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Construction of a Multiwired Molecular Cable of Micrometer Length by a Self-Assembly Process.

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Construction of a Multiwired Molecular Cable
of Micrometer Length by a Self-Assembly
Process**
C o r n e l u s F. v a n Nostrum, Stephen J. Picken, and
Roeland J. M . Nolte*
The engineering of molecules and molecular systems that can
form nanometer-sized structures is currently receiving a great
deal of attention." 31 An interesting challenge is the construction of molecular wires and molecular channels capable of
transporting electrons and ions. For example, phthalocyanines
substituted with long hydrocarbon side chains have been reported to form conducting inesophases in which the molecules are
stacked in columns. Electron conduction within the columns is
fast. whereas it is slow between the column^.[^-^^ In previous
papers we have shown that crown ether molecules can be
stacked to create ion conducting channels.[6, Here we describe
a novel liquid-crystalline molecule (1) that self-assembles in
channels built up from stacked crown ether rings and a surrounding hydrocarbon mantle. Isolated cables with molecular
thickness and a length of several micrometers can be recognized
in electron microscopy images.
Phthalocyanine 1 was prepared from crown ether 12 by a
cyclization reaction (see Scheme I ) . The crown ether was synthesized from 11. which in turn was assembled from the building
blocks 6 and 10. The starting compound for 6 was 3,4-dihydroxybenzaldehyde (2). This compound was alkylated with decyl
~
2
HO
7
HO
3
RO
' O
HO
ko
0
9
Br
RO
0
a
aBr
H
O
n
O
n
O
HO
O 3
rBr
f
RO
Jc
B
J
,THPono*cl
4
@o/
c"
n
19
aBr
RonoAc
Jd
Tosonono
10
RO
OAc
RO
l1
[**I
uu
CN
ti
chloroform solution to form a molecular cable. This cable contains a central wire of stacked phthalocyanines, four molecular
Dr S .I Picken
A K Z O Reseai-ch Laboratories. Arnhein (The Netherlands).
Thia reacarch NIS financially supported by the Dutch Innovatie-gericht Onder~~ekpropramm
a
(LOP)
of the Ministry of Economic Affairs. We thank R. van
Puijeiihroek ( A K Z O j for carrying out the SAXS measurements.
uu
nin
RO
Prof Dr. R. J. M . Nolte. C . F. van Nostrum
Department of Organic Chemistry. NSR Center
Uni\cisily o f Nijmegen
NL-6575 ED Ni-lmegen (The Netherlands)
Telrkix. Int code + (80)553450
onono
no on::
RO
1
[*I
'Ir"
Br
1
Scheme 1 . R = C,,,H2,:a ) D M E 1 i C ~ , ~ H ~(2.1
~ € 3cquiv).
r
K,CO, (2.2 equiv). N,.
16 h (S4'!'0); b) CHC1,;MeOH (1 : I . v;v). H,Oi (0.75 equiv). H,SO, (0.2 equiv). 5 h
(65%): c) THF:H,O (2.7:l. y v j , K(SO,j,NO (2.5 equiv). KH,PO, (0.6equiv).
Bu,N+CI- (0.4 equiv). 2 h (SO'%). d) AcOH/Ac,O ( l ; l , y v j , reflux, Zn (4 equiv).
reflux, 30 min. (88%): e ) CCI,. Br, (2 equiv). 0 C +room temperature ( R T ) . 16 h
(91 5'0); f ) fiBuOH, NaOH (2 equirj. CICH,CH,OCH,CH,OTHP (2equiv). N,.
retlux, 16 h. HCI (2.1 equivj. RT. 1 h (49%): g) pyridine. pTosC1 (2.4 c q u i ~ ) .
10 C. 2 11. RT. 16 h (93%), h) 6. nBuOH. NaOH (2.5 equiv). N,, rrilux. 10
(1 equiv), reflux. 16 h ( 5 8 % ) . 1) DMF:pyridine (200. I . v:v). CuCN (1 cquiv). N 2 .
reflux. 40 h ; subsequently. NH,OH:H,O. 0,. 2 h ( 7 5 % ) ;J ) (CH ,),N('H2CH20H.
reflux. 40 h (30%).
