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The development of aggregation-induced emission (AIE)-exhibiting compounds heavily relies on our evolving comprehension of their behavior at interfaces, an understanding that still remains notably limited. In this study, we explored the preparation of two-dimensional (2D) sensing films from 2,3-diphenylquinoxaline-based diazapolyoxa- and polyazamacrocycles displaying AIE via the Langmuir-Blodgett (LB) technique. This systematic investigation highlights the key role of the heteroatom-containing tether of 2,3-diphenylquinoxalines in the successful fabrication of Langmuir layers at the air-water interface and the transfer of AIE-emitting supramolecular aggregates onto solid supports. Using both diazapolyoxa- and polyazamacrocycles, we prepared AIE-exhibiting monolayer films containing emissive supramolecular aggregates on silica, mica, and quartz glass and characterized them using ultraviolet-visible (UV-vis) and photoluminescence (PL) spectroscopies, atomic force microscopy (AFM) imaging, and fluorescence microscopy. We also obtained multilayer AIE-emitting films through the LB technique, albeit with increased complexity. Remarkably, by employing the smallest macrocycle N2C3Q, we successfully prepared LB films suitable for the visual detection of acidic vapors. This sensing material, which contains a much lesser amount of organic dye compared with traditional drop-cast films, can be regenerated and utilized for real-life sample analysis, such as monitoring the presence of ammonia in the air and the freshness of meat.
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This work investigates the electron-donating capabilities of two 10-π electron nitrogen bridgehead bicyclic [5,6]-fused ring systems, imidazo[1,2-a]pyridine and imidazo[1,5-a]pyridine rings. Eight compounds with varying positions of electron-withdrawing moieties (TCF or DCI) coupled to the imidazopyridine ring were synthesized and studied. DCI-containing compounds (Ib-IVb) exhibited a purely dipolar nature with broad absorption bands, weak fluorescence, large Stokes shifts, and strong solvatochromism. In contrast, TCF-containing compounds (Ia-IVa) demonstrated diverse properties. Imidazo[1,2-a]pyridine derivatives Ia and IIa were purely dipolar, while imidazo[1,5-a]pyridine derivatives IIIa and IVa displayed a cyanine-like character with intense absorption and higher quantum yields of emission. The observed gradual red shift in optical properties with changing electron-donor groups (IIb < Ib < IIIb < IVb) and (IIa < Ia < IIIa < IVa) underscores the stronger electron-donor character of imidazo[1,5-a]pyridine compared to that of imidazo[1,2-a]pyridine. Furthermore, crystalline powders of imidazo[1,2-a]pyridine derivatives exhibited fluorescence despite minimal emission in solution. Two compounds (Ib and IVa) were successfully formulated into nanoparticles for potential in vivo imaging applications in zebrafish embryos.
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The development of luminescent molecular materials has advanced rapidly in recent decades, primarily driven by the synthesis of novel emissive compounds and a deeper understanding of excited-state mechanisms. Herein, we report a streamlined synthetic approach to light-emitting diazapolyoxa- and polyazamacrocycles N2CnOxQ and NyCnQ (n = 3-10; x = 2, 3; y = 2-5), incorporating a 2,3-diphenylquinoxaline residue (DPQ). This synthetic strategy based on macrocyclization through Pd-catalyzed amination reaction yields the target macrocycles in good or high yields (46-92%), enabling precise control over their structural parameters. A key role of the PhPF-tBu ligand belonging to the JosiPhos series in this macrocyclization was elucidated through DFT computation. This macrocyclization reaction eliminates the need for complex protecting-deprotecting procedures of secondary amine groups, offering a convenient and scalable method for the preparation of target compounds. Moreover, it boasts a potentially broad substrate scope, making it promising for structure-properties studies within photophysics, sensor development, and material synthesis. Photophysical properties of representative macrocycles were investigated, employing spectroscopic techniques and DFT computation. It was demonstrated that DPQ-containing macrocycles display aggregation-induced emission in a DCM-hexane solvent mixture despite the presence of flexible tethers within their structures. Single-crystal X-ray diffraction analysis of a representative compound N2C8O3Q allowed us to gain deeper insight into its molecular structure and AIE behaviour. The emissive aggregates of the N2C10O3Q macrocycle were immobilized on filter paper yielding AIE-exhibiting test strips for measuring acidity in vapors and in aqueous media.
