Excellent Photophysical Properties Research Articles

Arylazopyrazole-Modified Thiolactone Acrylate Copolymer Brushes for Tuneable and Photoresponsive Wettability of Glass Surfaces.

Photoswitches have long been employed in coatings for surfaces and substrates to harness light as a versatile stimulus to induce responsive behavior. We previously demonstrated the viability of arylazopyrazole (AAP) as a photoswitch in self-assembled monolayers (SAMs) on silicon and glass surfaces for photoresponsive wetting applications. We now aim to transfer the excellent photophysical properties of AAPs to polymer brush coatings. Compared to SAMs, polymer brushes offer enhanced stability and an increase of the thickness and density of the functional organic layer. In this work, we present thiolactone acrylate copolymer brushes which can be post-modified with AAP amines as well as hydrophobic acrylates, making use of the unique chemistry of the thiolactones. This strategy enables photoresponsive wetting with a tuneable range of contact angle change on glass substrates. We show the successful synthesis of thiolactone hydroxyethyl acrylate copolymer brushes by means of surface-initiated atom-transfer radical polymerization with the option to either prepare homogeneous brushes or to prepare micrometer-sized brush patterns by microcontact printing. The polymer brushes were analyzed by atomic force microscopy, time-of-flight secondary ion spectrometry, and X-ray photoelectron spectroscopy. Photoresponsive behavior imparted to the brushes by means of post-modification with AAP is monitored by UV/vis spectroscopy, and wetting behavior of homogeneous brushes is measured by static and dynamic contact angle measurements. The brushes show an average change in static contact angle of around 13° between E and Z isomer of the AAP photoswitch for at least five cycles, while the range of contact angle change can be fine-tuned between 53.5°/66.5° (E/Z) and 81.5°/94.8° (E/Z) by post-modification with hydrophobic acrylates.

Design and development of a mitochondrial-targeted photosensitizer for two-photon fluorescence imaging and photodynamic therapy

• A rationally designed mitochondrial-targeted photosensitizer, TTTP, for PDT • TTTP can track living cells in vitro and in vivo by two-photon fluorescence imaging • TTTP shows selective phototoxicity to cancer cells, particularly under irradiation • TTTP stimulates ROS in mitochondria, activating apoptosis to inhibit tumor growth Mitochondria are well-acknowledged as ideal targets for tumor therapy due to their important role in energy supply and cellular signal regulation. Mitochondria-specific photosensitizers have been reported to be critical for inducing cell apoptosis. Two-photon fluorescence imaging provides a new technique for delineating biological structures and activities in deep tissues. Herein, we developed a new aggregation-induced emission (AIE) active photosensitizer by attaching a pyridinium group for mitochondrial targeting. The rationally designed photosensitizer (TTTP) exhibited excellent photophysical properties, good biocompatibility, reactive oxygen species (ROS) stimulation ability, anticancer efficacy, and two-photon imaging properties. TTTP was highly taken up by cells and accumulated specifically in mitochondria but was selectively cytotoxic to cancer cells. Under light irradiation, the generation of ROS was significantly boosted, leading to actively induced apoptosis. The in vivo tumor photodynamic therapeutic efficacy of TTTP showed significant inhibition of tumor growth. Furthermore, the underlying mechanism of TTTP tumor suppression revealed that the apoptosis agonist Bax was markedly up-regulated while the antagonist Bcl-xL was down-regulated. This research provides a potential mitochondrial-targeted phototherapeutic agent for effective therapy and two-photon fluorescence imaging.

Suppression of Mid‐Gap Trap State in CsPbBr3 Nanocrystals with Br‐Passivation for Self‐Powered Photodetector

All‐inorganic halide perovskite nanocrystals (NCs) have attracted great attention, prized for their excellent photophysical properties. However, the insulating nature of alkylamine ligands impede the electrical performance of optoelectronic devices. The control content of passivating ligands and suppression of mid‐gap trap state from perovskite NCs is an essential step to boost the device performance. Therefore, in this report a facile one step ligand‐exchange procedure is employed by rinsing the perovskite film into excess of bromide content to passivate surface trap state along with the suppression of native alkylamine ligands. Remarkably, owing to the vacancies filling potential of cesium bromide, hysteresis behavior in the treated perovskite film was significantly suppressed. More importantly, the absorption and photoluminescence intensities as well as photoluminescence quantum yield of bromide passivated films were improved. The heterojunction photodetector based on the configuration of indium tin oxide (ITO)/ZnO/CsPbBr3‐CsBr/Au revealed a higher responsivity of 6.38 A W−1, fast response time of 270/277 ms and a higher value of specific detectivity 2.6 × 1013 Jones. This work provide a facile and effective approach to effectively passivate the surface trap states from perovskite NCs with control value of native alkylamine ligands. The simple device architecture further provides a promising approach to fabricate high performance self‐powered photodetectors.

