The utility of light as a therapeutic agent can be traced back over thousands of years when it was used in Ancient Egypt, India and China to treat a variety of skin diseases like psoriasis, vitiligo, rickets, cancer and psychosis. The isolation of porphyrins and their inherent tumor localizing properties coupled with its ability to generate reactive singlet oxygen when activated by light of particular wavelength which in turn results in cytotoxicity led to the emergence of a new modality namely, photodynamic therapy (PDT) as a therapeutic tool. The higher degree of selectivity offered by this modality and fewer side effects when compared to chemotherapy and radiotherapy has prompted the researchers around the globe to generate new photosensitizers. Porphyrins and expanded porphyrins are one class of molecules under intense investigation due to their photosensitizing ability for PDT application. Expanded porphyrins result from the expansion of the phi electron conjugation by increasing the number of heterocyclic rings or bridging carbons of the existing porphyrin framework. These chromophores show strong absorptions in the red region (650-800 nm) compared to that of normal 18phi porphyrins. The strong absorption of light by a water soluble nontoxic photosensitizing molecule in the therapeutic window resulting in maximum penetration of light into the tissues coupled with high singlet oxygen production will conceptualize an ideal photosensitizer. This review highlights various porphyrinoid sensitizers reported till date and their photosensitizing ability both in vitro and in vivo studies. Furthermore, the urgent need for developing ideal photosensitizer for PDT will also be highlighted.

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Research on synthesis of porphyrin isomers has gained momentum since the discovery of porphycene 1 by Vogel and coworkers and N-confused porphyrin 2 independently by Furuta et al. and Latos-Grazynski and co-workers. The other porphyrin isomers reported to date include, corrphycene, 3 hemiporphycene, 4 and isoporphycene 5 obtained by shuffling the four pyrrolic subunits and meso-carbon bridges. Extensive studies on Nconfused porphyrin 1 2 and doubly N-confused porphyrin 2 6 have witnessed unusual metalation chemistry leading to the formation of a metal-carbon bond inside the porphyrin cavity, stabilization of unusual oxidation states of metals, and the existence of different tautomeric forms. 2a,6-8 Expanded porphyrins 9 bearing N-confused pyrrole can not only complex 4d and 5d metals but also offer larger cavities for the formation of metal-carbon bonds. To the best of our knowledge there are no reports in the literature on the synthesis of expanded porphyrins bearing an N-confused ring. Herein, we wish to report the first successful synthesis of stable, aromatic modified sapphyrins bearing an N-confused pyrrole ring exhibiting an inverted structure.