Design and synthesis of pi-stacked conjugated oligomers and polymers

Conjugated oligomers and polymers are very attractive materials for organic electronic devices by virtue of their semiconducting properties. The transport of charge carriers along th- conjugated chains in one dimension does not provide a complete understanding of the semiconducting behavior of these materials. The electronic structure of conjugated organic materials depends on both the molecular structure and the three-dimensional packing of the conjugated chains with one another. To explore the effect of interchain interaction on optoelectronic properties of conjugated oligomers, we chose to explore benzo-fused bicyclo[4.4.1]undecane and pseudo-geminal [2.2]paracyclophane as convenient scaffolds to prepare oligomers that are held in a th-stacked manner. These scaffolds provide the opportunity to control the distance and orientation of conjugated segments and to study their electro-optical properties.;We have installed conjugated oligomers on the benzo-fused bicyclo[4.4.1]undecane core to prepare a series of stacked oligo(phenylene ethynylene)s and compare their spectroscopy and electrochemistry with their linear unstacked counterparts. In another approach, we explored the pseudo-geminal [2.2]paracyclophane as a scaffold to prepare the stacked oligo(phenylene vinylene)s. A combined experimental and theoretical study of well-defined stacked oligomers provided very useful insights into the effect of pi-th interactions on the electronic structure of closely packed conjugated chains. The significantly large Stokes shifts associated with our stacked compounds are due to the formation of an extended excimer-like state arising from stacking of entire length of the conjugated chains.;To extend the utility of pseudo-geminal (pg) cyclophane as a scaffold, we chose to explore the use of (pg) cyclophanes bearing alkyne, alkene and halogen substituents as monomers in the preparation of p-stacked conjugated polymers. The U-turn provided by the pseudo-geminal [2.2]paracyclophane core is useful to build ladder-type polymers consisting of conjugated units that are stacked over their entire length. The multilayered polymers exhibit the effect of extensive pi-pi interactions between the stacked conjugated tiers. This is most pronounced in the excited state with the formation of a phane state by virtue of the extended overlap along the entire length of the stacked chromophores.;Thus, the pi-stacked arctitectures (conjugated oligomers and polymers) serve as suitable platforms to develop an understanding of the interactions between stacked conjugated chains, since they more closely resemble the arrangement of the pi-systems of semiconducting organic oligomers and polymers in thin-film organic electronic devices.