Synthesis and photoluminescent properties of 1,1'-binaphthyl-based chiral phenylenevinylene dendrimers.
ABSTRACT New chiral, soluble binaphthyl derivatives that incorporate stilbenoid dendrons at the 6,6'-positions have been prepared. The synthesis of the new enantiopure dendrimers was performed in a convergent manner by Horner-Wadsworth-Emmons (HWE) reaction of the appropriately functionalized 1,1'-binaphthyl derivative (R)-1 and the appropriate dendrons (R)(2n)G(n)-CHO. Different electroactive units were incorporated in the peripheral positions of the dendrons in order to tune both the optical and electrochemical behavior of these systems. Fluorescence measurements on the chiral dendrimers reveal a strong emission with maxima between 409 and 508 nm depending upon the substitution pattern. Finally, the redox properties of the dendrimers were determined by cyclic voltammetry, showing the influence of the functional groups at the peripheral positions of the dendrimer on the redox behavior of these systems.
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ABSTRACT: This review explores how the occurrence of synchronized conformational fluctuations within a folded macromolecular structure contributes to its structural and functional properties. These fluctuations interconvert multiple conformational states that are separated by small energetic barriers. Internal motions that occur on very short time and length scales in proteins greatly influence processes such as ligand binding, catalysis, allostery and thermodynamic stability. Furthermore, recent evidence suggests that the residual conformational fluctuations are correlated within the folded structure of proteins. These observations suggest that the mechanism by which the residual motions contribute to the thermodynamic stability of proteins is related to the chiral amplification phenomenon observed in helical polymers and supramolecular assemblies. In these synthetic systems, extensive theoretical and experimental studies have demonstrated that conformational synchronization that occurs over extended distances amplifies small energetic differences relating conformational states leading to highly stable folded materials. The effect of these synchronized fluctuations on the conformational properties provides a model for the design of dendrimers that adopt folded conformations and amplify chiral structural perturbations.Progress in Polymer Science. 01/2005;
- ChemInform 08/2006; 35(36):2009-2017.
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ABSTRACT: Strong intermolecular interactions usually result in decreases in solubility and fluorescence efficiency of organic molecules. Therefore, amorphous materials are highly pursued when designing solution-processable, electroluminescent organic molecules. In this paper, a non-planar binaphthyl moiety is presented as a way of reducing intermolecular interactions and four binaphthyl-containing molecules (BNCMs): green-emitting BBB and TBT as well as red-emitting BTBTB and TBBBT, are designed and synthesized. The photophysical and electrochemical properties of the molecules are systematically investigated and it is found that TBT, TBBBT, and BTBTB solutions show high photoluminescence (PL) quantum efficiencies of 0.41, 0.54, and 0.48, respectively. Based on the good solubility and amorphous film-forming ability of the synthesized BNCMs, double-layer structured organic light-emitting diodes (OLEDs) with BNCMs as emitting layer and poly(N-vinylcarbazole) (PVK) or a blend of poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] and PVK as hole-transporting layer are fabricated by a simple solution spin-coating procedure. Amongst those, the BTBTB based OLED, for example, reaches a high maximum luminance of 8315 cd · m−2 and a maximum luminous efficiency of 1.95 cd · A−1 at a low turn-on voltage of 2.2 V. This is one of the best performances of a spin-coated OLED reported so far. In addition, by doping the green and red BNCMs into a blue-emitting host material poly(9,9-dioctylfluorene-2,7-diyl) high performance white light-emitting diodes with pure white light emission and a maximum luminance of 4000 cd · m−2 are realized.Advanced Functional Materials 10/2008; 18(20). · 10.44 Impact Factor
Synthesis and Photoluminescent Properties of
1,1′-Binaphthyl-Based Chiral Phenylenevinylene Dendrimers
Enrique Dı ´ ez-Barra,*,†J oaquı ´ n C. Garcı ´ a-Martı ´ nez,†Ria ´nsares del Rey,†
J ulia ´n Rodrı ´ guez-Lo ´pez,*,†Francesco Giacalone,‡J ose ´L. Segura,*,‡and Nazario Martı ´ n*,‡
Facultad de Ciencias Quı ´ micas, Universidad de Castilla-La Mancha, 13071-Ciudad Real, Spain, and
Departamento de Quı ´ mica Orga ´nica I, Facultad de Ciencias Quı ´ micas, Universidad Complutense,
Received J uly 22, 2002
New chiral, soluble binaphthyl derivatives that incorporate stilbenoid dendrons at the 6,6′-positions
have been prepared. The synthesis of the new enantiopure dendrimers was performed in a
convergent manner by Horner-Wadsworth-Emmons (HWE) reaction of the appropriately func-
tionalized 1,1′-binaphthyl derivative (R )-1 and the appropriate dendrons (R )2nGn-CHO. Different
electroactive units were incorporated in the peripheral positions of the dendrons in order to tune
both the optical and electrochemical behavior of these systems. Fluorescence measurements on
the chiral dendrimers reveal a strong emission with maxima between 409 and 508 nm depending
upon the substitution pattern. Finally, the redox properties of the dendrimers were determined by
cyclic voltammetry, showing the influence of the functional groups at the peripheral positions of
the dendrimer on the redox behavior of these systems.
