Engineering Band Gap and Photoconduction in Semiconducting Metal Organic Frameworks: Metal Node Effect

Wereport a systematic study on the correlation of the metal nodesin M-THQ conducting MOFs (M = Fe, Ni, Cu, and Zn; THQ = tetra-hydroxybenzoquinone)with their structure, photophysical property, and photoconductivity.We found that the structural preference in these MOFs is controlledby metal node identity where Cu prefers a square planar coordinationwhich leads to a 2D Kagome-type structure. Fe, Ni, and Zn prefer anoctahedral sphere which leads to a 3D structure. Fe-THQ has the smallestband gap and highest photoconduction as well as a long-lived ligand-to-metalcharge transfer state due to the mixed valence state revealed by time-resolvedoptical and X-ray absorption and terahertz spectroscopy. These resultsdemonstrate the importance of the metal node in tuning the photophysicaland photocatalytic properties of MOFs.