Multi-Redox Systems Based on Boron Subphthalocyanines

Abstract

Boron subphthalocyanines (SubPcs) are cone-shaped molecules comprised of three isoindole units bridged by aza-linkages and with a central boron atom containing an axial substituent. SubPcs are strong chromophores, but also redox-active molecules undergoing both reversible oxidation and reduction. By linking together SubPc units, multi-redox systems emerge that can take several redox states. Here I will show a variety of such scaffolds where SubPc units are either linked together at axial or peripheral positions by various acetylenic bridges. Bridges include various acyclic oligo(en)ynes and cyclic radiaannulenes containing both endo- and exocyclic carbon-carbon double bonds.1 The length and nature of the bridging unit determines whether the SubPc units are independent redox centers or whether there is communication between the units. Moreover, I will present structures were isoindole units of SubPc are replaced by thienopyrrole units2 as well as structures where the SubPc is linked to another redox-active unit, such as a triangulene.3 Experimentally determined redox potentials were compared to theoretically calculated ones, allowing us to move forward a reliable theoretical method for predicting redox properties. References a) H. Gotfredsen, L. Broløs, T. Holmstrøm, J. Sørensen, A. V. Mu ñ oz, M. D. Kilde, A. B. Skov, M. Santella, O. Hammerich, M. B. Nielsen, Org. Biomol. Chem. 2017, 15, 9809-9823; b) L. Broløs, M. D. Kilde, M. B. Nielsen, Org. Biomol. Chem. 2020, 18, 6077-6085; c) A. U. Petersen, M. G. Rasmussen, M. C. H. Thomsen, A. Ceuninck, M. B. Nielsen, Arkivoc 2020, vii, 145-157; d) H. Lissau, C. L. Andersen, F. E. Storm, M. Santella, O. Hammerich, T. Hansen, K. V. Mikkelsen, M. B. Nielsen, Chem. Commun. 2018, 54, 2763-2766. H. Gotfredsen, F. E. Storm, A. V. Muñoz, M. Santella, A. Kadziola, O. Hammerich, K. V. Mikkelsen, M. B. Nielsen, Chem. Eur. J. 2017, 23, 16194-16198. M. G. Rasmussen, M. F. Jespersen, O. Blacque, K. V. Mikkelsen, M. Juríček, M. B. Nielsen, Energy Sci. Eng. 2022, 10, 1752-1762. Figure 1