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

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.