Core-modified porphyrin based assemblies

Core-modified porphyrins, resulting from the replacement of one or two pyrrolic nitrogens with other hetero atoms such as O, S, Se, and Te possess very interesting and distinct properties compared to tetrapyrrolic porphyrins. Specially, the singlet state energy levels can be fine tuned with suitable modification of porphyrin core by substituting pyrrolic “N” with hetero atoms such as “O” and “S”. In this review, we discuss the synthesis of various core-modified porphyrin building blocks containing one, two, three and four functional groups by following various synthetic methodologies developed in the past decade and the use of these core-modified porphyrin building blocks in the construction of several covalently and non-covalently linked hetero porphyrin dyads, triads, tetrads and pentads containing one or more different types of porphyrin sub-units. The photophysical studies are also described to show the possibility of singlet–singlet energy transfer from one porphyrin sub-unit to another in these hetero porphyrin arrays