Broadband Near-Infrared Emission from Bi/Cr Co-Doped Aluminosilicate Glasses.

Bismuth-doped aluminosilicate glass has garnered significant attention due to its unique ultra-wide luminescence properties in the near-infrared (NIR) band. Enhancing the NIR luminescence of Bi-doped glass remains challenging. To achieve Bi-doped glass with more excellent luminescent properties, a series of Bi/Cr co-doped glasses were prepared, and the optical and structural properties of the samples were observed. The results indicate that low-concentration Cr doping broadens the luminescence range of Bi/Cr co-doped glass samples. The luminescence peak of Bi in the samples is at 1230 nm, while the peak of Cr is around 804 nm. The addition of an appropriate amount of Bi2O3 can enhance the NIR luminescence of Bi and Cr in the sample, realizing the energy conversion between Bi and Cr. Bi/Cr co-doped is a novel approach for achieving broadband NIR luminescence in glass materials.

Dinuclear Cyclometalated Pincer Nickel(II) Complexes with Metal-Metal-to-Ligand Charge Transfer Excited States and Near-Infrared Emission.

Facile non-radiative decay of low-lying metal-centered (MC) d-d excited states has been well documented to pose a significant obstacle to the development of phosphorescent NiII complexes due to substantial structural distortions between the d-d excited state and the ground state. Herein, we prepared a series of dinuclear Ni2II,II complexes by using strong σ-donors, carbene-phenyl-carbene (CNHC^Cphenyl^CNHC) pincer ligands, and prepared their dinuclear Pt2II,II and Pd2II,II analogues. Dinuclear Ni2II,II complexes bridged by formamidinate/α-carbolinato ligand exhibit short Ni-Ni distances of 2.947-3.054 Å and singlet metal-metal-to-ligand charge transfer (1MMLCT) transitions at 500-550 nm. Their 1MMLCT absorption energies are red-shifted relative to the Pt2II,II and Pd2II,II analogues at ~450 nm and ≤420 nm respectively. One-electron oxidation of these Ni2II,II complexes produces valence-trapped dinuclear Ni2II,III species, which are characterized by EPR spectroscopy. Upon photoexcitation, these Ni2II,II complexes display phosphorescence (τ=2.6-8.6 µs) in the NIR (800-1400nm) spectral region in 2-MeTHF and in solid state at 77 K, which is insensitive to π-conjugation of the coordinated [CNHC^Cphenyl^CNHC] ligand. Combined with DFT calculations, the NIR emission is assigned to originate from the 3dd excited state. Studies have found that the dinuclear Ni2II,II complex can sensitize the formation of singlet oxygen and catalyze the oxidation of cyclo-dienes under light irradiation.

Strategy to optimize the broadband near-infrared emission based on Eu2+-doped sulfureted garnet phosphors toward emerging spectroscopy applications.

Eu2+-doped near-infrared (NIR) emitting phosphors, known for their high efficiency, broadband emission and spectral tunability, have gained much attention. However, achieving efficient NIR emission based on Eu2+ remains a challenge due to the co-existence of Eu3+, especially in materials (i.e. garnets and apatites) containing trivalent lanthanide cations. In this study, a Eu2+ doped sulfureted NIR-emitting garnet phosphor Ca3(Sc, Eu)2Si3(O, S)12: Eu2+ is successfully designed and synthesized. Notably, a strategy for regulating the initial valence state of dopants is proposed by using prepared EuS instead of the conventional Eu2O3 as raw material, enhancing the NIR emission by 135 %. Moreover, a sulfuration strategy is further introduced to enhance the NIR-emitting intensity and internal quantum efficiency by 192 % and 167.8 %, and to improve thermal stability by 154 % at 120 °C. The luminescence origin of the unusual broadband NIR emission is re-examined through chemical unit co-substitution strategy by introducing [Al3+Hf4+] to replace [Sc3+Si4+] ion pairs. Meanwhile, the spectral regulation and the performance optimization mechanism are systematically discussed. Finally, a green light pumped NIR LED device with a photoelectric efficiency of 9.43 %@100 mA and output power of 22.74 mW@100 mA is fabricated, showing remarkable potential in nondestructive testing and biomedical imaging applications.

