Synthesis of novel cross-conjugated dendritic fluorophores containing both phenylenevinylene and phenyleneethynylene moieties

Article abstract of DOI:10.1021/jo026019x

New dendrons and dendrimers with dendritic arms composed of alternate phenyleneethynylene and phenylenevinylene moieties have been efficiently synthesized using orthogonal and convergent syntheses that combine Sonogashira and Horner-Wadsworth-Emmons react

Full text of DOI:10.1021/jo026019x

Syn th esis of Novel Cr oss-Con ju ga ted Den d r itic F lu or op h or es
Con ta in in g Both P h en ylen evin ylen e a n d P h en ylen eeth yn ylen e
Moieties
Enrique D´ıez-Barra,* J oaqu´ın C. Garc´ıa-Mart´ınez, and J ulia´n Rodr´ıguez-Lo´pez*
Facultad de Quı´mica, Universidad de Castilla-La Mancha, 13071-Ciudad Real, Spain
enrique.diez@uclm.es
Received J une 6, 2002
New dendrons and dendrimers with dendritic arms composed of alternate phenyleneethynylene
and phenylenevinylene moieties have been efficiently synthesized using orthogonal and convergent
syntheses that combine Sonogashira and Horner-Wadsworth-Emmons reactions. Two different
iterative routes have been developed that allow specific control over the placement of double and
triple bonds within the interior of the dendrimers. A preliminary study of the UV and photo-
luminescence (PL) properties of the resulting compounds is also described. All of the examples
prepared are blue-luminescent.
In tr od u ction
ment of new applications.5 Dendrimers with polyconju-
gated branches represent an important group within this
class of material. These compounds are interesting
because of their electrical, optical, nonlinear optical,
electroluminescent, and photophysical properties. For
example, such compounds have been used successfully
as both charge transporting6 and light-emitting materi-
als.7 On the other hand, several authors have also
demonstrated that both phenyleneethynylene8 and phe-
nylenevinylene dendritic7c arms can function as light-
harvesting antennae. Thus, conjugated dendrimers also
represent a promising new class of material for organic
LEDs.
In recent years organic molecules with high photolu-
minescence efficiencies have been the focus of intensive
research effort. Such compounds have been considered
as advanced materials for electronic and photonic ap-
plications.1 For this reason, it is important to devise
efficient methods for the synthesis of novel fluorophores
that are amenable to further chemical functionalization
or modification, which in turn can be elaborated to obtain
materials with tunable optoelectronic properties. In the
context of light-emitting polymers, the search for blue-
luminescent compounds is an ongoing challenge.2 Three
main strategies for the synthesis of blue-emitting poly-
mers have been reported: (i) a random interruption of
the conjugation along the chain, (ii) the presence of
backbone twists caused by steric interactions,3 and (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.4
Several studies have been published to date concerning
the synthesis and properties of conjugated light-emitting
(5) (a) Newkome, G. R.; Moorefield, C. N.; Vo¨gtle, F. Dendrimers
and Dendrons; Wiley-VCH: Weinheim, Germany, 2001. (b) Dendrimers
and Other Dendritic Polymers; Fre´chet, J . M. J ., Tomalia, D. A., Eds.;
Wiley: Chichester, 2001. (c) Hawker, C. J .; Wooley, K. L. Advances in
Dendritic Macromolecules; Newkome, G. R., Ed.; J ai Press Inc.:
Greenwich, CT, 1995; Vol. 2. (d) Vo¨gtle, F., Ed. Top. Curr. Chem. 1998,
197. (e) Bosman, A. W.; J anssen, H. M.; Meijer, E. W. Chem. Rev. 1999,
99, 1665. (f) Majoral, J . P.; Caminade, A. M. Chem. Rev. 1999, 99, 845.
(g) Zeng, F.; Zimmerman, S. C. Chem. Rev. 1997, 97, 1681. (h) Smith,
D. K.; Diederich, F. Chem. Eur. J . 1998, 4, 1353. (i) Vo¨gtle, F.;
Gestermann, S.; Hesse, R.; Schwierz, H.; Windisch, B. Prog. Polym.
Sci. 2000, 25, 987. (j) Grayson, S. M.; Fre´chet, J . M. J . Chem. Rev.
2001, 101, 3819.
(6) (a) Bettenhausen, J .; Strohriegl, P. Adv. Mater. 1996, 8, 507. (b)
Miller, L. L.; Duan, R. G.; Tully, D. C.; Tomalia, D. A. J . Am. Chem.
Soc. 1997, 119, 1005. (c) Shirota, Y.; Kuwabara, Y.; Inada, H.;
Wakimoto, T.; Nakada, H.; Yonemoto, Y.; Kawami, S.; Imai, K. Appl.
Phys. Lett. 1993, 65, 807. (d) Lupton, J . M.; Samuel, I. D. W.;
Beavington, R.; Burn, P. L.; Ba¨ssler, H. Adv. Mater. 2001, 13, 258.
(7) (a) Pillow, J . N. G.; Halim, M.; Lupton, J . M.; Burn, P. L.; Samuel,
I. D. W. Macromolecules 1999, 32, 5985. (b) Wang, P. W.; Liu, Y. J .;
Devadoss, C.; Bharathi, P.; Moore, J . S. Adv. Mater. 1996, 8, 237. (c)
Halim, M.; Pillow, J . N. G.; Samuel, I. D. W.; Burn, P. L. Adv. Mater.
1999, 11, 371.
Monodisperse dendritic materials have emerged as
attractive candidates for photonic applications. There has
been a substantial body of work published over the past
decade regarding the synthesis of new dendrimeric
structures and the study of such systems in the develop-
(1) (a) Seminario, J . M.; Tour, J . M. Molecular ElectronicssScience
and Technology; Aviran, A., Ratner, M., Eds.; New York Academy of
Science: New York, 1998. (b) Mu¨llen, K.; Wegner, G., Eds. Electronic
Materials: The Oligomer Approach; Wiley-VCH: New York, 1998.
