Dendrimeric oligo(phenylenevinylene)-extended dithieno[3,2-b:2′, 3′-d]phospholes - synthesis, self-organization, and optical properties

Article abstract of DOI:10.1002/chem.200802482

To establish this system as a fluorescent core in π-conjugated dendrimers, a series of oligo(phenylenevinylene) (OPV)-extended dithieno[3,2-b:2′,3′-d]phospholes has been prepared by means of a Wittig-Horner protocol with a dithienophosphole dialdehyde and

Full text of DOI:10.1002/chem.200802482

FULL PAPER
DOI: 10.1002/chem.200802482
Dendrimeric Oligo(phenylenev
N
inylene)-Extended Dithieno[3,2-b:2’,3’-
Carlos Romero-Nieto,[a, b] Sonia Merino,[b] Juliꢀn Rodrꢁguez-Lꢂpez,*[b] and
Thomas Baumgartner*[a]
Dedicated to Edgar Niecke on the occasion of his 70th birthday.
Abstract: To establish this system as a
fluorescent core in p-conjugated den-
drimers, a series of oligo(phenylenevi-
nylene) (OPV)-extended dithieno[3,2-
b:2’,3’-d]phospholes has been prepared
by means of a Wittig–Horner protocol
with a dithienophosphole dialdehyde
and appropriately functionalized phos-
phonates. The “zero-generation” model
compounds have provided the general
accessibility of OPV-functionalized di-
thienophospholes, and show varying
emission colors covering the optical
spectrum from green to red. Expansion
of the synthetic strategy towards the
corresponding first-generation den-
drimers has provided materials that
show intriguing self-organization fea-
tures in case of the phenyl-terminated
dendrimer, forming large one-dimen-
sional microfibres, as well as desirable
energy-transfer processes from the den-
drons to the dithienophoshole core re-
sulting in an enhanced emission inten-
sity for the latter. The present study
has revealed that the terminal end-
groups of the OPV branches have sig-
nificant impact on the optical features
of the OPV dendrimers as a whole.
Keywords: conjugation
mers · density functional calcula-
tions organic electronics
phosphorus heterocycles
·
dendri-
AHCTUNGTRENNUNG
·
·
Introduction
passing small molecules, oligomers, and polymers, have not
only proven to be quite successful in these applications, but
have also underscored the structural flexibility of organic
electronics in general. Among the larger assemblies, p-con-
jugated, shape-persistent dendrimers have evolved as a
promising class of materials in recent years, as they provide
both new methodologies and molecular architectures that
allow the controlled synthesis of large “super-molecules”
with well-defined microstructures and electronics.[8] Den-
drimers that are based on phenylenevinylene building
blocks, with meta arrangement of stilbene units in the
branches, are particularly interesting in this context.[9] Their
specific geometry furnishes them with photophysical proper-
ties that are quite beneficial for light-emitting applica-
tions.[10] In particular, the branches can act as light-harvest-
ing antennae that behave as an ensemble of almost inde-
pendent chromophores relaying incoming photons to the
emissive, central core. As a result of this energy transfer
(ET), the core then shows enhanced emission intensity.
In the context of organic electronics, the incorporation of
phosphorus centers into p-conjugated materials has also re-
cently drawn an increasing amount of attention.[11] The ver-
satile reactivity and electronic nature of phosphorus offer
considerable opportunities for the development of new ma-
Organic p-conjugated materials are known for their benefi-
cial photophysical and electronic properties that provide in-
triguing opportunities for the field of organic electronics.
Their (semi)conducting properties show great potential for
application in organic electronic devices such as molecular-
or polymer-based light-emitting diodes, photovoltaic cells,
field-effect transistors, or sensory materials, to name but a
few.[1–7] To date, a large variety of material classes, encom-
[a] C. Romero-Nieto, Prof. Dr. T. Baumgartner
Department of Chemistry, University of Calgary
2500 University Drive NW, Calgary
AB T2N 1N4 (Canada)
Fax : (+1)403-289-9488
E-mail: Thomas.baumgartner@ucalgary.ca
[b] C. Romero-Nieto, Prof. Dr. S. Merino, Prof. Dr. J. Rodrꢀguez-Lꢁpez
Facultad de Quꢀmica
Universidad de Castilla-La Mancha
13071 Ciudad Real (Spain)
Fax : (+34)926295318
E-mail: julian.rodriguez@uclm.es
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200802482.
Chem. Eur. J. 2009, 15, 4135 – 4145
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4135

terials with intriguing properties.[11b] Trivalent phosphorus
species, in general, can react with oxidizing agents or Lewis
acids, and they can also coordinate to transition metals, of-
fering a unique variety of synthetically facile possibilities to
efficiently modify the electronic properties of the product
materials.[11b,12] Phosphole-containing materials are of partic-
ular interest, due to the pyramidal structure of the tricoordi-
nate phosphorus center, which limits an efficient orbital in-
teraction of the phosphorus lone-pair with the conjugated
system. In addition, the phosphole system exhibits a peculiar
electronic structure, with a low-lying LUMO energy level
that is particularly attractive for organic electronics.[13] Rꢃau
and co-workers were among the first to incorporate the
phosphole moiety in extended p-conjugated materials[14] and
to utilize these in phosphole-based OLED devices.[15] A few
years ago, we introduced the dithieno[3,2-b:2’,3’-d]phos-
ACHTUNGTRENyNUGN lenevinylene) (OPV) systems involves Wittig–Horner cou-
pling reactions between aldehydes and phosphonates.[9] Con-
veniently, this synthetic strategy provides for a selective for-
mation of E-configured vinylene bridges,[10] which are bene-
ficial for the spatial placement of the dendritic segments
and ultimately for the dendrimer as a whole. For this
reason, we looked into the functionalization of the dithieno-
phosphole scaffold with formyl groups in the 2- and 6-posi-
tions of 1 (Scheme 1). Formylation can be achieved in good
yields (89%) by reaction of the 2,6-dilithiated dithieno-
phosphole, obtained according to a procedure published by
us earlier using lithium diisopropyl amide (LDA),[17a] with a
large excess DMF at low temperatures.
Compound 2 has a 31P NMR resonance at d=À19.8 ppm
that is only slightly low-field shifted with respect to that of
the parent system 1 (cf. À21.5 ppm),[16a] supporting the pres-
ervation of trivalent phosphorus center during the reaction;
1H and 13C NMR data are consistent with this assumption.
The fluorescence data of 2 exhibit red-shifted values for ex-
citation (lex =391 nm) and emission (lem =457 nm) that are
consistent with an extended delocalization of the p-system
throughout the formyl groups (see Table 1). Notably, the
ACHTUNGTRENNUNG
phole system (1, Scheme 1) to this field of research.[16] Our
Scheme 1. Synthesis of the diformylated dithienophosphole 2: a) 2 LDA,
THF, À788C; b) DMF (excess), À788C.
