The electronic band structure of a material refers to the arrangement of its energy levels, which are occupied by electrons. In the case of graphene, a single layer of carbon atoms arranged in a hexagonal lattice, the electronic band structure is unique due to its linear dispersion relation near the Dirac points. This leads to the electrons in graphene behaving as massless Dirac fermions, which gives rise to its exceptional electronic and optical properties.The optical properties of a material are determined by its interaction with light, which is influenced by the electronic band structure. In graphene, the linear dispersion relation results in a universal optical absorbance of approximately 2.3% for visible light, regardless of the wavelength. This is due to the interband transitions between the valence and conduction bands, which are allowed at any energy level in graphene.Compared to other 2D materials, graphene's optical properties are quite unique. For example, transition metal dichalcogenides TMDCs such as MoS2 and WS2 have a different electronic band structure, with a direct bandgap in the visible range. This leads to strong light absorption and photoluminescence, which can be exploited for optoelectronic applications such as photodetectors and solar cells. In contrast, graphene's zero-bandgap nature makes it more suitable for applications in transparent conductive electrodes and ultrafast photodetectors.Another class of 2D materials, hexagonal boron nitride hBN , has a wide bandgap of around 6 eV, making it an insulator with very low optical absorption in the visible range. This property makes hBN an excellent candidate for use as a dielectric layer in 2D material-based electronic devices.In summary, the relationship between the electronic band structure and the optical properties of graphene is governed by its unique linear dispersion relation, which results in a universal optical absorbance. This is different from other 2D materials like TMDCs and hBN, which have direct and wide bandgaps, respectively, leading to distinct optical properties and potential applications.