[Nd(NTA)2·H2O]3- complex with high-efficiency emission in NIR region.

The distinctive photophysical characteristics possessed by lanthanides, including europium, neodymium, and ytterbium, render them adaptable molecular tools for studying biological systems. Specifically, their enduring photoluminescence, precise emission spectra, and significant Stokes shifts allow for experiments not achievable with organic fluorophores or fluorescent proteins. Moreover, the capacity of these metal ions for luminescence resonance energy transfer and photon upconversion extends the potential applications of lanthanide probes even further. In this research, a new [Nd(NTA)2·H2O]3- complex was synthesized and its optical properties were assessed using practical characterization techniques such as UV-Vis absorption, photoluminescence, and FTIR. It was discovered that when the sample was excited by a 357 nm wavelength, it emitted a strong line at 1076 nm with a full-width at half maximum (FWHM) of 10 nm, a phenomenon not previously documented. The Judd-Ofelt theory and its intensity parameters were utilized in a theoretical approach to determine the fluorescence branching ratio and the radiative lifetime of the [Nd(NTA)2·H2O]3- complex. The absorption and luminescence spectra were then analyzed accordingly. Experimental findings validated the potential applications of the prepared sample in bioimaging.

Designing NIR AIEgens for lysosomes targeting and efficient photodynamic therapy of tumors.

Cancer is the most severe health problem facing most people today. Photodynamic therapy (PDT) for tumors has attracted attention because of its non-invasive nature, negligible adverse reactions, and high spatiotemporal selectivity. Developing biocompatible photosensitizers that can target, guide, and efficiently kill cancer cells is desirable in PDT. Here, two amphiphilic organic compounds, PS-I and PSS-II, were synthesized based on the D-π-A structure with a positive charge. The two AIEgens exhibited near-infrared emission, large Stokes shift, high 1O2 and O2-∙ generation efficiency, good biocompatibility, and photostability. They were co-incubated with cancer cells and eventually accumulated to lysosomes by cell imaging experiments. In vitro and in vivo experiments demonstrated that PS-I and PSS-II could effectively kill cancer cells and sufficiently inhibit tumor growth under light irradiation. PS-I had a higher fluorescence quantum yield in the aggregated state, which made it better for bio-imaging in imaging-guided photodynamic therapy. In contrast, PSS-II with a longer conjugated structure had more ROS generation to kill tumor cells under illumination, and the tumor growth inhibition of mice reached 71.95% during the treatment. No observable injury or undesirable outcomes were detected in the vital organs of the mice within the treatment group, suggesting that PSS-II/PS-I had a promising future in efficient imaging-guided PDT for cancer.

Efficient Near-Infrared Fluorophores Based on Cyanostyrene Derivatives for Two-Photon Fluorescence Bioimaging.

Organic fluorescent materials with red/near-infrared (NIR) emission are highly promising for use in biotechnology due to their exceptional advantages. However, traditional red/NIR fluorophores often exhibit weak emission at high concentrations or in an aggregated state due to the aggregate-caused quenching effect, which severely limits their applicability in biological imaging. To address this challenge, we developed a series of cyanostyrene derivatives with aggregation-induced emission characteristics, including 2,3-Bis-(4-styryl-phenyl)-but-2-enedinitrile (DPB), 2,3-Bis-{4-[2-(4-methoxy- phenyl)-vinyl]-phenyl}-but-2-enedinitrile (DOB), 2,3-Bis-{4-[2-(4-diphenylamino- phenyl)-vinyl]-phenyl}-but-2-enedinitrile (DTB), and 2,3-Bis-[4-(2-{4-[phenyl- (4-triphenylvinyl-phenyl)-amino]-phenyl}-vinyl)- phenyl]-but-2-enedinitrile (DTTB). Notably, these compounds exhibited intense solid state fluorescence owing to AIE effect, especially DTTB shows NIR emission with high solid state quantum efficiency (712 nm, ΦF=14.2 %). Then we prepared DTTB@PS-PEG NPs nanoparticles by encapsulating DTTB with the amphiphilic polymer polystyrene-polyethylene glycol (PS-PEG). Importantly, DTTB@PS-PEG NPs exhibited highly efficient NIR luminescence (ΦF=28.7 %) and a large two-photon absorption cross-section (1900 GM) under 800 nm laser excitation. The bright two-photon fluorescence of DTTB@PS-PEG indicated that it can be a highly promising candidate for two-photon fluorescence probe. Therefore, this work provides valuable insights for the design of highly efficient and NIR-emitting two-photon fluorescent probes.

