title: Study of cross-conjugated iso-polytriacetylenes and related oligoenynes.
abstract: Two series of monodisperse cross-conjugated oligomers based on enyne repeat units have been realized. The first class of molecules, iso-polytriacetylenes (iso-PTAs, 2), was divergently synthesized using an iterative sequence of palladium-catalyzed cross-coupling reactions of vinyl triflate 5 with terminal alkynes. The second series of oligoenynes (17-20) are based on an octatetrayne backbone, and result from homocoupling of the differentially protected iso-PTA oligomers 8-11. The longest member of this series, 20, spans ca. 5.6 nm from Si atom to Si atom and is composed of a contiguous sequence of 44 sp and sp(2) carbons. The lowest energy electronic absorption band for iso-PTA dimers in the progression 13 --> 9 --> 16 is consistently red-shifted as a result of extending the cross-conjugated structure. A similar comparison within each series (i.e., 16, 6-7, or 17-20), however, suggests little effect on the electronic characteristics of these molecules as oligomer length is increased. The solid-state properties of one derivative, 17, are also described.
authors.affiliation: Department of Chemistry, University of Alberta, Edmonton, AB T6G 2G2, Canada.
authors.forename: Yuming
authors.initials: Y
authors.lastname: Zhao
authors.forename: Robert
authors.initials: R
authors.lastname: McDonald
authors.forename: Rik R
authors.initials: RR
authors.lastname: Tykwinski