Synthesis of oligo(p-phenylene vinylene)-porphyrin-oligo(p-phenylene vinylene) triads as antenna molecules for energy transfer

Article abstract of DOI:10.1016/j.tet.2006.10.029

The oligo(p-phenylene vinylene)-porphyrin-oligo(p-phenylene vinylene) (P-OPVn, n=2, 4, where n is the number of phenyl rings) and the complex with Zn²⁺ based on P-OPVn were synthesized for investigating their photophysical properties via UV-vis

Full text of DOI:10.1016/j.tet.2006.10.029

Tetrahedron 63 (2007) 232–240
Synthesis of oligo(p-phenylene vinylene)-porphyrin-
oligo(p-phenylene vinylene) triads as antenna
molecules for energy transfer
Tonggang Jiu,a,b Yongjun Li,a,b Haiyang Gan,a,b Yuliang Li,a,b, Huibiao Liu,a,b Shu Wang,a,b
*
Weidong Zhou,a,b Chunru Wang,a,b Xiaofang Li,a,b Xiaofeng Liua,b and Daoben Zhua,b,
*
aBeijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Organic Solids, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100080, PR China
bGraduate School of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100080, PR China
Received 17 May 2006; revised 8 October 2006; accepted 10 October 2006
Available online 30 October 2006
Abstract—The oligo(p-phenylene vinylene)-porphyrin-oligo(p-phenylene vinylene) (P-OPVn, n¼2, 4, where n is the number of phenyl
rings) and the complex with Zn2+ based on P-OPVn were synthesized for investigating their photophysical properties via UV–vis, voltam-
metry, steady-state and time-resolved fluorescence spectra. In these molecules two OPV moieties as energy donors were linked to porphyrin
center by virtue of Wittig reaction. The detailed studies of photophysical properties indicate that OPV group can act as an antenna unit for
effective intramolecular energy transfer.
Ó 2006 Published by Elsevier Ltd.
1. Introduction
thermal, chemical, and photochemical stability.5 Incorporat-
ing porphyrin within molecular donor–acceptor systems, in
which porphyrin acts as an electron acceptor or donor linked
with appropriate donor or acceptor, is a viable route to de-
sign photovoltaic and molecular electronics.5 To the best
of our knowledge, there are limited examples of connected
systems prepared from porphyrin and oligo(p-phenylene
vinylene)s,5j,5k revealing their unique photophysical and
photochemical properties.
Studies of supramolecular systems bearing redox and photo-
electronic entities are valuable for designing light energy
harvesting systems as well as for developing redox and op-
toelectronic devices1,2. Covalent linkage of donor–acceptor
entities with one or more spacer units to control the distance
and orientation has been the popular choice2 even though
noncovalent linkage is considered to be nature’s choice of
assembling the different redox and photoactive entities in
the active centers of biological systems.3 To fully exploit
the benefits of these interesting materials, there is a need
for supramolecular systems with antenna unit. Antenna mol-
ecules, as interesting optoelectronic devices, have attracted
much attention in which one chromophore at one end of
the array can absorb photon and the other chromophore at
the opposite end of the array will emit photon subsequently.
For this purpose, a few elegantly designed donor–acceptor
type diads and triads have been synthesized and studied.2
OPV derivatives have been extensively studied on light-
emitting materials, field-effect transistors, supramolecular
assembly, and amphiphilic materials4 due to their high
absorption coefficient, strong donating ability, and good
Here we would like to report the synthesis and characteriza-
tion of a series of conjugated molecules in which OPV units
are linked to porphyrin with different lengths and describe an
ultrafast spectroscopic investigation of photoinduced energy
migration dynamics that takes place on these efficient light-
harvesting antenna supramolecules.
2. Results and discussion
2.1. Synthesis
The synthesis of a homologous series of oligo(p-phenyl-
ene vinylene)-porphyrin-oligo(p-phenylene vinylene) (P-
OPVn, n¼2, 4, where n is the number of phenyl rings) and
oligo(p-phenylene vinylene)-porphyrin-Zn-oligo(p-phenyl-
ene vinylene) (P-OPVn-Zn, n¼2, 4), are outlined in Scheme
1. The Wittig reaction, which generally gives a mixture of
Keywords: Energy transfer; Oligo(p-phenylene vinylene); Antenna; Fluo-
rescence lifetime.