(2) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem., Int.
Ed. 1998, 37, 402.
(3) Spiliopoulos, I. K.; Mikroyannidis, J . A. Macromolecules 2002,
35, 2149.
(4) Liao, L.; Pang, Y.; Ding, L.; Karasz, F. E. Macromolecules 2001,
34, 7300.
(8) (a) Xu, Z.; Moore, J . S. Acta Polym. 1994, 45, 83. (b) Devadoss,
C.; Bharathi, P.; Moore, J . S. J . Am. Chem. Soc. 1996, 118, 9635. (c)
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. (d)
Adronov, A.; Fre´chet, J . M. J . Chem. Commun. 2000, 1701.
10.1021/jo026019x CCC: $25.00 © 2003 American Chemical Society
Published on Web 12/14/2002
832
J . Org. Chem. 2003, 68, 832-838

Synthesis of Cross-Conjugated Dendritic Fluorophores
dendrimers based on either the phenylenevinylene or
phenyleneethynylene structure. However, to the best of
our knowledge there is no precedent for the synthesis of
dendrimers whose branches incorporate both of these
moieties at the same timesalthough it has recently been
demonstrated that the presence of both double and triple
bonds in a conjugated structure has a strong influence
on the resulting optoelectronic properties. For example,
poly(p-phenylenevinylene)s (PPVs) with tolane-bis-benzyl
moieties,9 conjugated oligomers and polymers with double
and triple bonds,10 and dithiafulvene-acetylene hybrid
chromophores11 have been studied as PLEDs, fluoro-
phores, and materials with electronic properties of inter-
est, respectively. In this context, and as a part of our
research program aimed at the construction of extended
and cross-conjugated π-electronic systems,12 we planned
to develop an efficient orthogonal and convergent syn-
thesis13 of new dendrimer architectures containing both
phenyleneethynylene and phenylenevinylene in an al-
ternating manner within the dendritic arms. These
materials were synthesized using two routes that allow
specific control over the placement of double and triple
bonds on the interior of the dendrimers. Our plan is based
on the combination of two coupling methods: the Sono-
gashira and Horner-Wadsworth-Emmons (HWE) reac-
tions. These reactions were used in an alternating order
to build up each successive layer. The methodology
reported here may be used as an accelerated access to a
wide range of conjugated dendrimers. We also present a
preliminary study of the UV and photoluminescence (PL)
properties of the resulting dendrons and dendrimers.
the need for the introduction of additional functional
group protection/deprotection steps.
Scheme 1 shows our two approaches to obtain homo-
geneous single functionality dendrons, which contained
either an iodo or formyl group at the focal point.
The first reaction sequence involved the HWE reaction
of two molecules of p-dodecyloxybenzaldehyde with diphos-
phonate A to form the first generation aryl iodide
(OC12H25)2G1-I. This step was followed by a Sonogashira
coupling with 3,5-bisethynylbenzaldehyde (B) to give the
corresponding second generation aldehyde (OC12H25)4G2-
CHO. A second HWE reaction between two molecules
of the second generation aldehyde and A afforded
(OC12H25)8G3-I.
The second method started with the Sonogashira
coupling of two molecules of (4-pentylphenyl)acetylene
with E to give the aldehyde dendron (C5H11)2G′1-CHO.
The higher generations were obtained by orthogonal use
of the Sonogashira and HWE coupling reactions between
the preceding generation and the appropriate building
blocks, A and B, respectively. In this manner the systems
up to and including the fourth generation dendron
(C5H11)16G′4-I were prepared.
Each generation of the dendrons is functionalized at
the central core and so further chemical manipulation
was possible. For example, (C5H11)8G′3-CHO could be
used to couple with triphosphonate D to give (C5H11)24G′4.
Dendrimers (OC12H25)6G2, (OC12H25)12G3, (C5H11)6G′2,
and (C5H11)12G′3 were also prepared in a similar way
by either Sonogashira or HWE reactions from the corre-
sponding dendrons and cores C or D (Scheme 1). The G′-
type dendrimers have their double bonds situated in the
odd layers and their triple bonds in the even layers,
whereas the G-type dendrimers have these bonds in the
opposite sense, i.e., double bonds in even layers and triple
bonds in odd layers.
In principle, both reaction sequences could be further
progressed through multiple cycles, although in practice
one would expect that higher molecules would be difficult
to prepare because of the well-documented progressive
reduction in the reactivity of the focal point in successive
generations. This phenomenon also accounts for the
decrease in yield with increasing generation of den-
drimer. Thus, unfortunately, the fourth generation den-
drimer (OC12H25)24G4 could not be obtained by reaction
of (OC12H25)8G3-I with 1,3,5-trisethynylbenzene, C. The
MALDI-TOF analysis of the crude product of this reaction
did not show any peak in the region of 9067 amu (the
value expected for a structure of this size). It is also worth
noting that HWE reactions generally gave better yields
than Sonogashira couplings.
Resu lts a n d Discu ssion
Syn th esis of Den d r on s a n d Den d r im er s. In the
convergent, orthogonal approach to the synthesis of
dendrimers bearing both phenylenevinylene and phen-
yleneethynylene linkages, two reactionssthe HWE and
Sonogashira reactionsswere employed alternately to
construct the successive layers of dendrons. Three dif-
ferent AB2-type building blocks (A, B, and E, Scheme 1)
were required as starting materials, as well as com-
mercially available 4-dodecyloxybenzaldehyde and (4-
pentylphenyl)acetylene, which both bear long-chain sub-
stituents aimed at improving the solubility of these
systems. The key to the overall strategy is that building
blocks A, B, and E possess mutually complementary
functional groups at the terminal positions while avoiding
(9) Becker, H.; Spreitzer, H.; Kreuder, W.; Kluge, E.; Schenk, H.;
Parker, I.; Cao, Y. Adv. Mater. 2000, 12, 42.