Table 1. Fluorescence spectroscopy data for 1, 2 and 4a–d.
lex [nm][a]
lem [nm][b]
fPL
1[11a]
2
4a
4b
4c
4d
338
391
401, 487
452, 484 (sh)
386, 498
415, 521
415
457
507
516
526
631
0.78[d]
0.03[d]
0.37[c]
0.35[c]
0.35[c]
0.25[c]
building block, which conjoins two thiophene subunits with
a central phosphole moiety through annelation, allows for
the selective and efficient tuning of the (opto)electronic
properties of the materials by functionalization of phospho-
rus atom or the main scaffold.[16,17] The materials obtained
in the context of our studies, display highly advantageous,
unprecedented photophysical properties with respect to
emission wavelengths, intensity, and tunability. Since then,
the groups of Yamaguchi[18] and Matano,[19] among others,
were able to further solidify the benefits of phosphole units
within p-conjugated assemblies, reporting materials with re-
markable optoelectronic properties. In 2007, Sanji, Shiraishi,
and Tanaka reported the first phosphole-cored dendrimers
with enhanced emission intensities resulting from an energy-
transfer (ET) from the branches to the core.[20]
In this paper we now report a new functionalization of
the dithienophosphole system and its subsequent incorpora-
tion into extended, p-conjugated dendrimers with donor or
acceptor end-groups. This study was performed with the in-
tention to incorporate the dithienophosphole unit as a fluo-
rescent core in dendrimeric structures and further enhance
the powerful photophysical properties of this system
through light-harvesting dendrons with m-phenylenevi-
[a] lmax for excitation. [b] lmax for emission. [c] Relative to fluorescein (in
0.01m KOH/ethanol); Æ15%; in CH2Cl2. [d] Relative to quinine sulfate
(0.1m H2SO4 solution); Æ15%; in CH2Cl2.
quantum yield of 2 experiences a dramatic drop down to
fPL =0.03 (from fPL =0.78 in 1) indicating significant
quenching caused by the formyl groups. We were also able
to obtain suitable single crystals of 2 for an X-ray diffraction
study from a concentrated CH2Cl2/hexanes (1:1) solvent
mixture at room temperature.[21] The structure and packing
of 2 in the solid state are shown in Figure 1. The bond
lengths and angles of the diformylated compound 2 are re-
lated to those of the parent dithienophosphole 1[16a] and
show good p-delocalization, as well as a doping effect of the
phosphorus center. Some slightly different metric parame-
ters can be attributed to the electronic effect of the formyl
groups. However, it is interesting to note that the formyl
groups lie in the same plane as the p-conjugated scaffold
(torsion angles <68) with the oxygen atoms oriented to-
wards the thiophene sulfur atoms. This orientation can be
explained by intermolecular interactions in the solid state,
for which a significant degree of p-stacking can be observed
between neighboring molecules (distance 3.457 ꢄ; Figure 1
inset).
ACHTUNGTRENNUNGnylene linkages.
Results and Discussion
Evaluation of the synthetic strategy with model compounds:
One of the general synthetic strategies toward oligo(phen-
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p-Conjugated Materials
FULL PAPER
Figure 1. Molecular structure (50% probability level) and packing (inset)
À
of 2 in the solid state. Selected bond lengths [ꢄ] and angles [8]: P1 C4
À
À
À
À
1.8280(19), P1 C7 1.8270(18), P1 C11 1.8436(18), C1 O1 1.215(2), C1
À
À
À
À
C2 1.454(3), C10 O2 1.209(2), C9 C10 1.451(3), C4 C5 1.388(2), C5 C6
À
1.444(2), C6 C7 1.388(2); C4-P1-C11 98.22(8), C4-P1-C7 88.43(8), C7-
P1-C11 102.02(8); torsion O1-C1-C2-S1 5.41, O2-C10-C9-S2 1.17.
Scheme 2. Synthesis of extended phenylenevinylene dithienophospholes:
a) 2.3 R-C6H4-CH2-P(O)
ACHTUNGTRENNUNG
4b: R=OMe, 4c: R=CF3); b) 2.3 Ph2N-C6H4-CH2-P(O)ACHTUNGTRENNUNG
2.2 tBuOK, THF, À788C, 4 h (4d: R=NPh2); c) H2O2 (excess), CH2Cl2,
RT (R =H).
With the diformylated dithienophosphole 2 in hand, the
feasibility and scope of accessing extended p-systems with
vinylene bridges by means of a Wittig–Horner protocol was
tested. The model studies involved the formation of a series
of “zero”-generation dendrimers, that is, phenyl-terminated
groups that were furnished with donor or acceptor groups in
the para-position. We were interested in how—if at all—
these peripheral groups would affect the optoelectronic
properties of the respective materials. The dialdehyde build-
ing block 2 was treated with an appropriate set of p-func-
tionalized benzyl phosphonates 3a–d (R-C6H4-CH2-P(O)-
NPh2 group. However, a prolonged reaction time (4 h) was
found to drive this reaction towards the desired difunction-
alized species 4d. All extended materials 4a–d exhibit 31P
magnetic resonances around d=À20.0(Æ0.2) ppm that are
A
1
almost identical with that of the dialdehyde 2. The H and
13C NMR data are also closely related to those of 2. The
3J
(H,H) coupling constants of 16.0
(Æ0.1) Hz for the vinylic
(OEt)2; a: R=H; b: OMe; c: CF3; d: NPh2) to form the cor-
protons clearly support the selective formation of E-config-
ured double bonds.[9,10] It should be emphasized that this
synthetic protocol also preserves the trivalent phosphorus
center of the dithienophosphole core. This very beneficial
feature allows the utilization of the versatile reactivity of
this center immediately after the coupling to further fine-
tune the electronic properties in subsequent reactions, with-
out any deprotection steps.[17b] Investigation of the optoelec-
tronic properties of the extended materials 4a–d by means
of fluorescence spectroscopy showed that the p-conjugated
system can be effectively expanded by this method, generat-
ing compounds with fluorescence emission colors that
depend on the functional group at the terminal periphery,
ranging from green to red (see Table 1). Notably, compared
to dialdehyde 2, their quantum yields are significantly im-
proved (fPL =0.24–0.37), but they are still lower than in the
parent phosphole 1 (cf. fPL =0.78), likely due to additional
degrees of freedom present in the extended materials. Im-
portantly, compound 4d shows the most red-shifted emission
value of a dithienophosphole-based molecular material to
date at lem =631 nm. Compared to a diphenylaniline-extend-
ed dithienophosphole (lem =566 nm) reported by us ear-
lier,[17b] the presence of the two additional double bonds in
responding vinylene-bridged, extended materials in the pres-
ence of tBuOK as base (Scheme 2). It should be mentioned
in this context that Wittig–Horner reactions with thienyl al-
dehydes have been found to be problematic in the past; a
deformylation byproduct is often formed.[22] To avoid this
undesired side reaction, we have devised a synthetic proto-
col, using native benzyl diethylphosphonate as reagent, by
which we were able to successfully generate an extended
structure 4a without any deformylation byproducts. With
the modified protocol (see experimental section), the donor-
and acceptor-functionalized species 4b and 4c, respectively,
could also be successfully synthesized. It should be noted
that the reaction towards 4c occurs even more readily than
with the native phenyl species, likely through the effect of
the p-CF3 group that activates the benzylic position for de-
protonation during the Wittig–Horner reaction stabilizing
the resulting anionic charge.
