Tunable fluorene-based dynamers through constitutional dynamic chemistry

Article abstract of DOI:10.1002/chem.200501037

Dynamic covalent imino-fluorene-based oligomers and polymers have been generated. They undergo constitutional recomposition under the effect of two parameters, acidity and Zn^II metal ions. As a result, marked changes in physical properties take

Full text of DOI:10.1002/chem.200501037

FULL PAPER
DOI: 10.1002/chem.200501037
Tunable Fluorene-Based Dynamers through Constitutional Dynamic
Chemistry
Nicolas Giuseppone, Gad Fuks, and Jean-Marie Lehn*[a]
Abstract: Dynamic covalent imino-
fluorene-based oligomers and polymers
have been generated. They undergo
constitutional recomposition under the
effect of two parameters, acidity and
ZnII metal ions. As a result, marked
changes in physical properties take
place. The results illustrate the re-
sponse of such a dynamic system to
chemical effectors (H+ and ZnII), thus
demonstrating the adaptive behavior of
the system under the pressure of exter-
nal factors. They also point to the pos-
sibility of modulating optical properties
(UV-visible absorption and fluores-
cence) by constitutional recomposition
in response to a specific trigger. Such
features allow the development of dy-
namic materials, the functional proper-
ties of which may respond to external
stimuli.
Keywords: dynamic combinatorial
chemistry · molecular diversity ·
polymers · stimuli-responsive sys-
tems · tunable functional materials
Introduction
sembly of metallosupramolecular architectures from dynam-
ic sets of specifically encoded ligands.[8]
Constitutional dynamic chemistry (CDC)[1] rests on the gen-
eration of plasticity in combinatorial systems whose constit-
uents result from reversible constitutional combination of a
set of basic building blocks. External stimuli may interact
with the mixture of constituents, and allow for a tunable reg-
ulation of the connectivities within the library. Indeed, such
molecular[2–5] or supramolecular systems,[1,6,7] linked through
covalent bonds or noncovalent interactions, respectively, are
able to evolve by responding to chemical or physical effec-
tors through reorganization of their constituents. Over the
last years molecular/covalent CDC has been implemented in
dynamic combinatorial chemistry (DCC), particularly in the
field of drug discovery.[3] Thus, the global thermodynamic
equilibria between real or virtual[3a] members of a library of
inhibitors are shifted by the presence of a biological target
in situ, through the amplification/selection of the constituent
with the highest affinity with its active site. The use of shape
recognition as a driving force, able to guide thermodynamic
equilibria, has also been exploited in the selective self-as-
Target binding is but one particular case of effect induced
by external stimuli, and encompass a much broader range of
triggering types; indeed, proton concentration or tempera-
ture markedly rearrange the constitutional composition of
entities interconnected through coupled equilibria in libra-
ries of imines.[9] In addition to enhancing the fundamental
understanding of the intrinsically adaptative behavior pres-
ent in such systems, this type of control emerges as a useful
tool to tune the composition of dynamic constitutional libra-
ries that are able to express various latent properties, which
are not observed with connectively static entities. CDC is
also of special interest for materials science, as it offers the
possibility of designing dynamic “smart materials”, allowing
either the expression/nonexpression or the fine tuning of a
given property under different environmental conditions
through well-defined constitutional reshuffling. Access to
such materials can be realized by the design and control of
dynamic polymers, named “dynamers”, in which monomers
are connected by reversible covalent bonds or noncovalent
interactions in dynamic molecular[5,10] or supramolecular[6]
polymers, respectively. Functional dynamers, incorporating
physically or chemically active components represent a par-
ticularly attractive type of dynamic materials.
[a] Dr. N. Giuseppone, G. Fuks, Prof. Dr. J.-M. Lehn
Institut de Science et dꢀIngØnierie SupramolØculaires (ISIS)
8, allØe Gaspard-Monge, BP 70028
67083 Strasbourg cedex
Oligofluorenes and polyfluorenes constitute a broad and
very attractive class of efficient photoactive and electroac-
tive compounds with high charge-carrier mobility and good
processability.[11] The great interest shown for these mole-
cules over the last years reflects their special relevance for
and Coll›ge de France, 75005 Paris (France)
Fax : (+33)390-245-140
E-mail: lehn@isis-ulp.org
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1723

manufacturing organic light-emitting diodes (OLEDs)[12]
and, especially, their use for display applications. Other un-
usual properties contribute also to this activity, such as a
doped polyelectrolyte anion conductivity and thermochrom-
ism.[13]
We herein demonstrate the ability of a set of oligo- and
polyiminofluorene-based dynamers to undergo tunable ex-
change processes through incorporation, decorporation, and
exchange of their monomeric entities by means of reversible
imine formation under the action of external stimuli, result-
ing in the generation of optical signals varying in both wave-
length and intensity, according to the general pattern shown
in Figure 1. In particular, fully conjugated dynamic poly-
the effector); this amounts to a sort of “self-sensing” process
that extends the range of self-processes towards (dynamic)
systems of increasing complexity.[1,10,14]
Finally, in addition to the selection aspect, the kinetics of
the exchange processes indicate that the ZnII driven evolu-
tion is catalyzed by the presence of the zinc itself by means
of a transimination pathway.
Results and Discussion
Synthesis and characterization of oligomeric and polymeric
stuctures:[15] To obtain reference data for the study of the
dynamic oligoimino- and polyiminofluorene entities in cou-
pled thermodynamic equilibria, we first synthesized a series
of model compounds so as to characterize their spectroscop-
ic properties. The systems investigated are based on the use
of the readily available 2,7-fluorenebiscarboxaldehyde A as
a core building block (Scheme 1).
Compound A readily reacts through imine formation with
aromatic and aliphatic amines in ethanol to give entities
ranging from the tris-component compounds 1–3 (termed
tris thereafter) to oligomeric 4 and 5 (when a capping agent
is used) and to polymeric 6–9 compounds (Scheme 2). The
products were isolated as white (2 and 6) and yellow (1, 3,
4, 5, 7, 8, 9) powders. Various analytic techniques were used
for the structure determination of the conjugated and non-
conjugated derivatives: MALDI-TOF mass spectrometry,
1H NMR and UV-visible spectroscopy, and fluorescence op-
tical studies.
Figure 1. General representation of the tunable exchange process in a li-
brary of fluorescent dynamers. The changes in the emission properties
result from the recombination of the photoactive monomeric components
incorporated into the polymeric structure by using external stimuli.
fluorenes can thus be generated. The behavior of the system
was investigated by 1H NMR studies correlated with UV-
visible and fluorescence spectroscopy under the effect of
either pH or metallic ions, and the control over its constitu-
tional dynamics has been achieved.
In addition, these studies revealed the emergence of a
more complex type of behavior whereby an effector
(namely ZnII ions) induces the upregulation of its own de-
tector (reorganization process and subsequent detection of
MALDI-TOF mass spectrometry confirmed the trimeric
structures of compounds 1–3, as well as the oligomeric and
polymeric structures of compounds 4–9. For the last ones,
the repetitive units were found to actually correspond to
monomeric fragments bearing one amine and one aldehyde
as well as some other smaller fragments (Figure 2, top). The
degree of polymerization (DP) values and the corresponding
masses are summed up in Table 1. In the case of oligomeric
structures 4 and 5, which were obtained by using capping
agents (aniline and aminofluorene, respectively), the
MALDI-TOF spectra show, as expected, shorter lengths
than the polymeric ones (one third for the DP values com-
pared to 8 and 7, respectively) with predominant formation
of the expected compounds 4 and 5 with n=1. The optical
properties are also correlated with these observations (vide
infra).
