Coupling of spins and light can enable photon-mediated scaling and control in quantum technologies, as demonstrated in trapped atom, ion, and solid-state spin qubits. Molecular analogs of such systems hold promise as a nascent qubit platform that can leverage the tools of synthetic chemistry to tailor quantum properties and integrate in nanoscale devices but have thus far been limited by broad optical transitions. In this talk I describe the development of optically addressable molecular qubits utilizing a central spin-bearing rare-earth ion. We demonstrate coherent microwave control of the spin ground-state and high-resolution spin-selective optical transitions. The resulting spin-optical interface enables high-contrast detection and optical generation of non-equilibrium spin polarization. This approach opens new doors for engineering and utilizing spin-photon coupling in heterogeneous molecular devices with capacity for chemical design.