Multi-Stimulus Responsive Nonconventional Fluorescent Supramolecular Polymeric Material

Abstract

Fluorescent supramolecular materials have attracted a lot of attention over the past few decades. However, those can respond to multiple stimuli are not often reported, especially for the nonconventional fluorescent materials. Here, a supramolecular material is reported that can respond to temperature/electrical heating, humidity, volatile acids/organic amines, and mechanical strain. This material is prepared by physical mixing oligomeric polyethyleneimine (o-PEI) and oligomeric polyacrylic acid (o-PAA). Although they are almost non-fluorescent, their combination produces bright fluorescence, and the emission bands shift to longer wavelengths as the amount of o-PAA increases. Calculations based on Density Functional Theory (DFT) show that there are strong noncovalent interactions between o-PEI and o-PAA, resulting in through-space conjugation and cluster-triggered emission. By studying the relationship between emission intensity, temperature, and molecular motion, the dependence of emission intensity on relaxation time is established, which will provide insight into the luminescence origin of nonconventional fluorescent materials. In addition, this material shows good self-healing ability. The luminescence, responsiveness and self-reparability are all related to the strong but reversible noncovalent bonds that link the o-PEI and o-PAA. This work not only highlights the value of supramolecular polymers, but also enriches the research of nonconventional fluorescent materials.