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This study presents the synthesis, the spectroscopic and electrochemical properties of new bis- and tetra-substituted azaboron-dipyrromethene (aza-BODIPY) dyes substituted by different electron donating groups connected to the aza-BODIPY core through a thiophene unit. In line with theoretical calculations, experimental measurements point out the positive impact of the thiophene group that behave as a secondary donor group leading to an enhancement of the intramolecular charge transfer process in comparison to previously reported aza-BODIPY dyes. This heterocycle has also been found to tune the oxidative potential and to stabilize the electro-generated species.
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Organic molecules have been intensively studied during the last few decades because of their photonics and biological applications. In this material class, the fluorene molecules present outstanding optical features, for example, high values of two-photon absorption (2PA) cross-sections, visible transparency, and high fluorescence quantum yield. Also, it is possible to improve the nonlinear optical response by modifying the fluorene molecular structure. In this context, herein, we have synthesized V and Y-shaped branching oligofluorenes containing two and three fluorene moieties in each branch. Such a molecular strategy may exponentially enhance the nonlinear optical response due to the coherent coupling among the molecular arms. Thus, we combined the use of femtosecond Z-scan spectroscopy and white light transient absorption spectroscopy (TAS) to understand the molecular structure and 2PA property relationship of branching oligofluorenes. The results show that there is a universal relationship between the 2PA cross-section and the effective π-electron number (Neff) given by σ2PA(GM) = (079 ± 0.03)Neff2, which is independent of the molecular shape (linear, V or Y-shaped). Therefore, the intramolecular charge transfer responsible for the cooperative effect among the branches does not occur. This statement is corroborated by the results of the femtosecond TAS technique.
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Correction for 'Light-induced in situ chemical activation of a fluorescent probe for monitoring intracellular G-quadruplex structures' by Marco Deiana et al., Nanoscale, 2021, 13, 13795-13808, https://doi.org/10.1039/D1NR02855C.
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The (Z) and (E)-isomers of an extended tetraphenylethylene-based chromophore with optimized two-photon-induced luminescence properties are separated and functionalized with water-solubilizing pendant polymer groups, promoting their self-assembly in physiological media in the form of small, colloidal stable organic nanoparticles. The two resulting fluorescent suspensions are then evaluated as potential two-photon luminescent contrast agents for intravital epifluorescence and two-photon fluorescence microscopy. Comparisons with previously reported works involving similar fluorophores devoid of polymer side chains illustrate the benefits of later functionalization regarding the control of the self-assembly of the nano-objects and ultimately their biocompatibility toward the imaged organism.
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Substâncias Luminescentes , Nanopartículas , Corantes Fluorescentes/química , Luminescência , Microscopia , Nanopartículas/química , PolímerosRESUMO
The fast relaxation processes in the excited electronic states of functionalized aza-boron-dipyrromethene (aza-BODIPY) derivatives (1-4) were investigated in liquid media at room temperature, including the linear photophysical, photochemical, and nonlinear optical (NLO) properties. Optical gain was revealed for nonfluorescent derivatives 3 and 4 in the near infrared (NIR) spectral range under femtosecond excitation. The values of two-photon absorption (2PA) and excited-state absorption (ESA) cross-sections were obtained for 1-4 in dichloromethane using femtosecond Z-scans, and the role of bromine substituents in the molecular structures of 2 and 4 is discussed. The nature of the excited states involved in electronic transitions of these dyes was investigated using quantum-chemical TD-DFT calculations, and the obtained spectral parameters are in reasonable agreement with the experimental data. Significant 2PA (maxima cross-sections â¼2000â GM), and large ESA cross-sections â¼10-20 â m2 of these new aza-BODIPY derivatives 1-4 along with their measured high photostability reveal their potential for photonic applications in general and optical limiting in particular.
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Boro , Corantes Fluorescentes , Compostos de Boro , Corantes Fluorescentes/química , Porfobilinogênio/análogos & derivados , Análise EspectralRESUMO
Aim: To propose a new multimodal imaging agent targeting amyloid-ß (Aß) plaques in Alzheimer's disease. Materials & methods: A new generation of hybrid contrast agents, based on gadolinium fluoride nanoparticles grafted with a pentameric luminescent-conjugated polythiophene, was designed, extensively characterized and evaluated in animal models of Alzheimer's disease through MRI, two-photon microscopy and synchrotron x-ray phase-contrast imaging. Results & conclusion: Two different grafting densities of luminescent-conjugated polythiophene were achieved while preserving colloidal stability and fluorescent properties, and without affecting biodistribution. In vivo brain uptake was dependent on the blood-brain barrier status. Nevertheless, multimodal imaging showed successful Aß targeting in both transgenic mice and Aß fibril-injected rats.
