title: Quantum Mechanical and Experimental Validation that Cyclobis(paraquat-p-phenylene) Forms a 1:1 Inclusion Complex with Tetrathiafulvalene.
abstract: The promiscuous encapsulation of π-electron-rich guests by the π-electron-deficient host, cyclobis(paraquat-p-phenylene) (CBPQT(4+)), involves the formation of 1:1 inclusion complexes. One of the most intensely investigated charge-transfer (CT) bands, assumed to result from inclusion of a guest molecule inside the cavity of CBPQT(4+), is an emerald-green band associated with the complexation of tetrathiafulvalene (TTF) and its derivatives. This interpretation was called into question recently in this journal based on theoretical gas-phase calculations that reinterpreted this CT band in terms of an intermolecular side-on interaction of TTF with one of the bipyridinium (BIPY(2+)) units of CBPQT(4+), rather than the encapsulation of TTF inside the cavity of CBPQT(4+). We carried out DFT calculations, including solvation, that reveal conclusively that the CT band emerging upon mixing TTF with CBPQT(4+) arises from the formation of a 1:1 inclusion complex. In support of this conclusion, we have performed additional experiments on a [2]rotaxane in which a TTF unit, located in the middle of its short dumbbell, is prevented sterically from interacting with either one of the two BIPY(2+) units of a CBPQT(4+) ring residing on a separate [2]rotaxane in a side-on fashion. This [2]rotaxane has similar UV/Vis and (1)H NMR spectroscopic properties with those of 1:1 inclusion complexes of TTF and its derivatives with CBPQT(4+). The [2]rotaxane exists as an equimolar mixture of cis- and trans-isomers associated with the disubstituted TTF unit in its dumbbell component. Solid-state structures were obtained for both isomers, validating the conclusion that the TTF unit, which gives rise to the CT band, resides inside CBPQT(4+).
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.
authors.forename: Karel J
authors.initials: KJ
authors.lastname: Hartlieb
authors.affiliation: Materials and Process Simulation Center (MC 139-74), California Institute of Technology, Pasadena, CA, 91125, USA.
authors.forename: Wei-Guang
authors.initials: WG
authors.lastname: Liu
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.|Howard Hughes Medical Institute, Department of Molecular Biology, Center for Computational and Integrative Biology, Massachusetts General Hospital, Boston, MA, 02114, USA.
authors.forename: Albert C
authors.initials: AC
authors.lastname: Fahrenbach
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.
authors.forename: Anthea K
authors.initials: AK
authors.lastname: Blackburn
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.
authors.forename: Marco
authors.initials: M
authors.lastname: Frasconi
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.
authors.forename: Nema
authors.initials: N
authors.lastname: Hafezi
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.
authors.forename: Sanjeev K
authors.initials: SK
authors.lastname: Dey
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.
authors.forename: Amy A
authors.initials: AA
authors.lastname: Sarjeant
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.
authors.forename: Charlotte L
authors.initials: CL
authors.lastname: Stern
authors.affiliation: Materials and Process Simulation Center (MC 139-74), California Institute of Technology, Pasadena, CA, 91125, USA. wag@wag.caltech.edu.
authors.forename: William A
authors.initials: WA
authors.lastname: Goddard
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA. stoddart@northwestern.edu.
authors.forename: J Fraser
authors.initials: JF
authors.lastname: Stoddart
keywords: DFT calculations; donor-acceptor systems; rotaxanes; tetrathiafulvalene