~
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bromide (+ 3) and subsequently converted into 3,4-bis(decoxy)phenol(4) by a Baeyer- Villiger type of oxidation.[*]Treatment of the phenol with Fremy's radical"] under phase transfer
conditions yielded 4.5-bis(decoxy)-l,2-benzoquinone
(5), which
was converted into 1.2-bis(acetoxy)-4.5-bis(decoxy)benzene (6;
for characterization see Table 1 ) by reduction with zinc.
acetic acidiacetic anhydride. The overall yield of 6 from 2 was
metal-free phthalocyanincs. However. when this solution was
cooled to room temperature a blue shift of the bands and ;L
broadening of the signals was observed. which is characteristic
of aggregated phthalocyanine species (Fig. 1 ) .
A
'1
I 0.8
A
Table I . Characteristic physical data of 1. 6. and 10
0.6
I ' IR ( C H C I , ) : i = 3294 (NH).
2925, 2853 (CH,). 1603. 1529. 1413 (AT),1490.
1391. 1369. 1 I 0 1 !phthalocyaninc). 1280(ArO). 1134(COC), 1 0 2 2 ( N H ) , 8 6 3cm '
(ArH): ' H NMR (400 M H r . CDCI,. 53 C ) : 6 = 6.64 ( 5 . 8H, A r H ) . 3.6-4.9 (111.
80H. CH,O). 1.2 1 X (111. 128H. CH,). 0.89 ( 3 . 24H. CH,): elemcntal 'illid
C,,,HI,,,N,O,,.CHCI,:
calcd C 67.36. H X.40. ?4 3 72. found C 67.lX. H 8 2
3.74 "4
6 : IK !KBi-). F = 2800-3100 !CH,, CH,. ArH). 1760 (C = 0).
1605. 1510 (Ar).
1220. I 180 cin ' fC,,O): H N M K (100 MH7. CDCI,): d = 6.68 !>. 1H.A r H 1. 3 1
' .1
(t.JH. CH,O). 1 . 2 6 ( s . 6H. CH,C = 0 ) .I .
.9~ni.3~tl.CH,).OH8(t.6H.CH,):
MS (CI). 171 z : 506 [:\{*I:
clcmcntal anal
C,,,H,,,O,. calcd C 71.11. H 0.95.
found C 71.42, H 9.82 Yo
0.4
0.2
0
300
~
10: IR(CHCI,) 3 = 2X00-?100(CH,. A r H ) . 1350. 117O(SO,). 1245. 1190(C,,O).
655 c n i - ' (ArBr); ' H N M R (100 MH7. CDCI,): d =7.13-7.85 (ni, XH. AI-H).7.03
(s. 7H. ArH). 3.6-4.25 ( i n . 16FI. CH,). 2.3X (s, 6H. C H , ) : MS (FAB): / T I : = ' 752
[.If +I]
+
38%. The synthesis of the second building block 10 was performed using more standard reactions. Catechol(7) was brominated and subsequently alkylated with tetrahydropyranyl(THP)-protected diethyleneglycol monochloride to give, after in
situ deprotection, compound 9. Reaction of 9 withp-toluenesulfonyl chloride gave compound 10 as a highly viscous oil in 42 YO
overall yield (Table 1). The coupling of the two fragments was
carried out by first hydrolyzing 6 and subsequently treating the
resulting catecholate in situ with 10. The two bromine atoms of
1 1 were substituted by nitrile groups with copper cyanide in
N,N-dimethylformamide (DMF). Finally, the resulting crown
ether 12 was converted into phthalocyanine 1 by refluxing in
N,N-dimethylaminoethanol (overall yield from 6 and 10 13 YO).
Compound 1 was purified by repeated recrystallization from
chloroform. Spectroscopic and elemental analysis were consistent with the proposed structure (Table 1 ) .
Crown ether phthalocyanine 1 showed thermotropic liquid
crystalline behavior as was evident from differential scanning
calorimetry (DSC), polarizing microscopy, and small angle Xray scattering (SAXS) measurements. A transition to a highly
viscous, birefringent mesophase was observed at 148 'C on heating ( A H= 130 kJmol-'). Large hysteresis was observed on
cooling: the transition to the crystalline phase occurred at
105 ' C . No transition to the isotropic phase was observed below
the decomposition temperature of the compound (320 'C). The
large number of peaks in the SAXS measurements at room
temperature indicated a crystalline phase. In the mesophase
at 170-C an intense peak, corresponding to a spacing of
35.10A, and a very broad peak, corresponding to 4.5A, were
visible. The former peak probably is the (100)reflection of a
hexagonal columnar phase with an intercolumnar distance of
40.5A.