* Corresponding authors. Tel.: +86 10 62588934; fax: +86 10 82616576
(Y.L.); e-mail: ylli@iccas.ac.cn
0040–4020/$ - see front matter Ó 2006 Published by Elsevier Ltd.
doi:10.1016/j.tet.2006.10.029

T. Jiu et al. / Tetrahedron 63 (2007) 232–240
233
Scheme 1. Synthesis of P-OPVn and P-OPVn-Zn, n¼2, 4.
cis- and trans-isomers, has been widely used to synthesize
conjugated, conducting oligomers and polymers. By further
exploration of this methodology, the keys for the preparation
of the antenna molecules are for synthesizing the linear, dif-
ferent lengths phenylene vinylene oligomers and conjugated
connecting with porphyrin-OPV moieties.
containing three phenyl rings bearing solubilizing dialkoxy
substituents such as hexyl, octyl, decyl, and dodecyl every
second phenylene ring. By capping more solubilizing sub-
stituents at the side chain, highly soluble OPVn containing
up to nine phenyl rings have been synthesized. To increase
the solubility of P-OPVn and P-OPVn-Zn, long alkoxyl
substituents were attached to the oligophenylene vinylene,
a common strategy in soluble polymer preparation. The me-
sityl substituents on the porphyrin ring also contribute to the
solubility.9 Due to the presence of the substituents, the triads
were soluble in common organic solvents such as toluene,
CH2Cl2, CHCl3, and THF. It also significantly reduced the
p–p aggregation of the P-OPVn and the self-quench of
porphyrin fluorescence.
Several strategies have been developed to synthesize homo-
logue series of laterally substituted OPVn in the past few
years.6 The general synthetic routes for OPVn are shown
in Scheme 2. In order to facilitate Wittig reaction of
a free-base porphyrin within two conjugated oligomer
chains, 4-(bromomethyl)benzaldehyde reacted with meso-
(mesityl)dipyrromethane with catalytic amounts of trifluoro-
acetic acid to yield the methyl halide substituted free-base
porphyrin in 25% yield.7 Large quantity of dipyrromethane
can be readily prepared according to Lindsey et al.8 P-OPVn
(n¼2 and 4) was prepared through a double Wittig reaction
of porphyrin bisphosphonium salts and the corresponding
OPV2 and OPV4 were obtained in low yields due to the
formation of several isomers. Quantitative metalation of
P-OPVn with Zn(OAc)2 afforded P-OPVn-Zn. The struc-
2.2. Electrochemistry
The electrochemical data for the triads from cyclic voltam-
metry with Bu4NPF6 (0.04 M in o-dichlorobenzene) as
supporting electrolyte in anodic oxidation and cathodic
reduction are shown in Table 1. The voltammetries of
P-OPVn (n¼2, 4) and P-OPVn-Zn (n¼2, 4) were carried
out using 10ꢁ5 mol Lꢁ1 concentration. The occurrence of a
cathodic redox process depended on the presence of OPV
segment that can decrease the LUMO energy level of por-
phyrin. Both compounds present a partially reversible oxida-
tion process around 1.08 V versus Ag wire. The CVanalysis
of P-OPV2 showed three reversible peaks in the redox part at
ꢁ1.44, ꢁ1.78, and ꢁ1.98 V versus Ag wire. On the other
hand, the potentials of oxidation wave were at 1.08 V and
1.40 V. The CV wave of P-OPV4 was similar to that of
P-OPV2. It exhibited four reversible peaks in reduction
wave and three irreversible peaks in oxidation wave. Almost
similar electrochemical behaviors were observed for
P-OPVn-Zn (Table 1). P-OPV2-Zn showed a partially
reversible oxidation process and the oxide potentials were
1
tures of new compounds were characterized by H NMR,
MALDI-TOF mass spectroscopy, and elemental analysis.
1
Their mp’s were all greater than 300 ꢀC. H NMR spectra
showed expected signals for the inner proton of free-base
porphyrin chromophores at around ꢁ2.59 ppm together
with the aromatic protons (at about 8.80 ppm) corresponding
to pyrrole of porphyrin.
