Delayed fluorescence

Patrick’s first paper as first author just appeared in PCCP: The role of excited-state character, structural relaxation, and symmetry breaking in enabling delayed fluorescence activity in push-pull chromophores. Well done Patrick!

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 [JACS 2014, 136, 18070] whereas the second one had significantly lower quantum yield for TADF [PCCP 2019, 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.

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.

3D visualisation of chemical shielding tensors

Aromaticity is a ubiquitous yet elusive concept in chemistry and chemists have spent a great deal of effort on developing methods to quantify and visualise aromaticity. One particularly popular method is the nucleus independent shift (NICS), which can be seen as a virtual NMR experiment carried out within a conjugated ring to evaluate the enhanced chemical shielding induced by aromatic ring-currents. Strikingly NICS also allows to quantify antiaromaticity, as this induces a net deshielding effect within the ring. NICS provides a powerful quantitative aromaticity criterion but the main challenge for its graphical representation is that the chemical shielding is a 3×3 tensor, which is difficult to visualise with the existing methods.

Therefore, we have developed a new method for the visualisation of chemical shielding tensors (VIST), which provides a local representation of the shielding tensor along with the molecular structure. The method, thus, allows to probe local aromaticity along with the underlying anisotropy of the shielding. The method is described in the preprint “3D Visualisation of chemical shielding tensors to elucidate aromaticity and antiaromaticity” available on ChemRxiv.

Within the preprent we exemplify the main concepts in the benzene and phenanthrene molecules and continue by studying

The underlying code is scheduled to be released within the next version of the TheoDORE wavefunction analysis package.

Release of TheoDORE 2.3.

Version 2.3 of the TheoDORE wavefunction analysis package is available. Download the current version below.

New features of TheoDORE 2.3:

  • Compute (unpaired) densities using orbkit
  • Fix for theo_test.bash
  • Fix for ORCA osc. strengths
  • Old RASSI interface removed (was not working properly)
TheoDORE – Download

Download the newest release of the TheoDORE wavefunction analysis program – TheoDORE 2.4 (22 April 2021)

Size: 12 MB
Version: 2.4

Full release notes:

Continue reading

Release of TheoDORE 2.2

Version 2.2 of the TheoDORE wavefunction analysis package is available. Download the current version below.

New features of TheoDORE 2.2:

  • Support for spin-unrestricted calculations (by Sebastian Mai) – currently only tested for ORCA
  • Substituent-induced electron localization (SIEL) as described in Chem. Sci. 2020, 10.1039/D0SC01684E
TheoDORE – Download

Download the newest release of the TheoDORE wavefunction analysis program – TheoDORE 2.4 (22 April 2021)

Size: 12 MB
Version: 2.4

Full release notes:

Continue reading

Directional excitations in photosensitisers

Characterising excited states in transition metal complexes by looking at pictures of orbitals can be a tedious task. Even more, it is hard to eliminate personal in the process and produce quantitative results. In a study led by Pedro Sánchez-Murcia from the University of Vienna, we have taken a closer look at this problem in the case of various substituted complexes deriving from the archetype Ru(bpy)3 with the aim of quantifying how different substituents influence the localisation of the excited electron. The result is presented in the article “Orbital-free photophysical descriptors to predict directional excitations in metal-based photosensitizers,” which just appeared in Chemical Science.

Paper: TheoDORE electronic structure analysis

The paper TheoDORE: A toolbox for a detailed and automated analysis of electronic excited state computations just appeared in the Journal of Chemical Physics in a special issue on Electronic Structure Software. Please, take a look if you are interested in speeding up the analysis of your excited-state computations. If you are already a user of TheoDORE, you can learn about the latest developments and obtain a compact overview of the underlying theory.

Paper: Nitrogen splitting

Splitting N2 is a challenging undertaking due to the strong triple bond holding the two nitrogen atoms together. Traditionally, this task is achieved via the Haber-Bosch process but recently interest has shifted to the possibilities of nitrogen splitting via homogeneous catalysis. Computations on the dinuclear transition metal complexes involved can be performed thanks to modern computational hardware and appropriate computer codes. However, the analysis of the excited states involved can become a significant challenge due to the large number of states and difficulties in assigning their character unambiguously. To tackle this problem, we have recently devised a strategy for a detailed analysis of the electronic wavefunctions of the states contributing to the reactive process. The associated paper, led by S. Rupp and V. Krewald from TU Darmstadt, just appeared in the European Journal of Inorganic Chemistry: Multi‐tier electronic structure analysis of Sita’s Mo and W complexes capable of thermal or photochemical N2 splitting.