Tuning Hot-Carrier Temperature in CsPbBr Perovskite Nanoplatelets through Metal Halide Passivation.

High carrier temperature and slow carrier cooling make perovskite nanostructures potential candidates for hot-carrier solar cells. Here, using time-resolved photoluminescence spectroscopy, hot-carrier dynamics is reported in strongly confined three-monolayer quasi-2D CsPbBr perovskite nanoplatelets characterized by sharp excitonic peaks in the absorption spectrum and narrow emission peaks in the blue region. Treatment with a PbBr-ligand solution resulted in a remarkable seven-fold increase in photoluminescence intensity, attributed to effective passivation of surface defects due to lead(II) and bromide vacancies.

Dynamics of Pyrene Excimer in a Cholesteryl-Based Supramolecular Host Matrix.

Aggregation-caused quenching (ACQ) reduces luminescence and compromises brightness in solid-state displays, necessitating strategies to mitigate its effects for enhanced performance. This study presents cost-effective method to mitigate ACQ of pyrene by co-assembling polycyclic aromatic hydrocarbons within low molecular weight gelator. Synthesized from readily available materials - cholesteryl chloroformate and pentaerythritol - in one-step reaction, gelator incorporates four cholesteryl units, reported to promote robust supramolecular gels in various solvents.

Two-Dimensional Fluctuation Correlation Spectroscopy (2D-FlucCS): A Method to Determine the Origin of Relaxation Rate Dispersion.

Relaxation rate dispersion, i.e., nonexponential or multicomponent kinetics, is observed in complex systems when measuring relaxation kinetics.

Extracting quantitative dielectric properties from pump-probe spectroscopy.

Optical pump-probe spectroscopy is a powerful tool for the study of non-equilibrium electronic dynamics and finds wide applications across a range of fields, from physics and chemistry to material science and biology. However, a shortcoming of conventional pump-probe spectroscopy is that photoinduced changes in transmission, reflection and scattering can simultaneously contribute to the measured differential spectra, leading to ambiguities in assigning the origin of spectral signatures and ruling out quantitative interpretation of the spectra. Ideally, these methods would measure the underlying dielectric function (or the complex refractive index) which would then directly provide quantitative information on the transient excited state dynamics free of these ambiguities.

Nonequilibrium Carrier Transport in Quantum Dot Heterostructures.

Understanding carrier dynamics and transport in quantum dot based heterostructures is crucial for unlocking their full potential for optoelectronic applications. Here we report the direct visualization of carrier propagation in PbS CQD solids and quantum-dot-in-perovskite heterostructures using femtosecond transient absorption microscopy. We reveal three distinct transport regimes: an initial superdiffusive transport persisting over hundreds of femtoseconds, an Auger-assisted subdiffusive transport before thermal equilibrium is achieved, and a final hopping regime.

Tetrafluoroborate-Induced Reduction in Defect Density in Hybrid Perovskites through Halide Management.

Hybrid-perovskite-based optoelectronic devices are demonstrating unprecedented growth in performance, and defect passivation approaches are highly promising routes to further improve properties. Here, the effect of the molecular ion BF , introduced via methylammonium tetrafluoroborate (MABF ) in a surface treatment for MAPbI perovskite, is reported. Optical spectroscopy characterization shows that the introduction of tetrafluoroborate leads to reduced non-radiative charge-carrier recombination with a reduction in first-order recombination rate from 6.

Ultrafast Tracking of Exciton and Charge Carrier Transport in Optoelectronic Materials on the Nanometer Scale.

We present a novel optical transient absorption and reflection microscope based on a diffraction-limited pump pulse in combination with a wide-field probe pulse, for the spatiotemporal investigation of ultrafast population transport in thin films. The microscope achieves a temporal resolution down to 12 fs and simultaneously provides sub-10 nm spatial accuracy. We demonstrate the capabilities of the microscope by revealing an ultrafast excited-state exciton population transport of up to 32 nm in a thin film of pentacene and by tracking the carrier motion in p-doped silicon.

Effect of T·T Mismatch on DNA Dynamics Probed by Minor Groove Binders: Comparison of Dynamic Stokes Shifts of Hoechst and DAPI.

Recognition of DNA base mismatches and their subsequent repair by enzymes is vital for genomic stability. However, it is difficult to comprehend such a process in which enzymes sense and repair different types of mismatches with different ability. It has been suggested that the differential structural changes of mismatched bases act as cues to the repair enzymes, although the effect of such DNA structural changes on surrounding water and ion dynamics is inevitable due to strong electrostatic coupling among them.

Rate and Amplitude Heterogeneity in the Solvation Response of an Ionic Liquid.

