In this report, a facile and eco-friendly method was developed to synthesize a potent antimicrobial agent, effective against fungus, bacteria, and virus. The biocompatible FDA approved polymer, polyethylene glycol (PEG), has been modified by ascorbic acid to form fluorescent polyethylene glycol-ascorbic acid complex (FL PEG AA). The flourescence of FL PEG AA complex could be tuned from green to red in the visible range with varying ascorbic acid(AA) concentrations. The Density Functional Theory (DFT) and the Time-Dependent Density Functional Theory (DT-DFT) on ascorbic acid–monoethylene glycol and ascorbic acid–hexaethylene glycol studies were performed to understand the electronic and bonding nature of FL PEG-ascorbic acid (FL PEG AA) system. The emission of FL PEG AA can be ascribed to the integrated core of FL PEG AA through strong hydrogen-bonding interactions. The fluorescence of FL PEG AA was successfully applied to understand its cellular uptake by breast cancer cells. The FL PEG AA complex showed significant inhibition of growth, when tested against fungus (Candida albicans), bacteria: gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) and the virus (Bacteriophage lambda). The antimicrobial activity of the FL PEG AA system supports the application of this novel formulation as a potent antimicrobial agent. Due to its viscous physical nature, the FL PEG AA complex could be applied as a coating agent or aerosol spray. © 2021 Elsevier Ltd