Perylenediimide--metal ion dyads for photo-induced electron transfer

A novel perylene diimide incorporating a tetradentate ligand was synthesized and the photophysical properties of its Cu(+), Cu(2+), and Fe(3+) complexes were investigated by fluorescence experiments.     

The influence of creep on cake solid volume fraction during filtration of core–shell particles

The solid volume fraction vs. pressure relationship used in conventional filtration models is determined by measuring the cake solid volume fraction after consolidation. However, some cakes creep during consolidation, so the solid volume fraction increases at constant pressure. Thus, the conventional method for determining the solid volume fraction vs. pressure relationship cannot be used for materials with significant creep. Cake creep has been observed when core–shell particles with hard poly(styrene) cores and water-swollen poly(acrylic acid) shells are filtered. The Terzaghi–Voigt combined model has been fitted to data obtained during consolidation to determine the transition point where creep begins to be dominating for cake compression. The solid volume fraction increases by 17–35% after the transition point, particularly in the case of particles with thick poly(acrylic acid) shells and thus a high initial water content. Hence, the solid volume fraction can increase significantly during cake creep and if the solid volume fraction vs. pressure relationship that controls the initial stages of filtration is to be determined then the filtration experiments must be stopped before creep dominates. This can be done by measuring the liquid pressure at the interface between piston and sample, and stop the experiment when the liquid pressure is lower than 5% of the applied pressure.     

Controlling Two‐Step Multimode Switching of Dihydroazulene Photoswitches

We present the synthesis and switching studies of systems with two photochromic dihydroazulene (DHA) units connected by a phenylene bridge at either para or meta positions, which correspond to a linear or cross‐conjugated pathway between the photochromes. According to UV/Vis absorption and NMR spectroscopic measurements, the meta‐phenylene‐bridged DHA–DHA exhibited sequential light‐induced ring openings of the two DHA units to their corresponding vinylheptafulvenes (VHFs). Initially, the VHF–DHA species was generated, and, ultimately, after continued irradiation, the VHF–VHF species. Studies in different solvents and quantum chemical calculations indicate that the excitation of DHA–VHF is no longer a local DHA excitation but a charge‐transfer transition that involves the neighboring VHF unit. For the linearly conjugated para‐phenylene‐bridged dimer, electronic communication between the two units is so efficient that the photoactivity is reduced for both the DHA–DHA and DHA–VHF species, and DHA–DHA, DHA–VHF, and VHF–VHF were all present during irradiation. In all, by changing the bridging unit, we can control the degree of stepwise photoswitching.     

Aromaticity‐Controlled Energy Storage Capacity of the Dihydroazulene‐Vinylheptafulvene Photochromic System

Photochemical conversion of molecules into high‐energy isomers that, after a stimulus, return to the original isomer presents a closed‐cycle of light‐harvesting, energy storage, and release. One challenge is to achieve a sufficiently high energy storage capacity. Here, we present efforts to tune the dihydroazulene/vinylheptafulvene (DHA/VHF) couple through loss/gain of aromaticity. Two derivatives were prepared, one with aromatic stabilization of DHA and the second of VHF. The consequences for the switching properties were elucidated. For the first type, sigmatropic rearrangements of DHA occurred upon irradiation. Formation of a VHF complex could be induced by a Lewis acid, but addition of H₂O resulted in immediate regeneration of DHA. For the second type, the VHF was too stable to convert into DHA. Calculations support the results and provide new targets. We predict that by removing one of the two CN groups at C‐1 of the aromatic DHA, the heat storage capacity will be further increased, as will the life‐time of the VHF. Calculations also reveal that a CN group at the fulvene ring retards the back‐reaction, and we show synthetically that it can be introduced regioselectively.     

Molecular junctions based on SAMs of cruciform oligo(phenylene ethynylene)s

Cruciform oligo(phenylene ethynylene)s (OPEs) with an extended tetrathiafulvalene (TTF) donor moiety (OPE5-TTF and OPE3-TTF) and their simple analogues (OPE5-S and OPE3) without conjugated substituents were used to form high-quality self-assembled monolayers (SAMs) on ultraflat gold substrates. Molecular junctions based on these SAMs were investigated using conducting-probe atomic force microscopy (CP-AFM). The TTF substituent changes the molecular orbital energy levels and decreases the HOMO-LUMO energy gap, resulting in a 9-fold increase in conductance for both TTF cruciform OPEs compared to the unsubstituted analogues. The difference in electrical transport properties of the SAMs was reproduced by the theoretical transport calculations for the single molecules.     

Watching Nanoparticles Form: An In Situ (Small‐/Wide‐Angle X‐ray Scattering/Total Scattering) Study of the Growth of Yttria‐Stabilised Zirconia in Supercritical Fluids

Understanding nanoparticle‐formation reactions requires multi‐technique in situ characterisation, since no single characterisation technique provides adequate information. Here, the first combined small‐angle X‐ray scattering (SAXS)/wide‐angle X‐ray scattering (WAXS)/total‐scattering study of nanoparticle formation is presented. We report on the formation and growth of yttria‐stabilised zirconia (YSZ) under the extreme conditions of supercritical methanol for particles with Y₂O₃ equivalent molar fractions of 0, 4, 8, 12 and 25 %. Simultaneous in situ SAXS and WAXS reveals a quick formation (seconds) of sub‐nanometre amorphous material forming larger agglomerates with subsequent slow crystallisation (minutes) into nanocrystallites. The amount of yttria dopant is shown to strongly affect the crystallite size and unit‐cell dimensions. At yttria‐doping levels larger than 8 %, which is known to be the stoichiometry with maximum ionic conductivity, the strain on the crystal lattice is significantly increased. Time‐resolved nanoparticle size distributions are calculated based on whole‐powder‐pattern modelling of the WAXS data, which reveals that concurrent with increasing average particle sizes, a broadening of the particle‐size distributions occur. In situ total scattering provides structural insight into the sub‐nanometre amorphous phase prior to crystallite growth, and the data reveal an atomic rearrangement from six‐coordinated zirconium atoms in the initial amorphous clusters to eight‐coordinated zirconia atoms in stable crystallites. Representative samples prepared ex situ and investigated by transmission electron microscopy confirm a transformation from an amorphous material to crystalline nanoparticles upon increased synthesis duration.