Ultralong luminescence lifetime imaging of edible plant tissue for humidity sensing in food packaging by a smartphone

The safety of luminescence sensors and probes used in food packaging should be seriously considered, while most luminescence sensors were artificially synthesized with unclear toxicity, and cannot be directly used as indicators that were in contact with food. To overcome this problem, a humidity indicator based on an edible plant tissue was developed without any chemical processing. We found that garlic bulbs could emit significant persistent luminescence after drying at room temperature. The luminescence lifetime decreases from hundreds of milliseconds to tens of milliseconds as humidity increases. The long-lived luminescence could easily be detected through smartphones without any sophisticated instruments. The edible garlic is expected to be used as a humidity indicator in food packaging without worrying about food safety. Furthermore, the interference of scattered light and short-lived fluorescence from foods and packages can be eliminated in time-resolved luminescence imaging, greatly increasing the signal-to-noise ratio.

Color-Tunable Room-Temperature Phosphorescence from Non-Aromatic-Polymer-Involved Charge Transfer

Polymeric room-temperature phosphorescence (RTP) materials especially multicolor RTP systems hold great promise in concrete applications. A key feature in these applications is a triplet charge transfer transition. Aromatic electron donors and electron acceptors are often essential to ensure persistent RTP. There is much interest in fabricating non-aromatic charge-transfer-mediated RTP materials and it still remains a formidable challenge to achieve color-tunable RTP via charge transfer. Herein, a charge-transfer-mediated RTP material by embedding quinoline derivatives within a non-aromatic polymer matrix such as polyacrylamide (PAM) or polyvinyl alcohol (PVA) is developed. Through-space charge transfer (TSCT) is achieved upon alkali- or heat treatment to realize a long phosphorescence lifetime of up to 629.90 ms, high phosphorescence quantum yield of up to 20.51%, and a green-to-blue afterglow for more than 20 s at room temperature. This color-tunable RTP emerges from a nonaromatic polymer to single phosphor charge transfer that has rarely been reported before. This finding suggests that an effective and simple approach can deliver new color-tunable RTP materials for applications including multicolor display, information encryption, and gas detection.

Metal oxide hybridization enhances room temperature phosphorescence of carbon dots-SiO2 matrix for information encryption and anti-counterfeiting

Room temperature phosphorescent (RTP) carbon dot (CD) materials have been widely used in various fields, but it is difficult to achieve a long lifetime, high stability and easy synthesis. In particular, realizing the phosphorescence emission of CDs using a metal oxide (MO) matrix is a challenge. Here, solid gels are synthesized via in situ hydrolysis, and then RTP CDs are synthesized based on a SiO2 matrix (CDs@SiO2) and hybridized with a MO matrix (CDs@SiO2-MO) by high-temperature calcination. Among the materials synthesized, Al2O3 matrix RTP CDs (CDs@SiO2-Al2O3) have a long phosphorescence lifetime of 689 ms and can exhibit yellow-green light visible to the naked eye for 9 s after the UV light (365 nm) is turned off. Compared with the green phosphorescence of CDs@SiO2, the yellow-green phosphorescence lifetime of CDs@SiO2-Al2O3 is enhanced by 420 ms. In addition, CDs@SiO2-Al2O3 maintains good stability of phosphorescence emission in water, strongly oxidizing solutions and organic solvents. As a result, CDs@SiO2-Al2O3 can be applied to the field of information encryption and security anti-counterfeiting, and this work provides a new, easy and efficient synthesis method for MO as an RTP CD matrix.

Light-Mediated Polymerization Catalyzed by Carbon Nanomaterials

Carbon nanomaterials, specifically carbon dots and carbon nitrides, play a crucial role as heterogeneous photoinitiators in both radical and cationic polymerization processes. These recently introduced materials offer promising solutions to the limitations of current homogeneous systems, presenting a novel approach to photopolymerization. This review highlights the preparation and photocatalytic performance of these nanomaterials, emphasizing their application in various polymerization techniques, including photoinduced i) free radical, ii) RAFT, iii) ATRP, and iv) cationic photopolymerization. Additionally, it discusses their potential in addressing contemporary challenges and explores prospects in this field. Moreover, carbon nitrides, in particular, exhibit exceptional oxygen tolerance, underscoring their significance in radical polymerization processes and allowing their applications such as 3D printing, surface modification of coatings, and hydrogel engineering.

