Aluminum(III) porphyrin: A unique building block for artificial photosynthetic systems

Despite being the most abundant metal on the Earth, aluminum(III) metal ion centered porphyrin (AlPor, where Por = Porphyrin) derivatives have received much less attention compared to the transition metal porphyrin derivatives. The exceptional dual bonding features, (i) the axial hydroxide readily reacts with carboxylic acid or alcohol and (ii) the Lewis acid Al center forms an adduct with a Lewis base such as pyridine or imidazole, make the AlPor a unique building block for the construction of ‘axial-bonding’ type multicomponent donor–acceptor systems for a variety of applications. Additionally, due to the rich redox chemistry and optical properties, the AlPor can act as either a photosensitizing electron acceptor or electron donor in donor–acceptor systems. Unlike the zinc(II) porphyrin (ZnPor), the AlPor based donor–acceptor provides an axial topology to investigate the sequential photoinduced energy transfer (EnT) and/or electron transfer (ET) processes in perpendicular to the porphyrin ring. This review surveys AlPor based multicomponent donor–acceptor systems designed to mimic the various components of natural photosynthesis to develop an artificial photosynthetic system for tapping solar energy. Additionally, the review examines the photocatalytic behavior of AlPor towards solar fuel production. Finally, we will discuss the similarities and differences between the ‘axial-bonding’ type AlPor and ZnPor systems.