Theoretical investigation of structural parameters, electronic and nonlinear optic properties of 3-phenylthiophene and its fluorine-substitued derivatives

In this study, the structure parameters, the electronic energies, thedipole moments, the highest occupied molecular orbital (HOMO)energies, the lowest unoccupied molecular orbital (LUMO) energies, thepolarizabilities, the anisotropic polarizabilities and hyperpolarizabilitiesvalues of 3-phenylthiophene and 3-(fluorophenyl)thiophenes formed bychanging the number and position of the fluorine atoms on the phenylring were calculated with DFT B3LYP/6-31++G(d,p) and HF/6-31++G(d,p)methods and the GAUSSIAN 98W program package. The electronicenergy, the dipole moment, the HOMO-LUMO energy difference, thepolarizability, the anisotropic polarizability and the hyperpolarizabilityvalues were obtained as a function of the dihedral angle which wasvaried from 0 to 180º intervals of 10º. In the both calculation methods,the effects of number and position of sübstitüent fluorine atom over3-(fluorophenyl)thiophenes have been discussed in details. Especially,the situation when the ortho-fluorine atoms are on the phenyl ring, thedihedral angle of the anti-form equilibrium state is closer to planarityabout 10º, than the syn-form equilibrium state. The results of molecularorbital calculations clearly show that there is the inverse relationshipbetween the variation of polarizability and HOMO-LUMO energydifferences by depending on dihedral angle. That is, HOMO-LUMOenergy differences values increase in the region of syn-form (for 0º< <90º) and decrease in the region of anti-form (for 90º< < 180º). Thepolarizability values decrease in the region of syn-form and increase inthe region of anti-form.