Tryptophan-Doped Poly(vinyl alcohol) Films with Ultralong-Lifetime Room-Temperature Phosphorescence and Color-Tunable Afterglow Under Ambient Conditions

The development of a persistent luminescence system with long-lived phosphorescence and color-tunable afterglow at room temperature represents a challenge, largely due to the intensive non-radiative deactivation pathway. In this study, an ultralong-lived room temperature phosphorescence (RTP) system has been achieved using a hydrogen-bonding strategy where poly(vinyl alcohol) (PVA) matrices were doped with tryptophan (Trp) derivatives. The PVA film doped with N-α-(9-Fluorenylmethoxycarbonyl)-L-tryptophan (Fmoc-L-Trp) exhibited a long-lived phosphorescence emission of up to 3859.70 ms, and a blue afterglow for a duration greater than 34 s, under ambient conditions. The introduction of two other fluorescent dyes (i. e., Rhodamine B and Basicred14) to the PVA film facilitates adjustment to the color of the afterglow from blue to orange, and pink, by a triplet-to-singlet Förster-resonance energy transfer (TS-FRET) process. These films have been successfully applied in silk-screen printing and in multicolor afterglow light-emitting diode (LED) arrays.

Dynamic Room Temperature Phosphorescence of Silane-Functionalized Carbon Dots Confining within Silica for Anti-Counterfeiting Applications

Room temperature phosphorescent (RTP) materials with long-lived, excitation-dependent, and time-dependent phosphorescence are highly desirable but very hard to achieve. Herein, this work reports a rational strategy of multiple wavelength excitation and time-dependent dynamic RTP color by confining silane-functionalized carbon dots (CDs) in a silica matrix (Si-CDs@SiO2). The Si-CDs@SiO2 possesses unique green-light-excitation and a change in phosphorescence color from yellow to green. A slow-decaying phosphorescence at 500 nm with a lifetime of 1.28 s and a fast-decaying phosphorescence at 580 nm with a lifetime of 0.90 s are observed under 365 nm of irradiation, which originated from multiple surface triplet states of the Si-CDs@SiO2. Given the unique dynamic RTP properties, the Si-CDs@SiO2 are demonstrated for applications in fingerprint recognition and multidimensional dynamic information encryption. These findings will open an avenue to explore dynamic phosphorescent materials and significantly broaden their applications.

Biobased and biodegradable films exhibiting circularly polarized room temperature phosphorescence

There is interest in developing sustainable materials displaying circularly polarized room-temperature phosphorescence, which have been scarcely reported. Here, we introduce biobased thin films exhibiting circularly polarized luminescence with simultaneous room-temperature phosphorescence. For this purpose, phosphorescence-active lignosulfonate biomolecules are co-assembled with cellulose nanocrystals in a chiral construct. The lignosulfonate is shown to capture the chirality generated by cellulose nanocrystals within the films, emitting circularly polarized phosphorescence with a 0.21 dissymmetry factor and 103 ms phosphorescence lifetime. By contrast with most organic phosphorescence materials, this chiral-phosphorescent system possesses phosphorescence stability, with no significant recession under extreme chemical environments. Meanwhile, the luminescent films resist water and humid environments but are fully biodegradable (16 days) in soil conditions. The introduced bio-based, environmentally-friendly circularly polarized phosphorescence system is expected to open many opportunities, as demonstrated here for information processing and anti-counterfeiting.

