Abstract

Understanding excited states of functional molecules beyond the molecular orbital picture

Felix Plasser F.Plasser@lboro.ac.uk

Department of Chemistry, Loughborough University, LE11 3TU, United Kingdom.

Excited electronic states are central to many areas of modern science encompassing crucial research themes such as lighting, photovoltaics, and chemical synthesis. Ever more intricate chromophores are synthesised to achieve the desired photophysical functions while modern computational methods can simulate ever more complex excited state phenomena accurately. The molecular structures are usually linked to the photophysical properties via a qualitative discussion of the energies and shapes of the frontier molecular orbitals (MO). Whereas this approach and the underlying MO picture is remarkably powerful for simple molecules, it fails for crucial modern applications. Firstly, the static MO picture is unable to describe exciton correlation in conjugated polymers.[1] Secondly, the singlet-triplet splitting, which is crucial for applications in delayed fluorescence and singlet fission, cannot be understood from the MO energies at all.[2] Thirdly, it is often desirable to move from a qualitative discussion of orbital shapes to a quantitative discussion that can even capture subtle trends following, e.g., as a consequence of chemical substitution.

It is the purpose of this talk to show how the design process of functional molecules can be supported by theory not only via a reproduction of experimentally measured quantities but also through a detailed description of the underlying electronic wavefunctions. We will start by illustrating how charge-transfer character can be quantitatively assessed for the excited states of push-pull systems to study the influence of chemical substitution and solvation.[3] We will continue by illustrating how charge-transfer character can be linked to the measured two-photon absorption strength.[4] Next, it will be shown in a target molecule for delayed fluorescence how a detailed consideration of all the excited states involved, rather than only a discussion of the frontier MOs, is needed to understand the photophysical behaviour.[5] Finally, it will be discussed how correlation effects in the excited states of conjugated polymers can be quantified and visualised.[1,6]

References

1. S. A. Mewes, J.-M. Mewes, A. Dreuw and F. Plasser, Phys. Chem. Chem. Phys., 2016, 18, 2548–2563.
2. P. Kimber and F. Plasser, submitted, , DOI:10.26434/chemrxiv.11559819.
3. P. Kautny, F. Glöcklhofer, T. Kader, J.-M. Mewes, B. Stöger, J. Fröhlich, D. Lumpi and F. Plasser, Phys. Chem. Chem. Phys., 2017, 19, 18055–18067.
4. F. Glöcklhofer, A. Rosspeintner, P. Pasitsuparoad, S. Eder, J. Fröhlich, G. Angulo, E. Vauthey and F. Plasser, Mol. Syst. Des. Eng., 2019, 4, 951–961.
5. S. Montanaro, A. J. Gillett, S. Feldmann, E. W. Evans, F. Plasser, R. H. Friend and I. A. Wright, Phys. Chem. Chem. Phys., 2019, 21, 10580–10586.
6. F. Plasser, ChemPhotoChem, 2019, 3, 702–706.

Biography

Felix Plasser was born and raised in Vienna, Austria. In 2012 he earned his Ph.D. at the University of Vienna in the group of Hans Lischka working on the photophysics of interacting nucleobases. In 2013 he moved to Heidelberg to spend two years at Ruprecht-Karls University in the group of Andreas Dreuw to study phosphorescent iridium complexes. He returned to Vienna in 2015 to join the group of Leticia González working on a variety of photoinduced molecular processes. In February 2018, he was appointed to a Lecturer position at the University of Loughborough, UK. Felix Plasser has worked on a wide range of topics in computational photochemistry regarding questions of biological and technological interest. His expertise lies in high-level electronic structure computations combined with detailed wavefunction analysis protocols and dynamics simulations. He has designed and developed the excited-state wavefunction analysis package TheoDORE. Furthermore, he has made significant contributions to the electronic structure packages COLUMBUS, Q-Chem, and MOLCAS as well as the nonadiabatic dynamics packages Newton-X and SHARC. To this date, he has published 61 peer-reviewed articles.