Node-Dependent Photoinduced Electron Transfer in Third-Generation 2D MOFs Containing Earth-Abundant Metal Ions

• Published in: Inorganic chemistry 2020-12, Vol.59 (23), p.17244-17250
• Main Authors: Steuber, Friedrich W, Gough, John J, Whelan, Éadaoin, Burtnyak, Lyubomyr, Bradley, A. Louise, Schmitt, Wolfgang
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.0c02475

Five isostructural 2D metal–organic frameworks (MOFs), based on a photoactive CuI metallolinker and mixed mono-/dinuclear secondary building units (SBUs), are reported. The MOFs 1­(M) (M = Mn, Co, Cu, Zn, and Cd) exhibit broad absorption across the visible-light spectrum and emission centered at ca. 730 nm. Upon photoexcitation, the rigidity of the framework hinders the pseudo-Jahn–Teller distortion of the metallolinker’s excited state, providing efficient intersystem crossing into the triplet state. Rapid luminescence quenching in 1­(Cu) and 1­(Co) suggests photoinduced electron transfer (PET) to the SBUs, whereas lifetimes of up to 22.2 ns are observed in 1­(Zn). The quantum yields relative to the parent photosensitizer (PS) decrease for metal nodes containing transition metal ions with partially occupied d-orbitals but increase for the d10 systems CdII and ZnII by a factor of up to 6. Importantly, the excited state decay rates directly correlate with the occupancy of the [MII(OH2)] x moieties in the MOFs providing nonradiative decay pathways via O–H oscillators. Cyclovoltammetry reveals minor changes in CuI/II oxidation potential, with excited-state reduction potentials for 1­(M) rivalling Ru analogues. These results establish bis­(diimine)­copper­(I) photosensitizers as viable metallolinkers for MOFs and present a rare example of an isostructural series obtained from a photosensitive metallolinker.