Enabling Highly Robust Full-Color Ultralong Room-Temperature Phosphorescence and Stable White Organic Afterglow from Polycyclic Aromatic Hydrocarbons

In this work, full-color and stable white organic afterglow materials with outstanding water, organic solvents, and temperature resistances have been developed for the first time by embedding the selected polycyclic aromatic hydrocarbons into melamine-formaldehyde polymer via solution polymerization. The afterglow quantum yields and lifetimes of the resulting polymer films were up to 22.7 % and 4.83 s, respectively, under ambient conditions. For the coronene-doped sample, its afterglow color could be linearly tuned between yellow and blue by adjusting the temperature, and it could still emit an intense blue afterglow with a lifetime of 0.68 s at 440 K. Moreover, the films showed a bright and stable white afterglow at 370 K with a lifetime of 2.80 s and maintained an excellent afterglow performance after soaking in water and organic solvents for more than 150 days. In addition, the application potential of the polymer films in information encryption and anti-counterfeiting was also demonstrated.

Multi-Responsive Afterglows from Aqueous Processable Amorphous Polysaccharide Films

Polymer-based room-temperature phosphorescence (RTP) materials, especially polysaccharide-based RTP materials, earn sustained attention in the fields of anti-counterfeiting, data encryption, and optoelectronics owing to their green regeneration, flexibility, and transparency. However, those with both ultralong phosphorescence lifetime and excitation wavelength-dependent afterglow are rarely reported. Herein, a kind of amorphous RTP material with ultralong lifetime of up to 2.52 s is fabricated by covalently bonding sodium alginate (SA) with arylboronic acid in the aqueous phase. The resulting polymer film exhibits distinguished RTP performance with excitation-dependent emissions from cyan to green. Specifically, by co-doping with other fluorescent dyes, further regulation of the afterglow color from cyan to yellowish-green and near-white can be achieved through triplet-to-singlet Förster resonance energy transfer. In addition, the water-sensitive properties of hydrogen bonds endow the RTP property of SA-based materials with water/heat-responsive characteristics. On account of the color-tunable and stimuli-responsive afterglows, these smart materials are successfully applied in data encryption and anti-counterfeiting.

Microwave-Responsive Flexible Room-Temperature Phosphorescence Materials Based on Poly(vinylidene fluoride) Polymer

The development of flexible, room-temperature phosphorescence (RTP) materials remains challenging owing to the quenching of their unstable triplet excitons via molecular motion. Therefore, a polymer matrix with Tg higher than room temperature is required to prevent polymer segment movement. In this study, a RTP material was developed by incorporating a 4-biphenylboronic acid (BPBA) phosphor into a poly(vinylidene fluoride) (PVDF) matrix (Tg =-27.1 °C), which exhibits a remarkable UV-light-dependent oxygen consumption phosphorescence with a lifetime of 1275.7 ms. The adjustable RTP performance is influenced by the crystallinity and polymorph (α, β, and γ phases) fraction of PVDF, therefore, the low Tg of the PVDF matrix enables the polymeric segmental motion upon microwave irradiation. Consequently, a reduction in the crystallinity and an increase in the α phase fraction in PVDF film induces RTP after 2.45 GHz microwave irradiation. These findings open up new avenues for constructing crystalline and phase-dependent RTP materials while demonstrating a promising approach toward microwave detection.

Room-temperature phosphorescent materials derived from natural resources

Room-temperature phosphorescent (RTP) materials have enormous potential in many different areas. Additionally, the conversion of natural resources to RTP materials has attracted considerable attention. Owing to their inherent luminescent properties, natural materials can be efficiently converted into sustainable RTP materials. However, to date, only a few reviews have focused on this area of endeavour. Motivated by this lack of coverage, in this Review, we address this shortcoming and introduce the types of natural resource available for the preparation of RTP materials. We mainly focus on the inherent advantages of natural resources for RTP materials, strategies for activating and enhancing the RTP properties of the natural resources as well as the potential applications of these RTP materials. In addition, we discuss future challenges and opportunities in this area of research.

