Stimuli-responsive nanotheranostic systems conjugated with AIEgens for advanced cancer bio-imaging and treatment

Aggregation-induced emission (AIE) is a unique phenomenon observed in various materials such as organic luminophores, carbon dots (CDs), organic-inorganic nanocomposites, fluorescent dye molecules, and nanoparticles (NPs). These AIE-active materials, or AIEgens, are ideal for balancing multifunctional phototheranostics and energy dissipation. AIE properties can manifest in organic fluorescent probes, rendering them effective for cancer treatment due to their ability to penetrate deeply and provide high therapeutic efficacy. This efficacy is attributed to their high photobleaching thresholds, ability to induce Stokes shifts, and capacity to activate fluorophores. Therefore, the development of innovative AIE-based materials for disease diagnosis and treatment, particularly for cancer, is both important and promising. Recent years have seen successful demonstrations of nanoparticles with AIE properties being used for photodynamic therapy (PDT) and multimodal imaging of tumor cells. These fluorophores have been shown to impact mitochondria and lysosomes, generate reactive oxygen species (ROS), activate the immune system, load and release drugs, and ultimately induce apoptosis in tumor cells. In this review, we examine previous studies on the manufacturing methods and effects of AIEgens on cancer cells, with a theranostic strategy of simultaneous treatment and imaging. We also investigate the factors affecting drug delivery on different cancer cells, including internal stimuli such as pH, ROS, enzymes, and external stimuli like near-infrared (NIR) light and ultrasound waves.

A series of tetraphenylene-acetonitrile AIE compounds with D-A-D' structure for drugs delivery systems of paclitaxel: Synthesis, structure-activity relationship and anti-tumors effect

Aggregation-induced emission (AIE) materials are attracting great attention in biomedical fields such as sensors, bioimaging, and cancer treatment, et al. due to their strong fluorescence emission in the aggregated state. In this contribution, a series of tetraphenylene-acetonitrile AIE compounds with D-A-D' structures were synthesized by Suzuki coupling reaction and Knoevenagel condensation, and their relationship of chemical structure and fluorescence properties was investigated in detail, among which TPPA compound was selected as the monomer owing to the longest emission wavelength at about 530 nm with low energy band gap ΔE 3.09 eV of neutral TPPA and 1.43 eV of protonated TPPA. Novel amphiphilic AIE PEG-TA copolymers were prepared by RAFT polymerization of TPPA and PEGMA with about 1.44×104 Mw and narrow PDI, and the molar ratio of TPPA in the PEG-TA1 and PEG-TA2 copolymers was about 23.4 % and 29.6 %. The as-prepared PEG-TA copolymers would self-assembled in aqueous solution to form core-shell structures with a diameter of 150-200 nm, and their emission wavelength could reversibly convert from 545 nm to 650 nm with excellent pH sensitivity. The CLSM images showed that the PEG-TA FONs and PTX drugs-loaded PTX-TA FONs could be endocytosed by cells and mainly enriched in the cytoplasm, and CCK-8 results showed that the PEG-TA FONs had excellent biocompatibility but PTX-TA FONs had high inhibition ratio for A549 cells, moreover, the flow cytometry also showed that PTX-TA FONs could result in the apoptosis of A549 cells with some extent anti-tumor effect.

Aggregation-Induced Emission-Active Biomacromolecules: Progress, Challenges, and Opportunities

Biomacromolecules featuring aggregation-induced-emission (AIE) characteristics generally present new properties and performances that are silent in the molecular state, providing endless possibilities for the evolution of biomedical applications. Tremendous achievements based on the research of AIE-active biomacromolecules have been made in synthetic exploration, material development, and practical applications. In this Perspective, we give a brief account in the development of AIE-active biomacromolecules. Remarkable progresses have been made in the exploration of AIE-active biomacromolecule preparation, structure-property relationships, and the relevant biomedical applications. The existing challenges and promising opportunities, as well as the future directions in AIE-active biomacromolecule research, are also discussed. It is expected that this Perspective can act as a trigger for the innovation of AIE-active biomacromolecule research and aggregate science.

