Amino Acid Residues Vary the Self-Assembly and Photophysical Properties of Diphenylamine-Cyanostilbene-Capped Amphiphiles

Although fluorescent materials based on diphenylamine (DPA) conjugated with cyanostilbene (CS) have been developed for biological applications as aggregation-induced emission chromophores with long-wavelength emissions, only DPACS derivatives of very high polarity and low polarity have been investigated previously. Herein, we report three DPACS-capped amino acid amphiphiles - DPACS-G, DPACS-S, and DPACS-D - of various hydrophobicities. Their self-assembly and photophysical properties in aqueous media are dependent upon the nature of their amino acid residues. Interestingly, under alkaline conditions, the introduction of a serine (S) residue in the DPACS chromophore (i. e., DPACS-S) resulted in a self-assembled hydrogel and the formation of nanorods with aggregation-induced emission enhancement characteristics. Experimental and theoretical studies of DPACS-S revealed that pi-pi stacking, electrostatic interactions, and extended intermolecular hydrogen bonding were the main driving forces behind its self-assembly.