DOI: 10.1002/chem.200601014 Fluorescent Perylene Diimide Rotaxanes: Spectroscopic Signatures of Wheel–Chromophore Interactions Jacob Baggerman, [a] Dhiredj C. Jagesar, [a] Renaud A. L. VallØe, [b] Johan Hofkens, [b] Frans C. De Schryver, [b] Frauke Schelhase, [c] Fritz Vçgtle, [c] and Albert M. Brouwer* [a] Introduction Rotaxanes are supramolecular nanoscale architectures which have recently attracted much attention because of their possible applications as molecular switches and motors. [1–3] Rotaxanes consist of a large ring, the wheel, and an axle, which is threaded through the wheel and kept in place by bulky stoppers at the end of the axle. Controlling the relative position of the wheel with respect to the axle is one of the main challenges for the desired applications. Movement of the wheel can be induced using redox, [4] acid/ base [5] or photochemical stimulation. [6] The displacement of the wheel is often monitored using NMR or changes in the optical absorbance spectra. The use of fluorescence for de- tecting the shuttling process in rotaxanes is less common. [7–12] It is well known in the field of molecular sen- sors that fluorescence is one of the most sensitive means of detection. [13] Moreover, fluorescence spectroscopy is very suitable for kinetic measurements with high time resolution and high dynamic range. For fluorescence to be useful as a probe for the position of the wheel it is important that inter- action between the wheel and the chromophore changes the properties of the latter. In this paper we describe a [2]rotaxane and a [3]rotaxane with a strongly fluorescent perylene diimide group. In the rotaxanes, the presence of the wheel(s) leads to changes in both the absorption and fluorescence properties of the chro- mophore. The axle is used as reference compound. Further- more the (spectro)electrochemical properties of the axle and the rotaxanes are reported. The measurements show that the wheel(s) stabilize(s) the anionic species. Also the fluorescence of individual molecules is studied. These are the first studies of a mechanically interlocked system at the single molecule level. Results and Discussion Synthesis : The rotaxanes were prepared using the so-called trapping method (Scheme 1). [14] The 4-tritylphenolate ion forms a complex with the wheel. This complex acts as a supramolecular nucleophile and reacts with the benzylic bromide to form the rotaxane. Because of the presence of Keywords: fluorescence spectrosco- py · rotaxanes · single-molecule studies · time-resolved spectrosco- py · UV/Vis spectroscopy Abstract: [2]- and [3]-rotaxanes with a tetraphenoxy perylene diimide core were synthesized. Hydrogen bonding between the wheel and the imide changes the opti- cal properties of the perylene chromophore: the absorption and fluorescence spec- tra are red-shifted. The decay times of the rotaxanes are shorter in comparison with that of the axle. Single molecule fluorescence measurements reveal relatively narrow distributions of emission maxima and decay times. The averages are in agreement with ensemble measurements. The observed red shifts make the pery- lene diimide a suitable chromophore for sensing the position of the wheel on the axle. [a] Dr. J. Baggerman, D.C. Jagesar, Dr. A. M. Brouwer Van ’t Hoff Institute for Molecular Sciences University of Amsterdam, Nieuwe Achtergracht 129 1018 WS Amsterdam (The Netherlands) Fax:(+ 31)20-525-5670 E-mail:A.M.Brouwer@uva.nl [b] Dr.R.A.L.VallØe,Prof.Dr.J.Hofkens,Prof.Dr.F.C.DeSchryver Department of Chemistry, KU Leuven, Celestijnenlaan 200F 3001 Heverlee (Belgium) [c] Dr. F. Schelhase, Prof.Dr. F. Vçgtle KekulØ-Institut für Organische Chemie und Biochemie der Universität Bonn Gerhard-Domagk-Strasse 1, 53121 Bonn (Germany) Supporting information for this article is available on the WWW under http://www.chemeurj.org/ or from the author. Chem.Eur.J. 2007, 13,1291–1299 # 2007 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 1291 FULL PAPER