established for rapid and convenient phenylalanine quantification. The assay involves phenylalanine dehydrogenase for the quantitative metabolization of phenylalanine and the formation of NADH, as well as nitroreductase combining a nitroaromatic substrate for the fluorescent quantification of NADH and subsequently phenylalanine. The phenylalanine levels in clinical serum determined by this fluorescence assay are consistent with those from HPLC. This straightforward approach provides a versatile strategy for the development of cost-effective and convenient assays for mass screening and metabolite monitoring.

Thermally Activated Upconversion with Metal-Free Sensitizers Enabling Exceptional Anti-Stokes Shift and Anti-counterfeiting Application.

Photochemical upconversion (UC) via triplet-triplet annihilation (TTA) has attracted considerable attention for its potential applications in solar energy conversion, photocatalysis, and bioimaging. Achieving a large anti-Stokes shift in photochemical UC is appealing but still a great challenge, especially for purely organic sensitizers. Here, we develop solid-state TTA UC systems with metal- and heavy atom-free dyes as the sensitizers, which sensitize the 9,10-diphenylanthracene acceptor through thermally activated triplet-triplet energy transfer. Solid-state UC emission with remarkable anti-Stokes shifts up to 1.10 eV is achieved owing to an evident enthalpy gain by the endothermic sensitization. The solid upconverter shows air-stable UC emission and potentials in dual-mode anti-counterfeiting and encryption applications. The present UC approach involving thermally activated sensitization enabled by purely organic dyes provides a versatile strategy to develop TTA UC materials with large anti-Stokes shift, air-tolerant emission, and environmental compatibility, which would have promising applications in information encryption, photochemical conversion, and bioimaging.

Funneling and Enhancing Upconversion Emission by Light-Harvesting Molecular Wires.

Triplet-triplet annihilation (TTA) upconversion has shown promising potentials in the augmentation of solar energy conversion. However, challenging issues exist in improving TTA upconversion efficiencies in solid-states, one of which is the back energy transfer from upconverted singlet annihilators to sensitizers, resulting in decreasing upconversion emission. Here we present a light-harvesting molecular wire consisting of dendrons with 9,10-diphenylanthracene derivatives (DPAEH) at the periphery and p-phenylene ethynylene oligomers (PPE) as the wire core. The peripheral DPAEH antenna funnels singlet excitonic energy to the wire on a 12 ps time scale. Incorporating the molecular wire into the TTA upconversion solid consisting of the DPAEH annihilator and the porphyrin sensitizer evidently improves the upconversion quantum yield from 1.5% to 2.7% upon 532 nm excitation by suppressing the back energy transfer from the singlet annihilator to the sensitizer. This finding offers a potential route to use a singlet energy light-harvesting architecture for enhancing TTA upconversion.

Thermally Activated Delayed Fluorescence via Triplet Fusion.

Manipulating triplet states is technically intriguing for organic semiconductors and photochemical conversion. Sensitized photon upconversion that converts low-energy photons into higher-energy ones via triplet fusion holds great potential in augmentation of photovoltaic devices and photocatalysis. Conventional requirement of exothermic triplet-triplet energy transfer in sensitized upconversion constrains the development of upconversion donor-acceptor pairs. We demonstrate an upconversion system by utilizing a triplet energy-deficient donor within a triplet acceptor matrix, in which efficient thermally activated triplet-triplet energy transfer overcoming an energy barrier of up to 180 meV and an over 5% upconversion quantum yield in the solid state are achieved upon 635 nm irradiation at 195 mW/cm2. The effective solid-state upconversion through thermally activated triplet-triplet energy transfer establishes a new pathway to extract triplet energy from low-lying sensitizers, transcending traditional restriction in matching components energy level.

Triplet-Triplet Annihilation Upconversion for Photocatalytic Hydrogen Evolution.

The solar generation of hydrogen by water splitting provides a promising path for renewable hydrogen production and solar energy storage. Upconversion of low-energy photons into high-energy photons constitutes a promising strategy to enhance the light harvesting efficiency of artificial hydrogen production systems. In the present study, upconversion micelles are integrated with Cd0.5 Zn0.5 S to construct solar energy conversion systems. The upconversion micelle is employed to upconvert red photons to cyan photons. Cd0.5 Zn0.5 S is sensitized by upconverted cyan light to produce hydrogen, but not by incident red light without triplet-triplet annihilation upconversion (TTA-UC). The performance of the upconversion photocatalytic system was dramatically affected by the concentration of Cd0.5 Zn0.5 S and the irradiation intensity. This novel system was able to produce about 2.3 µL hydrogen after 5 h of red light (629 nm) irradiation (2.4 mW cm-2 ). The present study provides a candidate for applications using low-energy photons for solar hydrogen generation.

