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

Five-coordinate complex formation of copper(II)-tetraphenylporphyrin (Cu(TP P)) and copper(II)-octaethylporphyrin (Cu(OEP)) have been studied in the pr esence of pyridine, 3-picoline and 4-picoline. Equilibrium constants in tol uene were determined at various temperatures ranged between 10 and 60 degre esC 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 qu ite close to each other and range from -16 to -19 kJ mol(-1). Besides the a bove enumerated donors four other (acetonitrile, benzonitrile, 2-picoline a nd 2,6-lutidine) were used to quench the luminescent trip-multiplet manifol d of the copper(II) porphyrins. These measurements were carried out at five different temperatures (20-60 degreesC) by two different techniques: (1) s teady state luminescence; and (2) laser flash photolysis. Thermodynamic par ameters of the activated complexes were calculated: DeltaS* ranges from -46 to -72 J mol(-1) K-1 while DeltaH(not equal) changes is between 1.6 and 11 .2 kJ mol(-1). (C) 2001 Elsevier Science B.V. All rights reserved.