Electronic, optical and charge transport properties of Zn–porphyrin–C60 MOFs: a combined periodic and cluster modeling

Density functional theory (DFT) calculations were performed on the 5,15 meso-positions of nine porphyrin-containing MOFs; Zn2(TCPB)–(NMe2–ZnP); (H4TCPB = 1,2,4,5-tetrakis(4-carboxyphenyl)benzene), (NMe2–ZnP = [5,15-bis[(4-pyridyl)-ethynyl]-10,20-bis-(dimethylamine) porphinato]zinc(ii)) functionalized with nitrogen-, oxygen-, and sulfur-containing groups to study their effects on the electronic, optical and transport properties of the materials. The properties of these materials have also been investigated by encapsulating fullerene (C60) in their pores (C60@MOFs). The results indicate that the guest C60 in the MOF generates high photoconductivity through efficient porphyrin/fullerene donor–acceptor (D–A) interactions, which are facilitated by oxygen and sulfur functionalities. DFT calculations show that C60 interacts favorably in MOFs due to negative Eint values. Encapsulated C60 molecules modify the electronic band structure, affecting the conduction band and unoccupied states of MOFs corresponding to C60 p orbitals. TD-DFT calculations show that incorporating C60 promotes D–A interactions in MOFs, leading to charge transfer in the near-infrared and visible photoinduced electron transfer (PET) from porphyrins to C60. Nonequilibrium Green's function-based calculations for MOFs with sulfur group, with and without C60, performed using molecular junctions with Au(111)-based electrodes show increased charge transport for the doped MOF. These insights into tuning electronic/optical properties and controlling charge transfer can aid in the design of new visible/near-infrared MOF-based optoelectronic devices.