Diffusion‐limited kinetics is a key mechanistic debate when consecutive photoelectron transfer (conPET) discussed in photoredox catalysis. In‐situ generated organic photoactive radicals can access catalytic systems as reducing alkaline metals that activate remarkably stable bonds. However, many cases, the extremely short‐lived transient nature of these doublet state open‐shell species has led to debatable studies, hindering adoption and development. Herein, we document use an isolated...

EuS and Ag2S colloidal semiconductor nanocrystals are observed to display optical properties characteristic of the corresponding bulk materials, yet have desirable processing nanocrystals. We envision that nanoparticles will play a complementary role quantum-confined structures as another building block for development new technologies.

Diffusion‐limited kinetics is a key mechanistic debate when consecutive photoelectron transfer (conPET) discussed in photoredox catalysis. In‐situ generated organic photoactive radicals can access catalytic systems as reducing alkaline metals that activate remarkably stable bonds. However, many cases, the extremely short‐lived transient nature of these doublet state open‐shell species has led to debatable studies, hindering adoption and development. Herein, we document use an isolated...

The acoustic phonon modes of colloidal CdSe nanoparticles in solution (293 K) are passively measured by a third order ultrafast heterodyne cross-polarized transient grating measurement. Using the observed size-dependence frequency, elastic properties determined. modulus is then used to ascertain information about relative surface energies nanocrystals and suggests extent depth reconstruction.

Evidence for an interaction between the quantum dot exciton fine structure states F = ±1 is obtained by measuring dynamics of transitions among those states, spin relaxation or flipping. An ultrafast transient grating experiment based on a crossed-linear polarization reported. By using selection rules absorption circularly polarized light, it demonstrated that possible to detect nominally degenerate even in rotationally isotropic system. The results colloidal CdSe dots reveal strong size...

The rate of exciton spin relaxation (flips) between the bright states (F = ±1) CdSe nanocrystals is reported as a function shape, for dots and nanorods. measured using an ultrafast transient grating method with crossed linearly polarization sequence. It found that depends on radius, not length, nanocrystals. That observation explained by deriving expression electronic coupling matrix element mixes states.

A two-dimensional (2D) optical coherent spectroscopy that correlates the double excited electronic states to constituent single is described. The technique, termed double-quantum coherence (2D-DQCS), makes use of multiple, time-ordered ultrashort pulses create and quantum coherences over time intervals between pulses. resulting 2D spectra map out energy correlation first state two-photon-allowed states. Measurements organic dye molecules show near-resonant offset for adding a second...

Acoustic phonon modes in colloidal semiconductor nanocrystals are of significant interest due to their role dephasing and as the main component homogeneous line broadening. Despite importance, these have proven elusive only recently been experimentally observed. This paper expands on results presented our earlier [V. M. Huxter, A. Lee, S. Lo, et al., Nano Lett. 9, 405 (2008)], where a cross polarized heterodyne detected ultrafast transient grating (CPH-3TG) technique was used observe...

Carotenoids play an essential role in photoprotection, interacting with other pigments to safely dissipate excess absorbed energy as heat. In cyanobacteria, the short time scale photoprotective mechanisms involve photoactive orange carotenoid protein (OCP), which binds a single carbonyl carotenoid. Blue-green light induces photoswitching of OCP from its ground state form (OCPO) metastable photoproduct (OCPR). OCPR can bind phycobilisome antenna and induce fluorescence quenching. The is...

Unlike the majority of molecular systems quantum dots can accommodate multiple excitations, which is a particularly important attribute for potential lasing applications. We demonstrate in this work concept using nth order nonlinear spectroscopies transient grating configuration as means selectively exciting (n−1)∕2 excitons semiconductor and probing subsequent relaxation dynamics. report direct observation multiparticle dynamics on ultrashort time scales through comparison third fifth...

