Recent progress in ion-regulated organic room-temperature phosphorescence.

Organic room-temperature phosphorescence (RTP) materials have attracted considerable attention for their extended afterglow at ambient conditions, eco-friendliness, and wide-ranging applications in bio-imaging, data storage, security inks, and emergency illumination. Significant advancements have been achieved in recent years in developing highly efficient RTP materials by manipulating the intermolecular interactions. In this perspective, we have summarized recent advances in ion-regulated organic RTP materials based on the roles and interactions of ions, including the ion-π interactions, electrostatic interactions, and coordinate interactions. Subsequently, the current challenges and prospects of utilizing ionic interactions for inducing and modulating the phosphorescent properties are presented. It is anticipated that this perspective will provide basic guidelines for fabricating novel ionic RTP materials and further extend their application potential.

Differential detection of H1N1 virus spiker proteins by two hexaphenylbutadiene isomers based on size-matching principle.

As one of the high pathogenic influenza viruses, H1N1 virus easily induces to serious diseases, even leading to death. To date, all detection methods for H1N1 virus had shortcomings, including high equipment cost, time consumption, and etc. Therefore, a novel detection method should be established to achieve more convenient, rapid, and low-cost detection. In this work, an isomer of HPBmN-I with aggregation-induced emission characteristic was firstly synthesized on the basis of our previous reported HPBpN-I. The results showed that HPBmN-I only selectively binds to N1 in the presence of H1, while HPBpN-I can exhibit total fluorescence response to H1 and N1 in H1/N1 mixture. The limited of detection (LOD) of HPBmN-I to N1 was estimated to be 20.82 ng/mL in normal saline (NS) according to the IUPAC-based approach. The simulation calculations based on molecular docking revealed that four HPBmN-I molecules combine well with the hydrophobic cavity of N1 and achieve the fluorescence enhancement due to size matching with each other. The combination of HPBpN-I and HPBmN-I as probes was successfully used to quantitatively detect H1 and N1 in real H1N1 virus. Compared to enzyme-linked immunosorbent assay (ELISA) method, the established method not only showed the same detection accuracy but also had the advantages of real-time, ease of preparation, and low-cost, demonstrating potential market prospects.

Two Key Descriptors for Designing Second Near-Infrared Dyes and Experimental Validation.

Second near-infrared (NIR-II) optical imaging technology has emerged as a powerful tool for diagnostic and image-guided surgery due to its higher imaging contrast. However, a general strategy for efficiently designing NIR-II organic molecules is still lacking, because NIR-II dyes are usually difficult to synthesize, which has impeded the rapid development of NIR-II bioprobes. Herein, based on the theoretical calculations on 62 multiaryl-pyrrole (MAP) systems with spectra ranging from the visible to the NIR-II region, a continuous red shift of the spectra toward the NIR-II region could be achieved by adjusting the type and site of substituents on the MAPs. Two descriptors (ΔEgs and µgs) were identified as exhibiting strong correlations with the maximum absorption/emission wavelengths, and the descriptors could be used to predict the emission spectrum in the NIR-II region only if ΔEgs ≤ 2.5 eV and µgs ≤ 22.55 D. The experimental absorption and emission spectra of ten MAPs fully confirmed the theoretical predictions, and biological imaging in vivo of newly designed MAP23-BBT showed high spatial resolution in the NIR-II region in deep tissue angiography. More importantly, both descriptors of ΔEgs and µgs have shown general applicability to most of the reported donor-acceptor-donor-type non-MAP NIR-II dyes. These results have broad implications for the efficient design of NIR-II dyes.

Fused-Ring Pyrrole-Based Near-Infrared Emissive Organic RTP Material for Persistent Afterglow Bioimaging.

