Heterometal incorporation in NH2-MIL-125(Ti) and its participation in the photoinduced charge-separated excited state

Abstract

Optical and X-ray spectroscopy studies reveal the location and role of Fe³⁺ sites incorporated through direct synthesis in NH₂-MIL-125(Ti). Fe K-edge XAS analysis confirms its metal–oxo cluster node coordination while time-resolved optical and X-ray transient absorption studies disclose its role as an electron trap site, promoting long-lived photo-induced charge separation in the framework. Notably, XTA measurements show sustained electron reduction of the Fe sites into the microsecond time range. Comparison with an Fe-doped MOF generated through post-synthetic modification indicates that only the direct synthesis approach affords efficient Fe participation in the charge separated excited state.