Synthetic macromolecules that contain π-conjugated
systems have attracted a great deal of attention owing
to their potential to act as photosynthetic antennas, as
molecular wires for electron and energy transfer, and also
as materials in organic photo- and electroluminescent
devices. In this regard, linear-chain polymers are the
systems most often prepared with these aims in mind.
However, such materials dosuffer from some limitations
such as broad molecular weight distribution, poorly
defined morphologies, and uncontrolled intra- and inter-
chain interactions.1Convergent and divergent synthetic
methodologies for the synthesis of dendrimers provide a
high degree of control in terms of the molecular size,
shape, and location of functional groups, leading to
almost total control over the molecular architecture.1,2
Thus, dendrimers have become suitable materials to
overcome the drawbacks of linear-chain polymers, and
dendritic structures have been shown to act as light-
harvesting antennas3and to be appropriate compounds
for optoelectronics applications.4
Chiral dendrimers5represent another important target
duetotheir possibleapplications in asymmetric catalysis,
in sensor technology, and for chemical separations. The
majority of the chiral dendrimers reported to date have
been prepared using dendrons or cores with stereogenic
centers. On the other hand, only a few examples are
known in which axial chirality is reported and all of these
compounds are based on 1,1′-binaphthyl derivatives.
1,1′-Binaphthol is a useful core unit because its ver-
satility and well-established chemistry permits the prepa-
ration of a wide range of different molecular structures.
Thus, nucleophilic aromatic substitution,6Heck,7Suzuki,8
†Universidad de Castilla-La Mancha.
(1) J iang, D.-L.; Aida, T. Dendrimers and Other Dendritic Polymers;
Fre ´chet, J . M. J ., Tomalia, D. A., Eds.; J ohn Wiley & Sons: Chichester,
(2) (a) Newkome, G. R.; Moorefield, C. N.; Vo ¨gtle, F. Dendrimers
and Dendrons; Wiley-VCH: Weinheim, 2001. (b) Grayson, S. M.;
Fre ´chet, J . M. J . Chem. Rev. 2001, 101, 3819. (c) Dendrimers IIIs
Design, Dimension, Function; Vo ¨gtle, F., Vol. Ed.; Top. Curr. Chem.
2001, 212. (d) Vo ¨gtle, F.; Gestermann, S.; Hesse, R.; Schwierz, H.;
Windisch, B. Prog. Polym. Sci. 2000, 25, 987. (e) Dendrimers IIs
Architecture, Nanostructure and Supramolecular Chemistry; Vo ¨gtle,
F., Vol. Ed.; Top. Curr. Chem. 2000, 210. (f) Bosman, A. W.; J anssen,
H. M.; Meijer, E. W. Chem. Rev. 1999, 99, 1665. (g) Majoral, J . P.;
Caminade, A. M. Chem. Rev. 1999, 99, 845. (h) Dendrimers; Vo ¨gtle,
F., Vol. Ed.; Top. Curr. Chem. 1998, 197. (i) Smith, D. K.; Diederich,
F. Chem. Eur. J . 1998, 4, 1353. (j) Zeng, F.; Zimmerman, S. C. Chem.
Rev. 1997, 97, 1681.
(3) (a) Weil, T.; Reuther, E.; Mu ¨llen, K. Angew. Chem., Int. Ed. 2002,
41, 1900. (b) Balzani, V.; J uris, A. Coord. Chem. Rev. 2001, 211, 97.
(c) Adronov, A.; Fre ´chet, J . M. J . Chem. Commun. 2000, 1701. (d) J iang,
D. L.; Aida, T. Nature 1997, 388, 454. (e) Shortreed, M. R.; Swallen,
S. F.; Shi, Z.-Y.; Tan, W.; Xu, Z.; Devadoss, C.; Moore, J . S.; Kopelman,
R. J . Phys. Chem. B 1997, 101, 6318. (f) Devadoss, C.; Bharathi, P.;
Moore, J . S. J . Am. Chem. Soc. 1996, 118, 9635. (g) Stewart, G. M.;
Fox, M. A. J . Am. Chem. Soc. 1996, 118, 4354.
(4) (a) Cameron, C. S.; Gorman, C. B. Adv. Funct. Mater. 2002, 12,
17. (b) Stone, D. L.; Smith, D. K.; McGrail, P. T. J . Am. Chem. Soc.
2002, 124, 856. (c) Marsitzky, D.; Vestberg, R.; Blainey, P.; Tang, B.
T.; Hawker, C. J .; Carter, K. R. J . Am. Chem. Soc. 2001, 123, 6965.
(d) Sakamoto, M.; Ueno, A.; Mihara, H. Chem. Eur. J . 2001, 7, 2449.
(e) Lupton, J . M.; Samuel, I. D. W.; Beavington, R.; Burn, P. L.; Ba ¨ssler,
H. Adv. Mater. 2001, 13, 258. (f) Halim, M.; Pillow, J . N. G.; Samuel,
I. D. W.; Burn, P. L. Adv. Mater. 1999, 11, 371.
(5) (a) Seebach, D.; Rheiner, P. B.; Greiveldinger, G.; Butz, T.;
Sellner, H. Top. Curr. Chem. 1998, 197, 125. (b) Thomas, C. W.; Tor,
Y. Chirality 1988, 10, 53. (c) Peerlings, H. W. I.; Meijer, E. W. Chem.
Eur. J . 1997, 3, 1563. (c) Pugh, V. J .; Hu Q.-S.; Pu, L. Angew. Chem.,
Int. Ed. 2000, 39, 3638.