Abstract in French: Des oligom›res et des polym›res rØversi-
bles de type iminofluor›nes ont ØtØ gØnØrØs. Ils subissent une
recomposition constitutionnelle sous lꢀinfluence des param›-
tres: concentration en protons et en ions zinc(ii). Il en rØsulte
des modifications prononcØes des propriØtØes optiques. Les
rØsultats illustrent les possibilitØs offertes par les changements
de constitution en rØponse à des stimuli chimiques (H+ et
ZnII), et ils dØmontrent lꢀadaptation de tels syst›mes sous la
pression de param›tres environnementaux. Cette modulation
de laconstitution permet lamodulation des propriØtØs opti-
ques (absorption UV-Vis et fluorescence) en fonction des sti-
muli imposØs. De tels syst›mes prØsentent un intØrÞt particu-
lier pour le dØveloppement de matØriaux dynamiques dont les
propriØtØs fonctionnelles se modifient en rØponse à des stimu-
lations externes.
1H NMR studies are particularly useful for obtaining
structural information about both static and dynamic enti-
ties, for it is possible to follow the polymer length as well as
its chemical composition by integration of the different
imine-type and remaining aldehyde proton signals (Figure 2,
bottom). Such data allow a detailed analysis of the molecu-
lar constitution during the exchange processes, as well as the
interpretation of the changes in optical properties. The poly-
1
mer length was estimated by H NMR spectroscopy, using
Equation (1); the different average DPs are given in
Table 1.
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Dynamic Combinatorial Chemistry
FULL PAPER
their absorption spectra de-
pending on their lengths. For
example, compound 1, which
contains three conjugated fluo-
rene moieties, absorbs at
394 nm; compound 5 with an
average DP of 2 absorbs at
414 nm; and for polyfluorene 8
(average DP of 10), a plateau is
reached at 418 nm. The general
behavior of compounds 1, 5,
and 8 is similar; in the fluores-
cence spectra emission wave-
lengths from blue to green at
460, 477, and 493 nm respec-
Scheme 1. Synthetic scheme for the five steps sequence leading to 2,7-fluorenebiscarboxaldehyde A from fluo-
rene. a) nBuLi (2 equiv), slow addition (0.5 h), THF, À788C; then 1-bromohexane, 3 equiv, À788C!RT, 12 h,
quantitative yield.[26] b) Paraformaldehyde (10 equiv), 08C; then 30% solution of HBr in acetic acid, 658C,
24 h, 88%.[26] c) Anhydrous sodium acetate (10 equiv), acetic acid anhydride (10 equiv), acetic acid, reflux,
24 h, mixture of mono and bisacetate (2:1), 30%. d) LiAlH4 (10 equiv), THF, reflux 18 h, 92%. e) PCC
(20 equiv), molecular sieves (50 mass%), silica gel (50 mass%), CH2Cl2, 4 h, then RT, 12 h, 75%.
tively, are observed. Compara-
ble responses are obtained for
compounds 4 and 7, containing
P
ꢀ
ꢁ
1,4-phenylenediamine moieties,
1
2
Imine 1H
Aldehyde 1H
P
with an average DP of 2 (labs =408 nm; lem =483 nm) and 16
(labs =420 nm; lem =490 nm), respectively.
Based on the characteristic variations in the physical
properties of the iminofluorene derivatives, as a function of
constitution and length, this type of system appeared to be
suitable for their implementation in constitutional dynamic
experiments and for the subsequent studies of the optical
signals.
ð1Þ
½DPnŠ ¼
þ 1
The dialdehyde A, trimer 2, and nonconjugated polymer 6
have very similar UV-visible spectra, with three absorption
bands below 350 nm, and only a slight difference is observed
in their purple/blue fluorescence emission spectra (416, 423,
and 431 nm, respectively; Figure 3 and Table 1). As expect-
ed, the conjugated imines exhibit a bathochromic shift in
Scheme 2. Synthetic scheme for the syntheses of oligomeric and polymeric structures 1–9 from 2,7-fluorenebiscarboxaldehyde A. All the reactions were
set up by mixing A with imine derivatives in ethanol for 12 h. a) 2 equiv aminofluorene. b) 3 equiv cyclopentylamine. c) 1 equiv trans-1,4-cyclohexyldia-
mine. d) 0.5 equiv 1,4-phenylendiamine, 1 equiv aniline. e) 0.5 equiv 2,7-diaminofluorene, 1 equiv 2-aminofluorene. f) 1 equiv 4,4’-diaminostilbene. g)
1 equiv 2,7-diaminofluorene. h) 1 equiv 1,4-phenylenediamine.
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J.-M. Lehn et al.
Figure 3. Top: UV-visible absorption spectra of structures A and 1–9 de-
picted in Scheme 2, recorded at 298 K in chloroform (see Table 1 for ab-
sorption values). Bottom: Normalized fluorescence spectra of structures
A and 1–9 depicted in Scheme 2 recorded at 298 K in chloroform (see
Table 1 for absorption values).
Figure 2. Top: MALDI-TOF spectroscopy in a ditranol matrix of com-
pound 7 bearing repetitive monomeric units (with their corresponding
mass fragments M and m) up to a degree of polymerization (DP) of 34
(MWꢀ15000). Bottom: 1H NMR spectrum of a mixed polymeric struc-
ture incorporating both 1,4-phenylenediamine and trans-1,4-cyclohexane-
diamine (1:1) in chloroform (c=10À4 m) at RT with labeled characteristic
signals of: remaining aldehyde (x), aromatic imine (y), and (cis + trans)
aliphatic imine (z).
ganization of the iminofluorene dynamers were based on
previous work, namely the use of protons as a triggering ef-
1
fector.[9] They involved the analysis by H NMR spectrosco-
py of the effect of acid on the constitutional dynamic behav-
ior of the library (CDL I) obtained from a 1:2:2 mixture of
2,7-fluorenebiscarboxaldehyde A, cyclopentylamine and 2-
Protonic modulation of the constitutional dynamic libraries:
Our first experiments on the control of constitutional reor-
aminofluorene
(Figure 4).
in
CDCl3
The mixture was analyzed for
a range of CF3CO2D concentra-
tions between 0 and 1m. The
various solutions were light
yellow for [CF3CO2D]=10À2 m,
then turned to orange on in-
creasing the acid concentration
to 10À1 m, and finally it evolved
to a deep red for [CF3CO2D]=
1m. These observations were
correlated with a dramatic evo-
lution of the library constitution
Table 1. Degree of polymerization, molecular weight, and optical properties obtained from MALDI-TOF,
1H NMR, UV-visible absorption, and fluorescence emission spectroscopy for compounds A and 1–9 depicted
in Scheme 2.
[a]
[b]
DPn
DPmax
MW[c] [gmolÀ1
]
c [molLÀ1
]
Abs. max. [nm] e [LmolÀ1 cmÀ1
]
Em. max. [nm]
A
1
2
4
5
6
7
8
9
–
–
–
2
2
–
–
–
8
6
14
32
18
25
390.5
716.4
524.4
1464
1816
4216
7400
5500
7332
5.05”10À5
1.50”10À5
7.62”10À5
5.42”10À6
5.36”10À6
6.68”10À5
1.56”10À5
1.16”10À5
1.15”10À5
343, 329, 311
394
342, 329, 310
408
414
345, 331, 309
420
418
422
2.09”104
9.15”104
1.69”104
2.18”105
2.08”105
2.12”104
8.00”105
6.80”105
8.09”105
416
460
423
483
477
431[d]
490
493
496
9
16
10
13
[a] The DP average is given in chloroform (10À4 m) and was determined by 1H NMR spectroscopy by using
Equation (1), except for compounds 4 and 5 for which the DP average was taken directly from MALDI-TOF
spectroscopy. [b] The DP maximum was taken from MALDI-TOF spectroscopy. [c] Calculated from the DP
average. [d] This value is given for an excitation wavelength at 380 nm. The excitation at 320 nm leads to an
emission at 370 nm.
1
as can be followed by H NMR
spectroscopy
(Figure 4,
bottom).[16]
For
0 <
[CF3CO2D]=10À3 m, the system,
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Dynamic Combinatorial Chemistry
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with the fact that the large difference in the bacicities of the
amines in the present system (about 6 pKa units), leads to a
predominant effect of the CF3CO2D concentration that
cannot be significantly affected within such a range of tem-
perature variations.