(10) (a) Hwang, G. T.; Son, H. S.; Ku, J . K.; Kim, B. H. Org. Lett.
2001, 3, 2469. (b) Mongin, O.; Porre`s, L.; Moreaux, L.; Mertz, J .;
Blanchard-Desce, M. Org. Lett. 2002, 4, 719. (c) Schenning, A. P. H.
J .; Tsipis, A. C.; Meskers, S. C. J .; Beljonne, D.; Meijer, E. W.; Bre´das,
J . L. Chem. Mater. 2002, 14, 1362. (d) Brizius, G.; Pschirer, N. G.;
Steffen, W.; Stitzer, K.; zur Loye, H.-C.; Bunz, U. H. F. J . Am. Chem.
Soc. 2000, 122, 12435. (e) Egbe, D. A. M.; Roll, C. P.; Birckner, E.;
Grummt, U.-W.; Stockmann, R.; Klemm, E. Macromolecules 2002, 35,
3825.
(11) Nielsen, M. B.; Moonen, N. N. P.; Boudon, C.; Gisselbrecht, J .-
P.; Seiler, P.; Gross, M.; Diederich, F. Chem. Commun. 2001, 1848.
(12) D´ıez-Barra, E.; Garc´ıa-Mart´ınez, J . C.; Merino, S.; del Rey, R.;
Rodr´ıguez-Lo´pez, J .; Sa´nchez-Verdu´, P.; Tejeda, J . J . Org. Chem. 2001,
66, 5664.
The peripheral groups selected in this work provided
good control of the solubility. All new compounds pre-
pared are highly soluble in THF as well as in chlorinated
solvents such as dichloromethane and chloroform, thus
allowing purification by conventional silica gel chroma-
tography. A suitable choice of starting materials could
provide a wide variety of dendritic architectures with
different peripheral moieties, although peripheral pen-
dant groups other than alkyl would be expected to afford
molecules with decreased solubility. An example of this
potential is shown by the synthesis of the second genera-
tion dendrimer 3 starting from the nucleus 1 and the
dendron 2 (Scheme 2).
(13) (a) Spindler, R.; Fre´chet, J . M. J . J . Chem. Soc., Perkin Trans.
1 1993, 913. (b) Zeng, F.; Zimmerman, S. C. J . Am. Chem. Soc. 1996,
118, 5326. (c) Freeman, A. W.; Fre´chet, J . M. J . Org. Lett. 1999, 1,
685.
J . Org. Chem, Vol. 68, No. 3, 2003 833

D´ıez-Barra et al.
SCHEME 1. Syn th esis of Den d r on s a n d Den d r im er sa
a
Reagents and conditions: (i) KButO, THF; (ii) PdCl2(PPh3)2, CuI, PPh3, Et3N/DMF, 60 °C.
Ch a r a cter iza tion . All new compounds were charac-
terized by various analytical techniques. MS and NMR
experiments proved very useful to confirm the structures
of the new compounds (see Experimental Section and
Supporting Information). The selectivity of the HWE
reaction is sufficiently high to generate all-trans isomers
within the limits of NMR detection. This stereochemistry
for the double bonds was established on the basis of the
1H NMR spectra of higher generations preclude the use
of this technique for the assessment of purity.
HRMS analyses of first-generation dendrons gave the
expected molecular ions. The MALDI-TOF technique
proved to be very useful for the identification of the
higher structures. All the spectra registered for the
higher generations showed peaks matching the calculated
molecular weights.
1
coupling constant of the vinylic protons in the H NMR
spectra (J ) 16-17 Hz).
Op tica l Sp ectr oscop ic Stu d ies. The UV-vis absorp-
tion and photoluminescence (PL) spectra of the dendrim-
ers and dendrons synthesized were recorded in CH2Cl2
at room temperature. The data obtained are summarized
in Table 1. As one would expect, the meta arrangement
through which the dendrons are linked causes the
absorption spectra to consist essentially of a simple
One drawback in the synthesis of these systems
concerns the determination of the purity, which can prove
difficult. The 1H NMR spectra of low-generation com-
pounds are well-resolved and did not show any evidence
of impurities. However, the broad lines observed in the
834 J . Org. Chem., Vol. 68, No. 3, 2003

Synthesis of Cross-Conjugated Dendritic Fluorophores
TABLE 1. UV/Vis a n d P h otolu m in escen ce (P L) Da ta
UV/Visa (CH2Cl2)
PLb (CH2Cl2)
max, nm
Stokes shifts,
cm-1
compd
λ
max, nm (ꢀ, M-1 cm-1
)
λ
Φfc
(OC12H25)4G2-CHO
(OC12H25)8G3-I
(OC12H25)6G2
322.0 (142 100)
321.0 (381 300)
320.5 (250 800)
321.5 (546 400)
311.0 (171 100)
311.5 (424 500)
311.5 (958 900)
311.5 (245 500)
311.5 (562 500)
311.0 (1 079 800)
412
409
412
407
377, 393
389, 403
388
397, 414
388, 403
400
6784
6752
7027
6583
5630, 6709
6396, 7289
6330
6965, 8000
6330, 7289
7103
<0.01
0.14
0.23
0.10
0.01
<0.01
0.06
0.12
0.13
0.07
(OC12H25
)
12G3
(C5H11)4G′2-I
(C5H11)8G′3-CHO
(C5H11)16G′4-I
(C5H11)6G′2
(C5H11
(C5H11
)
)
12G′3
24G′4
a
b
All spectra were recorded at room temperature at c = 3 × 10-6 M. All spectra were recorded at room temperature at c = 3 × 10-7
