Spectral studies to increase the efficiency and stability of laser dyes by charge-transfer reactions for using in solar cells: Charge-transfer complexes of Ponceau S with p-chloranil, chloranilic and picric acids

Abstract

Abstract 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) 2 ], [(Pon)(CLA) 2 ], and [(Pon)(PA) 2 ] 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) 2 -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) 2 ] charge-transfer complexes have been checked and are discussed.