文摘

Charge-transfer complexes formed from the reaction of Ponceau S dye with some π-acceptors such as tetrachloro-p-benzoquinone (p-chloranil; p-Chl), 2,5-dichloro-3,6-dihydroxybenzoquinone (chloranilic acid; CLA) and 2,4,6-trinitrophenol (picric acid; PA) have been studied in methanol at 25?°C. The final reaction products have been isolated and characterized using UV–Vis, mid-infrared, Raman laser, fluorescence spectra, and thermal stability measurements (TG/DTG), as well as elemental analysis of carbon, hydrogen, and nitrogen elements. The photometric titration curves for the reactions indicated that the data obtained refer to 1:2 Ponceau S charge-transfer complexes [(Pon)(p-Chl)2sub>], [(Pon)(CLA)2sub>], and [(Pon)(PA)2sub>] being formed. The infrared and Raman laser spectra interpreted the mode of charge-transfer interactions associated with the hydrogen bonding existing between two protons (–OH) of the S(=O)2sub>–OH group: a sulfonyl hydroxide Ponceau S donor and the acidic central position of acceptors for –C=O and –OH in the p-Chl and both CLA and PA, respectively. The activation parameters ΔE, ΔH, ΔS and ΔG were obtained from the DTG diagrams by using the Coats–Redfern method. The fluorescence efficiency data of free Ponceau S dye and the [(Pon)(acceptor)2sub>] charge-transfer complexes have been checked and are discussed.