Density Functional Theory Study of the Effect of Mono-Halogen Substitution on Electronic and Non-Linear Optical Properties of Porphyrin

Porphyrin is an organic macrocycle compound, with a chemical formular (C20H14N4) it act as important components in various technological application like solar cell, due to their flexibility and low production cost. In this work, DFT and TD-DFT were used to investigate the molecular geometry, HOMO-LUMO energy gap, global chemical indices, thermodynamic properties, non-linear optical properties, IR frequencies and IR intensities, open circuit voltage and UV-Vis spectrum of parent and substituted porphyrin molecules were calculated and noted. All the computations were performed by using Gaussian 03 package. Our result for the bond lengths indicates that the strongest bond was found in chloroporphyrin molecule with value of 1.0771(Å) and the highest bond angles was found to be . The calculated value of HOMO-LUMO energy gap shows that porphyrin will be more stable by the substitution of fluoride atom with HOMO-LUMO energy gap of 5.5865eV. The value of energy gap for parent porphyrin molecule (2.8885) eV was found to be very closer to the reported value of (2.920) eV. It was found that the zero point vibrational energy reduces, while the entropy and specific heat capacity of the molecules rises, due to the effect of the substitutions. The non-linear optical properties calculations shows that, the first-order hyperpolarizability values turn out to be ten times than that of the prototype urea ( esu) molecule, which is commonly used for the comparison of NLO properties with other materials. The computed frequencies and intensities result shows that fluoroporphyrin has slightly higher peak values of frequencies with corresponding intensities than the rest of the substituted porphyrin molecules. The open circuit voltage ranges from 2.0206-4.1568eV in the case of high LUMO and 0.9465-3.0828eV in the case of low LUMO, this value can be applied to organic solar cell. The UV-VIS spectrum, shows that due to the solvent effect there was an increase in the excitation energy and then slight increase in oscillator strength. Our finding shows that the hybrid halogenated compound may be utilized as an application in sensor and solar cells.