First report of Bot Canker (Diplodia corticola) in Pin Oak (Quercus palustris) in Tennessee.

Diplodia corticola is a fungal pathogen contributing to oak (Quercus spp.) decline in the Mediterranean and US (Félix et al., 2017; Ferreira et al.

First report of leaf anthracnose on the Whorled Sunflower, Helianthus verticillatus, caused by Colletotrichum fioriniae in the United States.

Whorled sunflower, Helianthus verticillatus Small, is an endangered (U.S. Fish and Wildlife Service 2014) perennial sunflower species indigenous to the southern United States (Matthews et al.

First report of Diplodia corticola causing dieback of white oak (Quercus alba) in Tennessee.

Diplodia corticola is a fungal pathogen causing oak dieback in Quercus (oak) spp. in parts of North America, northern Africa, and Europe (Ferreira et al., 2021; Smahi et al.

Photocatalytic Hydrogen Generation by CdSe/CdS Nanoparticles.

The photocatalytic hydrogen (H2) production activity of various CdSe semiconductor nanoparticles was compared including CdSe and CdSe/CdS quantum dots (QDs), CdSe quantum rods (QRs), and CdSe/CdS dot-in-rods (DIRs). With equivalent photons absorbed, the H2 generation activity orders as CdSe QDs ≫ CdSe QRs > CdSe/CdS QDs > CdSe/CdS DIRs, which is surprisingly the opposite of the electron-hole separation efficiency. Calculations of photoexcited surface charge densities are positively correlated with the H2 production rate and suggest the size of the nanoparticle plays a critical role in determining the relative efficiency of H2 production.

The influence of continuous vs. pulsed laser excitation on single quantum dot photophysics.

The impact of pulsed versus continuous wave (cw) laser excitation on the photophysical properties of single quantum dots (QDs) has been investigated in an experiment in which all macroscopic variables are identical except the nature of laser excitation. Pulsed excitation exaggerates the effects of photobleaching, results in a lower probability of long ON fluorescence blinking events, and leads to shorter fluorescence lifetimes with respect to cw excitation at the same wavelength and average intensity. Spectral wandering, biexciton quantum yields, and power law exponents that describe fluorescence blinking are largely insensitive to the nature of laser excitation.

Linear dipole behavior in single CdSe-oligo(phenylene vinylene) nanostructures.

We report on linearly polarized absorption and emission from individual (4.3 nm) CdSe quantum dots whose surfaces are coordinated with monodisperse oligo-phenylene vinylene ligands. Shown previously to suppress quantum dot blinking, we demonstrate here that the electronic interaction of photoexcited ligands with the quantum dot core is manifested as a strong polarization anisotropy in absorption (M = 0.

Quenching mechanism of Zn(salicylaldimine) by nitroaromatics.

Nitroaromatics and nitroalkanes quench the fluorescence of Zn(Salophen) (H2Salophen = N,N'-phenylene-bis-(3,5-di- tert-butylsalicylideneimine); ZnL(R)) complexes. A structurally related family of ZnL(R) complexes (R = OMe, di-tBu, tBu, Cl, NO2) were prepared, and the mechanisms of fluorescence quenching by nitroaromatics were studied by a combined kinetics and spectroscopic approach. The fluorescent quantum yields for ZnL(R) were generally high (Phi approximately 0.

Blinking suppression and intensity recurrences in single CdSe-oligo(phenylene vinylene) nanostructures: experiment and kinetic model.

We report time-resolved single molecule fluorescence imaging of individual CdSe quantum dots that are functionalized with oligomeric conjugated organic ligands. The fluorescence intensity trajectories from these composite nanostructures display both a strong degree of blinking suppression and intensity fluctuations with characteristic recurrence times on the order of 10-60 s. In addition, fluorescence decay rate measurements of individual hybrid nanostructures indicate significantly modified non-radiative quantum dot decay rates relative to conventional ZnS-capped CdSe quantum dots.

Fluorescence lifetimes and correlated photon statistics from single CdSe/oligo(phenylene vinylene) composite nanostructures.

We present measurements of fluorescence intensity trajectories and associated excited-state decay times from individual CdSe/oligo(phenylene vinylene) (CdSe-OPV) quantum dot nanostructures using time-tagged, time-resolved (TTTR) photon counting techniques. We find that fluorescence decay times for the quantum dot emitter in these composite systems are at least an order of magnitude shorter than ZnS-capped CdSe quantum dot systems. We show that both the blinking suppression and associated lifetime/count rate behavior can be described by a modified version of the diffusive reaction coordinate model which couples slow fluctuations in quantum dot electron (1Se, 1Pe) energies to Auger-assisted hole trapping processes, hence modifying both blinking statistics and excited-state decay rates.

Single-molecule studies of a model fluorenone.

Single-molecule fluorescence measurements of 2,7-bis(3,4,5-trimethoxyphenylethenyl)fluorenone (OFOPV) reveal narrow emission spectra concentrated around 540 nm, with weak emission at longer wavelengths. The wide scattering of emission-maximum wavelengths is attributed to varying molecular environments, with dimers or higher-order aggregates contributing to the low-energy emission. This spectral distribution indicates that emission from monomers of this model fluorenone is mostly green, which is consistent with contaminant emission (g-bands) often observed in fluorene- and polyfluorene-based organic light emitting diode (OLED) devices.

Coverage-mediated suppression of blinking in solid state quantum dot conjugated organic composite nanostructures.

Size-correlated single-molecule fluorescence measurements on CdSe quantum dots functionalized with oligo(phenylene vinylene) (OPV) ligands exhibit modified fluorescence intermittency (blinking) statistics that are highly sensitive to the degree of ligand coverage on the quantum dot surface. As evidenced by a distinct surface height signature, fully covered CdSe-OPV nanostructures (approximately 25 ligands) show complete suppression of blinking in the solid state on an integration time scale of 1 s. Some access to dark states is observed on finer time scales (100 ms) with average persistence times significantly shorter than those from ZnS-capped CdSe quantum dots.

Observation of enhanced energy transfer in individual quantum dot-oligophenylene vinylene nanostructures.

The temporal and spectral properties of luminescence from individual CdSe quantum dot-oligophenylene vinylene nanostructures (single quantum dots with conjugated organic ligands coordinated to the surface) are profoundly modified relative to blended films of the same components. These kinds of composite quantum dot-conjugated organic systems have attracted significant interest as a way to improve efficiency in photovoltaic device applications. By direct functionalization of the dot surface with the conjugated organic ligands, we realize a significant enhancement in energy transfer and luminescence stability.