Analytical Approach to Screen Semiconducting MOFs Using Bloch Mode Analysis and Spectroscopic Measurements

Abstract

A rapid and simple analytical approach is developed to screen the semiconducting properties of metal organic frameworks (MOFs) by modeling the band structure and predicting the density of state of isoreticular MOFs (IRMOFs). One can consider the periodic arrangement of metal nodes linked by organic subunits as a 1D periodic array crystal model, which can be aligned with any unit-cell axis included in the IRMOF's primitive cubic lattice. In such a structure, each valence electron of a metal atom feels the potential field of the entire periodic array. We allocate the 1D periodic array in a crystal unit cell to three IRMOFs-n (n = 1, 8, and 10) of the Zn 4 O(L) 3 IRMOF series and apply the model to their crystal lattices with unit-cell constants a = 25.66, 30.09, and 34.28 Å, respectively. By solving Schrodinger's equation with a Kronig−Penney periodic potential and fitting the computed energy spectra to IRMOFs' experimental spectroscopic data, we model electronic band structures and obtain densities of state. The band diagram of each IRMOF reveals the nature of its electronic structures and density of state, allowing one to identify its n-or p-type semiconducting behavior. This novel analytical approach serves as a predictive and rapid screening tool to search the MOF database to identify potential semiconducting MOFs.

Strongly Bound Excitons in Metal–Organic Framework MOF-5: A Many-Body Perturbation Theory Study

“…We note that if one neglects the lowest energy peak in the UV-Vis absorption spectra reported by the early study by Tachikawa et al 18 which was later attributed to the ZnO impurity (at 3.6 eV), the agreement with our results is excellent. In their work, the most intense band is located at ∼5.2 eV (240 nm) and the next one with much lower intensity is found at 4.3 eV (290 nm), in agreement with our study and with the recent experimental reports by Rathnayake et al 43…”

“…The BSE yields an optical gap of 4.5 eV with an intense absorption peak at 5.3 eV in good agreement with experimental studies. 24,43 The optical absorption is dominated by ligand-centered transitions at least up to ∼ 6 eV, also in agreement with inferences drawn in recent experimental studies. 16,20 The large dierence between the fundamental gap and optical band gap points to strongly bound excitons in the studied spectral region with binding energies of several eVs, previously not discussed in literature.…”

“…Direct and inverse photoemission spectroscopy should be employed to this purpose and we are condent that experiments of this kind will conrm our results. Optical absorption spectrum of MOF-5 computed using BSE/evGW /Gau-PBE (upper panel) and measured (lower panel) by Rathnayake et al 43 Hole and electron densities of the excitons reported as colored dots in the spectrum (lower gure).…”

Strongly Bound Excitons in Metal-Organic Framework MOF-5: A Many-Body Perturbation Theory Study

“…We note that if one neglects the lowest energy peak in the UV-Vis absorption spectra reported by the early study by Tachikawa et al 18 which was later attributed to the ZnO impurity (at 3.6 eV), the agreement with our results is excellent. In their work, the most intense band is located at ∼5.2 eV (240 nm) and the next one with much lower intensity is found at 4.3 eV (290 nm), in agreement with our study and with the recent experimental reports by Rathnayake et al 43…”

“…Direct and inverse photoemission spectroscopy should be employed to this purpose and we are condent that experiments of this kind will conrm our results. Absorption (a.u) Optical absorption spectrum of MOF-5 computed using BSE/evGW /Gau-PBE (upper panel) and measured (lower panel) by Rathnayake et al 43 Hole and electron densities of the excitons reported as colored dots in the spectrum (lower gure).…”