M. c Fluorescence quantum yield in dichloromethane determined relative to quinine sulfate dissolved in 1 N H2SO4.
SCHEME 2. P r ep a r a tion of Com p ou n d 3a
a
Reagents and conditions: (i) PdCl2(PPh3)2, CuI, PPh3, Et3N/
F IGURE 1. (a) Absorption and fluorescence emission spec-
tra of dendrimers (OC12H 25)6G2 (continuous line) and
(OC12H25 12G3 (dashed line) in CH2Cl2. (b) Absorption and
fluorescence emission spectra of dendrimers (C5H 11)6G′2
(continuous line), (C5H11 12G′3 (dashed line), and (C5H11 24G′4
(dotted line) in CH2Cl2. The fluorescence spectra were mea-
sured by exciting at the absorption maxima and are normal-
ized to a constant absorbance.
DMF, 60 °C.
)
superposition of the absorptions due to the different
chromophores, stilbene, and tolane moieties. These mol-
ecules are almost colorless and are absolutely transpar-
ent above 400 nm (see Figure 1). Only small changes
were observed in the onset of the absorption in the UV/
Vis spectra of the different generations. The absorptions
become much stronger, higher ꢀ, as the dendritic genera-
tion increases, a consequence of the increase in the
number of light absorbing stilbene and tolane units. The
absorption maxima, on the other hand, are very similar
since the meta linkages between the units cause little
change in conjugation as the dendrimer grows. When
spectra were registered at lower concentrations (10-7
range), changes were often observed in the chromicity of
the bands, with a higher value of ꢀ usually observed. Very
small changes in the shift were also detected. A satisfac-
tory explanation for these effects is not clear at the
moment, although, as it has been reported for the UV-
)
)
visible and fluorescence spectra of stilbenoid units,14,15
a
concentration-dependent aggregation is one possibility
that must be considered.
All of the molecules prepared in this work are fluores-
cent and emit blue light when irradiated at the absorp-
tion maxima. The fluorescence quantum yields, Φf, were
determined by using a solution of quinine sulfate in 1 N
(14) Meier, H.; Lehmann, M. Angew. Chem., Int. Ed. 1998, 37, 643.
(15) (a) Oldham, W. J ., J r.; Miao, Y.-J .; Lachicotte, R. J .; Bazan, G.
C. J . Am. Chem. Soc. 1998, 120, 419. (b) Cornil, J .; dos Santos, D. A.;
Crispin, X.; Silbey, R.; Bre´das, J . L. J . Am. Chem. Soc. 1998, 120, 1289.
(c) Catala´n, J .; Zima´nyi, L.; Saltiel, J . J . Am. Chem. Soc. 2000, 122,
2377.
J . Org. Chem, Vol. 68, No. 3, 2003 835

D´ıez-Barra et al.
benzaldehyde, B, was prepared by Sonogashira coupling of E
and trimethylsilylacetylene followed by desilylation with
NaOH/THF/H2O. See the Supporting Information for full
experimental procedures and spectroscopic data.
H2SO4 as the reference standard (Φs ) 0.546). The
intensity of the fluorescence from the higher generation
dendrimers is substantially lower than that from the
lower generations at the same molar concentration. A
comparable behavior was noted by Moore et al. in a
phenylacetylene dendrimer series,8b as well as in mono-
dendrons based on 9-phenylcarbazole.16 This phenom-
enon has been explained because the through-space
interaction between the fluorescent units becomes more
significant with increasing molecular size, providing
additional fluorescence quenching pathways. On the
other hand, (C5H11)4G′2-I shows a low fluorescence
quantum yield that can be attributed to effective quench-
ing by the iodine atom. The heavy atom effect should be
lower for (OC12H25)8G3-I and (C5H11)16G′4-I because the
iodine atoms are far away from the peripheral fluorescent
units. The fluorescence of dendrons bearing formyl groups
at the focal point is also strongly quenched. The higher
quantum yield observed for (OC12H25)6G2 when com-
pared with (C5H11)6G′2 might be a consequence of the
different peripheral functionalization, although the big-
ger dendrimers, (OC12H25)12G3 and (C5H11)12G′3, showed
similar values. A complete explanation of these results
is beyond the scope of this work and will need further
investigations. The magnitudes of the Stokes shifts
decrease as the generation number increases, a situation
that has also been observed in a phenylenevinylene
series.12
Gen er a l P r oced u r es for H or n er -Wa d sw or t h -E m -
m on s Rea ction s. Meth od A. All glassware was oven-dried
and cooled under Ar. To a stirred solution of the corresponding
phosphonate and aromatic aldehyde in anhydrous THF (30
mL per mmol of aldehyde), under argon, was added potassium
tert-butoxide in small portions (3 equiv per phosphonate
group). The deeply colored mixture was stirred at room
temperature for the period of time indicated. After hydrolysis
with water, the mixture was concentrated under vacuum and
the precipitated solid was filtered off. Meth od B. All opera-
tions were identical with those described for method A except
that, after hydrolysis with water, the mixture was extracted
with CH2Cl2 (×3). The combined organic layers were succes-
sively washed with water and brine, and then dried (MgSO4).
The solution was filtered and the solvent evaporated under
reduced pressure. The crude products were purified by column
chromatography (silica gel) and/or crystallization as indicated.
