Hydrogen-bonded complexes of aromatic crown ethers with (9-anthracenyl)methylammonium derivatives. Supramolecular photochemistry and photophysics. PH-controllable supramolecular switching

Article abstract of DOI:10.1021/ja9715760

The (9-anthracenyl)methylammonium and (9-anthracenyl)benzylammonium tetrakis(hexafluorophosphate) salts give hydrogen-bonded complexes in CH₂Cl₂ with aromatic crown ethers containing dibenzo (DB) or dinaphtho (DN) units. The association constants vary from 3 x 10³ to 1 x 10⁶ M^-1 in CH₂Cl₂, depending on the specific ammonium cation and crown ether involved. In a number of cases, pseudorotaxane-like geometries for the complexes are demonstrated by (a) ¹H NMR spectroscopy in solution, (b) X-ray crystallography in the solid state, and (c) mass spectrometry in the gas phase. The results obtained by absorption, emission, and excitation spectroscopy and excited lifetimes show that, as a consequence of the hydrogen bond driven recognition process, the anthracene chromophoric unit interacts with the aromatic units of the crown ethers. In the complexes involving the DB18C6, DB24C8, and DB30C10 macrocycles, the interaction leads to the complete quenching of the fluorescence of the dialkoxybenzene moieties and parallels sensitization of the anthracene fluorescence. In the complexes of 1/5-DN38C10, both the crown and the anthracene fluorescence are completely quenched, most likely by an energy-transfer cascade involving the triplet state of the dialkoxynaphthalene moiety. In the complexes of 2/3-DN30C10, the interaction between the anthracene moiety and the naphthalene rings of the crown ether is relatively strong, as indicated by the perturbation of the absorption bands, the disappearance of the fluorescence bands of the naphthalene- and anthracene-type chromophoric units, and the appearance of a new, broad fluorescence band. The complexes can also be formed by addition of CF₃COOH or CF₃SO₃H to CH₂Cl₂ solutions containing crown ether and amine. The association process between DB24C8 and (9-anthracenyl)benzylammonium salt can be reversed quantitatively upon addition of a suitable base and the complex can be formed again after treatment with acid.

Full text of DOI:10.1021/ja9715760

J. Am. Chem. Soc. 1997, 119, 10641-10651
10641
Hydrogen-Bonded Complexes of Aromatic Crown Ethers with
9-Anthracenyl)methylammonium Derivatives. Supramolecular
(
Photochemistry and Photophysics. pH-Controllable
†
Supramolecular Switching
‡
,§
,|
Peter R. Ashton, Roberto Ballardini,* Vincenzo Balzani,*
‡,⊥
#
‡
Marcos G o´ mez-L o´ pez, Simon E. Lawrence, M. Victoria Mart ´ı nez-D ´ı az,
|
|
§
,‡,⊥
Marco Montalti, Arianna Piersanti, Luca Prodi, J. Fraser Stoddart,* and
David J. Williams*,#
Contribution from Istituto FRAE-CNR, Via Gobetti 101, 40129 Bologna, Italy, Dipartamento di
Chimica “G. Ciamician” dell’UniVersit a` , Via Selmi 2, I-40126, Bologna, Italy, The School of
Chemistry, The UniVersity of Birmingham, Edgbaston, Birmingham B15 2TT, UK, and The
Department of Chemistry, Imperial College, South Kensington, London SW7 2AY, UK
X
ReceiVed May 15, 1997
Abstract: The (9-anthracenyl)methylammonium and (9-anthracenyl)benzylammonium tetrakis(hexafluorophosphate)
salts give hydrogen-bonded complexes in CH2Cl2 with aromatic crown ethers containing dibenzo (DB) or dinaphtho
3
6
-1
(
DN) units. The association constants vary from 3 × 10 to 1 × 10 M in CH2Cl2, depending on the specific
ammonium cation and crown ether involved. In a number of cases, pseudorotaxane-like geometries for the complexes
are demonstrated by (a) H NMR spectroscopy in solution, (b) X-ray crystallography in the solid state, and (c) mass
1
spectrometry in the gas phase. The results obtained by absorption, emission, and excitation spectroscopy and excited
lifetimes show that, as a consequence of the hydrogen bond driven recognition process, the anthracene chromophoric
unit interacts with the aromatic units of the crown ethers. In the complexes involving the DB18C6, DB24C8, and
DB30C10 macrocycles, the interaction leads to the complete quenching of the fluorescence of the dialkoxybenzene
moieties and parallels sensitization of the anthracene fluorescence. In the complexes of 1/5-DN38C10, both the
crown and the anthracene fluorescence are completely quenched, most likely by an energy-transfer cascade involving
the triplet state of the dialkoxynaphthalene moiety. In the complexes of 2/3-DN30C10, the interaction between the
anthracene moiety and the naphthalene rings of the crown ether is relatively strong, as indicated by the perturbation
of the absorption bands, the disappearance of the fluorescence bands of the naphthalene- and anthracene-type
chromophoric units, and the appearance of a new, broad fluorescence band. The complexes can also be formed by
addition of CF3COOH or CF3SO3H to CH2Cl2 solutions containing crown ether and amine. The association process
between DB24C8 and (9-anthracenyl)benzylammonium salt can be reversed quantitatively upon addition of a suitable
base and the complex can be formed again after treatment with acid.
Introduction
are reflected in a monitorable signal. The second one (“photon
reading”) is based on an interaction between components of a
supramolecular system which affects their photon response, such
that the occurrence of the interaction can be revealed (“read”)
by some form of excited state manifestationsusually lumines-
cence. In host-guest complexes, the photochemical and
photophysical properties of each component can be modified
profoundly upon complexation. Such changes can be useful in
obtaining information on the structure of a complex and also
in assisting the design of sensors for a variety of applications.
1
Much attention is being devoted currently to the interaction
between light and designed supramolecular systems, a number
of which exploit the energy and/or information content of
2
photons. This exploitation can be achieved by two different
routes.2 The first route (“photon writing”) involves a pho-
a,e
toreaction occurring in a supramolecular system that causes
(“writes”) some changes in the properties of the system which
†
Molecular Meccano, part 26. For part 25, see: Belohradsky, M.;
Hamers, C.; Menzer, S.; Raymo, F. M.; Shipway, A. N.; Stoddart, J. F.;
It is well-known that crown ethers can form complexes with
White, A. J. P.; Williams, D. J. Macromolecules, submitted.
+
3-5
RNH3 ions.
More recently, it has been shown that suitably
‡
University of Birmingham.
Istituto FRAE-CNR.
Universit a` di Bologna.
Address for correspondence: Department of Chemistry and Biochem-
+
§
|
⊥
chosen R2NH2 ions can thread through the cavities of ap-
propriately constituted crown ethers to give inclusion complexes
6,7
with pseudorotaxane-like geometries.
Our interest in the
istry, University of California at Los Angeles, 405 Hilgard Avenue, Los
Angeles, CA 90095. E-mail: stoddart@chem.ucla.edu.
development of photochemical molecular and supramolecular
#
Imperial College.
Abstract published in AdVance ACS Abstracts, October 1, 1997.
X
(2) (a) Balzani, V.; Scandola, F. In ComprehensiVe Supramolecular
Chemistry; Reinhoudt, D. N., Ed.; Pergamon Press: Oxford, England, 1996;
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Tetrahedron 1993, 49, 8267-8309. (c) de Silva, A. P.; McCoy, C. P. Chem.
Ind. 1994, 24, 992-996. (d) de Silva, A. P.; Gunaratne, H. Q. N.;
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Rice, T. E. Chem. ReV. 1997, 97, 1515-1566. (e) Scandola, F.; Bignozzi,
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(
1) (a) Balzani, V.; Scandola, F. Supramolecular Photochemistry;
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1
0514. (c) Wasielewski, M. R.; O’Neil, M. P.; Gosztola, D.; Niemczyck,
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S0002-7863(97)01576-X CCC: $14.00 © 1997 American Chemical Society

10642 J. Am. Chem. Soc., Vol. 119, No. 44, 1997
Ashton et al.
Scheme 1
9
on hydrogen bonds, has led us to explore whether interactions
+
between crown ethers and RR′NH2 ions can be exploited in
the design of systems of both photochemical and photophysical
+
interest. Thus, we have chosen two RR′NH2 ions and a range
of aromatic crown ethers, both exhibiting fluorescence proper-
ties, and studied the photoinduced processes that take place in
their complexes. Their structural features have been studied
1
by (a) X-ray crystallography in the solid state, (b) H NMR
spectroscopy in solution, and (c) mass spectrometry in the gas
phase. Finally, we describe in one of the 1:1 complexes a
reversible base-induced decomplexation process which can be
1
monitored by both H NMR spectroscopy and luminescence
studies.
