Communications
with a fixed polymer concentration but varying amounts of the alkali-
[13]In contrast, the homopolyimide, which is devoid of the
naphthalene unit, prepared from simple amine terminated
oligoethylene glycol and pyromellitic dianhydride, is white in
colour.
[14]1,5-Dimethoxynaphthalene was used as the model donor and the
pyromellitic diimide prepared from pyromellitic dianhydride
with 2-[2-(2-methoxyethoxy)ethoxy]ethylene amine was used as
the model acceptor.
[15]For examples of small molecule systems in which enhanced
charge-transfer complexation results from linking of the donor
and acceptor units, see: a) N. C Yang, Y. Gaoni, J. Am. Chem.
Soc. 1964, 86, 5022; b) J. W. Verhoeven, I. P. Drikx, T. J. Deboer,
Tetrahedron Lett. 1966, 7, 439; c) D. Kost, N. Peor, G. Sod-
Moriah, Y. Sharabi, D. T. Durocher, M. Raban, J. Org. Chem.
2002, 67, 6938.
[16]a) R. Forster in Organic Charge-Transfer Complex, Academic
Press, London, 1969; b) M. S. Cubberley, B. L. Iverson, J. Am.
Chem. Soc. 2001, 123, 7560.
metal salts. The UV/Vis studies were also carried out in a similar
manner, maintaining a fixed polymer concentration of 1 mm, in the
same solvent mixture. In the solvent titration experiment, the
polymer solution in chloroform was diluted in steps with a measured
volume of methanol and the charge-transfer band intensity was
monitored. The spectra were then corrected to adjust for the
decreasing polymer concentration with dilution. The NMR studies
were also done similarly, and the peak positions were monitored with
varying composition.
Received: January 27, 2004 [Z53860]
Keywords: charge transfer · donor–acceptor systems ·
.
polymers · solvophobic effect · supramolecular chemistry
[1]M. Muthukumar, C. K. Ober, E. L. Thomas, Science 1977, 277,
1225.
[17]A similar variation in the chemical shift of the acceptor protons,
going through a maximum with increasing solvent polarity was
noticed, which confirms the initial decrease prior to the increase
in the apparent association constant. Detailed NMR spectral
evolution as a function of solvent composition is included in the
Supporting Information.
[2]S. H. Gellman, Acc. Chem. Res. 1998, 31, 173.
[3]a) D. J. Hill, M. J. Mio, R. B. Prince, T. S. Huges, J. S. Moore,
Chem. Rev. 2001, 101, 3893; b) C. Schmuck, Angew. Chem. 2003,
115, 2552; Angew. Chem. Int. Ed. 2003, 42, 2448.
[4]T. Nakano, Y. Okamoto, Chem. Rev. 2001, 101, 4013.
[5]M. M. Green, J. W. Park, T. Sato, A. Teramoto, S, Lifson,
R. L. B. Selinger, J. V. Selinger, Angew. Chem. 1999, 111, 3328;
Angew. Chem. Int. Ed. 1999, 38, 3138.
[6]K. Maeda, S. Okada, E. Yashima, Y. Okamoto, J. Polym. Sci.,
Part A: Polym. Chem. 2001, 39, 3180.
[18]Similar upfield shifts of the signals for the donor and acceptor
protons upon charge-transfer complex formation was previously
reported, and may be ascribed to the perturbation of the
aromatic ring current causing a shielding effect: a) Y. Nakamura,
S. Minami, K. Iizuka, J. Nishimura, Angew. Chem. 2003, 115,
3266; Angew. Chem. Int. Ed. 2003, 42, 3158; see also referen-
ce [9c].
[19]The chemical shift value of the acceptor proton in pure CDCl 3 is
8.07 ppm as compared to 7.9 ppm in CDCl3/CH3CN (1:1 v/v). In
contrast, there was no change in the chemical shifts in the case of
a mixture of the model compounds at the same concentration.
[7]J. J. L. M. Cornelissen, A. E. Rowan, R. J. M. Nolte, N. A. J. M.
Sommerdijk, Chem. Rev. 2001, 101, 4039.
