Water Soluble Self-Aggregates Induced Green Emission of Biocompatible Citric Acid-PEG Hyper Branched Polymer

An aliphatic citric acid-PEG hyper-branched polymer (CPHP) with a π-bond on the polymer backbone was synthesized by a single- step melt reaction in which the polymerization and π-bond formation occur simultaneously. The chemical structure of CPHP was confirmed by FTIR, ¹H-NMR, ¹³C-NMR and MALDI-TOF mass spectral analyses. Aggregates are generally found to disperse in any solvent but the CPHP aggregates were soluble in water due to their hybrid nature. The π-bond in the aconitate unit induces green emission by CH/π interaction while the PEG unit of CPHP increases its solubility in water. The soluble aggregates induced green emission (SAIE) of the CPHP was investigated by UV-Visible absorption and emission spectra, time- correlated single photon counting (TCSPC) and zeta potential measurements. The fluorescence life time (τ_f) increased from 4.93 to11.38 ns with an increase in CPHP concentration. The fluorescence quantum yield (Φ_f) of CPHP can be altered by varying the concentration of CPHP.