The iodine–starch reaction has long been a subject of debate regarding the nature of the blue color observed. Recent studies suggest that the blue complex arises from an I₂–I₅⁻–I₂ unit within the amylose helix. Amylose, a linear polymer of glucose, forms helical structures that can accommodate iodine molecules. The interaction between iodine and amylose involves both I₂ and I⁻ species, with polyiodide anions playing a key role. The blue color is attributed to charge-transfer bands, with the most likely structure being a repeating unit of I₂–I₅⁻–I₂. This structure is supported by electronic structure calculations and experimental data, including UV-vis and DFT analyses. The presence of iodide ions is crucial for the formation of the complex, as they facilitate the solubilization of I₂ and contribute to the charge-transfer process. The color intensity and wavelength depend on the chain length of amylose and the concentration of iodide. The structural details of the complex, including the arrangement of iodine and water molecules, have been studied using various techniques such as X-ray diffraction, NMR, and UV-vis spectroscopy. The interaction between iodine and amylose is also influenced by the solvent and environmental factors, such as temperature and pH. The study highlights the importance of understanding the molecular mechanisms behind the iodine–starch reaction, which has applications in fields such as drug delivery and materials science. The complex is a key example of supramolecular interactions, demonstrating the role of non-covalent forces in forming stable structures. The research provides a comprehensive overview of the current understanding of the iodine–starch complex, emphasizing the significance of polyiodide species in the formation of the blue color.The iodine–starch reaction has long been a subject of debate regarding the nature of the blue color observed. Recent studies suggest that the blue complex arises from an I₂–I₅⁻–I₂ unit within the amylose helix. Amylose, a linear polymer of glucose, forms helical structures that can accommodate iodine molecules. The interaction between iodine and amylose involves both I₂ and I⁻ species, with polyiodide anions playing a key role. The blue color is attributed to charge-transfer bands, with the most likely structure being a repeating unit of I₂–I₅⁻–I₂. This structure is supported by electronic structure calculations and experimental data, including UV-vis and DFT analyses. The presence of iodide ions is crucial for the formation of the complex, as they facilitate the solubilization of I₂ and contribute to the charge-transfer process. The color intensity and wavelength depend on the chain length of amylose and the concentration of iodide. The structural details of the complex, including the arrangement of iodine and water molecules, have been studied using various techniques such as X-ray diffraction, NMR, and UV-vis spectroscopy. The interaction between iodine and amylose is also influenced by the solvent and environmental factors, such as temperature and pH. The study highlights the importance of understanding the molecular mechanisms behind the iodine–starch reaction, which has applications in fields such as drug delivery and materials science. The complex is a key example of supramolecular interactions, demonstrating the role of non-covalent forces in forming stable structures. The research provides a comprehensive overview of the current understanding of the iodine–starch complex, emphasizing the significance of polyiodide species in the formation of the blue color.