Results and Discussion
Synthesis. We have targetted the formation of inclusion
complexes between the salts 1-H‚PF6 and 2-H‚PF6, both
containing a photosensitizersan anthracene unitsas the terminal
substituent, and DB18C6, DB24C8, DB30C10, 1/5-DN38C10,
2/3-DN30C10, and BPP34C10 as the macrocyclic components
(
Figure 1). The amine precursor to the 1-H‚PF6 salt is
Figure 1. Formulas of the compounds and abbreviations used.
commercially available and the (9-anthracenyl)methylbenzy-
lammonium hexafluorophosphate 2-H‚PF6 was readily prepared7b
as follows (Scheme 1). Condensation of 9-anthraldehyde with
PhCH2NH2, followed by reduction (NaBH4/MeOH) of the imine,
yielded 2, which, after treatment with concentrated HCl followed
by counterion exchange (NH4PF6/H2O/Me2CO), afforded the
pure salt 2-H‚PF6.
8
devices, together with recent studies on photoinduced energy-
and electron-transfer processes in supramolecular systems based
(
4) (a) Shinkai, S.; Ishihara, M.; Ueda, K.; Manabe, O. J. Chem. Soc.,
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1
Gokel, G. W. Crown Ethers and Cryptands; The Royal Society of
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Pawlak, K.; Bradshaw, J. S.; Bruening, R. L. Chem. ReV. 1995, 95, 2529-
Photophysical Properties of the Components. The absorp-
tion and emission properties of the components are summarized
in Table 1. The absorption and emission spectra of 2-H‚PF6
and of the crown ethers DB24C8 and 1/5-DN38C10 are shown
2
586.
5) For interesting applications, see: (a) Izatt, R. M.; Nielsen B. L.;
1
0
(
in Figures 2 and 3. The absorption spectrum of 2-H‚PF6,
Christensen, J. J.; Lamb, J. D. J. Membrane Sci. 1981, 9, 263-271. (b)
Reetz, M. T.; Huff, J.; Rudolf, J.; Toeller, K.; Deege, A.; Goddard, R. J.
Am. Chem. Soc. 1994, 116, 11588-11584. (c) Izatt, R. M.; Wang, T.;
Hathaway, J. K.; Zhang, X. X.; Curtis, J. C.; Bradshaw, J. S.; Zhu, C. Y.;
Huszthy, P. J. Inclusion Phenom. 1994, 17, 157-175 and refrences therein.
(8) (a) Balzani, V.; Moggi, L.; Scandola, F. in Supramolecular Photo-
chemistry; Balzani, V., Ed.; Reidel: Dordrecht, 1987; pp 1-28. (b) Balzani,
V.; Scandola, F. Supramolecular Photochemistry; Horwood: Chichester,
1991; Chapter 12. (c) Campagna, S.; Denti, G.; Serroni, S.; Juris, A.;
Venturi, M.; Ricevuto, V.; Balzani, V. Chem. Eur. J. 1995, 1, 211-221.
(d) Barigelletti, F.; Flamigni, L.; Balzani, V.; Collin, J.-P.; Sauvage, J.-P.;
Sour, A. New J. Chem. 1995, 19, 793-798. (e) Parola, A. J.; Pina, F.;
Ferreira, E.; Maestri, M.; Balzani, V.; J. Am. Chem. Soc. 1996, 118, 11610-
11616. (f) G o´ mez-L o´ pez, M.; Preece, J. A.; Stoddart, J. F. Nanotechnology
1996, 7, 183-192. (g) Ashton, P. R.; Ballardini, R.; Balzani, V.; Boyd, S.
E.; Credi, A.; Gandolfi, M. T.; G o´ mez-L o´ pez, M.; Iqbal, S.; Philp, D.;
Preece, J. A.; Prodi, L.; Ricketts, H. G.; Stoddart, J. F.; Tolley, M. S.;
Venturi, M.; White, A. J. P.; Williams, D. J. Chem. Eur. J. 1997, 3, 152-
170. (h) Credi, A.; Balzani, V.; Langford, S. J.; Stoddart, J. F. J. Am. Chem.
Soc. 1997, 119, 2679-2681. (i) Pina, F.; Melo, M. J.; Maestri, M.;
Ballardini, R.; Balzani, V. J. Am. Chem. Soc. 1997, 119, 2679-2681. (j)
Murakami, H.; Kawabuchi, A.; Kotoo, K.; Kunitake, M.; Nakashima, N. J.
Am. Chem. Soc. 1997, 119, 7605-7606.
(
6) Kolchinski, A. G.; Busch, D. H.; Alcock, N. W. J. Chem. Soc., Chem.
Commun. 1995, 1289-1291.
7) (a) Ashton, P. R.; Campbell, P. J.; Chrystal, E. J. T.; Glink, P. T.;
(
Menzer, S.; Philp, D.; Spencer, N.; Stoddart, J. F.; Tasker, P. A.; Williams,
D. J. Angew. Chem., Int. Ed. Engl. 1995, 34, 1865-1869. (b) Ashton, P.
R.; Chrystal, E. J. T.; Glink, P. T.; Menzer, S.; Schiavo, C.; Stoddart, J. F.;
Tasker, P. A.; Williams, D. J. Angew. Chem., Int. Ed. Engl. 1995, 34, 1869-
1
871. (c) Glink, P. T.; Schiavo, C.; Stoddart, J. F.; Williams, D. J. Chem.
Commun. 1996, 1483-1490. (d) Ashton, P. R.; Chrystal, E. J. T.; Glink,
P. T.; Menzer, S.; Schiavo, C.; Spencer, N.; Stoddart, J. F.; Tasker, P. A.;
White, A. J. P.; Williams, D. J. Chem. Eur. J. 1996, 2, 709-728. (e) Ashton,
P. R.; Glink, P. T.; Stoddart, J. F.; Tasker, P. A.; White, A. J. P.; Williams,
D. J. Chem. Eur. J. 1996, 2, 729-736. (f) Ashton, P. R.; Glink, P. T.;
Mart ´ı nez-D ´ı az, M.-V.; Stoddart, J. F.; White, J. P.; Williams, D. J. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1930-1933. (g) Ashton, P. R.; Glink, P.
T.; Menzer, S.; Stoddart, J. F.; Tasker, P. A.; White, A. J. P.; Williams, D.
J. Tetrahedron Lett. 1996, 37, 6217-6220. (h) Ashton, P. R.; Collins, A.
N.; Fyfe, M. C. T.; Glink, P. T.; Menzer, S.; Stoddart, J. F.; Williams, D.
J. Angew. Chem., Int. Ed. Engl. 1997, 36, 59-62. (i) Ashton, P. R.; Collins,
A. N.; Fyfe, M. C. T.; Menzer, S.; Stoddart, J.F.; Williams, D. J. Angew.
Chem., Int. Ed. Engl. 1997, 36, 735-739. (j) Feiters, M. C.; Fyfe, M. C.
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(10) Montalti, M.; Ballardini, R.; Prodi, L.; Balzani, V. Chem. Commun.
1996, 2011-2012.

Hydrogen-Bonded Adducts of Aromatic Crown Ethers
J. Am. Chem. Soc., Vol. 119, No. 44, 1997 10643
Table 2. Association Constants (K Cl
, M-1) in CH at 298 Ka
DB18C6 DB24C8 DB30C10 1/5-DN38C10 2/3-DN30C10
Table 1. Absorption and Emission Properties in CH
2
Cl
2
Solution
a
2
2
at 298 K
absorption
max (nm) ꢀ (M- cm-1
fluorescence
+
4
5
4
5
3
3
5
5
1
-H 1.4 × 10 1.0 × 10 7.0 × 10
5.0 × 10
4.0 × 10
4.0 × 10
1
+
3
6
λ
)
λ
max (nm)
I
rel
τ (ns)
2-H 3.0 × 10 1.0 × 10 2.0 × 10
7.0 × 10
+
+
a
1
2
-H
-H
372
372
277
277
277
297
268
6000
7400
4900
5100
4600
16500
8800
421
423
310
312
312
345
342
100 12.0
82 10.0
4
5
5
68
104
Obtained by spectrofluorimetric measurements.
DB18C6
DB24C8
DB30C10
0.5
0.5
0.5
8.0
9.6
spectrum of crown ether 2/3-DN30C10 is slightly different than
that of 1/5-DN38C10, because of the difference between the
2,3- and 1,5-dimethoxynaphthalene units.