The optical absorption and emission variations due to the
acidity-induced reshuffling (Figure 5) are fully correlated
with the NMR studies. Thus, after equilibration at 298 K
and for [CF3CO2D]=0m, CDL I displays the characteristic
UV-visible absorption pattern of compound 2 (trace b), su-
perimposable to that of the reference spectrum of the isolat-
ed imine (trace a) with, in addition, a small shoulder corre-
sponding to residual mixed compound 10 and imine 1. For
[CF3CO2D]=10À1 m (trace c), the maximum of absorption
fits with the lmax of bis-aromatic imine 1 and finally, the ab-
sortion at 490 nm for a [CF3CO2D]=1m corresponds to pro-
tonated imine 1 (trace d). Also consistent with NMR data,
the photoluminescence properties of CDL I shows a dramat-
ic shift from 420 nm (blue) to 610 nm (red) over the same
range of CF3CO2D concentrations (traces f to i).
Figure 4. Top: Constitutional dynamic library of iminofluorenes (CDL I)
with CF3CO2D promoted component exchange in deuterated chloroform
leading to a mixture of trimeric species 1, 2 and 10. Bottom: Selected
1H NMR spectra (400 MHz) of CDL I (5.12”10À2 m in CDCl3) for various
CF3CO2D concentrations at 298 K. a) signal of aliphatic imine 2; b) imine
signals of mixed compound 10; c) signal of aromatic imine 1; d) signal of
protonated imine 1.
as expected, expresses mainly the bis-aliphatic imine 2 with
a ratio of 7:2.5:0.5 with respect to the mixed compound 10
and bis-aromatic derivative 1 respectively.[17,18] For higher
H+ concentrations, the system starts expressing more and
more of bis-aromatic adduct 1 and a total selectivity in favor
of 1 is obtained for [H+]=10À1 m (resonance imine signal at
d=8.65 ppm), although a lower global conversion is also
reached at this point.[19] Above this value, the aromatic
imine signal is shifted toward higher ppm values (Dd=
0.45 ppm), characteristic of protonated compound 1, with a
90% conversion. Increasing further the amount of acid
leads to a decomposition of the system into protonated free
amine and aldehyde. The selectivity and dissociation of the
system by hydrolysis are governed by the relative and abso-
lute pKa values of the two amines involved. As a conse-
quence, the most basic cyclopentylamine is protonated first
and taken out of the trimeric species 2, allowing for its sub-
stitution by the less basic 2-aminofluorene, until the latter
also undergoes protonation ([H+]>1m).
Figure 5. Top: UV-visible absorption spectra of CDL I in chloroform for
various concentrations in CF3CO2D (a: reference 2; b: CDL I, 0m; c:
CDL I, 10À1 m; d: CDL I, 1m). Bottom: Normalized fluorescence spectra
of CDL I in chloroform for various concentrations in CF3CO2D (e: refer-
ence 2; f: CDL I, 0m; g: CDL I, 10À4 m; h: CDL I, 10À1 m; i: CDL I, 1m).
For both experiments, the proton concentration values are given for a so-
lution of initial concentration 5.12”10À2 m in dialdehyde A; the spectra
were recorded after equilibration and subsequent dilution to reach the
values of [A]=2.6”10À5 m (top) and [A]=2.6”10À6 m (bottom). Dilution
is not expected to change the equilibria; as the measurements are con-
ducted in chloroform, the protonation state should not be significantly af-
fected; furthermore, no change in spectra over time has been observed.
It has previously been shown that temperature variations
can markedly change the distribution inside a dynamic set
of imines.[9] A study of the present system between 298 K
and 348 K in 5 K increments gave, unfortunately, no im-
provement of the selectivity.[19] These results are consistent
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J.-M. Lehn et al.
Finally, the reversibility of the overall system has been
evaluated by using triethylamine for neutralizing the reac-
tion mixture and returning to its original constitution. The
Indeed, even if CDL II preferentially expresses nonconju-
gated polyimine 6 (80% by H NMR spectroscopy) and if
1
the exchange effectively occurs towards formation of 8
when the [CF3CO2D] is increased, the system decomposes
quickly (a few minutes timescale) into short size oligomeric
structures, above 10À1 m acid, as shown by the various spec-
troscopic analyses. This dissociation of the polymers by acid
precluded the induction of the “doping effect” as it had
been done in CDL I (Figure 6, bottom) in order to extend
the exploitable optical domain.
1
reversibility (2Q1) was confirmed by H NMR experiments
three times in a row, and the fluorescence behavior also il-
lustrates the good monitoring of the system (Figure 6 top).
The non-normalized fluorescence spectra (bottom) empha-
size the two effects brought by the proton trigger: constitu-
tional recombination (fQh) and subsequent appearance of
an optical signal by interaction of the protons in excess with
the trimer, which had been previously formed under their
influence (hQi).
Modulation of the constitutional dynamic by metal ions
Interaction with metal ions: As a consequence of the difficul-
ties encountered with protonation, we extensively looked
for a suitable trigger capable of reorganizing polymeric sys-
tems, while preventing their dissociation by hydrolysis. The
fluorescence shift/enhancement caused by protons with com-
pound 1 prompted us to explore the interaction of such pol-
yiminofluorene structures with various Lewis acid metal
ions.
Interactions between C=N bonds and protons or metallic
ions are well known in the literature: imines may undergo
changes in optical properties upon metal-ion coordina-
tion,[20] and a few sensors were previously designed using
this chemical bond.[21]
Considering that optical changes would be a sign for the
interaction of given metal ions with the imine compounds,
we explored the optical responses of isolated polyimines 7
and 8 upon the addition of a broad range of metal ions and
a selection of some of the patterns thus obtained is repre-
sented in Figure 7, which shows the spectra obtained by ad-
dition of silver(ii), cadmium(ii), copper(ii), and zinc(ii) salts
to polymer 7. It is seen that the increase of the fluorescence
emission as well as its shift from the original position de-
pends on both the metal ion and the polymer structure. For
example, the behavior of 7 upon addition of silver triflate
(Figure 7, top left) results in the enhancement of the poly-
mer emission by a factor of ten, together with a bathochro-
mic shift of 125 nm to the yellow part of the spectrum
(lmax =575 nm). Addition of copper(ii) triflate to 7 leads to a
narrower band at the same wavelength and with a very
strong increase in intensity by a factor of 40 (Figure 7,
middle left). CdCl2 does not cause a shift in lmax, but a small
positive emission response (Figure 7, top right).
The crucial role played by the nature of the backbone and
its length is illustrated in the last three graphs representing
the responses of polymers 7 (middle right), 8 (bottom left)
and tris 1 (bottom right) upon addition of Zn(BF4)2·8H2O.
The differences between these spectra are striking: while
compounds 1 and 7 display bathochromic shifts (15 and
100 nm, respectively), compound 8 shows a hypsochromic
shift of 50 nm.
Figure 6. Top: Normalized fluorescence spectra of CDL I in chloroform
for various concentrations in CF3CO2D and Et3N (a: [CF3CO2D]=0m; b:
[CF3CO2D]=1m; c: b then neutralization to 0m in acid (2 min); d: b
then neutralization to 0m in acid (20 minutes); e: d then acidification to
[CF3CO2D]=1m. Bottom: Non-normalized fluorescence spectra of CDL
I in chloroform for various concentrations in CF3CO2D and for a same
excitation wavelength (400 nm) (f: [CF3CO2D]=0m; h: CF3CO2D]=
10À1 m; i: CF3CO2D]=1m). For both experiments, the proton concentra-
tion values are given for a solution of initial concentration 5.12”10À2 m in
dialdehyde A; the spectra were recorded after equilibration and subse-
quent dilution to reach the values of [A]=2.6”10À6 m (see also caption
to Figure 5).
On the basis of the results obtained for the “tris” system
CDL I, the possibility to inteconvert polyimines 6 and 8
(CDL II) was investigated. Again, the system appeared to
1
be coherent with expectation based on the H NMR studies,
Metal-ion-induced CDL reorganization: Taking the above
results as an indication for which metal ions may interact
with the studied dynamers, we investigated the possible re-
but the lower conversion to imine for [CF3CO2D]=10À1
m
did not allow the preservation of the polymeric structures.