Gen er a l P r oced u r e for Son oga sh ir a Rea ction s. All
glassware was oven-dried and cooled under Ar. To a stirred
solution of the corresponding alkyne and aromatic iodide in
anhydrous DMF/Et3N (1:1, 30 mL per mmol of iodide) and
molecular sieves (4 Å) heated at 60 °C under argon was added
a catalyst mixture of 5% PdCl2(PPh3)2, 5% CuI, and 10% PPh3.
The mixture was stirred for the indicated period of time at 60
°C. After evaporation of the solvent under reduced pressure,
chloroform was added and the molecular sieves were filtered
off. The solution was washed with saturated ammonium
chloride and brine and then dried (MgSO4). The solution was
filtered and the chloroform evaporated under vacuum. The
crude products were purified by column chromatography (silica
gel) and/or crystallization as indicated. In many cases, a second
chromatographic purification was performed.
(OC12H25)2G1-I: method A; reaction time 2 h; purified by
crystallization from CHCl3/EtOH; white solid; yield 93%. 1H
NMR (CDCl3) δ 0.88 (t, 6H, J ) 6.6 Hz), 1.2-1.6 (m, 36H),
1.79 (m, 4H), 3.98 (t, 4H, J ) 6.6 Hz), 6.86 (A of ABq, 2H, J )
16.5 Hz), 6.90 (A of ABq, 4H, J ) 8.7 Hz), 7.07 (B of ABq, 2H,
J ) 16.5 Hz), 7.44 (B of ABq, 4H, J ) 8.7 Hz), 7.49 (br s, 1H),
7.69 (d, 2H, J ) 1.5 Hz). 13C NMR and DEPT (CDCl3): δ 159.2
(C), 140.0 (C), 133.4 (CH), 129.7 (CH), 129.4 (C), 127.9 (CH),
124.6 (CH), 123.7 (CH), 114.7 (CH), 95.2 (C), 68.1 (CH2), 31.9
(CH2), 29.7 (CH2), 29.6 (CH2), 29.6 (CH2), 29.6 (CH2), 29.4
(CH2), 29.3 (CH2), 29.2 (CH2), 26.0 (CH2), 22.7 (CH2), 14.1
(CH3). MS (EI) m/e 776.7 (88), 440.2 (15), 269.2 (19), 253.2 (36),
251.2 (12), 228.2 (15), 213.2 (100), 207.1 (13), 165.1 (9), 119.1
(36). HRMS, m/e calcd for C46H65IO2 776.4029, found 776.4077.
(OC12H25)4G2-CHO: reaction time 20 h; purified by column
chromatography (hexanes/CH2Cl2, 8:2) followed by washing
with hot EtOH, further purification was achieved by crystal-
lization from hexanes; white solid; yield 64%. 1H NMR (CDCl3)
δ 0.89 (t, 12H, J ) 6.9 Hz), 1.2-1.6 (m, 72H), 1.79 (m, 8H),
3.98 (t, 8H, J ) 6.6 Hz), 6.90 (A of ABq, 8H, J ) 8.7 Hz), 6.95
(A of ABq, 4H, J ) 16.2 Hz), 7.13 (B of ABq, 4H, J ) 16.2 Hz),
7.45 (B of ABq, 8H, J ) 8.4 Hz), 7.54 (s, 6H), 7.95 (t, 1H, J )
1.5 Hz), 7.98 (d, 2H, J ) 1.5 Hz), 10.02 (s, 1H). 13C NMR and
DEPT (CDCl3) δ 190.8 (CHO), 159.2 (C), 139.6 (CH), 138.4 (C),
136.7 (C), 132.0 (CH), 129.5 (CH), 127.8 (CH), 125.2 (CH),
124.9 (CH), 123.0 (C), 114.8 (CH), 91.7 (C), 87.1 (C), 68.1 (CH2),
31.9 (CH2), 29.7 (CH2), 29.6 (CH2), 29.6 (CH2), 29.6 (CH2), 29.4
(CH2), 29.4 (CH2), 29.3 (CH2), 26.1 (CH2), 22.7 (CH2), 14.1
(CH3). MALDI-TOF (C103H134O5), m/e 1452.0.
Con clu sion s
New dendrons and dendrimers with alternating phen-
yleneethynylene and phenylenevinylene units in the
dendritic arms have been effectively synthesized up to
the fourth generation using orthogonal and convergent
synthetic routes that combine Sonogashira and Horner-
Wadsworth-Emmons reactions. The choice of the ap-
propriate iterative route afforded specific control over the
placement of double and triple bonds within the interior
of the dendrimers. The meta-substitution pattern causes
all chromophores to be independent and all of the
molecules showed good transparency in the visible region.
In addition, cross-conjugation led to blue-luminescent
molecules.
Exp er im en ta l Section
General experimental conditions have been reported previ-
ously.12 NMR spectra were recorded in CDCl3 solutions.
Chemical shifts are given in ppm relative to TMS (1H, 0.0 ppm)
or CDCl3 (13C, 76.9 ppm). All commercially available com-
pounds were used without further purification. The following
chemicals were prepared according to literature procedures:
1,3,5-trisethynylbenzene (C),17 1,3,5-tris(diethoxyphosphoryl-
methyl)benzene (D),18 3,5-dibromobenzaldehyde (E),18 1,3,5-
(o-ethynylphenyl)benzene (1),19 and 3,4,5-tridodecyloxybenz-
aldehyde.20 Diphosphonate A was prepared by Arbuzov reac-
tion of 1,3-bis(bromomethyl)-5-iodobenzene21 with triethyl
phosphite following a standard methodology. 3,5-Bisethynyl-
(OC12H25)8G3-I: method B; reaction time 2 h; purified by
column chromatography (hexanes/CH2Cl2, 8:2) followed by
crystallization from CHCl3/EtOH; pale yellow solid; yield 51%.
(16) Zhu, Z.; Moore, J . S. J . Org. Chem. 2000, 65, 116.
