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A series of platinum(II) calix [4]arene-based molecular tweezers was synthesized. The studies of the host-guest association with a charge-neutral cyclometalated platinum(II) complex showed a drastic color change and the turning on of near-infrared emission resulting from Pt•••Pt and π-π interactions. Control of the host-guest assembly process by varying the solvent composition can lead to a change from discrete host and guest molecules to high-ordered host-guest oligomers with the formation of sheet-like nanostructures, demonstrating a rare example of three-state supramolecular host-guest system with high solubility in solvents of diverse polarity. The change in host-guest assembly behaviors could be probed by drastic color changes from yellow to orange to green. The present study provides insights into the systematic design of solvent-responsive molecular materials using molecular tweezers-directed host-guest assembly, with potential applications in colorimetric sensing of changes in the micro-environment.
A series of platinum(II) calix [4]arene-based molecular tweezers was synthesized. The studies of the host-guest association with a charge-neutral cyclometalated platinum(II) complex showed a drastic color change and the turning on of near-infrared emission resulting from Pt•••Pt and π-π interactions. Control of the host-guest assembly process by varying the solvent composition can lead to a change from discrete host and guest molecules to high-ordered host-guest oligomers with the formation of sheet-like nanostructures, demonstrating a rare example of three-state supramolecular host-guest system with high solubility in solvents of diverse polarity. The change in host-guest assembly behaviors could be probed by drastic color changes from yellow to orange to green. The present study provides insights into the systematic design of solvent-responsive molecular materials using molecular tweezers-directed host-guest assembly, with potential applications in colorimetric sensing of changes in the micro-environment.
A series of platinum(II) calix [4]arene-based molecular tweezers was synthesized. The studies of the host-guest association with a charge-neutral cyclometalated platinum(II) complex showed a drastic color change and the turning on of near-infrared emission resulting from Pt•••Pt and π-π interactions. Control of the host-guest assembly process by varying the solvent composition can lead to a change from discrete host and guest molecules to high-ordered host-guest oligomers with the formation of sheet-like nanostructures, demonstrating a rare example of three-state supramolecular host-guest system with high solubility in solvents of diverse polarity. The change in host-guest assembly behaviors could be probed by drastic color changes from yellow to orange to green. The present study provides insights into the systematic design of solvent-responsive molecular materials using molecular tweezers-directed host-guest assembly, with potential applications in colorimetric sensing of changes in the micro-environment.
Molecular tweezer compounds 1-6 with convergent carboxyl groups are prepared from suitable functionalized I2.21and dithia[3.3]metacyclophane building blocks by using several multistep strategies. The C-C coupling of two cyclophanes according to the Hagihara method leads to alkynespacered double cyclophanes. These new preorganized, acyclic host compounds of the cyclophane-type react as molecular tweezers and can selectively "grasp" guest molecules and bind them strongly. X-ray analyses underline the syn conformations of the dithia[3.3]-a n d the anti conformation of the [2.2]metacyclophanes. Der Begriff der ,,molekularen Pinzetten" wurde erstmals von Whitlock et al. 1978 fur einen neuen Typ von acyclischen Wirtverbindungen eingefiihrt. Diese zeichnen sich durch eine parallele Anordnung von zwei Donor-oder Acceptorfunktionen aus (U-formige Konformation), zwischen die flache Gastmolekule eingelagert werden konnen"]. Im vergangenen Jahrzehnt wurden dann Verbindungen zuhfolekdare P i n z e t t e verschiedene Cllste I Molekdare P i n z e t t e mit komplexiertem Castmolekiil Abb. 1. Schema zur selektiven Komplexierung eines Gastmolekuls mit einer molekularen Pinzette theseziele waren die ublicherweise in syn-Konformation[6] vorliegenden ,,doppelten" Dithia[3.3]metacyclophane 1-3 und die in aizti-Konformation['] fixierten ,,doppelten" [2.2]Metacyclophane 4-6, bei denen durch Wahl unterschiedlicher Spacer die Rezeptorfunktionen in variabler Entfernung zueinander fixiert werden konnen. B 748 R. Giither, M. Nieger, K. Rissanen, F. Vogtle S26 Von den ,,doppelten" Cyclophanen 19 konnte nur fur das Isomer 19a eine Rontgenstruktur erhalten werden. Auch hier erkennt man die erwartete syn-Konformation der bei-045 den Dithia[3.3]metacyclophan-Einheiten. Durch die furdiese Cyclophan-Stereochemie geeignete Substitution konnten die tert-Butylestergruppen aufeinander zuzeigen. Zu dieser erwunschten konvergenten Anordnung der funktionellen Gruppen kommt es jedoch aufgrund des hohen Raumbedarfs der trrt-Butylestergruppen zunlchst nicht. Im Kristall weichen die beiden [3.3]Metacyclophan-Einheiten auf entgegengesetzte Molekulseiten (wieder bezogen auf die Biphenylebene) aus. Nach einer Esterspaltung ware allerdings durchaus eine konvergente Orientierung der beiden Carboxygruppen denkbar. Interessant sind auch die Fehlordnungen der Bruckenatome in den Cyclophan-Einheiten. So kommt es im Kristall zum einen zu der fur dieses Substitutionsmuster charakteristischen ,,Sessel/Sessel"-Konformation, zum anderen aber auch zu einer eher fur intraannular substituierte Dithia[3.3]metacyclophane ublichen ,,Sessel/Boot"-Konformation der Bruckenatome (Abb. 5).
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