Photoinduced interfacial charge separation dynamics in zeolitic imidazolate framework

Abstract

Owing to their porous structure and tunable framework, zeolitic imidazolate frameworks (ZIFs) have garnered considerable attention as promising photocatalytic materials. However, little is known regarding their photophysical properties. In this work, we report the photoinduced charge separation dynamics in a ZIF-67 thin film through interfacial electron transfer (ET) to methylene blue (MB⁺) via ultrafast transient absorption spectroscopy. We show that the ET process occurs through two distinct pathways, including an ultrafast (<200 fs) process from the [Co^II(mim)₂] units located on the surface of ZIF-67 film that are directly in contact with MB⁺ and a relatively slower ET process with a 101.4 ps time constant from the units in the bulk of the film that were isolated from MB⁺ by the surface units. This first direct evidence of the ET process from ZIF-67 to electron acceptor strongly suggests that ZIF materials may be used as intrinsic photocatalytic materials rather than inert hosts.