Room-Temperature Phosphorescence Enabled through Nacre-Mimetic Nanocomposite Design

Abstract

A generic, facile, and waterborne strategy is introduced to fabricate flexible, low-cost nanocomposite films with room-temperature phosphorescence (RTP) by incorporating waterborne RTP polymers into self-assembled bioinspired polymer/nanoclay nanocomposites. The excellent oxygen barrier of the lamellar nanoclay structure suppresses the quenching effect from ambient oxygen (k_q ) and broadens the choice of polymer matrices towards lower glass transition temperature (T_g ), while providing better mechanical properties and processability. Moreover, the oxygen permeation and diffusion inside the films can be fine-tuned by varying the polymer/nanoclay ratio, enabling programmable retention times of the RTP signals, which is exploited for transient information storage and anti-counterfeiting materials. Additionally, anti-interception materials are showcased by tracing the interception-induced oxygen history that interferes with the preset self-erasing time. Merging bioinspired nanocomposite design with RTP materials contributes to overcoming the inherent limitations of molecular design of organic RTP compounds, and allows programmable temporal features to be added into RTP materials by controlled mesostructures. This will assist in paving the way for practical applications of RTP materials as novel anti-counterfeiting materials.

Keywords: nacre-mimetics; nanocomposites; oxygen barrier; room-temperature phosphorescence.

Scheme 1

Schematic illustration of preparation and structure of the RTP‐copolymer/nanoclay nacre‐mimetic nanocomposite. The laminated nanoclay structure provides tunable oxygen barrier property that serves to mitigate the quenching effect from ambient oxygen on the triplet state of the RTP chromophores and thus controls the retention time of phosphorescence emission.

Figure 1

Characterization of RTP‐copolymers and lamellar nacre‐mimetic nanocomposites. a) Chemical structure, ¹H NMR spectra, and b) DSC thermograms of copolymers with corresponding T _g values. c) Photographs of BrNpA₂DMA₇₉mTEGA₁₉/NHT (50/50 w/w) film at: i) initial state; ii) steady state after 30 s under 365 nm light irradiation; and iii) a pure BrNpA₂DMA₇₉mTEGA₁₉ polymer film in a Petri dish after 30 s under 365 nm light irradiation, which does not develop phosphorescence (control). d) Photographs showing flexibility and transparency of a BrNpA₂DMA₇₉mTEGA₁₉/NHT (50/50 w/w) film. e) Cross‐sectional SEM images and f) 1D X‐ray diffractogram of BrNpA₂DMA₇₉mTEGA₁₉/NHT (50/50 w/w) films with varied polymer/nanoclay ratio and the corresponding d‐spacing between nanoclay layers (inset).

Figure 2

Time‐dependent photoluminescence properties of nacre‐mimetic RTP films. a) Photographic image series of the light‐up and fade‐away process of BrNpA₂DMA₇₉mTEGA₁₉/NHT films with varied polymer/nanoclay ratio. b) Normalized phosphorescence intensity of BrNpA₂DMA₇₉mTEGA₁₉/NHT (50/50 w/w) film during light‐up and fade‐away process at a test interval of 900 s (emission at 583 nm). Insets show the full photoluminescence spectra during light‐up and fade‐away. c) Normalized phosphorescence intensity (at 583 nm) of BrNpA₂DMA₇₉mTEGA₁₉/NHT films with varied polymer/nanoclay ratio at a test interval of 900 s. Inset shows the enlarged region of 2–12 h. d) RTP fade‐away times (retention times) of BrNpA₂DMA₇₉mTEGA₁₉/NHT films with varied polymer/nanoclay ratio at different test intervals (Figure S3, Supporting Information).

Figure 3

Demonstration of applications based on the RTP nacre‐mimetic nanocomposites. Oxygen sensors: a) Phosphorescence intensity at 583 nm of BrNpA₂DMA₇₉mTEGA₁₉/NHT (70/30 w/w) film under 365 nm irradiation at different oxygen concentration. Inset: spatially selective phosphorescence of a BrNpA₂DMA₇₉mTEGA₁₉/NHT (70/30 w/w) film under nitrogen flow through a needle (365 nm irradiation). b) The initial and steady phosphorescence intensity and the light‐up time, determined as the total time of light‐up process, of BrNpA₂DMA₇₉mTEGA₁₉/NHT (70/30 w/w) film at different oxygen concentration. Information coding: c) Photographs of the BrNpA₂DMA₇₉mTEGA₁₉/NHT (50/50 w/w) film with photolithographic QR code pattern in front of a photomask under daylight and under 365 nm light. The films are flexible and can be bent. d) Transient photolithographic patterning of BrNpA₂DMA₇₉mTEGA₁₉/NHT (70/30 w/w) film with fast writing and time‐dependent self‐erasing properties. Icons in (d) were made by Linector and Eucalyp from www.flaticon.com and are reproduced with permission. Permission for further reuse should be directed to Flaticon. Dual color information storage: e) Schematic illustration and photographs of the orthogonal multilayer patterning under 254/365 nm UV light irradiation using a combination of two RTP chromophores (BrBp and BrNpA). G, R, and Y represent the emission color of green, red, and yellow, respectively. Anti‐interception test: f) Schematic illustration of anti‐interception concept and g,h) the corresponding RTP retention time measurement in a global perspective (g) and a recipient perspective (h) to demonstrate the detection of prolonged retention time induced by interception. h) The light up event is at −4 h and the interception event is at −1 h taking into account a hypothetical transfer time of 1 h between interception and receiving by the recipient.