Water-soluble iridium(III) complexes as multicolor probes for one-photon, two-photon and fluorescence lifetime imaging

Fluorescence microscopy imaging provides an indispensable way to visualize morphological details in tissue with subcellular resolution. Of the various imaging agents currently available, heavy-metal complex based probes offer a powerful tool for live cell imaging, primarily due to their excellent photophysical properties, including evident Stokes shifts, high photoluminescence efficiency and relatively long emission lifetime of phosphorescent signals. Herein, we have designed and synthesized seven water soluble cationic iridium(III) solvato complexes (1 − 7) for live cell imaging. The emission colors of these iridium(III) complexes can be tuned from green to red in PBS buffer (phosphate buffered saline). In particular, multicolor phosphorescent imaging for cytoplasm staining of living cells has been realized. More importantly, two-photon excited imaging and fluorescence lifetime imaging microscopy have also successfully been applied for complex 7.

Strategy for Modulating Dihedral Angle Distribution for Enhanced Anti-Kasha TADF Behavior

D–A type thermally activated delayed fluorescence (TADF) materials with aggregation-induced emission (AIE) have attracted extensive research interest for their intense emission and high quantum yield in aggregated state. Herein, TADF molecules with vertical twisted structures are achieved by the methylation strategy which effectively separated the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). With the increase of the dihedral angle, 18 times enhancement of the photoluminescence quantum yield (PLQY) is realized in the aggregated state. The density functional theory (DFT) calculations demonstrate that these TADF molecules exhibit excellent photophysical properties in violation of Kasha’s rule: fluorescence originates from the higher energy electronic excited state (S2) rather than the S1 state.

Two-dimensional (n=1) ferroelectric film solar cells.

Molecular ferroelectrics that have excellent ferroelectric properties, a low processing temperature, narrow bandgap, and which are lightweight, have shown great potential in the photovoltaic field. However, two-dimensional (2D) perovskite solar cells with high tunability, excellent photo-physical properties and superior long-term stability are limited by poor out-of-plane conductivity from intrinsic multi-quantum-well electronic structures. This work uses 2D molecular ferroelectric film as the absorbing layer to break the limit of multiple quantum wells. Our 2D ferroelectric solar cells achieve the highest open-circuit voltage (1.29V) and the best efficiency (3.71%) among the 2D (n=1) Ruddlesden-Popper perovskite solar cells due to the enhanced out-of-plane charge transport induced by molecular ferroelectrics with a strong saturation polarization, high Curie temperature and multiaxial characteristics. This work aims to break the inefficient out-of-plane charge transport caused by the limit of the multi-quantum-well electronic structure and improve the efficiency of 2D ferroelectric solar cells.

Cy3 Cyanine Dye with Strong Fluorescence Enhancement for AGRO100 and Its Derivative.

Nucleic acids, as important substances for biological inheritance, have attracted extensive attention in the biomedical field. More and more cyanine dyes are emerging as one of the probe tools for nucleic acid detection due to their excellent photophysical properties. Here, we discovered that the insertion of the AGRO100 sequence can specifically disrupt the twisted intramolecular charge transfer (TICT) mechanism of the trimethine cyanine dye (TCy3), resulting in a clear "turn-on" response. Moreover, the fluorescence enhancement of TCy3 combined with the T-rich AGRO100 derivative is more obvious. One explanation for the interaction between dT (deoxythymidine) and positively charged TCy3 may be that its outer layer carries the most negative charge. This study provides a theoretical basis for the use of TCy3 as a DNA probe, which has promising applications in the DNA detection of biological samples. It also provides the basis for the following construction of probes with specific ability for recognition.

