Tetraphenylene-Coated Near-Infrared Benzoselenodiazole Dye: AIE Behavior, Mechanochromism, and Bioimaging

Colorimetric sensing for translational applications: from colorants to mechanisms

Colorimetric sensing offers instant reporting via visible signals. Versus labor-intensive and instrument-dependent detection methods, colorimetric sensors present advantages including short acquisition time, high throughput screening, low cost, portability, and a user-friendly approach. These advantages have driven substantial growth in colorimetric sensors, particularly in point-of-care (POC) diagnostics. Rapid progress in nanotechnology, materials science, microfluidics technology, biomarker discovery, digital technology, and signal pattern analysis has led to a variety of colorimetric reagents and detection mechanisms, which are fundamental to advance colorimetric sensing applications. This review first summarizes the basic components (e.g., color reagents, recognition interactions, and sampling procedures) in the design of a colorimetric sensing system. It then presents the rationale design and typical examples of POC devices, e.g., lateral flow devices, microfluidic paper-based analytical devices, and wearable sensing devices. Two highlighted colorimetric formats are discussed: combinational and activatable systems based on the sensor-array and lock-and-key mechanisms, respectively. Case discussions in colorimetric assays are organized by the analyte identities. Finally, the review presents challenges and perspectives for the design and development of colorimetric detection schemes as well as applications. The goal of this review is to provide a foundational resource for developing colorimetric systems and underscoring the colorants and mechanisms that facilitate the continuing evolution of POC sensors.

Construction of aggregation-induced emission photosensitizers through host-guest interactions for photooxidation reaction and light-harvesting

In the present work, we have designed and synthesized a triphenylamine modified cyanophenylenevinylene derivative (TPCI), which can self-assembly with cucurbit[6]uril (CB[6]) and cucurbit[8]uril (CB[8]) through host-guest interactions to form supramolecular complexes (TPCI-CB[6]) and supramolecular polymers (TPCI-CB[8]) in the aqueous solution. The supramolecular assemblies of TPCI-CB[6] and TPCI-CB[8] not only exhibited high singlet oxygen (1O2) production efficiency as photosensitizers, but also realized the application in the construction of artificial light-harvesting systems due to the excellent fluorescence properties in the aqueous solution. The production efficiency of 1O2 has been effectively improved after the addition of CB[6] and CB[8] for TPCI, which were applied as efficient photosensitizers in the photooxidation reactions of thioanisole and its derivatives with the highest yield of 98% in the aqueous solution. The excellent fluorescence properties of TPCI-CB[6] and TPCI-CB[8] can be used as energy donors in artificial light-harvesting systems with energy acceptors sulforhodamine 101 (SR101) and cyanine dye 5 (Cy5), in which one-step energy transfer processes of TPCI-CB[6]+SR101 and TPCI-CB[8]+Cy5, and a two-step sequential energy transfer process of TPCI-CB[6]+SR101+Cy5 were constructed to simulate the natural photosynthesis system.

Full-Color Emissive D-D-A Carbazole Luminophores: Red-to-NIR Mechano-fluorochromism, Aggregation-Induced Near-Infrared Emission, and Application in Photodynamic Therapy

The preparation of multifunctionalized luminophores with full-color emission based on an identical core skeleton is a significative but challenging research topic. In this work, eight donor-donor-acceptor (D-D-A)-type luminogens based on a central carbazole core bearing a C₆ hydrocarbon chain were designed by using different kinds of donor and acceptor units on the left and right, and synthesized in good yields. These D-D-A carbazole derivatives display deep-blue, sky-blue, cyan, green, yellow-green, yellow, orange and red fluorescence in the solid state, achieving full-color emission covering the whole visible light range under UV light illumination. Notably, the dicyano-functionalized triphenylamine-containing carbazole derivative exhibits rare aggregation-induced near-infrared emission and red-to-near-infrared mechano-fluorochromism with high contrast beyond 100 nm. Furthermore, the red-emissive luminogen can serve as a potential candidate for cell imaging and photodynamic therapy (PDT). This work not only provides reference for the construction of full-color emissive systems but also opens a new avenue to the preparation of multifunctionalized luminophores capable of simultaneous application in near-Infrared mechanical-force sensors and PDT fields.

