Recent advances in meso-alkylidenyl carbaporphyrinoids

Porphyrins and their structural analogs have drawn continuous attention owing to their physico-chemical properties associated with biological, medical and material chemistry. Consequently, many structural modifications of the porphyrin skeleton have been reported as a fundamental tool for tuning the physico-chemical properties and a variety of new classes of porphyrinoids have emerged. A vast number of applications such as photodynamic therapy (PDT), redox catalysis, chemosensors, nonlinear optical material (NLO) and two photon absorption (TPA) have been studied utilizing these systems. The "so called" meso-alkylidenyl porphyrins have been reported recently as alternative modification methods of the porphyrin skeleton. These compounds possess one or more exocyclic double bonds at meso-positions and are usually non-aromatic systems. The reported spectroscopic as well as structural properties well-corroborate the non-aromatic nature of the macrocycles. However, the protonation behavior and tautomerism are quite different from those of normal porphyrins. Considering the unique properties of meso-alkylidenyl carbaporphyrinoid macrocycles, we present a review on the recent advances in this area of chemistry.