Circularly Polarized Luminescence and Photoinduced Spin Polarization in Helicene-Bis-TEMPO Diradicals
S. Cadeddu, Rituparno Chowdhury, Chiara Delpiano Cordeiro, Saurav Parmar, A. Krämer, Marie Cordier≈, Anne Pensel, Nicolas Vanthuyne, Roberta Sessoli, Mario Chiesa, Yu‐Kai Liao, Richard H. Friend, Enrico Salvadori, Jochen Autschbach, Jeanne Crassous
Abstract
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.