Optoelectronic and nonlinear optical properties of conjugated aromatic polyimines.

摘要

A major effort in research in conjugated polymers has been directed to the development of the materials for optoelectronic and nonlinear optical device applications. Although conjugated polymers have been shown to exhibit promising features such as efficient electroluminescence and large third-order optical susceptibility, the basic structural factors that can improve their optoelectronic and nonlinear optical properties are not fully understood. This limitation arises mainly from the lack of systematic studies of the effects of molecular structure on properties. In this thesis research, a series of systematically designed conjugated aromatic polyimines has been synthesized and characterized, and their optical, optoelectronic, and nonlinear optical properties were investigated with an aim to understand the correlations of structure and properties in conjugated polymers.; A series of 24 homopolymers and 4 random copolymers of conjugated aromatic polyimines was synthesized, characterized by {dollar}{bsol}sp1{dollar}H NMR spectroscopy, and processed into thin films for the solid state studies.; The optical dispersion of refractive index was measured in the range of 700-2500 nm. A wide variation of refractive index with structure was observed and explained in terms of molar volume, {dollar}{bsol}pi{dollar}-electron delocalization, and polarizable heteroatoms. A refractive index data base that consists of 33 conjugated polymers was used to formulate a new group contribution calculation of the refractive index of conjugated polymers. The molar refraction of 24 functional groups was established and found to give accurate predictions of refractive index of conjugated polymers.; New light-harvesting thin film supramolecular assemblies, consisting of a conjugated rigid-rod polymer randomly dispersed in a matrix of rod-coil copolyimine nanocomposite, were prepared and shown to exhibit efficiency for singlet electronic energy transfer as high as 93%. It was found that the energy transfer efficiency can be regulated through variation of the supramolecular structure of the polymer nanocomposite assemblies.; Third order optical susceptibility {dollar}{bsol}chi{bsol}sp{lcub}(3){rcub}{dollar} was studied by third harmonic generation spectroscopy in the spectral range of 900-2400 nm (0.52-1.38 eV) and the optical dispersion was analyzed by 4-level essential state model. The structure-{dollar}{bsol}chi{bsol}sp{lcub}(3){rcub}{dollar} relationships of this class of materials reveal large nonresonant {dollar}{bsol}chi{bsol}sp{lcub}(3){rcub}{dollar} that is tunable by electron-donating side group substitutions, random copolymerization, and host-guest complexation. The model consisting of 4 electronic states was found to account for the observed dispersion and multiphoton resonances.