The effect of radical-radical distance on the spin-properties of light-emitting triarylmethyl-derived diradicals

Abstract

Triarylmethyl radicals are among the most prominent stable organic open-shell emitters, combining strong photoluminescence with well-defined spin states. Extending these systems to bridged diradicals introduces spin-spin interactions that are highly sensitive to the radical-radical distance. In this contribution, I will discuss a systematic series of triarylmethyl-derived diradicals, in which the inter-radical spacing is precisely controlled through tailored molecular bridges. Magnetic and spectroscopic investigations reveal a distance-dependent evolution of the ground state multiplicity, transitioning from weakly coupled doublet behavior to a more strongly coupled triplet ground state at short separations. This effect could enable spin-selective emission pathways. Notably, the emergence of a stable triplet ground state opens the prospect of realizing purely organic molecular color centers. Such systems could provide a quantum sensor platform for the detection of minute magnetic fields under ambient conditions.