Luminescence property of phosphoramidic acid oligomer nanodots in aqueous solution

Luminescent polymer dots have showed great potential applications in chemical sensing and bioimaging. Herein, phosphoramidic acid oligomers in aqueous solution can form nanodots (ONDs) with mean diameter of 50 ~ 60 nm. The ONDs display blue fluorescence of excitation-dependence and the fluorescence quantum yields can reach 4.16% to 9.71% under the maximum excitation and emission wavelengths. The steady and dynamic fluorescence quenching experiments by iodide ion show that the luminescence of ONDs originates to charge transfer (CT). The calculation on distribution of HOMO and LUMO of ONDs in monomer and dimer states supports further the CT mechanism, and the separated and localized distribution of HOMO and LUMO provides possible explanation on the excitation wavelength dependent luminescence based on internal and external CT. It is expected that the luminescent ONDS are useful in chemical or biological sensing fields.