Solvent-dependent ground-state distributions in a donor-acceptor redox-active bistable [2]catenane

Abstract

The solvent dependency of the ground-state distribution as well as the electrochemical switching behavior in a redox-active bistable donor-acceptor [2]catenane, containing bisthiotetrathiafulvalene (STTFS) and 1,5-dioxynaphthalene (DNP) recognition sites incorporated within a macrocyclic polyether encircled by the cyclobis(paraquat-p-phenylene) (CBPQT 4+) ring, has been investigated. There are two translational isomers: (i) the ground-state co-conformation (GSCC) in which the CBPQT 4+ ring encircles the STTFS unit and (ii) the metastable-state co-conformation (MSCC) in which the CBPQT 4+ ring encircles the DNP unit. 1H NMR spectroscopy indicates that the ground-state distribution of GSCC to MSCC varies from approximately 1:1 in MeCN to 7:1 in MeCN:H 2O (1:1, v/v) at 283K. The reversible electrochemical switching behavior of the [2]catenane was confirmed by 1H NMR and UV-Vis spectroscopies, as well as by cyclic voltammetry (CV). Additionally, variable scan-rate CV studies were compared with simulated CV data and show that the ground-state distribution of GSCC to MSCC is about 30:1 in MeCN:H 2O (1:1, v/v) at 298K. With the assistance of isothermal titration calorimetry of model compounds, it was found that the changing ground-state distribution in differing solvent systems is driven entropically rather than enthalpically. Copyright © 2012 John Wiley & Sons, Ltd.