Nonaromatic Polyacrylamide Eutectogels with Ultralong Room-temperature and High-temperature Phosphorescence

Ultralong organic phosphorescence (UOP) materials have attracted widespread attention due to their excellent photophysical properties and wide potential applications. However, UOP is difficult to be achieved in pure organic materials even those with large rigid -conjugated structures, not to mention nontraditional luminogens (NTLs) without or with only very limited through-bond conjugation and flexible structures. Herein, we present a novel strategy for fabricating polyacrylamide (PAM) eutectogels with UOP by solvent exchange of a nonaromatic hydrogel with a heavy-atom (bromine)-containing deep eutectic solvent (DES) followed by wet annealing at an elevated temperature. The eutectogels exhibit remarkable afterglows up to 9.5 s, room-temperature phosphorescence (RTP) lifetimes up to 622.5 ms and high phosphorescence QYs up to 17.6%, and very impressively, they also exhibit high temperature phosphorescence (HTP) with a lifetime of 366.2 ms even at 120 °C. The eutectogels also possess excellent mechanical properties, with a ultrahigh elastic modulus of 168.1 MPa and a tensile strength of 55.2 MPa, as well as superior organic solvent resistance and thermally stimulated shape memory behaviors. The DES solvent exchange facilitates the desolvation and self-aggregation of PAM and the wet annealing establishes effective interactions between DES and PAM, which enables strong spin-orbit coupling (SOC) and efficient intersystem crossing (ISC) at the solid (PAM)-liquid (DES) phase via the heavy atom effect. Furthermore, strong hydrogen network of the eutectogel effectively suppresses nonradiative decay. This work provides a universal strategy for preparing environmentally benign UOP materials with exceptional thermal stability and organic solvent resistance.