Surface functionalized perovskite nanocrystals: a design strategy for organelle-specific fluorescence lifetime multiplexing

Fluorescent molecules or materials with high photoluminescence quantum yields and stability towards photobleaching are ideally suited for multiplex imaging. Despite complying with such properties, perovskite nanocrystals (Pv-NCs) are rarely used for bioimaging owing to their toxicity and limited stability in aqueous media and towards human physiology. We aim to address these deficiencies by designing core–shell structures with Pv-NCs as the core and surface-engineered silica as the shell (SiO2@Pv-NCs) since silica is recognized as a biologically benign carrier material and is known to be excreted through urine. The post-grafting methodology is adopted for developing [SiO2@Pv-NCs]tpm and [SiO2@Pv-NCs]tsy (tpm: triphenylphosphonium ion, tsy: tosylsulfonamide) for specific imaging of mitochondria and endoplasmic reticulum (ER) of the live HeLa cell, respectively

Mechanisms of Photoredox Catalysts: The Role of Optical Spectroscopy

The photoinduced organic transformation has stimulated the organic chemistry community to develop light-driven renewed reaction methodologies, which in many cases are complementary to standard thermal catalysis. This revitalization of photoinduced transformations is in part due to the straightforward access to powerful photosensitizers. Among those, Ru(II) and Ir(III) polypyridyl complexes have been extensively utilized as prototypical photoredox catalyst. Despite the flourish of new organic reactivity, studies of photocatalytic cycles are still scarce. The current mechanistic proposal mostly relies on luminescence quenching studies, empirical redox potentials, and bond-dissociation energy values, which provide a partial picture of the real catalytic processes occurring. Besides, quantum efficiency and overall energy efficiency of photoredox organic transformation are not usually considered merit yet. On the other hand, during the last decades, the photochemistry community has studied the energy and electron transfer mechanism of transition metal complexes from the ground and the excited-state extensively, without fully understanding the catalytic photoredox cycles probably due to its complexity. Those studies are needed to develop new photoredox organic transformations further and make them more sustainable and energy-efficient. We outline an overview of selected basic concepts of photophysics and photochemistry encountered in the photocatalytic cycles in this context. Selected examples of studies are detailed in the review to illustrate how steady-state and time-resolved optical spectroscopy can be employed to elucidate catalytic intermediates and photocatalytic mechanisms. As such, this review aims to motivate mechanistic studies on photoredox catalysis and serve as a guide to perform them to develop more sustainable and energy-efficient chemical transformations

Photoresponsive polymer nanocarriers with multifunctional cargo

Nanoparticles with photoresponsive character can be assembled from amphiphilic macromolecular components and hydrophobic chromophores. In aqueous solutions, the hydrophobic domains of these species associate to produce spontaneously nanosized hosts with multiple photoresponsive guests in their interior. The modularity of this supramolecular approach to nanostructured assemblies permits the co-encapsulation of distinct subsets of guests within the very same host. In turn, the entrapped guests can be designed to interact upon light excitation and exchange electrons, energy or protons. Such photoinduced processes permit the engineering of properties into these supramolecular constructs that would otherwise be impossible to replicate with the separate components. Alternatively, noninteracting guests with distinct functions can be entrapped in these supramolecular containers to ensure multifunctional character. In fact, biocompatible luminescent probes with unique photochemical and photophysical signatures have already emerged from these fascinating investigations. Thus, polymer nanocarriers can become invaluable supramolecular scaffolds for the realization of multifunctional and photoresponsive tools for a diversity of biomedical applications

Crystal‐to‐Crystal Synthesis of Photocatalytic Metal–Organic Frameworks for Visible‐Light Reductive Coupling and Mechanistic Investigations

