Enhancing Persistent Luminescence of Cellulose by Dehydration for Label-Free Time-Resolved Imaging

Abstract

Organic persistent luminescence is usually emitted from synthesized materials containing π units (aromatic rings, double bonds, etc.). It is challenging but desirable to develop organic materials from renewable resources with tunable persistent luminescence to reduce environmental impact. Herein, we proposed an effective method to enhance the luminescence of cellulose, the most abundant natural renewable material free of π units. It was found that removing the crystal water in cellulose would increase the compactness of molecular packing and stabilize the hydroxyl clusters of polysaccharide chains, consequently leading to significant enhancement of phosphorescence with lifetime up to subseconds. This dehydration induced luminescence enhancement was found in not only purified cellulose but also cellulose-contained substances such as papers, cottons, and many other plant tissues. This indicated easier access to cellulose-based luminescence materials without chemical purification. In addition, label-free time-resolved luminescence imaging of plant tissues was achieved on a smartphone-based apparatus, since endogenous cellulose is distributed extensively in plants. Compared with synthetical luminophores, cellulose is a renewable and biodegradable source abundant in nature, not only readily available but also environmentally friendly. We believe this method may be used to develop other sustainable organic luminescence materials with a lack of π units for various optical applications.

Efficient Persistent Luminescence from Cellulose–Halide Mixtures for Optical Encryption

“…The steady-state luminescence spectra were different in emission intensity and maximum emission wavelength, indicating different excited states in these cellulose samples. To investigate the long-lived luminescence, time-gated spectra were measured and all samples exhibited delayed luminescence with a maximum emission wavelength ranging from 500 to 530 nm, which was due to the phosphorescence of cellulose. − The phosphorescence peak of cellulose doped with MgBr 2 could overlap with its steady-state luminescence peak, suggesting effective ISC through the external heavy-atom effect (Figure S1). Also, the difference between steady-state and time-gated spectra indicated a fluorescence peak around 400 nm.…”

“…The sample was excited using a 365 nm LED (Shenzhen Chundaxin Photoelectric Co., Ltd), and the luminescence was recorded using a smartphone (Redmi K30 Pro Xiaomi China). By switching on and off, videos of the persistent luminescence were recorded as 30 frames/s by the original software under Manual Focus in Pro mode, and then the recorded videos were processed for exponential fitting by MATLAB software according to the references . Finally, the luminescence lifetime images were constructed by using different colors to represent the lifetime values.…”

“…Recently, some natural products, such as phenolics, − proteins, , amino acids, gelatin, sodium alginate, oat β-glucan, and some carbohydrates − were reported to exhibit persistent phosphorescence at solid states. Unlike conventional organic luminescence compounds, some of these natural products contain no aromatic rings or even double bonds.…”

“…Among them, cellulose is a linear polymer of ringed d -glucose, which is free of π units but rich in O atoms. A previous work indicated that removing crystal waters would enhance the clustering-triggered emission, which was probably attributed to the interaction of electron-rich units (hydroxyls, carbonyls, etc.) through space .…”

Autofluorescence spectroscopy for quantitative analysis of cellulose nanocrystals

“…Other groups have also previously reported on the CTE fluorescence of cellulosic materials. [41][42][43][44][45][46][47] Highlights include correlating the quantum efficiency to the degree of crystallinity, 46,47 and assigning specific emissive bands to functional groups. 42,44 Importantly, despite the relatively weak autofluorescence signal of cellulose, we are confident that the fluorescence is not the result of contamination (commonly attributed to lignin and other phenolic compounds) due to previous reports on the fluorescence of cellulose from non-plant sources, 48,49 as well as in-depth photoluminescence studies on cellulose and other polysaccharides.…”