Conventional Chromophores Research Articles

Cluster and Kill: the Use of Clustering‐Triggered Emission Materials for Singlet Oxygen Photosensitization in Antimicrobial Photodynamic Therapy

AbstractThe emergence of light‐based technologies is revolutionizing modern medicine and healthcare by enabling precise disease diagnosis and treatment through various luminescent agents and imaging techniques. Despite challenges like biocompatibility, spectral tuning, and synthesis complexity, the primary issue is the aggregation‐caused quenching of emission on high concentrations or physiological conditions. In light of these problems, Clustering‐Triggered Emission (CTE), which involves the formation of atomic clusters to induce light absorption and the luminescence of unconventional chromophores, represents an all‐in‐one solution to the challenges identified. Given the potential for CTE materials to behave in ways previously only associated with conventional chromophores, it seems reasonable that highly oxidative reactive oxygen species can be formed from CTE excited states. The results demonstrate that it is possible to transfer the excess energy from the CTE long‐lived excited states to molecular oxygen, thereby producing singlet oxygen. It is also noteworthy that over 99.9% of Staphylococcus aureus cells can be eradicated using fluences comparable to those used in traditional systems under violet light irradiation. Uncovering these photophysical properties of CTE opens the door to a revolutionary breakthrough that can disrupt conventional photodynamic therapy and usher in a new era of CTE‐based photosensitizers.

Combining Multiple Photosensitizer Modules into One Supramolecular System for Synergetic Enhanced Photodynamic Therapy.

Photodynamic therapy (PDT), as an emerging cancer treatment, requires the development of highly desirable photosensitizers (PSs) with integrated functional groups to achieve enhanced therapeutic efficacy. Coordination-driven self-assembly (CDSA) would provide an alternative approach for combining multiple PSs synergistically. Here, we demonstrate a simple yet powerful strategy of combining conventional chromophores (tetraphenylethylene, porphyrin, or Zn-porphyrin) with pyridinium salt PSs together through condensation reactions, followed by CDSA to construct a series of novel metallo-supramolecular PSs (S1-S3). The generation of reactive oxygen species (ROS) is dramatically enhanced by the direct combination of two different PSs, and further reinforced in the subsequent ensembles. Among all the ensembles, S2 with two porphyrin cores shows the highest ROS generation efficiency, specific interactions with lysosome, and strong emission for probing cells. Moreover, the cellular and living experiments confirm that S2 has excellent PDT efficacy, biocompatibility, and biosafety. As such, this study will enable the development of more efficient PSs with potential clinical applications.

Combining Multiple Photosensitizer Modules into One Supramolecular System for Synergetic Enhanced Photodynamic Therapy

AbstractPhotodynamic therapy (PDT), as an emerging cancer treatment, requires the development of highly desirable photosensitizers (PSs) with integrated functional groups to achieve enhanced therapeutic efficacy. Coordination‐driven self‐assembly (CDSA) would provide an alternative approach for combining multiple PSs synergistically. Here, we demonstrate a simple yet powerful strategy of combining conventional chromophores (tetraphenylethylene, porphyrin, or Zn‐porphyrin) with pyridinium salt PSs together through condensation reactions, followed by CDSA to construct a series of novel metallo‐supramolecular PSs (S1–S3). The generation of reactive oxygen species (ROS) is dramatically enhanced by the direct combination of two different PSs, and further reinforced in the subsequent ensembles. Among all the ensembles, S2 with two porphyrin cores shows the highest ROS generation efficiency, specific interactions with lysosome, and strong emission for probing cells. Moreover, the cellular and living experiments confirm that S2 has excellent PDT efficacy, biocompatibility, and biosafety. As such, this study will enable the development of more efficient PSs with potential clinical applications.

Pillar[5]arene-Based Fluorescent Supramolecular Polymers Without Conventional Chromophores.

Fluorescent supramolecular polymers have garnered significant attention due to their successful integration of supramolecular polymers and fluorescence, offering vast potential for applications in sensing, imaging, optoelectronics, and photonics. In this study, we present a novel supramolecular polymer based on P5-OH, derived from mono-substituted pillararene macrocycles. Notably, these formed supramolecular polymeric aggregates exhibit a prominent blue emission, representing a rare instance of fluorescent polymers devoid of conventional chromophores. Furthermore, through the modification of alkyl chain ending groups attached to pillar[5]arenes, slight shifts in the emission peak could be observed. This research expands the scope of functional supramolecular polymeric systems utilizing pillararenes, providing valuable insights for the design of innovative luminescent materials and optical devices.