1
2b
1
2
/5-DN38C10
/3-DN30C10
1d
It is well-known that amines linked covalently to anthracene
quench its fluorescence by intramolecular electron transfer
involving the lone pair on the amino group. When the amino
group is protonated, the quenching process is prevented and
the strong, structured fluorescence band of the anthracene unit11
is present. The fluorescence spectrum (Figure 3) of 2-H‚PF6
shows such a structured fluorescence band. The fluorescence
spectrum of 1-H‚PF6 is very similar to that of 2-H‚PF6 (Table
).
Each crown ether exhibits (Table 1) an intense and short-
lived fluorescence. The fluorescence spectra of DB24C8 and
/5-DN38C10 are shown in Figure 3. In a rigid matrix at 77
1
1
K, the crown ethers also show a relatively strong phosphores-
cence band.
Complex Formation. When the amine precursors of 1-H‚-
PF6 and 2-H‚PF6 are dissolved in CH2Cl2 solutions of the crown
ethers, no change is observed in the spectra compared with those
Figure 2. Absorption spectra of the protonated derivative 2-H+ and
of the crown ethers DB24C8 and 1/5-DN38C10 in CH Cl solution at
98 K.
2
2
for the separate species. However, when the amine precursors
2
-
1
and 2 are replaced by the PF6 salts 1-H‚PF6 and 2-H‚PF6,
strong changes in the fluorescence properties (and, in one case,
also in the absorption spectrum, Vide infra) are observed. Such
changes indicate that complexes are being formed in which the
chromophoric groups of the protonated amines and crown ethers
undergo electronic interaction.
It is generally observed that, in CH2Cl2 solution, the
fluorescence intensities of the crown ethers decrease, up to
complete disappearance, on addition of 1-H‚PF6 or 2-H‚PF6.
Under the experimental conditions used for the photophysical
experiments, the predominant species were 1:1 complexes in
3
all cases. The Ka values obtained (Table 2) vary from 3 × 10
6
-1
to 1 × 10 M , depending on the specific ammonium ion and
crown ether involved.
Qualitatively similar changes in the fluorescence spectra can
be observed when CF3COOH or CF3SO3H are added to CH2-
Cl2 solutions containing a crown ether and the amines 1 or 2.
This observation confirms that a necessary condition for
complex formation is the protonation of the amines. A role is
also played, however, by the counterion of the protonated
Figure 3. Emission spectra of the derivative 2-H+ and of the crown
ethers DB24C8 and 1/5-DN38C10 in CH Cl solution at 298 K.
2
2
-
which above 270 nm is very similar to that of 1-H‚PF6, shows
the characteristic structured bands of the anthracene chro-
mophoric unit.11 The absorption spectrum of crown ether
DB24C8, which is practically identical to those of crown ethers
amines. In the case of CF3SO3 , the association constant of
-
the complex is considerably smaller than that for PF6 (e.g., 2
4
-1
× 10 M for 2-H‚CF3SO3 with DB24C8). In the case of
-
10
CF3COO , we have found previously that formation of a
complex between the protonated amine and the counterion
competes favorably with the formation of the complex between
the protonated amine and the crown ether, so that the formation
of the latter complex begins only after addition of more than
one equivalent of acid. In all cases, the spectral changes can
be fully reversed upon the addition of a suitable base like
tributylamine.
DB18C6 and DB30C10, shows the characteristic band for the
2a
1
,2-dimethoxybenzene chromophoric units.1 The absorption
spectrum of crown ether 1/5-DN38C10 shows the characteristic
bands of the naphthalene-type compounds.11 As expected, the
(
11) (a) Murov, S. L.; Carmichael, I.; Hug, G. L. Handbook of
Photochemistry; Dekker: New York, 1993. (b) Berlman, I. B. Handbook
of Fluorescence Spectra of Aromatic Compounds; Academic Press: London,
1
965. (c) Jaff e´ , H. H.; Orchin, M. Theory and Applications of UltraViolet
Spectroscopy; Wiley: New York, 1964.
12) (a) Anelli, P. L.; Ashton, P. R.; Ballardini, R.; Balzani, V.; Delgado,
X-ray Crystallography: Complexes between 2-H‚PF6 and
the Crown Ether DB24C8 in the Solid State. The solid state
structure (Figure 4) of the 1:1 complex formed between the
DB24C8 and 2-H‚PF6 shows there to be two independent
virtually identical 1:1 complexes (A and B) in the crystal. In
each case, the cation is threaded through the centers of the
DB24C8 macrocycles, the 1:1 complexes being stabilized by a
(
M.; Gandolfi, M. T.; Goodnow, T. T.; Kaifer, A. E.; Philp, D.; Pietraszk-
iewicz, M.; Prodi, L.; Reddington, M. V.; Slawin, A. M. Z.; Spencer, N.;
Stoddart, J. F.; Vicent, C.; Williams, D. J. J. Am. Chem. Soc. 1992, 114,
1
93-218. (b) Ballardini, R.; Gandolfi, M. T.; Prodi, L.; Ciano, M.; Balzani,
V.; Kohnke, F.; Shariari-Zavariah, H.; Spencer, N.; Stoddart, J. F. J. Am.
Chem. Soc. 1989, 111, 7072-7078.

10644 J. Am. Chem. Soc., Vol. 119, No. 44, 1997
Ashton et al.
Figure 4. The solid state superstructure of one (A) of the pairs of
crystallographically-independent 1:1 complexes, formed between DB24C8
+
and 2-H‚PF
6
, showing the intercomponent [N -H‚‚‚O] hydrogen
bonding and π-π stacking interactions. Hydrogen bonding geom-
etries: [N ‚‚‚O], [H‚‚‚O] distances (Å), [N -H‚‚‚O] angles (deg), (a)
.15, 2.15, 150; (b) 3.02, 2.35, 126; (c) 3.15, 2.23, 159. The equivalent
+
+
3
hydrogen bonding geometries in the other (B) independent complex
are (a) 2.98, 2.09, 154; (b) 3.01, 2.36, 125; (c) 3.04, 2.14, 157.
+
combination of [N -H‚‚‚O] hydrogen bonds between the
ammonium hydrogen atoms of the guest and the polyether
oxygen atoms of the host, and a face-to-face π-π stacking
interaction between one of the catechol rings of the DB24C8
and the anthracenyl ring of the cation 2-H‚PF6. In complex A,
the catechol and the anthracenyl rings are inclined by ca. 3°
and have a mean interplanar separation of 3.47 Å; in complex
B, these parameters are 2° and 3.50 Å, respectively. The only
significant difference between the two complexes, A and B, is
in the conformation adopted by the two cations. In both
Figure 5. 1H NMR (300 MHz, CDCl
dialkylammonium salt 2-H‚PF
and DB24C8, showing signals for both complexed (indicated on the
Figure with c) and uncomplexed (indicated on the Figure with uc)
species.
/MeCN, 6:1) spectra of (a) the
3
6
and (b) of a 1:1 mixture of 2-H‚PF
6
+
complexes, the C-CH2-NH2 -CH2-C backbones adopt an
all-anti geometry that is coplanar to better than 0.1 Å. Although
the plane of the anthracenyl ring system is, in each case, inclined
by 88° to the plane of the backbone, the phenyl rings adopt
differing twist angles of 44° and 27° in complexes A and B,
respectively. Inspection of the packing of the 1:1 complexes
reveals a chain of aromatic-aromatic edge-to-face interactions
1
decomplexation processes are both slow on the H NMR (300
MHz) time scale at room temperature.
1
The H NMR chemical shifts (δ values) for the different
components (DB24C8, BPP34C10, 1/5-DN38C10, and 2-H‚-
PF ) and of their changes (∆δ values) upon complexation are
6
“
linking” complexes A and B throughout the crystal. One of
reported in Table 3. In the case of DB24C8, large downfield
these interactions involves the edge of a catechol ring of one
complex (A) and the face of one of the terminal six-membered
rings of the anthracenyl ring in the neighboring complex (B)
shifts are detectable for the methylene protons (Ha and Hb)
+
adjacent to the NH2 center. Since similar downfield shifts have
7
a
already been reported for the formation of pseudorotaxane
complexes between the dibenzylammonium cation and DB24C8;
this result suggests the formation of a 1:1 complex with a
pseudorotaxane-like geometry in this case as well.