It is worth noting that under the same conditions the reac-
tion with the electron-rich, NPh2-functionalized benzyl phos-
phonate was found to be quite sluggish. The explanation for
this behavior, again, lies in the tendency for deprotonation
of the benzylic position, which now is deactivated by the p-
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4137

T. Baumgartner, J. Rodrꢀguez-Lꢁpez et al.
4d accounts for a red-shift of an additional 65 nm. Notably,
the emission value of 4d is only 27 nm less red-shifted from
text that the reported procedure was limited to the synthesis
of phosphonates with electron-donating substituents. By
modification of the conditions with prolonged reaction
times (see Experimental Section), however, we were able to
extend this strategy for a variety of substrates including
electron-withdrawing species, making it an efficient general
procedure for the conversion of dendritic benzyl alcohols
into benzyl phosphonates.
The three benzyl phosphonates 8a–c were then treated
with the dithienophosphole dialdehyde 2 in a similar proce-
dure as used for the zero-generation model compounds, fol-
lowed by in situ oxidation of the phosphorus center with hy-
drogen peroxide to provide the dendronized materials 9a–c
in decent isolated yields (9a: 53%; 9b: 43%; 9c: 49%).
The oxidation of the phosphorus center was performed to
provide air- and moisture-stable materials, but more impor-
tantly, to also enhance the acceptor character of the di-
the value of a dithienophosphole-containing polymer (lem
=
658 nm) reported by us recently,[23] which suggests a poten-
tial application of 4d as molecular dye in organic photovol-
taic cells.
To improve the acceptor properties of the central phos-
phorus atom,[16,17] as well as to obtain a suitable photophysi-
cal reference material for the targeted dendrimers (vide
infra), we oxidized the phosphorus atom of the phenyl-
ACHTUNGTRENNUNGvinylene extended compound 4a in our typical protocol
using hydrogen peroxide in dichloromethane at room tem-
perature.[16] Complete conversion of the trivalent phospho-
rus center to the phosphole oxide can be monitored by
31P NMR spectroscopy, showing a distinct lowfield shift for
the product 5 at d=18.6 ppm that is typical for these com-
1
pounds; H and 13C NMR spectra also show consistent data.
Another indication of the successful transformation of 5 is
the fluorescence emission at lem =551 nm that is red-shifted
by about Dlem =44 nm from that of the non-oxidized start-
ing material; oxidation of the phosphorus center in dithieno-
phospholes in general affords a red-shift of 40-50 nm due to
a lowered LUMO level.[16,17]
ACHTUNGTRENtNUGN hienophosphole core for an optimized energy transfer from
the branches. 31P NMR shifts of d=19.8 (9a), 13.4 (9b), and
18.3 ppm (9c) indicate the successful oxidation of the phos-
phorus centers, as they are in the typical range for oxidized
dithienophospholes (cf.: d=17.0(Æ3) ppm), and also relate
to the model compound 5 (d=18.6 ppm).[16,17] The different
shifts observed furthermore reflect the electronic impact of
1
Synthesis and properties of dendrimeric dithienophospholes:
the terminal end-groups on the conjugated system. H NMR
Having verified the general accessibility of phenylene-
data also support the formation of the desired dendrimers
vinylene-extended dithienophospholes through the “zero-
9a–c with trans-configured stilbene units (3J
ACHTUNGTRENNUNG(H,H)=
generation” model compounds, corresponding “first-genera-
tion” materials were synthesized in a similar Wittig–Horner
protocol. Appropriate benzyl phosphonates 8a–c were ob-
tained in a modified procedure from the one reported by
Marder et al.,[22a] using benzylic alcohols 7a–c (accessible
from the corresponding carboxylic acids 6a–c[24] by reduc-
tion with LiAlH4, Scheme 3), instead of the generally ap-
plied benzyl halides.[25] It should be mentioned in this con-
16.0 Hz). All three compounds exhibit significant thermal
stability, as determined by differential scanning calorimetry
(DSC), showing decomposition only above 3208C (9a:
T
decomp =379.88C; 9b:
Tdecomp =384.38C; 9c: Tdecomp =
323.08C), with melting points just below at Tm =340.88C
(9a) and Tm =379.28C (9b); 9c decomposes without prior
melting process.
Likely due to the polar nature of their terminal end-
groups, dendrimers 9b and 9c show satisfying solubility in a
variety of organic solvents, such as THF, chloroform, di-
chloromethane, and tetrachloroethane, whereas the “unsub-
stituted” dendrimer 9a is only somewhat soluble in THF
and tetrachloroethane. This fact can be explained by the
large, shape-persistent, planar p-system in 9a that allows for
extended p-stacking interactions between neighboring mole-
cules. As a matter of fact, dendrimer 9a self-organizes in
THF into large one-dimensional (1D) microfibres of
random length up to about 250 mm, but fairly consistent
narrow width (1.6–1.9 mm), as observed by deconvolution
fluorescence microscopy (Figure 2). It should be mentioned
that most nano-structured 1D morphologies to date are
based on inorganic materials, whereas the number of organ-
ic 1D morphologies is fairly limited. The self-organized 1D
microfibres of 9a are thus rather intriguing, as they might
prove useful for application in organic devices for which
high-order is required for superior charge-transport phe-
nomena (e.g., in organic field-effect transistors), in combina-
tion with the flexibility provided by the organic nature of
the materials.[26] A similar self-organization process is not
observed for 9b or 9c, probably due to the bulky nature of
Scheme 3. Synthesis of the dendronized dithienophosphole oxides 9a–c.
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p-Conjugated Materials
FULL PAPER
Table 2. Optical spectroscopy data for 5 and 9a–c.
[b]
labs
lex
lem
fPL
[nm]
[nm]
[nm]
5[a]
463
304, 470
461, 491(sh)
307, 463(sh), 499
582
551
558
654
15.5
22.4
9a[a]
solid state
calcd[c]
9b[a]
solid state
calcd[c]
9c[a]
517 (2.26)
305, 468
309, 462, 498
582
388, 554 19.0
654
517 (2.34)
300, 379, 470
300, 386, 461(sh), 500 457, 545 18.8
556 659
solid state
calcd[c]
412 (0.83), 532 (1.11)
[a] In 1,2-tetrachloroethane. [b] Quantum yield relative to fluorescein (in
0.01m KOH/ethanol); Æ15%, in CH2Cl2; excited at 470 nm. [c] Calculat-
ed values are vertical excitation energies at the TD-DFT B3LYP/6-31G*
level, intensity in brackets.
Figure 2. Confocal fluorescence micrographs of the self-organized 1D-
fibres of 9a in THF at different magnification rates, as indicated at the
bottom left corners of the figures (mm-scale).
the terminal end-groups that limit extended p-stacking inter-
actions.
It should be noted in this context that the 1D microfibres
of 9a are only stable in the presence of THF. Evaporation
of the solvent leads to a degeneration of the fibres and re-
sults in the formation of an amorphous powder. This obser-
vation indicates that the THF is very likely part of the self-
organization process, as well as the 1D-organizational struc-
ture as a whole, which is a known feature for OPV sys-
tems.[27] Although the supramolecular order is not sustained
in the solid state, the THF-suspended fibres could neverthe-
less potentially be utilized as a template in nano/micro-fabri-
cation processes.[2c,28]
Photophysical and light-harvesting properties: In accord-
ance with the zero-generation model compounds, expansion
of the p-conjugated system in first-generation dendrimers
9a–c also affords a red-shift of the photophysical properties
of the dithienophosphole core. As expected, the three com-
pounds 9a–c show fairly similar absorption and emission
Figure 3. UV/Vis absorption (top) and fluorescence emission (bottom, ex-
citation at lex =305 nm) spectra of compounds 5 and 9a–c. Intensities are
arbitrary for clarity and do not reflect relative relationships between
compounds.
maxima at labs =303(Æ3) and 469(Æ1) nm, as well as lem
=
551(Æ7) nm (see Table 2). The fluorescence values correlate
well with those for the oxidized zero-generation reference
compound 5 (Table 1). This supports the meta arrangement
of the stilbene units having no impact on the photophysics
of the p-system of the core, essentially isolating the branch-
es as independent chromophores. It should be noted that
the optical spectrum of 9c shows an additional absorption at
labs =379 nm that also correlates with an additional emission
band at lem =545 nm (Figure 3), resulting in a whitish yellow
color observed for 9c due to the simultaneous emission of
both bands (lem =457 and 545 nm).