Aggregation-Induced Emission (AIE), Life and Health

Light has profoundly impacted modern medicine and healthcare, with numerous luminescent agents and imaging techniques currently being used to assess health and treat diseases. As an emerging concept in luminescence, aggregation-induced emission (AIE) has shown great potential in biological applications due to its advantages in terms of brightness, biocompatibility, photostability, and positive correlation with concentration. This review provides a comprehensive summary of AIE luminogens applied in imaging of biological structure and dynamic physiological processes, disease diagnosis and treatment, and detection and monitoring of specific analytes, followed by representative works. Discussions on critical issues and perspectives on future directions are also included. This review aims to stimulate the interest of researchers from different fields, including chemistry, biology, materials science, medicine, etc., thus promoting the development of AIE in the fields of life and health.

Confinement effect of network-structured carbon dots/cellulose nanocellulose/magnesium hydroxide for enhanced heavy metal ions capture and immobilization

To solve pollution problem of heavy metal ions (HMIs) and recover them for sustainable development, a high-efficient-sewage treatment agent, carbon dots/cellulose nanofiber/Mg(OH)₂ (CCMg), has been fabricated via a simple hydrothermal method. A variety of characterizations show that cellulose nanofiber (CNF) formed a layered-net structure. Hexagonal Mg(OH)₂ flakes of about 100 nm has been attached on CNF. Carbon dots (CDs) around 10-20 nm in size were produced from CNF and distributed along CNF. The extraordinary structural feature endows CCMg with high removal performance towards HMIs. The up-taken capacities reach 992.8 and 667.3 mg g^-1 for Cd²⁺ and Cu²⁺, respectively. The composite bears excellent durability in treating wastewater. Notably, the qualification of the drinking water can be satisfied while applying CCMg to handle Cu²⁺ wastewater. The mechanism of removal process has been proposed. Practically, Cd²⁺/Cu²⁺ ions were immobilized by CNF due to the space confinement effect. It achieves the facile separation and recovery of HMIs from the sewage, and more importantly, eliminates the risk of secondary contamination.

Switchable and Highly Robust Ultralong Room-Temperature Phosphorescence from Polymer-Based Transparent Films with Three-Dimensional Covalent Networks for Erasable Light Printing

In this work, an efficient polymer-based organic afterglow system, which shows reversible photochromism, switchable ultralong organic phosphorescence (UOP), and prominent water and chemical resistance simultaneously, has been developed for the first time. By doping phenoxazine (PXZ) and 10-ethyl-10H-phenoxazine (PXZEt) into epoxy polymers, the resulting PXZ@EP-0.25 % and PXZEt@EP-0.25 % films show unique photoactivated UOP properties, with phosphorescence quantum yields and lifetimes up to 10.8 % and 845 ms, respectively. It is found that the steady-state luminescence and UOP of PXZ@EP-0.25 % are switchable by light irradiation and thermal annealing. Moreover, the doped films can still produce conspicuous UOP after soaking in water, strong acid and base, and organic solvents for more than two weeks, exhibiting outstanding water and chemical resistance. Inspired by these exciting results, the PXZ@EP-0.25 % has been successfully exploited as an erasable transparent film for light printing.

A Porphyrin-Based Organic Network Comprising Sustainable Carbon Dots for Photopolymerization

Sustainable carbon dots (CDs) based on furfuraldehyde (F-CD) resulted in a photosensitive material after pursuing the Alder-Longo reaction. The porphyrin moiety formed connects the F-CDs in a covalent organic network. This heterogeneous material (P-CD) was characterized by XPS indicating incorporation of the respective C, N and O moieties. Time resolved fluorescence including global analysis showed contribution of three linked components to the overall dynamics of the excited state. Electrochemical and photonic properties of this heterogeneous material facilitated photopolymerization in a photo-ATRP setup where either CuBr₂ /TPMA, FeBr₃ /Br^- or a metal free reaction setup activated controlled polymerization. Chain extension experiments worked in all three cases showing end group fidelity for activation of controlled block copolymerization using MMA and styrene as monomers. Traditional radical polymerization using a diaryl iodonium salt as co-initiator failed.