Photochemical Spin-State Switching of an All-Organic Molecular System with Visible Light

Abstract

Controlling the spin state of a molecule using the spatiotemporal properties of visible light is of interest for spintronic devices in information technology or (bio)medical applications. We, herein, report an all-organic visible light-induced photochromic system than can switch from a diamagnetic (singlet) to a paramagnetic (triplet) state. This is realized by precisely tuning orbital symmetry and internal molecular strain in a [5]helicene scaffold substituted with an indanedione π-acceptor. Irradiation with visible light at cryogenic temperatures gives a kinetically meta-stable paramagnetic diradical state with a solvent-dependent ground-state multiplicity (triplet or singlet), which can be thermally switched back to its initial diamagnetic state.