Phosphorescence-Based Visualization of the Dynamic Coordination-Driven Assembly in Gelation

Abstract

Coordination-driven supramolecular hydrogels feature excellent processability and dynamic responsibility and thus are appealing for applications such as biomedical photonics. Since they are constructed via hierarchical assembly, the gelation processes are difficult to control in a highly efficient manner, leading to limited transparency. For the formation of hydrogel, stepwise introduction of water is essential for the gelation. Phosphorescence with high H₂O sensitivity can be explored for in situ monitoring and precise understanding of the gelation process. Herein, a hydrogel from Gd³⁺-adenosine monophosphate (AMP) assembly was chosen as the model, which was formed via the strong Gd³⁺-PO3 coordination and π–π stacking of A bases. On the basis of the excellent guest inclusion and phosphorescence inducing of the Gd³⁺-AMP matrix, thioflavin-T (ThT, cyan fluorescence) and Pt(II) meso-tetra(4-carboxyphenyl) porphine (PtTCPP, red phosphorescence) were coencapsulated as the probe. Via the luminescence changes, the gelation process was visualized, and two kinds of cloudy side products (NPs and sol, indistinguishable to the naked eye) were identified. Further calorimetric investigation on the above cloudy side products allowed for improvement of the transparency of the hydrogel by changing the synthesis temperature. The obtained flexible and transparent room-temperature phosphorescence (RTP) hydrogel was explored for implantable optical waveguide-based oxygen sensing.