Control of Fluorescence of Organic Dyes in the Solid-State by Supramolecular Interactions

Fluorescent organic dyes play an essential role in the creation of new "smart" materials. Fragments and functional groups capable of free rotation around single bonds can significantly change the fluorescent organic dye's electronic structure under analyte effects, phase state transitions, or changes in temperature, pressure, and media polarity. Dependencies between steric and electronic structures become highly important in transition from a solution to a solid-state. Such transitions are accompanied by a significant increase in the dye molecular structure's rigidity due to supramolecular associates' formation such as H-bonding, π···π and dipole-dipole interactions. Among those supramolecular effects, H-bonding interactions, first of all, lead to significant molecular packing changes between loose or rigid structures, thus affecting the fluorescent dye's electronic states' energy and configuration, its fluorescent signal's position and intensity. All the functional groups and heteroatoms that are met in the organic dyes seem to be involved in the control of fluorescence via H-bonding: C-H···N, C-H···π, S = O···H-C, P = O···H, C-H···O, NH···N, C - H···C, C - H···Se, N-H···O, C - H···F, C-F···H. Effects of molecular packing of fluorescent organic dyes are successfully used in developing mechano-, piezo-, thermo- fluorochromes materials for their applications in the optical recording of information, sensors, security items, memory elements, organic light-emitting diodes (OLEDs) technologies.

Carbazole-based aggregation-induced phosphorescent emission-active gold(I) complexes with various phosphorescent mechanochromisms

A series of carbazole-containing gold(I) complexes modified with different substituents were successfully designed and synthesized, and their molecular structures were characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. The aggregation-induced behaviors of these gold(I) complexes were studied by ultraviolet/visible and photoluminescence spectroscopy. Meanwhile, their mechanical force-responsive emissive properties were also investigated via solid-state photoluminescence spectroscopy. Interestingly, all these gold(I)-based luminogenic molecules were capable of exhibiting aggregation-induced phosphorescent emission phenomena. Furthermore, their solids of three gold(I) complexes displayed contrasting mechano-responsive phosphorescence features. More specifically, trifluoromethyl or methoxyl-substituted luminophores 1 and 3 demonstrated mechanochromic behaviors involving blue-shifted phosphorescence changes, and their mechanoluminochromic phenomena were reversible. However, the solid-state phosphorescence of phenyl-substituted luminophor 2 was not sensitive to external mechanical force.

Prospects of NIR fluorescent nanosensors for green detection of SARS-CoV-2

The pandemic of the novel coronavirus disease 2019 (COVID-19) is continuously causing hazards for the world. Effective detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can relieve the impact, but various toxic chemicals are also released into the environment. Fluorescence sensors offer a facile analytical strategy. During fluorescence sensing, biological samples such as tissues and body fluids have autofluorescence, giving false-positive/negative results because of the interferences. Fluorescence near-infrared (NIR) nanosensors can be designed from low-toxic materials with insignificant background signals. Although this research is still in its infancy, further developments in this field have the potential for sustainable detection of SARS-CoV-2. Herein, we summarize the reported NIR fluorescent nanosensors with the potential to detect SARS-CoV-2. The green synthesis of NIR fluorescent nanomaterials, environmentally compatible sensing strategies, and possible methods to reduce the testing frequencies are discussed. Further optimization strategies for developing NIR fluorescent nanosensors to facilitate greener diagnostics of SARS-CoV-2 for pandemic control are proposed.

Development of a New Multiple Stimuli-Responsive Fluorescent Material Using the Minus Strategy Based on the Structure of Tetraphenyl-1,3-butadiene

In this study, we designed and synthesized a new class of aggregation-induced emission luminogens, which was inspired and developed from the structure of tetraphenyl-1,3-butadienes derivative (TPB-1) through the minus strategy by removing one of the phenyl groups. Among them, L1 and L4 exhibited an aggregation-induced emission effect and multistimuli-responsive chromic behavior. Moreover, two types of single crystals of L1 were obtained, and their different emission behaviors were elucidated clearly by analyzing the single-crystal data.

