A Simple Approach to Achieve Organic Radicals with Unusual Solid-State Emission and Extraordinary Stability

Herein, we report a simple approach to generate stable
luminescent radicals in the presence of gentle UV irradiation. The newly generated radical
species are capable of emitting unusual red light with a maximum fluorescence quantum
efficiency of 4.6% at ambient conditions in the solid state. Additionally, the luminescent
radicals show extraordinary stability with more than one-year life-span at ambient conditions.
X-ray diffraction study combined with photophysical and computational analyses reveal that
the unique molecular symmetry breaking in the crystalline state lead to the unusual formation
and stabilization of radical ion pairs via the photo-induced electron transfer (PET) process. Such
results represent the first time to achieve stable emissive radicals in the solid state at ambient
conditions via in-situ PET process.