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Dynamic Combinatorial Chemistry
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Figure 7. Top left: Fluorescence spectra at 298 K in CHCl3 of compound 7 (c=4”10À6 m) when adding increasing amounts of Ag(OTf) solubilized in
MeNO2. Excitation wavelength 390 nm for all the series. Top right: Fluorescence spectra at 298 K in CHCl3 of compound 7 (c=4”10À6 m) when adding
increasing amounts of CdCl2 solubilized in CHCl3. Excitation wavelength 333 nm for all the series. Middle left: Fluorescence spectra at 298 K in CHCl3
of compound 7 (c=4”10À6 m) when adding increasing amounts of Cu(OTf)2 solubilized in CH3CN; excitation wavelength 350 nm for all the series.
Middle right: Fluorescence spectra at 298 K in CHCl3 of fluorene polyimine 8 (c=4”10À6 m) when adding increasing amounts of Cu(OTf)2 (equivalent
with respect to initial A in 8) solubilized in CH3CN; excitation at 350 nm for all the series. Bottom left: Fluorescence spectra at 298 K in CHCl3 of fluo-
rene polyimine 8 (c=4.05”10À6 m) when adding increasing amounts of Zn(BF4)2·8H2O solubilized in CH3CN; excitation at 390 nm for all the series.
Bottom right: Fluorescence spectra at 298 K in CHCl3 of fluorene diimine 1 (c=4.05”10À5 m) when adding increasing amounts of Zn(BF4)2·8H2O solubi-
lized in CH3CN; excitation at 333 nm for all the series.
organization of libraries of iminofluorenes upon metal-
driven exchange. A wide set of metal salts were investigated
and, although most of them led to a recombination, only
Zn(BF4)2·8H2O appeared to selectively realize a full ex-
change between cylopentylamine and 2-aminofluorene in
these statistical values indicate that one aliphatic amine is
trapped by one ZnII ion. This observation is also consistent
with the shift of the signal of the proton on the a-carbon of
cyclopentylamine compared to its resonance in the free
amine (d=3.75 and 3.40 ppm, respectively). Zinc(ii) appa-
rently displays both the Lewis acidity and the proper inter-
action selectivity for catalyzing the exchange and for dis-
criminating between aromatic and aliphatic amines, in con-
trast to the other tested metal salts.[22] Moreover, the system
1
the model system CDL I (Figure 8). The H NMR titration
shows that the completion of the exchange is obtained for
two equivalents of zinc(ii) tetafluoroborate, while one equiv-
alent leads to a ratio of 1:1:2 in 1, 2, and 10 respectively:
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J.-M. Lehn et al.
similar to the bands displayed
by the isolated polymer 8. The
reversibility was shown by addi-
tion of hexamethylhexacyclen B
(one equivalent with respect to
Zn(BF4)2), which led to the
same pattern as was observed
for the system without zinc.[24]
Dynamic constitutional self-
sensing:[10] As seen above, the
fluorescence of polyiminofluor-
ene 8 itself in the presence of
Figure 8. Constitutional dynamic library of iminofluorenes, CDL I, with Zn(BF4)2·8H2O-promoted component
exchange (see Figure 4, top): 1H NMR spectra (400 MHz) of CDL I for different Zn(BF4)2·8H2O concentra-
tions at 298 K in CDCl3 (a=0m; b=3.10”10À2 m; c=6.20”10À2 m; d=8.68”10À2 m; e=1.24”10À1 m); initial
concentration of A: 5.12”10À2 m (see also Figure 1 in reference [10]).
various
amounts
of
ZnII
(Figure 7, bottom left) dis-
retains high conversion to imines in presence of ZnII that en-
ables an extension of its use to polymeric structures. The
ZnII ions can be seen as a “soft proton” capable of trapping
an aliphatic amine efficiently and thus allowing its exchange
for an aromatic one.
We then turned to the exchange of components in the
polymers formed from a 1:1:1 mixture of A, trans-1,4-cyclo-
hexanediamine and 2,7-diaminofluorene (CDL II) in etha-
nol at room temperature.[23] Selected 1H NMR measure-
ments associated with the corresponding UV-visible spectra
of polymeric CDL II under Zn(BF4)2·8H2O-promoted com-
ponent exchange are shown in Figure 9. CDL II consists in
principle of the two-component polymers 6 and 8 together
with a mixture of intermediate three-component A/cyclo-
hexyldiamine/diaminofluorene mixed species. Polymers 6
and 8 were prepared independently in the same conditions
1
as the reference compounds for H NMR, UV-visible, and
fluorescence spectroscopic studies. The composition of the
polymer mixture generated from the A/cyclohexyldiamine/
diaminofluorene mixture was characterized on the basis of
the NMR signal of the imine protons of 6 and 8, as well as
of the UV-visible electronic absorption bands and the fluo-
rescence emission (vide infra) of the isolated compounds. It
contained mainly (80% of the mixture with a cis/trans ratio
of 25:75) alternating fluorene/cyclohexane sequence 6, in-
corporating the more nucleophilic cyclohexane diamine and
displaying a characteristic absorption band at 345 nm. Inte-
À
gration of the imino CH and of the remaining aldehyde
proton NMR signals gave [Eq. (1) above] a DP of about 9
(MW~5000). By adding ZnII to CDL II, its color evolved
from a pale yellow (without zinc) to a red brown suspension
Figure 9. Top: Constitutional dynamic library of polymeric iminofluor-
enes, CDL II (A/cyclohexanediamine/diaminofluorene 1:1:1), with ZnII-
promoted component exchange and absorption spectra of the CDL re-
corded at 298 K in CDCl3 for various amounts of Zn(BF4)2·8H2O solubi-
lized in CD3CN. B=Hexamethylhexacyclen. Bottom: Selected 1H NMR
spectra (400 MHz) of CDL II for different A/Zn(BF4)2·8H2O ratios at
298 K in CDCl3 with [A]=10À4 m. For both experiments, the initial con-
centration in dialdehyde A was 5.12”10À2 m. The spectra were recorded
after equilibration and subsequent dilution to reach the values of [A]=
2.5”10À5 m (UV-visible spectroscopy) and [A]=10À4 m (1H NMR spec-
troscopy).
(two equivalents of zinc with respect to A). The change in
1
composition was followed by H NMR and UV spectroscopy
in chloroform (Figure 9).[23] The increase of the aromatic
À
and the concomitant decrease of the aliphatic imine CH
proton NMR signals indicated that the polymer incorporat-
ed an increasing amount of the diaminofluoene component,
up to practically pure 8.
Simultaneously, the absorption band at 345 nm decreased
and the band at 418 nm strongly increased, finally becoming
1730
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Dynamic Combinatorial Chemistry
FULL PAPER
played a shift from yellow to blue as well as an increase in
emission intensity (four times) in presence of large excess
(30 equivalents) of ZnII. No such changes were observed for
nonconjugated polymeric structure 6.
tral modifications. For higher amounts of zinc ions, new
emission bands appear at 400 and 430 nm and evolve to-
wards a very intense band at 420 nm for large amounts of
metal salt. These last effects may be considered as resulting
from the interaction of the fully aromatic polyimine 8 with
the ZnII ions; this interaction manifests itself by a marked
fluorescence change after more than two equivalents of ZnII
have been added to CDL II. It amounts to an ion-induced
signal generation (Figure 10, bottom). On a conceptual
level, these results express a synergistic adaptative behavior:
the addition of an external effector (e.g., zinc ions) drives a
constitutional evolution of the dynamic mixture towards the
selection and amplification of that species (compound 8)
which allows the generation of a (optical) signal indicating
the presence of the very effector that promoted its genera-
tion in the first place. This embodies a “constitutional dy-
namic self-sensing” process that extends the range of self-
processes.[14] A similar effect is found when the acid is used
for the reorganization of CDL I, resulting in a red shift and
a large increase in intensity after the exchange, as shown in
Figure 6 (bottom). The effect of both ZnII and H+ may
result from a sort of doping by a positively charged entity.