When compared to the spectrum of compound 5, it is evi-
dent that the well-matching, low-energy absorptions around
labs =470 nm, as well as the emission around lem =550 nm
for compounds 9a–c, arise from the extended dithieno-
phosphole core. Due to their similar wavelengths, the high-
energy absorptions around labs =305 nm, on the other hand,
likely stem from transitions within the stilbene branches, as
a corresponding transition is not present in the absorption
spectrum of 5. Importantly, the observed emission around
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4139

T. Baumgartner, J. Rodrꢀguez-Lꢁpez et al.
lem =550 nm, when exciting the compounds 9a–c at about
305 nm, supports the desired ET processes towards the core
from the branches that act as independent chromophores.
The additional transitions observed for compound 9c, could
probably be attributed to electronic processes involving
both the diphenylamino stilbene units and the dithieno-
phosphole core (vide infra).
To determine the light-harvesting efficiency of the branch-
es in compounds 9a–c, we employed the method reported
by Melinger, Peng and co-workers for oligo(phenyleneeth-
to Ebg =2.67 eV for 9a and 2.66 eV for 9b. The HOMOÀ1
and HOMOÀ2 in both compounds, on the other hand, rep-
resent the dendrons and support their nature as independent
chromophores. Although slight differences in energy and
shape exist between those orbitals, again likely due to the
electronic nature of the terminal CF3 group in 9b, both sets
of orbitals are essentially degenerate (9a: EHÀ1 =À5.559 eV,
E
HÀ2 =À5.560 eV; 9b: EHÀ1 =À6.009 eV, EHÀ2 =À6.015 eV).
Surprisingly, the orbital sequence in 9c is significantly differ-
ent. Whereas the LUMO has a similar shape to those of 9a
and 9b, a corresponding HOMO orbital is not observed.
Due to considerable p-conjugation of the amino nitrogen
atoms in the para position, and the resulting loss of symme-
try due to the somewhat twisted N-phenyl groups, the bond-
ing orbitals of 9c switch places. We have recently observed
similar behavior for amino-substituted, p-extended
benzo[1,2-b:5,4-b’]dithiophenes.[33] Consequently, the den-
drons are now represented by HOMO and HOMOÀ1,
whereas the extended p-conjugated dithienophosphole core
becomes HOMOÀ2. On the other hand, the band gap of 9c
(Ebg =2.58 eV) is not much different from that of 9a and 9b,
which is in line with the optical spectroscopy data. However,
it should be noted in this context that the energy differences
between HOMO, HOMOÀ1, and HOMOÀ2 in 9c are very
small. Again, the orbitals representing the dendrons
(HOMO, HOMOÀ1) are essentially degenerate at EH =
À4.832 eV and EHÀ1 =À4.834 eV, and the energy of the
HOMOÀ2 is EHÀ2 =À4.843 eV. Remarkably, HOMOÀ2 is
not limited to the extended dithienophosphole core; it ac-
tually expands throughout a significantly longer segment in-
volving two of the dendrons, including the terminal N-
phenyl groups. The additional band in the absorption spec-
tra of 9c can thus be attributed to the altered orbital se-
quence that also electronically links the dendrons with the
core. This is also supported by the TD-DFT calculations
that show a notable additional absorption band for 9c at
412 nm resulting from a transition from the branches to the
core, whereas the low-energy transition of 9c at 532 nm, as
well as the only significant bands for 9a and 9b at 517 nm
(for both), are located in the core. As for the emission prop-
erties of 9c (Figure 3, bottom), the electronic structure of
the dendrons appears to allow for an additional emission
coming from these chromophores (lem =457 nm), next to the
emission from the core at lem =545 nm. It is worth noting
ACHTUNGTRENNUNG
)
was obtained by comparison of the absorption and excita-
tion profiles for the compounds 9a–c, with normalized di-
thienophosphole absorptions, and relating the areas under
both curves to one another. The results confirm an energy
transfer from the light-harvesting branches to the dithieno-
phosphole core that amount to fET =55.7% for 9a, 40.5%
for 9b, and 58.8% for 9c. Although these values are not as
high as reported for the OPE dendrimers by Melinger and
Peng (fET =85-93%), they relate fairly well with the values
reported by Sanji and Tanaka for their phosphole-cored
dendrimers with “Frꢃchet-type” dendrons (cf. fET
<67%).[20] It should also be noted that compounds 9a–c
represent first-generation dendrimers; it is known, however,
that the light-harvesting efficiency of dendrimers in general
improves with increasing generations,[8f] and the present re-
sults can thus be considered a proof-of-principle study.
Organic p-conjugated molecules with trigonal geometry,
as it can be achieved by 1,3,5-substitution of a benzene ring,
have also been found to exhibit some nonlinear optical
(NLO) properties.[30] Two-photon absorption (TPA) phe-
nomena are among the most common for these materials.
Since the dendrimers 9a–c exhibit a corresponding substitu-
tion pattern at the “zero-generation” benzene ring, we have
also looked into the TPA behavior of the three compounds.
Using a pulsed Ti:sapphire laser (100 fs), we examined their
NLO behavior in dichloroethane by means of two-photon
excitation spectroscopy (TPE) upon excitation at 780 nm.[31]
However, although the three dendrimers showed some
TPE-behavior, their cross sections were found to be rather
small ranging from d=21.1–26.6 GM only.
Theoretical calculations: To gain a better understanding of
the ET processes observed for the dendrimers 9a–c, as well
to find an explanation for the occurrence of an additional
set of bands in the optical spectra of 9c, we performed DFT
calculations at the B3LYP/6-31G* level of theory, including
time-dependent measurements.[32] The relevant orbitals of
the energy-minimized structures are depicted in Figure 4. As
can be seen, the HOMO and LUMO of 9a and 9b are simi-
lar in shape, and the slight energy variations could be ex-
plained through the electronic effect of the terminal CF3
groups in 9b. Both orbitals represent the extended dithieno-
phosphole core, which is consistent with the optical spectros-
copy data obtained for both compounds (vide supra). The
same is true for the band gap of both materials amounting
that a similar emission feature is also observed for 9b (lem
=
388, 554 nm), but is much less pronounced (see Figure 3,
bottom).
