Direct observation of electron-cation geminate pair produced by picosecond laser pulse excitation in nonpolar solvent: excitation wavelength dependence of the electron thermalization length

How to Probe Hydrated Dielectrons Experimentally: Ab Initio Simulations of the Absorption Spectra of Aqueous Dielectrons, Electron Pairs, and Hydride

In the radiation chemistry of water, two hydrated electrons (ehyd-) can react to form H2 and OH-. Experiments and simulations suggest that this reaction occurs through a mechanism involving colocalization of two ehyd-'s into the same solvent cavity, forming a hydrated dielectron ( ( e h y d ) 2 2 - ) intermediate, with aqueous hydride (H-) as a subintermediate. However, there has been no direct experimental observation of either ( e h y d ) 2 2 - or H-. Here, we present TD-DFT-based predictions for the absorption spectrum of open-shell-singlet and triplet ehyd- pairs, ( e h y d ) 2 2 - , and H-. We find that relative to ehyd-, triplet and open-shell singlet electron pairs show spectral shifts to the blue and red, respectively. Additionally, we find that ( e h y d ) 2 2 - absorbs even further to the red, and that H- has a charge-transfer-to-solvent-like transition at wavelengths several eV to the blue, providing a direct experimental handle with which to probe these species. We propose a three-pulse transient absorption experiment that should allow detection of ( e h y d ) 2 2 - and H-.

Dynamics of electron ejection on photoionization of trans-stilbene and biphenyl in acetonitrile as observed with femtosecond time-resolved near-IR absorption spectroscopy

Photoionization in solution is a basic but complex phenomenon involving a solute, an ejected electron and surrounding solvent molecules. It may seem obvious that an electron is released immediately after...

High-bandwidth, high-sampling-rate, low-noise, two-probe transient photovoltage measuring system

In this article, we present a two-probe configuration for measuring transient photovoltage (TPV) signals from photo-electronic semiconductor devices. Unlike in a conventional one-probe system, the two electrodes of the devices under test in this study are both monitored in our new measuring system, giving rise to a significantly enhanced signal-to-noise ratio. Tentative experimental data ob tained from N, N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine-based organic semiconductor devices show that the bandwidth and the sampling rate of the system reach 1.5 GHz and 50 GS/s, respectively, without degradation of the noise level. In addition, the study of TPV signals on each individual electrode is allowed. The TPV values measured by the two individual probes are not identically equal to half of the differential TPV and will not cancel each other out as expected. This abnormal phenomenon is due to the photoelectric response of the photo-electronic material. This novel two-probe TPV measuring technique and abnormal TPV behavior might be useful for studying more dynamic processes in photo-electronic semiconductors.

Orientation Effects on Excited State Dynamics of Zinc Porphyrin–Free Base Porphyrin–Pyromellitimide Triads

The synthesis is described of fixed distance triads consisting of zinc porphyrin ( ZP ), metal-free porphyrin ( HP ) and pyromellitimide (I) in which the ZP and HP moieties are bridged by a rigid 4,4'-biphenylene spacer and related spacers, being held with dihedral angles defined by the torsional angle (θ) of the 4,4'-biphenylene spacer varying from nearly coplanar (θ = 0°, phenanthrene spacer) to nearly orthogonal (θ = 90°, 2,2',6,6'-tetramethylbiphenylene spacer). Using these models, the effects of the dihedral angle of the two porphyrins have been examined for singlet–singlet excitation energy transfer from ZP to HP , hole transfer from HP + to ZP and charge recombination of ZP +– HP – I – to the ground state. In the three processes examined, the observed rate constants are roughly in the order of 1d (coplanar)≥1c (nearly coplanar) >1a (tilted) >1b (orthogonal).