Exploring the relation between intramolecular conjugation and band dispersion in one-dimensional polymers

Making use of the inherent surface anisotropy of different high index surface planes vicinal to the low index Au(111) orientation, one-dimensional polymers have been synthesized following established procedures from two different precursor molecules. The successful polymerization of both 4,4″-dibromo-p-terphenyl and 5,5′-dibromo-salophenato-Co(II) precursors into poly(p-phenylene) and poly[salophenato-Co(II)], respectively, has been confirmed by scanning tunneling microscopy and low energy electron diffraction. Angle-resolved photoemission spectroscopy data reveal a highly dispersive band in the case of poly(p-phenylene) while no significant dispersion is resolved for poly[salophenato-Co(II)]. On the basis of density functional theory calculations, we explain this observation as a result of a high conjugation along the aromatic phenyl groups in poly(p-phenylene) that is absent in the case of poly[salophenato-Co(II)], where intramolecular conjugation is interrupted in the salophenato-Co(II) unit. Furthermore, we make use of multicenter and delocalization indexes to characterize the electron mobility (corresponding to a high band dispersion) along different paths associated with individual molecular orbitals.The authors thank for technical and human support provided by IZO-SGI SGIker of UPV/EHU and European funding (ERDF and ESF). Financial support comes from Eusko Jaurlaritza (Basque Government) through the projects IT-588-13, IT-756-13, and IT621-13 as well as from the Spanish MINECO/FEDER through Grants MAT2013-46593-C6-4-P and MAT2016-78293-C6-6-R, as well as projects CTQ2014-52525-P and FIS2016-75862-P. E.S., M.B., and R.W. gratefully acknowledge financial support from the Office of Naval Research via Grant N00014-16-1-2900 and the Deutsche Forschungsgemeinschaft via SFB668-B4.Peer Reviewe