Doubly, Triply and Multiply Pleated Sheets of Bipyridinium Radical Cation‐Incorporated Polymers Tuned by Four Cucurbiturils

Abstract

Depending on the size of their cavity, cucurbit[n]urils (CB[n], n=5, 7, 8, and 10) exhibit very different encapsulation selectivity. This feature has been utilized to tune the formation and switching of three kinds of pleated sheets of bipyridinium radical cation (BIPY•+)‐based polymers in water. Driven by the dimerization of the BIPY•+ units, the polymers spontaneously form multiply pleated sheets. These pleated foldamers can be reversibly converted into flexible pseudopoly‐rotaxanes, doubly and triply pleated sheets by CB[7], CB[8] and CB[10], respectively, through selective encapsulation of the macrocycles for one, two or three stacked BIPY•+ units. Adding adamantamonium (ADMT), hexamethylenetetramine (HMTA) or CB[5] to the respective solutions leads to taking away of the CB rings from the polymers due to the formation of more stable 1:1 complexes and as a result, multiply pleated sheets are recovered. UV‐vis absorption spectroscopy has been used to investigate the formation and conversion of the pleated and extended states of the polymers.

Photoredox Processes in the Aggregation and Gelation of Electron-Responsive Supramolecular Polymers Based on Viologen

“…This behavior was already suggested to occur in other types of supramolecular systems involving π-dimerization of viologens. 45,46 Interestingly, similar behaviors were also reported for supramolecular polymers based on perylene diimide derivatives showing that this phenomenon could be extended to other types of π-conjugated units. 47 High light intensity could be focalized on the samples upon conducting the irradiation through the objective of the microscope.…”

Triple Stack of a Viologen Derivative in a CB[10] Pair

“…In agreement with previous work on viologen derivatives, the broad absorption band centered at about 1050 nm and the intense band at 600 nm were unambiguously assigned to the formation of π-dimers resulting from the self-association of two VPI •+ molecules into diamagnetic, sandwich-shaped bimolecular complexes [( VPI •+ ) 2 ] dim 2+ , stabilized by a tight pairing of viologen units. In contrast to bipyridinium radical cation incorporated polymers, chemical reduction of the VPI 2+ 3 ·CB­[10] 2 complex revealed that CB[10] hampered the π-dimerization of the viologen-based radicals, as reflected by the large decrease in the intensity of the π-dimer band observed in the near-IR domain (solid-line spectrum of Figure b) and by the concomitant development of a set of transitions between 650 and 800 nm assigned to “free” viologen radicals …”

Light-Controlled Aggregation and Gelation of Viologen-Based Coordination Polymers

“…At this point, our best guess is that the molecules self-assemble into liquid crystal due to the photo-induced formation of 3 presenting an appropriate rod-shaped structure. Following this hypothesis, these more rigid structures could then form tactoids due to inter-molecular interactions with adjacent boxes by an orbital overlap involving more than two viologen radical cations as already reported. , The metal–metal interaction between palladium complexes might also be at stake.…”