Opto-Spintronics: Photoisomerization-Induced Spin State Switching at 300 K in Photochrome Cobalt–Dioxolene Thin Films

Controllable
quantum systems are under active investigation for
quantum computing, secure information processing, and nonvolatile
memory. The optical manipulation of spin quantum states provides an
important strategy for quantum control with both temporal and spatial
resolution. Challenges in increasing the lifetime of photoinduced
magnetic states at T > 200 K have hindered progress
toward utilizing photomagnetic materials in quantum device architectures.
Here we demonstrate reversible light-induced magnetization switching
in an organic thin film at device operating temperatures of 300–330
K. By utilizing photochromic ligands that undergo structural changes
in the solid state, the changes in ligand field associated with photoisomerization
modulate the ligand field and in turn the oxidation and spin state
of a bound metal center. Green light irradiation (λexc = 550 nm) of a spirooxazine cobalt–dioxolene complex induces
photoisomerization of the ligand that in turn triggers a reversible
intramolecular charge-transfer coupled spin-transition process at
the cobalt center. The generation of photomagnetic states through
conversion between a low-spin Co­(III)–semiquinone doublet and
a high-spin Co­(II)–bis-semiquinone sextet state has been demonstrated
in both solution and the solid state and is described as a photoisomerization-induced
spin–charge excited state (PISCES) process. The high transition
temperature (325 K) and long-lived photoinduced state (τ = 10
s at 300 K) are dictated by the photochromic ligand. Theory provides
effective modeling of the phenomenon and long-term strategies to further
modulate the lifetimes of photomagnetic states for quantum information
technologies at the single molecule level.