(6) Gandhi, P.; Huang, B.; Gallucci, J . C.; Parquette, J . R. Org. Lett.
2001, 3, 3129.
3178 J . Org. Chem. 2003, 68, 3178-3183
10.1021/jo026222s CCC: $25.00 © 2003 American Chemical Society
Published on Web 03/18/2003
and Williamson12reactions have been used for the
synthesis of 1,1′-binaphthyl derivatives. Bazan et al. have
recently reported thesynthesis of 6,6′-bis(polyphenylene-
vinylene)-substituted 1,1′-binaphthol derivatives and
have shown the importance of the molecular topology of
the binaphthyl framework for the design of noncrystal-
lizable organic chromophores.7Pu et al. have used 1,1′-
bi-2-naphthol derivatives to construct novel rigid and
cross-conjugated optically activedendrimers with phenyl-
acetylene-based dendrons. They also demonstrated that
a very efficient energy migration occurs from the cross-
conjugated dendrons to the central core, leading to
greatly enhanced fluorescenceat higher generations. This
is the first example of an efficient energy migration
conducted in an optically pure dendritic system.9The
same authors recently reported the usefulness of these
dendrimers as enantioselective fluorescence sensors for
the recognition of chiral amino alcohols.8
Blue-luminescent polymers are usually prepared by
three main strategies: (i) a random interruption of the
conjugation along the chain by copolymerization with
nonconjugated monomers, (ii) the presence of a back-
bone twist caused by steric interactions as in the case of
widely studied poly-p-phenylenes (PPP), polyfluorenes,
polytetrahydropyrenes, poly-2,8-indenoflurene, and lad-
der-type PPP,13and (iii) the use of cross-conjugation. The
first approach affords polymers that suffer from the
drawback that emission usually occurs from the more
conjugated segments only. The second set of materials,
on the other hand, have very little potential for fine-
tuning. Only cross-conjugation gives rise to an efficient
and predictable method to interrupt the conjugation in
the system.14Thus, dendritic polyphenylenevinylenes,
also called stilbenoid dendrimers, are interesting and
In a previous communication11we reported a Horner-
Wadsworth-Emmons approach to new soluble cross-
conjugated chiral luminescent dendrimers bearing meth-
oxy groups on the periphery. We report here the synthesis,
characterization, chiroptical properties, UV-vis and
fluorescence measurements, and electrochemical behav-
ior of new dendrimers based on 1,1′-binaphthol with
cross-conjugated arms and electron-donor and electron-
acceptor groups at the periphery.
R esults and Discussion
Synthesis and Characterization of Chiral Den-
drimers. The synthesis of dendrimers (R )4nGn-Bn
was achieved in a convergent manner by Horner-
Wadsworth-Emmons (HWE) reaction of the 1,1′-binaph-
thyl derivative (R )-116and the appropriate dendrons
(R )2nGn-CHO15ain KtBuO/THF (Scheme 1).
All new compounds were characterized using various
analytical techniques. MS and NMR experiments proved
very useful to confirm the structures of the compounds
(see Experimental Section and Supporting Information).
The NMR spectra indicate that these dendrimers main-
tain a C2 symmetry in solution. The selectivity of the
HWEreaction is sufficiently high to generate all-
trans isomers within the limits of NMR detection. This
stereochemistry for the double bonds was unequivo-
cally established for the first generation dendrimers
(OCH3)4G1-Bn and (NBu2)4G1-Bn on the basis of
the coupling constant of the vinylic protons in the1H
NMR spectra (J ≈ 16 Hz), where the AB quartet for the
double bond linking the binaphthyl core and the dendron
could be distinguished (Figure 1). In the rest of com-
pounds there is some overlapping of signals that pre-
cludes the unambiguous determination of the coupling
constant; however, thereis noreason toobtain a different
Assessment of the overall purity of these molecules
proved difficult. The1H NMR spectra of thesedendrimers
are well-resolved and do not reveal impurities, but the
high number of lines in the 0.8-1.5 and 7-8 ppm zones
could obscure the presence of small amounts of other
LSIMS mass spectroscopic analyses of (OCH3)4G1-Bn
and (OCH3)8G2-Bn gave the expected molecular ions.
The MALDI-TOF spectra of (NBu2)4G1-Bn, (NBu2)8G2-
Bn, (CF3)4G1-Bn, and (CF3)8G2-Bn showed peaks match-
ing the calculated values for the expected molecular
weights. However, the mass spectrum of (CF3)8G2-Bn
showed evidence of some degree of contamination. Fur-
ther purification of this compound was achieved by
(7) Ostrowski, J . C.; Hudack, J r., R. A.; Robinson, M. R.; Wang, S.;
Bazan, G. C. Chem. Eur. J . 2001, 7, 4500.
(8) Gong, L.-Z.; Hu, Q.-S.; Pu, L. J . Org. Chem. 2001, 66, 2358.
(9) Hu, Q.-S.; Pugh, V.; Sabat, M.; Pu, L. J . Org. Chem. 1999, 64,
(10) Go ´mez, R.; Segura, J . L.; Martı ´ n, N. J . Org. Chem. 2000, 65,
(11) Dı ´ ez-Barra, E.; Garcı ´ a-Martı ´ nez, J . C.; Rodrı ´ guez-Lo ´pez, J .;
Go ´mez, R.; Segura, J . L.; Martı ´ n, N. Org. Lett. 2000, 2, 3651.
