Theoretical study of the linear and nonlinear optical properties of the Photosensibilizer molecules: Photofrin and foscan in gas phase

A theoretical study on the static linear (α) and nonlinear (β and γ) optical properties in gas phase of Photofrin and Foscan molecules is reported. These compounds are known as porphyrin derivatives which act as photosensibilizers in photo dynamic therapy for cancer treatment. The geometric parameters of Photofrin and Foscan were fully optimized using ab initio and Density Functional Theory levels, at Hartree-Fock and B3LYP hybrid functional approach, respectively. The STO-3G, 3-21G* and the 3-21+G standard basis sets were employed for the calculations. The 3-21+G basis set is augmented with one s and three p diffuse functions for carbon, nitrogen, oxygen and sodium atoms. The bond distances and the bond angles of the two optimized molecules obtained with different method/basis set combinations show only minor variation. The Hartree-Fock and B3LYP methods provide a suitable evaluation of the geometrical and optical properties of Photofrin and Foscan molecules, since the calculated α_ave, β_v and γ_ave results are in good agreement with previous reports for similar porphyrin derivatives. The optical properties of Foscan and Photofrin molecules have the same tendencies: the α_ave results have an almost linear relationship with the conjugated bond number, the β_v results are mainly determined by the nature and symmetry of the susbstituent groups to the porphyrin centre and the γ_ave results are extremely depending on the calculation strategies.