Hydrogen-Bonding-Driven Nontraditional Photoluminescence of a β-Enamino Ester.

Nontraditional luminogens (NTLs) do not contain any conventional chromophores (large π-conjugated structures), but they do show intrinsic photoluminescence. To achieve photoluminescence from NTLs, it is necessary to increase the extent of through-space conjugation (TSC) and suppress nonradiative decay. Incorporating strong physical interactions such as hydrogen bonding is an effective strategy to achieve this. In this work, we carried out comparative studies on the photoluminescence behaviors of two β-enamino esters with similar chemical structures, namely methyl 3-aminocrotonate (MAC) and methyl (E)-3-(1-pyrrolidinyl)-2-butenoate (MPB). MAC crystal emits blue fluorescence under UV irradiation. The critical cluster concentration of MAC in ethanol solutions was determined by studying the relationship between the photoluminescence intensity (UV-visible absorbance) and concentration. Furthermore, MAC exhibits solvatochromism, and its emission wavelength redshifts as the solvent polarity increases. On the contrary, MPB is non-emissive in both solid state and solutions. Crystal structures and theoretical calculation prove that strong inter- and intramolecular hydrogen bonds lead to the formation of large amounts of TSC of MAC molecules in aggregated states. No hydrogen bonds and thus no effective TSC can be formed between or within MPB molecules, and this is the reason for its non-emissive nature. This work provides a deeper understanding of how hydrogen bonding contributes to the luminescence of NTLs.

Constructing unconventional fluorescent molecules by imidazoline ring and its salt of carboxylic acid and their application

Recently, fluorescent compounds without conventional chromophores have attracted considerable attention. One of the effective strategies for forming unconventional fluorescent compounds is to figure out the unconventional chromophores, then to develop more excellent fluorescent molecules with these structures. The imidazoline ring is one of the unconventional chromophores exhibiting fluorescence because of its planarity and rigidity. The imidazoline ring was used as the raw material for constructing unconventional fluorescent molecules in this paper. When acetic acid was introduced into imidazoline (2-MZ) to form 2-methylimidazoline acetate (2-MZA), the fluorescence significantly increased. Furthermore, by analyzing the change in fluorescence during the crystal and solution states of 2-MZ and 2-MZA, the result demonstrated the intermolecular interaction, that is, clusters of aggregated oxygen atoms influenced molecular fluorescence. Moreover, we explored the applications of 2-MZ and its ionic liquid in metal ion recognition, pH sensing, and fluorescent staining in living HeLa cells.

Clustering emission of cucurbit[n]urils in the solid- and solution-state induced by the outer surface interactions of cucurbit[n]urils

Atypical luminescent compounds that do not contain conventional chromophores emit light due to clustering and have important basic research value and a broad range of potential applications. To date, most atypical luminescent compounds are small molecules or polymers containing groups such as cyano, carbonyl and hydroxyl. In this work, driven by some sporadic and accidental luminescence phenomena observed for cucurbit[n]urils (Q[n]s), the luminescent properties and mechanism of Q[n]s in the solid- and solution-state were systematically studied and the clustering emission of Q[n]s confirmed. Our experiments have revealed that the self-induced outer-surface interactions of Q[n]s (OSIQ) are the most important driving force resulting in the clustering emission of Q[n]s. Substances that can weaken the effect of self-induced OSIQ, such as the presence of various aromatic compounds and anions, may weaken or quench the clustering emission of Q[n]s. This not only reveals the new characteristics and mechanism of the clustering emission of Q[n]s, but also provides new insights on how to utilize the clustering emission of Q[n]s and construct new types of macrocyclic luminescence systems.

