With rational designability, versatile tunability, and quantum coherence, molecular electron spin qubits could offer new opportunities for quantum information science, enabling simplified implementation of quantum algorithms and chemical-specific quantum sensing. The development of these transformative technologies relies on coherent addressing of single molecular electron spin qubits with high initialization, manipulation, and readout fidelities. This is formidable to conventional electron spin resonance spectroscopy, which is widely used for coherent addressing of ensemble electron spins, due to its low initialization efficiency and readout sensitivity. Taking advantage of single spin detectability of single-molecule spectroscopy, scanning tunneling microscopy, atomic force microscopy, and quantum metrology, several strategies have been developed to empower electron spin resonance spectroscopy with single qubit addressability. In this Emerging Topic, we introduce principles and technical implementation of strategies for coherently addressing single molecular electron spin qubits and point out their challenges in molecular design and/or decoherence suppression. We discuss future directions to overcome these challenges and to improve single qubit addressing technologies, which will facilitate the advancement of molecular quantum information science.

Many-body interactions in condensed matter could lead to emergent phenomena spanning superconductivity, ferromagnetism, and exciton condensation, etc. The emergence of these phenomena often requires highly ordered spatial arrangements of the inter-acting species to enforce specific space symmetries and interacting strengths. Metal−organic frameworks (MOFs), crystalline materi-als formed by self-assembly of metal ions and organic ligands, allow precise design of their crystal structures and sophisticated tun-ing of Coulombic interaction or magnetic coupling among lattice sites. Such atomic-level designability combined with high crystallin-ity and versatile types of lattices (e.g. kagome and honeycomb lattices) render MOFs as a great platform to investigate emergent physics. In this Emerging Topic, we summarize recent studies evidencing emergent phenomena in MOFs including strong correla-tions, superconductivity, charge density wave, long-range magnetic order, and quantum spin liquid. We highlight the great potential of MOFs as quantum materials and discuss challenges including growth of high-quality single crystals and in-depth physical charac-terizations to reveal insights into the nature of physical properties of MOFs.