Helically Chiral Donor–Acceptor Double Hetero[4]helicenes with Circularly Polarized Thermally Activated Delayed Fluorescence

AbstractAlthough helically chiral heterohelicenes are widely adopted in chiroptical studies, those with circularly polarized thermally activated delayed fluorescence (CP‐TADF), which are highly valuable for circularly polarized organic light‐emitting diodes (CP‐OLEDs), are rarely realized. Moreover, the core skeletons of known CP‐TADF heterohelicenes are limited to the p‐ and n‐doped structures with multiresonance effect. In this study, a new type of helically chiral CP‐TADF heterohelicenes featuring a fused donor–acceptor core skeleton is successfully designed and constructed. Enantiomers possessing high configurational stability are achieved and separated, and they efficiently emit CP light with dissymmetry factors reaching 3.1 × 10−3 in doped films. Owing to the excellent photophysical properties, a high‐performance CP‐OLED with the maximum external quantum efficiency of up to 20.0% and an electroluminescence dissymmetry factor reaching 2.9 × 10−3 is obtained. This new type of CP‐TADF heterohelicenes provides a large space for the development of high‐performance CP‐TADF materials for various applications.

Robust salt-shelled metal halide for highly efficient photoluminescence and wearable real-time human motion perception

All-inorganic metal halide perovskites (MHPs) with the formula CsPbX3 (X = Cl-, Br-, I-) have excellent photophysical properties and low-cost fabrication, offering exciting opportunities for flexible electronics. However, the suboptimal quantum yield and inferior stability of solid-state MHPs impede their diverse wearable applications. Here, a straightforward water evaporation crystallization strategy for the preparation of salt-shelled metal halide solids is proposed. The well-designed CsPbBr3@KBr material exhibits narrow green photoluminescence (full-width at half-maximum ∼ 20 nm), high quantum yield (87.3 %), and favourable light irradiation and thermal stability. Thus, their applications in waterborne transparency inks and flexible photoluminescent films are demonstrated. Especially, they can be employed as fillers of polyvinyl alcohol (PVA) for high-performance positive friction materials in triboelectric nanogenerators (TENGs), and the output performance of the TENG is 2.3 times higher than the pristine one. As a proof-of-concept, a wearable photoluminescent sensor with a voltage response range of 0–100 kPa and a response time of 125 ms is constructed, which can potentially be served as a passive sensor-in-screen configuration to detect motions of various parts of the human body. It is believed that such metal halides will unleash the possibility of a broad variety of applications in lightweight and multifunctional wearable electronics.

Engineering of a novel D-A type fluorophore with hydrogen bond-induced enhanced emission property for sensitively detecting endogenous HOCl in living cells and tissues.

Fluorescence imaging has been widely employed for biomedical research and clinical diagnostics. With ease of synthesis and excellent photophysical properties, D-A type fluorophores are widely designed for fluorescence imaging. However, traditional D-A type fluorophores are solvatochromic which reduces the fluorescence brightness in the biological system. To solve this problem and build on our previous work, we devised a novel HIEE fluorophore MTC with typical anti-solvatochromic fluorescence. Furthermore, the activated fluorescent probe designed based on MTC showed excellent imaging performance. We believe that the strategy based on the fluorophores with typical anti-solvatohromic fluorescence can be a useful platform for designing fluorescent probes for high-brightness imaging in the biological system.

Semiconducting Polymer Dots for Point-of-Care Biosensing and In Vivo Bioimaging: A Concise Review.

In recent years, semiconducting polymer dots (Pdots) have attracted much attention due to their excellent photophysical properties and applicability, such as large absorption cross section, high brightness, tunable fluorescence emission, excellent photostability, good biocompatibility, facile modification and regulation. Therefore, Pdots have been widely used in various types of sensing and imaging in biological medicine. More importantly, the recent development of Pdots for point-of-care biosensing and in vivo imaging has emerged as a promising class of optical diagnostic technologies for clinical applications. In this review, we briefly outline strategies for the preparation and modification of Pdots and summarize the recent progress in the development of Pdots-based optical probes for analytical detection and biomedical imaging. Finally, challenges and future developments of Pdots for biomedical applications are given.

