title: Hierarchical Growth of Supramolecular Structures Driven by Pimerization of Tetrahedrally Arranged Bipyridinium Units.
abstract: A shape-persistent molecule, featuring four bipyridinium units, has been synthesized that upon reduction undergoes intermolecular pimerization because of the rigid architecture of the molecule. The pimerization process has been investigated by a variety of techniques, such as absorption measurements, EPR spectroscopy, as well as gamma and pulse radiolysis, and compared with the behavior of a model compound. Computational studies have also been performed to support the experimental data. The most interesting feature of the tetramer is that pimerization occurs only above a threshold concentration of monoreduced species, on the contrary to the model compound. Furthermore, there is an increase of the apparent pimerization constant by increasing the concentration of reduced bipyridinium units. These results have been interpreted by the fact that pimerization is favored in the tetrahedrally shaped molecule because of a cooperative mechanism. Each multiply reduced molecule can indeed undergo multiple intermolecular interactions that enhance the stabilization of the system, also leading to hierarchical supramolecular growth. The resulting supramolecular system formed by such intermolecular pimerization should exhibit a diamond-like structure, as suggested by a simplified modeling approach. The intermolecular nature of the pimerization process occurring in the tetramer has been demonstrated by measuring the corresponding bimolecular rate constant by pulsed radiolysis experiments.
authors.affiliation: Dipartimento di Chimica "G. Ciamician", Università di Bologna, via Selmi 2, 40126, Bologna, Italy.
authors.forename: Marianna
authors.initials: M
authors.lastname: Marchini
authors.affiliation: Dipartimento di Chimica "G. Ciamician", Università di Bologna, via Selmi 2, 40126, Bologna, Italy.|Present address: Dipartimento di Scienze e, Tecnologie Agro-alimentari, Università di Bologna, viale Fanin 50, 40127, Bologna, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Baroncini
authors.affiliation: Dipartimento di Chimica "G. Ciamician", Università di Bologna, via Selmi 2, 40126, Bologna, Italy.|Interuniversity Center for the Chemical Conversion of Solar Energy, Bologna Unit, Università di Bologna, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Bergamini
authors.affiliation: Dipartimento di Chimica "G. Ciamician", Università di Bologna, via Selmi 2, 40126, Bologna, Italy.|Interuniversity Center for the Chemical Conversion of Solar Energy, Bologna Unit, Università di Bologna, Italy.
authors.forename: Paola
authors.identifier: http://orcid.org/0000-0001-8916-1473
authors.initials: P
authors.lastname: Ceroni
authors.affiliation: Istituto per la Sintesi Organica e la Fotoreattività, Consiglio Nazionale delle Ricerche, via Gobetti 101, 40129, Bologna, Italy.
authors.forename: Mila
authors.initials: M
authors.lastname: D'Angelantonio
authors.affiliation: Dipartimento di Chimica "G. Ciamician", Università di Bologna, via Selmi 2, 40126, Bologna, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Franchi
authors.affiliation: Dipartimento di Chimica "G. Ciamician", Università di Bologna, via Selmi 2, 40126, Bologna, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Lucarini
authors.affiliation: Dipartimento di Chimica "G. Ciamician", Università di Bologna, via Selmi 2, 40126, Bologna, Italy.
authors.forename: Fabrizia
authors.initials: F
authors.lastname: Negri
authors.affiliation: Institute of Nuclear Chemistry and Technology, 16 Dorodna Str., 03-195, Warsaw, Poland.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Szreder
authors.affiliation: Dipartimento di Chimica "G. Ciamician", Università di Bologna, via Selmi 2, 40126, Bologna, Italy.|Interuniversity Center for the Chemical Conversion of Solar Energy, Bologna Unit, Università di Bologna, Italy.
authors.forename: Margherita
authors.identifier: http://orcid.org/0000-0002-8753-0973
authors.initials: M
authors.lastname: Venturi
keywords: EPR spectroscopy; electrochemistry; photochemistry; radiolytic reduction; viologen