Porphyrins are tetrapyrrole macrocycles that can coordinate transition metal ions such as iron, cobalt and magnesium and are able to perform a diversity of functions and applications. In biological systems, these molecules are associated with proteins involved in photosynthesis, cell respiration, cell death, antioxidant defence, among others. The stability and versatile applications of porphyrins inspired the synthesis of derivatives including 5,10,15,20-tetrakis(N-methyl pyridinium-4-yl)porphyrin (TMPyP) that is the object of the present chapter. In synthetic porphyrins such as TMPyP, the catalytic and photochemical properties can be achieved by the coordination with a diversity of central metal ions. In photodynamic therapy (PDT), TMPyP and other porphyrins act as photosensitizers. The photochemical properties of TMPyP and other porphyrins are also useful for the fabrication of solar cells. The catalytic properties require the presence of a central metal. The MnTMPyP have antioxidant activity that is influenced the capacity of membrane binding, substituents, and meso substituents. Manipulation of the interfacial confinement properties is one of the newest application areas of porphyrins. The association of porphyrins with different surfaces modulates the electronic and physicochemical properties of these molecules. All of these properties are the object of experimental and theoretical studies discussed in the present chapter.