Zinc plays two distinct roles: it is a selection trigger and
fluorescence-enhancing agent, as it interacts selectively with
the amines and imines in the system. In the following part
of the discussion, we highlight that ZnII ions furthermore act
as catalyst for the recombination process.
The combined effects of the ZnII ions, that is, simultane-
ous modification of constitution and fluorescence enhance-
ment, were examined by adding increasing amounts of
metal salt, from 0 to 30 equivalents, to CDL II (Figure 10,
top; see also the preliminary report, reference [10]). As indi-
cated above, the constitution of the polymeric structure
changes progressively from 6 towards genuine 8 at two
equivalents of zinc salt, accompanied by pronounced spec-
Kinetic and mechanistic aspects of the constitutional dynam-
ic processes: In the course of our investigations, we ob-
served some interesting kinetic aspects of the effect of both
protons and zinc ions on the constitutional dynamic libraries
discussed above. Whereas the time required to form 2 at
equilibrium from aldehyde A and free amines in the forma-
tion of CDL I was about 24 h (Figures 4 and 8), the ex-
change process for going from 2 to 1, in presence of ZnII
ions, took less than one minute (the equilibration was even
1
too fast to be followed by H NMR spectroscopy). On the
other hand, the backward reaction (regeneration of com-
pound 2 from 1, Scheme 3) using hexamethylhexacyclene as
a zinc trapping agent,[24] takes 30 minutes to reach the equi-
librium (t1/2 =3.5 min) (entry 8, Table 2).
These observations pointed to a possible activation of the
exchange process by the ZnII ions. The half-life of the for-
mation of the aliphatic bis-imine 2 starting from compound
1 (as formed in situ from its components) in presence of two
Figure 10. Top: Fluorescence spectra at 298 K in CHCl3 of the CDL II of
fluorene polyimines of Figure 9, on addition of increasing amounts of Zn-
(BF4)2·8H2O (equivalent with respect to initial A in CDL II) solubilized
in CH3CN; excitation at 320 nm. Bottom: Partial titration (0 to 4 equiv
ZnII) in the same conditions as the spectra shown in the top part of the
figure, illustrating the self-sensing occurring after the component ex-
change process (sensor formation) is completed, that is, beyond 2 equiv
of ZnII (see also Figure 3 in reference [10]).
Scheme 3. Constitutional reorganization CDL I where the reaction is set up from the compound 1 formed in situ. The results obtained by variations of
the two parameters (relative quantity of cyclopentylamine and relative quantity of zinc) are reported in Table 2.
Chem. Eur. J. 2006, 12, 1723 – 1735
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1731

J.-M. Lehn et al.
Table 2. Thermodynamic and kinetic data for the equilibration of the re-
action starting from different ratios of mixture 1/cyclopentylamine and
leading to 2 and free aminofluorene (Scheme 3) in the presence of addi-
tives.
Entry
X equiv
Equiv of
additive
% of 2 at
t1/2 [min][b]
the equilibrium[a]
1
2
3
4
5
6
7
2
5
1
2
3
4
5
–
–
100
100
0
15
7.5
–
2Zn
2Zn
2Zn
2Zn
2Zn
0
5
–
<1
<1
<1
25[c]
100
[a] The relative percentage is given compared to a reference which is de-
fined from the equilibrium of CDL I in initial conditions (formation from
free aldehyde
A and amines). [b] Based on the formation of 2.
[c] Products 1, 2, 10 are expressed in a ratio equal to 1:1:2.
and five equivalents of cyclopentylamine in chloroform
without metal ions (entries 1 and 2, Table 2) was found to
be 15 and 7.5 minutes, respectively, by NMR measurements.
This indicates that the exchange leading to 2 is faster than
its formation from aldehyde A; it probably occurs by means
of a transimination pathway rather than a hydrolysis/con-
densation one. As each ZnII ions traps a cyclopentylamine
molecule, there is no effect of the metal cation on the rate
of this conversion of 1 to 2 with one or two equivalents of
amine (Table 2, entries 3 and 4). In presence of an excess
(3–5 equivalents) of amine, equilibration occurs in less than
one minute, full conversion being reached for five equiva-
lents (Table 2, entries 5–7). The fast rates observed reveal a
catalytic effect of ZnII ions as the reaction is faster than for
the two control experiments (Table 2, entries 1 and 2). That
this effect is due predominantly to the metal cations and not
to protons, which might be formed by hydrolysis of the Zn-
(BF4)2·8H2O salt, was indicated by the fact that, within
CDL I (Scheme 3), 1) the rate of the 2!1 conversion re-
mained very slow on addition of two equivalents of
CF3CO2D in absence of salt, and 2) the rate of the 1!2 con-
version remained fast on addition of triethylamine as proton
trap.
Furthermore, in the course of the conversion of CDL I
from predominantly 2 to 1 on addition of acid and back to 1
on addition of triethylamine as proton scavenger, the forma-
tion of a significant amount (up to 32%) of monoaldehyde
was observed by NMR spectroscopy. In contrast, only traces
(less than 5%) of monoaldehyde were detected when the
same conversions were performed in presence of ZnII ions
(Figure 11).
Taken together, the results obtained point to two mecha-
nistic pathways: on one hand, a hydrolysis/condensation one
when H+ is used, and on the other hand, a transimination-
type exchange when zinc(ii) is present. This conclusion
agrees with and is supported by an extensive investigation
of the catalysis of similar transimination reactions by
scandium(iii) ions as Lewis acid.[8b,25]
Figure 11. Top: Evolution with time of the exchange process inside CDL
I when ZnII ions are trapped with hexamethylhexacyclene B; plotted
from 1H NMR data and labeled as follows: black triangles (2); dots (1);
open triangles (10, mixed imine); diamonds (aromatic monoaldehyde).
Bottom: Evolution with time of the exchange process inside CDL I when
H+ ions are neutralized with triethylamine; plotted from 1H NMR data
and labeled as described in the top scheme.
Conclusion
The constitutional composition of a dynamic molecular ma-
terial based on fluorenylimines, generated from a set of
components connected by reversible covalent bonds, has
been modulated by external effectors. Highly selective com-
ponent exchange has been obtained by using protons or ZnII
ions as effectors. Zn(BF4)2·8H2O was found to be the most
efficient trigger for controlled rearrangement of the polyi-
mine structures, without the drawback of hydrolysis as
occurs in the presence of H+. The data obtained indicate
that the exchange takes place mainly through a zinc(ii)-cata-
lyzed transimination mechanism. In view of the important
role played by fluorene-derived polymers as materials for
light-emitting devices (LEDs),[12] the present polyiminofluor-
enes[15] constitute a dynamic analogue, which may display in-
triguing potential as dynamic LEDs (Dyna-LEDs), capable
of responding to external solicitations by physical or chemi-
cal triggers.
In addition to inducing selection, ZnII ions also lead to a
fluorescence shift/enhancement. On a conceptual level, both
features brought together express a synergistic adaptative
behavior: the addition of an external effector (e.g., zinc
ions) drives a constitutional evolution of the dynamic mix-
ture towards the selection and amplification of the species
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Chem. Eur. J. 2006, 12, 1723 – 1735

Dynamic Combinatorial Chemistry
FULL PAPER
equilibrated for 24 h at room temperature and the exchange reactions
were performed upon addition of increasing amounts of CF3CO2D
(direct addition using a teflon coated microsyringe) or Zn(BF4)2·8H20
dissolved in a CD3CN (5–50 mL, 0.2–8.0 vol% of CD3CN in EtOH), at
the same temperature. The reaction product was a pale yellow solution
and precipitate ([A]i =5.12”10À2 m). For spectral characterization, this
product was either dissolved in chloroform (for UV-visible and fluores-
cence spectroscopy) or evaporated to dryness under vacuum, without
(compound 8) that in return allows the generation of a (op-
tical) signal indicating the presence of the very effector that
promoted its generation in the first place. This embodies a
“constitutional dynamic self-sensing” process, which extends
the range of self-processes. Such constitutional reorganiza-
tion of a system, particularly a dynamer library, is of special
interest for the design of dynamic “smart” materials, allow-
ing the expression/fine tuning of a given virtual (latent)
property and/or producing an adaptative response under the
pressure of external conditions. Moreover, the self-sensing
behavior (whereby an effector induces the upregulation of
its own detector) represents a further step in the emergence,
at both the molecular and supramolecular levels, of dynamic
systems of increasing complexity.
