Synthesis of Unsymmetrical meso-Substituted Porphyrins, 1. 5,15-A2B2- and 5,15-A2BC-Type Porphyrins with Donor and Acceptor Groups for Use in Nonlinear Optics and Photodynamic Therapy

Abstract

Development of new efficient 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 ?- 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-A2B2 and 5,15-A2BC meso substitution patterns suitable for applications in optical limiting and photodynamic therapy. The functionalization of A2?type starting material via organolithium and palladium catalyzed crosscoupling reactions is an efficient means which enables the introduction of almost any desired meso substituent. We report on the nonlinear absorptive properties of our A2B2 and A2BC 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-A2B2 substitution pattern provides more promising candidates for use in optical limiting.