Conclusions
In conclusion, we have functionalized the dithieno[3,2-
b:2’,3’-d]phosphole scaffold with formyl groups at the 2- and
6-position that allowed for an extension of the p-conjugated
system with phenylenevinylene groups through a Wittig–
Horner protocol. Studies towards the general accessibility
have provided dithienophosphole materials with significant-
4140
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Chem. Eur. J. 2009, 15, 4135 – 4145

p-Conjugated Materials
FULL PAPER
Figure 4. Important molecular orbitals and energies of the minimized structures for compounds 9a–c (B3LYP/6-31G* level of theory).
ly reduced band gaps covering the full optical spectrum, de-
pending on the electronic nature of the terminal groups
used. Extension of this protocol towards first generation
OPV dendrimers has provided a series of dendrimers with
electron-withdrawing, -neutral, as well as -donating terminal
groups. The nature of the end groups used has been found
to have significant impact on the self-organization, but more
importantly, also on the optical and energy-transfer proper-
ties of the materials. Due to the rigid, planar, extended p-
system of the phenyl-terminated dendrimer, 9a self-organiz-
es into 1D microfibres in THF, whereas the bulky end
groups in 9b and 9c do not seem to allow for extended
structures. In terms of optical properties, the three dendrim-
ers show enhanced fluorescence emission from the core
ranging between 40% to almost 60% intensity increase,
again depending on the end-groups employed. Optical spec-
troscopy and theoretical DFT-calculations have revealed
that the electronic structure of the NPh2-terminated material
9c exhibits some significantly different electronic properties
to those observed for the other two dendrimers 9a and 9b,
which can be attributed to the electron-donating character
of the end-groups in 9c. These end-groups make the den-
drons noticeably strong chromophores, resulting in the oc-
currence of an additional emission band, next to the (en-
hanced) emission band from the dithienophosphole core
that is common for all three compounds. In summary, the
present study has confirmed that the intriguing photophysi-
cal properties of the dithienophosphole system can be fur-
ther improved by embedding this unit as core in p-conjugat-
ed dendrimers and we are currently expanding this approach
to larger generation OPV dendrimers. We are also targeting
the implementation of this core in a variety of other conju-
gated and non-conjugated dendrimers in the future.
Experimental Section
General procedures: Reactions were carried out in dry glassware and
under inert atmosphere of purified argon or nitrogen using Schlenk tech-
niques. Solvents were dried using an MBraun solvent purification system.
Chem. Eur. J. 2009, 15, 4135 – 4145
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4141

T. Baumgartner, J. Rodrꢀguez-Lꢁpez et al.
Column chromatography was carried out using silica gel (70–230 mesh,
60 ꢄ) and aluminum oxide (activated, neutral, Brockmann I, standard
grade, ꢀ150 mesh, 58 ꢄ). nBuLi (2.5m in hexane), H2O2, diethyl benzyl-
phosphonate, and tBuOK were purchased from Aldrich and used as re-
ceived. LDA was prepared by treating diisopropylamine (freshly distilled)
with nBuLi in THF at À788C, and used immediately. Dithieno[3,2-b:2’,3’-
d]phosphole (1),[16a] diethyl 4-(trifluoromethyl)benzylphosphonate,[34] di-
ethyl 4-methoxybenzylphosphonate,[22a] 4-(diphenylamino)-benzylphos-
phonate,[22a] and the dendritic carboxylic acids 6a–c[24] were prepared by
literature methods. 1H NMR, 13C{1H} NMR, and 31P{1H} NMR spectra
were recorded on Bruker AC200, Bruker DMX-300, or Bruker DRX-400
spectrometers, respectively. Chemical shifts were referenced to external
85% H3PO4 (31P) or TMS (13C, 1H). Elemental analyses were performed
at the Department of Chemistry at the University of Calgary. Electron
ionization (70 eV) mass spectra were run on a Finigan SSQ 7000 spec-
trometer, and ionization electrospray in a Bruker Daltonic Esquire 3000
spectrometer. Optical spectroscopy data were recorded using a Jasco FP-
6500/6600 spectrofluorometer and UV-Vis-NIR Cary 5000 spectropho-
tometer. Thermal analyses were performed using a TA-Q200 DSC instru-
ment.
19.4 Hz, thiophene), 120.4 (s, -CH=CH-), 114.7 (s, Ar), 55.8 ppm (s,
-OCH3); 31P{1H} NMR (162 MHz, 258C, CDCl3): d=À20.0 ppm; elemen-
tal analysis calcd (%) for C32H25O2PS2: C 71.62, H 4.70; found: C 71.36,
H 4.47.
Compound 4c: Column chromatography: SiO2, CH2Cl2/pentane 1:9;
orange solid, yield: 149 mg, 81%; 1H NMR (300 MHz, 258C, CD2Cl2):
d=7.60 (s, 8H; ArH), 7.42–7.30 (m, 7H), 7.24 (s, 2H; thiophene),
6.97 ppm (d, J=15.9 Hz, 2H; 2ꢅCH=CH-); 13C{1H} NMR (75 MHz,
258C, CD2Cl2): d=149.0 (d, 1J
2J(C,P)=6.3 Hz, thiophene), 141.0 (s, Ar), 132.0 (d, 2J
Ph), 130.2 (s, ArH), 129.5 (s, ArH), 129.4 (s, Ar), 127.5 (d, 2J
19.3 Hz, o- thiophene), 127.2 (s, ArH), 126.9 (s, ArH), 126.8 (s, -CH=CH-),
126.2 (q, 3J(C,F)=3.7 Hz, ArH), 124.9 (s, -CH=CH-), 124.8 ppm (q, 1J-
(C,F)=271.8 Hz, -CF3); 31P{1H} NMR (162 MHz, 258C, CDCl3): d=
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
À19.8 ppm; elemental analysis calcd (%) for C32H19F6PS2: C 62.74, H
3.13; found: C 62.59, H 3.31.
Compound 4d: Compound 4d was obtained according to the standard
procedure (see above). However, the reaction time was 4 h instead of 1 h
at low temperature. Column chromatography: Al2O3, CH2Cl2/pentane
3:7; red solid, yield: 192 mg, 79%; 1H NMR (200 MHz, 258C, CDCl3):
d=7.34–7.23 (m, 17H), 7.13–7.01 (m, 20H), 6.84 ppm (d, J=16.2 Hz,
2H; 2ꢅCH=CH-); 13C{1H} NMR (100 MHz, 258C, CD2Cl2): d=148.2 (d,
Synthesis of 2: LDA (1.9 mL, 2m in THF) was added to a solution of di-
thieno[3,2-b:2’,3’-d]phosphole (500 mg, 1.84 mmol) in dry THF (40 mL)
at À788C. After 10 min, the volatiles were removed under reduced pres-
sure. Subsequently, THF (40 mL) and DMF (1.4 mL, 18.36 mmol) were
added at À788C. The reaction was stirred 10 min at low temperature.
After that, the crude was allowed to reach room temperature and stirred
for another 2 h. H2O was added and the mixture was neutralized with 2m
HCl. The product was extracted with dichloromethane (ꢅ3) and dried
with MgSO4. The crude was filtrated over neutral alumina, concentrated,
and precipitated with pentane to afford a yellow solid (yield: 538 mg,
1J
ACTHNUTRGNE(UNG C,P)=9.1 Hz, ipso-thiophene), 148.1 (s, Ar), 148.0 (s, Ar), 147.9 (s,
Ar), 136.7 (s, Ar), 132.9 (d, 2J
ACTHUNRTGNE(GNU C,P)=20.4 Hz, o-Ph), 131.4 (s, Ar), 130.0
(s, Ar), 129.9 (s, ArH), 129.7 (s, ArH), 129.4 (d, 3J
N
2
128.1 (s, ArH), 127.7 (s, ArH), 125.7 (d, J
N
ArH), 123.8 (s, ArH), 123.8 (s, ArH), 120.8 ppm (s, ArH); 31P{1H} NMR
(162 MHz, 258C, CDCl3): d=À20.0 ppm; elemental analysis calcd (%)
for C54H39N2PS2: C 79.97, H 4.85 N 3.45; found: C 79.85, H 4.77, N 3.59.
