Monatshefte f€ ur Chemie 136, 509–517 (2005) DOI 10.1007/s00706-004-0260-0 A Spectroscopic Study of Charge Transfer Complexes of Tetraphenylporphyrin Saleh A. Azim  , Raafat M. Issa, and Eynas A. Saleh Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt Received June 20, 2004; accepted (revised) September 3, 2004 Published online January 19, 2005 # Springer-Verlag 2005 Summary. The fluorescence quenching and complexation behaviour of tetraphenylporphyrin (TPP) with some organic acceptors such as chloranilic acid (CHL), 5,5 0 -dithiobis-2-nitrobenzoic acid (DTNB), or 3,4-dinitrobenzoic acid (DNB) and tetravalent metal ions such as Th 4þ and Zr 4þ have been studied in methanol. The second-order fluorescence quenching rate constant (k q ), the association constant (K), the molar absorption coefficient ("), and the thermodynamic parameters of the complexation process (DG  , DH  , and DS  ) have been evaluated using different organic solvents. Keywords. Tetraphenylporphyrin complexes; Fluorescence quenching; Metals; Porphyrin. Introduction Porphyrin derivatives have attracted interest in recent years due to their potential use in the field of photodynamic therapy (PDT) [1, 2]. The interaction of porphyrin bases with metal ions has been extensively studied [3, 4]. They also have important applications in photocatalysis, photochemical conversion, and storage of solar en- ergy as well as photosynthesis, photobiology, and photomedicine [5, 6]. We have described the fluorescence quenching and the complexation of TPP with some tetravalent metal ions in organic solvents at different temperatures. Less attention, however, has been devoted to interaction between porphyrin bases and electron- deficient organic compounds. In this paper we report the dynamics of the interaction between a prototype porphyrin derivative, tetraphenylporphyrin (TPP), and some nitroaromatic accep- tors, e.g. chloranilic acid (CHL), 3,4-dinitrobenzoic acid (DNB), and 5,5 0 -dithiobis- 2-nitrobenzoic acid (DTNB).  Corresponding author. E-mail: saleh_abdelazim@yahoo.com