Porpholactone and Metal Complexes: Effect of Lactonization of ß-Pyrrole

Abstract

The development of “porphyrin-like” molecules (porphyrinoids) and related tetrapyrroles has attracted considerable attention for the potential as optical materials and photosensitizers for photodynamic therapy (PDT). Porpholactones (TPPLs) are an important but relatively unstudied class of tetrapyrroles, which combine some of the features of porphyrins and chlorins. To explore the effect ß-Lactonization on the electronic structures and spectral properties is of importance to expand the porpholactone chemistry. In recent years, we focused on the synthesis, characterization and the application of porpholactone and their metal complexes. Based on the skeleton of porpholactones, the β-lactone moiety provides an access to tune their NIR optical characteristics, amphilicity and cellular behaviour. More importantly, the relative orientation of the β-dilactone moieties significantly influences their electronic structures and photophysical properties, for example, the Qy band of trans-porphodilactone is red shifted 19 nm compared to that of the cis-isomer with a 2-fold increase in the absorption intensity. Trans-isomer exhibit much higher singlet oxygen quantum yield and the related PDT efficiency than cis-isomer upon irradiation at their Qv bands, respectively. Thus, these results reveal the importance of relative orientation of b-substituents on optical properties at NIR regions.