Compound 5: H2O2 (0.5 mL, 30% w.t. in water) was added dropwise into
a solution of compound 4a (50 mg, 0.1 mmol) in CH2Cl2 (30 mL). The re-
action was stirred for 3 h at room temperature. The crude was washed
with H2O and dried over MgSO4. Precipitation from CH2Cl2/hexanes, af-
forded an orange solid (yield: 47 mg, 96%). 1H NMR (400 MHz, 258C,
CD2Cl2): d=7.76 (dd, J=14.8 Hz, J=7.6 Hz, 2H; o-PPh), 7.57 (tq, J=
7.6 Hz, J=3.2 Hz, 1H; p-PPh), 7.48–7.44 (m, 6H; Ar), 7.36 (t, J=7.2 Hz,
4H; Ar), 7.28 (tt, J=7.2 Hz, J=1.2 Hz, 2H; Ar), 7.19 (d, J=16.4 Hz,
2H; -CH=CH-), 7.12 (d, J=2.8 Hz, 2H; thiophene), 6.96 ppm (d, J=
16 Hz, 2H; -CH=CH-); 13C{1H} NMR (100 MHz, 258C, CD2Cl2): d=
148.1 (s, thiophene), 147.9 (s, thiophene), 144.3 (s, thiophene), 139.3 (d,
1
89%). H NMR (300 MHz, 258C, CDCl3): d=9.93 (s, 2H; CHO), 7.86 (s,
2H; thiophene), 7.41–7.28 ppm (m, 5H; ArH); 13C{1H} NMR (100 MHz,
258C, CD2Cl2): d=183.1 (s, CHO), 152.1 (d, 1J
ACHTUNGTRENNUNG
phene), 149.0 (s, C-thiophene), 148.2 (d, 2J
A
2
2
136.2 (d, J
G
ACHTUNGTREN(NGNU C,P)=21.4 Hz, o-
3
Ph), 131.6 (d, JACHTUNGTRENNUNG
ACHTUNGTRENNUNG
(C,P)=8.3 Hz, m-Ph); 31P{1H} NMR (162 MHz, 258C, CDCl3): d=
À19.8 ppm; MS (EI, 70 eV): m/z (%): 328 (100) [M+], 299 (20) [M+
ÀCHO]; elemental analysis calcd (%) for C16H9O2PS2: C 58.53, H 2.76;
found: C 58.82, H 2.76.
1J
(d, J
G
ACHTUNGTRENNUNG
General Wittig–Horner reaction procedure: Solid tBuOK (75 mg,
0.67 mmol) was added in small portions to a solution of 2 (100 mg,
0.3 mmol) and the corresponding phosphonate 3a–d (0.7 mmol) in THF
(50 mL) at À788C. After 1 h, the reaction was allowed to reach room
temperature and stirred for another 4 h. H2O was added, and the crude
was neutralized with 2m HCl. The product was extracted with CH2Cl2,
and the organic layer was dried over MgSO4. After evaporation of the
solvent, the crude was purified as indicated in each case (see below):
AHCTUNGTRENNUNG
129.4 (s, Ar), 128.7 (s, ArH), 127.0 (s, ArH), 124.8 (d, JACHTUNGTRENNUNG
o-P), 121.6 (s, ArH) ppm; 31P{1H} NMR (162 MHz, 258C, CD2Cl2): d=
18.6 ppm; HRMS calcd for C30H21POS2 [M+]: 492.0771; found: 492.0754.
General procedure for the dendritic benzyl alcohols: LiAlH4 (7.12 mL,
1m in THF) was added dropwise to a solution of the corresponding den-
dritic carboxylic acid 6a–c[24] (3.24 mmol) dissolved in THF (100 mL) at
08C. After 1 h, the reaction was allowed to reach room temperature and
stirred for another hour. The reaction mixture was then quenched with
water and neutralized with 2m HCl. The organic solvent was removed
and the precipitate formed was filtrated and purified as indicated in each
case, as follows:
Compound 4a: Column chromatography: SiO2, CH2Cl2/pentane 1:9;
1
orange solid, yield: 103 mg, 72%; H NMR (300 MHz, 258C, CDCl3): d=
7.47–7.44 (m, 5H; ArH), 7.41–7.25 (m, 10H; ArH), 7.21 (d, J=16.2 Hz,
2H; 2ꢅCH=CH-), 7.18 (s, 2H; thiophene), 6.94 ppm (d, J=16.2 Hz, 2H;
2ꢅCH=CH-); 13C{1H} NMR (75 MHz, 258C, CD2Cl2): d=148.4 (d, 1J-
A
ACHTUNGTRENNUNG
Compound 7a: The collected white precipitate was spectroscopically
AHCTUNGTRENNUNG
pure and used for the next step without further purification (yield:
930 mg, 92%). H NMR (400 MHz, 258C, [D6]acetone): d=7.73 (br
1
AHCTUNGTRENNUNG
126.8 (s, Ar), 126.3 (d, 2J
ACTHNUGRTENUNG(C,P)=19.3 Hz, thiophene), 122.5 ppm (s, Ar);
s, 1H; ArH), 7.63 (d, 4H; J=7.6 Hz; ArH), 7.53 (brs, 2H; ArH), 7.39 (t,
4H; J=7.6 Hz; ArH), 7.32–7.26 (m, 6H; ArH), 4.70 ppm (brs, 2H;
-CH2-OH); 13C{1H} NMR (100 MHz, 258C, [D6]acetone): d=145.3 (s;
Ar), 139.7 (s, Ar), 139.4 (s, Ar), 130.7 (s, ArH), 130.6 (s, 4ꢅArH), 130.4
(s, ArH), 129.5 (s, ArH), 128.4 (s, 4ꢅArH), 125.8 (s, ArH), 125.3 (s,
ArH), 65.5 ppm (s, -CH2OH) ppm; MS (EI, 70 eV) m/z (%): 312 (100)
[M+].
31P{1H} NMR (162 MHz, 258C, CDCl3): d=À19.9 ppm; elemental analy-
sis calcd (%) for C30H21PS2: C 75.60, H 4.44; found: C 75.27, H 4.30.
