Oxygen Harvesting from Carbon Dioxide

A recent study, led by Benjamin Buckley and Felipe Iza from Loughborough University, presents an innovative use of carbon dioxide. Using a plasma, carbon dioxide is turned into a source of atomic oxygen, which is used as a waste-free oxidant for the oxidation of alkenes to epoxides. The study, a collaborative work between engineering, synthesis and computation, just appeared in Chemical Science: Oxygen Harvesting from Carbon Dioxide: Simultaneous Epoxidation and CO Formation.

Excited-state symmetry breaking

A recent study led by Zoltan Szakacs and Eric Vauthey from the University of Geneva explores excited-state symmetry breaking in donor-acceptor-donor systems. The associated paper just appeared in PCCP: Excited-state symmetry breaking in 9,10-dicyanoanthracene-based quadrupolar molecules: the effect of donor-acceptor branch length

The main idea behind this work is to use symmetry-selection rules and the associated forbidden transitions to probe how inversion symmetry is broken during the photodynamics. See [JPCL 2021, 12, 4067] for an initial discussion of the idea.

Baird aromaticity

Can you sort these molecules according to increasing triplet excitation energies?

Some basic considerations might suggest that energies go down as the size of the molecule increases. But this is incorrect. The decisive feature of these molecules is their ground-state antiaromaticity along with their potential for excited-state Baird aromaticity. Triplet excitation energies increase sharply going from 1 (0.1 eV) via 2 (1.9 eV) to 3 (2.6 eV). This can be understood in the sense that antiaromaticity is blurred as the molecule becomes larger.

More strikingly, when going from 3 to 4 or 5, the energy drops again dramatically down to 1.0 eV. This effect is explained following Ayub et al. by the simple fact that these molecule possess resonance structures with simultaneous quartets and sextets.

In a recent paper, Exploitation of Baird Aromaticity and Clar’s Rule for Tuning the Triplet Energies of Polycyclic Aromatic Hydrocarbons, we investigate these phenomena in detail using a recently developed method for the visualisation of chemical shielding tensors (VIST) along with an analysis of natural transition orbitals. In addition, a model for rationalising the dia- and paramagnetic shielding effects observed in (anti)aromatic systems is presented.

See also TCA, 2020, 139, 113 on a discussion of related bipenylene derivatives.

Highly sensitive Al measurements

A new study led by J. Lachner from the Helmholtz-Zentrum Dresden describes a method for detecting 26Al via Ion-Laser Interaction Mass Spectrometry using a particle accelerator.

Quantum chemical calculations highlight the different energetics of 26MgO and 26AlO, which are separated with high specificity despite being isobars.

The article just appeared in the International Journal of Mass Spectrometry: Highly sensitive 26Al measurements by Ion-Laser-InterAction Mass Spectrometry

Elucidating the Electronic Structure of TADF emitters

Thermally activated delayed fluoresence (TADF) is an exciting modern research area aimed at producing new OLED emitters. From a theoretical perspective TADF is particularly fascinating because it requires a detailed understanding of the different terms that contribute to the singlet and triplet excitation energies of the molecules studied. In a recent study led by Yihan Shao from the University of Oklahoma, we investigated a recently developed TADF emitter and showed how a combination of different wavefunction analysis tools provides deep insight into its excited-state properties. The paper just appeared in J. Phys. Chem. Lett.: Elucidating the Electronic Structure of a Delayed Fluorescence Emitter via Orbital Interactions, Excitation Energy Components, Charge-Transfer Numbers, and Vibrational Reorganization Energies.

Exciton-exciton annihilation

A new study led by C. Heshmatpour and J. Hauer from TU München studies exciton-exciton annihilation in a squaraine trimer. The experiment exploits 5th-order optical spectroscopy to study the evolution of the trimer after two-photon excitation into its bi-exciton state. Quantum chemistry computations performed by M. Menger, now located at Groningen, provide the required parameters to model the experimental signals within a Frenkel exciton model. The associated article Annihilation Dynamics of Molecular Excitons Measured at a Single Perturbative Excitation Energy just appeared in J. Phys. Chem. Lett.

Photoredox catalysis

A study led by O. Koleoso and M. C. Kimber at Loughborough University explored a new route of synthesising conjugated N-acyliminium compounds. The article entitled “A complementary approach to conjugated N-acyliminium formation through photoredox-catalyzed intermolecular radical addition to allenamides and allencarbamates” just appeared in a thematic issue on Advances on photoredox catalysis in the Beilstein Journal of Organic Chemistry.