High-Multiplicity States in Luminescent Organic Radicals

Organic luminescent radicals present a new and exciting platform for exploring molecular functionalities at the interface of their unique optical and spin properties.[1] Near-unity internal quantum efficiency for red emission was demonstrated for donor-acceptor structures based on the tris(2,4,6-trichlorophenyl)methyl (TTM) radical.[2] This opens these materials towards applications in technologies ranging from organic light-emitting diodes and photovoltaics with eliminated triplet losses, to photomagnetic devices and molecular-scale information transfer.<br/><br/>Here we present a new family of molecules based on the TTM radical motif which contain high-multiplicity states in their emission mechanism. By combining light-induced EPR with ultrafast transient absorption and temperature-dependent transient luminescence spectroscopy we find a mechanism that uniquely supports both a high emission yield and a high yield of generation of the high-spin species. This is enabled by very low activation barriers between excited states, which arises from energy level matching in our molecular design. Pulsed EPR spectroscopy allows us to characterize the potential of our system for future quantum information science applications.<br/><br/>References<br/>[1] Teki, Y., Chem. Eur. J. 26, 980 (2020)<br/>[2] Ai, X., Evans, E.W., Dong, S. et al., Nature 563, 536–540 (2018)