Compound 4b: Column chromatography: SiO2, CH2Cl2/pentane 1:1;
orange solid, yield: 109 mg, 67%; 1H NMR (400 MHz, 258C, CD2Cl2):
d=7.45–7.40 (m, 6H; ArH), 7.35–7.32 (m, 3H), 7.15 (s, 2H; thiophene),
7.14 (d, J=16.0 Hz, 2 H; 2ꢅCH=CH-), 6.93–6.89 (m, 6H), 3.84 ppm (s,
6H; 2ꢅOCH3); 13C{1H} NMR (75 MHz, 258C, CD2Cl2): d=160.1 (s, Ar),
Compound 7b: The precipitate was washed with ethanol affording a
white solid (yield: 1.29 g, 89%). 1H NMR (500 MHz, 258C, CDCl3): d=
7.62 (s, 8H; ArH), 7.59 (s, 1H; ArH), 7.50 (s, 2H; ArH), 7.23 (d, 2H; J=
16.5 Hz; -CH=CH-), 7.19 (d, 2H; J=16.5 Hz; -CH=CH-), 3.20 (d, 2H;
J=5.5 Hz; -CH2OH) ppm; 13C{1H} NMR (100 MHz, 258C, CD2Cl2): d=
148.1 (d, 1J
thiophene), 140.7 (s, Ar), 132.9 (d, 2J
(C,P)=9.9 Hz, m-Ph), 129.5 (s, ipso-Ph), 129.4 (d, J
128.3 (s, p-Ph), 128.1 (s, Ar), 128.1 (s, -CH=CH-), 125.5 (d, 2J
AHCTUNGTRENNUNG
G
ACHTUNGTREN(NUNG C,P)=6.5 Hz,
AHCTUNGTRENNUNG
N
ACHTUNGTRENNUNG
4142
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ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 4135 – 4145

p-Conjugated Materials
FULL PAPER
147.4 (s, Ar), 143.0 (s, Ar), 141.4 (s, Ar), 138.0 (s, Ar), 131.3 (s, 2ꢅArH),
128.3 (s, ArH), 127.3 (s, 4ꢅArH), 126.2 (q, JACTHNUTRGNEUGN(C,F)=3.9 Hz; 4ꢅArH),
Compound 9a: After the oxidation, the reaction was quenched with
water and the THF removed. The resulting red solid was filtered and
washed with diethyl ether, acetone and ethanol (yield: 144 mg, 53%).
1H NMR (400 MHz, 258C, C2D4Cl2): d=7.80 (dd, J=13.2 Hz, J=8.0 Hz,
2H; o-Ph), 7.59–7.53 (m, 17H), 7.42 (tq, J=7.2 Hz, J=3.2 Hz; 8H),
7.34–7.30 (m, 5H; Ar), 7.26–7.14 (m, 11H; Ar), 7.00 ppm (d, J=16 Hz,
2H; -CH=CH-); 13C{1H} NMR (100 MHz, 258C, C2D4Cl2): d=147.1 (s,
thiophene), 147.0 (s, thiophene), 143.9 (s, Ar), 143.7 (s, Ar), 139.4 (s, Ar),
125.4 (s, 2ꢅArH), 125.0 (s, ArH), 65.3 ppm (s, -CH2OH); MS (EI,
70 eV): m/z (%): 448 (100) [M+].
Compound 7c: The precipitate was washed with hot ethanol affording a
yellow solid (yield: 1.80 g, 86%). 1H NMR (400 MHz, 258C,
[D6]acetone): d=7.66 (brs, 1H; ArH), 7.54 (d, 4H; J=8.5 Hz; ArH),
7.49 (brs, 2H; ArH), 7.34–7.30 (m, 7H; ArH), 7.27 (d, 2H; J=16.5 Hz;
-CH=CH-), 7.17 (d, 2H; J=16.5 Hz; -CH=CH-), 7.10–7.60 (m, 13H; Ar),
7.02 (d, 4H; J=8.5 Hz; ArH), 4.68 ppm (d, 2H; J=6.0 Hz; -CH2OH);
13C{1H} NMR (100 MHz, 258C, [D6]acetone): d=149.5 (s, Ar), 149.3 (s,
Ar), 145.2 (s, Ar), 139.9 (s; Ar), 133.7 (s, Ar), 131.3 (s, 8ꢅArH), 130.1 (s,
ArH), 129.4 (s, 4ꢅArH), 128.9 (s; ArH), 126.3 (s, 8ꢅArH), 125.4 (s, Ar),
125.2 (s, 4ꢅArH), 125.1 (s, CH, 4ꢅArH), 125.0 (s, ArH), 65.5 ppm (s,
-CH2OH); MS (EI, 70 eV): m/z (%): 646 (100) [M+].
138.3 (s, Ar), 138.1 (s, Ar), 136.9 (s; Ar), 130.7 (d, J
129.5 (s, Ar), 128.9 (d, J(C,P)=13.3 Hz; Ar), 128.7 (s, ArH), 127.9 (s,
ArH), 126.6 (s, Ar), 124.6 (d, J(C,P)=14.2 Hz; Ar), 124.3 (s, ArH), 123.7
ACHTUNGTREN(NUGN C,P)=11.7 Hz; Ar),
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
(s; ArH), 121.6 (s, Ar), 120.6 ppm (s, Ar); 31P{1H} NMR (162 MHz, 258C,
C2D2Cl4): d=19.8 ppm; MS (ESI, positive ions): m/z: 901.13 [M+H+];
HRMS calc for C62H45N4OPS2 [M+]: 900.2649; found: 900.2614.
Compound 9b: Once the crude was oxidized, the final product was puri-
fied by column chromatography (SiO2, eluent: from CHCl3/THF 10:0 to
CHCl3/THF 1:9), giving a red solid (yield: 152 mg, 43%). 1H NMR
(400 MHz, 258C, CD2Cl2): d=7.79 (dd, J=13.2 Hz, J=7.2 Hz, 2H; o-
Ph), 7.69–7.57 (m, 21H), 7.48 (dt, J=8.0 Hz, J=3.2 Hz, 2H; m-Ph), 7.30
(d, J=16.0 Hz, 2H; -CH=CH-), 7.25 (s, 8H; Ar), 7.19 (d, J=2.4 Hz, 2H;
thiophene), 7.0 ppm (d, J=16.0 Hz, 2H; -CH=CH-); 13C{1H} NMR
(100 MHz, 258C, C2D4Cl2): d=144.9 (s, Ar), 141.9 (s, Ar), 140.5 (s, Ar),
137.7 (s, Ar), 137.3 (s, Ar), 136.7 (s, Ar), 130.9 (s, Ar), 130.4 (s, Ar), 130.0
(s, Ar), 129.2 (s, Ar), 128.2 (s, Ar), 126.9 (s, ArH), 125.8 (m, Ar), 125.0 (s,
Ar), 124.7 (s, Ar), 122.9 (s, Ar), 120.0 ppm (s, Ar); 31P{1H} NMR
(162 MHz, 258C, C2D2Cl4): d=13.4 ppm; MS (ESI, positive ions): m/z:
1173.00 [M++H], 1196.02 [M++Na]; elemental analysis calcd (%) for
C66H41F12OPS2: C 67.57, H 3.52; found: C 67.96, H 3.11.
