title: Fluctuating exciton localization in giant π-conjugated spoked-wheel macrocycles.
abstract: Conjugated polymers offer potential for many diverse applications, but we still lack a fundamental microscopic understanding of their electronic structure. Elementary photoexcitations (excitons) span only a few nanometres of a molecule, which itself can extend over microns, and how their behaviour is affected by molecular dimensions is not immediately obvious. For example, where is the exciton formed within a conjugated segment and is it always situated on the same repeat units? Here, we introduce structurally rigid molecular spoked wheels, 6 nm in diameter, as a model of extended π conjugation. Single-molecule fluorescence reveals random exciton localization, which leads to temporally varying emission polarization. Initially, this random localization arises after every photon absorption event because of temperature-independent spontaneous symmetry breaking. These fast fluctuations are slowed to millisecond timescales after prolonged illumination. Intramolecular heterogeneity is revealed in cryogenic spectroscopy by jumps in transition energy, but emission polarization can also switch without a spectral jump occurring, which implies long-range homogeneity in the local dielectric environment.
authors.affiliation: Kekulé-Institut für Organische Chemie und Biochemie der Universität Bonn, Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany.
authors.forename: A Vikas
authors.initials: AV
authors.lastname: Aggarwal
authors.forename: Alexander
authors.initials: A
authors.lastname: Thiessen
authors.forename: Alissa
authors.initials: A
authors.lastname: Idelson
authors.forename: Daniel
authors.initials: D
authors.lastname: Kalle
authors.forename: Dominik
authors.initials: D
authors.lastname: Würsch
authors.forename: Thomas
authors.initials: T
authors.lastname: Stangl
authors.forename: Florian
authors.initials: F
authors.lastname: Steiner
authors.forename: Stefan-S
authors.initials: SS
authors.lastname: Jester
authors.forename: Jan
authors.initials: J
authors.lastname: Vogelsang
authors.forename: Sigurd
authors.initials: S
authors.lastname: Höger
authors.forename: John M
authors.initials: JM
authors.lastname: Lupton
mesh_terms: D031541:Fluorescence Resonance Energy Transfer; D047028:Macrocyclic Compounds / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D011108:Polymers / Q000737:chemistry*
chemical_list: D047028:Macrocyclic Compounds; D011108:Polymers