Efficient afterglow across liquid, hydrogel, and solid states enabled by naphthalimide-doped polyacrylate copolymer emulsions under UV/visible excitation

Abstract

While room-temperature phosphorescence (RTP) materials have been predominantly realized in solid films, the development of liquid and hydrogel systems that retain ultralong afterglow remains highly desirable. Here, we report a high-solid-content (∼30%) afterglow emulsion system based on an electron-deficient naphthalimide (NI) derivative as the luminescent dopant and a copolymer matrix of methyl methacrylate (MMA) with methyl acrylate (MA), denoted as P(MMA/MA). Although the NI-doped P(MMA/MA) exhibits a much lower glass transition temperature than the PMMA homopolymer, it surprisingly delivers a longer afterglow duration (t_ag), revealing that matrix rigidity is not the sole determinant of ultralong RTP. Under ambient conditions, the NI-doped P(MMA/MA) emulsion achieves a lifetime of up to 1.95 s (t_ag ≈ 29 s), while the corresponding solid film exhibits a lifetime of 2.18 s (t_ag ≈ 34 s), placing both among the top-performing systems in their respective states. Beyond UV excitation, both the emulsion and the film can also be activated using safer 405 nm visible light, yielding t_ag values of up to 14 s and 16 s, respectively. When blended with poly(vinyl alcohol), the emulsion forms stretchable hydrogels with a t_ag of ∼20 s, significantly surpassing most reported hydrogel-based RTP materials. Furthermore, through phosphorescence resonance energy transfer, we extend the emission into the red region, producing emulsions with t_ag exceeding 10 s and demonstrating the spectral tunability of this approach across the green-to-red range. This work provides a versatile strategy for designing multistate RTP materials with long afterglow and good processability, showing promise for applications in bioimaging, sensing, and information encryption.