Immobilization of the photosensitizers on the solid surface for the application in the photooxidation reactions

It has been shown recently that photosensitizers may be successfully immobilized on the solid surfaces, which leads to the development of new solid photoactive materials. These materials possess several advantages compared to the bulk, homogeneous systems - the ease of operation and easier purification of the product of the surface-promoted reaction. In the presented chapter we are focusing on differentiated routes of the photosensitizers’ immobilization and properties of these systems. The first part describes the photoactive solid materials, which are created via non-covalent incorporation of the photosensitizers into the polymer matrixes. The second part focuses on the utilization of covalent bonding of the photoactive molecules to the solid substrate in the processes known as grafting. This strategy ensures higher stability resulting from the formation of the stable bond between the molecule and the solid surface atoms. The covalent bonding is accomplished by two approaches including the surface modification of the substrate and consecutive reactions with the unmodified photosensitizer or the preliminary conversion of the photoactive molecule to another chemical form which in turn is effectively bound to the solid substrate. Recent applications of the new photoactive materials are demonstrating their evident advantages. It is proven that even the monolayer of photoactive molecules present on the surface of solid substrate is sufficient in an effective generation of singlet oxygen. This excited form of oxygen has exceptionally high oxidation potential and a high degree of stereoselectivity, but due to its short life time must be generated in situ in the photoreaction system. Also, the immobilized photosensitizers can be successfully applied in the oxidation reactions such as Diels - Adler cycloaddition [4+2], oxidation of phenol and its derivatives, or oxidation of sulfides in the aqueous solutions. A wide discussion of these immobilization concepts is provided in the presented chapter based on the recent literature reports with a prospect of their applications in the photooxidation reactions.