Optical characterization and DFT-based band structure analysis of the zero-dimensional hybrid material (C7H8N3)2CdI4

Abstract

This work reports on the photophysical properties of organic inorganic naturally self-assembled material bis (2-aminobenzimidazole) tetraiodocadmate (C₇H₈N₃)₂CdI₄. The crystal structure consists of isolated CdI₄ tetrahedra surrounded by 2-aminobenzimidazole cations. The two organic and inorganic units building this material are optically active, giving rise to optical properties involving the competition and the interaction of two inorganic and organic luminescent molecules. When excited by ultraviolet light irradiation, this hybrid material exhibits a strong greenish emission centered at 500 nm that can be seen even with the naked eye at room temperature, which can be attributed to the organic molecule. A decrease in temperature leads to the appearance of new emission bands at 550, 575 and 600 nm, which shift the chromaticity toward warmer regions of the visible spectrum. This emission at low temperature is supposed to be due to excitonic recombination involving a resonant energy transfer (RET) mechanism in which CdI₄ tetrahedra act as a donor and (2-aminobenzimidazole) molecule acts as an acceptor. This assignment is supported by theoretical band structure calculations in terms of density functional theory (DFT). The emergence of additional low-temperature emission bands highlights a fascinating competition between Frenkel-type excitons localized on the organic molecule and Wannier-type excitons associated with the CdI₄ tetrahedra, suggesting complex excitonic interactions within the hybrid system.