1
heating, and a sample dissolved in chloroform (for H NMR spectroscopy
as well as UV-visible and fluorescence spectral determinations); when
both procedures were used they gave the same results. The concentration
of the solutions used for NMR spectroscopy was 10À4 m in CDCl3.
9,9-Dihexyl-9H-fluorene-2,7-dicarbaldehyde (A): The dialdehyde was
synthesized from the corresponding diol,[26] by using the following proto-
col. Pyridinium chlorochromate (5 g), activated molecular sieves (4 Š;
1 g) and silica gel (1 g) were mixed together in dry methylene chloride
(20 mL) and cooled to 08C by using an ice bath. A solution of the diol
(2 g) in methylene chloride (20 mL) was added dropwise, and the reac-
tion was stirred 4 h at 08C and then for a further 12 h at room tempera-
ture. The reaction mixture was filtered through a pad of silica gel with
methylene chloride as solvent, and then the crude product was evaporat-
ed, purified by flash chromatography (solvent system hexane/AcOEt
85:15), and obtained as a white powder. Yield 85%; m.p. 51–528C; ele-
mental analysis calcd (%) for C27H34O2: C 82.82, H 9.01; found: C 82.64,
Experimental Section
General aspects: All reagents and solvents were purchased at the highest
commercial quality and were used without further purification unless oth-
erwise noted. Yields refer to purified (1H NMR spectroscopy) homogene-
ous materials. 1H NMR spectra were recorded on a Bruker Avance 400
and Bruker 250 spectrometers. The spectra were internally referenced to
1
3
H 8.77; H NMR (400 MHz) (CDCl3): d=0.53–0.59 (m, 4H), 0.76 (t, J=
6.8 Hz, 6H), 0.98–1.13 (m, 12H), 2.08–2.11 (m, 4H), 7.92–7.97 (m, 6H),
10.13 ppm (s, 2H); 13C NMR (CDCl3): d=13.90, 22.50, 23.75, 29.50,
31.40, 40.00, 55.55, 121.30, 123.35, 130.30, 136.40, 145.60, 152.85,
192.20 ppm; MS (electrospray): m/z (%): 391.3 (100) [M+H]+; HRMS:
calcd: 391.2632; found: 391.2592; UV/Vis (CHCl3, 5.05”10À5 molLÀ1):
l=343, 329, 311 nm; fluorescence: lmax =416 nm.
1
the residual proton solvent signal. In the H NMR assignments, the chem-
ical shifts are given in ppm. The coupling constants J are listed in Hz.
The following notation is used for the 1H NMR spectral splitting pat-
terns: singlet (s), doublet (d), triplet (t), multiplet (m), broad (br). The
temperatures that are given for the kinetic and thermodynamic data were
directly measured and regulated in the NMR probe by using a thermo-
couple. Electrospray (ESI and ESI-TOF) studies were performed on a
Bruker Micro TOF mass spectrometer (sample solutions were introduced
into the mass spectrometer source with a syringe pump with a flow rate
of 160 mLminÀ1). MALDI-MS was carried out on a Bruker Autoflex or
on a Perspective Biosystems Voyager Pro DEwith dithranol as matrix.
Melting Points (m.p.) were recorded on a Kofler Heizblock and on a
Büchi Melting Point B-540 apparatus and are uncorrected. Microanalyses
were performed by the Service de Microanalyse, Institut de Chimie, Uni-
versitØ Louis Pasteur.
(E)-N-{{7-[(E)-(9H-Fluoren-2-ylimino)methyl]-9,9-dihexyl-9H-fluoren-2-
yl}methylene}-9H-fluoren-2-amine (1): The product was synthesized by
using the general method and obtained as a bright yellow powder (yield
95%). M.p. 188–1908C; 1H NMR (400 MHz) (CDCl3): d=0.65–0.75 (m,
4H), 0.80 (t, 3J=6.8 Hz, 6H), 1.06–1.16 (m, 12H), 2.13–2.18 (m, 4H),
3
3
3
3.99 (s, 4H), 7.36 (qd, J=8.2 Hz, J=2 Hz, 4H), 7.41 (t, J=7.6 Hz, 2H),
7.53 (s, 2H), 7.41 (d, 3J=7.3 Hz, 2H), 7.82–7.89 (m, 6H), 7.92–7.95 (m,
2H), 8.03 (s, 2H), 8.68 ppm (s, 2H); 13C NMR (CDCl3): d=14.05, 22.60,
23.85, 29.70, 31.55, 37.00, 40.35, 117.70, 119.75, 120.25, 120.40, 120.60,
122.60, 125.05, 126.50, 126.85, 128.95, 136.00, 139.90, 141.45, 143.50,
143.60, 144.50, 151.10, 152.25, 160.00 ppm; MS (electrospray): m/z (%):
717.3 (100) [M+H]+; HRMS: calcd: 717.4203; found: 717.4166; UV/Vis
(CHCl3, 1.50”10À5 molLÀ1): l=394 nm; fluorescence: lmax =460 nm.
General procedures for the synthesis of isolated imines and polyimines:
Equimolar amounts of amine and aldehydes were solubilized or suspend-
ed in ethanol at a concentration of 0.1m and the reaction mixtures were
refluxed overnight under vigorous stirring. The solutions were then either
evaporated to dryness and the crude residues were purified by flash chro-
matography or, after cooling of the solutions to 08C, the precipitates
formed from the reaction mixture were filtered and washed with cold
ethanol and the compounds crystallized or precipitated from AcOEt/
hexane mixtures.
(E)-N-{{7-[(E)-(Cyclopentylimino)methyl]-9,9-dihexyl-9H-fluoren-2-yl}-
methylene}cyclopentanamine (2): The product was synthesized by using
the general method and obtained as a white powder (yield 88%). M.p.
88–908C; 1H NMR (400 MHz) (CDCl3): d=0.55–0.62 (m, 4H), 0.77 (t,
3J=6.8 Hz, 6H), 0.98–1.13 (m, 12H), 1.71–1.79 (m, 8H), 1.89–1.96 (m,
8H), 2.08–2.11 (m, 4H), 3.78–3.86 (m, 2H), 7.70 (s, 2H), 7074 (s, 4H),
8.39 ppm (s, 2H); 13C NMR (CDCl3): d=14.00, 22.55, 23.65, 24.75, 29.60,
31.50, 34.50, 40.25, 55.25, 72.15, 120.10, 122.32, 127.46, 135.85, 142.75,
151.70, 159.20 ppm; MS (electrospray): m/z (%): 512.4 (100) [M+H]+;
HRMS: calcd: 525.4203; found: 525.4214; UV/Vis (CHCl3, 7.62”
10À5 molLÀ1): l=342, 329, 310 nm; fluorescence: lmax =423 nm.
General procedure for crossover experiments in CDL I and determina-
tions of thermodynamic and kinetic data: A typical protocol was realized
by the preparation of a fresh solution of the compounds to exchange in
CDCl3 (0.6 mL, 5.12”10À2 m in A) in a NMR tube. To avoid the catalysis
of the transimination reaction, the traces of acid in the deuterated
chloroform were removed by flash chromatogaphy through neutral alu-
mina, immediately prior to use. The NMR tubes were topped with teflon
caps in order to keep a constant concentration and avoid water evapora-
tion upon heating. The mixtures were equilibrated for 24 h at room tem-
(E)-N-{{9,9-Dihexyl-7-[(E)-(phenylimino)methyl]-9H-fluoren-2-yl}methy-
lene}benzenamine (3): The product was synthesized by using the general
method and obtained as a brown-yellow waxy solid (yield 95%). M.p.
