Sulfuric Acid Assisted Preparation of Red-Emitting Carbonized Polymer Dots and the Application of Bio-Imaging

Red-emitting carbonized polymer dots (CPDs) was prepared from p-phenylenediamine (p-PD) aqueous solution with the assistance of sulfuric acid (H2SO4), and the optical properties and bio-imaging application were studied in this paper. Compared with other strong acids-assisted systems, SA-CPDs (prepared from H2SO4-assisted system, average diameter is ~ 5 nm) is the brightest. The photoluminescence Quantum Yields (QYs) is 21.4% (in water), and the product yield is 16.5%. SA-CPDs aqueous solution emits at 600 nm when excited by the light from 300 to 580 nm. The emission wavelength is independent on the excitation wavelength. Formation energies of CPDs in two ways were calculated to show that longitudinal growth (forming polymers) is difficult, and the transverse growth (forming CPDs) is easy. In addition, the two-photon photoluminescence properties (emitting at 602 nm when excited by 850 nm femtosecond pulse laser) of SA-CPDs were also utilized in the experiments for HeLa cells staining and shown to have potential applications in bio-imaging.