Investigating the Effects of Mono-Halogen-Substitutions on the Electronic, Non-Linear Optical and Thermodynamic Properties of Perylene Based on Density Functional Theory

Perylene (C20 H12) is polycyclic aromatic hydrocarbons (PAHs) used in the production of organic field- effect transistors, organic photovoltaic cells, and biosensors. In this work, the molecular geometry, HOMO-LUMO energy gap, global indices, thermodynamic properties, non-linear optical properties, IR frequencies, and intensities of isolated perylene and its substituted molecules were calculated and reported. DFT/B3LYP using 6-311+G(d) basis sets was used for the work. All the computations were performed by using Gaussian 03 package and revealed that the substitutions affect the optimized parameters of the titled molecule. The results obtained for the bond lengths indicate that the strongest bond is C19-H12 with a value of 1.0757Å found in 1-fluoroperylene while the bond angles were found to be so close to 1200, revealing that the molecules are planar benzene in which the carbon atoms are hybridized. The calculated value of the energy gap of 3.0572 eV shows that perylene has higher stability in a chemical reaction by substitution of fluorine. The value of the energy gap is closer to the reported value in the literature (2.9740 and 2.9935) eV. The molecule was found to be harder and less reactive in a chemical reaction by substitution of fluoride atom with a chemical hardness of 1.5286 eV. It was found that the specific heat capacity and entropy of the molecule increased while zero-point vibrational energy decreased due to the effect of the substitutions. From the results obtained for non-linear optical properties, it was found that substitution of bromine gives a higher value of the first-order hyperpolarizability with a value of 1.2748 x10-30 esu, which is at least 3 fold than that of prototype urea (0.3728 x10-30 esu) molecule. This suggests that 1-bromoperylene can be the best candidate for non-linear optical applications among the substituted molecules. The calculated frequencies and intensities results show that 1-bromoperylene with a value of 826.37 cm-1 at 96.9614 km/mol has the most intense frequency among the substituted molecules. The results of this work indicate that choosing a better halogen atom and basis sets can improve the electronic and nonlinear optical properties of the titled molecule for better applications.