Photoinduced Electron Transfer-Promoted Reactions Using Exciplex-Type Organic Photoredox Catalyst Directly Linking Donor and Acceptor Arenes

Directly linked donor and acceptor arenes, such as phenanthrene/naphthalene/biphenyl and 1,3-dicyanobenzene were found to work as photoredox catalysts in the photoreactions of indene, 2,3-dimethyl-2-butene, and 4-methoxyphenylacetic acid. The new stable organic photocatalyst forms an intramolecular exciplex (excited complex) when irradiated in a polar solvent and shows redox catalyst activity, even at low concentrations. To the best of our knowledge, this is the first example of an intramolecular exciplex working as a redox catalyst.

Halogen-Bond Assisted Photoinduced Electron Transfer

The formation of a halogen-bond (XB) complex in the excited state was recently reported with a quadrupolar acceptor–donor–acceptor dye in two iodine-based liquids (J. Phys. Chem. Lett. 2017, 8, 3927–3932). The ultrafast decay of this excited complex to the ground state was ascribed to an electron transfer quenching by the XB donors. We examined the mechanism of this process by investigating the quenching dynamics of the dye in the S1 state using the same two iodo-compounds diluted in inert solvents. The results were compared with those obtained with a non-halogenated electron acceptor, fumaronitrile. Whereas quenching by fumaronitrile was found to be diffusion controlled, that by the two XB compounds is slower, despite a larger driving force for electron transfer. A Smoluchowski–Collins–Kimball analysis of the excited-state population decays reveals that both the intrinsic quenching rate constant and the quenching radius are significantly smaller with the XB compounds. These results point to much stronger orientational constraint for quenching with the XB compounds, indicating that electron transfer occurs upon formation of the halogen bond.

Time-spliced X-ray diffraction imaging of magnetism dynamics in a NdNiO3 thin film

Diffraction imaging of nonequilibrium dynamics at atomic resolution is becoming possible with X-ray free-electron lasers. However, there are unresolved problems with applying this method to objects that are confined in only one dimension. Here I show that reliable one-dimensional coherent diffraction imaging is possible by splicing together images recovered from different time delays in an optical pump X-ray probe experiment. The time and space evolution of antiferromagnetic order in a vibrationally excited complex oxide heterostructure is recovered from time-resolved measurements of a resonant soft X-ray diffraction peak. Midinfrared excitation of the substrate is shown to lead to a demagnetization front that propagates at a velocity exceeding the speed of sound, a critical observation for the understanding of driven phase transitions in complex condensed matter.

Effect of Cis-Backbone on Optical Properties of Polyphenylacetylene

By controlling the temperature of chemical reaction, we synthesized four polyphenylacetylene samples, in which the percentages of cis configurations were determined to be 65, 75, 85 and 100%, respectively. Ultraviolet-visible and fluorescence studies show that the cis-configured backbones have posed significant effects on the optical absorption and fluorescence of the polyphenylacetylenes. Upon the 325-nm excitation, the dilute solutions of these cis-polyphenylacetylenes give off weak fluorescence with their peak located at about 390 nm, but the concentrated solutions of the polymer can give off strong orange-red fluorescence with their peak located at about 600 nm. With Hückel tight binding theory, both the E-k dispersion relations and the density of states were calculated for cis-polyphenylacetylene. Our results suggest that the blue photoluminescence of polyacetylenes origins from the backbone enhanced -conjugation of the phenyl chromophors in the polymer, and that intermolecular interactions can occur in the excited complex of the polymer.