Fluorescence enhancement of a tetrazole-based pyridine coordination polymer hydrogel

Hydrogelation of a pyridine derivative (1) possessing tetrazole moieties as end groups, without long alkyl chain groups, results in the formation of a Mg(NO₃)₂ coordination polymer gel. The polymer exhibits a strong fluorescence enhancement upon gel formation. 1 can also be gelated with a variety of magnesium anions such as SO₄^2-, NO ₃^-, Cl^-, Br^- and I^-, indicating that the coordination polymer gel formation of 1 does not strongly depend on anions. The SEM and AFM images of Mg²⁺ coordination polymer gel 1 display a fibrillar network several micrometres long, with widths in the range of 60-70 nm and thicknesses of about 3 nm. In addition, photophysical studies show that the hydrogel exhibits a typical π-π* transition and gives rise to high fluorescence behavior. The coordination polymer hydrogel exhibits viscoelastic behavior as evidenced from the rheological studies.