Extraordinary Photostability Research Articles

New Type Annihilator of π-Expanded Diketopyrrolopyrrole for Robust Photostable NIR-Excitable Triplet-Triplet Annihilation Upconversion.

Near-infrared light excitable triplet-triplet annihilation upconversion (NIR TTA-UC) materials have attracted interest in a variety of emerging applications such as photoredox catalysis, optogenetics, and stereoscopic 3D printing. Currently, the practical application of NIR TTA-UC materials requires substantial improvement in photostability. Here, we found that the new annihilator of π-expanded diketopyrrolopyrrole (π-DPP) cannot activate oxygen to generate superoxide anion via photoinduced electron transfer, and its electron-deficient characteristics prevent the singlet oxygen-mediated [2 + 2] cycloaddition reaction; thus, π-DPP exhibited superior resistance to photobleaching. In conjunction with the NIR photosensitizer PdTNP, the upconversion efficiency of π-DPP is as high as 8.9%, which is eight times of the previously reported PdPc/Furan-DPP. Importantly, after polystyrene film encapsulation, less than 10% photobleaching was observed for this PdTNP/π-DPP-based NIR TTA-UC material after four hours of intensive NIR light exposure. These findings provide a type of annihilator with extraordinary photostability, facilitating the development of NIR TTA-UC materials for practical photonics.

Engineering sub-10 nm fluorescent nanodiamonds for quantum enhanced biosensing

There is an increasing interest in the sensing of magnetic, electric, and temperature effects in biological systems on the nanoscale. While there are existing classical sensors, the possibility of using quantum systems promises improved sensitivity and faster acquisition time. So far, much progress has been made in diamond color centers like the nitrogen-vacancy (NV) which not only satisfy key requirements for biosensing, like extraordinary photostability and non-toxicity, but they also show promise as room-temperature quantum computers/sensors. Unfortunately, the most-impressive demonstrations have been done in bulk diamond, since NVs in fluorescent nanodiamonds (FNDs) tend to have inferior properties. Yet FNDs are required for widespread nanoscale biosensing. In order for FND-based quantum sensors to approach the performance of bulk diamond, novel approaches are needed for their fabrication. To address this need we discuss opportunities for engineering the growth of FNDs.

Understanding the Visible Absorption of Electron Accepting and Donating CNDs.

Carbon nanodots (CNDs) synthesized from citric acid and formyl derivatives, that is, formamide, urea, or N-methylformamide, stand out through their broad-range visible-light absorbance and extraordinary photostability. Despite their potential, their use has thus far been limited to imaging research. This work has now investigated the link between CNDs' photochemical properties and their chemical structure. Electron-rich, yellow carbon nanodots (yCNDs) are obtained with in situ addition of NaOH during the synthesis, whereas otherwise electron-poor, red carbon nanodots (rCNDs) are obtained. These properties originate from the reduced and oxidized dimer of citrazinic acid within the matrix of yCNDs and rCNDs, respectively. Remarkably, yCNDs deposited on TiO2 give a 30% higher photocurrent density of 0.7mAcm-2 at +0.3V versus Ag/AgCl under Xe-lamp irradiation (450nm long-pass filter, 100mWcm-2 ) than rCNDs. The difference in overall photoelectric performance is due to fundamentally different charge-transfer mechanisms. These depend on either the electron-accepting or the electron-donating nature of the CNDs, as is evident from photoelectrochemical tests with TiO2 and NiO and time-resolved spectroscopic measurements.

Self-generating CoFe2O4 as electric channel in Z-scheme CoO(111)/CoFe2O4/Fe2O3 photocatalyst for synchronous photocatalytic degradation and hydrogen production

Semiconductor photocatalysis is a promising technology in environmental protection and renewable energy production. In this work, a novel Z-scheme CoO(111)/CoFe2O4/Fe2O3 photocatalyst with a highly active surface is successfully synthesized via solid state reaction (SSR) method and then is used to realize the synchronous photocatalytic degradation of Rhodamine B and H2 production under sunlight irradiation. The as-prepared Z-scheme CoO(111)/CoFe2O4/Fe2O3 photocatalyst heated at 450 °C for 2.0 h displays an excellent photocatalytic activity. It can be attributed to the generation of adequate amount of CoFe2O4 between CoO(111) and Fe2O3, which can be regarded as an effective electric channel to accelerate the electron migration from conduction band of Fe2O3 to valence band of CoO. Furthermore, the agglomerated electrons on the exposed (111) active facet of CoO can reduce the H+ to generate hydrogen. Under the same conditions, within four periods the Z-scheme CoO(111)/CoFe2O4/Fe2O3 photocatalyst still shows the outstanding photocatalytic activity and extraordinary photo-stability. Moreover, a related mechanism on the synchronous photocatalytic degradation of Rhodamine B and H2 production under sunlight irradiation over the Z-scheme CoO(111)/CoFe2O4/Fe2O3 photocatalyst is presented. Perhaps, this present work can offer an idea for highly efficient hydrogen production utilizing organic pollutants.