Because of rigidity and planarity of the p-conjugated phen-
ylene vinylene units, unsubstituted PPV and higher homo-
logues of related OPVn are highly insoluble. To preserve
their unique characteristics (or functional properties) and
alleviate their solubility problem, we have previously syn-
thesized a series of highly light-emitting coplanar OPV3

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T. Jiu et al. / Tetrahedron 63 (2007) 232–240
Scheme 2. Oligo(p-phenylene vinylene) monomer.
Table 1. Electrochemical data for the triads
Compound
Potentiala/V
P3
ox
P2
ox
P1
ox
P1
red
P2
red
P3
red
P4
E
red
E
E
E
E
E
E
P-OPV2
P-OPV4
P-OPV2-Zn
P-OPV4-Zn
1.40
1.06
1.12
1.18
1.08
0.96
0.56
0.87
ꢁ1.44
ꢁ1.02
ꢁ1.14
ꢁ1.13
ꢁ1.78
ꢁ1.40
ꢁ1.71
ꢁ1.44
ꢁ1.98
ꢁ1.74
1.77
1.49
1.73
ꢁ2.04
ꢁ2.05
ꢁ1.74
a
Cyclic voltammograms (CV) were performed in a solution of o-dichlorobenzene using Glassy carbon electrode as working electrode, platinum wire as counter
electrode, and Ag electrode as the reference electrode at a scan rate of 20 mV/s at room temperature under the protection of nitrogen.
0.56, 1.12, and 1.49 V versus Ag wire. A comparison
between the redox potentials of the P-OPV4 and that of
the P-OPV4-Zn recorded under similar solution conditions
revealed small shifts of 10–120 mV, suggesting the existence
of ground-state interactions between the porphyrin p-ring
and OPV moiety.
2.3. Steady-state absorption spectra
As shown in Figure 1, the absorption maxima of the P-OPV2
and P-OPV4 Soret bands (422 nm and 424 nm, respectively)
were all slightly red-shifted and broader than that of the
corresponding tetraphenylporphyrin (TPP) (418 nm) due to
p-conjugation effect.10 This phenomenon can be attributed
to the presence of an intramolecular donor–acceptor frame-
work between the porphyrin unit, an electron-withdrawing
group, and OPV moiety, an electron-rich unit, which de-
Figure 1. UV–vis absorption spectra recorded in chloroform solutions of
creases the p–p* energy gap. There was no significant
P-OPVn (n¼2, 4) and P-OPVn-Zn (n¼2, 4) with concentration 2ꢂ
10ꢁ6 mol/L. The inset is the corresponding Q bands absorption of
P-OPVn and P-OPVn-Zn.
difference from 550 nm to 750 nm between P-OPV2 and
P-OPV4, in the UV–vis spectra as an extended function of

T. Jiu et al. / Tetrahedron 63 (2007) 232–240
235
the conjugated length of the OPVunits. The absorption spec-
tra of P-OPVn-Zn showed the typical pattern of regular
metal porphyrin with two Q bands in addition to the Soret
band. Compared with that of TPP, the absorption bands of
the P-OPV2-Zn (426 nm) and P-OPV4-Zn (425 nm) were
obviously red-shifted and broader. This indicated that the
p-conjugation of the Zn-porphyrin moiety was extended
into the OPV spacer, allowing electronic communication be-
tween the two conjoint units in the ground and excited states.
Also, the interaction between porphyrin ring and Zn contrib-
uted to the red shift of absorption spectra.
difference from one another. One similarity among all triads
is that the emission occurred essentially from the porphyrin
emission band even though the excitation light was absorbed
primarily by the OPV component. This observation indi-
cated efficient energy transfer from the excited oligo(p-
phenylene vinylene) (OPV*) to the ground state of porphyrin
and porphyrin-Zn. The difference is that P-OPVn-Zn
showed a red emission peak at 600 nm with a shoulder
around 650 nm when excited at 424 nm. The fluorescence
photographs of P-OPVn (n¼2, 4) and P-OPVn-Zn are
inserted in Figure 2, along with the photographs of OPVn
(n¼2, 4) and TPP. As shown in Figure 2, when excited at
365 nm corresponding to the fluorescence spectra, P-OPV2
underwent a dramatic color change from blue of OPV2 to
red, and P-OPV4 exhibited the intermediate color of red por-
phyrin and green OPV4. P-OPVn-Zn (n¼2, 4) also showed
interesting color change of nacarat and bottle green, respec-
tively.