(the associated [H‚‚‚π] distance and [C-H‚‚‚π] angle are 2.79
Å and 68°). The other edge-to-face interaction is between the
edge of one of the catechol rings in complex B and the face of
the π-stacked catechol ring in complex A. Here, the [H‚‚‚π]
distance and [C-H‚‚‚π] angle are 2.92 Å and 163°, respectively.
The ∆δ value (∆δ ) 0.93 ppm) for the benzylic methylene
protons is larger than that (∆δ ) 0.30 ppm) for the anthracenyl-
methyl protons, suggesting that, while the benzylic methylene
group can penetrate into the cavity of the DB24C8, the
anthracenylmethyl group cannot because of the steric hindrance
1
H NMR Spectroscopy: Formation of the Complexes
between 2-H‚PF6 and the Crown Ether DB24C8 in Solution.
The addition of equimolar amounts of the crown ether DB24C8
6
to a solution of 2-H‚PF6 in a mixture of CDCl3 and CD3CN
of the proximal 9-substituted anthracene moiety. However,
1
(
6:1, v/v) at 25 °C produces significant shifts in the H NMR
upon complexation, while the resonance assigned to the Hc
proton of the anthracenyl group becomes strongly deshielded,
the signals assigned to the Hd and He protons become shielded.
Furthermore, the protons located on the macrocyclic polyether’s
catechol ring resonate as two sets of signals that are shifted
strongly upfield with respect to the signal associated with the
uncomplexed crown ether as a consequence of the π-π stacking
interactions between the anthracene moiety of the guest and
the catechol rings of the host (Figure 4). A bidimensional NOE
experiment was undertaken on an equimolar mixture of 2-H‚-
PF6 and DB24C8 in CDCl3 and CD3CN (6:1, v/v) as solvent
1
signals assigned to both of the components. The H NMR
spectra of 2-H‚PF6 in its free form and of an equimolar mixture
of 2-H‚PF6 and DB24C8 in a solution of CDCl3 and CD3CN
(
6:1, v/v) at 25 °C are shown in parts a and b of Figure 5,
respectively. The assignments of the resonances are based on
NOE experiments. The spectrum of 2-H‚PF6, recorded in the
presence of DB24C8, shows (Figure 5b) distinguishable sets
of resonances for (1) free 2-H‚PF6, (2) free DB24C8 and (3)
+
the 1:1 complex between the crown ether and the RR′NH2
ion, indicating that the kinetics of the complexation and

Hydrogen-Bonded Adducts of Aromatic Crown Ethers
J. Am. Chem. Soc., Vol. 119, No. 44, 1997 10645
1
Table 3. Chemical Shifts (δ values) and Chemical Shift Changes (∆δ values) in the H NMR (300 MHz, CHCl
3
/MeCN, 6:1, rt) Spectral Data
of the Dialkylammonium Salt 2-H‚PF
6
with 1 molar equiv of the Three Crown Ethers-DB24C8, BPP34C10, 1/5-DN38C10supon
Complexation
2
-H‚PF
6
δ
DB24C8 δ
complex δ
∆δ
BPP34C10 δ
complex δ
∆δ
1/5-DN38C10 δ
complex δ
∆δ
Ha
Hb
Hc
Hd
He
Hf
Hg
Hh
Hi
4.30
5.12
7.78
8.53
7.99
5.23
5.42
8.33
8.00
7.73
6.56
6.20
0.93
0.30
0.34
-0.53
-0.11
-0.23
-0.59
4.10
5.10
7.99
8.51
7.77
-0.2
4.22
5.06
7.96
8.49
7.75
-0.08
-0.06
-0.03
-0.04
-0.09
-0.02
0.00
-0.02
-0.07
6.79
6.79
6.62
6.48
-0.14
7.63
7.06
6.34
7.59
7.02
6.34
-0.04
-0.04
-0.05
Hj
Hk
system at 25 °C. Further evidence for the formation of a 1:1
complex between 2-H‚PF6 and DB24C8 with a pseudorotaxane-
like geometry has been obtained from the identification of
intermolecular interactionssnamely, between the protons on the
crown ether’s polyether chain and the benzylic methylene
protons Ha and the Hc protons on the anthracenyl group. The
fact that an NOE is observed between the benzylic methylene
protons Ha and the O-methylene protons associated with the
DB24C8’s polyether chain confirms the hypothesis that the
benzylic group can penetrate deeply into the crown ether’s
cavity.
1
Since the equilibrium kinetics are slow on the H NMR time
scale for an equimolar mixture of 2-H‚PF6 and DB24C8 in a
mixture of CDCl3 and CD3CN (6:1, v/v) at 25 °C, it is possible
to determine the absolute concentration of the three species at
equilibrium from integration of the spectrum, and hence, a single
1
3
point determination of the association constant can be made.
Figure 6. The superstructure in the crystal of the 1:2 complex formed
In this manner, a Ka value of 12 600 M- was obtained for the
1
+
between BPP34C10 and 2-H‚PF
6
, showing the [N -H‚‚‚O] hydrogen
1
:1 complex.
+
bonding. Hydrogen bonding geometries: [N ‚‚‚O], [H‚‚‚O] distances
+
Mass Spectrometry: Formation of the Complex between
-H‚PF6 and the Crown Ether DB24C8 in the Gas Phase.
When LSI mass spectrometry was used to characterize the
(Å), [N -H‚‚‚O] angles (deg): (a) 2.99, 2.04, 168; (b) 2.96, 2.01, 169.
2
177°, the former twist being about the N-C bond toward the
anthracene ring. The inclinations of the C-N bonds to their
adjacent phenyl and anthracenyl rings are 50° and 84°,
respectively. The intracomplex separation between the two
complex formed between 2-H‚PF6 and the crown ether DB24C8,
+
a peak for the [M - PF6] ion was observed at m/z 746 for
[
DB24C8‚1-H][PF6], confirming the 1:1 stoichiometry of the
complex in the gas phase.
+
NH2 centers is 8.5 Å. Investigation of the packing of the 1:2
X-ray Crystallography: Complex between 2-H‚PF6 and
the Crown Ether BPP34C10 in the Solid State. The X-ray
analysis of the 1:2 complex formed between BPP34C10 and
complexes reveals the presence of an elegant two-dimensional
π-stacked sheet with, in one direction, centrosymmetrically
related pairs of anthracenyl rings being in a slightly offset
parallel stacked geometry (mean interplanar separation of 3.35
Å) and, in the other, π-stacked hydroquinone rings, also related
by Ci symmetry (mean interplanar separation 3.48 Å, centroid-
centroid distance 4.09 Å).
7
b
2
-H‚PF6 reveals (Figure 6) a characteristic geometry, namely
+
the threading of a pair of RR′NH2 cations through the center
of the BPP34C10 macrocycle in a Ci symmetric arrangement.
The 1:2 complex is stabilized by two pairs of [N -H‚‚‚O]
hydrogen bonds between the NH2 centers and the second and
+
+
1H NMR Spectroscopy: Formation of the Complexes
between 2-H‚PF6 and the Crown Ether BPP34C10 in
Solution. The addition of equimolar amounts of the crown ether
BPP34C10 to a solution of 2-H‚PF6 in a mixture of CDCl3 and
fourth oxygen atoms of each polyether loop. There are no
secondary intracomplex [C-H‚‚‚O], [C-H‚‚‚π], or π-π in-
teractions. The conformation of the cation differs significantly
from that observed in the complex between DB24C8 and 2-H‚-
1
CD3CN (6:1, v/v) at 25 °C produces shifts in the H NMR
+
PF6, the C-CH2-NH2 -CH2-C backbones being nonplanar
signals (Table 3). The observed changes in chemical shifts were
not so pronounced as the ones recorded after addition of
equimolar amounts of DB24C8 to a solution of the ammonium
with torsional twists about the two C-N bonds of 104° and
(13) Connors, K. A. Binding Constants, Wiley, New York, 1987.

10646 J. Am. Chem. Soc., Vol. 119, No. 44, 1997
Ashton et al.
by 84° to the ring plane, whereas that adjacent to the phenyl
ring is inclined by 33° and 47°sthere being two alternate
orientations for the phenyl ring in the structure. The intramo-
lecular N‚‚‚N separation is 9.1 Å. The mode of packing of the
1
:2 complexes differs from that observed for the BPP34C10
analog in that the π-π stacking is only unidirectional, involving
the 1,5-dioxynaphthalene ring systems of the 1/5-DN38C10
macrocycles. The naphtho rings are parallel with an interplanar
separation of 3.38 Å, but offset such that one of the hydrogen
atoms of the attached OCH2 group in one molecule is directed
into the center of one of the six-membered rings of the 1,5-
dioxynaphthalene ring system of the next complex. The [H‚‚‚π]
distance is 2.64 Å and the associated [C-H‚‚‚π] angle is 149°.