(12) (a) Peerlings, H. W. I.; Meijer, E. W. Eur. J . Org. Chem. 1998,
573. (b) Rosini, C.; Superchi, S.; Peerlings, H. W. I.; Meijer, E. W. Eur.
J . Org. Chem. 2000, 61.
(13) Setayesh, S.; Grimsdale, A. C.; Weil, T.; Enkelmann, V.; Mu ¨llen,
K.; Meghdadi, F.; List, E. J . W.; Leising, G. J . Am. Chem. Soc. 2001,
123, 946 and references therein.
(14) Liao, L.; Pang, Y.; Ding, L.; Karasz, F. E. Macromolecules 2001,
(15) (a) Dı ´ ez-Barra, E.; Garcı ´ a-Martı ´ nez, J . C.; Merino, S.; del Rey,
R.; Rodrı ´ guez-Lo ´pez, J .; Sa ´nchez-Verdu ´, M. P.; Tejeda, J . J . Org. Chem.
2001, 66, 5664. (b) Segura, J . L.; Go ´mez, R.; Martı ´ n, N.; Guldi, D. M.
Org. Lett. 2001, 3, 2645. (c) Meier, H.; Lehmann, M.; Kolb, U. Chem.
Eur. J . 2000, 6, 2462. (d) Halim, M.; Pillow, J . N. G.; Samuel, I. D.
W.; Burn, P. L. Adv. Mater. 1999, 11, 371. (e) Dı ´ ez-Barra, E.; Garcı ´ a-
Martı ´ nez, J . C.; Rodrı ´ guez-Lo ´pez, J . Tetrahedron Lett. 1999, 40, 8181.
(f) Meier, H.; Lehmann, M. Angew. Chem., Int. Ed. Engl. 1998, 37,
643. (g) Pilow, J . N. G.; Burn, P. L.; Samuel, I. D. W.; Halim, M. Synth.
Met. 1999, 102, 1468. (h) Maddux, T. M.; Yu, L. J . Am. Chem. Soc.
1997, 119, 9079. (i) Ma, D.; Lupton, J . M.; Beavington, R. Burn, P. L.;
Samuel, D. W. Adv. Funct. Mater. 2002, 12, 507.
(16) Go ´mez, R.; Segura, J . L.; Martı ´ n, N. Org. Lett. 2000, 2, 1585.
F IGUR E 1. Thedoublebond signals in the1H NMR spectrum
of (NBu2)4G1-Bn. TwoAB quartets can be observed with J ≈
16 Hz. ABq2 corresponds to the double bond linking the
J . Org. Chem, Vol. 68, No. 8, 2003 3179
column chromatography, although a significant amount
of product was also lost during this process. The mass
spectrum subsequently showed a much purer product,
although a peak at m/z 1006.2 was evident, which could
correspond to the carboxylic acid (CF3)4G1-COOH de-
rived from oxidation of the starting material. A similar
situation has been previously observed by us in a case
where some second generation dendrons were treated
under HWE conditions and the substrate had a higher
degree of steric hindrance around the reactive site.15a
Optical Spectroscopic Studies of the Chiral Den-
drimers. The UV-vis absorption and PL spectra of
dendrimers (R )4nGn-Bn wererecorded in CH2Cl2at room
temperature (Figure 2). The data obtained are sum-
marized in Table 1. Owing to the meta arrangement
through which the dendrons are linked, it was expected
that the absorption spectra would consist of a simple
superposition of the absorptions due to the stilbene
dendrons and the binaphthyl core. Indeed, strong bands
with maxima at 317-367 nm, associated with the stil-
bene units, are observed. In some cases small shoulders
at ca. 340 nm can be observed, and these are associated
with the core. The absorptions become much stronger as
the dendritic generation grows owing tothe exponential
increase in the number of light-absorbing phenylene-
vinyleneunits. Thesemolecules arealmost colorless, with
the exception of the dialkylaminoderivatives. When the
spectra wererecorded at lower concentrations (10-7-10-8
M range), tworesolved bands wereoften observed instead
of a single absorption as well as changes in the shift and
chromicity of the bands (higher ?). A satisfactory expla-
nation for these effects is unclear at the moment and will
require further investigations. Several authors have
pointed out that a concentration-dependent aggregation
provokes changes in theUV-vis and fluorescencespectra
of stilbenoid units.15f,17Theabsorption maxima show only
very small blue-shifts upon increasing the generation.
This is expected since the meta linkage of the stilbene
SCHE ME 1. Synthesis of 1,1′-Binaphthyl-Based Chiral Phenylenevinylene Dendrimers R4nGn-Bn
T ABL E 1.
