S. Leroy et al. / Tetrahedron Letters 42 (2001) 1665–1667
1667
troscopy of the ZnCl2 complexes of 1 and 2 was
investigated in solvents of different polarity in order to
confirm the occurrence of electron transfer as quenching
mechanism. As illustrated in Fig. 1 for compound 1, the
emission maximum was observed to shift dramatically
to the red when the polarity was increased (Table 1).
This solvatochromic effect is typical of donor/acceptor
molecules displaying a highly polar excited state due to
the occurrence of photoinduced intramolecular charge
transfer (ICT).18 Upon zinc complexation, the terminal
bpy ligand in compounds 1 and 2 becomes a strong
electron withdrawing group, which promotes ICT state
formation. From the dependence of the emission maxi-
mum on the solvent polarity factor, a line was obtained
for the zinc complexes of 1 and 2 using the Lippert–
Mataga equation,18 allowing us to obtain a value for the
dipole moment of the excited state of the zinc complexes
greater than 25 D. This behaviour is consistent with that
reported for a family of Zn(II) complexes of bipyridine
derivatives substituted with a strong donor group which
show large dipolar nonlinearities.19 Furthermore, when
Zn(BF4)2 was used instead of ZnCl2, the fluorescence
maximum in the spectrum of 1 shifted from 614 to 642
nm in THF, consistent with the higher Lewis acidity of
the zinc ion bearing the tetrafluoroborate counteranions.
This feature provides a further method to control the
fluorescence emission properties of these systems. Com-
pounds 1 and 2 are rigid rod shaped complexing
molecules which are shown not only to function as
fluorescent switches but also to operate directional pho-
toinduced charge separation upon Zn2+ ion binding.
They represent promising photoactive p-systems for the
development of photonic and electronic devices. We are
currently investigating the photophysical properties of
these systems using time-resolved ultrafast spectroscopy.
6. Schwob, P. H. F.; Levin, M. D.; Michl, J. Chem. Rev.
1999, 99, 1863–1933.
7. (a) Harriman, A.; Hissler, M.; Ziessel, R. Phys. Chem.
Chem. Phys. 1999, 1, 4203–4211; (b) Hissler, M.; Harri-
man, A.; Khatyr, A.; Ziessel, R. Chem. Eur. J. 1999, 5,
3366–3381.
8. Bodenant, B.; Weil, T.; Businelli-Pourcel, M.; Fages, F.;
Barbe, B.; Pianet, I.; Laguerre, M. J. Org. Chem. 1999, 64,
7034–7039.
9. (a) Rodriguez, A. L.; Peron, G.; Duprat, C.; Vallier, M.;
Fouquet, E.; Fages, F. Tetrahedron Lett. 1998, 39, 1179–
1182; (b) Soujanya, T.; Philippon, A.; Leroy, S.; Vallier,
M.; Fages, F. J. Phys. Chem. A 2000, 104, 9408–9414.
10. (a) Ley, K. D.; Li, Y.; Johnson, J. V.; Powell, D. H.;
Schanze, K. S. J. Chem. Soc., Chem. Commun. 1999,
1749–1750; (b) Swager, T. M.; Gil, C. J.; Wrighton, M. S.
J. Phys. Chem. 1995, 99, 4886–4893; (c) Khatyr, A.;
Ziessel, R. J. Org. Chem. 2000, 65, 3126–3134.
11. Bunz, U. H. F. Chem. Rev. 2000, 100, 1605–1644.
12. Sakai, N.; Majumdar, N.; Matile, S. J. Am. Chem. Soc.
1999, 121, 4294–4295.