Synthesis, photophysical and electrochemical properties of π-conjugated pyrene based down-shifting molecules with fluorinated aryl groups

Pyrene molecule, with excellent photophysical properties (strong absorption cross section, excellent emission properties and a long-excited state lifetime), excellent thermal and photochemical stability, has been widely used as a building block for the synthesis of pyrene-based fluorophores for optoelectronic applications. In this work, we report the synthesis of two series of pyrene–π–A compounds, series I (3–6) and II (10–13), in which nitro, cyano, cyanoacrylonitrile and cyanoacrylic acid as electron acceptor groups are connected to the pyrene core via aryl or fluoroaryl π-conjugating bridges. The incorporation of fluorine atom on the π-extension bridge cause a slightly red-shift at emission wavelength (λem) in solution and polymethylmethacrylate (PMMA) films and increase the Stokes shift due to greater stabilization of molecular orbitals in the excited state, especially for series I. Solvatochromic measurements and theoretical computational studies suggest a higher intramolecular charge transfer in the excited state for series II when compared to series I due to their stronger electron acceptor moieties. All pyrene derivatives are stable and exhibited initial mass loss at temperature above 200 °C. The good photophysical and thermal properties of the synthesized pyrene derivatives, associated with high molar absorption coefficients in the UV spectrum and good fluorescence emission in the range of 430–480 nm (series I) and 505–567 nm (series II) in PMMA films, make them possible candidates for organic light-emitting diode (OLED) and luminescent down-shifting (LDS) layers for stable perovskite solar cells, respectively.

Perovskite-like Silver Halide Single-Crystal Microbelt Enables Ultrasensitive Flexible X-ray Detectors.

Lead halide perovskite single crystals have attracted wide interest in the field of X-ray detection due to their excellent photophysical properties. However, their inherent toxicity and high thickness restrict their applications in flexible devices. In this paper, designing a micronanometer-scale X-ray detector based on all-inorganic lead-free CsAg2I3 (CAI) single crystal microbelts (MBs) has addressed the above issues. These CAI single crystal MBs can be synthesized on various substrates with high crystal quality and excellent stability. Based on their excellent characteristics of the CAI MBs, we fabricate single CAI MB devices with an Au/CAI/Au structure, which shows not only good ultraviolet photoresponse characteristics, but also excellent X-ray detection performance. The optimized CAI photodetectors exhibit a responsivity of 23.59 mA/W, a high detectivity of 1010 Jones, and a fast response speed. For X-ray detection performance, a sensitivity of up to 515.49 μC Gyair-1 cm-2 and a detection limit of as low as 14.65 μGyair s-1 are achieved with outstanding operation stability and excellent long-term stability. Furthermore, our devices also showed excellent applicability for X-ray imaging, which is promising for their use in X-ray detection and imaging. Finally, flexible X-ray detectors are fabricated by using thin CAI single-crystal MBs and demonstrate good flexibility under different bending radii and bending cycles. Our work shows the potential for developing highly sensitive flexible integrated micro/nano optoelectronic devices by using lead-free perovskite analogue single crystals.

Dihydrophenazine-derived thermally activated delayed fluorescence emitters for highly efficient orange and red organic light-emitting diodes

Thermally activated delayed fluorescence (TADF) emitters in the long wavelength region usually suffer from severe nonradiative decay according to the energy-gap law, and show relatively large energy split (ΔEST) between the lowest singlet and triplet excited states which compromise efficient up-conversion. Here, we report three orange and red TADF emitters comprising 5, 10-disubstituted phenazine electron-donor and quinoxaline-derived electron-acceptors, which show excellent TADF properties and yield efficient organic light-emitting diodes (OLEDs). These symmetrical acceptor-donor-acceptor (A-D-A) type and rodlike molecules concurrently exhibit high photoluminescence quantum yields up to 85% and fast reverse intersystem crossing. Experimental and theoretical studies reveal that these excellent photophysical properties are attributed the synergistic effect of structural rigidity, steric hindrance and strength of the donor and acceptor units. Doped OLEDs based on these emitters achieved high maximum external electroluminescence quantum efficiencies up to 19.9%, and maximum luminance surpassing 31240 cd/m2.