Precise Molecular Design of a Pair of New Regioisomerized Fluorophores With Opposite Fluorescent Properties

Aggregation-induced emission (AIE) has attracted much attention in the past 2 decades. To develop novel AIE-active materials, ACQ-to-AIE transformation via regioisomerization is one of the most straightforward method. However, most of the reported ACQ-to-AIE transformations are achieved by migrating bulky units. In this work, a facile conversion was realized by migrating a small pyrrolidinyl group from para- to ortho-position on the rofecoxib scaffold. As a result, a pair of new isomers named MOX2 and MOX4 exhibited AIE behavior and ACQ activity, respectively. Moreover, MOX2 also showed solvatochromic, mechanochromic, and acidochromic properties with reversible multi-stimulus behavior. Single crystal X-ray analysis of MOX2 revealed that the molecular conformation and its packing mode were responsible for the AIE emission behavior. Further investigation indicated that MOX2 showed high lipid droplets staining selectivity. Taken together, the current work not only provides a new design philosophy for achieving ACQ-to-AIE conversion by migrating a small pyrrolidinyl group but also presents a promising candidate MOX2 for potential applications such as in security ink, optical recording and biological applications.

Solvent-Modulated Chiral Self-Assembly: Selective Formation of Helical Nanotubes, Nanotwists, and Energy Transfer

As the medium for self-assembly processes, solvents strongly influence the supramolecular assemblies via specific solute-solvent interactions, which may result in effective modulation of properties, self-assembled nanostructures, and functions through varying the solvent. Here, two kinds of pyridine-cyanostilbene functionalized chiral amphiphiles (l/d-PyPhG and l-PyG) were designed, and their self-assembly behaviors in different solvents were investigated. It was found that both amphiphiles formed gels in dimethyl sulfoxide (DMSO) and self-assembled into right-handed nanotwists, while they formed suspensions in ethanol consisting of left-handed nanotubes. Although the molecular chirality in the compounds remained unchanged in the two solvents, the nanoassemblies showed opposite handedness at the nanoscale together with opposite circular dichroism (CD) and circularly polarized luminescence (CPL) signals. Furthermore, when the amphiphiles were co-assembled with an achiral dye, it was found that efficient energy transfer took place in the systems composed of nanotubes rather than those composed of nanotwists. Therefore, by assembling molecules with the same molecular chirality in different solvents, a selective formation of helical nanotubes or nanotwists and the regulation of handedness as well as energy transfer efficiency were achieved.

Recent Advances in Aggregation-Induced Emission Active Materials for Sensing of Biologically Important Molecules and Drug Delivery System

The emergence and development of aggregation induced emission (AIE) have attracted worldwide attention due to its unique photophysical phenomenon and for removing the obstacle of aggregation-caused quenching (ACQ) which is the most detrimental process thereby making AIE an important and promising aspect in various fields of fluorescent material, sensing, bioimaging, optoelectronics, drug delivery system, and theranostics. In this review, we have discussed insights and explored recent advances that are being made in AIE active materials and their application in sensing, biological cell imaging, and drug delivery systems, and, furthermore, we explored AIE active fluorescent material as a building block in supramolecular chemistry. Herein, we focus on various AIE active molecules such as tetraphenylethylene, AIE-active polymer, quantum dots, AIE active metal-organic framework and triphenylamine, not only in terms of their synthetic routes but also we outline their applications. Finally, we summarize our view of the construction and application of AIE-active molecules, which thus inspiring young researchers to explore new ideas, innovations, and develop the field of supramolecular chemistry in years to come.

AIE active polymers for biological applications

The discovery of aggregation-induced emission (AIE) phenomenon, significantly altered the understanding of the scientific world about the luminophore aggregation. Polymers with AIE features have recently emerged as promising materials with wide range of applications in optoelectronics devices, chemosensors, bioimaging, cancer theranostics and drug delivery. By introducing the AIE active molecule into the polymer structure, novel materials encompassing the characteristics properties of both the functional materials such as excellent brightness, versatile structure modification, high biocompatibility, exceptional stability and facile processability are achieved. This chapter presents the advances in synthetic design as well as potential biological applications of AIE active polymers, beginning with a brief introduction to the AIE phenomenon. The versatile synthetic route, easier functionalization, and light up feature of the AIE active polymers offer direct visualization of the physiological processes within or outside the living organisms. This chapter also precisely describes the photodynamic therapy/photothermal therapy (PDT/PTT) with up-to-date advancement of AIE active polymer and their emerging applications in biomedical field. The AIE active Photosensitizers (PSs) are much more efficient in singlet oxygen (¹O₂) production than their small molecule AIE active PSs due to their enhanced inter system crossing (ISC) process and improved light-harvesting ability. Additionally, the present chapter aims to focus on all recent AIE active polymers for drug screening and drug delivery. The AIE active polymer often shows decent drug loading capacity, high stability and good biocompatibility comprising image guided drug monitoring features. Lastly, the concluding discussion reveals the future prospective of the AIE active polymers.