Organic near-infrared room temperature phosphorescence (RTP) materials offer remarkable advantages in bioimaging due to their characteristic time scales and background noise elimination. However, developing near-infrared RTP materials for deep tissue imaging still faces challenges since the small band gap may increase the non-radiative decay, resulting in weak emission and short phosphorescence lifetime. In this study, fused-ring pyrrole-based structures were employed as the guest molecules for the construction of long wavelength emissive RTP materials. Compared to the decrease of the singlet energy level, the triplet energy level showed a more effectively decrease with the increase of the conjugation of the substituent groups. Moreover, the sufficient conjugation of fused ring structures in the guest molecule suppresses the non-radiative decay of triplet excitons. Therefore, a near-infrared RTP material (764 nm) was achieved for deep penetration bioimaging. Tumor cell membrane is used to coat RTP nanoparticles (NPs) to avoid decreasing the RTP performance compared to traditional coating by amphiphilic surfactants. RTP NPs with tumor-targeting properties show favorable phosphorescent properties, superior stability, and excellent biocompatibility. These NPs are applied for time-resolved luminescence imaging to eliminate background interference with excellent tissue penetration. This study provides a practical solution to prepare long-wavelength and long-lifetime organic RTP materials and their applications in bioimaging.

Microwave-Responsive Flexible Room-Temperature Phosphorescence Materials Based on Poly(vinylidene fluoride) Polymer.

The development of flexible, room-temperature phosphorescence (RTP) materials remains challenging owing to the quenching of their unstable triplet excitons via molecular motion. Therefore, a polymer matrix with Tg higher than room temperature is required to prevent polymer segment movement. In this study, a RTP material was developed by incorporating a 4-biphenylboronic acid (BPBA) phosphor into a poly(vinylidene fluoride) (PVDF) matrix (Tg =-27.1 °C), which exhibits a remarkable UV-light-dependent oxygen consumption phosphorescence with a lifetime of 1275.7 ms. The adjustable RTP performance is influenced by the crystallinity and polymorph (α, ß, and γ phases) fraction of PVDF, therefore, the low Tg of the PVDF matrix enables the polymeric segmental motion upon microwave irradiation. Consequently, a reduction in the crystallinity and an increase in the α phase fraction in PVDF film induces RTP after 2.45 GHz microwave irradiation. These findings open up new avenues for constructing crystalline and phase-dependent RTP materials while demonstrating a promising approach toward microwave detection.

Helical Self-Assembly and Fe3+ Detection of V-Shaped AIE-Active Chiral Tetraphenylbutadiene-Based Polyamides.

Chiral aggregation-induced emission (AIE) molecules have drawn attention for their helical self-assembly and special optical properties. The helical self-assembly of AIE-active chiral non-linear main-chain polymers can produce some desired optical features. In this work, a series of V-shaped chiral AIE-active polyamides P1-C3, P1-C6, P1-C12 and linear P2-C3, P2-C6, bearing n-propyl/hexyl/dodecyl side-chains, based on tetraphenylbutadiene (TPB), were prepared. All target main-chain polymers exhibit distinct AIE characteristics. The polymer P1-C6 with moderate length alkyl chains shows better AIE properties. The V-shaped main-chains and the chiral induction of (1R,2R)-(+)-1,2-cyclohexanediamine in each repeating unit promote the polymer chains display helical conformation, and multiple helical polymer chains induce nano-fibers helicity when the polymer chains aggregate and self-assemble in THF/H2 O mixtures. Simultaneously, the helical conformation polymer chains and helical nano-fibers cause P1-C6 produce strong circular dichroism (CD) signals with positive Cotton effect. Moreover, P1-C6 could also occur fluorescence quenching response to Fe3+ selectively with a low detection limit of 3.48 µmol/L.

Organic room-temperature phosphorescence materials for bioimaging.

Organic room-temperature phosphorescence (RTP) materials are currently the focus of research in the field of bioimaging. In comparison with the conventional imaging modalities based on organic fluorescent dyes, RTP materials with long lifetime enable time-resolved imaging to improve the imaging resolution by avoiding autofluorescence. In this review, we will start with summarizing strategies for achieving high performance RTP materials for bioimaging, including the development of RTP-compounds, host-guest doping materials, and supramolecular assemblies. We then discuss the optimization of nanonization processes to obtain RTP nanoparticles with controllable size, high dispersibility, and improved stability. The differences between top-down and bottom-up approaches are further described. Finally, we briefly introduce the emerging methods for preparing RTP materials for bioimaging.

