Supramolecular nonconventional fluorescent material with tunable emission and electrothermal responsiveness

Over the past two decades, nonconventional fluorescent compounds have been attracting the attention of researchers. However, the discovery of new materials and the exploration of their luminous properties, mechanisms and applications are still limited by the delicate design, extraordinary skill and time-consuming synthesis. Here, a simple method is proposed to prepare nonconventional fluorescent materials by physically blending the Nitrogen-rich oligomeric polyethyleneimine (oligo-PEI) and Oxygen-rich tartaric acid (TA). The strong Coulomb force between these two compounds bind them together, resulting in the clustering of the electron-rich groups and enhanced through-space conjugation. As the relative amount of TA increases, the maximum emission peak gradually shifts from 460 nm to 540 nm. In addition, the intensity of the emission peak at 540 nm increased significantly, with the highest value being 8 times the original value. This reveals the great potential of supramolecular materials in freely modulating their fluorescence properties. To gain insight into the interactions between oligo-PEI and TA, density functional theory (DFT) calculations were performed and meaningful results were obtained. Moreover, the relationship between fluorescent intensity, temperature and relaxation time of nonconventional fluorescent materials was quantitatively determined. On this basis, electrothermal responsiveness of oligo-PEI/TA was investigated. Within 2 min, the fluorescence intensity decreased by about 30 % as the temperature was raised from 30 °C to 40 °C by electric heating. In short, this work will be a good reference for scholars interested in nonconventional fluorescent materials.