ISMSC 2007 - Università degli Studi di Pavia

Preparation and Properties of Rotaxanes Formed by Dimethyl-β -
cyclodextrin and Oligo(thiophene)s with β-Cyclodextrin Stoppers
Kazuya Sakamoto, Yoshinori Takashima, Hiroyasu Yamaguchi, Akira Harada
Department of Macromolecular Science, Graduate School of Science, Osaka University, 1-1,
Machikaneyama-chou, Toyonaka, Osaka 560-0043, Japan
Email: harada@chem.sci.osaka-u.ac.jp
Polythiophenes and oligothiophenes have
attracted widespread interest due to their
applications as single-molecule electronics
devices and light-emitting diodes. Recently,
conjugated poly(rotaxane)s, in which the
conjugated polymer backbone is covered at
the molecular level by wrapping macrocyclic
molecules have been studied as insulated
molecular wires by many research groups.
We also reported the formation and crystal
structure of the β-cyclodextrin (β-
CD)−bithiophene inclusion complex and
polymerization of the corresponding inclusion
complexes in a selective way to give pseudopoly-(rotaxane)s.
1
Herein, we have prepared 2,6-di-O-methylβ-CD
(DM-β-CD)−oligothiophene based
[2]rotaxanes (2T-[2]rotaxane, 3T-[2]rotaxane)
and [3]rotaxanes (4T-[3]rotaxane, 6T-
[3]rotaxane) shown in Figure 1 and investigate
their photophysical properties. The
fluorescence maximum wavelength of
rotaxane shifted to a longer wavelength with
an increase in the conjugation length. The
fluorescence intensity of rotaxane in aqueous
media was higher than that of dumbbell
shaped molecules (without DM-β-CD on axis).
The increase in the fluorescence intensities of
rotaxane is caused by the suppression of
intermolecular interaction, indicative of the
effect of insulated oligothiophene with DM-β-
CD. The inclusion ratio of rotaxanes
influenced their quantum yields in aqueous
solutions.
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Figure 1. Chemical structures of DM-β-CDoligothiophene
rotaxanes with β-CD stoppers.
Figure 2. Fluorescence spectra of 2T-
[2]rotaxane (a), 2T-dumbbell (b), 3T-[2]rotaxane
(c), 3T-dumbbell (d), 4T-[3]rotaxane (e), and 6T-
[3]rotaxane (f), in H2O, 15µM, λex=378 nm (2T),
407 nm (3T), 438 nm (4T), 449 nm (6T).
[1] (a) Takashima, Y.; Oizumi, Y.; Sakamoto, K.; Miyauchi, M.; Kamitori, S.; Harada, A.
Macromolecules 2004, 37, 3962-3964. (b) Takashima, Y.; Sakamoto, K.; Oizumi, Y.;
Yamaguchi, H.; Kamitori, S.; Harada, A. J. Inclusion Phenom. Macrocycl. Chem. 2006, 56, 45-
53.
[2] Sakamoto, K.; Takashima, Y.; Yamaguchi, H.; Harada, A. J. Org. Chem. 2007, 72, 459-465.
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Host-Guest Chemistry of Tetramethoxy Resorcinarene Crowns: Bis-Crown-5
vs. Tribenzo-Bis-Crown-6
Kirsi Salorinne and Maija Nissinen
Department of Chemistry, NanoScience Center, University of Jyväskylä, P.O. Box 35, 40014
JYU, Finland
Calixcrowns 1 are a widely studied class of compounds due to their abilities to complex cations
and act as receptors or ionophores, in which both the properties arising from the crown ether
unit and the calixarene skeleton contribute to the host-guest chemistry of these compounds. We
wanted to further explore this family of compounds and introduced resorcinarene as the
platform. As opposed to calixarene, the phenolic hydroxyl groups are situated on the upper rim
of resorcinarene, which enables the crown ether bridges to form on the open end of the cavity
and, therefore, makes the resorcinarene bowl available to take part in guest binding. We chose
tetramethoxy resorcinarene 2 as the platform because it provides two sites for crown ether
bridging creating two crown “pockets” for guest inclusion.
The selectivity toward guest binding is determined by the functionality at the crown ether unit,
which prompted us to design two different resorcinarene bis-crown ethers: Bis-crown-5 3 (BC5)
and tribenzo-bis-crown-6 (TBBC6) (see figure below). The complexation properties toward
alkali metal cations (K + , Rb + and Cs + ) were studied by means of 1 H NMR spectroscopic titration,
picrate extraction and crystallographic methods.
O
MeO
MeO
O
R R
R
R
O
OMe
OMe
O
BC5 =
TBBC6 =
O O O O O
O
O
O O
O O
Figure. Schematic presentation of tetramethoxy resorcinarene bis-crown ethers BC5 and
TBBC6 (R=C2H5).
[1] (a) R. Ungaro, In Calicarenes in Action; L. Mandolini, R. Ungaro, Eds.; Imperial College
Press: London, England, 2000. (b) K.R. Sharma and Y.K. Agrawal, Rev. Anal. Chem. 2004, 23,
133-158. (c) C. Alfiere, E. Dradi, A. Pochini, R. Ungaro and G.D. Andreetti, J. Chem. Soc..
Chem. Commun. 1983, 1075-1077.
[2] M.J. McIldowie, M. Mocerino, B.W. Skelton and A.H. White, Org. Lett. 2000, 2, 3869-3871.
[3] K. Salorinne and M. Nissinen, Org. Lett. 2006, 8, 5473-5476.