UV-vis, Photoluminescence (PL ), Optical R otation, and E lectrochemical Data
λmax, nm (?, M-1cm-1)
λmax, nm (λexc, nm)
(OMe)4G1-Bn329.5 (171500) 409 (329.5)
(OMe)8G2-Bn 326.5 (336600)425 (326.5)
(NBu2)4G1-Bn 367.5 (208600)496 (360.5)
(NBu2)8G2-Bn363.0 (324900)508 (360.5)
(CF3)4G1-Bn 317.5 (143100)444 (317.5)
(CF3)8G2-Bn 316.5 (391800) 431 (316.5)
aAll spectra were recorded in CH2Cl2at room temperature at c ) 3 × 10-6M, except for (OCH3)4G1-Bn and (OCH3)8G2-Bn where
c ) 1 × 10-6M.bAll spectra were recorded in CH2Cl2at room temperature at c ) 3 × 10-7M, except for (OCH3)4G1-Bn and (OCH3)8G2-
Bn where c ) 1 × 10-7M.cFluorescence quantum yield in dichloromethane determined relative to quinine sulfate dissolved in 1 N
H2SO4.dRecorded in CH2Cl2at c ) 1 × 10-3M, except for (OCH3)8G2-Bn and (CF3)8G2-Bn where c ) 4 × 10-4M.eScan rate: 100
mV‚s-1in dry CH2Cl2(0.1 M n-Bu4NClO4) using SCE as reference and GCE as working electrodes.fThis oxidation wave can only be
observed after multiple scans.
Dı ´ ez-Barra et al.
3180 J . Org. Chem., Vol. 68, No. 8, 2003
units should cause little change in conjugation as the
dendrimer grows. The small blue-shift may be explained
in terms of a decrease in the planarity of the conjugated
backbone. Low energy absorption bands were not ob-
served, a situation in agreement with the lack of conju-
gation between the dodecyloxynaphthalene and the stil-
bene units. Through-bond or through-space interactions
between the twomoieties donot take place in the ground
The dendrimers emit strong blue light under UV
irradiation, showing typical bands for the stilbenoid
compounds reported previously by us.15a,bThe fluores-
cence quantum yields, Φf, were determined by using a
solution of quinine sulfate in 1 N H2SO4as the reference
standard (Φs) 0.546). The intensity of the fluorescence
from compounds (R )8G2-Bn, the higher generation den-
drimers, is substantially lower than that from their
corresponding counterparts (R )4G1-Bn. Similar behavior
has been previously observed for other structurally rigid
dendrons3f,18and has been accounted for by the many
modes used to dissipate the excitation energy in larger
dendrons, a property that enhances the nonradiative
decay. The through-space interaction between the fluo-
rescent units become more significant with increasing
molecular size, providing additional fluorescence quench-
It has been claimed that stilbenedendrons areefficient
energy transmitters.4fSimilar emissions in the range
400-500 nm for stilbene moieties and core do not allow
us to unequivocally assume that such a property is
present in all of our 1,1′-binaphthyl dendrimers, although
these systems may be envisioned as appropriate candi-
dates for energy transfer processes. In any case, all of
themolecules described herearenew chiral blue-emitting
phenylenevinylene-based dendrimers that are highly
Chiroptical Properties. The optical rotation data
for the studied chiral dendrimers are summarized in
Chen19and Meijer12studied the effect of dendritic
branches at the 2,2′-positions of the 1,1′-binaphthyls on
the optical rotation of the chiral binaphthyl-core-based
dendrimers and observed a change in the molar optical
rotation upon passing from lower to higher generation
dendrons. In contrast, Pu and co-workers showed that
substitution at the 4,4′,6,6′-positions of the binaphthyl
corewith rigid phenyleneethynylene-based dendrons does
not significantly change the 1,1′-binaphthyl dihedral
anglesat least from generation zero to generation two.9
In our case, we observed in the 1,1′-dendron-substituted
binaphthyls that molar optical rotation values for first
and second generation dendrimers are significantly dif-
ferent despite the fact that the substitution is in the 6,6′-
positions. This finding is in agreement with the obser-
vations reported by Pu and co-workers on a family of
optically active dendrimers containing a 1,1′-binaphthyl
core with cross-conjugated phenylene dendrons at the
4,4′- and 6,6′-positions.8The authors suggest that, in this
case, the changes in molar optical rotation with increas-
ing dendron generation might not be solely due to a
change in the binaphthyl dihedral angle. In our case also
the increased steric interactions between phenylene-
vinylene units may play an effective role in the molar
optical rotation variation.
E lectrochemical Behavior. The electrochemical fea-
tures of thebinaphthyl-based phenylenedendrimers were
investigated by cyclic voltammetry at room temperature
(Table 1). Dichloromethane was used as the solvent, and
tetrabutylammonium perchlorate (0.1 M) was employed
as the supporting electrolyte in a conventional three-
compartment cell, equipped with glassy carbon, SCE, and
platinum wire as electrode, reference electrode, and
auxiliary electrode, respectively.
The redox behavior of the stilbenoid dendrons shows
an anodic shift of the oxidation potentials on going from
the trifluoromethane- and methoxy-based systems tothe
(17) (a) Catala ´n, J .; Zima ´nyi, L.; Saltiel, J . J . Am. Chem. Soc. 2000,
122, 2377. (b) Cornil, J .; dos Santos, D. A.; Crispin, X.; Silbey, R.;
Bre ´das, J . L. J . Am. Chem. Soc. 1998, 120, 1289. (c) Oldham, J r., W.
J .; Miao, Y.-J .; Lachicotte, R. J .; Bazan, G. C. J . Am. Chem. Soc. 1998,
(18) (a) Devadoss, C.; Bharathi, P.; Moore, J . S. Macromolecules
1998, 31, 1, 8091. (b) Zhu, Z.; Moore, J . S. J . Org. Chem. 2000, 65,
(19) Chen, Y.-M.; Chen, C.-F.; Xi, F. Chirality 1998, 10, 661.
