Active control over the shape, composition, and crystalline habit of nanocrystals has long been a goal. Various methods have been shown to enable postsynthesis modification of nanoparticles, including the use of the Kirkendall effect, galvanic replacement, and cation or anion exchange, all taking advantage of enhanced solid-state diffusion on the nanoscale. In all these processes, however, alteration of the nanoparticles requires introduction of new precursor materials. Here we show that for cesium lead halide perovskite nanoparticles, a reversible structural and compositional change can be induced at room temperature solely by modification of the ligand shell composition in solution. The reversible transformation of cubic CsPbX3 nanocrystals to rhombohedral Cs4PbX6 nanocrystals is achieved by controlling the ratio of oleylamine to oleic acid capping molecules. High-resolution transmission electron microscopy investigation of Cs4PbX6 reveals the growth habit of the rhombohedral crystal structure is composed of a zero-dimensional layered network of isolated PbX6 octahedra separated by Cs cation planes. The reversible transformation between the two phases involves an exfoliation and recrystalliztion process. This scheme enables fabrication of high-purity monodispersed Cs4PbX6 nanoparticles with controlled sizes. Also, depending on the final size of the Cs4PbX6 nanoparticles as tuned by the reaction time, the back reaction yields CsPbX3 nanoplatelets with a controlled thickness. In addition, detailed surface analysis provides insight into the impact of the ligand composition on surface stabilization that, consecutively, acts as the driving force in phase and shape transformations in cesium lead halide perovskites.

Design of an extensive supramolecular three-dimensional network that is both robust and adaptive represents a significant challenge. The molecular system PP2b based on a perylene diimide chromophore (PDI) decorated with polyethylene glycol groups self-assembles in aqueous media into extended supramolecular fibers that form a robust three-dimensional network resulting in gelation. The self-assembled systems were characterized by cryo-TEM, cryo-SEM, and rheological measurements. The gel possesses exceptional robustness and multiple stimuli-responsiveness. Reversible charging of PP2b allows for switching between the gel state and fluid solution that is accompanied by switching on and off the material's birefringence. Temperature triggered deswelling of the gel leads to the (reversible) expulsion of a large fraction of the aqueous solvent. The dual sensibility toward chemical reduction and temperature with a distinct and interrelated response to each of these stimuli is pertinent to applications in the area of adaptive functional materials. The gel also shows strong absorption of visible light and good exciton mobility (elucidated using femtosecond transient absorption), representing an advantageous light harvesting system.

We present a self-assembly method to construct CdSe/ZnS quantum dot-gold nanoparticle complexes. This method allows us to form complexes with relatively good control of the composition and structure that can be used for detailed study of the exciton-plasmon interactions. We determine the contribution of the polarization-dependent near-field enhancement, which may enhance the absorption by nearly two orders of magnitude and that of the exciton coupling to plasmon modes, which modifies the exciton decay rate.

Light-induced radical generation is the hallmark of fundamental processes and many applications including photosynthesis and photodynamic therapy (PDT). In this manuscript, we present two novel observations made upon monitoring light-induced generation of reactive oxygen species (ROS) in aqueous solutions by WST11, a water-soluble derivative of the photosynthetic pigment Bacteriochlorophyll a (Bchl). Using a host of complementary experimental techniques including time-resolved spectroscopy at the subpicosecond to the millisecond range, ESR spectroscopy, electrochemistry, spectroelectrochemistry, oximetry, and protein mass spectroscopy, we first show that in aqueous solutions WST11 generates only superoxide (O 2 -•) and hydroxyl (OH • ) radicals with no detectable traces of singlet oxygen. Second, we show that WST11 makes a noncovalent complex with human serum albumin (HSA) and that this complex functions as a photocatalytic oxidoreductase at biologically relevant concentrations enabling approximately 15 cycles of electron transfer from the associated HSA protein to molecular oxygen in the solution. These findings rule out the paradigm that porphyrin and chlorophyll based PDT is mainly mediated by formation of singlet oxygen, particularly in vascular targeted photodynamic therapy (VTP) with sensitizers that undergo photoactivation during circulation in the plasma, like [Pd]-Bacteriopheophorbide (WST09, Tookad). At the same time, our findings open the way for new design paradigms of novel sensitizers, since O 2 -• and OH • radicals are well-recognized precursors of important pathophysiological processes that can be activated for achieving tumor eradication. Moreover, the finding that promiscuous protein scaffolds become sinks for holes and electrons when holding light-activated pigments provides a new insight to the evolution and action mechanism of natural light activated oxidoreductases (such as photosynthetic reaction centers) and new guidelines for the preparation of synthetic-light converting machineries.