The two-pronged approach of heteroatoms and substituents to achieve a synergistic regulation of the ESIPT process in amino 2-(2′-hydroxyphenyl)benzoxazole derivatives

Amino 2-(2′-hydroxyphenyl)benzazole derivatives are a class of molecules with excellent photophysical properties. Most of them can be applied as a fluorescent probe via the excited-state intramolecular proton transfer (ESIPT) process. In this work, we focus on the effects of heteroatoms (O, S) and substituents (acetylacetone, hydrogen) in the derivatives. Using DFT/TDDFT methods with the B3LYP-D3BJ functionals, the absorption and emission peaks are in good agreement with the experimental data. Results of optimized structures, infrared vibrational spectra, and reduced density gradient present the existence of the ESIPT process in the S1 state in these molecules, it also indirectly shows that the heteroatom S is more than O, and the substituent acetylacetone is more than hydrogen has stronger hydrogen bonds. The proton transfer (PT) potential energy curves (PECs) qualitatively show that it is easier for the heteroatom S to induce ESIPT than that of O. The same for the substituent acetylacetone than that of hydrogen. Under the joint influence of the simultaneous stacking of heteroatom S and acetylacetone substituent, the energy barrier of the PT process can be effectively lowered, realizing a synergistic strategy, which can provide some guidance for the design of fluorescent materials.

Chalcones: Versatile intermediates in heterocyclic synthesis

AbstractChalcones are a fascinating and well‐studied group of organic molecules. Synthesis of chalcones has been one of the essential areas of organic synthesis over the last few decades because of their immense therapeutic and excellent photophysical properties. Furthermore, these chalcone derivatives can be utilized to make a variety of heterocyclic compounds, especially five‐ and six‐membered heterocycles. Heterocyclic compounds have a long history in chemistry, primarily in pharmaceuticals. However, synthesizing some specific heterocyclic molecules remains challenging and requires multistep processes with few possible intermediates. Chalcones can be considered as one of the most useful, readily available intermediates in heterocyclic synthesis. Herein, the synthesis of various potential heterocyclic compounds using chalcones as an intermediate is elaborated. This review shows the untapped potential of chalcones in organic synthesis. Also, it will assist the chemist in designing new heterocycles by adopting these strategies.

Functional supramolecular aggregates based on BODIPY and aza-BODIPY dyes: control over the pathway complexity

The recent advances in the supramolecular assembly of BODIPY and aza-BODIPY dyes are reviewed, emphasizing the control over the kinetic pathway complexity of this class of dyes, and the prospects for future research are summarized.

Rapid construction of bicyclic triazoline skeletons with dual-state emissionviacycloaddition reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with vinyl azides

Fluorescent bicyclic triazolines with excellent photophysical properties were easily and conveniently synthesized and showed intense deep-blue photoluminescence with quantum yields of up to 78% and 87% in solution and the solid state, respectively.

Heterocyclic Suzuki-Miyaura coupling reaction of metalla-aromatics and mechanistic analysis of site selectivity.

Pd-catalyzed Suzuki-Miyaura cross-coupling is one of the most straightforward and versatile methods for the construction of functionalized arenes and heteroarenes but site-selective cross-coupling of polyhalogenated (hetero)arenes containing identical halogen substituents remains a challenging problem. Herein, we report a new candidate for heterocyclic Suzuki-Miyaura coupling reaction. This candidate has been applied in organometallic systems by combining classical aryl boronic acid reagents with non-classical heteroarenes. Experimental and computational studies of the mechanism of the reactions were performed, with an emphasis on the identity of the reactive species in the oxidative addition step and the nature of the precise site selectivity. The influence of both the aromaticity of the metalla-aromatic substrates and the steric and electronic properties of the halogenated sites are studied in detail.

Synthesis and in vitro photodynamic activity of aza-BODIPY-based photosensitizers.

Aza-BODIPY dyes have recently come to attention owing to their excellent chemical and photophysical properties. In particular, their absorption and emission maxima can efficiently be shifted to the red or even to the NIR spectral region. On this basis, aza-BODIPY derivatives are widely investigated as fluorescent probes or phototherapeutic agents. Here we report the synthesis of a set of novel aza-BODIPY derivatives as potential photosensitizers for use in photodynamic therapy. Triazolyl derivatives were obtained via Cu(I)-catalyzed azide-alkyne cycloaddition as the key step. In vitro photodynamic activities of the newly synthesized compounds were evaluated on the A431 human epidermoid carcinoma cell line. Structural differences influenced the light-induced toxicity of the test compounds markedly. Compared to the initial tetraphenyl aza-BODIPY derivative, the compound bearing two hydrophilic triethylene glycol side chains showed substantial, more than 250-fold, photodynamic activity with no dark toxicity. Our newly synthesized aza-BODIPY derivative, acting in the nanomolar range, might serve as a promising candidate for the design of more active and selective photosensitizers.