F IGUR E 2. Absorption and fluorescence emission spectra of
dendrimers (R )4G1-Bn (s) and (R )8G2-Bn (- - -) in CH2Cl2at
room temperature. The fluorescence spectra are normalized
to a constant absorbance.
J . Org. Chem, Vol. 68, No. 8, 2003 3181
more strongly electron-donating dibutylamino-based ana-
logues (Bu2N)4G1-Bn and (Bu2N)8G2-Bn (Eox
As far as the reduction potentials are concerned, only
the trifluoromethane-based systems show an electro-
chemically irreversible wave (Ered
mV) within the window of the solvent. This electrochemi-
cal behavior is in agreement with the stronger donating
ability of the dibutylamino group and the stronger
accepting ability of the trifluoromethane moiety. Thus,
the redox behavior of these systems depends on the
electronic nature of the functional groups at peripheral
positions of the dendrons. As expected, the CV of the
CF3-substituted dendrimer shows the reduction peak at
around -0.9 V, thus showing theacceptor ability of these
dendrons. Regarding the oxidation potential of the den-
dritic structures, the first oxidation potential appears at
around 0.6 V for the NBu2-substituted derivatives, 1.09
V for the methoxy derivatives, and around 1.1 V for the
CF3derivatives. These oxidation potential values could
suggest that the N,N-dibutylstilbene moiety is respon-
sible for the first oxidation potential observed for
(Bu2N)4G1-Bn and (Bu2N)8G2-Bn, whereas in theMeO-
and CF3-derivatives the central core involving the naph-
thaleneunit is responsiblefor thefirst oxidation potential
A most interesting observation for theseoptically active
dendrimers is that the first two irreversible oxidation
potentials, which are observed after one single scan,
disappear after multiple scans while a new chemically
reversible oxidation wave (∆E ≈ 100 mV) appears
between the previously observed waves (see Table 1,
Figure 3). This behavior clearly indicates that the den-
drimers areelectrochemically unstableand, after thefirst
oxidation, give rise to a new electroactive species that
exhibits electrochemically reversible behavior. This elec-
trochemical behavior, as well as the characterization of
the species formed, requires further electrochemical
studies, and these are currently under way in our
laboratories. However, the lack of stability of the radical-
cations could be a problem for their further use in the
preparation of organic LEDs.
1≈ 0.6 V).
≈ -0.9 V, ∆E ≈ 100
In summary, we have developed a general synthetic
route for the preparation of optically active stilbenoid
dendrimers containing enantiopure binaphthyl cores. In
the present study we focused our attention on the
possibility of tuning both optical and redox properties by
means of chemical modification of the peripheral groups
on the dendrimers. Considering the large number of
functionalized fluorophores synthesized in recent years
with specific electrochemical and photophysical proper-
ties, we feel that a remarkable aspect of this contribution
is that it represents an effectiveapproach tothesynthesis
of chiral luminescent materials in which the emission
colors, electron affinity, and ionization potentials can be
Unfortunately, on the basis of the electrochemical
results, this particular group of compounds may not be
suitable for LEDs because of redox instability; however,
given the good solubility imparted by the long alkyl
chains and the strong fluorescence of these systems, they
may also be useful as fluorescent sensors for the dis-
crimination of chiral molecules.
E xperimental Section
General. The general experimental conditions have been
reported previously.15a[R]D values were determined using a
sodium lamp (λ ) 589 nm) at room temperaturein a cylindrical
cell of 1 dm length and a volume of 1 mL. Cyclic voltammo-
grams were recorded on a potentiostat/galvanostat equipped
with electrochemical analysis software and a GCE (glassy
carbon) as working electrode, SCE as reference electrode, Bu4-
NClO4 as supporting electrolyte, and dichloromethane as
solvent. The mass spectra were obtained by the Universidad
Auto ´noma de Madrid (Servicio Interdepartamental de Inves-
tigacio ´n, S.I.D.I.) mass spectroscopy facility. Spectra matri-
ces: 3-nitrobenzyl alcohol (HRMS, LSIMS) and dithranol
(MALDI-TOF). Poly(ethylene glycol) was used for internal
Binaphthyl phosphonate derivative (R )-116and dendrons
(R )2nGn-CHO15awere prepared according toprocedures previ-
ously reported by us.
General Procedure for Horner-Wadsworth-E mmons
R eaction. Method A. All glassware was oven-dried and
cooled under Ar. To a stirred solution of the diphosphonate
(R )-1 (0.1 mmol) and the corresponding dendritic aldehyde
(R )2nGn-CHO (0.2 mmol) in anhydrous THF (10 mL) under
argon was added potassium tert-butoxide (0.6 mmol) in small
portions. The red mixture was stirred at room temperature
for the indicated period of time. The reaction was quenched
with water, neutralized with 1 N HCl, extracted with CH2Cl2
(× 3), and dried (MgSO4). After filtration and evaporation of
the solvent, the crude product was either washed with CHCl3/
EtOH and the insoluble dendrimer isolated by filtration or
purified by column chromatography (silica gel, hexanes/EtAcO
mixtures). Method B. All operations were identical to those
described for Method A except that, after quenching and
neutralization, the insoluble compound was isolated by filtra-
(OMe)4G1-Bn. Method A. Reaction time: 5 h. White solid.