Extraordinary Photostability and Davydov Splitting in BN-Sandwiched Single-Layer Tetracene Molecular Crystals.

Two-dimensional molecular crystals have been beyond the reach of systematic investigation because of the lack or instability of their well-defined forms. Here, we demonstrate drastically enhanced photostability and Davydov splitting in single and few-layer tetracene (Tc) crystals sandwiched between inorganic 2D crystals of graphene or hexagonal BN. Molecular orientation and long-range order mapped with polarized wide-field photoluminescence imaging and optical second-harmonic generation revealed high crystallinity of the 2D Tc and its distinctive orientational registry with the 2D inorganic crystals, which were also verified with first-principles calculations. The reduced dielectric screening in 2D space was manifested by enlarged Davydov splitting and attenuated vibronic sidebands in the excitonic absorption and emission of monolayer Tc crystals. Photostable 2D molecular crystals and their size effects will lead to novel photophysical principles and photonic applications.

Efficient perovskite titanate photocatalysts for oxygen evolution reactions

Exploring titanate based perovskites to harness solar energy represents a very significant interest in the field of photocatalysis. Unique properties of activation under light irradiation, tunable band gap energies with extraordinary photostability craft perovskite titanates as an efficient semiconductor photocatalyst for photocatalytic performance. Herein, highly active and stable perovskite titanates such as PbTiO3, CoTiO3 and BaTiO3 were synthesized through a simple low cost citric gel method. The as-synthesized phototocatalysts were well characterized by X-ray diffraction (XRD), Ultra violet Spectroscopy and Photoluminescence techniques. The results revealed that CoTiO3 exhibited an excellent photocatalytic performance towards oxygen evolution and multiple reproducible characteristic features under visible light illumination. The highest oxygen evolution yield was up to 98.12 μmol/h. The high photocatalytic activity toward O2 evolution is due to minimal recombination rate of photogenerated charge carriers in the material, as elucidated from photoluminescence spectroscopy analysis. Overall, the present work may provide a new reference for the fabrication of various high-quality perovskite titanates, promoting their potential for different photocatalytic applications.

A pH-sensitive coordination polymer network-based nanoplatform for magnetic resonance imaging-guided cancer chemo-photothermal synergistic therapy

Developing various kinds of nanoplatforms with integrated diagnostic and therapeutic functions would be significant for imaging-guided precision treatment of cancer. However, it is still a challenge to organically integrate therapeutic and imaging components into a single nano-system rather than simply mixing. Herein, an iron-gallic acid network-based nanoparticle (Fe-GA@PEG-PLGA) was designed for magnetic resonance imaging (MRI)-guided chemo-photothermal synergistic therapy of tumors. The tumor spatial location and size information can be accurately achieved due to T1 MRI based on Fe3+ coordination with GA in Fe-GA network. Furthermore, the nanoparticle exhibited extraordinary photostability and photothermal therapy capacity exceeded 42 °C within 100 s under 808 nm laser irradiation. Meanwhile, the Fe-GA polymeric network can be disassembled in tumor acidic environment and the released drug GA can induce apoptosis. This study demonstrated that the Fe-GA network-based nanoparticle is a promising diagnostic and therapeutic agent for theranostic application and further clinic translation.

Enhancing Luminescence and Photostability of CsPbBr3 Nanocrystals via Surface Passivation with Silver Complex

We demonstrate that Ag(I) complex can fix bromide on the nanocrystal surface, reduce surface trap density, and as a result efficiently passivate the surface of CsPbBr3 nanocrystals. This passivation makes the photoluminescence (PL) intensity increase several times. The PL kinetics study clearly shows that the decay lifetime increased after the passivation. TEM and XPS analyses demonstrated the existence of Ag on the nanocrystal surface. In addition, we utilize single-particle spectroscopy combined with in situ light analysis to further confirm the PL enhancement effect. On the contrary, the passivation leads to the extraordinary photostability of CsPbBr3 nanocrystals, with 80% PL intensity retained after UV illumination for 5 days under ambient conditions.