13. Actually, this procedure led to the obtention of compound
1 in a mixture of the bis-pyrenyl and bis-bipyridyl sym-
metrical derivatives. All three compounds could be easily
separated using column chromatography. Compound 1
was obtained in a pure all-trans form (20% isolated yield),
1
as confirmed by H NMR spectroscopy and X-ray struc-
1
tural analysis. 1: H NMR (CDCl3, 400 MHz) l 0.93 (m,
6H), 1.37 (m, 16H), 1.6 (m, 4H), 1.9 (m, 4H), 4.1 (m, 4H),
7.21 (s, 1H), 7.31 (s, 1H), 7.33 (m, 1H), 7.66, 7.22 (dd,
J
AB=16 Hz, 2H), 7.84 (t, 1H), 8.10 (m, 8H), 8.30, 7.68
(dd, JAB=16.0 Hz, 2H), 8.35 (d, 1H), 8.44 (d, 2H), 8.53
(d, 1H), 8.70 (d, 1H), 8.82 (d, 1H). MS (IE) m/z 740 [M+].
Anal. calcd for C52H56N2O2: C, 84.28; H, 7.62; N, 3.78.
Found: C, 83.88; H, 7.23; N, 3.93.
14. Wang, B.; Wasielewsky, M. R. J. Am. Chem. Soc. 1997,
119, 12–21.
Acknowledgements
15. Polin, J.; Schmobel, E.; Balzani, V. Synthesis 1998, 321–
324.
1
16. 2: H NMR (CDCl3, 200 MHz) l 0.82 (m, 6H), 0.92 (m,
We are indebted to Mrs. Paulette Lapouyade for techni-
cal assistance. We gratefully acknowledge the CNRS,
Universite´ Bordeaux 1 and La Re´gion Aquitaine for
financial support.
24H), 4.14 (q, 4H), 7.12 (s, 1H), 7.20 (s, 1H), 7.43 (m, 2H),
7.83 (t, 1H), 8.12 (m, 8H), 8.48 (m, 1H), 8.60 (m, 1H), 8.69
(m, 2H), 8.85 (d, 1H); MS (FAB+) m/z 737.5 [M+H+].
Anal. calcd for C52H52N2O2: C, 84.75; H, 7.11; N, 3.80.
Found: C, 84.12; H, 7.07; N, 3.89.
17. Time-resolved laser spectroscopy measurements (temporal
resolution 50 ps) allowed us to obtain monoexponential
fluorescence decays for 1 and 2 in the presence of an excess
of either ZnCl2 or ZnBF4, which confirmed the occurrence
of a single 1:1 species in THF solution. In more polar
coordinating solvents, such as methanol or acetonitrile,
multiexponential decays were obtained when the emission
was monitored at the red shifted low emitting band of the
complex. In this case, electrospray mass spectrometry
pointed to the formation of the 1:1 complex as the major
component, along with small amounts of bis-ligand Zn(II)
complex species.
References
1. (a) Czarnik, A. W.; Desvergne, J.-P. Chemosensors of Ion
and Molecule Recognition; Kluwer: Boston, 1997; (b) de
Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.;
Huxley, A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice,
T. E. Chem. Rev. 1997, 97, 1515–1566.
2. Joshi, H. S.; Jamshidi, R.; Tor, Y. Angew. Chem. 1999,
111, 2888–2891; Angew. Chem. Int. Ed. 1999, 38, 2722–
2725 and references cited therein.
3. de Silva, A. P.; Gunaratne, H. Q. N.; McCoy, C. P. J. Am.
Chem. Soc. 1997, 119, 7891–7892.
18. (a) Rettig, W. Angew. Chem. Int. Ed. 1986, 25, 971–988;
(b) Maus, M.; Rettig, W.; Bonafoux, D.; Lapouyade, R.
J. Phys. Chem. A 1999, 103, 3388–3401.
4. de Silva, A. P.; Dixon, I. M.; Gunaratne, H. Q. N.;
Gunnlaugsson, T.; Maxwell, P. R. S.; Rice, T. E. J. Am.
Chem. Soc. 1999, 121, 1393–1394.
19. Le Bozec, H.; Renouard, T. Eur. J. Inorg. Chem. 2000,
229–239.
5. Sohna Sohna, J.-E.; Jaumier, P.; Fages, F. J. Chem. Res.
(S) 1999, 134–135.
.