Deep-red fluorescent poly(acrylic acid) hydrogel: Proton transfer to the water soluble dibasic luminescent dye followed by ion-pair formation

We developed a simple and versatile strategy to fabricate a highly luminescent and deep-red emitting supra molecular hydrogel (lambda(em,max) = 651 nm, phi(F) = 0.17). The strategy is based on using water-soluble and highly luminescent bis-pyridine molecule, V-EO7PyDCS (1), which makes a direct acid-base proton transfer and subsequent ion-pair formation with commercial poly(acrylic acid) (PAA) in water to form the luminescent supra molecular hydrogel in-situ. It was shown that the ionic interaction between the pyridinium cation in the protonated form of 1 and carboxylate anion in that of PAA was responsible for the effective gelation as to make the transparent hydrogel of similar to 98% water content. Concurrently, the protonated form of 1 showed a highly efficient deep-red fluorescence in this supramolecular hydrogel according to its excellent dynamic ion-pair formation and photophysical behaviors. It is noteworthy that these hydrogels are homogeneous and transparent due to the excellent water solubility of di-basic crosslinker 1.

Automated summary

A simple and versatile strategy was developed to fabricate a highly luminescent and deep-red emitting supramolecular hydrogel by using water-soluble and highly luminescent bis-pyridine molecule in combination with commercial poly(acrylic acid). The resulting hydrogel has a high water content, homogeneous and transparency, with efficient deep-red fluorescence.