Yield: 95%.1H NMR (CDCl3): δ 0.85 (t, 6H, J ) 6.9 Hz), 0.87-
1.50 (m, 40H), 3.84 (s, 12H), 3.90-4.10 (m, 4H), 6.92 (A of ABq,
8H, J ) 8.7 Hz), 7.01 (A of ABq, 4H, J ) 16.2 Hz), 7.16 (B of
ABq, 4H, J ) 16.2 Hz), 7.12-7.36 (m, 8H), 7.42 (d, 2H, J )
9.0 Hz), 7.49 (B of ABq, 8H, J ) 8.7 Hz), 7.50-7.53 (m, 6H),
7.92 (d, 2H, J ) 1.2 Hz), 7.95 (d, 2H, J ) 9.0 Hz).13C NMR
and DEPT (CDCl3): δ 159.3 (C), 154.9 (C), 138.2 (twosignals,
2 C), 133.9 (C), 132.4 (C), 130.1 (C), 129.3 (two signals, 2 C),
128.6 (CH), 127.8 (CH), 127.6 (CH), 126.9 (CH), 126.4 (CH),
F IGUR E 3. Cyclic voltammograms for dendrimer (NBu2)8G2-
Bn at room temperature (solvent CH2Cl2, supporting electro-
lyte 0.1 M Bu4NClO4, scan rate 100 mV/s).
Dı ´ ez-Barra et al.
3182 J . Org. Chem., Vol. 68, No. 8, 2003
125.9 (CH), 123.8 (CH), 123.3 (CH), 120.6 (C), 116.0 (CH),
114.1 (CH), 69.6 (OCH2), 55.3 (OCH3), 32.0 (CH2), 29.8 (CH2),
29.7 (CH2), 29.6 (twosignals, 2 CH2), 29.4 (twosignals, 2 CH2),
29.2 (CH2), 25.7 (CH2), 22.7 (CH2), 14.2 (CH3). HRMS (LSIMS)
m/e calcd for C96H106O61354.7989, found 1354.7998.
(OMe)8G2-Bn. Method A. Reaction time: 5 h. White solid.
Yield: 70%.1H NMR (CDCl3): δ 0.85 (t, 6H, J ) 6.6 Hz), 0.90-
1.50 (m, 40H), 3.82 (s, 24H), 3.88-4.06 (m, 4H), 6.91 (A of ABq,
16H, J ) 8.7 Hz), 7.00 (A of ABq, 8H, J ) 16.2 Hz), 7.15 (B of
ABq, 8H, J ) 16.2 Hz), 7.15-7.40 (m, 16H), 7.42 (d, 2H, J )
9.0 Hz), 7.48 (B of ABq, 16H, J ) 8.7 Hz), 7.44-7.60 (m, 18H),
7.90-7.96 (m, 4H).13C NMR (CDCl3): δ 159.3, 154.9, 138.2,
138.1, 137.9, 137.8, 133.9, 132.3, 130.0, 129.3, 128.9, 128.6,
127.8, 127.0, 126.3, 124.0, 123.7, 123.4, 120.6, 115.9, 114.1,
69.6, 55.3, 32.0, 29.8, 29.7, 29.6, 29.4 (twosignals), 29.2, 29.1,
25.7, 22.7, 14.2. HRMS (LSIMS) m/e calcd for C164H162O10
2291.2168, found 2291.2237.
(NBu2)4G1-Bn. Method A. Reaction time: 15 h. Purified
by column chromatography. Yellow oil. Yield: 94%.1H NMR
(CDCl3): δ 0.86 (t, 6H, J ) 6.9 Hz), 0.96 (t, 24H, J ) 7.5 Hz),
0.9-1.3 (m, 40H), 1.30-1.50 (m, 16H), 1.50-1.68 (m, 16H),
3.29 (t, 16H, J ) 7.5 Hz), 3.88-4.05 (m, 4H), 6.64 (A of ABq,
8H, J ) 9.0 Hz), 6.91 (A of ABq, 4H, J ) 15.9 Hz), 7.12 (B of
ABq, 4H, J ) 16.2 Hz), 7.16 (A of ABq, 2H, J ) 15.9 Hz), 7.20
(d, 2H, J ) 8.4 Hz), 7.33 (B of ABq, 2H, J ) 16.2 Hz), 7.41 (B
of ABq, 8H, J ) 8.7 Hz), 7.47 (broad s, 8H), 7.52 (dd, 2H, J )
9.0 Hz, J ) 1.2 Hz), 7.90-7.97 (m, 4H).13C NMR and DEPT
(CDCl3): δ 154.8 (C), 147.8 (C), 138.8 (C), 137.9 (C), 133.8 (C),
132.6 (C), 129.4 (C), 129.2 (CH), 129.0 (CH), 128.9 (CH), 128.0
(CH), 127.8 (CH), 126.7 (CH), 125.9 (CH), 124.5 (C), 123.8
(CH), 123.6 (CH), 122.8 (CH), 122.4 (CH), 120.7 (C), 116.0
(CH), 111.6 (CH), 69.7 (OCH2), 50.8 (NCH2), 32.0 (CH2), 29.7
(CH2), 29.7 (CH2), 29.6 (CH2), 29.5 (CH2), 29.5 (CH2), 29.4
(CH2), 29.2 (CH2), 25.7 (CH2), 22.7 (CH2), 20.4 (CH2), 14.1
(CH3), 14.0 (CH3). MALDI-TOF (C124H166N4O2) m/e 1743.8.
