Optical Spin Polarization of a Narrow‐Linewidth Electron‐Spin Qubit in a Chromophore/Stable‐Radical System

Photoexcited organic chromophores appended to stable radicals can serve as qubit and/or qudit candidates for quantum information applications. 1,6,7,12‐Tetra‐(4‐tert‐butylphenoxy)‐perylene‐3,4 : 9,10‐bis(dicarboximide) (tpPDI) linked to a partially deuterated α,γ‐bisdiphenylene‐β‐phenylallyl radical (BDPA‐d (16)) was synthesized and characterized by time‐resolved optical and electron paramagnetic resonance (EPR) spectroscopies. Photoexcitation of tpPDI‐BDPA‐d (16) results in ultrafast radical‐enhanced intersystem crossing to produce a quartet state (Q) followed by formation of a spin‐polarized doublet ground state (D (0)). Pulse‐EPR experiments confirmed the spin multiplicity of Q and yielded coherence times of T (m)=2.1±0.1 μs and 2.8±0.2 μs for Q and D (0), respectively. BDPA‐d (16) eliminates the dominant (1)H hyperfine couplings, resulting in a single narrow line for both the Q and D (0) states, which enhances the spectral resolution needed for good qubit addressability.