Coplanar angle change inspired liquid polarity sensing based on pyrene bonded graphene nanoribbons†

Liquid polarity plays an important role in healthcare, cell biology, molecular biology, drug delivery, and cell culture applications, and therefore the development of polarity-sensing sensors is of great importance. Here, a novel pyrene-bonded cove-type graphene nanoribbon (cGNRs-Pyrene) sensor has successfully been developed for liquid polarity sensing. An electron transfer complex (CTC) would be built when the cGNRs-Pyrene sensor was dispersed in the N-methyl-2-pyrrolidone (NMP) solution, while π–π stacking at higher concentrations induces aggregation-caused quenching (ACQ) and a decrease in fluorescence intensity. In addition, the cGNRs-Pyrene sensor exhibits an intramolecular charge transfer (ICT) effect, with its fluorescence intensity varying in different polar environments due to changes in the torsion angle between the pyrene groups and the core structure, making it suitable for liquid polarity sensing. In the THF–H₂O system, the fluorescence intensity of the cGNRs-Pyrene sensor exhibited a linear correlation with the polarity ratio (5–80%H₂O, R² = 0.9794). This sensor was used to monitor lipid droplet (LD) polarity in oleic acid-treated cells, sensitively detecting LDs' polarity changes, demonstrating significant potential for liquid polarity sensing in healthcare applications.