Generally, alkoxy- and crown-ether-substituted phthalocyanines are highly soluble in organic solvents. Surprisingly. 1 was
only soluble in boiling chloroform and in boiling toluene. A
solution of 1 (at a concentration of 7 m g n i L - ' o r more) in
chloroform formed a gel on cooling. A UV/Vis spectrum of a
dilute solution (1 1 p ~ of) 1 in chloroform at 50 "C showed a split
Q-band at 660 and 700 nm that is typical for nonaggregated
Fig. 1 .
UV \!I> spectw o f I
400
in
500
chloroform ( I 1 p v l
600
iii
700
800
A [nm] +
25 C ( and and 5 0 C ( --).
The structure of the aggregates was elucidated with the help
of transmission electron microscopy (TEM). Compound 1
(7mg) was boiled in chloroform (1 mL), and after the solution
had cooled. ii drop of the resulting gel was placed on a carboncoated copper grid. After one minute the grid was blotted dry
and shadowed with platinum at an angle of approximately 45 ,
Two representative T E M pictures are shown in Figure 2. At low
A
B
Fig 2. Transmission cleclron inicrographs of a gel of 1 in chloroform. A ) : Isolated
single strands nnd bundles of pamllel strands o f I . B ) . Magnification showing
individual strands of molecules I . which have dinmetcrs of 60 A
magnifications fibers with a length in the order of micrometers.
which form a network structure. are observed. At higher magnifications these fibers are seen to consist of bundles of single
parallel strands. The thickness of these strands equals the diameter of a molecule of 1 as estima!ed from CPK space-filling
molecular models. that is, 50-60 A. Several isolated strands
can be observed with the same diameter. At lower concentrations of I in chloroform, that is. below the gel-forming point,
fibers are still present. but they are smaller, and no network is
formed.
The conclusion from these experiments is that crown ether
phthalocyanine 1 self-assembles into extremely long stacks of
molecular thickness. which consist of more than lo4 molecules.
To the best of our knowledge, evidence for the formation of such
large phthalocyanine aggregates has not been reported before.
Apparently, the attractive forces between the molecules are so
strong that complete solvation is prevented at room tempera-
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ture. As shown schematically in Figure 3 a stack
of molecules I can be
considered to be a multiwired molecular cable.
In view of its structural
resemblance
to
the
crown-ether-substituted
phthalocyanine
polymers previously studied
by us,['] it is reasonable
to postulate that the
molecular cable is capable of conducting ions
and electrons. Apart
-electron
wire
from that. the transition
of 1 from the solid state
Fig 3 Schem,itic rcprescntation of the
to the mesophase is
initltiwii-ed iiiolecular cable formed by
probably accompanied
sell-asscmhl) o f ct-omii ether phthalocyatiiiir I I n h c mcsuphase the indi\idual
bv a change in electronic
molecule\ prohahl! I-otate around their
and ionic conductive
stacl\ing a \ i \ (rcc ref [ I O ] ) .
properties. We are currently investigating this
in detail, as well a s the polymerization of the dihydroxysilicon
derivative of 1 to give a polymerized molecular cable.
50-60A
-
cannot form stable metal complexes. The goal of our research
work is the synthesis of macrocycles that have only a few fluorine atoms incorporated into the cyclic structure. Upon complexation of metal ions, the fluorine should act as a "detector",
since the 19FN M R signals shift upon c o m p l e ~ a t i o n . [The
~ ] high
sensitivity, combined with a large signal dispersion and the absence of a natural background make "F N M R spectroscopy an
ideal tool for inve~tigation.[~l
Recently we reported the synthesis of a partially fluorinated
[2,2,2]~ryptand.[~]
This compound forms complexes with metal
ions; however, the "F N M R signals shift only slightly upon
complexation, since no direct metal-fluorine contacts are
formed. Such an interaction becomes more likely if a carbonfluorine bond is directed towards the center of the crown ether.
The relatively small steric demand of the fluorine atom is not
expected to interfere with the binding of metal ions: on the
contrary it is hoped that formation of a o-donor bond between
fluorine and the metal ion will increase the stability of the metal
complexes.
The building block used for the synthesis of the fluorine-containing macrocycles was 1,3-bis(bromomethyl)-2-fluorobenzene
( I ) , which was treated with tetraethyleneglycol. ethyleneglycol.
or azacrown ethers to yield fluorocrown ethers (Scheme I).'']