1
H NMR Spectroscopy: Formation of the Complexes
between 2-H‚PF6 and the Crown Ether 1/5-DN38C10 in
Solution. The addition of equimolar amounts of the crown ether
1
/5-DN38C10 to a solution of 2-H‚PF6 in a mixture of CDCl3
Figure 7. The superstructure in the crystal of the 1:2 complex formed
1
and CD3CN (6:1, v/v) at 25 °C produces shifts in the H NMR
signals (Table 3). The observed changes in chemical shifts were
not so pronounced as the ones recorded after addition of
equimolar amounts of DB24C8 to a solution of the ammonium
salt 2-H‚PF6. In the case of the macrocycle 1/5-DN38C10,
downfield shifts are also observed for the methylene protons,
particularly the benzylic methylene ones, and upfield shifts for
the Hc, Hd, and He protons of the anthracenyl group in the
ammonium cation. Upon complexation, the signals for the 1,5-
dioxynaphthalene rings of the crown ether are shifted upfield.
The three distinct sets of resonances for the free components
and for the complex are not observed (cf., the complex with
DB24C8), presumably because the equilibrium between the
+
1
/5-DN38C10 and 2-H‚PF
6
, showing the [N -H‚‚‚O] hydrogen
+
bonding. Hydrogen bonding geometries: [N ‚‚‚O], [H‚‚‚O] distances
+
(Å), [N -H‚‚‚O] angles (deg): (a) 3.02, 2.07, 168; (b) 2.98, 1.96, 161.
salt 2-H‚PF6. In the case of BPP34C10, downfield shifts are
also observed for the methylene protons, particularly the
benzylic methylene ones, and upfield shifts for the Hc, Hd,
and He protons of the anthracenyl moiety in the ammonium
cation. Upon complexation, the signals for the hydroquinone
rings of the crown ether are shifted upfield. The three distinct
sets of resonances for the free components and for the complex
are not observed as in the case of the complex with DB24C8,
presumably because the equilibrium between the complexed and
1
complexed and the uncomplexed species is fast on the H NMR
1
the uncomplexed species is now fast on the H NMR time scale
time scale at room temperature. Thus, the chemical shifts listed
in Table 3 are the time-averaged signals for the complexed and
uncomplexed species involving 1/5-DN38C10 and 2-H‚PF6. It
was not possible to perform complexation experiments in
CD2Cl2 with 1/5-DN38C10 because of the insolubility of this
crown ether in this solvent. When CDCl3 was used as the
solvent, in which the crown ether is indeed soluble, it did not
extract the salt 2-H‚PF6. In the H NMR spectrum, only signals
for the uncomplexed crown ether are present. Similar results
were obtained when attempting to use BPP34C10 to extract
2
at room temperature. Thus, the chemical shifts listed in Table
3
are the time-averaged signals for the complexed and uncom-
plexed species involving BPP34C10 with 2-H‚PF6. The
2
-H·PF6 salt has a very low solubility in CD2Cl2, but it can be
dissolved in the presence of an equimolar amount of BPP34C10.
Additionally, it is interesting to note that the H NMR spectrum,
1
obtained after filtration of a suspension of an excess of 2-H·PF6
in CD2Cl2 containing BPP34C10, showed a stoichiometry
associated with a 1:2 complex, [BPP34C10‚(2-H‚PF6)2].
Mass Spectrometry: Formation of the Complex between
1
-H‚PF6 into CDCl3.
Mass Spectrometry: Formation of the Complex between
-H‚PF6 and the Crown Ether 1/5-DN38C10 in the Gas
2
-H‚PF6 and the Crown Ether BPP34C10 in the Gas Phase.
When LSI mass spectrometry was used to characterize the
2
complex formed between 2-H‚PF6 and BPP34C10, a peak for
Phase. When LSI mass spectrometry was used to characterize
the complex formed between 2-H‚PF6 and 1/5-DN38C10, a peak
+
the [M - PF6] ion was observed at m/z 1277 for [BPP34C10‚(2-
H)2][PF6], confirming that the 1:2 stoichiometry also exists in
the gas phase.
+
for the [M - PF6] ion was observed at m/z 1377 for [1/5-
DN38C10‚(2-H)2][PF6], confirming that the 1:2 stoichiometry
X-ray Crystallography: Complex between 2-H‚PF6 and
the Crown Ether 1/5-DN38C10 in the Solid State. The solid
state structure of the 1:2 complex formed between 1/5-DN38C10
and 2-H‚PF6 shows (Figure 7) the two cations to be threaded
through the center of the macrocycle, adopting an overall
geometry similar to that observed for the 1:2 complex involving
BPP34C10. The superstructure once again has crystallographic
also exists in the gas phase.
Photophysical Processes in the Complexes
Complexes with Dibenzocrown Ethers DB18C6-DB30C10.
The complexes of 1-H‚PF6 and 2-H‚PF6 with the crown ethers
DB18C6-DB30C10 exhibit very similar properties in their UV/
vis spectra. The absorption spectra of the CH2Cl2 solutions,
containing equimolar amounts of protonated amines and crown
+
Ci symmetry and is stabilized by a combination of [N -H‚‚‚O]
and [C-H‚‚‚π] hydrogen bonding interactions. The former are
+
-4
between the NH2 centers and the second and fourth oxygen
ethers (1.0 × 10 M), are very close to that of the sums of the
atoms of the polyether loops, whereas the latter is from a
naphthyl hydrogen atom H-2 and one of the outer six-membered
rings of an adjacent anthracenyl ring systemsthe [H‚‚‚π]
distances and [C-H‚‚‚π] angles are 2.92 Å and 143°, respec-
separate components.
Upon excitation at 276 nm (where most of the light is
absorbed by the crown ether moiety (Figure 2)), the crown ether
DB24C8 fluorescence (λmax ) 312 nm) is almost completely
quenched and that of the protonated amine (λmax ) 423 nm) is
much higher than that expected for the separate components
(Figure 8). This means that the fluorescent excited state of the
crown ether is deactivated by energy transfer to the lower lying
+
tively. The C-CH2-NH2 -CH2-C backbones of each cation
are again nonplanar with C-N torsional angles of 87° (toward
the anthracenyl group) and 77° (toward the phenyl group). The
C-N bond adjacent to the anthracenyl ring system is inclined

Hydrogen-Bonded Adducts of Aromatic Crown Ethers
J. Am. Chem. Soc., Vol. 119, No. 44, 1997 10647
Complexes with 2/3-DN30C10. For the complexes of 1-H‚-
PF6 and 2-H‚PF6 with the crown ether 2/3-DN30C10, the
absorption spectrum of the complex is noticeably different from
the sum of the spectra of separate components (Figure 10).
Particularly worth noting is the presence of an absorption tail
above 400 nm, not present in the spectrum of the separate
compounds, which suggests the presence of an energy level
arising from the interaction between the two components. Such
an interaction is likely to be charge-transfer in nature since the
2
,3-dinaphtho chromophoric unit of the crown ether is an
11a
electron donor (its oxidation occurs at +1.39 V in MeCN)
and the anthracene unit of the protonated amine can play the
role of electron acceptor (reduction potential, -1.97 V for
1
1a
9
-methylanthracene in MeCN).
Figure 8. Fluorescence spectra of a CH
2
Cl
2
solution containing 1 ×
-
4
1
0
M 2-H‚PF
6
and DB24C8 (full lines) compared with the sum of
In the fluorescence spectrum of a CH2Cl2 solution containing
-4
the spectra of the separated components (dashed lines). The excitation
wavelength is 276 nm.
equimolar amounts (1.0 × 10 M) of 2-H‚PF6 and 2/3DN30C10
upon excitation at 290 nm (where most of the light is absorbed
by the crown ether moiety), the intensity of the crown ether
band (λmax ) 342 nm) is extremely weak and a new, broad
band with λmax ) 435 nm appears (Figure 11). The broad band
is also observed when excitation is performed at 361 nm, where
only the anthracene chromophoric unit absorbs light. When
excitation is performed at 290 nm (where light is mostly
absorbed by the 2,3-dinaphtho chromophoric unit of the crown
ether), the experimental spectrum matches that expected in the
case of 100% energy-transfer efficency in the complex from
the fluorescent excited state of the 2,3-dinaphtho crown ether
to the state responsible for the broad band with λmax ) 435 nm.