[8]J. C. Nelson, J. G. Saven, J. S. Moore, P. G. Wolynes, Science
1997, 277, 1793; a more recent report describes an elegant way to
crosslink photochemically the helical conformation in high
molecular weight poly(1,3-phenylene ethynylene)s: R. S.
Hecht, A. Khan, Angew. Chem. 2003, 115, 6203; Angew. Chem.
Int. Ed. 2003, 42, 6021.
[20]The program EQNMR version 2.10 was used to calculate the
K
values from the variation of the chemical shift of the acceptor
proton. (Freeware developed by M. J. Hynes, Chemistry Depart-
ment, University College, Galway, Ireland). It is evident that the
association constant does not directly parallel the extent of
change seen in either the charge-transfer absorbance or the
chemical shift. It may be reasoned that the extent of change
experienced by the donor and acceptor units (both in their NMR
and UV/Vis spectra), owing to metal-ion complexation by the
loop, would greatly depend on the final geometry of the donor–
acceptor complex. Thus, formation of a strong complex with the
metal ion need not necessarily bring the donor and acceptor
units in the optimum geometry for most effective charge-transfer
interaction. Further studies are currently being done on model
conor–acceptor oligomers to gain better insight into these
aspects.
[9]a) R. S Lokey, B. L. Iverson, Nature 1995, 375, 303; b) J. Q.
Nguyen, B. L. Iverson, J. Am. Chem. Soc. 1999, 121, 2639; c) A. J.
Zych, B. L. Iverson, J. Am. Chem. Soc. 2000, 122, 8898; d) G. J.
Gabriel, B. L. Iverson, J. Am. Chem. Soc. 2002, 124, 15174.
[10]For well-defined oligomers containing perylene units linked by
oligoethylene glycol units, see: a) W. Wang, L-S. Li, G. Helms, H-
H. Zhou, A. D. Q. Li, J. Am. Chem. Soc. 2003, 125, 1120;
b) A. D. Q. Li, W. Wang, L-Q. Wang, Chem. Eur. J. 2003, 9, 4594;
c) for a postulated self-assembly in similar polymeric systems
containing perylene bisimide units linked through flexible
spacers, see:E. E. Neuteboom, S. C. J. Meskers, E. W. Meijer,
R. A. J. Janssen, Macromol. Chem. Phys. 2004, 205, 217.
[11]Early comprehensive studies on podands clearly demonstrated
the possibility of open-chain analogues of crown ethers to
complex with metal ions and generate folded structures. Several
workers exploited such metal-ion-induced folding to modulate
photophysical behavior in small molecules. For comprehensive
reviews, see: a) F. Vogtle, E. Weber, Angew. Chem. 1979, 91, 813;
Angew. Chem. Int. Ed. Engl. 1979, 18, 753; b) H. G. Lohr, F.
Vogtle, Acc. Chem. Res. 1985, 18, 65; for examples of photo-
physical studies, see: c) H. G. Lohr, F. Vogtle, Chem. Ber. 1985,
118, 914; d) A. Ajayaghosh, E. Arunkumar, J. Daub, Angew.
Chem. 2002, 114, 1844; Angew. Chem. Int. Ed. 2002, 41, 1766;
e) Y. Suzuku, T. Morozumi, H. Nakamura, M. Shimomura, T.
Hayashita, R. A. Bartsh, J. Phys. Chem. B 1998, 102, 7910; f) B.
Tummler, G. Maass, F. Vogtle, H. Sieger, U. Heimann, E. Weber,
J. Am. Chem. Soc. 1979, 101, 2588.
[21]The maximum change is noticed for the methylene protons of
the central region of the loop, which move downfield, whereas
the methylene protons immediately adjacent to the chromo-
phores move slightly upfield with K+ and Na+ and change little
in the case of Li+. A similar variation was reported by Vogtle and
co-workers in the case of podands (see reference [11a]). All the
spectral variations are included in the Supporting Information.
[12]Experimental details regarding the synthesis and characteriza-
tion of the monomer and the polymer are available in the
Supporting Information.
3268
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Angew. Chem. Int. Ed. 2004, 43, 3264 –3268