Recent Progress in Polymeric AIE-Active Drug Delivery Systems: Design and Application

Aggregation-induced emission (AIE) provides a new opportunity to overcome the drawbacks of traditional aggregation-induced quenching of chromophores. The applications of AIE-active fluorophores have spread across various fields. In particular, the employment of AIEgens in drug delivery systems (DDSs) can achieve imaging-guided therapy and pharmacodynamic monitoring. As a result, polymeric AIE-active DDSs are attracting increasing attention due to their obvious advantages, including easy fabrication and tunable optical properties by molecular design. Additionally, the design of polymeric AIE-active DDSs is a promising method for cancer therapy, antibacterial treatment, and pharmacodynamic monitoring, which indeed helps improve the effectiveness of related disease treatments and confirms its potential social importance. Here, we summarize the current available polymeric AIE-active DDSs from design to applications. In the design section, we introduce synthetic strategies and structures of AIE-active polymers, as well as responsive strategies for specific drug delivery. In the application section, typical polymeric AIE-active DDSs used for cancer therapy, bacterial treatment, and drug delivery monitoring are summarized with selected examples to elaborate on their wide applications.

Programmable Assembly of π-Conjugated Polymers

π-Conjugated polymers have numerous applications due to their advantageous optoelectronic and mechanical properties. These properties depend intrinsically on polymer ordering, including crystallinity, orientation, morphology, domain size, and π-π interactions. Programming, or deliberately controlling the composition and ordering of π-conjugated polymers by well-defined inputs, is a key facet in the development of organic electronics. Here, π-conjugated programming is described at each stage of material development, stressing the links between each programming mode. Covalent programming is performed during polymer synthesis such that complex architectures can be constructed, which direct polymer assembly by governing polymer orientation, π-π interactions, and morphological length-scales. Solution programming is performed in a solvated state as polymers dissolve, aggregate, crystallize, or react in solution. Solid-state programming occurs in the solid state and is governed by polymer crystallization, domain segregation, or gelation. Recent progress in programming across these stages is examined, highlighting order-dependent features and assembly techniques that are unique to π-conjugated polymers. This should serve as a guide for delineating the many ways of directing π-conjugated polymer assembly to control ordering, structure, and function, enabling the further development of organic electronics.

Highly Selective and Sensitive Aggregation-Induced Emission of Fluorescein-Coated Metal Oxide Nanoparticles

We report the synthesis, characterization, and photophysical properties of novel metal oxide nanoparticles (NPs) coated with specially designed fluorescein substituents which are capped with electron-withdrawing groups. The fluorescein-coated nanoparticles were synthesized in excellent yields, and their structures were confirmed using various advanced spectroscopic, instrumental, and surface analysis techniques, revealing the formation of the target functionalized nanoparticles (FNPs) which show superior chemical and thermal stabilities. In addition, the photophysical properties of the FNPs were examined using UV-visible absorption and fluorescence spectroscopy. These latter techniques disclosed aggregation-induced emission (AIE) properties for most of the target FNPs, namely those which are soluble in common organic solvents at selective concentration ranges of water fractions in the solvent mixture.

Conjugated Polymers with Aggregation-Induced Emission Characteristics for Fluorescence Imaging and Photodynamic Therapy

Accurate diagnosis and treatment have been extensively developed in the field of biomedicine, which put forward higher requirements for the development of biomedical materials with high efficiency and selectivity. Among them, conjugated polymers featuring aggregation-induced emission (AIE) characteristics (AIE conjugated polymers) have stood out in recent years owing to their unique properties, such as intense solid emission, high light-harvesting ability, efficient energy transfer, and high ¹ O₂ generation ability, which empower them with effective biomedical functions in fluorescence imaging (FLI), photodynamic therapy (PDT), FLI-guided PDT, two-photon excited photodynamic therapy (2PE-PDT), etc. In this review, we highlight recent progress in AIE conjugated polymers and their applications in anticancer and antibacterial areas based on FLI and PDT, and summarize the mechanism of color-tuned fluorescence emission and efficient ¹ O₂ generation ability. The challenges and perspectives for the future development of AIE conjugated polymers are also discussed.

