A robust stimuli responsive Eu³⁺ - Metalo organic hydrogel and xerogel emitting white light

Recently, there is incredible growth on optoelectronic properties of new supramolecular gels and white-light-emitting (WLE) metalo-organic gel comprised with single lanthanide metal ion having stimuli-responsive property is not yet reported. Here, we report a mandelic acid (MA)-triethylene tetraamine (TETA)-Eu-acetate conjugate (4.5:1:0.4 mol ratio), producing stimuli-sensitive WLE hydrogel exhibiting thermoreversible, thixotropic, pH-switchable, self-standing and self-healing properties. Energy minimized structure suggests complexation between MA-TETA conjugate and Eu³⁺ ion. Fluorescence intensity of MA-TETA conjugate decreases with increasing Eu³⁺ concentration indicating energy transfer from MA-TETA to Eu³⁺. Decay of donor fluorescence intensity follows Stern-Volmer equation and energy transfer efficiency is 42%. WLE gel has Quantum yield 11.4% and Förster distance 1.7 Å. Hydrogel and xerogel show WLE on excitation at 330 and 350 nm having CIE coordinates (0.34, 0.33) and (0.28, 0.32), respectively. WLE gel has Correlated colour temperature 5148 K, appropriate for cool day light emission and on coating over UV-LED bulb it emits bright white light.