Effect of axial substitution on the ultrafast dynamics and third-order optical nonlinearity of metallophthalocyanines films

The ultrafast dynamics of the excited excitons of three axially substituted amorphous metallophthalocyanine (MPc) films were investigated by the femtosecond pump–probe technique at image and 400 nm. By considering the exciton–exciton annihilation, the internal conversion and the inter-system crossing, the ultrafast dynamics of the excitons can be well simulated with a three-level model. The third-order optical nonlinearities of these films were measured by Z-scan technique at wavelength of 800 nm. In order to illuminate the axial substitution effect on the samples, we carried out the geometry determination calculation base on the Hartree–Fock theory with basis-set of 3–21 G for the three molecules. The real and imaginary parts of the molecular nonlinear hyperpolarizability γ, were evaluated with the equation of sum-over-states from the quantum theory. The results showed the axial substitution has great effect on the optical nonlinearity of the MPcs.