Evidence of Photoinduced Charge Separation in the Metal–Organic Framework MIL‐125(Ti)‐NH2

Abstract Herein, we describe the photochemical behavior of the porous metal–organic framework MIL‐125(Ti)‐NH 2 , built up from cyclic Ti 8 O 8 (OH) 4 oxoclusters and 2‐aminoterephthalate ligands. While MIL‐125(Ti)‐NH 2 does not emit upon excitation at 420 nm, laser flash photolyses of dry samples (diffuse reflectance) or aqueous suspensions (transmission) of the solid have allowed detecting a transient characterized by a continuous absorption from 390 to 820 nm decaying in the sub‐millisecond timescale, which is quenched by oxygen. This transient has been attributed to the charge‐separation state. Firm evidence for this assignment was obtained by lamp irradiation of aqueous suspensions of MIL‐125(Ti)‐NH 2 in the presence of electron‐donor ( N,N,N′N′ ‐tetramethyl‐ p ‐phenylenediamine) or electron‐acceptor (methylviologen) probe molecules, which has allowed the visual detection of the corresponding radical ions, in agreement with the occurrence of photoinduced charge separation in MIL‐125(Ti)‐NH 2 .