Spin-related excited-state phenomena in photochemistry

The spin of electrons plays a vital role in chemical reactions and processes, and the excited state generated by the absorption of photons shows abundant spin-related phenomena. However, the importance of electron spin in photochemistry studies has been rarely mentioned or summarized. In this review, we briefly introduce the concept for spin photochemistry based on the spin multiplicity of excited state, which leads to the observation of various spin-related photophysical properties and photochemical reactivities. Then we focus on the recent advances in terms of light-induced magnetic properties, excited-state magneto-optical effects, and spin-dependent photochemical reactions. The review aims to provide a comprehensive overview to utilize the spin multiplicity of excited state in manipulating the above photophysical and photochemical processes. Finally, we discuss the existing challenges in the emerging field of spin photochemistry, and the future opportunities such as smart magnetic materials, optical information technology, and spin-enhanced photocatalysis.