Modulation of Aggregation-Induced Emission by Excitation Energy Transfer: Design and Application

Excitation energy transfer (EET) as a fundamental photophysical process is well-explored for developing functional materials with tunable photophysical properties. Compared to traditional fluorophores, aggregation-induced emission luminogens (AIEgens) exhibit unique advantages for building EET systems, especially serving as energy donors, due to their outstanding photophysical properties such as bright fluorescence in aggregation state, broad absorption and emission spectra, large Stokes shift, and high photobleaching resistance. In addition, the photophysical properties of AIEgens can be modulated by energy transfer for improved luminescence performance. Therefore, a variety of EET systems based on AIEgens have been constructed and their applications in different areas have been explored. In this review, we summarize recent progress in the design strategy of AIE-based energy transfer systems for light-harvesting, fluorescent probes and theranostic systems, with an emphasis on design strategies to achieve desirable properties. The limitations, challenges and future opportunities of AIE-EET systems are briefly outlined. Design strategies and applications (light-harvesting, fluorescent probe and theranostics) of AIEgen-based excitation energy systems are discussed in this review.

An oroxylin A-loaded aggregation-induced emission active polymeric system greatly increased the antitumor efficacy against squamous cell carcinoma

Squamous cell carcinoma (SCC) is a usually responds poorly to treatment suffers from poor therapeutic benefits while oroxylin A (OA) is a promising flavonoid with high anticancer efficacy against various cancer types. Here in our study, in order to reveal the potential of OA based drug delivery systems (DDSs) in the treatment of SCC, we firstly revealed that OA had a certain pharmacodynamic effect on skin SCC (A431 cells). Afterwards, OA was loaded into a newly synthesized aggregation-induced emission (AIE)-active polymer to construct OA-loaded PDots for the first time. Our results revealed that OA-loaded PDots showed preferable drug loading and enhanced stability. Moreover, the DDS was also capable of self-illumination in the aggregate state to reveal the uptake profile. Most importantly, the DDS showed much more elevated anticancer benefits than free OA in vitro and advanced tumor targetability in vivo, suggesting that it might be a promising system against SCC.

Aggregation-Induced Emission Properties in Fully π-Conjugated Polymers, Dendrimers, and Oligomers

Aggregation-Induced Emission (AIE) in organic molecules has recently attracted the attention of the scientific community because of their potential applications in different fields. Compared to small molecules, little attention has been paid to polymers and oligomers that exhibit AIE, despite having excellent properties such as high emission efficiency in aggregate and solid states, signal amplification effect, good processability and the availability of multiple functionalization sites. In addition to these features, if the molecular structure is fully conjugated, intramolecular electronic interactions between the composing chromophores may appear, thus giving rise to a wealth of new photophysical properties. In this review, we focus on selected fully conjugated oligomers, dendrimers and polymers, and briefly summarize their synthetic routes, fluorescence properties and potential applications. An exhaustive comparison between spectroscopic results in solution and aggregates or in solid state has been collected in almost all examples, and an opinion on the future direction of the field is briefly stated.

Conjugated microporous polymers using a copper-catalyzed [4 + 2] cyclobenzannulation reaction: promising materials for iodine and dye adsorption

A new design strategy is disclosed to synthesize conjugated microporous polymers using a Cu-catalyzed [4 + 2] cyclobenzannulation reaction. The polymers reveal BET surface areas up to 794 m² g⁻¹ and promising uptake of iodine and methylene blue.

Engineering fluorescent semiconducting polymer nanoparticles for biological applications and beyond

We summarize the recent advances in engineering approaches to obtain functionalized semiconducting polymer nanoparticles (SPNs) for biological applications. The challenges and outlook of fabricating functionalized SPNs are also provided.