We experimentally demonstrate a nonlinear spectroscopic method that is sensitive to exciton-exciton interactions in Frenkel exciton system. Spatial overlap of one-exciton wavefunctions leads coupling between them, resulting two-exciton eigenstates have the character many single-exciton pairs. The mixed gives rise four-wave-mixing frequency generation signal. When only part linear excitation spectrum complex excited with three spectrally tailored pulses separate spatial directions,...

The optical properties and ultrafast dynamics of hexaethyl tripyrrin-1,14-dione (H3TD1) are tuned by hydrogen-bonding interactions between the solute solvent. In solvents with low affinity, H3TD1 preferentially forms hydrogen-bonded dimers, whereas in that can either donate or accept hydrogen bonds is present as a monomer. distinction dimer monomer determines system, faster internal conversion observed form. were characterized using time-correlated single photon counting, fluorescence...

In recent years, in-situ generated organic radicals have been used as highly potent photoinduced electron transfer (PET) agents resulting in catalytic systems reducing alkaline metals that can activate remarkably stable bonds. However, the transient nature of these doublet state open-shell species has led to debatable mechanistic studies, hindering adoption and development. Herein, we document use an isolated neutral radical a photoreducing with reduction potential lower than – 3.5 V vs SCE....

The application to inductively coupled plasma mass spectrometry (ICP-MS) of a calibration method called the TCM (tandem method) is described. involves simultaneous introduction sample and standard into by two nebulizers operated in parallel. Figures merit were determined comparing results obtained with those produced using additions external was used as probe severity matrix effect induced. test solutions this study contained Cu, Y, Pt Pb analytes 10 mM Ba 35 Na generators. Classical...

Radicals and other open-shell molecules play a central role in chemical transformations redox chemistry. While radicals are often highly reactive, stable radical systems desirable for range of potential applications, ranging from materials chemistry catalysis to spintronics quantum information. Here we investigate the ultrafast properties system with temperature-dependent spin-tunable properties. This complex, Cu(II) hexaethyl tripyrrin-1,14-dione, accommodates unpaired electrons localized...

The rapid development of light-activated organic photoredox catalysts has led to the proliferation powerful synthetic chemical strategies with industrial and pharmaceutical applications. Despite advancement in approaches, a detailed understanding mechanisms governing these reactions lagged. Time-resolved optical spectroscopy provides method track catalysis processes reveal energy pathways that drive reaction mechanisms. These measurements are sensitive key such as charge or transfer,...

Hydroxylation reactions are important in biological processes and synthetic schemes. Many challenging hydroxylation have been achieved using photoredox catalytic methods. For the oxidative of arylboronic acids, methylene blue has used successfully as a catalyst to produce phenyl groups. Here we use broadband transient absorption spectroscopy determine mechanism reaction with phenylboronic acid presence N,N-diisopropylethylamine. Our results show that proceeds through triplet state oxygen,...

Over the past few years, photoredox catalysis has led to significant transformations in modern synthetic chemistry. It allowed development of new pathways for assembly complex molecular scaffolds using light as a driving force. However, investigations ultrafast light-initiated mechanisms required these reactions are relatively scarce. Here we follow dynamics red-light organic photocatalyst, N,N′-di-n-propyl-1,13-dimethoxyquinacridinium (nPr-DMQA+), aerobic oxidative hydroxylation...

Methylene blue is used as a red-light photoredox catalyst for oxidative hydroxylation reactions. At typical loadings methylene forms dimers that do not participate in the reaction limiting availability of catalyst.

Broadband two-dimensional electronic spectroscopy is applied to investigate the photophysics of photoactive orange carotenoid protein, which involved in nonphotochemical quenching cyanobacteria. Differences dynamics between light and dark forms arise from different structure protein pocket, with consequences for biological role two forms.

Stable open- and closed-shell Pd(II) Cu(II) complexes of hexaethyl tripyrrin-1,14-dione (TD1) produce triplet, doublet or singlet states depending on the metal center redox state ligand. form neutral TD1 featuring ligand-based radicals, thus resulting in triplet states, respectively. The reversible one-electron oxidation removes an unpaired electron from ligand, generating states. optical properties time-resolved dynamics these systems are studied here using steady-state ultrafast transient...