TY  - UNPB
ID  - pittir6310
UR  - http://d-scholarship-dev.library.pitt.edu/6310/
A1  - Norris, Benjamin Nathaniel
TI  - Sequenced Phenylene-Vinylene Oligomers and Copolymers
Y1  - 2011/06/30/
N2  - The role of sequence in determining the properties of oligomers and polymers is poorly understood despite Nature's formidable examples of libraries of macromolecules whose function is determined by monomer order. A series of oligomers and copolymers bearing poly(para-phenylene-vinylene) sequences was prepared and the dependence of both optoelectronic and thermal properties on monomer order was determined. The optoelectronic properties of three series (dimers, trimers, and tetramers) of oligo(phenylene-vinylenes) OPVs were found to depend on the sequence of donor and acceptor units. These oligomers were prepared using a simple and robust homologation based on Horner-Wadsworth-Emmons (HWE) reactions. Increased donor content was important, and the best sequences (highest absorption and emission maxima, earliest first oxidation potentials, and smallest HOMO-LUMO gaps) contained two adjacent donors without having two adjacent acceptors. Sequences with low donor content or donors with acceptors spaced between them exhibited less desirable properties. The thermal properties of these OPVs are also sequence dependent. The observed trends suggest design principles that could be utilized to prepare specific longer oligomers with attractive properties.Sequenced OPVs were also prepared by a novel iterative olefin cross-metathesis (CM) strategy. The synthesis relies on assembly of orthogonal monomers in a selective CM reaction. The key coupling step proceeded in fair to good yields, and OPVs with 2-5 phenyl units with alternating substitution patterns were prepared. The orthogonal end groups were exploited to prepare donor-acceptor complexes and repeating sequence copolymers. Olefin metathesis was also exploited to prepare fully-substituted symmetric OPVs.Rod-coil copolymers containing well-defined phenylene-vinylene chromophores separated by flexible linkers of precise length have been prepared by acyclic diene metathesis (ADMET) or by HWE polycondensation. The ADMET polymerizations proceeded in good to quantitative yields with moderate molecular weights. The HWE polycondensation route allowed us to prepare rod-coil polymers with varying oxygen content and placement in the linkers in good to excellent yields with high molecular weights. The physical properties of these copolymers varied significantly with composition.
AV  - public
KW  - acyclic diene metathesis; horner wadsworth emmons; olefin metathesis; organic photovoltaics; segmer; sequenced copolymers
ER  -