Site-selective measurement of coupled spin pairs in an organic semiconductor

SL Bayliss, Leah Weiss, A Mitioglu, K Galkowski, Z Yang, K Yunusova, A Surrente, KJ Thorley, J Behrends, R Bittl, JE Anthony, Akshay Rao (+7 others)
From organic electronics to biological systems, understanding the role of intermolecular interactions between spin pairs is a key challenge. Here we show how such pairs can be selectively addressed with combined spin and optical sensitivity. We demonstrate this for bound pairs of spin-triplet excitations formed by singlet fission, with direct applicability across a wide range of synthetic and biological systems. We show that the site-sensitivity of exchange coupling allows distinct triplet
more » ... to be resonantly addressed at different magnetic fields, tuning them between optically bright singlet (S = 0) and dark triplet, quintet (S = 1, 2) configurations: this induces narrow holes in a broad optical emission spectrum, uncovering exchange-specific luminescence. Using fields up to 60 T, we identify three distinct triplet-pair sites, with exchange couplings varying over an order of magnitude (0.3-5 meV), each with its own luminescence spectrum, coexisting in a single material. Our results reveal how site-selectivity can be achieved for organic spin pairs in a broad range of systems.
doi:10.17863/cam.25592 fatcat:dyc6avljybh5blzd3xzbtfbrwa