(17) Weber, E.; Hecker, M.; Koepp, E.; Orlia, W.; Czugler, M.;
Cso¨regh, I. J . Chem. Soc., Perkin Trans. 2 1988, 1251.
(18) Deb, S. K.; Maddux, T. M.; Yu, L. J . Am. Chem. Soc. 1997, 119,
9079.
(19) Collins, S. K.; Yap, G. P. A.; Fallis, A. G. Org. Lett. 2002, 4, 11.
(20) Li, W.-R.; Kao, K.-C.; Yo, Y.-C.; Lai, C. K. Helv. Chim. Acta
1999, 82, 1400.
(21) (a) Ducheˆne, K.-H.; Vo¨gtle, F. Synthesis 1986, 659. (b) D´ıez-
Barra, E.; Garc´ıa-Mart´ınez, J . C.; Guerra, J .; Hornillos, V.; Merino,
S.; del Rey, R.; Rodr´ıguez-Curiel, R. I.; Rodr´ıguez-Lo´pez, J .; Sa´nchez-
Verdu´, P.; Tejeda, J .; Tolosa, J . Arkivoc 2002, V, 17.
836 J . Org. Chem., Vol. 68, No. 3, 2003

Synthesis of Cross-Conjugated Dendritic Fluorophores
1H NMR (CDCl3) δ 0.88 (t, 24H, J ) 6.6 Hz), 1.2-1.5 (m,
144H), 1.75 (m, 16H), 3.90 (t, 16H, J ) 6.6 Hz), 6.84 (A of ABq,
16H, J ) 8.7 Hz), 6.8-7.1 (m, 20H), 7.40 (B of ABq, 16H, J )
8.7 Hz), 7.4-7.7 (m, 21H). 13C NMR and DEPT (CDCl3) δ 159.0
(C), 139.2 (C), 138.2 (C), 137.2 (C), 134.7 (CH), 133.9 (CH),
129.5 (CH), 129.2 (CH), 128.4 (CH), 128.2 (CH), 127.8 (CH),
127.4 (C), 125.3 (CH), 124.6 (CH), 124.3 (C), 124.1 (C), 123.4
(C), 114.7 (CH), 92.5 (C), 90.5 (C), 88.4 (C), 68.0 (CH2), 31.9
(CH2), 29.7 (CH2), 29.7 (CH2), 29.6 (CH2), 29.5 (CH2), 29.4
(CH2), 29.3 (CH2), 26.1 (CH2), 22.7 (CH2), 14.1 (CH3). MALDI-
TOF (C214H273IO8), m/e 3099.7.
(OC12H25)6G2: reaction time 24 h; purified by column
chromatography (hexanes/CH2Cl2, 9:1) followed by washing
with hot hexanes; pale yellow solid; yield 54%. 1H NMR
(CDCl3) δ 0.88 (t, 18H, J ) 6.9 Hz), 1.2-1.6 (m, 108H), 1.79
(m, 12H), 3.97 (t, 12H, J ) 6.6 Hz), 6.90 (A of ABq, 12H, J )
8.7 Hz), 6.94 (A of ABq, 6H, J ) 16.2 Hz), 7.13 (B of ABq, 6H,
J ) 16.2 Hz), 7.46 (B of ABq, 12H, J ) 9.0 Hz), 7.54 (br s,
9H), 7.72 (s, 3H). 13C NMR (CDCl3) δ 159.1, 138.3, 134.2, 129.6,
129.4, 127.9, 127.9, 125.4, 124.7, 124.1, 123.4, 114.7, 90.7, 87.8,
68.1, 31.9, 29.7, 29.6, 29.6, 29.6, 29.4, 29.4, 29.3, 26.1, 22.7,
14.1. MALDI-TOF (C150H198O6), m/e 2096.6.
(C5H11)16G′4-I: method B; reaction time 12 h; purified by
column chromatography (CCl4) followed by crystallization from
CHCl3/EtOH; pale yellow solid; yield 32%. 1H NMR (CDCl3) δ
0.87 (t, 48H, J ) 6.6 Hz), 1.2-1.4 (m, 64H), 1.5-1.7 (m, 32H),
2.53 (t, 32H, J ) 7.8 Hz), 6.8-7.2 (m, including A of ABq, 52H,
J ) 8.1 Hz), 7.3-7.7 (m, including B of ABq, 77H, J ) 8.1
Hz). 13C NMR (CDCl3) δ 143.5, 143.4, 138.9, 137.3, 137.1,
137.0, 134.7, 133.5, 132.0, 131.6, 129.6, 129.0, 128.4, 127.8,
125.1, 124.1, 123.9, 123.6, 120.2, 95.3, 90.2, 89.9, 88.1, 35.9,
31.5, 30.9, 22.5, 14.1. MALDI-TOF (C326H305I), m/e 4349.9.
(C5H11)6G′2: method B; reaction time 1 h; purified by
column chromatography (hexanes/CH2Cl2, 8:2) followed by
crystallization from CHCl3/EtOH; white solid; yield 86%. 1H
NMR (CDCl3) δ 0.90 (t, 18H, J ) 6.9 Hz), 1.2-1.4 (m, 24H),
1.63 (m, 12H, J ) 7.2 Hz), 2.62 (t, 12H, J ) 7.5 Hz), 7.1-7.2
(m, including A of ABq, 18H, J ) 8.1 Hz), 7.47 (B of ABq, 12H,
J ) 8.1 Hz), 7.59 (m, 6H), 7.66 (br s, 6H). 13C NMR and DEPT
(CDCl3) δ 143.7 (C), 137.7 (C), 137.5 (C), 133.5 (CH), 131.6
(CH), 129.6 (CH), 129.2 (CH), 128.5 (CH), 127.9 (CH), 124.5
(CH), 124.2 (C), 120.1 (C), 90.3 (C), 87.9 (C), 35.9 (CH2), 31.5
(CH2), 30.9 (CH2), 22.5 (CH2), 14.0 (CH3). MS (FAB+), m/e
1406.0 (100), 1004.8 (23), 776.5 (25). HRMS, m/e calcd for
C
108H109 1405.8529, found 1405.8475.