The design and study of a new contrast agent targeting amyloid-ß (Aß) plaques in Alzheimer's disease (AD) is proposed. Aß plaques are the earliest pathological sign of AD, silently appearing in the brain decades before the symptoms of the disease are manifested. While current detection of Aß plaques is based on nuclear medicine (a technique using a radioactive agent), a different kind of contrast agent is here evaluated in animal models of AD. The contrast agent consists of a nanoparticle made of gadolinium and fluorine ions (core), and decorated with a molecule previously shown to bind to Aß plaques (grafting). The core is detectable with MRI and x-ray imaging, while the grafting molecule is detectable with fluorescence imaging, thus allowing different imaging methods to be combined to study the pathology. In this work, the structure, stability and properties of the contrast agent have been verified in vitro (in tubes and on brain sections). Then the ability of the contrast agent to bind to Aß plaques and provide a detectable signal in MRI, x-ray or fluorescence imaging has been demonstrated in vivo (in rodent models of AD). This interdisciplinary research establishes the proof of concept that this new class of versatile agent contrast can be used to target pathological processes in the brain.
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Doença de Alzheimer , Nanopartículas , Camundongos , Ratos , Animais , Doença de Alzheimer/diagnóstico por imagem , Distribuição Tecidual , Peptídeos beta-Amiloides/metabolismo , Camundongos Transgênicos , Encéfalo/diagnóstico por imagem , Encéfalo/metabolismo , Imagem Multimodal , Modelos Animais de DoençasRESUMO
Fluorene-based molecules exhibit significant nonlinear optical responses and multiphoton absorption in the visible region, which, combined with the high fluorescence quantum yield in organic solvents, could make this class of materials potentially engaging in diverse photonics applications. Thus, herein, we have determined the two-photon absorption (2PA) of oligofluorenes containing three, five, and seven repetitive units by employing the wavelength-tunable femtosecond Z-scan technique. Our outcomes have shown that the 2PA cross-section in oligofluorenes presents an enhanced value of around 18 GM per Neff, in which Neff is the effective number of π-electrons, for the pure 2PA allowed transition (11Ag-like â 21Ag-like). Furthermore, a weak 2PA transition was observed in the same spectral region strongly allowed by one-photon absorption (11Ag-like â 11Bu-like). This last result suggests a molecular symmetry perturbation, probably induced by the molecular disorder triggered by the increase of moieties in the oligofluorene structure. We have calculated the permanent dipole moment difference related to the lowest-energy transition using the Lippert-Matagaformalism and the 2PA sum-over-states approach to confirm this assumption. Moreover, we have estimated the fundamental limits for the 2PA cross-section in oligofluorenes.
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We elucidate the crucial role of the cetyl trimethylammonium bromide (CTAB) surfactant in the anisotropic growth mechanism of gold nano-bipyramids, nano-objects with remarkable optical properties and high tunability. Atomistic molecular dynamics simulations predict different surface coverages of the CTAB (positively charged) heads and their (bromide) counterions as function of the gold exposed surfaces. High concentration of CTAB surfactant promotes formation of gold nanograins in solution that work as precursors for the smooth anisotropic growth of more elongated nano-bipyramidal objects. Nanobipyramids feature higher index facets with respect to nanorods, allowing higher CTAB coverages that stabilize their formation and leading to narrower inter-micelles channels that smooth down their anisotropic growth. Absorption spectroscopy and scanning electron microscopy confirmed the formation of nanograins and demonstrated the importance of surfactant concentration on driving the growth towards nano-bipyramids rather than nanorods. The outcome explains the formation of the monodisperse bipyramidal nano-objects, the origin of their controlled shapes and sizes along with their remarkable stability.
