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Excited-State Dynamics of Non-Luminecent and Luminescent π-Radicals.

Recently, the potential use of organic π-radicals (unpaired π-spin systems delocalized through π-conjugation) and related spin systems has been expanded to modern technological applications. The unique excited-state dynamics of organic π-radicals can be useful to improve the stability of photochemically unstable organic compounds, make the polarization transfer applicable to information technology, and achieve effective up-conversion of interest for luminescence bioimaging, among others. Furthermore, highly luminescent and stable π-radicals have been recently reported, which are especially interesting for application in organic light-emitting devices due to their potential to provide an internal quantum efficiency of 100%. Thus, the excited-state nature of stable π-radicals as well as the control of their excited-state spin dynamics are emerging topics both in fundamental science and related technological applications. In this minireview, we focus on the excited-state dynamics of both photostable non(weakly)-luminescent and luminescent π-radicals, which are located opposite to each other. In particular, we cover the following topics: (1) effective generation of high-spin photoexcited states and control of the excited-state dynamics using non-luminescent π-radicals, (2) unique excited-state dynamics of luminescent π-radicals and radical excimers, and (3) applications utilizing excited-state dynamics of π-radicals.