Revealing the polarity decrease of cardiomyocyte in the septic cardiomyopathy by a lipid droplets-targeting fluorescent probe with NIR emission.

Septic cardiomyopathy (SCM) is the main cause of death in critically ill patients with sepsis. However, its definitive pathogenic mechanisms remain to be elucidated. Lipid droplets (LDs) are important sub-organelles that store lipids and participate in intracellular lipid metabolism. Abnormal aggregation and altered polarity of LDs are associated with the development of several cardiac diseases. To date, visualization of abnormal polarity in models of SCM has not been achieved. Herein, we designed and synthesized the probe BDP-551, a polarity-sensitive probe possessing a donor-π-acceptor (D-π-A) structure. BDP-551 exhibits excellent photostability, high LDs targeting, near-infrared (NIR) emission (up to 678 nm) and strong polarity sensitivity. With the help of confocal imaging microscopy, the BDP-551 was able to detect the polarity changes induced in the SCM model cells and visualize the yolk sac region in hypoxic as well as inflamed living zebrafish. In addition, the BDP-551 has been successfully applied to visualize the polarity changes of mice hearts with SCM, proving a decrease of microenvironmental polarity in the development of SCM. Therefore, BDP-551 in this study can be used as a reliable tool to investigate polarity fluctuations and provide new insights into the associated pathogenic and therapeutic mechanisms on SCM.

A tumor-targeting two-photon fluorescent probe with a far-red to NIR emission for imaging basal hypochlorite in cancer cells and tumor.

Cancer cells have a high abundance of hypochlorite compared to normal cells, which can be used as the biomarker for imaging cancer cells and tumor. Developing the tumor-targeting fluorescent probe suitable for imaging hypochlorite in vivo is urgently demanded. In this article, based on xanthene dye with a two-photon excited far-red to NIR emission, a tumor-targeting two-photon fluorescent probe (Biotin-HClO) for imaging basal hypochlorite in cancer cells and tumor was developed. For ClO-, Biotin-HClO (20.0 µM) has a linear response range from 15.0 × 10-8 to 1.1 × 10-5 M with a high selectivity and a high sensitivity, a good detection limit of 50 nM and a 550-fold fluorescence enhancement with high signal-to-noise ratio (20 mM PBS buffer solution with 50 % DMF; pH = 7.4; λex = 605 nm; λem = 635 nm). Morover, Biotin-HClO exhibited excellent performance in monitoring exogenous and endogenous ClO- in cells, and has an outstanding tumor-targeting ability. Subsequently, Biotin-HClO has been applied for imaging ClO- in 4T1 tumor tissue to distinguish from normal tissue. Furthermore, Biotin-HClO was successfully employed for high-contrast imaging 4T1 tumor in mouse based on its tumor-targeting ability. All these results proved that Biotin-HClO is a useful analytical tool to detect ClO- and image tumor in vivo.

A Stable Chichibabin Diradicaloid with Near-Infrared Emission.

Conjugated molecules with multiple radical centers such as the iconic Chichibabin diradicaloid hold promise as building blocks in materials for quantum sensing and quantum information processing. However, it is a considerable challenge to design simple analogues of the Chichibabin hydrocarbon that are chemically inert, exhibit high diradical character and emit light at a distinct wavelength that may offer an optical readout of the spin state in functional ensembles. Here we describe the serendipitous discovery of the stable TTM-TTM diradicaloid, which exhibits high diradical character, a striking sky-blue color and near-infrared (NIR) emission (in solution). This combination of properties is unique among related diradicaloids and is due to the presence of hydrogen and chlorine atoms in "just the right positions", allowing a perfectly planar, yet predominantly benzenoid bridge to connect the two sterically stabilized radical centers. In-depth studies of the optical and magnetic properties suggest that this structural motif could become a mainstay building block of organic spin materials.

A sensing label or gel loaded with an NIR emission fluorescence probe for ultra-fast detection of volatile amine and fish freshness.

