Optically addressable molecular spin qubits are promising systems for quantum information processing due to their tunability, modularity and scalability. In this thesis, I will give an overview of the development of a chromium(IV)-based optically addressable molecular spin qubit. The ability to chemically synthesize these spin-bearing molecules provides a bottom-up approach to the design of their spin and optical properties. I will describe how the spin coherence of the molecular qubit is enhanced by inserting the molecule into a non-isostructural host matrix and generating noise-protected clock transitions. We model the coherence from first principles as a function of the qubit’s changed symmetry, and further experimentally demonstrate improved spin contrast and spin-lattice relaxation time for this qubit. I will also discuss the effects of isotopic modification of the nuclear spin environment on the spin and optical properties of the chromium molecular qubit system, with insights into the decoherence mechanisms provided by first principles theoretical calculations. Finally, I will present progress towards growth of thin films of these molecular spin qubits with the goal of integration with devices. These results demonstrate our ability to optimize the spin-optical interfaces of molecular qubits through chemical design and highlight the promise of molecular spin qubits as building blocks of quantum technologies.