48–508C; 1H NMR (400 MHz) (CDCl3): d=0.60–0.67 (m, 4H), 0.78 (t,
3J=6.8 Hz, 6H), 1.03–1.13 (m, 12H), 2.08–2.14 (m, 4H), 7.29–7.31 (m,
6H), 7.43–7.47 (m, 4H), 7.88–7.99 (m, 6H), 8.60 ppm (s, 2H); MS (elec-
trospray): m/z (%): 541.4 (100) [M+H]+; HRMS: calcd: 541.3577; found:
1
perature and H NMR spectra were recorded upon addition of increasing
amounts of CF3CO2D (direct addition using a teflon coated microsyr-
inge) or Zn(BF4)2·8H20 dissolved in CD3CN (5–50 mL, 0.2–8.0 vol% of
CD3CN in CDCl3), at the same temperature.
541.3597; UV/Vis (pyridine, 1 gmLÀ1): l=400 nm; fluorescence: lmax
=
465 nm.
(E+Z)-7-[(9H-Fluoren-2-ylimino)methyl]-9,9-dihexyl-9H-fluorene-2-car-
baldehyde (10): The product was synthesized by using the general
method and obtained as a bright yellow oil (yield 66%); 1H NMR
(400 MHz) (CDCl3): d=0.57–0.69 (m, 4H), 0.75–0.80 (m, 6H), 1.05–1.13
General procedure for crossover experiments in CDL II and determina-
tions of thermodynamic and kinetic data: A typical protocol was realized
by the preparation of a fresh solution of the compounds to exchange in
EtOH (3 mL, 5.12”10À2 m in A) in a 10 mL flask. The mixtures were
Chem. Eur. J. 2006, 12, 1723 – 1735
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1733

J.-M. Lehn et al.
(m, 12H), 2.08–2.14 (m, 4H), 3.99 (s, 2H), 7.32–7.38 (m, 2H), 7.44 (t,
3J=7.2 Hz, 1H), 7.52 (s, 1H), 7.59 (d, 3J=7.5 Hz, 1H), 7.81–7.90 (m,
3H), 7.92–7.98 (m, 4H), 8.02 (br, 1H), 8.68 (s, 1H), 10.12, 10.13 ppm (2s,
1H); 13C NMR (CDCl3): d=13.90, 13.95, 14.00, 22.45, 22.55, 22.60, 23.75,
23.80, 29.50, 29.60, 29.65, 31.40, 31.45, 31.55, 36.95, 40.05, 40.20, 55.50,
117.65, 119.75, 120.20, 120.40, 120.55, 120.65, 121.20, 121.30, 122.65,
122.75, 123.20, 123.35, 125.00, 126.55, 126.85, 128.90, 130.30, 130.45,
135.85, 136.45, 136.80, 140.05, 141.35, 142.65, 143.35, 144.50, 145.60,
146.60, 150.90, 152.25, 152.35, 152.80, 152.85, 159.65, 160.00, 192.20,
192.30 ppm; MS (electrospray): m/z (%): 554.4 (100) [M+H]+; HRMS:
calcd: 554.3417; found: 554.3392.
[3] a) J.-M. Lehn, Chem. Eur. J. 1999, 5, 2455; b) A.V. Eliseev, J.-M.
Lehn, Combin. Chem. Biol. 1999, 243, 159; c) O. Ramstrçm, J.-M.
Lehn, Nat. Rev. Drug Discovery 2002, 1, 26.
[4] a) R. L. Cousins, S. A. Poulsen, J. K. M. Sanders, Curr. Opin. Chem.
Biol. 2000, 4, 270; b) R. S. Otto, R. L. E. Furlan, J.K. M. Sanders,
Curr. Opin. Chem. Biol. 2002, 6, 321; c) B. Klekota, B. L. Miller,
TIBTECH 1999, 17, 205; d) V. Wittmann, Nachr. Chem. 2002, 50,
724.
[5] For dynamic materials, see: a) J.-M. Lehn in Supramolecular Sci-
ence: Where It Is and Where It Is Going (Eds.: R. Ungaro, E. Dalca-
nale), Kluwer, Dordrecht (The Netherlands), 1999, p. 287; b) Polya-
cylhydrazones: W. G. Skene, J.-M. Lehn, Proc. Natl. Acad. Sci. USA
2004, 101, 8270.
Oligomer (4): The product was synthesized by using the general method
and obtained as
a bright yellow powder (yield 79%); M.p. 2268C
(decomp); 1H NMR (250 MHz, pyridine): d=0.72 (br, 14H), 1.02 (br,
30H), 2.24 (br, 8H), 7.45–7.60 (br, 8H), 8.10–8.20 (br, 12H), 8.50 (br,
6H), 8.86 ppm (br, 4H); MS (MALDI-TOF) (n=1): m/z (%): 1003.6
(100) [M+H]+ (polymeric structures are observed up to n=10); HRMS
(electrospray) (n=1): calcd: 1003.6612; found: 1003.6668; UV/Vis
(CHCl3, 5.42”10À6 molLÀ1): l=408 nm; fluorescence: lmax =483 nm.
[6] a) Supramolecular Polymers, 2nd ed. (Ed.: A. Ciferri), Taylor Fran-
cis, New York, 2004; b) J.-M. Lehn in Supramolecular Polymers, 2nd
ed. (Ed.: A. Ciferri), Taylor Francis, New York, 2004, Chapter 1,
p. 3; c) J.-M. Lehn, Polym. Int. 2002, 51, 825.
[7] B. Hasenknopf, J.-M. Lehn, B. O. Kneisel, G. Baum, D. Fenske,
Angew. Chem. 1996, 108, 1987; Angew. Chem. Int. Ed. Engl. 1996,
35, 1838.
[8] a) J. Nitschke, J.-M. Lehn, Proc. Natl. Acad. Sci. USA 2003, 100,
11970; b) N. Giuseppone, J.-L. Schmitt, J.-M. Lehn, Angew. Chem.
2004, 116, 5010; Angew. Chem. Int. Ed. 2004, 43, 4902; c) O. Storm,
U. Lüning, Chem. Eur. J. 2002, 8, 793; d) K. Severin, Chem. Eur. J.
2004, 10, 2565; e) D. Schultz, J. R. Nitschke, Proc. Natl. Acad. Sci.
USA 2005, 102, 11191.
Oligomer (5): The product was synthesized by using the general method
and obtained as a bright yellow powder (yield 76%); M.p. (decomposi-
tion) 3008C; 1H NMR (250 MHz; pyridine): d=0.72 (br, 14H), 1.03 (br,
30H), 2.24 (br, 8H), 4.95 (br, 6H), 7.45–7.60 (br, 8H), 7.90–8.30 (m,
16H), 8.50–860 (br, 8H), 8.93 ppm (br, 4H); MS (MALDI-TOF) (n=1):
m/z (%): 1292.3 (100) [M+Na]+ (polymeric structures are observed up
to n=10); HRMS (electrospray) (n=1): calcd: 1267.7514; found:
1267.7508; UV/Vis (CHCl3, 5.36”10À6 molLÀ1): l=414 nm; fluorescence:
lmax =477 nm.
[9] N. Giuseppone, J.-M. Lehn, Chem. Eur. J. 2006, 12, 1715 (preceding
paper).
[10] N. Giuseppone, J.-M. Lehn, J. Am. Chem. Soc. 2004, 126, 11448.
[11] For recent reviews on polyfluorenes, see: a) M. Leclerc, J. Polym.
Sci. Part A 2001, 39, 2867; b) U. Scherf, S. Riechel, U. Lemmer, R. F.
Mahrt, Curr. Opin. Solid State Mater. Sci. 2001, 5, 143; c) U. Scherf,
E. J. W. List, Adv. Mater. 2002, 14, 477.
[12] a) J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K.
Mackay, R. H. Friend, P. L. Burn, A. B. Holmes, Nature 1990, 347,
539; b) Y. Ohmori, A. Uchida, K. Muro, K. Yoshino, Jpn. J. Appl.
Phys. Part 2 1991, 30, L1941; c) Pei, Q.; Yang, Y. J. Am. Chem.