Microfluidic-based modulation of triplet exciton decay in organic phosphorescent nanoparticles for size-assisted photodynamic antibacterial therapy.

The modulation of triplet exciton decay in organic room-temperature phosphorescence (RTP) materials has been considered as a promising strategy for highly efficient photodynamic therapy. In this study, we report an effective approach based on microfluidic technology to manipulate the triplet exciton decay for generating highly reactive oxygen species (ROS). BQD shows strong phosphorescence upon doping into crystalline BP, indicating the high generation of triplet excitons based on the host-guest interaction. Through microfluidic technology, BP/BQD doping materials can be precisely assembled to form uniform nanoparticles with no phosphorescence but strong ROS generation. The energy decay of the long-lived triplet excitons of BP/BQD nanoparticles emitting phosphorescence has been successfully manipulated via microfluidic technology to generate 20-fold enhanced ROS than that of BP/BQD nanoparticles prepared by nanoprecipitation. The in vitro antibacterial studies indicate that BP/BQD nanoparticles have high specificity against S. aureus microorganisms with a low minimum inhibition concentration (10-7 M). BP/BQD nanoparticles below 300 nm show size-assisted antibacterial activity, demonstrated using a newly developed biophysical model. This novel microfluidic platform provides an efficient approach to convert host-guest RTP materials into photodynamic antibacterial agents and to promote the development of antibacterial agents without cytotoxicity and drug-resistance issues based on the host-guest RTP systems.

Direct in situ photolithography of perovskite quantum dots based on photocatalysis of lead bromide complexes.

Photolithography has shown great potential in patterning solution-processed nanomaterials for integration into advanced optoelectronic devices. However, photolithography of perovskite quantum dots (PQDs) has so far been hindered by the incompatibility of perovskite with traditional optical lithography processes where lots of solvents and high-energy ultraviolet (UV) light exposure are required. Herein, we report a direct in situ photolithography technique to pattern PQDs based on the photopolymerization catalyzed by lead bromide complexes. By combining direct photolithography with in situ fabrication of PQDs, this method allows to directly photolithograph perovskite precursors, avoiding the complicated lift-off processes and the destruction of PQDs by solvents or high-energy UV light, as PQDs are produced after lithography exposure. We further demonstrate that the thiol-ene free-radical photopolymerization is catalyzed by lead bromide complexes in the perovskite precursor solution, while no external initiators or catalysts are needed. Using direct in situ photolithography, PQD patterns with high resolution up to 2450 pixels per inch (PPI), excellent fluorescence uniformity, and good stability, are successfully demonstrated. This work opens an avenue for non-destructive direct photolithography of high-efficiency light-emitting PQDs, and potentially expands their application in various integrated optoelectronic devices.

Constructing Hypoxia-Tolerant and Host Tumor-Enriched Aggregation-Induced Emission Photosensitizer for Suppressing Malignant Tumors Relapse and Metastasis.

Photodynamic immunotherapy is a promising treatment strategy that destroys primary tumors and inhibits the metastasis and relapse of distant tumors. As reactive oxygen species are an intermediary for triggering immune responses, photosensitizers (PSs) that can actively target and efficiently trigger oxidative stress are urgently required. Herein, pyrrolo[3,2-b]pyrrole as an electronic donor is introduced in acceptor-donor-acceptor skeleton PSs (TP-IS1 and TP-IS2) with aggregation-induced emission properties and high absorptivity. Meanwhile, pyrrolo[3,2-b]pyrrole derivatives innovatively prove their ability of type I photoreaction, indicating their promising hypoxia-tolerant advantages. Moreover, M1 macrophages depicting an ultrafast delivery through the cell-to-cell tunneling nanotube pathway emerge to construct TP-IS1@M1 by coating the photosensitizer TP-IS1. Under low concentration of TP-IS1@M1, an effective immune response of TP-IS1@M1 is demonstrated by releasing damage-associated molecular patterns, maturating dendritic cells, and vanishing the distant tumor. These findings reveal insights into developing hypoxia-tolerant PSs and an efficient delivery method with unprecedented performance against tumor metastasis.

