Synthesis of a redox-active pyrene-FLFL-dopamine amphiphile and investigation of their self-assembly at different pH leading to microfibrous formation

Abstract

N-(1-((1-((3,4-dihydroxyphenethyl)amino)-1-oxo-3-phenylpropan-2-yl)amino)-1-oxo-3-phenylpropan-2-yl)-4-(pyren-1-yl)butanamide (Py-F_L-F_L-DP) was synthesised using the traditional amide coupling reactions of 1-pyrene butyric acid, boc-l-phenyl alanine, l-phenyl alanine methyl ester and dopamine. Py-F_L-F_L-DP shows a pH dependant aggregation between pH 4 and 10 which can be monitored spectroscopically, resulting in a reversible quinol/hydroquinone oxidation – reduction transformation of the dopamine moiety. The photoexcitation of Py-F_L-F_L-DP at λ_ex 345 nm at higher pH preferentially results in AIE photorelaxation mechanism in comparison to thermal relaxation or intramolecular charge transfer (ICT). SEM micrographs show the formation of fibrillar nanostructure with increasing pH specially at pH 10. The CD experiment offered deeper insights into the chirality that developed in the nanofiber self-assemblies at pH levels 7 to 10, which is attributed to the twisted conformations of the pyrene moieties within the self-assembled structure. The unique pH-dependent self-assembly and redox behavior of Py-FL-FL-DP, particularly its reversible optical and structural changes in response to pH variations, make it a promising candidate for real-time pH monitoring in biomedical applications, such as intracellular imaging and the design of controlled drug delivery systems targeting pH-sensitive environments.