(NBu2)8G2-Bn. Method A. Reaction time: 17 h. Purified
by column chromatography. Yellow oil. Yield: 84%.1H NMR
(CDCl3): δ 0.85 (t, 6H, J ) 7.2 Hz), 0.96 (t, 48H, J ) 7.5 Hz),
0.9-1.3 (m, 40H), 1.30-1.50 (m, 32H), 1.50-1.68 (m, 32H),
3.29 (t, 32H), 3.9-4.1 (m, 4H), 6.65 (A of ABq, 16H, J ) 8.7
Hz), 6.93 (A of ABq, 8H, J ) 16.2 Hz), 7.14 (B of ABq, 8H, J
) 16.2 Hz), 7.23-7.66 (m, 34H), 7.43 (B of ABq, 16H, J ) 8.7
Hz), 7.57 (d, 2H, J ) 9.0 Hz), 7.94-8.00 (m, 4H).13C NMR
(CDCl3): δ 154.9, 147.8, 138.9, 138.3, 138.1, 137.6, 133.9, 132.4,
129.3, 129.2, 128.4, 127.8, 126.9, 125.8, 124.5, 123.9, 123.7,
123.5, 123.2, 122.5, 120.7, 116.0, 111.6, 69.7, 50.8, 32.0, 29.8,
29.7, 29.6, 29.5, 29.4, 29.2, 25.7, 22.7, 20.4, 14.1 (CH3), 14.0
(CH3). MALDI-TOF m/e 3070.0.
(CF3)4G1-Bn. Method A. Reaction time: 5 h 30 min. White
solid. Yield: 71%.1H NMR (CDCl3): δ 0.83 (t, 6H, J ) 7.2
Hz), 0.9-1.5 (m, 40H), 3.90-4.05 (m, 4H), 7.13 (A of ABq, 2H,
J ) 16.2 Hz), 7.19 (s, 8H), 7.23 (d, 2H, J ) 8.7 Hz), 7.33 (B of
ABq, 2H, J ) 16.2 Hz), 7.43 (d, 2H, J ) 9.3 Hz), 7.52 (dd, 2H,
J ) 9.0 Hz, J ) 1.2 Hz), 7.53 (broad s, 2H), 7.58 (d, 4H, J )
1.2 Hz), 7.60 (s, 16H), 7.91 (d, 2H, J ) 1.5 Hz), 7.94 (d, 2H, J
) 9.3 Hz).13C NMR (CDCl3): δ 155.0, 140.6, 138.5, 137.4,
134.0, 132.1, 130.7, 130.1#, 129.9, 129.6#, 129.6*, 129.4, 129.3,
129.2,#128.8#, (#q, J ) 32 Hz), 127.8, 127.1, 126.6, 126.0*, 125.6
(q, J ) 4 Hz), 124.6, 124.1, 123.7,* 120.5, 118.8* (*q, J ) 270
Hz, CF3), 116.0, 69.6, 32.0, 29.8, 29.7, 29.6, 29.4, 29.2, 25.7,
22.7, 14.1. MALDI-TOF (C96H94F12O2) m/e 1507.2.
(CF3)8G2-Bn. Method B. Reaction time: 6 h. White solid.
Yield: 63%.1H NMR (THF-d8): δ 0.85 (t, 6H, J ) 6.9 Hz),
1.0-1.5 (m, 40H), 3.95-4.10 (m, 4H), 7.19-7.82 (m, 84H),
7.98-8.04 (m, 4H).13C NMR and DEPT (THF-d8): δ 156.1 (C),
142.3 (C), 139.6 (C), 139.4 (C), 139.1 (C), 138.8 (C), 135.0 (C),
133.4 (C), 132.8 (CH), 131.9 (CH), 130.9*, 130.5#, 130.5 (CH),
130.2 (CH), 130.2 (CH), 130.1#, 129.7#, 129.5 (CH), 129.3#(#q,
J ) 31.6 Hz, C), 128.7 (CH), 128.2 (CH), 127.9 (CH), 127.7
(CH), 127.3*, 126.8 (CH), 126.5 (q, J ) 4 Hz, CH), 125.6 (CH),
125.1 (CH), 124.6 (CH), 124.4 (CH), 123.6*, 121.4 (C), 120.1*
(*q, J ) 270 Hz, CF3), 116.5 (CH), 70.0 (OCH2), 32.9 (CH2),
30.8 (CH2), 30.7 (CH2), 30.6 (CH2), 30.4 (CH2), 30.4 (CH2), 30.2
(CH2), 26.8 (CH2), 23.6 (CH2), 14.5 (CH3). MALDI-TOF
(C164H138F24O2) m/e 2596.8.
Spanish DGES (PB98-0818A and BQ2002-1327) and
the J unta de Comunidades de Castilla La Mancha
(GC-02-013) is gratefully acknowledged. J .C.G.-M.
also acknowledges the receipt of a predoctoral fellow-
ship from the J unta de Comunidades de Castilla-La
Financial support from the
Supporting Information Available: Copies of1H NMR
available free of charge via the Internet at http://pubs.acs.org.
13C NMR spectra for all compounds. This material is
J . Org. Chem, Vol. 68, No. 8, 2003 3183