An acceptor-shielding strategy of photosensitizers for enhancing the generation efficiency of type I reactive oxygen species and the related photodynamic immunotherapy.

Developing efficient photosensitizers (PSs) that can generate type I reactive oxygen species (ROS) under illumination is considered an effective way to improve photodynamic therapy (PDT) outcomes due to the hypoxic nature of the tumor environment, but also is very challenging. Herein, a new PS of the multiarylpyrrole (MAP) derivative with a typical donor-acceptor structure was synthesized to efficiently generate type I ROS by using an acceptor-shielding strategy in their aggregated state. The enhanced generation mechanism of type I ROS originated from its ultralong triplet lifetime and the narrow singlet-triplet energy gap of the MAP. More importantly, type I ROS can transform protumoral M2 macrophages (M2) into antitumoral M1 macrophages (M1), which showed synergistic immunotherapy in in vivo experiments. Therefore, introducing shielding groups into acceptors provides general guidance for developing efficient PSs in the aggregation state for clinical PDT.

Mitochondrial targeted AIEgen phototheranostics for bypassing immune barrier via encumbering mitochondria functions.

Photodynamic therapy combined with immunogenic cell death has been proposed to overcome the unsolvable problems of single therapy, such as high levels of tumor recurrence and treatment resistance of tumors. Previous works on this theme have mostly concentrated on endoplasmic reticulum (ER)-stressed damage-associated molecular patterns (DAMPs), ignoring the secretion and function of mitochondria-related DAMPs. Herein, our work reports two intersystem crossing photosensitizers based on well-designed multiarylpyrrole structures and draws valuable attention to mitochondria-related DAMP-TFAM (mitochondrial transcription factor) when cancer cells are under forceful oxidative stress. The tumors vanished, and immunogenic experiments were applied to illuminate the advantages of double treatment. Our discovery of new mitochondria-related DAMPs compensates for the lack of ER-stressed DAMPs and offers an innovative target for immunity therapy.

Halogen Bonding: A New Platform for Achieving Multi-Stimuli-Responsive Persistent Phosphorescence.

Monotonous luminescence has always been a major factor limiting the application of organic room-temperature phosphorescence (RTP) materials. Enhancing and regulating the intermolecular interactions between the host and guest is an effective strategy to achieve excellent phosphorescence performance. In this study, intermolecular halogen bonding (CN⋅⋅⋅Br) was introduced into the host-guest RTP system. The interaction promoted intersystem crossing and stabilized the triplet excitons, thus helping to achieve strong phosphorescence emission. In addition, the weak intermolecular interaction of halogen bonding is sensitive to external stimuli such as heat, mechanical force, and X-rays. Therefore, the triplet excitons were easily quenched and colorimetric multi-stimuli responsive behaviors were realized, which greatly enriched the luminescence functionality of the RTP materials. This method provides a new platform for the future design of responsive RTP materials based on weak intermolecular interactions between the host and guest molecules.

Clusterization-Triggered Color-Tunable Room-Temperature Phosphorescence from 1,4-Dihydropyridine-Based Polymers.

A series of poly(1,4-dihydropyridine)s (PDHPs) were successfully synthesized via one-pot metal-free multicomponent polymerization of diacetylenic esters, benzaldehyde, and aniline derivatives. These PDHPs without traditional luminescent units were endowed with tunable triplet energy levels by through-space conjugation from the formation of different cluster sizes. The large and compact clusters can effectively extend the phosphorescence wavelength. The triplet excitons can be stabilized by using benzophenone as a rigid matrix to achieve room-temperature phosphorescence. The nonconjugated polymeric clusters can show a phosphorescence emission up to 645 nm. A combination of static and dynamic laser light scattering was conducted for insight into the structural information on formed clusters in the host matrix melt. Moreover, both the fluorescence and phosphorescence emission can be easily tuned by the variation of the excitation wavelength, the concentration, and the molecular weight of the guest polymers. This work provides a unique insight for designing polymeric host-guest systems and a new strategy for the development of long wavelength phosphorescence materials.

Rational design of pyrrole derivatives with aggregation-induced phosphorescence characteristics for time-resolved and two-photon luminescence imaging.

