title: Molecular length dictates the nature of charge carriers in single-molecule junctions of oxidized oligothiophenes.
abstract: To develop advanced materials for electronic devices, it is of utmost importance to design organic building blocks with tunable functionality and to study their properties at the molecular level. For organic electronic and photovoltaic applications, the ability to vary the nature of charge carriers and so create either electron donors or acceptors is critical. Here we demonstrate that charge carriers in single-molecule junctions can be tuned within a family of molecules that contain electron-deficient thiophene-1,1-dioxide (TDO) building blocks. Oligomers of TDO were designed to increase electron affinity and maintain delocalized frontier orbitals while significantly decreasing the transport gap. Through thermopower measurements we show that the dominant charge carriers change from holes to electrons as the number of TDO units is increased. This results in a unique system in which the charge carrier depends on the backbone length, and provides a new means to tune p- and n-type transport in organic materials.
authors.affiliation: Department of Chemistry, Columbia University, New York 10027, USA.
authors.forename: Emma J
authors.initials: EJ
authors.lastname: Dell
authors.affiliation: Department of Applied Physics and Mathematics, Columbia University, New York 10027, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Capozzi
authors.affiliation: Department of Chemistry, Columbia University, New York 10027, USA.
authors.forename: Jianlong
authors.initials: J
authors.lastname: Xia
authors.affiliation: Department of Applied Physics and Mathematics, Columbia University, New York 10027, USA.
authors.forename: Latha
authors.initials: L
authors.lastname: Venkataraman
authors.affiliation: Department of Chemistry, Columbia University, New York 10027, USA.
authors.forename: Luis M
authors.initials: LM
authors.lastname: Campos
mesh_terms: D011108:Polymers / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013876:Thiophenes / Q000737:chemistry*
chemical_list: D011108:Polymers; D013876:Thiophenes