These results show that, in the complex of 2/3-DN30C10,
both the fluorescent excited state of the crown ether and the
fluorescent excited state of the protonated amine are completely
quenched by a lower energy excited state resulting from the
interaction of the two chromophoric units. Such an excited state,
indicated by CT in Figure 9c, is responsible for the broad
emission band with λmax ) 435 nm and most likely also for the
low-energy tail of the absorption spectrum (Vide supra).
Apparently, in the complexes involving 2/3-DN30C10, the
interaction between the anthracene moiety and the aromatic units
of the crown ether is relatively stronger than it is for the other
complexes. It should also be noted that the state responsible
for the broad emission is not (completely) quenched by the lower
lying triplet excited state of the crown ether (Figure 9c). This
is consistent with the charge-transfer nature of the emitting level,
a situation which could imply a considerable reorganizational
barrier for deactivation to the localized crown ether level.
fluorescent excited state of the anthracene moiety of the
protonated amine (Figure 9a). Upon excitation in the absorption
bands of the anthracene moiety, a fluorescence band is observed
which matches closely that of the protonated amine alone. A
comparison between the absorption and excitation spectra in
the whole spectral region shows that energy transfer from the
crown ether to the anthracene moiety is 100% efficient in the
complex. At 77 K, the phosphorescence band of the crown
ether is not present in the complex.
Complexes with 1/5-DN38C10. For the complexes of 1-H‚-
PF6 and 2-H‚PF6 with the crown ether 1/5-DN38C10, the
absorption spectra are very close to the sum of the spectra of
the separate components. In the fluorescence spectrum of a
-4
CH2Cl2 solution containing equimolar amounts (1.0 × 10 M)
of 1-H‚PF6 or 2-H‚PF6 and 1/5-DN38C10, upon excitation at
2
96 nm (where most of the light is absorbed by the crown ether
moiety, Figure 2), the intensity of the crown ether band (λmax
345 nm) is smaller and that of the protonated amine (λmax )
32 nm) is higher than that expected for the separate compo-
)
4
nents. At first sight, this would suggest that the fluorescent
excited state of the crown ether is deactivated by energy transfer
to the lower lying fluorescent excited state of the anthracene
moiety of the protonated amine. Closer scrutinity of the results,
however, shows that the observed effect is related to the fraction
of unassociated species. Since the emission spectrum of 1/5-
DN38C10 overlaps the absorption spectrum of the anthracene
chromophoric unit of the protonated amine, the light emitted
by the fraction of free crown ether molecules is absorbed by
the fraction of free 2-H‚PF6 species, causing a trivial sensitiza-
tion effect. When such an effect is taken into account, it is
clear that, in the complexes, the fluorescence of the crown ether
moiety is completely quenched by the anthracene unit, without
causing any sensitized emission from the latter. We have also
found that, upon excitation at 361 nm (where only the anthracene
chromophoric unit absorbs light, Figure 2), the intensity of the
anthracene is quenched by the formation of the complex with
the crown ether. These results indicate that, in the complex
involving 1/5-DN38C10, both the fluorescence of the crown
ether and the fluorescence of the protonated amine are com-
pletely quenched. This is not surprising if we consider the
energy ordering of the excited states of the two chromophoric
units (Figure 9b). In these complexes, the anthracene fluores-
cence does not survive because the triplet state of the dioxy-
naphthalene moiety lies below the S1 excited state of the
anthracene unit. At 77 K, one can see that the phosphorescence
band of the crown ether is also quenched, presumably by energy
transfer to the lower lying triplet excited state of the anthracene
unit (which is not emissive).
Complexation Reversibility by Deprotonation and Repro-
14
1
tonation. Experiments, monitored by H NMR spectroscopy,
were performed in order to demonstrate the reversibility of the
complexation process occurring between DB24C8 and 2-H·PF6
+
by deprotonating and reprotonating the RR′NH2 ion. An
equimolar solution of DB24C8 and 2-H‚PF6 was prepared in a
mixture of CDCl3 and CD3CN (6:1, v/v) at 25 °C (Figure 12a),
and then a slight molar excess of quinuclidine was added to
the solution to deprotonate the NH2 center (Figure 12b).
Finally, CF3COOH was added to reprotonate the amine (Figure
+
1
2c). The same procedure was followed in the fluorescence
-
4
experiment, but using a 1 × 10 M equimolar CH2Cl2 soluton
of DB24C8 and 2-H‚PF6.
1
Upon inspection of the three H NMR spectra (Figure 12a-
c), it is clear that, initially, we observed the 1:1 complex, which
then disassembles into the two components on adding the base.
Upon addition of CF3COOH, all signals for the complex are
(
14) For a recent example of how pH can effect the topology of
supramolecular systems, see: Shimizu, T.; Kogiso, M.; Masuda, M. J. Am.
Chem. Soc. 1997, 119, 6209-6210 and references cited therein.

10648 J. Am. Chem. Soc., Vol. 119, No. 44, 1997
Ashton et al.
Figure 9. Schematic energy-level diagrams for the complexes of 1-H‚PF
6
or 2-H‚PF
6
with (a) 1,2-dibenzocrown ethers DB18C6-DB30C10, (b)
,5-dinaphtho crown ether 1/5-DN38C10, and (c) 2,3-dinaphtho crown ether 2/3-DN30C10.
1
Figure 10. Absorption spectra of a CH
2
Cl
and 2/3-DN30C10 (full lines) compared with the sum
of the spectra of the separated components (dashed lines).
2
solution containing 1 ×
-4
10
M 2-H‚PF
6
Figure 11. Fluorescence spectra of a solution of a CH
2
Cl
2
solution
-4
containing 1 × 10 M 2-H‚PF
6
and 2/3-DN30C10 (full lines) compared
Figure 12. 1H NMR (300 MHz, CDCl
1:1 mixture of 2-H‚PF and DB24C8, of (b) a 1:1 mixture of 2-H‚PF
and DB24C8 after addition of quinuclidine, and of (c) a 1:1 mixture
of 2-H‚PF and DB24C8 after addition of quinuclidine and subsequently
CF COOH.
/MeCN, 6:1) spectra of (a) a
with the sum of the spectra of the separated components (dashed lines).
The excitation wavelength is 290 nm.
3
6
6
1
then observed once again in the H NMR spectrum, confirming
6
the reversibility of the process. It is interesting to note that the
resonances for Hauc and Hbuc, after reprotonation by addition
of CF3COOH, are slightly shifted with respect to the resonances
for the same protons in 2-H‚PF6 (Figure 12a). Presumably, this
effect is a result of the presence in solution of both the
3
CF3COO and the PF6 counterions. The solvation of the NH2+
center, after having been complexed by DB24C8, results in no
significant shift for the resonance of the Hac and Hbc, as shown
-
-

Hydrogen-Bonded Adducts of Aromatic Crown Ethers
J. Am. Chem. Soc., Vol. 119, No. 44, 1997 10649
unit. In the complexes of 2/3DN30C10, the interaction between
the anthracene moiety and the aromatic units of the crown ether
is relatively strong, as indicated by perturbation of the absorption
bands. The fluorescence of both the naphtho and the anthracene
chromophoric units is completely quenched, and a new, broad
luminescence band with λmax ) 435 nm, assigned to a charge-
transfer level, dominates the emission spectrum.
9,15
These results extend the notion that electronic interactions,
sufficiently strong to change the luminescence properties and
to cause intercomponent energy- and/or electron-transfer pro-
cesses, can be driven by association processes based on
hydrogen bonds. These observations will help in the design of
new families of supramolecular systems capable of exploiting
the energy and/or information content of light.
Finally, the reversible on-off switching of complex formation
+
of the RR′NH2 ion with DB24C8 has been investigated. Upon
+
addition of a suitable base, deprotonation of the NH2 center
takes place, thus causing the dethreading of the DB24C8
macrocycle. Addition of a suitable acid reprotonates the amine
and the original 1:1 pseudorotaxane-like inclusion complex is
regenerated, rendering the cycle reversible. This process can
1
be monitored by H NMR and fluorescence spectroscopy.
The next logical step in the search for nanoscale switchable
Figure 13. Fluorescence spectra (λexc ) 276 nm, CH
a) a 1:1 mixture of 2-H‚PF and DB24C8, (b) a 1:1 mixture of 2-H‚-
PF and DB24C8, after addition of quinuclidine, and (c) a 1:1 mixture
of 2-H‚PF
quently CF
2 2
Cl solution) of
systems is the construction of a discrete molecular speciessa
(
6
16
17
[
2]rotaxane comprising two nondegenerate stations in its
6
dumbbell-shaped component. Investigations in this direction
6
and DB24C8, after addition of quinuclidine and subse-
1
8
are underway.
