Angle‐Resolved Iridescent Day‐Long Afterglow in Flexible Polymeric Exciplex Films

Abstract The creation of polymer‐based persistent luminescence materials exhibiting tunable afterglow colors hold significant promise for anti‐counterfeiting, flexible displays, and data storage. Nevertheless, realizing day‐long organic persistent luminescence featuring angle‐resolved afterglow color remains challenging. Herein, a day‐long organic afterglow (DOA) system is developed by doping 9‐(naphthalen‐2‐yl)‐9′‐phenyl‐9H,9′H‐3,3′‐bicarbazole into polyethylene terephthalate. This system demonstrates a remarkably long afterglow (>24 h ambient, >100 h at 4 °C), ranking among the longest durations reported for polymeric afterglow materials. The DOA originates from radiative recombination of charge‐separated radicals, which reform the emissive exciplex state. Importantly, this recombination is modulated by the donor/acceptor energy gap, and the cation radicals are stabilized by charge delocalization over the donor components. Furthermore, by integrating this long‐persistent luminescent system into designed polymeric multilayer interference structures, iridescent afterglow color with distinct viewing‐angle dependence is achieved. Based on the exciplex's broad emission, the angle‐resolved DOA color exhibits wide spectral tunability, covering red, green, and blue hues, making it suitable for complex security features. Additionally, the system demonstrates exceptional mechanical flexibility and plastic‐ deformation‐dependent optical properties, thereby expanding the potential of color‐tunable organic afterglow materials for advanced applications in authentication technologies and optical security features.