A simple benzopyran-based fluorescence probe DCA-Apa detection of volatile amine has been synthesized. DCA-Apa can recognize volatile amines by dual channel mode (changing from blue to light yellow in sunlight, and from weak pink to orange under 365 nm) in pure water system. DCA-Apa has the advantages of ultra-fast response (∼6 s), NIR emission (655 nm), and a good fluorescence response for many amines. The sensing label or gel loaded with DCA-Apa was prepared by the dipping or mixing method using filter paper or gelatin as solid carriers, which can identify volatile amine vapor and monitor the freshness of salmon by colorimetric and fluorescent dual channels. When the color of the label changes to light yellow-green or the fluorescence of the label becomes orange fluorescence (365 nm UV lamp), it indicates that the fish has rotted. The two-channel method makes up for the deficiency of the single colorimetric method, and establishes a theoretical foundation for more precise assessment of fish freshness.

A near-infrared fluorescent probe with two-photon excitation for in situ imaging of NQO1 in human colorectum cancer tissue.

Colorectum cancer has become one of the most fatal cancer diseases, in which NAD(P)H: quinone oxidoreductase 1 (NQO1) plays a role in intracellular free radical reduction and detoxification and has been linked to colorectum cancer and chemotherapy resistance. Therefore, rational design of optical probe for NQO1 detection is urgent for the early diagnosis of colorectum cancer. Herein, we have developed a novel two-photon fluorescent probe, WHFD, which is capable of selectively detecting of intracellular NQO1 with two-photon (TP) absorption (800 nm) and near-infrared emission (620 nm). Combination with a substantial Stokes shift (175 nm) and biocompatibility, we have assessed its suitability for in vivo imaging of endogenous NQO1 activities from HepG2 tumor-bearing live animals with high tissue penetration up to 300 µm. Particularly, we for the first time used the probe to image NQO1 activities from human colorectum cancer samples by using TP microscopy, and proving our probe possesses reliable diagnostic performance to directly in situ imaging of cancer biomarker and can clearly distinguish the boundary between human colorectum cancer tissue and their surrounding normal tissue, which shows great potential for the intraoperative navigation.

Near-infrared fluorescent indolizine-dicyanomethylene-4H-pyran hybrids for viscosity imaging in living cells.

The development of near-infrared organic fluorescent dyes with tunable emission profiles is highly required in the field of biological sensing and imaging. In this paper, we designed and synthesized two organic fluorescent dyes, DCM-1 and DCM-2, through the hybridization of indolizine and dicyanomethylene-4H-pyran skeleton. These two compounds show near-infrared fluorescence with emission maximum approximately at 640 and 680 nm, respectively. Notably, both DCM-1 and DCM-2 have specific responses to viscosity without being interfered by biological relevant species. Cell experiments demonstrate that DCM-1 and DCM-2 can detect dynamic changes in viscosity within living cells, suggesting their potential applications in chemical biology research.

A near-infrared aggregation-induced emission photosensitizer targeting mitochondria for depleting Cu2+ to trigger light-activated cancer cells oncosis.

Abnormally high levels of copper in tumors stimulate malignant proliferation and migration of cancer cells, which proposes a formidable challenge for the thorough therapy of malignant tumors. In this work, we developed a reliable, mitochondria-targeted near-infrared aggregation-induced emission fluorescent probe, TTQ-Th, whose thiourea moiety specifically could recognize mitochondria even both upon loss of mitochondrial membrane potential or in fixated cells, and can capture copper overexpressed by tumor cells, leading to severe copper deficiency. In parallel, TTQ-Th can generate sufficient reactive oxygen species (ROS) upon photoexcitation, while copper deficiency inhibits expression of related copper-based enzymes, resulting in a decline in ATP production. Such energy deficiency, combined with reduced MMP and elevated oxidative stress can lead to critical cell oncosis. Both in vitro and intracellular experiments can illustrate that the elevated ROS has remarkable damage to tumor cells and contributes to the elimination of the primary tumor, while copper deficiency further hinder tumor cell migration and induces G0/G1 cell cycle arrest in a dose-dependent manner, which is an efficacious strategy for the treatment of malignant tumors.