2.4. Emission measurements
Fluorescence spectra (422 nm excitation) of P-OPVn and P-
OPVn-Zn in CHCl3 solution are shown in Figure 2. The
emission spectra of the OPV2, OPV4, and TPP are also
shown for comparison. Both of P-OPVn (n¼2, 4) exhibited
an intense red emission peak at 651 nm with a shoulder
around 716 nm when excited at 422 nm, while tetraphenyl-
porphyrin (TPP)11 showed two relatively weak emission
peaks at around 650 nm and 714 nm. Upon incorporation
of OPVn moiety into triads, compared with TPP the peaks
(651 nm) of P-OPVn were broadened and slightly red-
shifted. Energy transfer from OPV segments to porphyrin
core led to this relatively red shift of porphyrin emission
peak and the decrease of emission intensity of OPV. For
P-OPV4, the remaining emission of the shoulder (467–
493 nm) from OPV accounted for the competition between
the direct emission from OPV unit and energy transfer to
porphyrin. The fluorescence quantum yields (Ff) of P-
OPV2 and P-OPV4 were found to be 13% and 14%, respec-
tively. The fact that the fluorescence quantum yields of
P-OPVn increase compared with TPP (Ff¼0.11)12 sug-
gested that OPV group conjugated connecting with porphy-
rin core can promote the intramolecular energy transfer and
increase the probability to generate the excited state due to
increasing the absorption. The emission properties of
P-OPVn-Zn and P-OPVn showed both similarity to and
2.5. Steady-state fluorescence spectra comparison
The energy transfer behaviors of the triads have been studied
by both steady-state and time-resolved fluorescence spectra.
The changes of the fluorescence emission spectra of P-OPVn
(n¼2, 4) by changing the excitation wavelength with uni-
form concentration in CHCl3 solution are shown in Figure 3.
3Ph and OPV5 were used as reference molecules to investi-
gate the interaction between OPV moiety and porphyrin core
in the triads. The emissions of P-OPVn were monitored us-
ing excitation at several wavelengths where either the OPVn
or the porphyrin primarily absorbs. As shown in Figure 3a,
upon irradiation of the triad at 351 nm, where the 3Ph ab-
sorption outclassed that of the porphyrin, the emission spec-
trum was dominated by porphyrin core fluorescence. Only
a small amount of OPV moiety’s excited-state fluorescence
was observed. In Figure 3b, the spectra of P-OPV4 are sim-
ilar to that of P-OPV2. The fluorescence of OPV5 segment
attached to porphyrin remarkably decreased relative to
OPV5 molecule excited at 421 nm. Comparison of the
S1/S0 emission spectra of the various P-OPVn-Zn and
OPVn revealed trends similar to those described above.
Due to concentration quench effect the fluorescence proper-
ties were investigated at the concentration of 2ꢂ10ꢁ6 mol/L.
The P-OPV2-Zn emission intensity in the region 375–
550 nm was reduced significantly and red-shifted. The
remains indicated that the P-OPV2-Zn in the excited state
not only transfers energy to the middle Zn-porphyrin core
but also returns to the ground state by emission at 450–
490 nm. P-OPV4-Zn showed similar optical character by
monitoring the emission band (450–500 nm). All these re-
sults showed that, when OPVn was attached to porphyrin
(or Zn-porphyrin), the fluorescence of the OPVn moieties
was significantly quenched as compared with OPV reference
molecules and the fluorescence of the porphyrin core
increased. This fully demonstrated the antenna effect of
OPV moieties arranged on both sides of the central energy
acceptor. For the reasons of the observed decrease of
OPVn emission intensity, the occurrence of the following
processes was suggested: excited energy transfer from
OPVn to the porphyrin (or Zn-porphyrin) entity within the
triads. This process is illustrated in Figure 4. In the following
sections the time-resolved emission spectral results are dis-
cussed in order to verify the quenching pathways.
