Spectroscopic studies on the intermolecular charge transfer interaction of Fe(II)- and Fe(III)-phthalocyanines with 2,3,5,6-tetrachloro-1,4-benzoquinone and its application in colorimetric sensing of amino acids and amines

Abstract

The interactions of Fe IIPc and Fe IIIPc with π-acceptor 2,3,5,6-tetrachloro-1,4-benzoquinone ( p-chloranil, p-CHL) have been investigated spectroscopically (UV/vis and FT-IR) and spectrofluorimetrically at three different temperatures. The stoichiometry of the complexes was found to be 1:1. The results of electronic spectral studies indicated that the formation constant for Fe IIPc- p-CHL system is found to be higher than that for Fe IIIPc- p-CHL system. This observation is well supported by the results of fluorescence quenching studies and the association constants calculated for Fe IIPc- p-CHL system is 4.2 × 10 3 mol L −1 and that for Fe IIIPc- p-CHL system is 2.2 × 10 3 mol L −1. The data are discussed in terms of physico-chemical parameters viz. molar extinction coefficient, oscillator strength, dipole moment, ionization potential, dissociation energy and thermodynamic parameters. The results indicated that the formation of π–π CT complex is spontaneous and endothermic. Preliminary studies indicated that the CT complex can effectively be used as a colorimetric agent for sensing amino acids and amines.