A new pyrene-dihydrophenazine dyad was prepared. Oxidation of the neutral species produced a bis(radical cation) species, which was characterized by the absorptions of their component radical cations in the visible region. A thermally accessible triplet state was observed in the ESR measurement in frozen n-PrCN. The energy gap between the singlet and triplet states was determined to be 2J/k(B) = -36 +/- 3 K.
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http://dx.doi.org/10.1021/ol9009927 | DOI Listing |
J Am Chem Soc
December 2022
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
Molecular recognition, based on noncovalent bonding interactions, plays a central role in directing supramolecular phenomena in both chemical and biological environments. The identification and investigation of weakly associated recognition motifs, however, remains a major challenge, especially when the motifs are interlinked with and obscured by other robust binding modes in complicated systems. For example, although the host-guest recognition between the radical cations of both cyclobis(paraquat--phenylene) (CBPQT) and 4,4'-bipyridinium (BIPY) salts has been thoroughly investigated, the question of whether other binding modes exist between these two positively charged entities is the subject of some debate because of the complexity and dynamic nature of this supramolecular system.
View Article and Find Full Text PDFAngew Chem Int Ed Engl
January 2023
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
The tetracationic cyclophane, cyclobis(paraquat-p-phenylene), also known as the little blue box, constitutes a modular receptor that has facilitated the discovery of many host-guest complexes and mechanically interlocked molecules during the past 35 years. Its versatility in binding small π-donors in its tetracationic state, as well as forming trisradical tricationic complexes with viologen radical cations in its doubly reduced bisradical dicationic state, renders it valuable for the construction of various stimuli-responsive materials. Since the first reports in 1988, the little blue box has been featured in over 500 publications in the literature.
View Article and Find Full Text PDFAngew Chem Int Ed Engl
November 2021
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
Complexation between a viologen radical cation (V ) and cyclobis(paraquat-p-phenylene) diradical dication (CBPQT ) has been investigated and utilized extensively in the construction of mechanically interlocked molecules (MIMs) and artificial molecular machines (AMMs). The selective recognition of a pair of V using radical-pairing interactions, however, remains a formidable challenge. Herein, we report the efficient encapsulation of two methyl viologen radical cations (MV ) in a size-matched bisradical dicationic host - namely, cyclobis(paraquat-2,6-naphthalene) , i.
View Article and Find Full Text PDFJ Am Chem Soc
January 2021
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
The solid-state properties of organic radicals depend on radical-radical interactions that are influenced by the superstructure of the crystalline phase. Here, we report the synthesis and characterization of a substituted tetracationic cyclophane, cyclobis(paraquat--1,4-dimethoxyphenylene), which associates in its bisradical dicationic redox state with the methyl viologen radical cation () to give a 1:1 inclusion complex. The (super)structures of the reduced cyclophane and this 1:1 complex in the solid state deviate from the analogous (super)structures observed for the reduced state of cyclobis(paraquat--phenylene) and that of its trisradical tricationic complex.
View Article and Find Full Text PDFJ Am Chem Soc
April 2020
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
Two new highly charged [2]catenanes-namely, ·6PF and ·6PF-were synthesized by exploiting radical host-guest templation between derivatives containing BIPY radical cations and the meta analogue of cyclobis(paraquat--phenylene). In contrast to related [2]catenanes that have been isolated as air-stable monoradicals, both ·6PF and ·6PF exist as air-stable singlet bisradicals, as evidenced by both X-ray crystallography in the solid state and EPR spectroscopy in solution. Electrochemical studies indicate that the first two reduction peaks of these two [2]catenanes are shifted significantly to more positive potentials, a feature which is responsible for their extraordinary stability in air.
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