Figure 2. Normalized emission spectra recorded in chloroform solutions of
P-OPVn (n¼2, 4), P-OPVn-Zn, and TPP recorded at 5 nm slits with 422 nm
excitation and OPVn with 333 nm, 380 nm excitations, respectively. Inset:
fluorescence photographs of P-OPVn, P-OPVn-Zn, OPVn, and TPP
recorded in chloroform solutions with 365 nm excited.

236
T. Jiu et al. / Tetrahedron 63 (2007) 232–240
Figure 3. (a), (b) Steady-state fluorescence spectra of P-OPVn (n¼2, 4), TPP, 3Ph, and OPV5 excited by different wavelengths recorded in chloroform solutions
with uniform concentration (2ꢂ10ꢁ5 mol/L). (c), (d) Steady-state fluorescence spectra of P-OPVn-Zn (n¼2, 4), 3Ph, and OPV5 recorded in chloroform solu-
tions with uniform concentration (2ꢂ10ꢁ6 mol/L).
2.6. Time-resolved nanosecond fluorescence measure-
ments
resolved nanosecond fluorescence spectroscopy. The photo-
physical data are summarized in Table 2. Our experiment
was performed in chloroform solution at room temperature.
The experiments on lifetime measurements were carried out
by exciting these triads at 400 nm and monitoring the OPV
The dynamics of energy transfer behavior between the two
chromophore units was examined by employing the time-
Figure 4. Energy level diagrams for the photoinduced energy transfer processes for the P-OPVn and P-OPVn-Zn triads. The excited-state energies were
obtained from the absorption and emission spectra.

T. Jiu et al. / Tetrahedron 63 (2007) 232–240
237
Table 2. Photophysical parameters of the triads (298 K) investigated in chloroform solution (0.1 mM)
Triads and monomer
P-OPV2
Monitoring band
t1 (ns)
t2 (ns)
tav (ns)
Ff
kEnt (sꢁ1
)
OPV
Porphyrin
OPV
Porphyrin
OPV
Porphyrin
OPV
Porphyrin
OPV
OPV
0.167 (61%)
1.02 (13%)
0.254 (15%)
1.08 (16%)
1.54 (89%)
2.00 (97%)
1.13 (88%)
1.90 (93%)
1.16
0.944 (39%)
9.19 (87%)
1.34 (85%)
9.10 (84%)
4.10 (11%)
7.90 (3%)
0.47
8.12
1.17
7.81
1.82
2.18
1.39
2.13
0.13
3.3ꢂ1011
2.1ꢂ1011
2.6ꢂ1010
4.0ꢂ1010
P-OPV4
0.14
P-OPV2-Zn
P-OPV4-Zn
0.027
0.056
3.30 (12%)
5.13 (7%)
3Ph
OPV5
Zn-TPP
0.99
1.14 (91%)
3.77 (9%)
1.38
0.914
Porphyrin
2.015
0.03012
moiety’s emission band, where the emission spectrum was
dominated by OPV fluorescence. The OPVn fluorescence
time profiles of the triads, P-OPV2 and P-OPV4, could be fit-
ted satisfactorily to biexponential decay. The short lifetimes
of the components were found to be about 0.167 ns (61%)
and 0.944 ns (39%) for P-OPV2, suggesting the occurrence
of intramolecular energy transfer from the excited OPV2 to
porphyrin in the triad. For P-OPV4 triads, the lifetime was
found to be around 0.254 ns (15%) and 1.342 ns (85%),
respectively. Similarly the porphyrin fluorescence time
profiles of the triads were fitted satisfactorily to biexponen-
tial decay by monitoring the porphyrin-emission band
at 651 nm. In addition, the excited-state lifetimes of
P-OPVn-Zn (n¼2, 4) were determined and the values are
given in Table 2 along with those obtained previously for
the comparative monomer. In general, the lifetimes for the
Zn-porphyrin monomers were in the range 1.5–2.5 ns. By
monitoring the Zn-porphyrin-emission band at 600 nm, the
lifetimes of P-OPVn-Zn (2.18, 2.13 ns) were found to
be longer than that of Zn-TPP (2.0 ns). Significantly, the
porphyrin excited-state lifetimes of P-OPVn (n¼2, 4) were
8.12 and 7.81 ns, respectively, which were shorter than
that of the free-base porphyrin (13 ns), due to strong donor–
acceptor interaction between OPV units and porphyrin.
