Superb Nonlinear Absorption of Triphenylene‐Based Metal–Organic Frameworks Associated with Abundant Metal d Electrons

Abstract The exploitation of high‐performance nonlinear optical (NLO) materials is necessitated by the broad application of ultra‐intensive and ultra‐fast lasers. The superb nonlinear absorption and electronic‐structure‐related NLO response of M 3 HHTP 2 are introduced here, where M is Co(II), Ni(II), or Cu(II) and HHTP is 2,3,6,7,10,11‐hexahydroxytriphenylene. With the laser excitation at 532 nm, the Cu 3 HHTP 2 exhibits a two‐photon absorption (2PA) cross‐section of 1.38 ± 0.11 × 10 7 GM, a value much larger than those of most reported NLO materials so far. The NLO response of M 3 HHTP 2 correlates strongly with the number of metal d electrons. With metal d electrons number increasing from 7 to 10, the optical nonlinearity of M 3 HHTP 2 under the laser excitation at 532 nm varies from three‐photon absorption (3PA) in Co 3 HHTP 2 , a combination of 3PA and 2PA in Ni 3 HHTP 2 , to 2PA in Cu 3 HHTP 2 . Abundant metal d electrons can mitigate the ground‐state depletion, and therefore the 2PA is enhanced. Accordingly, the superb nonlinear absorption of Cu 3 HHTP 2 can be associated with abundant d electrons in Cu.