Efficient, Near‐Infrared Light‐Induced Photoclick Reaction Enabled by Upconversion Nanoparticles

Abstract Photoclick reactions combine the selectivity of classical click chemistry with the high precision and spatiotemporal control afforded by light, finding diverse utility in surface customization, polymer conjugation, photocross‐linking, protein labeling, and bioimaging. Nonetheless, UV light, pivotal in prevailing photoclick reactions, poses issues, especially in biological contexts, due to its limited tissue penetration and cell‐toxic nature. Herein, a reliable and versatile strategy of activating the photoclick reactions of 9,10‐phenanthrenequinones ( PQ s) with electron‐rich alkenes ( ERA s) with near infrared (NIR) light transduced by spectrally and structurally customized upconversion nanoparticles ( UCNP s) is introduced. Under NIR irradiation, the UCNP s become UV/blue nanoemitters uniformly distributed in the reaction system. Enabled by the customized UCNP s, 800 or 980 nm light effectively activates the photocycloaddition reactions via radiative energy transfer in both general and triplet–triplet energy transfer (TTET)‐mediated PQ‐ERA systems. In particular, the novel sandwich structure UCNP s achieve the click reaction with up to 76% production yield in 10 min under NIR light irradiation. Meanwhile, the tricky side effect of photoclick product absorption‐induced quenching is successfully circumvented from the fine‐tuning of the upconversion spectrum. Moreover, through‐tissue irradiation experiments, the authors show that the UCNP ‐ PQ‐ERA reaction unlocks the full potential of photoclick reactions for in vivo applications.