Pure organic room-temperature phosphorescent (RTP) materials have been suggested to be promising bioimaging materials due to their good biocompatibility and long emission lifetime. Herein, we report a class of RTP materials. These materials are developed through the simple introduction of an aromatic carbonyl to a tetraphenylpyrrole molecule and also exhibit aggregation-induced emission (AIE) properties. These molecules show non-emission in solution and purely phosphorescent emission in the aggregated state, which are desirable properties for biological imaging. Highly crystalline nanoparticles can be easily fabricated with a long emission lifetime (20 µs), which eliminate background fluorescence interference from cells and tissues. The prepared nanoparticles demonstrate two-photon absorption characteristics and can be excited by near infrared (NIR) light, making them promising materials for deep-tissue optical imaging. This integrated aggregation-induced phosphorescence (AIP) strategy diversifies the existing pool of bioimaging agents to inspire the development of bioprobes in the future.

Multicomponent Spiropolymerization of Diisocyanides, Diethyl Acetylenedicarboxylate, and Halogenated Quinones.

Multicomponent spiropolymerization (MCSP) provides an efficient synthetic tool for the construction of spiropolymers based on nonspiro monomers. In this study, a method of MCSP using diisocyanides 1, diethyl acetylenedicarboxylate 2, and halogenated quinones 3 is developed for the in situ construction of bis-spiropolymers with high molecular weights (Mw up to 29 200) and good yields (up to 87.7%) under mild reaction conditions. The structure of the obtained bis-spiropolymers is confirmed by gel permeation chromatography, Fourier transform infrared spectroscopy, and nuclear magnetic resonance analysis. Halogenated bis-spiropolymers show good thermal stability, good solubility, and film-forming ability. The photosensitizer rhodamine B is used as a doping agent to induce the photodegradation of the polymer P1a3c into small-molecule segments, which results in the slow release of halogenated spiro-groups under irradiation with simulated sunlight. This finding reveals that P1a3c has the potential to be applied in pesticides. Therefore, this MCSP is a novel method for preparing halogen-containing bis-spiropolymers, which accelerates the development of multifunctional polymer materials.

Efficient and organic host-guest room-temperature phosphorescence: tunable triplet-singlet crossing and theoretical calculations for molecular packing.

Organic host-guest doped materials exhibiting the room temperature phosphorescence (RTP) phenomenon have attracted considerable attention. However, it is still challenging to investigate their corresponding luminescence mechanism, because for host-guest systems, it is very difficult to obtain single crystals compared to single-component or co-crystal component materials. Herein, we developed a series of organic doped materials with triphenylamine (TPA) as the host and TPA derivatives with different electron-donating groups as guests. The doped materials showed strong fluorescence, thermally activated delayed fluorescence (τ: 39-47 ms), and efficient room temperature phosphorescence (Φ phos: 7.3-9.1%; τ: 170-262 ms). The intensity ratio between the delayed fluorescence and phosphorescence was tuned by the guest species and concentration. Molecular dynamics simulations were used to simulate the molecular conformation of guest molecules in the host matrix and the interaction between the host and guest molecules. Therefore, the photophysical properties were calculated using the QM/MM model. This work provides a new concept for the study of molecular packing of guest molecules in the host matrix.

On-Chip Multicolor Photoacoustic Imaging Flow Cytometry.

On-chip imaging flow cytometry has been widely used in cancer biology, immunology, microbiology, and drug discovery. Pure optical imaging combined with flow cytometry to derive chemical, structural, and morphological features of cells provides systematic insights into biological processes. However, due to the high concentration and strong optical attenuation of red blood cells, preprocessing is necessary for optical flow cytometry while dealing with whole blood. In this study, we develop an on-chip photoacoustic imaging flow cytometry (PAIFC), which combines multicolor high-speed photoacoustic microscopy and microfluidics for cell imaging. The device employs a micro-optical scanner to achieve a miniaturized outer size of 30 × 17 × 24 mm3 and ultrafast cross-sectional imaging at a frame rate of 1758 Hz and provides lateral and axial resolutions of 2.2 and 33 µm, respectively. Using a multicolor strategy, PAIFC is able to differentiate cells labeled by external contrast agents, detect melanoma cells with an endogenous contrast in whole blood, and image melanoma cells in blood samples from tumor-bearing mice. The results suggest that PAIFC has sufficient sensitivity and specificity for future cell-on-chip applications.