Compared with P-OPVn, the lifetimes of P-OPVn-Zn
(n¼2, 4) exhibited obvious decrease to 2.18 and 2.13 ns,
respectively, these results indicated that a strong interaction
existed between OPV unit and porphyrin (Zn) moiety.
behavior of OPV moiety can be explained in terms of the
enhanced energy transfer between the two moieties and
the reduced intermolecular quenching, which resulted in
an increase of the emission intensity of the porphyrin core.
3. Conclusions
In summary, we prepared a series of porphyrin-containing
OPVantenna units based on a concise synthetic approach in-
volving few building blocks. These molecules were func-
tionalized with OPV groups as antenna unit for showing
pure red emission. The energy transfer behavior between
the two chromophore moieties was investigated by employ-
ing steady-state and time-resolved fluorescence spectra. In-
terestingly, compared with the lifetime values (8.12 and
7.81 ns, respectively) of P-OPVn(n¼2, 4), the lifetimes of
P-OPVn-Zn (n¼2, 4) showed obvious decrease to 2.18 and
2.13 ns, respectively, These results indicated that the OPV
antenna unit played a key role for the unique properties of
energy transfer in the molecule system.
4. Experimental
4.1. Materials and instruments
Most of the chemical reagents were purchased from Acros or
Aldrich Corp. and were utilized as received unless indicated
otherwise. All solvents were purified using standard proce-
dures. Column chromatography was performed on silica
gel (size 160–200 mesh). UV–vis spectra were taken on a
Hitachi U-3010 spectrometer, and fluorescence spectra were
measured on a Hitachi F-4500 spectrofluorometer. Cyclic
voltammograms (CV) were recorded on CHI660B voltam-
metric analyzer (CH Instruments, USA). The CV was
performed in a solution of Bu4NPF6 (0.04 M) in o-dichloro-
benzene at a scan rate of 20 mV/s at room temperature
under the protection of nitrogen. Glassy carbon electrode
was used as the working electrode and Pt wire was used as
the counter electrode. An Ag electrode was used as the
reference electrode. Time-resolved fluorescence spectra
were measured using a photo-counting streak camera
(C2909, amamatstu). This machine uses a femto-second la-
ser source running at 1 KHz. The laser’s output wavelength
can be set to the desired excitation with OPA (OPA-800CF,
Spectra Physics). The fluorescence lifetimes were measured
on an Edinburgh Instruments Ltd FLS920. NMR spectra
were obtained on a Bruker Avance DPS-400 (400 MHz)
À
Á
Fref=F ꢁ 1
kEnt
¼
ð1Þ
tref
From Eq. 1,13 combined with the steady-state data, it
was possible to estimate the rate constant of the OPV/por-
phyrin energy transfer process, which turned out to be
3.3ꢂ1011 sꢁ1 for P-OPV2 and 2.6ꢂ1010 sꢁ1 for P-OPV2-
Zn. In Eq. 1, F and Fref are the OPV fluorescence quantum
yields of the multicomponent triads and of the reference
compounds, whereas tref is the singlet lifetime of the latter.
In the same way, the energy transfer rate constant for P-
OPV4 and P-OPV4-Zn can be calculated as 2.1ꢂ1011 sꢁ1
and 4.0ꢂ1010
s
ꢁ1, respectively. Altogether with the steady-
state studies, this unique interaction may mainly attribute
to the OPV antenna role as the result of energy transfer
from OPVn to porphyrin (Zn) core; also, the electron trans-
fer cannot be ruled out. We have obtained the average time
constant (tav) out of these two decay components for the
four triads shown in Table 2. This fluorescence quenching

238
T. Jiu et al. / Tetrahedron 63 (2007) 232–240
spectrometer. MALDI-TOF mass spectrometric measure-
ments were performed on a Bruker Biflex MALDI-TOF
mass spectrometer.
