Effect of halogen substitution on the electronic and optical behavior of C₁₆H₁₀X₂O₂(X = F, cl, Br and I) organic semiconductors

In this study, a comprehensive analysis of the structural, electronic, and optical properties of C₁₆H₁₀X₂O₂ compounds (where X = F, Cl, Br, I) was conducted using first-principles calculations based on Density Functional Theory (DFT). The results demonstrate that the substitution of different halogens significantly influences the electronic structure and optical properties of these organic compounds. Structural data revealed a systematic relationship between crystal lattice constants and the atomic radius and electronegativity of the substituted halogen atoms, with an observed increase in the c/a and c/b ratios when moving from F to I. Electronic band structure analysis showed that the band gap follows the pattern Br < Cl < F < I, indicating that brominated derivatives exhibit more pronounced semiconducting behavior. Partial Density of States (PDOS) curves confirm the pivotal role of halogen p orbitals in determining the properties of upper valence bands. Regarding optical properties, reflectivity, absorption, refractive index, and loss function spectra were analyzed across an energy range of 0-40 eV, revealing systematic variations correlated with the type of halogen substituent. Chlorine-containing compounds exhibited the highest reflectivity, absorption, and loss function values in the 15-25 eV range, while iodine-containing compounds showed the highest refractive index in the low-energy region. These structure-property relationships provide valuable insights for designing organic materials with specific electronic and optical properties for advanced organic electronics applications.