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Two-photon lithography is a potential route to produce high-resolution 3D ceramics. However, the large shrinkage due to the elimination of an important organic counterpart of the printed material during debinding/sintering remains a lock to further development of this technology. To limit this phenomenon, an original approach based on a composite resin incorporating 45 wt% ultrasmall (5 nm) zirconia stabilized nanoparticles into the zirconium acrylate precursor is proposed to process 3D zirconia microlattices and nanostructured optical surfaces. Interestingly, the nanoparticles are used both as seeds allowing control of the crystallographic phase formed during the calcination process and as structural stabilizing agent preventing important shrinkage of the printed ceramic. After 3D photolithography and pyrolysis, the weight and volume loss of the microstructures are drastically reduced as compared to similar systems processed with the reference resin without nanoparticles, and stable 3D microstructures of cubic zirconia are obtained with high spatial resolution. In the case of a patterned surface, the refractive index of 2.1 leads to a diffraction efficiency large enough to obtain microfocusing with linewidths of 0.1 µm, and the demonstration of a microlens array with a period as small as 0.8 µm.
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Nanopartículas , Nanoestruturas , Cerâmica , Cristalização , Teste de Materiais , Impressão Tridimensional , Pirólise , Propriedades de Superfície , ZircônioRESUMO
Light-activated functional materials capable of remote control over duplex and G-quadruplex (G4) nucleic acids formation at the cellular level are still very rare. Herein, we report on the photoinduced macrocyclisation of a helicenoid quinoline derivative of binaphthol that selectively provides easy access to an unprecedented class of extended heteroaromatic structures with remarkable photophysical and DNA/RNA binding properties. Thus, while the native bisquinoline precursor shows no DNA binding activity, the new in situ photochemically generated probe features high association constants to DNA and RNA G4s. The latter inhibits DNA synthesis by selectively stabilizing G4 structures associated with oncogenic promoters and telomere repeat units. Finally, the light sensitive compound is capable of in cellulo photoconversion, localizes primarily in the G4-rich sites of cancer cells, competes with a well-known G4 binder and shows a clear nuclear co-localization with the quadruplex specific antibody BG4. This work provides a benchmark for the future design and development of a brand-new generation of light-activated target-selective G4-binders.
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Corantes Fluorescentes , Quadruplex G , DNA , Ligantes , TelômeroRESUMO
Singlet-triplet interconversions (intersystem crossing, ISC) in organic molecules are at the basis of many important processes in cutting-edge photonic applications (organic light-emitting devices, photodynamic therapy, etc.). Selection rules for these transitions are mainly governed by the spin-orbit coupling (SOC) phenomenon. Although the SOC relies on complex relativistic phenomena, theoreticians have, with time, developed increasingly sophisticated and efficient approaches to gain access to a satisfactory evaluation of its magnitude. However, recent works have highlighted the remarkable and somehow unexpected efficiency of dimers of small conjugated molecules in terms of ISC quantum yields, whose origin has not been completely investigated. In this work, we bring a coupled experimental and theoretical analysis of the origin of the unusually large ISC efficiency on a series of such dimers that differ by their nature (covalent or supramolecular). We show that considering the dynamical nature of the SOC, and especially its dependence on angular orientations between the dimer subunits sometimes overlooked in the literature, it is necessary to rationalize some counterintuitive experimental observations. This combined experimental and theoretical work paves the way for new molecular engineering rules for SOC control.
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Fotoquimioterapia , DimerizaçãoRESUMO
This work provides an overview of the recent advances in the field of two-photon absorbing chromophores active in the short-wavelength infrared (SWIR) spectral range. Herein the common strategies and main structure-property relationships that lead to near-infrared (NIR) electronic absorption of chromophores are described. A complete review of the molecules that feature two-photon absorption (2PA) beyond 1100 nm is presented for the purpose of further use in optical power limiting applications in the SWIR band. Recent progress in the development of optical power limiting in this particular spectral region is reported with emphasis on the use of the two-photon induced excited state absorption (ESA) process as an optical power limiting enhancer.
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Although tetraphenylethylene (TPE) and its derivatives have been the most commonly used building blocks in the construction of molecules with aggregation-induced emission (AIE) properties, no absolute consensus exists regarding the mechanisms at the origin of the phenomenon. Restriction of intramolecular rotations (RIR) of peripheral phenyls has historically been a dominant paradigm, which has served as a valuable guideline in the molecular engineering of AIEgens. Yet, an increasing number of recent works have established that photoisomerization or photocyclization may actively participate in the nonradiative dissipation of the excitation energy. In this paper, the first experimental evaluation of the quantum efficiencies of these different processes is reported, and photoisomerization is shown to be by far the dominant photophysical pathway in solution, accounting for virtually all nonradiative decay of the molecule's excited state in degassed solution.
