Stable Fluorenyl Radicals Showing Tunable Doublet Emission

Neutral organic radicals with intrinsic spin-allowed doublet emission have emerged as a promising class of luminescent materials, garnering significant research interest. However, the development of stable luminescent radicals with tunable emission remains challenging. Herein, we present the synthesis of a series of 9-(2,4,6-trichlorophenyl)-substituted fluorenyl radicals functionalized with various substituents at the 3,6-positions. These radicals exhibit enhanced stability through efficient spin delocalization and kinetic protection. Notably, they display red-shifted photoluminescence compared to traditional polychlorotriphenylmethyl radicals, with maximum emission wavelengths ranging from 679 nm to 744 nm. The mechanisms underlying the doublet emission, as well as their electrochemical properties, have been thoroughly investigated.