Radically Enhanced Dual Recognition

Xiao-Yang Chen; Haochuan Mao; Yuanning Feng; Kang Cai; Dengke Shen; Huang Wu; Long Zhang; Xingang Zhao; Hongliang Chen; Bo Song; Yang Jiao; Yong Wu; Charlotte L Stern; Michael R Wasielewski; J Fraser Stoddart

doi:10.1002/anie.202109647

Radically Enhanced Dual Recognition

Angew Chem Int Ed Engl. 2021 Nov 22;60(48):25454-25462. doi: 10.1002/anie.202109647. Epub 2021 Sep 7.

Authors

Xiao-Yang Chen¹, Haochuan Mao^{1

2}, Yuanning Feng¹, Kang Cai³, Dengke Shen⁴, Huang Wu¹, Long Zhang¹, Xingang Zhao¹, Hongliang Chen¹, Bo Song¹, Yang Jiao¹, Yong Wu¹, Charlotte L Stern¹, Michael R Wasielewski^{1

2}, J Fraser Stoddart^{1

5

6

7}

Affiliations

¹ Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
² Institute for Sustainability and Energy at Northwestern, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.
³ Department of Chemistry, Nankai University, 94 Weijin Road, Nankai District, Tianjin, 300071, China.
⁴ Institutes of Physical Science and Information Technology, Anhui University, Hefei, 230601, China.
⁵ School of Chemistry, University of New South Wales, Sydney, NSW, 2052, Australia.
⁶ Stoddart Institute of Molecular Science, Department of Chemistry, Zhejiang University, Hangzhou, 310027, China.
⁷ ZJU-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou, 311215, China.

PMID: 34342116
DOI: 10.1002/anie.202109647

Abstract

Complexation between a viologen radical cation (V^.+ ) and cyclobis(paraquat-p-phenylene) diradical dication (CBPQT^2(.+) ) 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)^2(.+) , i.e., CBPQN^2(.+) . Central to this dual recognition process was the choice of 2,6-bismethylenenaphthalene linkers for incorporation into the bisradical dicationic host. They provide the space between the two bipyridinium radical cations in CBPQN^2(.+) suitable for binding two MV^.+ with relatively short (3.05-3.25 Å) radical-pairing distances. The size-matched bisradical dicationic host was found to exhibit highly selective and cooperative association with the two MV^.+ in MeCN at room temperature. The formation of the tetrakisradical tetracationic inclusion complex - namely, [(MV)₂ ⊂CBPQN]⁴⁽^.+) - in MeCN was confirmed by VT ¹ H NMR, as well as by EPR spectroscopy. The solid-state superstructure of [(MV)₂ ⊂CBPQN]⁴⁽^.+) reveals an uneven distribution of the binding distances (3.05, 3.24, 3.05 Å) between the three different V^.+ , suggesting that localization of the radical-pairing interactions has a strong influence on the packing of the two MV^.+ inside the bisradical dicationic host. Our findings constitute a rare example of binding two radical guests with high affinity and cooperativity using host-guest radical-pairing interactions. Moreover, they open up possibilities of harnessing the tetrakisradical tetracationic inclusion complex as a new, orthogonal and redox-switchable recognition motif for the construction of MIMs and AMMs.

Keywords: binding stoichiometry; host-guest systems; molecular recognition; radical-pairing interactions.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.

Grants and funding

CHE-1900422/national science foundation