Received: March 26. 1994
Revised version: June 21. 1994 [Z 6799 IE]
German version: Aiigcu.. Chciii. 1994. 106. 2298
<; M Whitesidcs. J. P. Mathias. C. T Seto. S c i o i c e 1991, 2.74. 1312.
[2] JLM. 1.ehn. 1 i i , y < , i ~C ' l w n 1990. 102, 1347: A11~ycn CIn,i?l. I n / . Ed EirgI. 1990.
[I]
29. 1704.
[i]A. ll,ir:ida. J. Li. M .Kamachi. S r i r n w 1993, 364. 516.
[3] J. Sinion. 1'. Ba\soul i n Piirliri/o~~i~unii,c\,
Prii/)w~i<,.\md Applimrioiis, l4/.2
C . C . Lernoff. A B. P. Lclcr). VCH. New York. 1993. pp. 223-299
Schoutcn. J. M. Warman, M. P. de Hans. J F. van der Pol. J. W. Zwikker.
J , ,4111 ( ' l i u i i . So( 1992. 114. 9028.
/ l ~ ~ ~2.7.
l / <5398.
~ \
[h] M F M . Roks. R . J. M . Nolte. . ~ ~ ~ J ~ ~ ( i i i i ( l 1992.
[7] 0 F. Siclcken. L. A. \ a n de K i d . 1%: Drcnth, J. Schoonman. R J M . Noltr. J.
,1111. ( ' l i < ~ i i.So<.
~.
1990. 112. 30x6
[XI M . Zlat\umoto. H Kohayashi, Y Hotta, J. Urg. Clioii. 1984, 4Y. 4740.
"91 H . Liiiiinci. D. C . Lankin. S. W Horgan. C ' l i i w t . Rev 1971, 71, 229.
[lo] A . P M Kenteens, B. A Markies. J. F. van der Pol. R. J. M . Kolte, J A i n
C . l i c , i i i Yiii.. 1990. i12. 8x00.
3
4 @=I),
5 (n=2), 6 (n=3)
Scheme 1. a ) KOrBu, tetraeth>leneglycol.h ) KOrBu. cthylencglycol. c ) Na,CO,.
ara[9 + 3n]crown-(ii+ 3 ) .
Complexes of Partially Fluorinated Macrocycles
with a Metal-Fluorine a-Donor Bond and
Their Suitability as Metal Ion Indicators**
Herbert Plenio" and Ralph Diodone
Even though a rather large number of macrocyclic polyethers
is known.'" only few fluorine-containing crown ethers"] have
been reported, and in most of these all of the hydrogen atoms
are substituted by fluorine. As a result of the electron-withdrawing nature of the CF2 units, the oxygen or nitrogen atoms in
these pol yethers no longer exhibit Lewis basicity and therefore
[*I
[**I
1)r H Plcnio. Dip1.-Chem. R. Diodone
I i i ? t i t u t fitr Anorganische und Analytische Chemie dcr Universilit
Albertwasse 21. D-79104 Freihurg ( F R G )
Tclel;i\: I n l . code + (761 )203-5987
Ttiii \%ark m'iis supported by the Fond? der Chcmischen Industne. Tlic authors
thanl, 1'1-ol' D r H Vahrenkamp for his support and Dr E. Kcller for hints in
deteruiining the crqstal structure.
The macrocyclic ligands 2-6 were obtained in yields of 30 to
80 % . In these compounds the carbon-fluorine bond is directed
towards the region that is expected to be the binding site for
metal ions.
The reaction of compounds 2. 4, 5, and 6 with metal salts
leads to the complexation of a metal ion, while at the same time
the 'H, 13C, and "F N M R resonances of the ligands are shifted; in contrast, no such effects were observed for 3. The "F
N M R resonances (300 K) reported for the various metal complexes represent the averaged '"F N M R signals for the metalfree and metal-containing ligands (fast exchange). The absolute
values of these signal shifts are, however, only large in the "F
N M R spectra. in which values up to A 6 = 8.8 have been observed.
Figure 1 shows the differences in chemical shift ( A h ) obtained
by adding an approximately tenfold molar excess of metal salt
to the fluoroxylene bis(crown ethers) 4-6; however. in most
cases addition of metal salt beyond a twofold excess does
not markedly change the position of the signals. It was
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