Nontraditional Organic/Polymeric Luminogens with Red‐Shifted Fluorescence Emissions

AbstractNontraditional organic/polymeric luminogens, which do not contain any conventional chromophores like large π‐conjugated benzene rings and/or heterocycles, have attracted rapidly growing attention owing to their importance in the fundamental understanding of photoluminescence mechanisms and potential practical applications. However, compared to traditional luminogens, most nontraditional luminogens (NTLs) emit fluorescence in the blue region, and only very limited NTLs with green, yellow, and red emissions have been reported. It is of great scientific and practical importance to develop NTLs with red‐shifted emissions and understand their mechanisms. This review first provides a brief overview of the types of NTLs based on heteroatoms in them, the luminescence mechanism and luminescent characteristics of NTLs, then summarizes recent progress in NTLs with red‐shifted emissions and the main strategies employed, i.e., introducing multiple nonconventional chromophores, introducing intra‐/intermolecular interactions to rigidify clusters, and introducing electron‐giving/withdrawing groups into molecules to lower the gap between the HOMO–LUMO energy levels. This review also provides the perspectives and outlook on future development of NTLs with red‐shifted emissions.

Hyperbranched poly(ester ether)s as an amplified fluorescence sensor for selective and sensitive Fe3+ detection and bioimaging

AbstractChromophore‐free fluorescent hyperbranched polymers have attracted widespread attention as fluorescent sensors. However, achieving highly selective and sensitive detection with such sensors remains a major challenge. Herein, two kinds of hyperbranched poly(ester ether) fluorescent sensors (HBPEE1 and HBPEE2) without conventional chromophores were synthesized to provide a simple and effective method for the selective and sensitive detection of Fe3+. Benefiting from the branched structure and the aggregation of numerous oxygen‐rich groups, both hyperbranched poly(ester ether)s emitted strong blue fluorescence in solution, and compared with HBPEE2, HBPEE1 had a higher absolute quantum yield of 14.3% due to its larger molecular weight and denser structure. HBPEE1 exhibited an amplified fluorescence quenching response and superior selectivity and sensitivity in the recognition of Fe3+ among various metal ions. The fluorescence intensity of HBPEE1 at 450 nm showed a good linearity with the Fe3+ concentration in the range of 5–450 μM with the detection limit of 0.04 μM. Multiple Fe3+ detections with high reversibility have been achieved using EDTA‐2Na, which further confirmed the detection mechanism. In addition, the HBPEE1 sensor possessed low toxicity and can be employed for Fe3+ imaging in living cells, making it a potential candidate for biological research and clinical diagnosis.

Recent advances in oligomers/polymers with unconventional chromophores

Unorthodox chromophores enjoy the advantages of better hydrophilicity, large structural diversity, low-cost and facile synthesis, high chain flexibility and good biocompatibility compared to conventional chromophores, leading to many applications.

Fluorescence resonance energy transfer fluorescent polymer dots without conventional chromophores: Synthesis, emission mechanism and applications as Cu2+ probe and fluorescent ink

Recently, the non-aromatic fluorescent materials without benzene rings in their structures have aroused widespread interest. In this work, a citric acid functionalized polyethyleneimine oligomer, CA-PEI, was synthesized through acyl chloride method. In CA-PEI, the polyethyleneimine was bonded to citric acid molecule with a molar ratio of 1:1 through an amide bond, which was confirmed by NMR, FTIR, GPC and XPS. The results indicated that CA-PEI had dual excitation and dual emission properties, and the two emission centers were derived from n–σ* and n–π* transition, respectively. CA-PEI was used to synthesize the light-emitting polymer dots N-PDs through a hydrothermal reaction. Interestingly, compared with CA-PEI, N-PDs had dual excitation and single emission properties, and its Stoke's shift was as high as 193 nm. This can be attributed to the compact structure of N-PDs, which promoted the fluorescence resonance energy transfer (FRET) process. Importantly, N-PDs can serve as excellent probes in response to Cu2+, with a detection limit as low as 2.5 nmol L−1. The response mechanism involves the formation of a copper amine complex between Cu2+ and the PEI part of N-PDs, which then quenches the fluorescence emission of N-PDs through the fluorescence inner-filter effect. N-PDs as well were applied as an encryptable fluorescent ink.

