Coulombic Control of Charge Transfer in Radicals with Quartet Recycling Luminescence

Excitonsinorganicmaterialsareemergingasanattractiveplatformfortunablequantum technologies. Structures with near-degenerate doublet and triplet excitations in linked trityl radical, acene and carbazole units can host quartet states. These high spin states canbecoherentlymanipulated,andlaterdecayradiativelyviatheradicaldoublettransi- tion. However,thisrequirescontrollingthedeexcitationpathwaysofallmetastablestates. Here we establish design rules for efficient quartet generation and recycling to lumines- cence, using different connection arrangements of the molecular units. We discover that electronic coupling strength between these units dictates quartet formation and delayed emission yields, particularly through a Coulombically tuned acene-radical charge trans- fer state. This state acts as a source of non-radiative decay when acene-radical separa- tionissmall,butfacilitatesreversibledoublet-quartetinterconversionwhenacene-radical separation is large. Using these rules we report a material with 55% luminescence yield, where 94% of emitting excitons are recycled from the quartet with a 1.0 µs lifetime. This revealsthecentralroleofmolecular topology in luminescentquantum materials.