Redox‐Active Monopyrrolotetrathiafulvalene‐Based Rotaxane Incorporating the Dihydroazulene/Vinylheptafulvene Photo/Thermoswitch

Abstract

A dumbbell‐shaped molecule with a central monopyrrolo‐tetrathiafulvalene (MPTTF) unit and a 1,1‐dicyano‐dihydroazulene (DHA) photoswitch as one of the two end‐groups was prepared and subsequently converted into a [2]rotaxane with cyclobis(paraquat‐p‐phenylene) (CBPQT4+) as the ring component. Investigations revealed that both the DHA and its vinylheptafulvene (VHF) photoisomer prevent deslipping of CBPQT4+. It was found that the presence of the CBPQT4+ ring on the MPTTF‐DHA dumbbell changes the rate of the thermal back‐conversion of VHF into DHA, i.e., this conversion was found to be accelerated by the presence of the positively charged CBPQT4+ ring. Studies also showed that DHA forms a weak complex with CBPQT4+, which seems to originate from weak interactions between the cyano group located on DHA and the bipyridinium α‐protons on CBPQT4+. The rotaxane was subjected to various oxidation experiments, but these were, unfortunately, accompanied by some decomposition of the molecule; yet, movement of the CBPQT4+ ring from the MPTTF unit towards the DHA moiety seems to occur upon oxidation of the MPTTF unit, promoted by the weak interaction between the DHA moiety and CBPQT4+.

Molecular photoswitches in aqueous environments

“…108 The thermal lifetime of the metastable vinylheptafulvene (VHF) depends on substituents and medium it is embedded in and is usually in the minute to hours range. [515][516][517] The compound was not yet used in aqueous systems, but in liquid crystals, 518 polymer films, 519 in macrocycles, 520 rotaxanes, 521 for solar energy storage, 522,523 or to photocontrol emission properties. 515 Moreover, the DHA/VHF couple can be combined with further photochromic units to assemble multi-stage switches 404,[524][525][526][527] or with electrochemically active unit to achieve photoswitchable redox properties.…”

Electrochemically switchable rotaxanes: recent strides in new directions

“…4a). 44 The CBPQT 4+ wheel of [2]rotaxane 3 4+ is threaded on a redox-active monopyrrolo-tetrathiafulvalene axle, which is terminated on one side with a 1,1-dicyano-dihydroazulene moiety, a molecular photo-and thermoswitch (Fig. 4b).…”