Intrinsic emission and tunable phosphorescence of perfluorosulfonate ionomers with evolved ionic clusters

Intrinsic emission from unorthodox luminogens without traditional conjugated building blocks is drawing increasing attention. However, the emission mechanism is still controversial. Herein, we demonstrate the intriguing emission from perfluorosulfonate ionomers (PFSIs), which can be explained by the clustering triggered emission (CTE) mechanism. Despite being free of any conventional chromophores, PFSIs exhibit bright emission and multi-color phosphorescence (77 K) in concentrated solutions, powders and membranes with obvious aggregation-induced emission (AIE) characteristics. Clustered sulfonic acids are responsible for the light emission, and their connection and evolution are deeply explored via X-ray diffraction (XRD) and small angel X-ray scattering (SAXS), in which the electron overlap determined by the clustered status results in the extended conjugation and simultaneously rigidified conformations. These results demonstrate that it is feasible to use fluorescence analysis to explore the ionic cluster structure and evolution of PFSI, and it can be applied in the pure organic luminescent field as well.

Facile synthesis of intrinsically photoluminescent hyperbranched polyethylenimine and its specific detection for copper ion

Recently, intrinsically photoluminescent polymers (IPPs) without any conventional chromophores have aroused increasing attention and been extensively investigated. Simple and green synthetic method is definitely preferred for the production of such polymer. In this work, intrinsically photoluminescent hyperbranched polyethylenimine (IP-HPEI) was facilely prepared through directly heating the viscous neat HPEI under air. Since none of solvents, organic modifiers, purification and pressure vessel is required, it can be claimed that this is a simpler and greener method to prepare IPPs in comparison with other reports. Moreover, this simple technique favors the large scale preparation of IP-HPEIs. 1H NMR, FTIR, XPS, TGA and fluorescence characterizations supported that air oxidation led to the generation of luminogens in HPEIs and tertiary amine oxides were the real luminogens, not the oximes reported by others. At pH 6, IP-HPEI could be used as fluorescent sensor to selectively detect Cu2+ ions with an LOD value of 0.72 μM.

An AB2‐Type Supramolecular Hyperbranched Polymer Based on Pillar[5]arene Host–Guest Recognition: Construction and Its pH‐Responsiveness

Supramolecular hyperbranched polymers not only possess the polymeric properties of hyperbranched polymers but also obtain additional stimuli-responsiveness due to the dynamic properties of non-covalent interactions. Herein, a novel supramolecular hyperbranched polymer constructed by an AB2 -type copillar[5]arene is reported. NMR spectroscopy, scanning electron microscopy, and viscosity experiments are utilized to characterize the self-aggregate process of the AB2 monomers. Interestingly, the supramolecular hyperbranched polymer exhibits pH-responsiveness. After protonation of the AB2 monomers by trifluoroacetic acid, the binding ability among the monomers becomes stronger, leading to the formation of supramolecular hyperbranched polymers with viscosity change. Additionally, although no conventional chromophores are doped, the supramolecular hyperbranched polymer shows a blue emission under irradiation. The fluorescence can be quenched upon addition of trifluoroacetic acid. This study enriches the field of supramolecular polymers with new building blocks and architectures and provided a new effective method for the fabrication of smart polymer materials with stimuli-responsiveness and special functions.

Inkjet-Printed Photoluminescent Patterns of Aggregation-Induced-Emission Chromophores on Surface-Anchored Metal-Organic Frameworks.

Organic chromophores that exhibit aggregation-induced emission (AIE) are of interest for applications in displays, lighting, and sensing, because they can maintain efficient emission at high molecular concentrations in the solid state. Such advantages over conventional chromophores could allow thinner conversion layers of AIE chromophores to be realized, with benefits in terms of the efficiency of the optical outcoupling, thermal management, and response times. However, it is difficult to create large-area optical quality thin films of efficiently performing AIE chromophores. Here, we demonstrate that this can be achieved by using a surface-anchored metal-organic framework (SURMOF) thin film coating as a host substrate, into which the tetraphenylethylene (TPE)-based AIE chromophore can be printed. We demonstrate that the SURMOF constrains the AIE-chromophore molecular conformation, affording efficient performance even at low loading densities in the SURMOF. As the loading density of the AIE chromophore in the SURMOF is increased, its absorption and emission spectra are tuned due to increased interaction between AIE molecules, but the high photoluminescent quantum yield (PLQY = 50% for this AIE chromophore) is maintained. Lastly, we demonstrate that patterns of the AIE chromophore with 70 μm feature sizes can be easily created by inkjet printing onto the SURMOF substrate. These results foreshadow novel possibilities for the creation of patterned phosphor thin films utilizing AIE chromophores for display or lighting applications.

Instantaneous, Simple, and Reversible Revealing of Invisible Patterns Encrypted in Robust Hollow Sphere Colloidal Photonic Crystals.

