Isoreticular Squaraine‐Linked Titanium‐Organic Frameworks for Photocatalytic Water Splitting to Hydrogen Under Visible Light

Abstract Inspired by the excellent photocatalytic activity of TiO₂, titanium metal‐organic frameworks (Ti‐MOFs) with broad absorption of visible light are regarded as promising photocatalysts, but carboxylate‐linkers used in them are mainly limited to the large extended π‐electron systems. Developing Ti‐MOFs using organic linkers with a donor–acceptor–donor (D–A–D) structure is expected to improve their charge separation but is still challenging. Herein the design of two new isoreticular Ti‐MOFs, Ti₆‐SQ1 and Ti₆‐SQ2 are reported, by using squaraines bearing different electron donors as organic linkers. Discrete fourier transform (DFT) calculations demonstrate that ligand‐to‐metal charge transfer (LMCT) from the acceptor units of squaraines to the Ti₆‐oxo secondary building units (SBUs) drives the photocatalytic water splitting to hydrogen reaction. Compared with Ti₆‐SQ2, the shorter distance between the squaraine centers and the Ti₆‐oxo SBUs in Ti₆‐SQ1 makes stronger LMCT, showing higher photocatalytic hydrogen evolution efficiency of 11.5 mmol g⁻¹ h⁻¹ under visible light (λ > 420 nm), which is ≈8 times that of Ti‐based MOF photocatalysts reported so far. This work provides a new strategy to design Ti‐MOF photocatalysts and understand their structure‐property relationship.