We were interested in understanding the difference in thermally activated delayed fluorescence (TADF) between two closely related donor-acceptor-donor systems using either an anthraquinone and benzodithiophenedione acceptor units, respectively. The first one was known to be an effective TADF emitter [JACS2014, 136, 18070] whereas the second one had significantly lower quantum yield for TADF [PCCP2019, 21, 10580].
Rather than just presenting energies, it was the purpose of this paper to shed detailed insight into the wavefunctions involved. Notable differences in the wavefunctions and charge-transfer character were found between the two molecules. Even more striking differences existed between different computational methods.
After evaluating electronic structure methods, we presented geometry optimisations in solution, highlighting the importance of symmetry breaking for producing an emissive lowest singlet state. The role of different solvation models was discussed as well.
Molecules interacting with light undergo fascinating photodynamical processes inducing chemical reactions, transferring energy, or converting electronic energy into heat. These processes can be elucidated computationally via photodynamics simulations. However, these can be computationally highly demanding making the simulation of many interesting processes unfeasible.
A possible route to overcome this problem and to allow for efficient dynamics simulations is by combining vibronic coupling models (describing the energies) with the surface hopping method (describing the dynamics). We have introduced this idea two years ago [PCCP, 2019, 21, 57]. A new paper in Accounts of Chemical Research summarises developments since then: Surface Hopping Dynamics on Vibronic Coupling ModelsAcc. Chem. Res.2021, 52, 3760.
A recent study led by F. Glöcklhofer from Imperial College, London, investigates the properties of substituted conjugated macrocycles. The first (pre-review) version just appeared on Open Research Europe:
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.
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.
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.