Microscopic and macroscopic nonlinear optical properties in the gas phase calculation

Abstract

In this dissertation, Finite Field (FF) and time-dependent density functional theory (TD-DFT) calculations were carried out in order to probe the relationship between microscopic and macroscopic nonlinear optical properties. For second-order nonlinear optics, a supramolecularly ordered non-centrosymmetric structure is required. The understandings of the supramolecular organization and of non-covalent intermolecular interactions with various conformations of a chemically identical molecule are main aims of crystal engineering in order to predict the crystal structures and to achieve the desired physical properties. Among the crystal engineering approach, to achieve an acentric molecular orientation in crystals, using molecular asymmetry and nonrod-shaped π-conjugated cores are of current interest because of their approach concerned with molecules design. In order to more insight into the relationship between microscopic and macroscopic nonlinear optical properties, the angle (θ) between the direction of the maximum first hyperpolarizability $\Beta_{max}$ and the dipole moment $\mu$ of chromophores has investigated using ab initio methods. Additionally, this dissertation present ab initio and density functional studies of the π-π interaction energies of a few experimentally monosubstituted-benzene dimers in both parallel- and antiparallel-displaced forms. As a substituent OH group was selected as a donor (D) and F, CN, and $NO_2$ were chosen as acceptors (A) according to their importance in organic nonlinear optical materials. The MP2, SCS-MP2, DFT-D, and DF-DFT-SAPT methods were employed to calculate and compare the interaction energies and their energy components. For A-A and D-D dimers, antiparallel-displaced dimers are found more stable. However, For D-D dimer system (phenol dimer), antiparallel displaced dimer is more stable.