Intrinsic anti-Stokes emission in living HeLa cells

Intrinsic fluorescence of biological material, also called auto-fluorescence, is a well-known phenomenon and has in recent years been used for imaging, diagnostics and cell viability studies. Here we show that in addition to commonly observed auto-fluorescence, intrinsic anti-Stokes emission can also be observed under 560 nm or 633 nm excitation. The anti-Stokes emission is shown to be spatially located on/in the mitochondria. The findings presented here show that sensitive imaging experiments e.g. single molecule experiments or two-photon excitation imaging can be compromised if intracellular anti-Stokes emission is not accounted for. On the other hand, we suggest that this anti-Stokes emission could be exploited as an additional modality for mitochondria visualization and cell viability investigation even in systems that are already labeled with commonly used fluorophores that rely on normal Stokes-based detection

Spatially Localized Synthesis and Structural Characterization of Platinum Nanocrystals Obtained Using UV Light

Platinum nanocrystals with a fine control of the crystal domain size in the range 1.0–2.2 nm are produced by tuning the NaOH concentration during the UV-induced reduction of H$_2$PtCl$_6$ in surfactant-free alkaline ethylene glycol. The colloidal solutions obtained are characterized by transmission electron microscopy and pair distribution function analysis, allowing analysis of both atomic and nanoscale structures. The obtained nanoparticles exhibit a face-centered cubic crystal structure even for the smallest nanoparticles, and the cubic unit cell parameter is significantly reduced with decreasing crystallite size. It is further demonstrated how the “UV-approach” can be used to achieve spatial control of the nucleation and growth of the platinum nanocrystals, which is not possible by thermal reduction

UV-induced syntheses of surfactant-free precious metal nanoparticles in alkaline methanol and ethanol

Surfactant-free UV-induced syntheses of Pt and Ir nanoparticles in alkaline methanol and ethanol are presented. Small size nanoparticles ca. 2 nm in diameter are obtained without surfactants in a wide range of base concentration

We are never ever getting (back to) ideal symmetry:structure and luminescence in a ten-coordinated europium(iii) sulfate crystal

Our theoretical treatment of electronic structure in coordination complexes often rests on assumptions of symmetry. Experiments rarely provide fully symmetric systems to study. In solution, fluctuation in solvation, variations in conformation, and even changes in constitution occur and complicates the picture. In crystals, lattice distortion, energy transfer, and phonon quenching is in play, but we are able to have distinct symmetries. Yet the question remains: How is the real symmetry in a crystal compared to ideal symmetries? Moreover, at what level of detail do we need to study a system to determine, if the electronic structure behaves as if it has ideal symmetry? Here, we have revisited the Continues Shape Measurement (CShM) approach developed by Ruiz-Martínez and Alvarez to evaluate the structure of ten-coordinated europium(III) ions in a K5Na[Eu2(SO4)6] structure. By comparing the result of the symmetry deviation analysis to luminescence data, we are able to show the effect of small deviations from ideal symmetry. We suggest using a symmetry deviation value, σideal, determined by using our updated approach to Continues Shape Measurements, where we also align the structure via our AlignIt code. AlignIt includes normalization and relative orientation in the symmetry comparison, and by combining the calculated values with the experimentally determined energy level splitting, we were able create the first point on a scale that can show how close to ideal an experimental structure actually is

Spatially Localized Synthesis and Structural Characterization of Platinum Nanocrystals Obtained Using UV Light

Platinum nanocrystals with a fine control of the crystal domain size in the range 1.0–2.2 nm are produced by tuning the NaOH concentration during the UV-induced reduction of H$_2$PtCl$_6$ in surfactant-free alkaline ethylene glycol. The colloidal solutions obtained are characterized by transmission electron microscopy and pair distribution function analysis, allowing analysis of both atomic and nanoscale structures. The obtained nanoparticles exhibit a face-centered cubic crystal structure even for the smallest nanoparticles, and the cubic unit cell parameter is significantly reduced with decreasing crystallite size. It is further demonstrated how the “UV-approach” can be used to achieve spatial control of the nucleation and growth of the platinum nanocrystals, which is not possible by thermal reduction

A Universal Concept for Bright, Organic Solid State Emitters - Doping of Small Molecule Ionic Isolation Lattices with FRET Acceptors

Brightly fluorescent solid-state materials are highly desirable tools in bioimaging, optoelectronic applications and energy harvesting. However, close contact between π-systems leads to strong electronic coupling and often subse-quent quenching of the emitters in dense solid-state materials. Recently, we developed a method to prohibit strong coupling based on small molecule ionic isolation lattices (SMILES) that efficiently isolate fluorophores while in paral-lel ensuring very high densities of the dyes. Nevertheless, efficient FRET energy migration in such dense systems is inevitable. While attractive for energy harvesting applications, FRET also significantly compromises quantum yields of fluorescent solids by funneling excitation energy to dark trap states like crystal defects. Here we investigate the underlying property of FRET and exploit it to our favor by intentionally introducing fluorescent dopants into SMILES materials, acting as FRET acceptors with favorable photophysical properties. This doping is shown to outcompete en-ergy migration to dark trap states, while also ruling out reabsorption effects in dense SMILES materials, resulting in universal fluorescent solid state materials (thin films, powders, crystals) with superior properties. These include emission quantum yields reaching as high as 50-65 %, programmable fluorescence lifetimes with mono-exponential decay, and independent selection of absorption and emission maxima. The volume normalized brightness of these FRET-based SMILES now reach values up to 32200 M-1 cm-1 nm-3 and can deliver freely tunable spectroscopic properties for the fabrication of super bright advanced optical materials

Fast Structural Dynamics in Concentrated HCl Solutions: From Proton Hopping to the Bulk Viscosity

Concentrated acid solutions, particularly HCl, have been studied extensively to examine the proton hopping and infrared spectral signatures of hydronium ions. Much less attention has been given to the structural dynamics of concentrated HCl solutions. Here, we apply optical heterodyne detected–optical Kerr effect (OHD-OKE) measurements to examine HCl concentration-dependent dynamics from moderate (0.8 m) to very high (15.5 m) concentrations and compare the results to the dynamics of NaCl solutions, as Na+ is similar in size to the hydronium cation. Both HCl and NaCl OHD-OKE signals decay as triexponentials at all concentrations, in contrast to pure water, which decays as a biexponential. Two remarkable features of the HCl dynamics are the following: (1) the bulk viscosity is linearly related to the slowest decay constant, t3, and (2) the concentration-dependent proton hopping times, determined by ab initio MD simulations and 2D IR chemical exchange experiments, both obtained from the literature, fall on the same line as the slowest structural dynamics relaxation time, t3, within experimental error. The structural dynamics of hydronium/chloride/water clusters, with relaxation times t3, are responsible for the concentration dependence of microscopic property of proton hopping and the macroscopic bulk viscosity. The slowest time constant (t3), which does not have a counterpart in pure water, is 3 ps at 0.8 m and increases by a factor of ∼2 by 15.5 m. The two fastest HCl decay constants, t1 and t2, are similar to those of pure water and increase mildly with the concentration