Stable Boron-Containing Blue-Photoluminescent Radicals

It is highly urgent to develop synthetic strategies to make new category of stable luminescent radicals with desired emission wavelength. In this study, we have isolated two dioxoborocyclic radicals ( 3 and 4 ) by a direct sy nthetic rou te. They were charac terized by UV, EPR spectroscopy and SQUID measurements. Their structures were obtained by single crystal X ray diffraction. Both radicals produce blue photoluminescence (458 nm for 3 and 478 nm for 4 ) by radiative decay from higher excited states (D₂/D₃) to the ground state (D₀) based on theoretical calculation, breaking Kasha rule. The work records a new kind of radical emitters and the first stable radicals with blue emission bands.