Electron transfer from singlet fission dimers: possibilities and limitations

Photocatalytic production of H₂ or hydrocarbons requires multiple electrons, and therefore the absorption of multiple photons and accumulation of photoexcited charges. Alternatively, multiexciton generation (MEG) could loosen this requirement. Despite extensive studies of singlet fission (SF), an MEG process, for solar cells, its use in photocatalysis has only recently been demonstrated. Herein, we present a detailed investigation of electron transfer (ET) from two tetracene based SF dimers, on time scales spanning the initial singlet excited state-triplet pair (TT) equilibrium and the longer-lived free triplet states. We find that the TT state behaves similarly to the singlet and thus can be used to increase the lifetime of singlet reactivity. We also show that in these covalently linked SF dimers, where TT recombines to form one free triplet, achieving more than 100% ET is challenging. Together with these findings and the input from theoretical calculations, we discuss the possibilities and limitations of ET from these dimers. By highlighting strategies to mitigate detrimental TT recombination pathways, these insights provide design principles for next-generation SF chromophores tailored for solar energy conversion and photoredox catalysis.