This award is made jointly by the Office of Special Projects in the Chemistry Division and by the Division of Materials Research in support of the computational studies of Dr. David Yaron. Semi-empirical quantum chemistry models will be developed and applied to the photophysics of conjugated polymers. Simultaneous fits will be developed based on experimental data on oligomers and polymers and on different polymeric systems to provide for the investigation of the operative screening mechanisms. By developing a single consistent approach for polyacetylenes, polydiacetylenes and poly(paraphenylenevinylene), parameters will be developed that can be applied to other polymers. Coulomb screening between electrons and holes in excited states will be included through explicit calculations of the polarization induced in surrounding polymer chains, and through explicit calculations of on-chain screning mechanisms. Equation-of-motion formalisms developed for nonlinear optics will be used to calculate excited states, providing a size-consistent and computationally feasible approach to the excited states of long polymer chains. The major advantage of conjugated polymers over inorganic materials in optical and electronic applications is the ability to control structure at the molecular level by synthesis, and at the macromolecular level by self-assembly. The development of semi-empirical models will allow for the prediction of structure-property relationships in important classes of materials and provide a basis for the design of new materials.
