Nonconventional Fluorescent Non-Isocyanate Polyurethane Foams for Multipurpose Sensing Applications

Fluorescent foams with interconnected pores are attractive for the detection and quantification of various products. However, many fluorescent probes are suffering from aggregation-caused fluorescence quenching in their solid/aggregated state, are costly, and/or not straightforward to incorporate in foams, limiting their utility for this application. Herein, non-isocyanate polyurethane foams, prepared by the simple water-induced self-blowing process, present a nonconventional fluorescence behaviour, i.e. they are intrinsically fluorescent with a multicolor emission without requiring ex situ traditional fluorescent probes. These foams demonstrate utility for capturing-sensing gaseous formaldehyde (an emblematic indoor air pollutant), as well as for detecting and quantifying various metal ions (Fe²⁺, Cu²⁺, Fe³⁺, Hg²⁺). They are also able to selectively sense tetracycline antibiotic in a ratiometric way with a high sensitivity. By exploiting the unique multicolor photoluminescent foam properties, a smartphone-compatible device is used for the facile antibiotic quantification. This nonconventional fluorescence behaviour is discussed experimentally and theoretically, and is mainly based on clusteroluminescence originating from multiple hydrogen bonding and hetero-atomic sub-luminophores, thus from aggregation-induced emission luminogens that are naturally present in the foams. This work illustrates that easily accessible non-conventional fluorescent NIPU foams characterized by a modular emission wavelength have an enormous potential for multiple substrates detection and quantification.