Investigation of horseradish peroxide and hydrogen peroxide mediated synthesis of amino-functional oligomers: Characterization and fluorescence study

Abstract

The insightful mechanism of two oligomerization methods using either horseradish peroxide (HRP)/hydrogen peroxide (H2O2) (enzymatic approach), or H2O2 (35% aqueous) (chemical approach) on 4-phenoxy aniline (PA) and 4-(4-chlorophenoxy)aniline (PACl) as two amino-functional monomers was studied. Four oligomers syn- thesized were described by FT-IR, UV-Vis, 1H-NMR and 13C-NMR techniques for the molecular structure analysis. The oligomers substituted with chlorine had stronger electron acceptor ability, which enhanced the intra- molecular charge transfer between the donating moiety and chlorine acceptor substituent, resulting in a 48 nm red shift of the λmax for the n→π* electronic transition. Oligomers prepared by horseradish peroxidase shows better fluorescence properties than the monomers. The use of oxidoreductase enzyme (HRP) as the catalyst, for the one-step oligomerization of the monomers demonstrated to yield fluorescent products. Photoluminescence (PL) measurements enlightened that emission quantum yields of PACl-E in DMF were found to be 18% and 4.2% at the maximum emission wavelength of 412 nm and 482 nm, respectively. it is considered as green oligo- merization/polymerization method Since HRP catalysis provided a green oxidative oligomerization method of aniline and their derivatives, four oligomers were produced by peroxidase-catalyzed oxidation oligomerization in relation to their electronic properties. HOMO-LUMO energy levels were calculated to make comments about electrochemical (E′ g) band gaps of the oligomers which were lower than those of their regarding monomers. SEM images were provided to study the morphology of the oligomers. Intermolecular dihydrophenazine formation in the course of enzymatic oligomerization would eventuate in highly ordered structures.