Fluorescent TPE Macrocycle Relayed Light-Harvesting System for Bright Customized-Color Circularly Polarized Luminescence

Artificial systems for sequential chirality transmission/amplification and energy relay are perpetual topics that entail learning from nature. However, engineering chiral light-harvesting supramolecular systems remains a challenge. Here, we developed new chiral light-harvesting systems with a sequential Förster resonance energy transfer process where a designed blue-violet-emitting BINOL (1,1'-Bi-2-naphthol) compound, BINOL-di-octadecylamide (BDA), functions as an initiator of chirality and light absorbance, a new green-emitting hexagonal tetraphenylethene-based macrocycle (TPEM) with aggregation-induced emission serves as a conveyor, and Nile red (NiR) or/and a near-infrared dye, tetraphenylethene (TPE)-based benzoselenodiazole (TPESe), are the terminal acceptors. Benefiting from the close contact and large optical overlap between donors and acceptors at each level, triad and tetrad relaying systems sequentially and efficiently furnish chirality transmission/amplification and energy transfer along the cascaded line BDA-TPEM-NiR (or/and TPESe), leading to bright customized-color circularly polarized luminescence (CPL) and bright white-light-emitting CPL (CIE coordinates: 0.33, 0.34) with an amplified dissymmetry factor (glum) of 3.5 × 10-2 over a wide wavelength range. This work provides a new direction for the construction of chiral light-harvesting systems for a broad range of applications in chiroptical physics and chemistry.

[1]Benzothieno[3,2-b][1]benzothiophene-Based Dyes: Effect of Ancillary Moiety on Mechanochromism and Aggregation-Induced Emission

It is an established fact that [1]benzothieno[3,2-b][1]benzothiophene (BTBT) is a champion molecule for high mobility OFETs devices. Recently it is also utilized in dye-sensitized solar cells (DSSCs) and organic photovoltaics...

The efficiency of MSC‐based targeted AIE nanoparticles for gastric cancer diagnosis and treatment: An experimental study

Mesenchymal stem cells (MSCs), due to their tumor tropism, are strongly recruited by various solid tumors and mobilized by inflammatory signals in the tumor microenvironment. However, effective cellular uptake is critical for MSC‐based drug delivery. In this study, we synthesized a spherical copolymer, polyethylenimine–poly(ε‐caprolactone), with aggregation‐induced emission (AIE) material and the anticancer drug, paclitaxel, coloaded onto its inner core. This was followed by the addition of a transactivator of transcription (TAT) peptide, a type of cell‐penetrating peptide, to modify the nanoparticles (NPs). Finally, the MSCs were employed to carry the TAT‐modified AIE‐NPs drug to the tumor sites and assist in simultaneous cancer diagnosis and targeted tumor therapy. In vitro, the TAT‐modified AIE‐NPs showed good biocompatibility, targeting, and stability in an aqueous solution besides high drug‐loading and encapsulation efficiency. In vitro, the AIE‐NPs exhibited a controllable release under a mildly acidic environment. The in vivo and in vitro studies showed high antitumor efficacy and low cytotoxicity of the AIE‐NP drug, whereas biodistribution confirmed the tumor tropism of MSCs. To summarize, the MSC‐based AIE‐NP drugs loaded with TAT possessed good biocompatibility and high antitumor efficacy via the enhanced NP‐drug uptake. In addition, the tumor tropism of MSCs provided selective drug uptake by the tumor cells and thus reduced the systemic side effects.