A Highly NIR Emissive Cu16Pd1 Nanocluster.

The construction of stable copper nanoclusters (Cu-NCs) with near-infrared (NIR) emission that can be used for catalysis is highly desired, yet remains a challenge. Herein, an atomically precise bimetallic Cu/Pd NC with a molecular formula of Cu16Pd1L10(PPh3)2(Pz)6 (Pz = 3,5-(CF3)2Pyrazolate, L = 4-CH3OPhC≡C-), abbreviated as Cu16Pd1, is synthesized. Single-crystal X-ray crystallographic analysis of Cu16Pd1 reveals a Cu10Pd1 kernel with pseudo-gyroelongated square bipyramid confirmation surrounded by other 6 Cu(I) ions and protected ligands. Interestingly, it exhibits strong NIR emission with the highest photoluminescence quantum yield (PLQY) among all the Cu NCs/Cu alloys (λem > 800 nm) in the solid-state, and also displays NIR emission in solution. Experimental results and theoretical calculations suggest that the impressive NIR emission is attributed to abundant supramolecular interactions in the solid-state, including intramolecular metal-metal and intermolecular interactions. Of note, the bimetallic Cu16Pd1 can catalyze the reduction of 4-nitrophenol. This work provides a novel method for synthesizing Cu/Pd NCs and reminds that the less studied Cu/Pd NC can serve as outstanding luminescent material, which is seldom noticed in atomically precise nanoclusters.

Dual Nature of Thiophene Harnessed in the Design of Near-Infrared Emitters via Antiaromaticity Relief.

Near-infrared (NIR) emitters are of great interest for applications in bioimaging and modern technology. Yet the design of such materials with decent characteristics is challenging due to intrinsic limitations. In a recent article, Murai and Yamaguchi report the synthesis of NIR emitters with appreciable fluorescence quantum yields reaching 0.02 at 878 nm in CH2 Cl2 solution. The low band gaps were achieved by a new design strategy exploiting antiaromaticity relief. This concept was realized for compounds consisting of an antiaromatic azepine central ring fused to thiophene moieties. In these systems, thiophene unfolds its dual nature. On the one hand, it contributes to the high antiaromaticity of azepine; on the other hand, it exerts a stabilizing effect on azepine through the formation of a quinoid structure, which reduces its antiaromaticity and shifts the absorption and emission maxima into the NIR region.

Synergistic Enhancement of Near-Infrared Emission in CsPbCl3 Host via Co-Doping with Yb3+ and Nd3+ for Perovskite Light Emitting Diodes.

Perovskite nanocrystals (PeNCs) have emerged as a promising class of luminescent materials offering size and composition-tunable luminescence with high efficiency and color purity in the visible range. PeNCs doped with Yb3+ ions, known for their near-infrared (NIR) emission properties, have gained significant attention due to their potential applications. However, these materials still face challenges with weak NIR electroluminescence (EL) emission and low external quantum efficiency (EQE), primarily due to undesired resonance energy transfer (RET) occurring between the host and Yb3+ ions, which adversely affects their emission efficiency and device performance. Herein, we report the synergistic enhancement of NIR emission in a CsPbCl3 host through co-doping with Yb3+/Nd3+ ions for perovskite LEDs (PeLEDs). The co-doping of Yb3+/Nd3+ ions in a CsPbCl3 host resulted in enhanced NIR emission above 1000 nm, which is highly desirable for NIR optoelectronic applications. This cooperative energy transfer between Yb3+ and Nd3+ can enhance the overall efficiency of energy conversion. Furthermore, the PeLEDs incorporating the co-doped CsPbCl3/Yb3+/Nd3+ PeNCs as an emitting layer exhibited significantly enhanced NIR EL compared to the single doped PeLEDs. The optimized co-doped PeLEDs showed improved device performance, including increased EQE of 6.2% at 1035 nm wavelength and low turn-on voltage. Our findings highlight the potential of co-doping with Yb3+ and Nd3+ ions as a strategy for achieving synergistic enhancement of NIR emission in CsPbCl3 perovskite materials, which could pave the way for the development of highly efficient perovskite LEDs for NIR optoelectronic applications.

Red/NIR emissive aggregation-induced emission-active photosensitizers with strong donor-acceptor strength for image-guided photodynamic therapy of cancer.

