Perylene diimide-based supramolecular polymer with temperature-sensitive ratiometric fluorescence responsiveness in solution and gels

Abstract

A novel amphiphilic fluorescence building block with perylene diimide (PDI) as the core and quadruple H-bonding groups (UPy) as wings (UPy–PDI–UPy) has been synthesized. It shows interesting thermo-responsive ratiometric dual-emission properties in both aqueous solution and the hydrogel state. Further contrast experiments with two other analogous derivatives, namely UPy–TPDI–UPy and TEG–PDI–TEG, indicated that the presence of supramolecular aggregation induced an emission enhancement effect between the UPy–PDI–UPy molecules, attributed to the synergetic effect of intermolecular intrinsic π–π stacking, the hydrophobic effect and highly directional quadruple H-bonding. In DMF/H₂O (v : v = 1 : 1), UPy–PDI–UPy self-assembles into nanoparticles with obvious ratiometric fluorescence responsiveness towards temperature in the range of 20–80 °C. Moreover, UPy–PDI–UPy can form a thermo-responsive hydrogel by dispersing in PEG-containing aqueous solution. The hydrogels show a temperature-dependent ratiometric dual-emission with a narrow responsive range of 20–39 °C and an excellent renewable property. This innovative research helps to fabricate novel responsive luminescent materials by using the supramolecular self-assembly behavior.