Catalyst-Free Multicomponent Cyclopolymerizations of Diisocyanides, Activated Alkynes, and 1,4-Dibromo-2,3-Butanedione: a Facile Strategy toward Functional Polyiminofurans Containing Bromomethyl Groups.

Polymers containing iminofuran (PIFs) are rarely reported due to the lack of simple and effective synthesis methods. In this work, a novel multicomponent cyclopolymerization (MCCP) of diisocyanides, activated alkynes, and 1,4-dibromo-2,3-butanedione using catalyst-free one-pot reactions under mild conditions to prepare PIFs containing bromomethyl groups is reported. PIFs with good solubility and thermal stability are obtained with high Mw s (up to 19 600) and good yields (up to 89.5%) under optimized polymerization conditions. The structure of the PIFs is characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and gel permeation chromatography. The photophysical properties indicate that polymers P1a2b3 and P1c2b3 have cluster-triggered emission characteristics. Thin films made from PIFs quickly degrade under UV irradiation. Moreover, the obtained polymers are decorated with bromomethyl and carboxylate groups in the side chain, which can be postfunctionalized to prepare multifunctional materials, such as star branched polymers and biomedical carrier materials. Thus, this work not only enriches the field of polymerization based on isocyanates and activated alkynes but also provides a facile strategy toward functional iminofuran polymers.

Functional Isocyanide-Based Polymers.

Research interest in the isocyanide-based reaction can be traced back to 1921 when the Passerini reaction was first reported. However, most of these research efforts did not lead to important progress in the synthesis of isocyanide-based polymers (IBPs). The major challenge resides in the lack of highly efficient polymerization methods, which limits large-scale preparation and applications. Modern organic chemistry provides efficient access to develop functional IBPs on the basis of isocyanide chemistry. However, it is still challenging to prepare the IBPs with small molecular isocyanide reaction. Our investigations into catalyst exploration and polymerization methodology have prompted the synthesis of a series of IBPs. Two classes of isocyanide monomers can be used for the construction of IBPs. The first class includes monomers with a single isocyanide. Novel catalysts for the synthetic chemistry of isocyanide allow the introduction of functional pendants into the linear polymer chains. This molecular functionalization endows the polymers with an array of new functional properties. For example, the incorporation of a chromophore on the polymeric side chain provides novel functional properties, such as aggregation-induced emission and optical activity. Diisocyanide monomers can be also utilized for the construction of heterocyclic, spiro-heterocyclic, and bispiro-heterocyclic polymers in the polymeric backbones. A new concept of "multi-component spiropolymerization" has been developed for the preparation of spiropolymers using the catalysis-free one-pot reaction. Proper structural design allows for the preparation of a heterocyclic polymeric chain with natural bioactivity and biological compatibility, generating new IBPs with biofunctionalities.In this Account, we discuss progress mainly made in our lab and related fields for the design of isocyanide monomers, exploration of new catalysts, and optimization of reaction conditions. The subsequent section discusses the characteristic properties and applications of selected examples of these functional polymers, mainly focusing on their optical applications. We have investigated the UV-sensitive IBPs that could potentially be used for lithography applications. One-pot highly efficient polymerization of diisocyanides and CO2 under mild conditions can provide a new method for realizing the reuse of CO2 and reducing the greenhouse effect. Through a combination of structural modifications, IBPs bearing dimethylbenzene moieties exhibit characteristics of black materials that can be potentially utilized as pyroelectric sensors, thermal detectors, and optical instruments. Most recently, our group synthesized a spiro-heterocyclic IBP with clusterization-triggered emission properties that can be used to discriminate cancer cells from normal cells and provides a new method for the treatment of cancer. The studies reviewed in this Account suggest that polymerization with isocyanide chemistry can be implemented in diverse functional macromolecules and materials.