Five-coordinate complex formation and luminescence quenching study of copper(II) porphyrins

Five-coordinate complex formation of copper(II)–tetraphenylporphyrin (Cu(TPP)) and copper(II)–octaethylporphyrin (Cu(OEP)) have been studied in the presence of pyridine, 3-picoline and 4-picoline. Equilibrium constants in toluene were determined at various temperatures ranged between 10 and 60 °C from which thermodynamic parameters were determined. The entropy change is between −81 and −92 J mol−1 K−1 while the enthalpy values are also quite close to each other and range from −16 to −19 kJ mol−1. Besides the above enumerated donors four other (acetonitrile, benzonitrile, 2-picoline and 2,6-lutidine) were used to quench the luminescent trip-multiplet manifold of the copper(II) porphyrins. These measurements were carried out at five different temperatures (20–60°C) by two different techniques: (1) steady state luminescence; and (2) laser flash photolysis. Thermodynamic parameters of the activated complexes were calculated: ΔS# ranges from −46 to −72 J mol−1 K−1 while ΔH≠ changes is between 1.6 and 11.2 kJ mol−1.