Self-assembling systems, whose structure and function can be reversibly controlled in situ are of primary importance for creating multifunctional supramolecular arrays and mimicking the complexity of natural systems. Herein we report on photofunctional fibers self-assembled from perylene diimide cromophores, in which interactions between aromatic monomers can be attenuated through their reduction to anionic species that causes fiber fission. Oxidation with air restores the fibers. The sequence represents reversible supramolecular depolymerization-polymerization in situ and is accompanied by a reversible switching of photofunction.

Both in vivo and ex vivo observations support the hypothesis that bone mineral formation proceeds via disordered precursor phases. The characteristics of the precursor phases are not well defined, but octacalcium phosphate-like, amorphous calcium phosphate-like, and HPO-enriched phases were detected. Here we use in vivo Raman spectroscopy and high-resolution wide-angle X-ray diffraction (WAXD) to characterize and map at 2 μm resolution the mineral phases in the rapidly forming tail fin bones of living zebrafish larvae and zebrafish larvae immediately after sacrifice, respectively. Raman spectroscopy shows the presence of an acidic disordered calcium phosphate phase with additional characteristic features of HPO at the bone-cell interface. The complexity in the position and shape of the ν PO peak viewed by in vivo Raman spectroscopy emphasizes the heterogeneity of the mineral during bone formation. WAXD detects an additional isolated peak, appearing alone or together with the characteristic diffraction pattern of carbonated hydroxyapatite. This unidentified phase is located at the interface between the mature bone and the surrounding tissue, similar to the location at which the disordered phase was observed by Raman spectroscopy. The variable peak positions and profiles support the notion that this is an unstable disordered precursor phase, which conceivably crystallized during the X-ray diffraction measurement. Interestingly, this precursor phase is co-aligned with the c-axes of the mature bone crystals and thus is in intimate relation with the surrounding collagen matrix. We conclude that a major disordered precursor mineral phase containing HPO is part of the deposition pathway of the rapidly forming tail fin bones of the zebrafish.

Halide perovskites, HaPs, can show remarkable to outstanding properties and photovoltaic (PV) devices in which they are the absorber can show excellent performances. [1-4] Apart from the PV results, also light-emission, radiation detection, and other electronics are explored. [5-8] During their relatively short history, numerous questions have arisen about the materials' properties and functions with many central ones still under discussion, such as the proposed idea of defect tolerance which awaits experimental evidence. At the same time, already several observables have been linked to fascinating phenomena, such as anharmonicity [9] and high entropy. [10] Ion migration in HaPs belongs to the latter class and has been widely discussed. Migrating ions modify conductivity and junction architecture with consequences for the overall efficiency of junction devices, such as solar cells. A wide consensus identifies halides, specifically I − and Br − , as the migrating ions, although, still without the gold standard experiment of isotope tracing. Remarkably, with some notable exceptions, there is no mention of contributions of protons to ion migration, although their absence in HaPs containing CH 3 NH 3 + (MA +) and HC(NH 2) 2 (FA +) (as the A cation in ABX 3) would be remarkable. In the past years of our research on dynamic effects in halide perovskites (self-healing and ion Ion diffusion affects the optoelectronic properties of halide-perovskites (HaPs). Until now, the fastest diffusion has been attributed to the movement of the halides, largely neglecting the contribution of protons, on the basis of computed density estimates. Here, the process of proton diffusion inside HaPs, following deuterium-hydrogen exchange and migration in MAPbI 3 , MAPbBr 3 , and FAPbBr 3 single crystals, is proven through D/H NMR quantification, Raman spectroscopy, and elastic recoil detection analysis, challenging the original assumption of halide-dominated diffusion. The results are confirmed by impedance spectroscopy, where MAPbBr 3-and CsPbBr 3-based solar cells respond at very different frequencies. Water plays a key role in allowing the migration of protons as deuteration is not detected in its absence. The water contribution is modeled to explain and forecast its effect as a function of its concentration in the perovskite structure. These findings are of great importance as they evidence how unexpected, waterdependent proton diffusion can be at the basis of the ≈7 orders of magnitude spread of diffusion (attributed to I − and Br −) coefficient values, reported in the literature. The reported enhancement of the optoelectronic properties of HaP when exposed to small amounts of water may be related to the finding.

We experimentally investigate carrier multiplication (CM) in type II CdTe/CdSe quantum dot (QD) heterostructures by the means of a simple and robust subnanosecond transient photoluminescence spectroscopy setup. Experimental conditions were set to minimize the blurring of the CM signature by extraneous effects. The extracted photon energy threshold for CM is consistent with previous studies in CdSe and CdTe QDs (around 2.65 times the type II energy band gap) and we can infer an upper bound to CM yield. This study indicates that, while CM is probably present in type II QD heterostructures below the CM threshold for each constituent separately, it exhibits only a modest yield.