Synthesis and Spectral Properties of Gem-Dimethyl Chlorin Photosensitizers

Chlorins that bear a gem-dimethyl group, which attributes their resistance to oxidation, are of interest for applications in photomedicine. Herein, we present the synthesis and the photophysical properties of two geminal-dimethyl chlorins (dihydroporphyrins) and their free base counterparts that act as efficient singlet oxygen generators and thus exhibit potential for use in photodynamic therapy (PDT) as anticancer or antimicrobial agents upon further derivatization. A complete characterization of their spectral and photophysical properties is accompanied by density functional calculations (DFT) as well as time dependent (TD) DFT to investigate the features of the frontier molecular orbitals. To demonstrate the potential of these compounds, standard palladium mediated reaction yielded a porphyrin-chlorin dyad in moderate yield.