(OC12H25)12G3: method B; reaction time 1 h; purified by
(C5H11 12G′3: reaction time 12 h; purified by column
)
column chromatography (CH2Cl2) followed by washing with
1
chromatography (CCl4) followed by crystallization from EtAcO/
EtOH; pale yellow solid; yield 38%. 1H NMR (CDCl3) δ 0.88
(t, 36H, J ) 6.6 Hz), 1.2-1.4 (m, 48H), 1.5-1.7 (m, 24H), 2.56
(t, 24H, J ) 7.2 Hz), 7.0-7.2 (m, including A of ABq, 36H, J
) 6.8 Hz), 7.42 (B of ABq, 24H, J ) 6.9 Hz), 7.50-7.72 (m,
30H). 13C NMR and DEPT (CDCl3) δ 143.5 (C), 137.5 (C), 137.2
(C), 134.3 (CH), 133.6 (CH), 131.6 (CH), 129.1 (CH), 128.7
(CH), 128.4 (CH), 128.2 (CH), 125.2 (CH), 124.2 (C), 123.9 (C),
123.7 (C), 120.1 (C), 90.3 (C), 88.3 (C), 88.0 (C), 35.9 (CH2),
31.5 (CH2), 30.9 (CH2), 22.5 (CH2), 14.0 (CH3). MALDI-TOF
(C234H222), m/e 3033.6.
hot EtOH; white solid; yield 71%. H NMR (CDCl3) δ 0.88 (t,
36H, J ) 6.6 Hz), 1.2-1.6 (m, 216H), 1.73 (m, 24H), 3.89 (t,
24H, J ) 6.6 Hz), 6.7-7.7 (m, 90H). 13C NMR and DEPT
(CDCl3) δ 158.9 (C), 138.0 (C), 137.5 (C), 137.5 (C), 129.6 (C),
129.4 (CH), 129.0 (CH), 127.8 (CH), 125.3 (CH), 124.5 (CH),
124.1 (C), 123.5 (CH), 114.6 (CH), 90.5 (C), 88.7 (C), 68.0 (CH2),
31.9 (CH2), 29.7 (CH2), 29.7 (CH2), 29.6 (CH2), 29.5 (CH2), 29.4
(CH2), 26.1 (CH2), 22.7 (CH2), 14.1 (CH3). MALDI-TOF
(C318H408O12), m/e 4422.6.
(C5H11)2G′1-CHO: reaction time 7 h; purified by column
chromatography (hexanes/CH2Cl2, 8:2); colorless oil; yield 97%.
1H NMR (CDCl3) δ 0.90 (t, 6H, J ) 6.9 Hz), 1.2-1.4 (m, 8H),
1.55-1.70 (m, 4H), 2.62 (t, 4H, J ) 7.5 Hz), 7.19 (A of ABq,
4H, J ) 8.3 Hz), 7.46 (B of ABq, 4H, J ) 8.3 Hz), 7.89 (t, 1H,
J ) 1.5 Hz), 7.94 (d, 2H, J ) 1.5 Hz), 10.00 (s, 1H). 13C NMR
and DEPT (CDCl3) δ 190.9 (CHO), 144.1 (C), 139.4 (CH), 136.6
(C), 131.6 (CH), 128.6 (CH), 125.1 (C), 119.6 (C), 91.7 (C), 86.6
(C), 35.9 (CH2), 31.4 (CH2), 30.9 (CH2), 22.5 (CH2), 14.0 (CH3).
MS (EI) m/e 446.3 (100), 389.2 (60), 343.1 (11), 332.1 (25), 166.2
(14). HRMS, m/e calcd for C33H34O 446.2610, found 446.2590.
(C5H11)4G′2-I: method B; reaction time 2 h; purified by
crystallization from CHCl3/EtOH; white solid; yield 91%. 1H
NMR (CDCl3) δ 0.90 (t, 12H, J ) 6.6 Hz), 1.20-1.45 (m, 16H),
1.63 (m, 8H, J ) 7.8 Hz), 2.62 (t, 8H, J ) 7.8 Hz), 7.06 (s, 4H),
7.18 (A of ABq, 8H, J ) 8.4 Hz), 7.47 (B of ABq, 8H, J ) 8.4
Hz), 7.56 (br s, 1H), 7.60-7.62 (m, 6H), 7.77 (d, 2H, J ) 1.5
Hz). 13C NMR and DEPT (CDCl3) δ 143.7 (C), 139.3 (C), 137.1
(C), 134.6 (CH), 133.7 (CH), 131.6 (CH), 129.2 (CH), 128.8
(CH), 128.5 (CH), 128.2 (CH), 124.4 (CH), 124.3 (C), 120.0 (C),
95.2 (C), 90.4 (C), 87.8 (C), 35.9 (CH2), 31.5 (CH2), 30.9 (CH2),
22.5 (CH2), 14.0 (CH3). MS (FAB+), m/e 1089.5 (100), 963.6
(11), 686.3 (25). HRMS, m/e calcd for C74H73I 1088.4757, found
1088.4749.
