Luminescent organic radicals toward breakthrough of organic optoelectronics

Conventional closed-shell organic fluorescent emitters have two spin configurations, that is, singlet and triplet states. The singlet state is spin-allowed for radiative decay, while the spin-forbidden triplet state is dark; thus most triplet excitons are hard to produce luminescence. In comparison with closed-shell organic emitters, luminescent organic radicals are a kind of open-shell molecules, which only show a spin-allowed doublet state, resulting in 100% exciton utilization in theory. Hence, luminescent organic radicals have attracted great attention in the field of organic optoelectronics. In this chapter, we would introduce the luminescent mechanism, key parameters, materials types, and the multifarious applications of luminescent organic radicals in detail. Fundamental design principles, the inherent correlation between the molecular structures and optoelectronic features as well as an overview of the recent development in varied luminescent organic radicals with a particular emphasis on their different types of stable triarylmethyl and nitrogen radicals, photo-induced and mechanochromic radicals are presented. The successful breakthrough in the technical and theoretical challenges of designing highly efficient luminescent organic radicals may pave the way for shaping the future of organic electronics.