Stable nitrogen-centered radicals with anti-Kasha emission

Abstract

Luminescent radicals with anti-Kasha emission have the potential to extend the spectral range of luminescent radicals to the short wavelength region. Although these radicals are promising, they remain rare and often unstable. In this study, we designed and synthesized two nitrogen-centered radicals with anti-Kasha ultraviolet emission that demonstrate excellent stability in an ambient atmosphere. Their emissions are around 355 nm with a maximum photoluminescence quantum yield (PLQY) of 7.7% in cyclohexane solution at room temperature. Unlike peripheral fluorescence substituent chromophores, the emissions of both radicals show an obvious solvatochromic effect. Experiments and calculation results demonstrate the involvement of the radical moiety in the emission process. This study provides a convenient method to obtain luminescent radicals with anti-Kasha emission.