3
COOH.
Experimental Section
in Figure 12a,c. However, the uncomplexed NH2+ center
experiences the effect of these different counterions, and so the
chemical shifts alter considerably.
General Methods. The routine procedures have been described
elsewhere.19 Chemicals were purchased from Aldrich and used without
further purification. The crown ethers DB18C6, DB24C8, and
DB30C10 and 9-[(methylamino)methyl]anthracene (1) are commercial
The reversibility of the complexation process is clearly
confirmed by the fluorescence experiment (Figure 13). The
emission spectrum (λexc ) 276 nm, where light is mostly
absorbed by the crown ether moiety) of an equimolar solution
of DB24C8 and 2-H‚PF6, in which the formation of a complex
is demonstrated by the occurrence of energy transfer from the
excited states of the crown to the fluorescent excited state of
the anthracene moiety, is displayed in Figure 13a. The
disassembling of the complex by adding the base is shown by
the complete recovery of the fluorescence band of the dialkoxy-
benzene units of DB24C8 (Figure 13b). Upon addition of acid,
the spectral changes are almost quantitatively reversed (Figure
20
21
22
products. BPP34C10, 2/3-DN30C10, and 1/5-DN38C10 were
prepared, according to literature procedures. The absortion and
emission experiments were carried out in CH
except for the phosphorescence spectra which were performed in a rigid
2 2
Cl solution at 298 K,
(15) (a) Fages, F.; Desvergne, J.-P.; Bouas-Laurent, H.; Marsau, P.; Lehn,
J.-M.; Kotzyba-Hilbert, F.; Albrecht-Gary, A.-M.; Al-Joubbeh, M. J. Am.
Chem. Soc. 1989, 111, 8672-8680. (b) Desvergne, J.-P.; Fages, F.; Bouas-
Laurent, H.; Marsau, P. Pure Appl. Chem. 1992, 64, 1231-1238. (c) Balzani,
V.; Ballardini, R.; Gandolfi, M. T.; Prodi, L. In Frontiers in Supramolecular
Organic Chemistry and Photochemistry; Schneider, H.-J., D u¨ rr, H., Eds.;
VCH: Weinheim, 1991; pp 371-391. (d) Ballardini, R.; Balzani, V.; Credi,
A.; Gandolfi, M. T.; Kotzyba-Hilbert, F.; Lehn, J.-M.; Prodi, L. J. Am.
Chem. Soc. 1994, 116, 5741-5746.
1
3c).
(16) Schill, G. Catenanes, Rotaxanes and Knots; Academic Press: New
York, 1971.
Conclusions
(17) (a) Ashton, P. R.; Bissell, R. A.; Spencer, N.; Stoddart, J. F.; Tolley,
M. S. Synlett 1992, 914-918. (b) Ashton, P. R.; Bissell, R. A.; G o´ rski, R.;
Philp, D.; Spencer, N.; Stoddart, J. F.; Tolley, M. S. Synlett 1992, 919-
922. (c) Ashton, P. R.; Bissell, R. A.; Spencer, N.; Stoddart, J. F.; Tolley,
M. S. Synlett 1992, 923-926. (d) Bissell, R. A.; C o´ rdova, E.; Kaifer, A.
E.; Stoddart, J. F. Nature (London) 1994, 369, 133-137. (e) Amabilino,
D. B.; Ashton, P. R.; Boyd, S. E.; G o´ mez-L o´ pez, M.; Hayes, W.; Stoddart,
J. F. J. Org. Chem. 1997, 62, 3062-3075. (f) Anelli, P. L.; Asakawa, M.;
Ashton, P. R.; Bissell, R. A.; Clavier, G.; G o´ rski, R.; Kaifer, A. E.; Langford,
S. J.; Mattersteig, G.; Menzer, S.; Philp, D.; Slawin, A. M. Z.; Spencer,
N.; Stoddart, J. F.; Tolley, M. S.; Williams, D. J. Chem. Eur. J. 1997, 3,
RR′NH2+ ions containing an anthracene moiety give rise to
complexes with crown ethers containing dibenzo, i.e., dialkoxy-
benzene (DB), or dinaphtho, i.e., dialkoxynaphthalene (DN)
units. For some of the complexes of 2-H‚PF6, a pseudorotaxane
1
structure is demonstrated by H NMR spectroscopy, X-ray
crystallography, mass spectrometry, and spectrofluorimetry. The
association constants decrease according to the counterion series,
-
-
-
PF6 > CF3SO3 > CF3COO . In the complexes, relatively
weak electronic interactions take place between the chro-
mophoric units present in the two components. In all cases,
the fluorescence of the dialkoxybenzene or dialkoxynaphthalene
units of the crown is completely quenched. In the complexes
of the DB18C6, DB24C8, and DB30C10 macrocycles, the
quenching of the fluorescence of the dialkoxybenzene units is
accompanied by a parallel sensitization of the anthracene
fluorescence. In the complexes of 1/5-DN38C10, the anthracene
fluorescence is also completely quenched, most likely by energy
transfer from the S1 excited state of the anthracene moiety to
the lower lying triplet excited state of the dialkoxynaphthalene
1
113-1135.
(18) Mart ´ı nez-D ´ı az, M.-V.; Spencer, N.; Stoddart, J. F. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 1904-1907.
(19) Asakawa, M.; Ashton, P. R.; Brown, C. L.; Fyfe, M. C. T.; Menzer,
S.; Pasini, D.; Scheuer, C.; Spencer, N.; Stoddart, J. F.; White, A. J. P.;
Williams, D. J. Chem. Eur. J. 1997, 3, 1136-1150.
(20) Helgeson, R. C.; Tarnowski, T. L.; Timko, J. M.; Cram, D. J. J.
Am. Chem. Soc. 1977, 99, 6411-6418.
(21) Colquhoun, H. M.; Goodings, E. P.; Maud, J. M.; Stoddart, J. F.;
Wolstenholme, J. B.; Williams, D. J. J. Chem. Soc., Perkin Trans. 2 1985,
607-624.
(22) Ashton, P. R.; Ballardini, R.; Balzani, V.; Credi, A.; Gandolfi, M.
T.; Menzer, S.; P e´ rez-Garc ´ı a, L.; Prodi, L.; Stoddart, J. F.; Venturi, M.;
White A. J. P.; Williams, D. J. J. Am. Chem. Soc. 1995, 117, 11171-
11197.

1
0650 J. Am. Chem. Soc., Vol. 119, No. 44, 1997
Table 4. Crystal Data, Data Collection and Refinement Parametersa
data [DB24C8‚2-H][PF
‚PF
Ashton et al.
6
]
[BPP34C10‚(2-H)
2
][PF
6
]
2
2 6 2
[1/5-DN38C10‚(2-H) ][PF ]
formula
solvent
C
46
H
52NO
8
6
C
72
H
80
N
2
O10‚2PF
6
C
80
H
84
N
2
O
10‚2PF
6
MeCN‚CHCl
1844.3
3
formula weight
color, habit
crystal size/mm
lattice type
space group
cell dimensions
a/Å
891.9
colorless prisms
1423.3
colorless prisms
colorless prisms
0.46 × 0.33 × 0.27
0.73 × 0.66 × 0.60
0.63 × 0.33 × 0.30
triclinic
triclinic
triclinic
P1h
P1h
P1h
12.622(2)
17.099(2)
21.970(5)
94.36(2)
102.53(2)
103.16(1)
4468(2)
11.023(1)
12.594(1)
14.259(2)
74.27(1)
72.63(1)
64.17(1)
1677.4(4)
11.335(2)
13.126(2)
17.640(3)
70.96(1)
73.03(1)
66.50(1)
2235.4(6)
b/Å
c/Å
R/deg
â/deg
γ3/deg
V/Å
b
c
c
Z
D
4
1
1
/g cm-
3
1.326
1.409
744
1.370
956
c
F(000)
1872
radiation used
µ/mm
θ range/deg
no. of unique reflections
measured
Mo KR
Mo KR
Cu KR
-
1
0.14
0.16
2.81
1.8-22.5
1.8-22.5
2.7-60.0
11689
4390
6570
observed, |F
d
o
| > 4σ(|F
o
|)
5173
1120
0.085
0.198
0.096, 4.822
0.77, -0.25
2984
461
0.047
0.109
0.048, 0.531
0.20, -0.17
4377
558
0.081
0.213
0.130, 2.460
0.41, -0.41
no. of variables
R
1
e
wR
weighting factors a, bf
largest difference peak, hole/eÅ
2
-
3
a
2
b
Details in common: graphite monochromated radiation, ω-scans, Siemens P4 diffractometer, refinement based on F , 293 K. There are two
c
symmetry. d
crystallographically independent molecules in the asymmetric unit. The molecule has crystallographic C
wR
i
R
1
) ∑||F
o
| - |F
c
||/∑|F |.
o
e
2
2
2
2
2
1/2
f
-1
2
2
2
2
) {∑[w(F
o
- F
c
) ]/∑[w(F
o
) ]} . w ) σ (F ) + (aP) + bP.
o
matrix at 77 K. Equipment for photophysical measurements and
procedures have been described previously.
