Small-Molecules-Induced Metal–Organic-Framework-based Photosensitizer for Greatly Enhancing H₂ Production Efficiency

Five metal–organic framework (MOF)-based photosensitizers2pyrrole⊂APPT-Cd-ClO₄^– (1), 3pyrrole⊂APPT-Cd-ClO₄^– (2), 2(N-methylpyrrole)⊂APPT-Cd-ClO₄^– (3), 2(2-methylpyrrole)⊂APPT-Cd-ClO₄^– (4), and 2(3-methylpyrrole)⊂APPT-Cd-ClO₄^– (5)were constructed by an effective small-molecule-induced strategy. The saturated- or supersaturated adsorption of small pyrrole and its methyl derivatives into Cd-MOF to construct strong visible-light-absorbing MOF-based photosensitizers 1–5 that contain active radicals resulted in the exponential increase in the H₂ production rate from photocatalytic water splitting. Solid-sate UV–vis and ESR spectra verified the strong visible light absorption and free radical characteristics of the host–guest MOFs. Single-crystal X-ray analysis revealed the structure–function relationship. The rich hydrogen-bonding interactions between the host and guest should be responsible for the efficient charge transfer between the host MOF and guest and its excellent optoelectronic activity. The superior electron transfer between the radical MOF and catalytic centers contributed to the enhanced catalytic performance. The rational design of small-molecule-induced photosensitizers to greatly improve catalytic performance in this work opens up an alternative avenue of MOF-based materials toward efficient photocatalysis.