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5,10,15,20-Tetrakis(4-hydroxyphenyl) porphyrin (THPP) is a synthetic meso tetraarylporphyrin. Its structure comprises a ring of four pyrrole units connected by methine bridges, featuring a mobile electronic system and four meso-phenyl rings, each with a polarity-increasing para-hydroxyl group. THPP dissolves in organic solutions and exhibits strong absorption in the visible region, giving it an intense color. The compound can adjust its electron distribution, which improves its interaction with metal surfaces. It acts as a mixed-type inhibitor, primarily adsorbing via electrostatic forces between the metal surface and its highly polarizable porphyrin ring. The para hydroxyl groups further aid adsorption, especially on hydrated and oxide-covered metals.

5,10,15,20-Tetrakis(4-hydroxyphenyl) porphyrin (THPP) is a synthetic porphyrin compound that belongs to the group of meso tetraarylporphyrins. It has a ring made of four pyrrole units connected by methine –CH= bridges, a very mobile electronic system, these properties are very important in the adsorption process of these compounds on diverse metals surfaces and four phenyl rings attached at the meso positions. Each phenyl ring has a hydroxyl group in the para position, which slightly increases the polarity of the molecule. Because of its structure, THPP dissolves in organic solution, the yield of porphyrins in condensation reaction decreases if there is water in the reaction medium. The compound has strong absorption in the visible region, which gives it an intense color typical of porphyrin molecules.
In addition to its structural properties, THPP can adjust its electron distribution, which enhances its interaction with metal surfaces. It acts as a mixed type of inhibitor, mainly adsorbing through electrostatic forces between the metal surface and the highly polarizable porphyrin ring. The para hydroxyl groups further support this adsorption, especially on hydrated and oxide covered metals