Photoinduced Stable Circularly Polarized Luminescent Radicals From a Triphenylamine-Attached Planar Chiral Pillar[5]Arene

Photoinduced organic radicals with unique luminescent properties are highly sought-after due to their important prospects in synthetic chemistry and materials science. However, the current development of organic free radicals, including photoinduced ones, is significantly limited and faces challenges related to stability and poor luminescence behavior. Taking advantage of the photoelectric activity of triarylamine, we herein describe an unusual luminescent radical, which can be rapidly generated by UV irradiation of a solid-state triarylamine-functionalized π-conjugated pillar[5]arene (EtP5NN) in air, accompanied by luminescent color switching from bluish-violet to sky-blue. The persistent radicals within EtP5NN with a half-life of 12.7 h suggest that the pillar[5]arene skeleton straightforwardly improves the stability of radicals. The sterically bulky triarylamine groups inhibit the racemization of planar chiral pillar[5]arene and allow the optical resolution of this system. The enhancement of circularly polarized luminescence (CPL) is triggered by UV irradiation of the enantiomers (pS/pR-EtP5NN) in the solid state.