Photo-controlled vacancies and conductivity within single crystals of silver chalcogenolate cluster-based MOFs

Structural vacancies in crystalline solids have great potential in tuning optoelectronic properties for specific applications. However, the random distribution of vacancies is still an intractable problem when creating materials with completely reproducible functions. Here, we report that the growth of crystals from solution approaching perfect single crystallization of assembled silver clusters (SC-1, where SC denotes single crystal), featuring a two-dimensional (2D)-three-dimensional (3D) interpenetrating conformation. By controlling the ultraviolet (UV) irradiation time, SC-1 transformed into SC-2-0.8 and then into SC-2-0.5, where partial trifluoroacetic acid (TFA) and the linker molecules (1,2,4,5-tetracyanobenzene, termed TCNB) possessed a 0.8 or 0.5 occupancy in the crystallography, forming ordered vacancies at specific sites. This course led to a deepened color, a diminished photoluminescence, a narrowed energy gap, and an average 50-fold increase in the single-crystal electron conductivity, together with a 3D-3D interpenetrating conformation. Over time, under the original conditions, SC-1 regrew into SC-3, which had a 3D noninterpenetrating conformation with no crystallographic vacancies and a conductivity similar to that of SC-1. This work elucidates the correlation between the tunable vacancy number and electrical conductivity at the atomic level, providing a method for facilitating electronic communication between cluster-building units and creating ordered-vacancy conducting materials.