General procedure for the dendritic phosphonates: Iodine (1.1 equiv)
was added to a mixture of the corresponding benzylic alcohol 7a–c
(1 equiv) and triethyl phosphite (2 mL) at 08C. After stirring for 10 min
at low temperature, the crude reaction mixture was allowed to reach
room temperature. The reaction was stirred 2 h and heated to reflux for
a further 5 h at 1408C. The excess of triethyl phosphite was removed
under vacuum. The product was purified as indicated in each case, as fol-
lows:
Compound 8a: The solid was crystallized from ethyl acetate/hexanes af-
fording a white solid (yield: 552 mg, 72%). 1H NMR (400 MHz, 258C,
[D6]acetone): d=7.73 (brs 1H; ArH), 7.63 (d, 4H; J=7.6 Hz; ArH), 7.49
(brs, 2H; ArH), 7.39 (t, 4H; J=7.6 Hz; ArH), 7.31–7.24 (m, 6H; ArH),
4.04 (q, 4H; J=7.2 Hz; O-CH2-CH3), 3.23 (d, 2H; J=21.6 Hz; -CH2-P),
1.23 ppm (t, 6H; J=7.2 Hz; O-CH2-CH3); 13C{1H} NMR (100 MHz,
258C, CDCl3): d=139.8 (d, J=2.9 Hz; Ar), 139.3 (s, Ar), 135.3 (d, J=
9.2 Hz; Ar), 130.9 (s, ArH), 130.6 (s, 4ꢅArH), 130.1 (s, ArH), 129.5 (s,
ArH), 129.2 (s, J=6.7 Hz; ArH), 128.4 (s, 4ꢅArH), 125.0 (d, J=3.0 Hz;
ArH), 63.4 (d, J=6.8 Hz; 2ꢅOCH2CH3), 34.9 (d, J=137.3 Hz; -CH2P),
17.8 ppm (d, J=5.9 Hz; 2ꢅOCH2CH3); 31P{1H} NMR (162 MHz, 258C,
CDCl3): d=26.1 ppm; MS (EI, 70 eV): m/z (%): 432 (55) [M+].
Compound 9c: After oxidation, the final compound was purified by
column chromatography (SiO2, eluent: from CH2Cl2/acetone 9.9:0.1 to
CH2Cl2/acetone 9:1), giving a red solid (yield: 172 mg, 49%). 1H NMR
(400 MHz, 258C, CD2Cl2): d= 7.78 (dd, J=13.2 Hz, J=7.6 Hz, 2H; o-
PPh), 7.59–7.54 (m, 3H; Ar), 7.47–7.42 (m, 11H; Ar), 7.28 (t, J=8.0 Hz,
18H), 7.19–7.01 (m, 45H; Ar), 7.98 ppm (d, J=16.0 Hz, 2H; -CH=CH-);
13C{1H} NMR (100 MHz, 258C, CD2Cl2): d=159.0 (s, Ar), 148.2 (s, Ar),
148.1 (s, ArH), 144.4 (s, Ar), 139.1 (s, Ar), 137.7 (s, Ar), 133.1 (s, Ar),
Compound 8b: The crude product was washed several times with hex-
131.7 (s, Ar), 131.4 (d, JACTHNUTRGNE(NUG C,P)=11.0 Hz; Ar), 130.2 (s, Ar), 129.9 (s,
anes affording
a
light yellow solid (yield: 500 mg, 88%). 1H NMR
ArH), 129.7 (s, Ar), 129.6 (s, Ar), 128.0 (s, ArH), 126.8 (s, Ar), 126.5 (s,
Ar), 125.2 (s, Ar), 124.4 (s, Ar), 123.9 (s, ArH), 123.8 (s, ArH), 120.1 (s,
Ar), 121.7 ppm (s, Ar); 31P{1H} NMR (162 MHz, 258C, CD2Cl2): d=
18.3 ppm; MS (ESI, positive ions): m/z: 1569.23 [M++H], 1592.25 [M+
+Na], 1607.21 [M++K]; elemental analysis calcd (%) for
C110H81N4OPS2: C 84.15, H 5.70, N 3.57; found: C 84.28, H 5.55, N 3.17.
(300 MHz, 258C, CDCl3): d=7.62 (s, 8H; ArH), 7.57 (brs, 1H; ArH),
7.43 (s, 2H; ArH), 7.18 (s, 4H; -CH=CH-), 4.07 (q, 4H; J=4.9 Hz; O-
CH2-CH3), 3.20 (d, 2H; J=21.6 Hz; -CH2P), 1.28 ppm (t, 6H; J=4.9; O-
CH2-CH3); 13C{1H} NMR (100 MHz, 258C, CDCl3): d=140.5 (d, J=
1.4 Hz; Ar), 137.4 (d, J=3.0 Hz; Ar), 132.8 (d, J=3.0 Hz; Ar), 130.5 (s,
ArH), 129.5 (q, J=32.6 Hz; Ar), 127.9 (s, ArH), 127.9 (s, Ar), 126.6 (s,
4ꢅArH), 125.7 (q, J=3.7 Hz; 4ꢅArH), 123.9 (d, J=3.5 Hz; ArH), 122.8
(s, Ar), 62.3 (d, J=6.8 Hz; 2ꢅOCH2CH3), 33.7 (d, J=138.7 Hz; -CH2P),
16.4 ppm (d, J=5.8 Hz; 2ꢅOCH2CH3); 31P{1H} NMR (162 MHz, 258C,
CDCl3): d=25.0 ppm; MS (EI, 70 eV): m/z (%): 568 (100) [M+].
Acknowledgements
Compound 8c: The crude was washed several times with hexanes afford-
ing a yellow solid (yield: 706 mg, 92%). 1H NMR (300 MHz, 258C,
CDCl3): d=7.53 (brs, 1H; ArH), 7.42 (d, 4H; J=8.7 Hz; ArH), 7.30–
7.25 (m, 10H; ArH), 7.12–7.02 (m, 20H; ArH), 4.03 (q, 4H; J=4.9 Hz;
O-CH2CH3), 3.20 (d, 2H; J=21.6 Hz; -CH2P), 1.28 ppm (t, 6H; J=4.9;
O-CH2CH3); 13C{1H} NMR (100 MHz, 258C, CDCl3): d=149.4 (s, Ar),
149.3 (s; Ar), 140.0 (d, J=2.8 Hz; Ar), 135.1 (d, J=9.0 Hz; Ar), 133.5 (s,
ArH), 131.3 (s, 8ꢅArH), 130.2 (s, ArH), 129.4 (s, 4ꢅArH), 128.7 (s,
ArH), 128.6 (s, ArH), 128.6 (s, ArH), 126.3 (s, 8ꢅArH), 125.1 (d, J=
7.5 Hz; ArH), 124.7 (s; ArH), 63.3 (d, J=6.6 Hz; 2ꢅOCH2CH3), 34.9 (d,
J=137.1 Hz; -CH2P), 17.8 ppm (d, J=5.8 Hz; 2ꢅOCH2CH3); 31P{1H}
NMR (162 MHz, 258C, CDCl3): d=26.6 ppm; MS (EI, 70 eV): m/z (%):
767 (100) [M+].
Financial support by Natural Sciences and Engineering Research Council
(NSERC) of Canada, MEC of Spain (projects CTQ2006-08871 and
NAN2004-08843-C05-02), and Junta de Comunidades de Castilla-La
Mancha (project PCI08-0033) is gratefully acknowledged. C.R.N. thanks
Junta de Comunidades de Castilla-La Mancha for a scholarship. T.B.
thanks Alberta Ingenuity for a New Faculty Award. We also thank Dr. J.
Konu for the X-ray data collection, as well as Prof. D. T. Cramb and K.
Yaehne for the TPE measurements.
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p-Conjugated Materials
FULL PAPER
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Received: November 27, 2008
Published online: March 12, 2009
Chem. Eur. J. 2009, 15, 4135 – 4145
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4145