Spectrofluorimetric Determination of Association Constants. The
association constants of the complexes can be estimated by analizing
the decrease in fluorescence intensity of the crown ether as a function
mL) and H
in Vacuo and purification by silica gel column chromatography
(eluent: MeOH/CH Cl , 1:30) afforded the amine 2 (5.74 g, 80%) as
a pale yellow solid with mp > 48 °C dec. The amine 2 (2.00 g, 6.7
mmol) was dissolved in MeOH (50 mL). Concentrated HCl was added
dropwise (pH < 2), and the reaction mixture was stirred for a further
2 h. Evaporation of the solvent and recrystallization of the crude
2 4
O (50 mL) and then dried (MgSO ). Removal of the solvent
1
2a
2
2
of the 1-H‚PF
6
6
or 2-H‚PF concentration. The intensity, read at the
maximum of the crown ether band, was corrected in order to take into
2
3
account inner filter and instrumental effects, and then it was fitted to
cr where Ccr is the concentration of uncomplexed crown and
cr is the proportionality constant between the corrected emission
product from a mixture of MeOH/Et O afforded the pure ammonium
2
I
φ
corr ) φcr
C
hydrochloride salt 2-H‚Cl (770 mg, 34%) as a pale yellow solid with
mp > 204 °C dec. The hydrochloride salt (770 mg, 2.3 mmol) was
then suspended in Me CO (30 mL), and an aqueous solution of NH -
intensity (in arbitrary units) and the concentration of the uncomplexed
crown ether. Ccr satisfies eq 1, where C°cr is the total concentration of
the crown ether and Ccom the complex concentration.
2
4
PF (752 mg, 4.6 mmol) was added. The reaction mixture was stirred
6
for 30 min. Evaporation of the solvent afforded pale yellow crystals
of the ammonium hexafluorophosphate salt 2-H‚PF
off, washed with H O, and air-dried (1.00 g, 98%): mp > 187 °C
dec.); H NMR (300 MHz, CD COCD ) δ 4.25 (s, 2H; CH N), 5.02
s, 2H; CH N), 7.35 (s, 5H; aromatic CH), 7.35-7.48 (m, 4H;
6
which were filtered
C ) C° - C
(1)
cr
cr
com
2
1
(
(
3
3
2
C
com satisfies the usual 1:1 binding expression in eq 2 where C°am
is the total concentration of added ammonium ion.
2
anthracene H-2, H-4, H-5, H-7), 7.80 (d, J2,3 ) J7,8 ) 9.0 Hz, 2H;
anthracene H-2, H-8), 7.95 (d, J3,4) J5,6 ) 9.0 Hz, 2H; anthracene
2
com
C
- (C° + C° + 1/K )C + C° C° ) 0
(2)
13
cr
am
a
cr
am
cr
H-4, H-5), 8.49 (s, 1H; anthracene H-10); C NMR (75.5 MHz, CD
3
-
COCD ) δ 44.3, 53.3, 124.1, 126.4, 128.3, 130.0, 130.27, 130.6, 131.3,
3
Equilibrium constants K
data with both K and φcr as adjustable parameters and minimizing the
sum of squares of residuals.
9-Anthracenyl)methylbenzylammonium Hexafluorophosphate
2-H‚PF ). A solution of 9-anthracenealdehyde (4.95 g, 0.024 mol)
and benzylamine (2.59 g, 0.024 mol) in PhMe (150 mL) was heated
under reflux with stirring in a Dean-Stark apparatus for 14 h. After
the reaction mixture had been cooled down to room temperature, the
solvent was removed in Vacuo to give the imine as brownish solid.
The solid was dissolved in hot MeOH (100 mL), followed by
a
were then obtained by simulation of the
+
6
1
C
31.8, 132.2, 206.1; MS (LSI) m/z 298 [M - PF
] , 207 [M - PF
6
-
20
a
+
6
H
5
CH
2
] , 191 [M - PF
6
- C
6
H
5
CH
2
NH]. Anal. Calcd for C22
H
-
6
NPF : C, 59.6; H, 4.55; N, 3.16. Found C, 59.8; H, 4.42; N, 3.02.
(
X-ray Crystallography. Single crystals, suitable for X-ray crystal-
lographic analysis for all three complexes, were grown by liquid
(
6
diffusion of i-Pr
of the crystal data, data collection, and refinement parameters for the
three complexes ([DB24C8‚2-H][PF ], [BPP34C10‚(2-H) ][PF , and
/5-DN38C10‚(2-H) ][PF ) is given in Table 4. All three structures
2
O into a MeCN solution of the compound. A summary
6
2
6 2
]
1
2
6 2
]
were solved by direct methods and were refined by full-matrix least-
portionwise addition of NaBH
4
(2.73 g, 0.072 mol) and heating under
reflux with stirring for 10 h. The reaction mixture was then allowed
to cool down to room temperature, and concentrated HCl was added
2
squares data based on F . All major occupancy non-hydrogen atoms
were refined anisotropically, the minor occupancy atoms isotropically.
+
The positions of the hydrogen atoms on the NH
2
centers were located
(
pH < 2). After evaporation of the solvent, the residue was suspended
in H O (50 mL) and extracted with CH Cl
(4 × 50 mL). The
combined extracts were washed with 5% aqueous NaHCO
(2 × 60
from ∆F maps and then optimized; the remaining hydrogen atoms were
assigned isotropic thermal parameters, U(H) ) 1.2Ueq (C,N), [U(H) )
2
2
2
3
1
.5Ueq (C-Me)], and were allowed to ride on the parent C/N atoms.
(23) Credi, A.; Prodi, L. Spectrochimica Acta, Part A, in press.
In both [DB24C8‚2-H][PF ] and [BPP34C10‚(2-H) ][PF , one of the
6
2
6 2
]

Hydrogen-Bonded Adducts of Aromatic Crown Ethers
J. Am. Chem. Soc., Vol. 119, No. 44, 1997 10651
-
PF
[
6
anions was disordered and alternate partial occupancy orientations
] and 66:34 in [BPP34C10‚(2-H) ][PF
were identified. In [BPP34C10‚(2-H) ][PF , the benzyl ring of the
cation was disordered over two (55:45 occupancy) positions. Also, in
BPP34C10‚(2-H) ][PF , a full occupancy included MeCN and a
CHCl solvent molecule were found. Computations were carried out
using the SHELXT PC program system. The crystallographic data
excluding structure factors) for the structures reported in Table 4 have
Acknowledgment. This work was supported by MURST,
CNR (Progetto Strategico Tecnologie Chimiche Innovative), and
University of Bologna (Funds for Selected Topics) in Italy and
by the EC contract FMRX-CT96-0076. We thank Ministerio
de Educaci o´ n y Ciencia (Spain) for a Postdoctoral Fellowship
to M.-V.M.-D. and Eusko Jaurlaritza, Hezkuntza, Unibertsitate
eta Ikerketa Saila, for a Predoctoral Fellowship to M.G.-L.
60:40 in [DB24C8‚2-H][PF
6
2
6 2
] ]
2
6 2
]
[
2
6 2
]
3
2
4
(
been deposited with the Cambridge Crystallographic Data Centre as
supplementary publication number (CDC-100764). Copies of the data
can be obtained free of charge on application to the Director, CCDC,
Supporting Information Available: Spectroscopic data for
2
[
(
and 2-H‚Cl and X-ray data for [DB24C8‚2-H][PF6],
BPP34C10‚(2-H)2][PF6]2, and [1/5-DN38C10‚(2-H)2][PF6]2
1
3
2 Union Road, Cambridge, CB12 1EZ, UK (Fax, Int Code + (1223)
36 0033; e-mail, teched@chemcrys.cam.ac.uk).
34 pages). See any current masthead page for ordering and
Internet access instructions.
(24) SHELXTL PC version 5.03, Siemens Analytical X-Ray Instruments
Inc., Madinson, WI, 1994.
JA9715760