Ultrasensitive reversible chromophore reaction of BODIPY functions as high ratio double turn on probe.

Chromophore reactions with changes to conjugation degree, especially those between the conjugated and unconjugated state, will bring a large spectral variation. To realize such a process, a meso-naked BODIPY (MNBOD) with two electron-withdrawing groups around the core is designed and synthesized. The resulting system is extremely sensitive to bases. The red, highly fluorescent solution readily becomes colorless and non-fluorescent after base addition; however, the color and fluorescence can be totally and instantly restored by addition of acid or formaldehyde. Analyses show that two identical MNBODs are connected by a C-C single bond (sp3) at the meso-position through a radical reaction that results in an unconjugated, colorless dimer complexed with bases. When the bases are consumed, the dimer immediately dissociates into the red, highly fluorescent, conjugated MNBOD monomer. With 260 nm spectral change and over 120,000 turn-on ratio, this chromophore-reaction can be utilized as a sensitive reaction-based dual-signal probe.

Förster Resonance Energy-Transfer-Based Ratiometric Fluorescent Indicator for Quantifying Fluoride Ion in Water and Toothpaste.

A Förster resonance energy-transfer (FRET)-based ratiometric fluorescent indicator Cou-FITC-Si toward fluoride ion has been designed and synthesized by combining coumarin unit and fluorescein derivative as energy donor and acceptor, respectively. The fluorescein unit is capped with tert-butyldiphenylchlorosilane. The indicator gives out emission responses based on switch-on of the FRET process that triggered by the desilylation mediated by the fluoride ion. The fluorescence emission spectrum of Cou-FITC-Si presents a significant bathochromic shift of 59 nm after the addition of fluoride ion with up to 180-fold increase of the fluorescence intensity ratio. The limit of detection of the Cou-FITC-Si indicator system toward fluoride ion was estimated to be 3.3 ppb. Furthermore, this indicator has been successfully applied for quantifying the fluoride ion of different concentrations from commercially available toothpaste.

Light-Harvesting Organic Nanocrystals Capable of Photon Upconversion.

Harvesting and converting low energy photons into higher ones through upconversion have great potential in solar energy conversion. A light-harvesting nanocrystal assembled from 9,10-distyrylanthracene and palladium(II) meso-tetraphenyltetrabenzoporphyrin as the acceptor and the sensitizer, respectively effects red-to-green upconversion under incoherent excitation of low power density. An upconversion quantum yield of 0.29±0.02 % is obtained upon excitation with 640 nm laser of 120 mW cm-2 . The well-organized packing of acceptor molecules with aggregation-induced emission in the nanocrystals dramatically reduces the nonradiative decay of the excited acceptor, benefits the triplet-triplet annihilation (TTA) upconversion and guides the consequent upconverted emission. This work provides a straightforward strategy to develop light-harvesting nanocrystals based on TTA upconversion, which is attractive for energy conversion and photonic applications.

Pd-Porphyrin Oligomers Sensitized for Green-to-Blue Photon Upconversion: The More the Better?

A series of directly meso-meso-linked Pd-porphyrin oligomers (PdDTP-M, PdDTP-D, and PdDTP-T) have been prepared. The absorption region and the light-harvesting ability of the Pd-porphyrin oligomers are broadened and enhanced by increasing the number of Pd-porphyrin units. Triplet-triplet annihilation upconversion (TTA-UC) systems were constructed by utilizing the Pd-porphyrin oligomers as the sensitizer and 9,10-diphenylanthracene (DPA) as the acceptor in deaerated toluene and green-to-blue photon upconversion was observed upon excitation with a 532 nm laser. The triplet-triplet annihilation upconversion quantum efficiencies were found to be 6.2 %, 10.5 %, and 1.6 % for the [PdDTP-M]/DPA, [PdDTP-D]/DPA, and [PdDTP-T]/DPA systems, respectively, under an excitation power density of 500 mW cm(-2) . The photophysical processes of the TTA-UC systems have been investigated in detail. The higher triplet-triplet annihilation upconversion quantum efficiency observed in the [PdDTP-D]/DPA system can be rationalized by the enhanced light-harvesting ability of PdDTP-D at 532 nm. Under the same experimental conditions, the [PdDTP-D]/DPA system produces more (3) DPA* than the other two TTA-UC systems, benefiting the triplet-triplet annihilation process. This work provides a useful way to develop efficient TTA-UC systems with broad spectral response by using Pd-porphyrin oligomers as sensitizers.

