Fluorescent and Room-Temperature Phosphorescent Poly(allylamine hydrochloride)–Sodium Polyacrylate Polyelectrolyte Complex and Its Application in Constructing a Förster Resonance Energy Transfer System

Nontraditional luminogens (NTLs) have attracted rapidly growing attention due to their unique photophysical properties and photoluminescence (PL) mechanism. However, most NTLs suffer from short-wavelength emissions and low PL quantum yields, which strongly limit their applications. Developing NTLs with superior PL properties is of great scientific and practical significance. In this work, we prepared a type of polyelectrolyte complex (PEC) based on poly(allylamine hydrochloride) (PAH) and sodium polyacrylate (PAANa) and studied its PL behaviors. The strong ionic bonding in the PEC leads to the formation of more extended through-space conjugation (TSC) and enhanced conformational rigidity. Therefore, the PAH–PAANa hydrogel and xerogel exhibit higher PL quantum yields as well as red-shifted fluorescence emissions compared to the components. Very impressively, the PAH–PAANa hydrogel and xerogel also exhibit room-temperature phosphorescence (RTP) emissions with lifetimes of 14.9 and 145.6 ms, respectively. Moreover, a Förster resonance energy transfer (FRET) system is constructed by using the PAH–PAANa PEC as the energy donor and a commercial organic dye as the energy acceptor, and multicolor fluorescence and RTP emissions and tunable afterglow lifetimes are achieved. Applications in information storage and encryption of the FRET system are also demonstrated. This work provides an idea for realizing red-shifted and enhanced emission of NTLs and constructing FRET systems to enrich their applications.