In contrast with conventional liquids, ionic liquids have solvation dynamics with more rate dispersion and with average times that do not agree with dielectric measurements. A kinetic analog of multidimensional spectroscopy is introduced and used to look for heterogeneity in simulations of coumarin 153 in [Im12][BF4]. Strong heterogeneity is found in the diffusive solvation rate.

Power-Law Solvation Dynamics in G-Quadruplex DNA: Role of Hydration Dynamics on Ligand Solvation inside DNA.

G-quadruplex DNA (GqDNA) structures act as promising anticancer targets for small-molecules (ligands). Solvation dynamics of a ligand (DAPI: 4',6-diamidino-2-phenylindole) inside antiparallel-GqDNA is studied through direct comparison of time-resolved experiments to molecular dynamics (MD) simulation. Dynamic Stokes shifts of DAPI in GqDNA prepared in H2O buffer and D2O are compared to find the effect of water on ligand solvation.

When is a single molecule heterogeneous? A multidimensional answer and its application to dynamics near the glass transition.

Even for apparently simple condensed-phase processes, bulk measurements of relaxation often yield nonexponential decays; the rate appears to be dispersed over a range of values. Taking averages over individual molecules is an intuitive way to determine whether heterogeneity is responsible for such rate dispersion. However, this method is in fundamental conflict with ergodic behavior and often yields ambiguous results.

Sequence-Dependent Solvation Dynamics of Minor-Groove Bound Ligand Inside Duplex-DNA.

Ligand binding to minor-grooves of DNA depends on DNA-base sequence near its binding-site. However, it is not known how base-sequences affect the local solvation of ligand inside minor-grooves of DNA. Here we present a comprehensive study on sequence-dependent solvation dynamics of ligand inside duplex-DNA by measuring the static and dynamic fluorescence Stokes shifts of a popular groove-binder, DAPI, inside DNA minor-grooves created by four different sequences; d(5'-CGCGAATTCGCG-3')2, d(5'-CGCGTTAACGCG-3')2, d(5'-CGCGCAATTGCGCG-3')2, and d(5'-CGCGCTTAAGCGCG-3')2, having different sequences near DAPI-binding site.

Probe Position-Dependent Counterion Dynamics in DNA: Comparison of Time-Resolved Stokes Shift of Groove-Bound to Base-Stacked Probes in the Presence of Different Monovalent Counterions.

Time-resolved fluorescence Stokes shifts (TRFSS) of 4',6-diamidino-2-phenylindole (DAPI) inside the minor groove of DNA are measured in the presence of three different monovalent counterions: sodium (Na(+)), rubidium (Rb(+)), and tetrabutylammonium (TBA(+)). Fluorescence up-conversion and time-correlated single photon counting are combined to obtain the time-resolved emission spectra (TRES) of DAPI in DNA from 100 fs to 10 ns. Time-resolved Stokes shift data suggest that groove-bound DAPI can not sense the counterion dynamics because the ions are displaced by DAPI far from the probe-site.

Understanding ligand interaction with different structures of G-quadruplex DNA: evidence of kinetically controlled ligand binding and binding-mode assisted quadruplex structure alteration.

The study of ligand interaction with G-quadruplex DNA is an active research area, because many ligands are shown to bind G-quadruplex structures, showing anticancer effects. Here, we show, for the first time, how fluorescence correlation spectroscopy (FCS) can be used to study binding kinetics of ligands with G-quadruplex DNA at the single molecule level. As an example, we study interaction of a benzo-phenoxazine ligand (Cresyl Violet, CV) with antiparallel and (3 + 1) hybrid G-quadruplex structures formed by human telomeric sequence.

Fluorescence correlation spectroscopy: an efficient tool for measuring size, size-distribution and polydispersity of microemulsion droplets in solution.

Fluorescence correlation spectroscopy (FCS) is an ideal tool for measuring molecular diffusion and size under extremely dilute conditions. However, the power of FCS has not been utilized to its best to measure diffusion and size parameters of complex chemical systems. Here, we apply FCS to measure the size, and, most importantly, the size distribution and polydispersity of a supramolecular nanostructure (i.

Probe position dependence of DNA dynamics: comparison of the time-resolved Stokes shift of groove-bound to base-stacked probes.

Time-resolved fluorescence Stokes shift dynamics of a fluorescent probe, 4',6-diamidino-2-phenylindole (DAPI), inside the minor groove of the DNA is measured over five decades in time spans from 100 fs to 10 ns. Two different techniques, fluorescence up-conversion and time correlated single photon counting, are combined to obtain the time-resolved emission spectra of DAPI in DNA over the entire five decades in time. Having the dynamics of groove-bound DAPI in DNA measured over such a broad time window, we are able to convincingly compare our data to earlier time-resolved fluorescence results of a base-stacked probe that replaces a DNA base pair.