5,15-A2B2- and 5,15-A2BC-Type Porphyrins with Donor and Acceptor Groups for Use in Nonlinear Optics and Photodynamic Therapy

Development of efficient new synthetic strategies leading to more diversified substitution patterns of porphyrin rings is of great importance as it expands the potential applicability of these compounds and provides a more accurate way of tailoring their properties for a specific application. Changes in the electronic and conformational structures induced by different substituents are manifested by unique properties which are of interest for many applications ranging from amphiphilic porphyrins for photodynamic therapy, push-pull systems for optical applications, chiral systems useful in catalysis, to donor-acceptor systems suitable for electron transfer studies. Different chemical strategies were demonstrated for access to unsymetrically substituted porphyrins with nonequivalent beta or meso substituents. For the latter we have adopted the functionalization of preformed porphyrins in order to obtain a diverse range of porphyrin structures with 5,15-A(2)B(2) and 5,15-A(2)BC meso substitution patterns suitable for applications in optical limiting and photodynamic therapy. The functionalization of A(2)-type starting materials by organolithium and palladium-catalyzed cross-coupling reactions is an efficient means to enable the introduction of almost any desired meso substituent. We report the nonlinear absorptive properties of our A(2)B(2) and A(2)BC porphyrins and show that there is strong correlation between structural features and the optical limiting efficiency. The nonlinear optical studies indicate that the 5,15-A(2)B(2) substitution pattern provides more promising candidates for use in optical limiting.