The colors of photonic crystals are based on their periodic crystalline structure. They show clear advantages over conventional chromophores for many applications, mainly due to their anti-photobleaching and responsiveness to stimuli. More specifically, combining colloidal photonic crystals and invisible patterns is important in steganography and watermarking for anticounterfeiting applications. Here a convenient way to imprint robust invisible patterns in colloidal crystals of hollow silica spheres is presented. While these patterns remain invisible under static environmental humidity, even up to near 100% relative humidity, they are unveiled immediately (≈100 ms) and fully reversibly by dynamic humid flow, e.g., human breath. They reveal themselves due to the extreme wettability of the patterned (etched) regions, as confirmed by contact angle measurements. The liquid surface tension threshold to induce wetting (revealing the imprinted invisible images) is evaluated by thermodynamic predictions and subsequently verified by exposure to various vapors with different surface tension. The color of the patterned regions is furthermore independently tuned by vapors with different refractive indices. Such a system can play a key role in applications such as anticounterfeiting, identification, and vapor sensing.

Multiple Stimuli-Responsive Fluorescent Sensor from Citric Acid and 1-(2-Aminoethyl)piperazine.

Multiresponsive fluorescent supramolecular materials are quite interesting, for they combine the multiresponsiveness of supramolecules and the high sensitivity of fluorescent materials. Different from the multiresponsive supramolecular materials based on host-guest interactions, in this report, a supramolecular ionic network was fabricated by 1-(2-aminoethyl)piperazine and citric acids via ionic interactions. Despite the fact that there are no conventional chromophores, the obtained supramolecular ionic material can emit strong fluorescence. Most interestingly, the thin film of this supramolecular ionic material can change its fluorescent intensity in response to four external stimuli, including humidity, triethylamine, acetic acid, and temperature. Beneficial to the supramolecular ionic structure, this multiresponsive fluorescent sensor is self-healable. It is found that a new route has been opened to prepare the multiresponsive fluorescent sensors.

Ice Squeezing Induced Multicolor Fluorescence Emissions from Polyacrylamide Cryogels.

Being short of conventional chromophores, polyacrylamide is generally not regarded as a fluorescent material. Exactly the polymerization of dilute solutions of acrylamide and N,N'-methylenebisacrylamide led to thick liquids at 60°C, showing no fluorescence. Things changed when the phase transition of water was involved. The squeezing effect of ice crystals not only created polymeric solids (cryogels) at - 20°C, but also endowed them unexpected fluorescence emissions. The macroporous cryogels are mainly blue fluorescent polymers. However yellow and red fluorescence were also achieved by changing the ingredient ratios. A series of instrumental detections revealed that the multicolor fluorescence were based on exquisite amido stacking induced from ice squeezing. If people make good use of the squeezing effect of the heaven-sent molecule to manipulate the interactions of monomer functionalities, cryogenic polymerization can be a promising method to produce diverse polymeric materials.

Unprecedented strong blue photoluminescence from hyperbranched polycarbonate: From its fluorescence mechanism to applications

ABSTRACTFluorescent polymers without π‐aromatic structure have been a hot spot in recent years. Polycarbonate has been applied in industry for many years; however, the fluorescent behavior of the polycarbonate has not been reported yet. Therefore, a kind of hyperbranched polycarbonate (HBPC) has been synthesized under solvent and catalyst‐free condition. Unexpectedly, the novel HBPC containing no conventional chromophores exhibits unimagined bright blue fluorescence under the irradiation of 334 nm UV light. The intensity of the HBPC fluorescence is rising in step with its concentration going up, showing an aggregation‐induced enhanced emission (AIEE). It is more interestingly that the fluorescence of HBPC could be affected by pH and metal ions. Specifically, the fluorescence of HBPC is extraordinarily sensitive to the Fe3+. TEM micrographs show that the HBPC self‐assemble to clustering in water. Rudimentary investigation illustrates that the formation of cluster accounts for the unexpected fluorescence in the HBPC. This phenomenon is typical of Clustering‐Triggered emission (CTE). This study exhibits a novel route for the design of CTE fluorescent polymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3690–3696

ChemInform Abstract: Crystallization‐Induced Phosphorescence of Pure Organic Luminogens

AbstractReview: [30 refs.