A Novel Strategy to Design and Construct AIE-active Mechanofluorochromic Materials via Regulation of Molecular Structure

In this work, we first designed and synthesized tetraphenylene-fused aryl-imidazole derivatives TM-1-4 via regulation of molecular structure, which were consisted of 1H-imidazo[4,5-f][1,10]phenanthroline, 1H-phenanthro[9,10-d]imidazole, 4,5-diphenyl-1H-imidazole, 3,3'-(1H-imidazole-4,5-diyl)dipyridine moieties and AIE-active tetraphenylethene units, respectively. The results illustrated that TM-1-4 exhibited clear AIE characteristics. Meanwhile, TM-2 and TM-3 show excellent solid emission properties (Φ_TM-2 =13.73 % and Φ_TM-3 =36.21 %), whereas TM-1 and TM-4 exhibit the opposite properties (Φ_TM-1 =1.48 % and Φ_TM-4 =4.83 %). The multiple rotors (pyridine and benzene ring) causes twisted conformations of the molecule that prevents π-π stacking and enhances solid emission(ΦTM-2<ΦTM-3, ΦTM-1<ΦTM-4). Significantly, TM-2 and TM-3 also exhibited reversible mechanochromic behavior (Emission red shifts: Δλ_TM-2 =43 nm and Δλ_TM-3 =41 nm) with color changes between blue and green emissions. The powder X-ray diffraction (PXRD) suggested the disordered state of ground sample could be readily returned to an ordered crystalline. Therefore, the mechanochromisms of TM-2 and TM-3 are ascribable to the phase transformation between crystal and amorphous structure. The single crystal X-ray analysis of TM-2 reveals a twisted conformation for TPE moiety and the absence of π-π intermolecular stacking. These excellent optical properties of TM-2 and TM-3 make them potentially applications in mechanochromic materials and imaging agents.

A high-contrast photoacoustic agent with near-infrared emission

Benzobisthiadiazole as a typical electron acceptor, has been widely used to design fluorescent dyes and photoacoustic (PA) agents. With the strategy of constructing donor-acceptor-donor (D-A-D) type of electron characteristics, benzobisthiadiazole derivatives tend to behave stable in near-infrared absorption and emission, which is beneficial to PA imaging. In this chapter, two molecular design strategies are combined to improve the photoacoustic imaging effects of new PA contrast agent IR-1302 NPs, by installing strengthened conjugated bridges and electron donors. The nanoparticles exhibit high-contrast noninvasive photoacoustic imaging in tumor models with longer wavelength absorption and emission and show potential as a clinic contrast agent.

Recent progress in fluorescent probes for bacteria

Food fermentation, antibiotics, and pollutant degradation are closely related to bacteria. Bacteria play an irreplaceable role in life. However, some bacteria seriously threaten human health and cause large-scale infectious diseases. Therefore, there is a pressing need to develop strategies to accurately monitor bacteria. Technology based on molecular probes and fluorescence imaging is noninvasive, results in little damage, and has high specificity and sensitivity, so it has been widely applied in the detection of bacteria. In this review, we summarize the recent progress in bacterial detection using fluorescence. In particular, we generalize the mechanisms commonly used to design organic fluorescent probes for detecting and imaging bacteria. Moreover, a perspective regarding fluorescent probes for bacterial detection is discussed.

Coordination-Induced Emission from Tetraphenylethylene Units and Their Applications

Thanks to the potential of aggregation-induced emission (AIE) phenomena, improved stabilities, and the good selectivity and sensitivity of the chemical responses exhibited by the products, coordination-driven self-assembly with tetraphenylethylene (TPE) units has recently received much attention and has been widely investigated for application in chemical sensors, cell imaging agents, light-harvesting systems, and others. Several reviews have emerged on the topics of AIE chemistry and aggregation-induced emission luminogen (AIEgen)-based supramolecular assembles, however, there is still a distinct lack of full overviews of emission enhancement from the viewpoint of metal-coordination effects. Thus, this minireview offers recent advances that have been made in the design and application of TPE-based metallacycles, metallacages, metal-organic frameworks (MOFs) and coordination polymers (CPs).

Photophysical properties of 4-(5-methylthiophen-2-yl)pyridinium–cyclic enolate betaine dyes tuned by control of twisted intramolecular transfer

In this paper, thienylpyridinium–cyclic enolate betaine (TPB) dyes were reported as unique skeletons of fluorescent donor–acceptor type molecules.

