Optical read and write of spin states in organic diradicals

TL;DR

This paper reports the discovery of a molecular diradical with optical read and write capabilities of spin states, demonstrating potential for quantum technology applications through its unique spin-photon interface properties.

Contribution

The study introduces a novel organic diradical molecule with tunable spin states and high quantum yield, enabling optical control and readout of spin states in organic molecules.

Findings

Demonstrated photoluminescence at 640 and 700 nm for triplet and singlet states.

Achieved up to 8% microwave-driven contrast in photoluminescence.

Established near-unity quantum yield for both spin manifolds.

Abstract

Optical control and read-out of the ground state spin structure has been demonstrated for defect states in crystalline semiconductors, including the diamond NV- center, and these are promising systems for quantum technologies. Molecular organic semiconductors offer synthetic control of spin placement, in contrast to current limitations in these crystalline systems. Here we report the discovery of spin-optical addressability in a diradical molecule that comprises two trityl radical groups coupled via a fluorene bridge. We demonstrate the three important properties that enable operation as a spin-photon interface: (i) triplet and singlet spin states show photoluminescence peaked at 640 and 700 nm respectively; this allows easy optical measurement of ground state spin. (ii) the ground state spin exchange is small (~60 {\mu}eV) that allows preparation of ground state spin population. This can be achieved by spin-selective excited state intersystem crossing, and we report up to 8% microwave-driven contrast in photoluminescence. (iii) both singlet and triplet manifolds have near-unity photoluminescence quantum yield, which is in contrast to the near-zero quantum yields in prior reports of molecular diradicals. Our results establish these tuneable open-shell organic molecules as a platform to engineer tailor-made spin-optical interfaces.