Strong fluorescence of poly(N-vinylpyrrolidone) and its oxidized hydrolyzate

Discovering fluorescence of existing compounds, which are generally regarded as non-fluorescent, is of important academic and technical significance. This article reports the fluorescence of common compounds containing pyrrolidone ring(s) and their oxidized hydrolyzates. Poly(N-vinylpyrrolidone) (PVP), polymerized from a very weak fluorescent monomer N-vinyl-2-pyrrolidone (NVP), exhibits strong intrinsic fluorescence. Moreover, the fluorescence of its "hydrolyzate" is dramatically enhanced by about 1000 times. The "hydrolyzate" of N-methyl-pyrrolidone (NMP) also exhibits significantly enhanced fluorescence. By studying the chemical structures and fluorescence of the hydrolyzates, the enhanced fluorescence is attributed to the formation of secondary amine oxide. The much stronger fluorescence of the polymers compared to the corresponding small molecular compounds is ascribed to the "aggregation-induced emission" (AIE) effect of the luminophores. PVP and its oxidized hydrolyzate also show some phenomena different to the common AIE effect. The fluorescence of PVP and its oxidized hydrolyzate shows stimuli response to metal ions and pH values. This study introduces novel fluorescent materials for various potential applications.