Light-mediated therapies such as photodynamic therapy (PDT) are considered emerging cancer treatment strategies. However, there are still lots of defect with common photosensitizers (PSs), such as short emission wavelength, weak photostability, poor cell permeability, and low PDT efficiency. Therefore, it is very important to develop high-performance PSs. Recently, luminogens with aggregation-induced emission (AIE) characteristics and red/near-infrared (NIR) emissive have been reported as promising PSs for image-guided cancer therapy, due to them being able to prevent autofluorescence in physiological environments, their enhanced fluorescence in the aggregated state, and generation of reactive oxygen species (ROS). Herein, we developed PSs named TBTCPM and MTBTCPM with donor-acceptor (D-A) structures, strong red/NIR, excellent targeting specificities to good cell permeability, and high photostability. Interestingly, both of them can efficiently generate ROS under white light irradiation and possess excellent killing effect on cancer cells. This study, thus, not only demonstrates applications in cell image-guided PDT cancer therapy performances but also provides strategy for construction of AIEgens with long emission wavelengths.

Dithienoazepine-Based Near-Infrared Dyes: Janus-Faced Effects of a Thiophene-Fused Structure on Antiaromatic Azepines.

We here disclose that the incorporation of thiophene rings into a seven-membered 8π azepine in a fused fashion produces a useful antiaromatic core for near-infrared (NIR) dyes. In contrast to dibenzazepine derivatives with bent structures, dithieno-fused derivatives with electron-accepting groups adopt flat conformations in the ground state. The dithieno-fused derivatives exhibited broad absorption spectra that cover the visible region as well as sharp emission bands in the NIR region, which are considerably red-shifted relative to those of the dibenzo-fused congeners. Theoretical study revealed two contradictory effects of the less-aromatic thiophene-fused structure, i.e., the enhancement of the antiaromaticity of the adjacent azepine ring and the relief of the antiaromaticity through the contribution of a quinoidal resonance form. The combination of the dithienoazepine core with cationic electron-accepting groups produced a NIR fluorescent dye with an emission at 878 nm in solution.

Heterometallic lanthanide complexes with site-specific binding that enable simultaneous visible and NIR-emission.

Macrocyclic lanthanide complexes have become widely developed due to their distinctive luminescence characteristics and wide range of applications in biological imaging. However, systems with sufficient brightness and metal selectivity can be difficult to produce on a molecular scale. Presented herein is the stepwise introduction of differing lanthanide ions in a bis-DO3A/DTPA scaffold to afford three trinuclear bimetallic [Ln2Ln'] lanthanide complexes with site-specific, controlled binding [(Yb2Tb), (Eu2Tb), (Yb2Eu)]. The complexes display simultaneous emission from all LnIII centers across the visible (TbIII, EuIII) and near infra-red (YbIII) spectrum when excited via phenyl ligand sensitization at a wide range of temperatures and are consequently of interest for exploiting imaging in the near infra-red II biological window. Analysis of lifetime data over a range of excitation regimes reveals intermetallic communication between TbIII and EuIII centers and further develops the understanding of multimetallic lanthanide complexes.

Near infrared in and out: Deep imaging for scrap leather induced autophagy in vivo by an ultrasensitive two-photon polarity probe.

As one of the important means for eukaryotic cells to maintain homeostasis, autophagy allows for transporting deformed biomacromolecules and damaged organelles to lysosome for digestion and degradation. The process of autophagy entails the merging of autophagosomes and lysosomes, culminating in the breakdown of biomacromolecules. This, in turn, leads to a change in lysosomal polarity. Therefore, fully understanding the changes of lysosomal polarity during autophagy is of significance to the study of membrane fluidity and enzymatic reaction. However, the shorter emission wavelength has greatly damaged the imaging depth, thus seriously limiting its biological application. Therefore, in this work, a near infrared in and out lysosome-targeted polarity-sensitive probe NCIC-Pola was developed. The fluorescence intensity of NCIC-Pola showed an approximate 1160-fold increase when the polarity decreased under two-photon excitation (TPE). In addition, the excellent fluorescence emission wavelength (692 nm) enabled the deep imaging analysis of scrap leather induced autophagy in vivo.