Poly(vinyl alcohol)-Derived Fluorescent Nonconjugated Polymer Dots for Fluorescence Calligraphy and Cellular Imaging

Nonconjugated polymer dots (NCPDs) are envisaged to excel over traditional heavy metal-based quantum dots and organic fluorescent dyes in various practical applications owing to their lower toxicity, high biocompatibility, excellent photostability, and ease of surface modification. Unlike other polymers, poly(vinyl alcohol) (PVA) has rarely been explored for the synthesis of NCPDs, despite being a biocompatible and biodegradable polymer. This work focuses on unlocking the potential of PVA to be utilized as a sole carbon source for the synthesis of self-passivated NCPDs. Herein, we introduce a straightforward, scalable, and eco-friendly method for synthesizing luminescent NCPDs from PVA. We employed a NaOH-assisted hydrothermal approach (180 °C, 4 h) for the rapid synthesis of highly luminescent NCPDs from PVA. In the formation of such NCPDs, PVA served two crucial functions: acting as the carbon source and as a surface passivating agent. PVA-derived NCPDs exhibited bright multicolor fluorescence, pH-dependent emission properties, and excellent thermal and photostability with a remarkable photoluminescence quantum yield of 44.1%. The extensive characterization results provided valuable insights into the formation and the luminescence mechanism of the NCPDs. The internal hydrophobic core of NCPDs is enfolded by the external hydrophilic polymer chains and plentiful functional moieties preserved after incomplete carbonization. Hydrogen-bond-mediated supramolecular interactions lead to a rigid entanglement of the polymer chains and immobilization of subfluorophores, leading to the origin of strong blue fluorescence. Endowed with strong fluorescence and low toxicity, PVA-derived NCPDs are promising candidates for multifunctional applications, viz., fluorescence calligraphy, cellular imaging, and fluorometric sensing of Ag+ ions.