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Neuroinflammation is a process common to several brain pathologies. Despites its medical relevance, it still remains poorly understood; there is therefore a need to develop new in vivo preclinical imaging strategies to monitor inflammatory processes longitudinally. We here present the development of a hybrid imaging nanoprobe named NP3, that was specifically designed to get internalized by phagocytic cells and imaged in vivo with MRI and bi-photon microscopy. NP3 is composed of a 16 nm core of gadolinium fluoride (GdF3), coated with bisphosphonate polyethylene glycol (PEG) and functionalized with a Lemke-type fluorophore. It has a hydrodynamic diameter of 28 ± 8 nm and a zeta potential of -42 ± 6 mV. The MR relaxivity ratio at 7 T is r1/r2 = 20; therefore, NP3 is well suited as a T2/T2* contrast agent. In vitro cytotoxicity assessments performed on four human cell lines revealed no toxic effects of NP3. In addition, NP3 is internalized by macrophages in vitro without inducing inflammation or cytotoxicity. In vivo, uptake of NP3 has been observed in the spleen and the liver. NP3 has a prolonged vascular remanence, which is an advantage for macrophage uptake in vivo. The proof-of-concept that NP3 may be used as a contrast agent targeting phagocytic cells is provided in an animal model of ischemic stroke in transgenic CX3CR1-GFP/+ mice using three complementary imaging modalities: MRI, intravital two-photon microscopy and phase contrast imaging with synchrotron X-rays. In summary, NP3 is a promising preclinical tool for the multiscale and multimodal investigation of neuroinflammation.
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Meios de Contraste , Gadolínio , Animais , Imageamento por Ressonância Magnética , Imagem Multimodal , PolietilenoglicóisRESUMO
Long-lived room temperature phosphorescence from organic molecular crystals attracts great attention. Persistent luminescence depends on the electronic properties of the molecular components, mainly π-conjugated donor-acceptor (D-A) chromophores, and their molecular packing. Here, a strategy is developed by designing two isomeric molecular phosphors incorporating and combining a bridge for σ-conjugation between the D and A units and a structure-directing unit for H-bond-directed supramolecular self-assembly. Calculations highlight the critical role played by the two degrees of freedom of the σ-conjugated bridge on the chromophore optical properties. The molecular crystals exhibit RTP quantum yields up to 20 % and lifetimes up to 520â ms. The crystal structures of the efficient phosphorescent materials establish the existence of an unprecedented well-organization of the emitters into 2D rectangular columnar-like supramolecular structure stabilized by intermolecular H-bonding.
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Aza-boron dipyrromethenes (aza-BODIPYs) presenting a benzothiadiazole substitution on upper positions are described. The strong electron-withdrawing effect of the benzothiadiazole moiety permits enhancement of the accepting strength and improves the delocalization of the aza-BODIPY core to attain a significant degree of electronic communication between the lower donating groups and the upper accepting groups. The nature of the intramolecular charge transfer is studied both experimentally and theoretically. Linear spectroscopy highlighted the strongly redshifted absorption and emission of the synthesized molecules with recorded fluorescence spectra over 1000â nm. Nonlinear optical properties were also investigated. Strong enhancement of the two-photon absorption of the substituted dyes compared with the unsubstituted one (up to 4520â GM at 1300â nm) results in an approximately 15-20 % improvement of the optical power limiting performances. These dyes are therefore a good starting point for further improvement of optical power limiting in the short-wave IR range.
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This paper aims at designing chromophores with efficient aggregation-induced emission (AIE) properties for two-photon fluorescence microscopy (2PFM), which is one of the best-suited types of microscopy for the imaging of living organisms or thick biological tissues. Tetraphenylethylene (TPE) derivatives are common building blocks in the design of chromophores with efficient AIE properties. Therefore, in this study, extended TPE AIEgens specifically optimized for two-photon absorption (2PA) are synthesized and the resulting (E/Z) isomers are separated using chromatography on chiral supports. Comparative characterization of the AIE properties is performed on the pure (Z) and (E) isomers and the mixture, allowing us, in combination with powder X-ray diffraction and solid-state NMR, to document a profound impact of crystallinity on solid-state fluorescence properties. In particular, we show that stereopure AIEgens form aggregates of superior crystallinity, which in turn exhibit a higher fluorescence quantum yield compared to diastereoisomers mixtures. Preparation of stereopure organic nanoparticles affords very bright fluorescent contrast agents, which are then used for cellular and intravital two-photon microscopy on human breast cancer cells and on zebrafish embryos.