Molecules present a versatile platform for quantum information science1,2 and are candidates for sensing and computation applications3,4. Robust spin-optical interfaces are key to harnessing the quantum resources of materials5. To date, carbon-based candidates have been non-luminescent6,7, which prevents optical readout via emission. Here we report organic molecules showing both efficient luminescence and near-unity generation yield of excited states with spin multiplicity S > 1. This was achieved by designing an energy resonance between emissive doublet and triplet levels, here on covalently coupled tris(2,4,6-trichlorophenyl) methyl-carbazole radicals and anthracene. We observed that the doublet photoexcitation delocalized onto the linked acene within a few picoseconds and subsequently evolved to a pure high-spin state (quartet for monoradical, quintet for biradical) of mixed radical–triplet character near 1.8 eV. These high-spin states are coherently addressable with microwaves even at 295 K, with optical readout enabled by reverse intersystem crossing to emissive states. Furthermore, for the biradical, on return to the ground state the previously uncorrelated radical spins either side of the anthracene shows strong spin correlation. Our approach simultaneously supports a high efficiency of initialization, spin manipulations and light-based readout at room temperature. The integration of luminescence and high-spin states creates an organic materials platform for emerging quantum technologies.
Neutral π-radicals have potential for use as light emitters in optoelectronic devices due to the absence of energetically low-lying non-emissive states. Here, we report a defect-free synthetic methodology via mesityl substitution at the para-positions of tris(2,4,6-trichlorophenyl)methyl radical. These materials reveal a number of novel optoelectronic properties. Firstly, mesityl substituted radicals show strongly enhanced photoluminescence arising from symmetry breaking in the excited state. Secondly, photoexcitation of thin films of 8 wt% radical in 4,4’-bis(carbazol-9-yl)-1,1’-biphenyl host matrix produces long lived (in the order of microseconds) intermolecular charge transfer states, following hole transfer to the host, that can show unexpectedly efficient red-shifted emission. Thirdly, covalent attachment of carbazole into the mesitylated radical gives very high photoluminescence yield of 93% in 4,4’-bis(carbazol-9-yl)-1,1’-biphenyl films and light-emitting diodes with maximum external quantum efficiency of 28% at a wavelength of 689 nm. Fourthly, a main-chain copolymer of the mesitylated radical and 9,9-dioctyl-9H-fluorene shows red-shifted emission beyond 800 nm.
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