Nonconventional luminophores devoid of remarkable conjugates have attracted considerable attention due to their unique luminescence behaviors, updated luminescence mechanism of organics and promising applications in optoelectronic, biological and medical fields. Unlike classic luminogens consisting of molecular segments with greatly extended electron delocalization, these unorthodox luminophores generally possess nonconjugated structures based on subgroups such as ether (–O–), hydroxyl (–OH), halogens, carbonyl (CO), carboxyl (–COOH), cyano (CN), thioether (–S–), sulfoxide (SO), sulfone (OSO), phosphate, and aliphatic amine, as well as their grouped functionalities like amide, imide, anhydride and ureido. They can exhibit intriguing intrinsic luminescence, generally featuring concentration-enhanced emission, aggregation-induced emission, excitation-dependent luminescence and prevailing phosphorescence. Herein, we review the recent progress in exploring these nonconventional luminophores and discuss the current challenges and future perspectives. Notably, different mechanisms are reviewed and the clustering-triggered emission (CTE) mechanism is highlighted, which emphasizes the clustering of the above mentioned electron rich moieties and consequent electron delocalization along with conformation rigidification. The CTE mechanism seems widely applicable for diversified natural, synthetic and supramolecular systems.

Nonconventional luminophores: characteristics, advancements and perspectives.

Methylammonium Tin Tribromide Quantum Dots for Heavy Metal Ion Detection and Cellular Imaging

Highly selective and sensitive fluorescence detection of tetracyclines based on novel tungsten oxide quantum dots

Linear and nonlinear optical characteristics of PVA/CMC/PEG blended polymer loaded with ZnS formed at different temperatures

Poly-L-aspartic acid based nonconventional luminescent biomacromolecules with efficient emission in dilute solutions for Al3+ detection.

In contrast to conventional fluorescent polymers featured by large conjugation structures, a new class of fluorescent polymers without any conjugations is gaining great interest in immerging applications beyond the possibility to achieve by the conjugated polymers. Poly(ethylene glycol) (PEG), widely used in biomedical fields for a long time owing to its nontoxicity and nonimmunogenicity, is found to be fluorescence emissive in the solid state and in aqueous solution, though deemed as not fluorescent in numerous reports. Through systematic study under different conditions, the emission is ascribed to the cluster formation of its chains; thereby the blue-shift of the emission with the excitation wavelength was interpreted through the Forster resonance energy transfer. The clusterization was ascertained through size measurements, Fourier transform infrared spectroscopy, NMR analyses, and the dependence on temperature, pH, and nonsolvent presence. Tested in the presence of competitive metal ions, selective emission quenching by Fe³⁺ and Cr⁶⁺ was observed. PEG was used as a sensor for the detection of Cr⁶⁺, Fe³⁺, and H₂O₂, outperforming most of the reported sensors alike. Its uses for data encryption and cell imaging were also presented. This work provides therefore a novel face of PEG with great potential in a variety of emerging applications, in particular, as sensors in the biomedical area.

Fluorescence Behavior and Mechanisms of Poly(ethylene glycol) and Their Applications in Fe3+ and Cr6+ Detections, Data Encryption, and Cell Imaging

Tetracyclines are well-known antibiotics and widely used against a variety of bacterial infections. Their monitoring and detection have been an important issue. To this end, a vast number of methods have been developed; fluorescence sensing is one of the most reported. However, most of the reported sensors are made from transition metals with sophisticated multiprocesses; polymers are hardly seen for this purpose, particularly biocompatible ones. Herein, an aqueous solution of poly(ethylene glycol) (PEG), well known for being biocompatible, is shown to emit under excitation of 280 nm, while the solutions of selected tetracyclines, namely, doxycycline (DOX) and tetracycline (TC), are non-emissive under the same conditions. In the binary solutions of PEG-DOX or PEG-TC, PEG emission is sharply quenched with high sensitivity and selectivity. PEG was then used as a sensor for DOX and TC detections in water with high performance compared to reported studies. The same tests were also done by DOX spiking in milk and tap water, demonstrating that DOX was practically fully recovered. The quenching mechanism was ascribed to the interaction between the O atoms of PEG in clusters and specific heteroatom groups on tetracycline molecules through hydrogen bonding, elucidated from FTIR and NMR analyses. Therefore, this work provides a novel, fully green, easy to operate, low cost, and reliable protocol for tetracycline monitoring and detection and opens new potential application for PEG.

Chunqi Sun

Papers

Fluorescence Behavior and Mechanisms of Poly(ethylene glycol) and Their Applications in Fe3+ and Cr6+ Detections, Data Encryption, and Cell Imaging

Full Green Detection of Antibiotic Tetracyclines Using Fluorescent Poly(ethylene glycol) as the Sensor and the Mechanism Study.