Highly Emissive Nanoparticles Based on AIE-Active Molecule and PAMAM Dendritic "Molecular Glue".

The highly emissive nanoparticles Gn-TCMPE (n = 0-4) were prepared by using PAMAM dendrimers as "molecular glue" to adhere an AIE-active molecule tetra(4-(carboxymethoxy)phenyl)ethylene (TCMPE). The electrostatic interaction of ammonium-carboxylate ion pairs provides a driving force between TCMPE and PAMAM dendrimers to form the nanoparticles Gn-TCMPE (n = 0-4), which is validated by the FTIR and (1)H NMR spectra. The formation of nanoparticles dramatically blocks the nonradiative pathway and enhances the fluorescence of TCMPE. The quantum yields of Gn-TCMPE gradually boost at first and then reach to a plateau with increasing the generation of PAMAM dendrimers, and the highest absolute quantum yields are obtained to be 0.42 and 0.64 for Gn-TCMPE (n = 2-4) in methanol dispersion and solid phases, respectively. The fluorescence of the nanoparticles can be tuned by addition of trifluoroacetic acid (TFA). Furthermore, the G4-TCMPE has been successfully applied to selectively image cytoplasm of Hela cells with excellent photostability and low cytotoxicity. This study provides a novel noncovalent strategy for developing highly emissive and robust organic materials fitting for cell fluorescence imaging.

Dendritic ionic liquids based on imidazolium-modified poly(aryl ether) dendrimers.

A series of dendritic ionic liquids (DILs) based on imidazolium-modified poly(aryl ether) dendrimers IL-Br-Gn (n=0-3) were synthesized by a modified convergent approach and "click" chemistry. The resulting DILs exhibited high thermal resistance with decomposition temperatures up to 270 °C and low glass transition temperatures in the range of approximately -5-0 °C. All IL-Br-Gn were found to be miscible with water at any ratio and could encapsulate hydrophobic molecules. The reversible phase transfer of the DILs between the aqueous and organic phases was accomplished by simple anion exchange between the hydrophilic Br(-) anion and the hydrophobic bis(trifluoromethylsulfonyl)amide anion (NTf2(-)). IL-Br-Gn could be used as transporters to shuttle hydrophobic molecules between the organic and aqueous phases efficiently. The present work provides a new kind of transporting materials with potential applications in substance separation, drug delivery, and biomolecule transport.

Enhanced photocatalytic hydrogen production from an MCM-41-immobilized photosensitizer-[Fe-Fe] hydrogenase mimic dyad.

A covalently linked photosensitizer-catalytic center dyad Ps-Hy, consisting of two bis(2-phenylpyridine)(2,2'-bipyridine)iridium(iii) chromophores (Ps) and a diiron hydrogenase mimic (Hy) was constructed by using click reaction. Ps-Hy was incorporated into K(+)-exchanged molecular sieve MCM-41 to form a composite (Ps-Hy@MCM-41), which has been successfully applied to the photochemical production of hydrogen. The catalytic activity of Ps-Hy@MCM-41 is ∼3-fold higher as compared with that of Ps-Hy in the absence of MCM-41. The incorporation of Ps-Hy into MCM-41 stabilizes the catalyst, and consequently, advances the photocatalysis. The present study provides a potential strategy for improving catalytic efficiency of artificial photosynthesis systems using mesoporous molecular sieves.

Tetrathiafulvalene terminal-decorated PAMAM Dendrimers for triggered release synergistically stimulated by redox and CB[7].

A series of polyamidoamine (PAMAM) dendrimers with tetrathiafulvalene (TTF) at the periphery (Gn-PAMAM-TTF), generation 0-2, were synthesized. These functionalized dendrimers exist as nanospheres with diameters around 80-100 nm in aqueous phase, which can encapsulate hydrophobic molecules. The terminal TTF groups can go through a reversible redox process upon addition of the oxidizing and reducing agents. Each terminal TTF(+•) group of the oxidized Gn-PAMAM-TTF assembled with cucurbit[7]uril (CB[7]) forming a 1:1 inclusion complex with association constants of (3.14 ± 0.36) × 10(5), (1.29 ± 0.12) × 10(6), and (1.79 ± 0.24) × 10(6) M(-1) for generation 0-2, respectively, even at the aggregate state. The formation of the inclusion complex loosened the structure of the nanospheres and initiated the release of cargo, and the release mechanism was validated by dynamic light scattering (DLS), cryo-transmission electron microscopy (TEM), and electron paramagnetic resonance (EPR) experiments. This study provides a potential strategy for the development of drug delivery systems synergistically triggered by redox and supramolecular assembly.