Zvaná přednáška – Henrik Ottosson

The use of excited state aromaticity and antiaromaticity (ESA & ESAA) to rationalize excited state properties and processes has grown rapidly in recent years.^1,2 There is a plethora of possible applications of the ESA & ESAA concepts, however, there are also limitations, complications and pitfalls. Excited state aromaticity is often taken as synonymous to Baird-aromaticity,³ i.e., aromaticity of 4nπ-electron cycles in their lowest π,π* triplet states. Yet, instead of Baird-aromatic, some molecules are Hückel-aromatic or Hückel-Baird hybrid aromatic in their lowest excited states, while others are excited at different functional moieties than at the conjugated rings.^4-6 Singlet excited states are more numerous than the triplet states, and they are often more intricate computationally. States with different numbers of πα- and πβ-electrons (e.g., n,π* states of some heteroaromatics) may also appear as aromatic according to computations.⁷ Finally, there are differences between various computational methods and aromaticity descriptors. Thus, for the proper and efficient utilization of the ESA & ESAA concepts in various applications there are a number of fundamental aspects that need to be explored. In the talk I will give a brief overview of various complications, yet also show how the concepts can be of potential use in areas ranging from astrochemistry via organic photoreactivity and photophysics to design of new chromophores for tentative use in singlet fission photovoltaics.

1. L. J. Karas, J. I. Wu, Nat. Chem. 14, 723 (2022).
2. J. Yan, T. Slanina, J. Bergman, H. Ottosson, Chem. Eur. J. 29, e202203748 (2023).
3. N. C. Baird, J. Am. Chem. Soc. 94, 4941 (1972).
4. W. Zeng, O. El Bakouri, D. Szczepanik, H. Bronstein, H. Ottosson, Chem. Sci. 12, 6159 (2021).
5. K. Jorner, F. Feixas, R. Ayub, R. Lindh, M. Solà, H. Ottosson, Chem. Eur. J. 22, 2793 (2016).
6. S. Escayola, C. Tonellé, E. Matito, A. Poater, H. Ottosson, M. Solà, D. Casanova, Angew. Chem. Int. Ed. 60, 10255 (2021).
7. N. Proos Vedin, S. Escayola, S. Radenkovic, M. Solà, H. Ottosson, ChemRxiv, DOI 10.26434/chemrxiv-2023-jx5I5 (2023).