Synthesis and Photocatalytic Properties of Titanium‐Porphyrinic Aerogels

We present novel titanium‐porphyrinic gels (TPGs) and titanium‐porphyrinic aerogels (TPAs), in which porphyrinic ligand tetrakis(4‐carboxyphenyl)porphyrin is coordinated to Ti‐oxo clusters. These hierarchically porous TPAs, with micro‐, meso‐, and macropores and reactant‐concentration‐dependent Brunauer‐Emmett‐Teller surface areas of 407–738 m2 g−1, are prepared by CO2 critical point drying of TPGs. Although the Ti4+ → Ti3+ photoreduction of TPAs is less efficient than that of crystalline microporous Ti‐porphyrinic framework DGIST‐1, prompt diffusion of O2 and spin‐trapping agents into the TPA pores causes the rapid generation of reactive oxygen species (ROS), as observed by EPR spectroscopy. When used as an ROS scavenger, large 1,3‐diphenylisobenzofuran is degraded by the best‐performing TPA 10 times faster than by DGIST‐1, suggesting that the accessibility of molecules (reactants) to pores (reactive centers) strongly influences photocatalytic activity. Hierarchically porous titanium‐porphyrinic aerogels (TPAs) facilitate rapid accessibility to guest molecules for adsorption or to catalytically active sites. The visible‐light‐responsive photocatalytic activity of TPAs was examined by monitoring the generation of reactive oxygen species and the oxidative coupling of benzylamine to afford N‐benzylidenebenzylamine.