(C5H11)8G′3-CHO: reaction time 24 h; purified by column
chromatography (CCl4) followed by washing with hot EtOH;
further purification was achieved by crystallization from
hexanes; pale yellow solid; yield 41%. 1H NMR (CDCl3) δ 0.89
(t, 24H, J ) 6.6 Hz), 1.20-1.40 (m, 32H), 1.61 (m, 16H, J )
7.5 Hz), 2.60 (t, 16H, J ) 7.8 Hz), 7.1-7.2 (m, including A of
ABq, 24H, J ) 8.4 Hz), 7.46 (B of ABq, 16H, J ) 8.4 Hz), 7.56-
7.62 (m, 18H), 8.00 (t, 1H, J ) 1.5 Hz), 8.02 (d, 2H, J ) 1.5
Hz), 10.02 (s, 1H). 13C NMR and DEPT (CDCl3) δ 190.7
(CHO), 143.7 (C), 139.5 (CH), 137.7 (C), 137.3 (C), 136.7 (C),
133.6 (CH), 132.1 (CH), 131.6 (CH), 130.9 (CH), 129.2 (CH),
129.0 (CH), 128.7 (CH), 128.5 (CH), 125.5 (CH), 124.7 (C),
124.3 (C), 123.4 (C), 120.1 (C), 91.2 (C), 90.4 (C), 87.8 (C), 87.6
(C), 35.9 (CH2), 31.5 (CH2), 30.9 (CH2), 22.5 (CH2), 14.0 (CH3).
MALDI-TOF (C159H150O), m/e 2077.0.
(C5H11)24G′4: method B; reaction time 12 h; purified by
column chromatography (hexanes/CH2Cl2, 8:2) followed by
crystallization from CHCl3/EtOH; pale yellow solid; yield 65%.
1H NMR (CDCl3) δ 0.85 (t, 72H, J ) 6.6 Hz), 1.15-1.40 (m,
96H), 1.40-1.50 (m, 48H), 2.49 (br s, 48H), 6.7-7.7 (m, 192H).
13C NMR (CDCl3) δ 143.2, 137.1, 133.5, 131.6, 128.9, 128.3,
123.9, 120.3, 120.2, 90.1, 89.1, 88.2, 88.1, 35.9, 31.6, 30.8, 22.5,
14.0. MALDI-TOF (C486H456), m/e 6296.6.
Compound 2: reaction time 1 h 30 min; purified by crystal-
lization from EtAcO/EtOH; white solid; yield 97%. 1H NMR
(CDCl3) δ 0.88 (t, 18H, J ) 6.6 Hz), 1.2-1.6 (m, 108H), 1.7-
1.9 (m, 12H), 3.95-4.04 (m, 12H), 6.71 (s, 4H), 6.86 (A of ABq,
2H, J ) 16.2 Hz), 7.02 (B of ABq, 2H, J ) 16.2 Hz), 7.51 (br
s, 1H), 7.72 (d, 2H, J ) 1.2 Hz). 13C NMR and DEPT (CDCl3)
δ 153.3 (C), 139.7 (C), 138.7 (C), 133.8 (CH), 131.9 (C), 130.4
(CH), 125.8 (CH), 123.8 (CH), 105.3 (CH), 95.2 (C), 73.6 (CH2),
69.2 (CH2), 31.9 (CH2), 31.9 (CH2), 30.3 (CH2), 29.8 (CH2), 29.7
(CH2), 29.7 (CH2), 29.7 (CH2), 29.6 (CH2), 29.4 (CH2), 29.4
(CH2), 29.4 (CH2), 26.1 (CH2), 22.7 (CH2), 14.1 (CH3). HRMS,
m/e calcd for C94H162IO6 1514.1416, found 1514.1380.
Compound 3: reaction time 7 h; purified by column chro-
matography (hexanes/CH2Cl2, 7:3); yellow oil; yield 85%. 1H
NMR (CDCl3) δ 0.84-0.88 (m, 54H), 1.2-1.6 (m, 324H), 1.78
(m, 36H), 3.90-4.00 (m, 36H), 6.65 (s, 12H), 6.79 (A of ABq,
6H, J ) 16.2 Hz), 6.86 (B of ABq, 6H, J ) 16.2 Hz), 7.24 (br
s, 6H), 7.39 (br s, 3H), 7.55-7.59 (m, 6H), 7.62-7.66 (m, 6H),
8.08 (s, 3H). 13C NMR and DEPT (CDCl3) δ 153.2 (C), 143.8
(C), 140.1 (C), 138.5 (C), 137.8 (C), 132.8 (CH), 132.2 (C), 129.7
(CH), 129.6 (CH), 129.4 (CH), 128.8 (CH), 128.2 (CH), 127.3
(CH), 126.5 (CH), 124.2 (CH), 123.8 (C), 121.5(C), 105.2 (CH),
92.8 (C), 89.6 (C), 73.5 (CH2), 69.2 (CH2), 31.9 (CH2), 30.4
(CH2), 29.8 (CH2), 29.7 (CH2), 29.7 (CH2), 29.5 (CH2), 29.4
(CH2), 26.2 (CH2), 26.2 (CH2), 22.7 (CH2), 14.1 (CH3). MALDI-
TOF (C312H498O18), m/e 4536.8.
Ackn owledgm en t. Financial support from the Span-
ish DGI (BQU2002-1327) is gratefully acknowledged. J .
J . Org. Chem, Vol. 68, No. 3, 2003 837

D´ıez-Barra et al.
copies of 1H NMR and 13C NMR spectra for all compounds.
This material is available free of charge via the Internet at
http://pubs.acs.rg.
C. Garc´ıa-Mart´ınez acknowledges the receipt of a pre-
doctoral fellowship from the J unta de Comunidades de
Castilla-La Mancha.
Su p p or tin g In for m a tion Ava ila ble: Additional experi-
mental procedures, compound characterization data, and
J O026019X
838 J . Org. Chem., Vol. 68, No. 3, 2003