A Universal AIE-Luminogen to Probe Polymer Mobility

Polymer-based materials, from composites to hybrid ones, are part of our daily life, contribute to fundamental societal advancements, and showcase increasingly complex design, so that seizing their microscale properties poses new and unmet challenges. Monitoring polymer chain mobility is a fundamental task to understand materials properties, but despite promises, luminescence methods are currently applicable only within narrow experimental conditions. We describe an aggregation-induced emission (AIE)-based fluorescent rotor showing unique temperature-independent photophysics that stands out as universal probe for polymer relaxation time and viscosity, correlated to macromolecular chain mobility: Its fluorescence lifetime is independent on the polymer chemical nature and on temperature, while being highly sensitive to the low mobility regime typical of cooperative segmental motions of rubbery polymers, close to the glass transition. The calibration curve obtained with five different polymers allows even nonexperts to assess local mobility in polymers with a single measurement. Fluorescence lifetime imaging microscopy (FLIM) yields quantitative mobility maps of complex and dynamic materials with sub-micrometric resolution. This robust and versatile tool allows access to polymer dynamics even in complex and responsive materials, in a broad temperature range, in real space and time.