Nanomaterials with Supramolecular Assembly Based on AIE Luminogens for Theranostic Applications

One of the major pursuits of biomedical science is to develop advanced strategies for theranostics, which is expected to be an effective approach for achieving the transition from conventional medicine to precision medicine. Supramolecular assembly can serve as a powerful tool in the development of nanotheranostics with accurate imaging of tumors and real-time monitoring of the therapeutic process upon the incorporation of aggregation-induced emission (AIE) ability. AIE luminogens (AIEgens) will not only enable fluorescence imaging but will also aid in improving the efficacy of therapies. Furthermore, the fluorescent signals and therapeutic performance of these nanomaterials can be manipulated precisely owing to the reversible and stimuli-responsive characteristics of the supramolecular systems. Inspired by rapid advances in this field, recent research conducted on nanotheranostics with the AIE effect based on supramolecular assembly is summarized. Here, three representative strategies for supramolecular nanomaterials are presented as follows: a) supramolecular self-assembly of AIEgens, b) the loading of AIEgens within nanocarriers with supramolecular assembly, and c) supramolecular macrocycle-guided assembly via host-guest interactions. Meanwhile, the diverse applications of such nanomaterials in diagnostics and therapeutics have also been discussed in detail. Finally, the challenges of this field are listed in this review.

A specific aggregation-induced emission-conjugated polymer enables visual monitoring of osteogenic differentiation

Osteogenic differentiation is the basis of bone growth and repair related to many diseases, in which evaluating the degree and ability of osteogenic transformation is quite important and highly desirable. However, fixing or stopping the growth of cells is required for conventional methods to monitor osteogenic differentiation, which cannot realize the full investigation of the dynamic process. Herein, a new anion conjugated polymer featuring aggregation-induced emission (AIE) characteristics is developed with excellent solubility for in-situ monitoring the process of osteogenic differentiation. This novel polymer can bind with osteogenic differentiated cells, and the intracellular fluorescence increases gradually with the enhancement of osteogenic differentiation. Moreover, it possesses good biosafety with negligible effect on cell activity and osteogenic differentiation, which cannot be realized by the typical method of Alizarin Red S staining. Further study shows that the polymer crosses the cell membrane through endocytosis and enriches in lysosomes, whereas no obvious fluorescence is detected with other cells, including non-differentiated osteoblast cells, under the same conditions, demonstrating the high selectivity. This is the first fluorescent probe with excellent specificity to realize real-time observation of the process of osteogenic differentiation. Therefore, PTB-EDTA shows great promise in the study of osteogenic differentiation and related applications.

Conjugated polymers as nanoparticle probes for fluorescence and photoacoustic imaging

In this review, the role of conjugated polymer nanoparticles (CPNs) in emerging bioimaging techniques is described.

Synthesis of conjugated polymers via cyclopentannulation reaction: promising materials for iodine adsorption

A new class of conjugated polymers is prepared by means of a versatile palladium-catalyzed cyclopentannulation reaction using a series of specially designed diethynyl aryl synthons with the commercially available 9,10-dibromoanthracene DBA monomer.

AIE/FRET-based versatile PEG-Pep-TPE/DOX nanoparticles for cancer therapy and real-time drug release monitoring

Based on the biological significance of self-assembling peptides in program cell death, promoting proliferation of stem cells and suppressing immune responses, stimuli-responsive polypeptide nanoparticles have attracted more and more attention.

Remodeling the tumor microenvironment to improve drug permeation and antitumor effects by co-delivering quercetin and doxorubicin

The tumor microenvironment (TM) plays a critical role in the progress of tumors. However, the TM remodeling effects of currently available therapies remain largely unexplored in many previous reports. In our study, a hyaluronic acid (HA)-modified zeolitic imidazolate framework (ZIF) was successfully fabricated (HA/ZIF) and employed to load doxorubicin (Dox) and quercetin (Que) simultaneously for cancer therapy. The Que and Dox co-loaded HA/ZIF (HA/ZIF/DQ) showed preferable stability under physiological conditions, pH-responsive drug release in an acidic environment and preferential homing capacity to the CD44 receptor-overexpressed HepG2/ADR cells. More importantly, our results revealed that enhanced anticancer efficacy was achieved through the combination of Que and Dox via the tumor microenvironment remodeling effect of Que to potentiate drug penetration into deep tumor tissues.

