Organic Free Radicals as Circularly Polarized Luminescence Emitters

Chiroptical properties of two chiral atropisomers of propeller-like trityl-based radical derivatives have been analyzed. A new absolute configuration (AC) assignment has been made, according to the combination of experimental and theoretical data. In this sense, their ACs have been determined through the comparison of the Cotton effects recorded by electronic circular dichroism (ECD) with the theoretical ECD of the open shell structures obtained by TD-DFT calculations. Finally, their circularly polarized luminescence (CPL) responses have been addressed. Remarkably, this is the first description of organic free radicals as intrinsic CPL emitters. Opposite signed CPL has been detected for each pair of conformers, with acceptable luminescent dissymmetry factors (|g_lum |≈0.5-0.8×10^-3 ) considering their pure organic nature. In fact, highly efficient chiral emissions have been demonstrated, according to the comparison of |g_lum | with their respective absorption anisotropy factors (|g_abs |). This pioneering study lays the foundations for the optimization of new magnetically active organic chiral emitters.