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

Abstract

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 E_int 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.