Donor-Acceptor-Type Conjugated Polymer-Based Multicolored Drug Carriers with Tunable Aggregation-Induced Emission Behavior for Self-Illuminating Cancer Therapy

Nowadays, multicolored drug carriers have exhibited high significance in designing self-illuminating drug delivery systems to adapt different experimental conditions. In this study, we developed an efficient strategy for self-illuminating antitumor therapy using multicolored aggregation-induced emission (AIE)-active drug carriers by tuning electron donor moieties in donor-acceptor (D-A) structures. Three amphipathic conjugated polymers, P1 to P3, were successfully synthesized using an AIE-active tetraphenylethylene (TPE) moiety and donor-acceptor (D-A)-type electronic structure. Interestingly, the fluorescence behavior of P1 to P3 could be tuned between aggregation-caused quenching and AIE by changing the electron donor moiety. Their fluorescence color in aqueous solution could be easily adjusted from yellow to red by choosing stronger electron donors. After the anticancer drug paclitaxel was loaded, two AIE-active polymers, P1 and P2, could be engineered into polymer dots (Pdots) and applied in self-illuminating cancer therapy. The Pdots could not only reveal their location by a yellow- or red-colored fluorescence signal but also exhibit almost two times in vivo antitumor efficacy, high biocompatibility, and obvious tumor-targeting behavior compared to the commercially available anticancer drug Taxol. Furthermore, P2dots exhibited similar in vivo antitumor efficacy and biocompatibility compared to nonemission Abraxane, a commercially available drug delivery system. This work demonstrates the significant application of a D-A-type structure in the design of self-illuminating drug delivery systems.

A new approach to developing diagnostics and therapeutics: Aggregation-induced emission-based fluorescence turn-on

Fluorescence imaging is a promising visualization tool and possesses the advantages of in situ response and facile operation; thus, it is widely exploited for bioassays. However, traditional fluorophores suffer from concentration limits because they are always quenched when they aggregate, which impedes applications, especially for trace analysis and real-time monitoring. Recently, novel molecules with aggregation-induced emission (AIE) characteristics were developed to solve the problems encountered when using traditional organic dyes, because these new molecules exhibit weak or even no fluorescence when they are in free movement states but emit intensely upon the restriction of intramolecular motions. Inspired by the excellent performances of AIE molecules, a substantial number of AIE-based probes have been designed, synthesized, and applied to various fields to fulfill diverse detection tasks. According to numerous experiments, AIE probes are more practical than traditional fluorescent probes, especially when used in bioassays. To bridge bioimaging and materials engineering, this review provides a comprehensive understanding of the development of AIE bioprobes. It begins with a summary of mechanisms of the AIE phenomenon. Then, the strategies to realize accurate detection using AIE probes are discussed. In addition, typical examples of AIE-active materials applied in diagnosis, treatment, and nanocarrier tracking are presented. In addition, some challenges are put forward to inspire more ideas in the promising field of AIE-active materials.

DOX Loaded Aggregation-induced Emission Active Polymeric Nanoparticles as a Fluorescence Resonance Energy Transfer Traceable Drug Delivery System for Self-indicating Cancer Therapy

In this study, an AIE-active polymer (FTP) was successfully prepared and employed to load anti-cancer drug doxorubicin (DOX) for self-indicating cancer therapy via dual FRET process. Our results demonstrated that the FTP polymer could self-assemble into nanoparticles (NPs) in aqueous solutions to give strong fluorescence emission via intramolecular FRET process. The DOX loaded FTP NPs (drug loading content: 21.77%) were homogeneous particles with size around 50 nm and neutral surface charge, which showed preferable colloidal stability, hemolysis and selective drug release with comparable in vivo antitumor effects to DOX·HCl. In particular, the FRET process between FTP (donor) and DOX (acceptor) could serve as indicator for monitoring the in vitro and in vivo drug release profile, which might be a promising platform to realize real-time monitoring of drug localization and release during the delivery process. STATEMENT OF SIGNIFICANCE: 1. An amphiphilic polymer containing aggregation-induced emission segments and polyethylene glycol (PEG) chains (FTP) was firstly synthesized, which is capable of exerting strong fluorescence via intramolecular Förster resonance energy transfer (FRET) in the aggregate state. 2. The FTP polymer could self-assembled into homogeneous nanoparticles in aqueous environment with decent DOX loading capacity. 3. The DOX loaded FTP nanoparticles can afford FRET-traceable monitoring of the drug release both in vitro and in vivo.

Multi-stimuli responsive properties switch by intra- and inter-molecular charge transfer constructed from triphenylamine derivative

The compound TPA-BI exhibited multi-responsive fluorescence behaviors caused by inter-molecular charge transfer (CT) and intra-molecular CT formation.