On-demand modulating afterglow color of water-soluble polymers through phosphorescence FRET for multicolor security printing

Abstract

Developing full-color organic ultralong room temperature phosphorescence (OURTP) materials with continuously variable afterglow emission is of considerable practical importance in diverse optoelectronic applications but remains a formidable challenge. Here, we present an effective strategy for on-demand engineering of afterglow color in water-soluble polymeric systems via efficient phosphorescence Förster resonance energy transfer. Using a blue afterglow emitting water-soluble polymer as host and a series of fluorescent emitters with varied emissive colors as guests, afterglow emission is rationally modulated, conferring the full-color afterglow emission ranging from blue to red and even white with ultralong lifetimes up to 4.2 s and photoluminescence quantum yields of 36%.These water-soluble multicolor-emitting polymeric afterglow systems can function as OURTP security inks, and multilevel information encryption was successfully established by RGB-based multicolor security printing. These results present important guidance in developing high-performance afterglow polymers with on-demand color tuning ability for remarkable optoelectronic applications.

Fig. 1.. Afterglow color modulation in polymeric systems through P-FRET.

(A) Simplified Jablonski diagram for P-FRET process. ISC, intersystem crossing. (B) Schematic diagram for preparing OURTP polymeric systems with full-color afterglow emission and molecular structures of the polymeric host of PAMCz and fluorescent guests of sodium 3,9-perylene dicarboxylate (PDB), sodium fluorescein (Fluc), rhodamine 123 (Rh123), and rhodamine B (RhB), respectively. (C) Phosphorescence spectrum (delayed time, 10 ms) of PAMCz in amorphous film (in gray shade) and absorption spectra of the guests in deionized water (10⁻⁵ M). a.u., arbitrary units.

Fig. 2.. Photophysical properties of Fluc-doped PAMCz films under ambient conditions.

(A and B) Steady-state PL (A) and delayed PL (B) spectra of Fluc/PAMCz films at different doping weight concentrations. Insets: Photographs of the corresponding Fluc/PAMCz films taken at UV-on and UV-off states. (C) Phosphorescence lifetime decay profiles of the pure PAMCz (0.0 wt % Fluc/PAMCz) film at 414 nm and the Fluc/PAMCz films at different doping weight concentrations at 560 nm. (D) Key parameters for the phosphorescence energy transfer process. (E) Commission Internationale de l’Eclairage (CIE) 1931 coordinates of afterglow emission of the Fluc/PAMCz films at different doping weight concentrations. (F and G) Excitation-phosphorescence mappings of PAMCz (F) and 0.05 wt % Fluc/PAMCz (G) films.

Fig. 3.. Mechanism and feasibility confirmation of the P-FRET for full-color afterglow.

(A) Mechanism of fluorescence and phosphorescence FRET processes. (B) Photographs of 1.0 wt % PDB/PAMCz, 0.1 wt % Rh123/PAMCz, and 2.0 wt % RhB/PAMCz films taken under and after the removal of the 254-nm excitation source. (C to K) Afterglow emission spectra (C to E), CIE 1931 coordinates (F to H), and excitation phosphorescence emission mapping (I to K) of PDB-doped (C, F, and I), RhB123-doped (D, G, and J), and RhB-doped (E, H, and K) PAMCz films at different doping weight concentrations.

Fig. 4.. On-demand modulation of the afterglow color.

(A) Schematic diagram of color-tunable organic afterglow systems in a user-controlled manner and the full-color palette photographs generated through varying the hybrid components in polymeric systems. (B to F) CIE 1931 coordinates (B) and afterglow emission spectra (C to F) of 0.1 wt % PDB/PAMCz (cyan, C), 0.5 wt % RhB/PAMCz (magenta, D), 0.1 wt % Rh123/PAMCz (yellow, E) and 0.04 wt % Rh123/PAMCz (white, F) films with their photographs taken after the removal of 254-nm UV light (insets).

Fig. 5.. Multicolor security printing using the water-soluble RGB polymeric afterglow materials as inks.

(A) Graphical representation of RGB ink cartridges filled with the multicolor OURTP polymers using a commercial ink-jet printer. (B to D) Ink printing security patterns of the quick response (B, top) and bar (B, bottom) codes, as well as the multicolor patterns of roses (C, top), Olympic rings (C, bottom), and NJUPT character (D) taken under and after the removal of 254-nm excitation source.