Cyanine-based fluorescent indicator for mercury ion and bioimaging application in living cells

A commercial cyanine dye IR-780 and a thioether-containing dicarboxylic acid ligand were used to construct the near-infrared fluorescent probe, which was used as a near-infrared fluorescent indicator for the determination of mercury ions in water and in living cells. This indicator displayed high specificity towards Hg²⁺ without any interference from other detecting species. Especially, the emission at 790 nm dramatically increased more than 25 times after interacting with Hg²⁺. The binding experiment showed that the indicator formed 1:1 complex with Hg²⁺. More, this indicator could be applied in the visualization of Hg²⁺ in living cells and measuring the Hg²⁺ concentration of tap-water sample.

A highly specific probe for the imaging of inflammation-induced endogenous nitric oxide produced during the stroke process

In this study, a turn-on two-photon fluorescent probe (Lyso-TP-NO) for nitric oxide (NO) was developed. It was synthesized using 4-ethylamino-1,8-naphthalimide as the two-photon fluorophore and N-methylaniline moiety as the reaction site. The probe and fluorophore were tested under one- and two-photon modes. The fluorescence intensity of the system was enhanced 23.1-fold after reacting with NO in the one-photon mode. However, the maximal two-photon action cross-section value of 200 GM was obtained under excitation at 840 nm. The probe exhibits high selectivity and sensitivity over other reactive oxygen species (ROS) and reactive nitrogen species (RNS), with a detection limit as low as 3.3 nM. The two-photon fluorescence imaging of living cells and mouse brain tissues can capture inflammation-induced endogenous NO production in lysosomes during stroke occurrence.

An Amphiphilic Micromolecule Self-Assembles into Vesicles for Visualized and Targeted Drug Delivery

Described here is the first example of the construction of multifunctional drug delivery systems by employing an amphiphilic micromolecule. The intrinsic aggregation-induced emissive and tumor-targeting amphiphilic conjugate of β-d-galactose with tetraphenylethene (TPE-Gal), in which the hydrophobic TPE moiety spontaneously acts as the imaging chromophore and the hydrophilic Gal moiety spontaneously acts as the targeting ligand and galactosidase trigger, can self-assemble into fluorescent vesicles that can efficiently load both water-soluble and -insoluble anticancer drugs. In vitro and in vivo evaluations revealed that the pH/β-d-galactosidase dual-responsive doxorubicin (DOX)-loaded vesicles TPE-Gal@DOX exhibited good targeting effect and higher antitumor efficacy than free DOX. H&E staining analysis displayed remarkable necroses and weak cell proliferation in the tumor area and no toxicity to major organs, indicating the superior targeting antitumor therapeutic efficacy of TPE-Gal@DOX.

Fluorescence detection of fluorine ions in biological fluids based on aggregation-induced emission

Traditional chemical and biological sensors developed through aggregation-induced emission (AIE) are mainly based on “Turning on” pattern of fluorescence enhancement, which often has poor selectivity and can be easily interfered with by other substances. On this basis, an AIE-based tetraphenyl ethylene (TPE) derivative (TPE-COOH) was prepared in this study and aggregated by adding Al³⁺, so as to form the TPE-COOH/Al³⁺ polymer. TPE-COOH fluorescence was enhanced through AIE principle, thus realizing the “Turning on” state. F⁻ could bind to Al³⁺ after the addition of F⁻ ions which would result in the decomposition of TPE-COOH/Al³⁺ aggregate, dissolved state of TPE-COOH and gradual reduction of fluorescence intensity of the system, thus realizing “Turning off” state. Moreover, F⁻ ions in biological fluid were analyzed and detected through such AIE-based “Turning on-off” pattern. The linear range of this method for F⁻ detection was 3–12 μM and the detection limit was 0.9 μM.

Schematic diagram of fluorescence detection of F⁻ ions in biological fluids based on TPE-COOH/Al³⁺ polymer Aggregation-Induced Emission (AIE) “Turning on–off” mode.

Near-infrared heptamethine cyanines (Cy7): from structure, property to application

Heptamethine cyanine dyes (Cy7) have attracted much attention in the field of biological application due to their unique structure and attractive near infrared (NIR) photophysical properties.