Postmodification of reticular materials with well‐defined catalysts is an appealing approach to produce new catalytic functional materials with improved stability and recyclability, but also to study catalysis in confined spaces. A promising strategy to this end is the postfunctionalization of crystalline and robust metal–organic frameworks (MOFs) to exploit the potential of crystal‐to‐crystal transformations for further characterization of the catalysts. In this regard, two new photocatalytic materials, MOF‐520‐PC1 and MOF‐520‐PC2, are straightforwardly obtained by the postfunctionalization of MOF‐520 with perylene‐3‐carboxylic acid (PC1) and perylene‐3‐butyric acid (PC2). The single crystal‐to‐crystal transformation yielded the X‐ray diffraction structure of catalytic MOF‐520‐PC2. The well‐defined disposition of the perylenes inside the MOF served as suitable model systems to gain insights into the photophysical properties and mechanism by combining steady‐state, time‐resolved, and transient absorption spectroscopy. The resulting materials are active organophotoredox catalysts in the reductive dimerization of aromatic aldehydes, benzophenones, and imines under mild reaction conditions. Moreover, MOF‐520‐PC2 can be applied for synthesizing gram‐scale quantities of products in continuous‐flow conditions under steady‐state light irradiation. This work provides an alternative approach for the construction of well‐defined, metal‐free, MOF‐based catalysts.We thank the ICIQ Foundation, the European Research Foundation for project ERC‐2014‐CoG 648304 (J.L.‐F.), MINECO (CTQ2016‐80038‐R; J.L.‐F.), and AGAUR 2017‐SGR‐1647 (J.L.‐F.) for funding. S.S.M. and N.K. are grateful to Marie‐Curie COFUND and JyC for postdoctoral scholarships, respectively.Peer reviewe

Understanding light-driven H2 evolution through the electronic tuning of aminopyridine cobalt complexes

A new family of cobalt complexes with the general formula [CoII(OTf)2(Y,XPyMetacn)] (1R, Y,XPyMetacn = 1-[(4-X-3,5-Y-2-pyridyl)methyl]-4,7-dimethyl-1,4,7-triazacyclononane, (X = CN (1CN), CO2Et (1CO2Et), Cl (1Cl), H (1H), NMe2 (1NMe2)) where (Y = H, and X = OMe when Y = Me (1DMM)) is reported. We found that the electronic tuning of the Y,XPyMetacn ligand not only has an impact on the electronic and structural properties of the metal center, but also allows for a systematic water-reduction-catalytic control. In particular, the increase of the electron-withdrawing character of the pyridine moiety promotes a 20-fold enhancement of the catalytic outcome. By UV-Vis spectroscopy, luminescence quenching studies and Transient Absorption Spectroscopy (TAS), we have studied the direct reaction of the photogenerated [IrIII(ppy)2(bpy˙−)] (PSIr) species to form the elusive CoI intermediates. In particular, our attention is focused on the effect of the ligand architecture in this elemental step of the catalytic mechanism. Finally, kinetic isotopic experiments together with DFT calculations provide complementary information about the rate-determining step of the catalytic cycle

Ultrasensitive Reagent for Ratiometric Detection and Detoxification of iAsIII in Water and Mitochondria

Toxicity induced by inorganic arsenic as AsO33– (iAsIII) is of global concern. Reliable detection of the maximum allowed contaminant level for arsenic in drinking water and in the cellular system remains a challenge for the water quality management and assessment of toxicity in the cellular milieu, respectively. A new Ir(III)-based phosphorescent molecule (AS-1; λExt = 415 nm and λEms = 600 nm, Φ = 0.3) is synthesized for the selective detection of iAsIII in an aqueous solution with a ratiometric luminescence response even in the presence of iAsV and all other common inorganic cations and anions. The relatively higher affinity of the thioimidazole ligand (HPBT) toward iAsIII led to the formation of a fluorescent molecule iAsV–HPBT (λExt = 415 nm and λEms = 466 nm, Φ = 0.28) for the reaction of iAsIII and AS-1. An improved limit of quantitation (LOQ) down to 0.2 ppb is achieved when AS-1 is used in the CTAB micellar system. Presumably, the cationic surfactants favor the localization of AS-1@CTABMicelle in mitochondria of MCF7 cells, and this is confirmed from the images of the confocal laser fluorescence scanning microscopic studies. Importantly, cell viability assay studies confirm that AS-1@CTABMicelle induces dose-dependent detoxification of iAsIII in live cells. Further, luminescence responses at 466 nm could be utilized for developing a hand-held device for the in-field application. Such a reagent that allows for ratiometric detection of iAsIII with LOQ of 2.6 nM (0.5 ppb) in water, as well as helps in visualizing its distribution in mitochondria with a detoxifying effect, is rather unique in contemporary literature

Nanoparticles for super-resolution microscopy: intracellular delivery and molecular targeting

Following an overview of the approaches and techniques used to acheive super-resolution microscopy, this review presents the advantages supplied by nanoparticle based probes for these applications. The various clases of nanoparticles that have been developed toward these goals are then critically described and these discussions are illustrated with a variety of examples from the recent literature