Preparation and Characterization of Poly-1,2,3-triazole with Chiral 2(5H)-Furanone Moiety as Potential Optical Brightening Agents.

A series of novel heterocyclic polymers with fluorescent brightening properties are synthesized via Click polymerization. Fast synthesis of poly-1,2,3-triazoles (Mn ≥ 9.31 kDa) is described herein, with a high yield of up to 95%. The Click polymerization approach has a number of advantages, including facile operation and outstanding isolation yield. The resultant polymers have a high thermal stability, excellent UV resistance, as well as acid and light fastness. On embedding with optical brightening agents, the polymers display strong fluorescent brightening properties in the tetrahydrofuran solution. Moreover, these products have a strong solution emission intensity and extraordinary photostability under UV light.

Chemiluminescence and electrochemiluminescence applications of metal nanoclusters

Due to strong photoluminescence, extraordinary photostability, excellent biocompatibility, and good water-solubility, metal nanoclusters have attracted enormous attention since discovered. They are found to be novel fluorescence labels for biological applications and environmental monitoring. Recently the chemiluminescence (CL) or electrochemiluminescence (ECL) of metal nanoclusters has received increasing attention. This review covers recent vibrant developments in this field of the past 5 years, and highlights different functions of metal nanoclusters in various CL and ECL systems, such as luminophores, catalysts, and quenchers. Latest synthetic methods of metal nanoclusters used in CL or ECL are also summarized. Furthermore, we discuss some perspectives and critical challenges of this field in the near future.

Inorganic-organic hybrid nanoprobe for NIR-excited imaging of hydrogen sulfide in cell cultures and inflammation in a mouse model.

Hydrogen sulfide (H2S) is an important gaseous signaling agent mediated by many physiological processes and diseases. In order to explore its role in biological signaling, much effort has been focused on developing organic fluorescent probes to image H2S. However, these downconversion H2S probes are impractical for bio-imaging beyond a certain depth because of the short tissue penetration of UV/visible light (as an excitation source). In most circumstance, these probes are also not suitable for long-term assay due to photo-bleaching. Herein, a new design to detect H2S based on the coumarin-hemicyanine (CHC1)-modified upconversion nanophosphors is reported. This inorganic-organic integrated nanoprobe is demonstrated to display a fast response time with a large ratiometric upconversion luminescence (UCL) enhancement, and extraordinary photo-stability. CHC1-UCNPs not only can be used for ratiometric UCL monitoring of pseudo-enzymatic H2S production in living cells, but can also be used to identify the risk of endotoxic shock through ratiometric UCL imaging of tissue and measurement of endogenous H2S levels in plasma. The first ratiometric UCL H2S nanoprobe reported here may be further developed as the next-generation diagnostic tool for the detection of inflammatory-related diseases.

Strong Two-Photon-Induced Fluorescence from Photostable, Biocompatible Nitrogen-Doped Graphene Quantum Dots for Cellular and Deep-Tissue Imaging

Bright two-photon fluorescent probes are highly desirable to be able to optically probe biological activities deep inside living organisms with larger imaging depth, minor autofluorescence background, and less photodamage. In this study, we report the biocompatible nitrogen-doped graphene quantum dots (N-GQDs) as efficient two-photon fluorescent probes for cellular and deep-tissue imaging. The N-GQD was prepared by a facile solvothermal method using dimethylformamide as a solvent and nitrogen source. The two-photon absorption cross-section of N-GQD reaches 48,000 Göppert-Mayer units, which far surpasses that of the organic dyes and is comparable to that of the high performance semiconductor QDs, achieving the highest value ever reported for carbon-based nanomaterials. More importantly, a study of penetration depth in tissue phantom demonstrates that the N-GQD can achieve a large imaging depth of 1800 μm, significantly extending the fundamental two-photon imaging depth limit. In addition, the N-GQD is nontoxic to living cells and exhibits super photostability under repeated laser irradiation. The high two-photon absorption cross-section, large imaging depth, good biocompatibility, and extraordinary photostability render the N-GQD an attractive alternative probe for efficient two-photon imaging in biological and biomedical applications.