The electronic structure and dynamics of the excited triplet state of octaethylaluminum(III)-porphyrin investigated with advanced EPR methods

Angelo Carella; Susanna Ciuti; Haakon T A Wiedemann; Christopher W M Kay; Arthur van der Est; Donatella Carbonera; Antonio Barbon; Prashanth K Poddutoori; Marilena Di Valentin

doi:10.1016/j.jmr.2023.107515

The electronic structure and dynamics of the excited triplet state of octaethylaluminum(III)-porphyrin investigated with advanced EPR methods

J Magn Reson. 2023 Aug:353:107515. doi: 10.1016/j.jmr.2023.107515. Epub 2023 Jun 22.

Authors

Angelo Carella¹, Susanna Ciuti¹, Haakon T A Wiedemann², Christopher W M Kay³, Arthur van der Est⁴, Donatella Carbonera¹, Antonio Barbon⁵, Prashanth K Poddutoori⁶, Marilena Di Valentin⁷

Affiliations

¹ Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy.
² Department of Chemistry, Saarland University, Campus B 2.2, 66123 Saarbrücken, Germany.
³ Department of Chemistry, Saarland University, Campus B 2.2, 66123 Saarbrücken, Germany; London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, UK.
⁴ Department of Chemistry, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario, Canada.
⁵ Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy. Electronic address: antonio.barbon@unipd.it.
⁶ Department of Chemistry & Biochemistry, University of Minnesota Duluth, 1038 University Drive, Duluth, MN 55812, USA.
⁷ Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy. Electronic address: marilena.divalentin@unipd.it.

PMID: 37364432
DOI: 10.1016/j.jmr.2023.107515

Abstract

The photoexcited triplet state of octaethylaluminum(III)-porphyrin (AlOEP) was investigated by time-resolved Electron Paramagnetic Resonance, Electron Nuclear Double Resonance and Electron Spin Echo Envelope Modulation in an organic glass at 10 and 80 K. This main group element porphyrin is unusual because the metal has a small ionic radius and is six-coordinate with axial covalent and coordination bonds. It is not known whether triplet state dynamics influence its magnetic resonance properties as has been observed for some transition metal porphyrins. Together with density functional theory modelling, the magnetic resonance data of AlOEP allow the temperature dependence of the zero-field splitting (ZFS) parameters, D and E, and the proton A_ZZ hyperfine coupling (hfc) tensor components of the methine protons, in the zero-field splitting frame to be determined. The results provide evidence that the ZFS, hfc and spin-lattice relaxation are indeed influenced by the presence of a dynamic process that is discussed in terms of Jahn-Teller dynamic effects. Thus, these effects should be taken into account when interpreting EPR data from larger complexes containing AlOEP.