This work demonstrates for the first time that a photochromic metal organic framework (pMOF) can be employed as a promising class of NIR-II photothermal material based on the photoinduced donor-acceptor intermolecular charge transfer process. After further surface-modification, such UV-activated pMOF-a nanoparticles allow the strong inhibition of 4T1 cancer cells under 1064 nm laser irradiation.