Circularly Polarized Luminescence and Photoinduced Spin Polarization in Helicene-Bis-TEMPO Diradicals

Readily accessible high spin excited states are highly coveted due to their potential use in spintronic and quantum sensing applications. Adding a chiral twist to this problem potentially allows for control of the emergent spin polarization through the helicity of the system. Herein we report the realization of a novel, chiral, diradical system, H6-bis-TEMPO, consisting of two TEMPO radicals bridged by a chiral carbo[6]helicene, which after photoexcitation of the helicene core generates a weakly coupled three-spin system comprising the helicene triplet (S = 1) and the two TEMPO radicals (S = 1/2). Time-resolved absorption and theoretical calculations help explain the specific photophysics of this system, while time-resolved EPR shows that the TEMPO radicals become spin polarized once the photoexcited spin intermediate has decayed. Comparison with a nonradical bis-dibenzoate capped helicene H6-bis-BENZ experimentally validates the results. This work constitutes a first step toward the realization of molecular systems able to generate spin polarization through helical chirality at the single-molecule level. Moreover, the helically chiral TEMPO persistent radical showscircularly polarized luminescence.