Soc. 1996, 118, 7416; d) D. Neher, Macromol. Rapid Commun. 2001,
22, 1365; e) S. Becker, C. Ego, A. C. Grimsdale, E. J. W. List, D.
Marsitzky, A. Pogantsch, S. Setayesh, G. Leising, K. Müllen, Synth.
Met. 2002, 125, 73; f) for solution-phase electroluminescence, see:
J. B. Edel, A. J. deMello, J. C. deMello, Chem. Commun. 2002, 1954.
[13] a) M. Ranger, M. Leclerc, Macromolecules 1999, 32, 3306; b) P.
Blondin, J. Bouchard, S. BeauprØ, M. BelletÞte, G. Durocher, M. Le-
clerc, Macromolecules 2000, 33, 5874.
Polymer (6): The product was synthesized by using the general method
and obtained as a white powder (yield 95%); M.p. (decomp) 2708C;
1H NMR(400 MHz) (CDCl3): d=0.60 (br, 4H), 0.78 (m, 6H), 1.05–1.13
(m, 12H), 1.62 (br, 2H), 1.90–2.08 (m, 6H), 2.10–2.20 (br, 4H), 3.39 (br,
2H), 2.08–2.11 (m, 4H), 7.75–7.85 (m, 6H), 8.50 ppm (s, 2H); MS
(MALDI-TOF; repeated fragments of the main unit): m/z: 470 [M+H]+
(polymeric structures are observed up to n=14); UV/Vis (CHCl3, 6.68”
10À5 molLÀ1): l=345, 331, 309 nm; fluorescence: lmax =431 (lexit =380),
lmax =370 nm (lexit =320 nm).
Polymer (7): The product was synthesized by using the general method
and obtained as a bright yellow powder (yield 96%); M.p. >3608C
1
(decomp); H NMR (400 MHz) (CDCl3): d=0.65 (br, 4H), 0.78 (m, 6H),
1.05–1.13 (m, 12H), 2.10–2.20 (br, 4H), 7.40–7.60 (br, 4H), 7.80–7.95 (br,
4H), 8.02 (s, 2H), 8.67 (s, 2H); MS (MALDI-TOF; repeated fragments
of the main unit): m/z: 463 [M+H]+ (polymeric structures are observed
up to n=32); UV/Vis (CHCl3, 1.56”10À5 molLÀ1): l=420 nm; fluores-
cence: lmax =490 nm.
[14] J.-M. Lehn, Supramolecular Chemistry—Concepts and Perspectives,
VCH, Weinheim, 1995, Chapters 9 and 10.
Polymer (8): The product was synthesized by using the general method
and obtained as a bright yellow powder (yield 98%); M.p. >3608C
[15] During the course of our studies, polymers related to polyimino-
fluorenes were described, as good candidates for optoelectronic de-
vices, but they were not used for dynamic chemistry, see: K. Hyun-
Chul, K. Jong-Seong, K. Kie-Soo, P. Honk-Ki, B. Sungsik, R. Moon-
hor, J. Polym. Sci. Part A 2004, 42, 825.
[16] a) The resonance imine signals were assigned on the basis of the
spectra of isolated compounds 1 and 2; b) before being subjected to
exchange, the library was equilibrated for 24 h in chloroform from
starting materials; c) when the amount of CF3CO2D increases, the
rate of the equilibration process is faster than the time necessary for
running a proton NMR experiment; these kinetic aspects (b and c
are discussed below.
[17] Starting with a 5:2:1 solution of cyclopentylamine/2-aminofluorene/
2,7-fluorenedicarboxaldehyde, leads to a system that contains only
compound 1 in the same conditions of H+ concentration and tem-
perature. The use of an equimolar ratio is nevertheless important
for further polymerization reactions.
1
(decomp); H NMR (400 MHz) (CDCl3): d=0.69 (br, 4H), 0.78 (m, 6H),
1.00–1.20 (br, 12H), 2.10–2.20 (br, 4H), 4.00(br, 2H), 7.33–7.40 (m, 2H),
7.40–7.60 (m, 2H), 7.80–8.00 (m, 6H), 8.03 (s, 2H), 8.70 ppm (s, 2H); MS
(MALDI-TOF; repeated fragments of the main unit): m/z: 551 [M+H]+
(polymeric structures are observed up to n=18); UV/Vis (CHCl3, 1.16”
10À5 molLÀ1): l=418 nm; fluorescence: lmax =493 nm.
Polymer (9): The product was synthesized by using the general method
and obtained as a bright yellow powder (yield 94%); M.p. >3608C
1
(decomp); H NMR (400 MHz) (CDCl3): d=0.65 (br, 4H), 0.78 (m, 6H),
1.00–1.20 (br, 12H), 2.00–2.20 (br, 4H), 7.20 (s, 2H), 7.35 (d, 3J=7.3 Hz,
4H), 7.63 (d, 3J=7.3 Hz, 4H), 7.83–7.88 (m, 4H), 8.01 (s, 2H), 8.64 ppm
(s, 2H); MS (MALDI-TOF; repeated fragments of the main unit): m/z:
565 [M+H]+ (polymeric structures are observed up to n=25); UV/Vis
(CHCl3, 1.15”10À5 molLÀ1): l=422 nm; fluorescence: lmax =496 nm.
[18] The conversion aspect (ꢀImines/ꢀAldehydes) is not discussed for
each H+ concentration as this ratio is always higher than 97%,
except for 10À1 m (85%) and for values above 1m.
[19] For example, at 348 K and for [CF3CO2D]=1m, bis-imine 1 starts to
decompose into the monoaromatic imine monoaldehyde (product
[1] a) J.-M. Lehn, Proc. Natl. Acad. Sci. USA 2002, 99, 4763; b) J.-M.
Lehn, Science 2002, 295, 2400.
[2] S. J. Rowan, S. J. Cantrill, G. R. L. Cousins, J. K. M. Sanders, J. F.
Stoddart, Angew. Chem. 2002, 114, 938; Angew. Chem. Int. Ed.
2002, 41, 898.
1734
www.chemeurj.org
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 1723 – 1735

Dynamic Combinatorial Chemistry
FULL PAPER
11, see experimental part) and free aldehyde A, in agreement with
previous observations on the effect on increasing the temperature at
high acid concentrations.[9] At the same temperature and for
[CF3CO2D]=0m, the conversion is not affected but the selectivity is
a somewhat lower compared to the 298 K experiment.
ing, and a sample dissolved in chloroform (for 1H NMR as well as
UV-visible and fluorescence spectral determinations); when both
procedures were used they gave the same results. The concentration
of the solutions used for NMR spectroscopy was 10À4 m.
[24] The stability constant value for the complexation of ZnII with hex-
amethylhexacyclene B in water is 13.29. See, “Cryptands”: B. Die-
trich, Compr. Supramol. Chem. 1996, 1, 153.
[20] K. Yamamoto, M. Higuchi, S. Shlki, M. Tsuruta, H. Chiba, Nature
2002, 415, 509.
[21] Qing T. Zhang, James M. Tour, J. Am. Chem. Soc. 1997, 119, 9624.
[22] Most of them give a nonselective exchange process together with
hydrolysis of the imines bonds (Ag(OTf),Cu(Otf)2, Ln(Otf)3, etc.).
[23] The reaction product was a pale yellow solution and precipitate
([A]i =5.12”10À2 m). For spectral characterization, this product was
either dissolved in chloroform (for UV-visible and fluorescence
spectroscopy) or evaporated to dryness under vacuum, without heat-
[25] N. Giuseppone, J.-L. Schmitt, E. Schwartz, J.-M. Lehn, J. Am. Chem.
Soc. 2005, 127, 5528.
[26] Y. Jin, J. Ju, J. Kim, S. Lee, J. Y. Kim, S. H. Park, S.-M. Son, S.-H.
Jin, K. Lee, H. Suh, Macromolecules 2003, 36, 6970–6975.
Received: August 24, 2005
Published online: January 3, 2006
Chem. Eur. J. 2006, 12, 1723 – 1735
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1735