4.1.3. 4-(4-(4-Styrylstyryl)-2,5-bis(dodecyloxy)styryl)-
benzaldehyde OPV4 and 1,4-bis(4-styrylstyryl)-2,5-bis-
(dodecyloxy)benzene OPV5. To a solution of benzyl-
triphenylphosphonium bromide (0.86 g, 1.99 mmol) and
OPV3 (1.40 g, 1.99 mmol) in methylene chloride (50 mL)
was added lithium ethoxide solution (2.5 mL, 1.0 M in
ethanol) dropwise via a syringe at room temperature. The
solution was stirred for 20 min. The solvent was then
removed from the resulting solution under reduced pres-
sure. The mixture and iodine (500 mg) in methylene chlo-
ride (50 mL) was stirred at room temperature overnight.
The dark brown solution was then diluted with methylene
chloride and washed consecutively with aqueous Na2S2O3
solution (1.0 M, 2ꢂ75 mL) and water. After concentration
on a rotary evaporator, this solution was loaded onto a silica
gel column and eluted with a mixture of petroleum ether
and methylene chloride (1:1 v/v). This afforded 0.62 g of
OPV4 and 0.34 g of OPV5 as fluorescent solids. 1H
NMR (CDCl3): d (ppm) OPV4: 0.87 (d, 6H, J¼3.6 Hz),
1.25–1.55 (m, 36H), 1.87–1.89 (m, 4H), 4.04–4.09 (m,
4H), 7.12–7.16 (m, 5H), 7.18–7.20 (m, 2H), 7.37 (t, 2H,
J¼7.2 Hz), 7.48–7.52 (m, 7H), 7.61–7.67 (m, 3H), 7.87
(d, 2H, J¼7.6 Hz), 9.99 (s, 1H). MALDI-TOF MS: m/z:
780 [M+H]+.
4.1.1. 4-Styrylbenzaldehyde OPV2 and 1,4-distyrylbenz-
ene 3Ph. To a solution of benzyltriphenylphosphonium
bromide16 (0.22 g, 0.5 mmol) and terephthalaldehyde
(0.08 g, 0.6 mmol) in methylene chloride (25 mL) was
added lithium ethoxide solution (1.5 mL, 1.0 M in ethanol)
dropwise via a syringe at room temperature. The solution
was stirred for 30 min. The solvent was then removed
from the resulting solution under reduced pressure. A solu-
tion of this isomer mixture and iodine (20 mg) in methylene
chloride (50 mL) was stirred at room temperature overnight.
The dark brown solution was then diluted with methylene
chloride and washed consecutively with aqueous Na2S2O3
solution (1.0 M, 2ꢂ25 mL) and water. After concentration
on a rotary evaporator, this solution was loaded onto a silica
gel column and eluted with a mixture of hexane and methyl-
ene chloride (1:1 v/v). This afforded 0.07 g of OPV2 and
3Ph as fluorescent solids. The solids were dissolved in meth-
1
ylene chloride and purified by flash chromatography. H
NMR (CDCl3) d (ppm) OPV2: 7.07 (d, 1H, J¼16.0 Hz),
7.19 (d, 1H, J¼17.5 Hz), 7.28 (d, 1H, J¼7.0 Hz), 7.35 (t,
2H, J¼7.6 Hz), 7.49 (d, 2H, J¼8.0 Hz), 7.57 (d, 2H,
J¼8.0 Hz), 7.80 (d, 2H, J¼8.0 Hz), 9.93 (s, 1H). MS (EI):
208 (M).
OPV5: 0.87 (s, 6H), 1.15–1.36 (m, 36H), 1.88–1.89 (m, 4H),
4.03–4.08 (m, 4H), 7.12–7.13 (m, 6H), 7.23–7.25 (m, 6H),
7.34–7.39 (m, 4H), 7.52 (s, 8H). MALDI-TOF MS: m/z:
854 [M+H]+.
3Ph: 7.12 (s, 4H), 7.24–7.28 (m, 2H), 7.36 (t, 4H, J¼7.2 Hz),
7.51 (s, 6H), 7.53 (s, 2H). MS (EI): 282 (M).
4.1.4. P-OPV2. To a solution of porphyrin bisphosphonium
salts (45 mg, 0.03 mmol) and OPV2 (20 mg, 0.09 mmol) in
25 mL of dry CH2Cl2 was added lithium ethoxide solution
(0.25 mL, 1.0 M in ethanol) dropwise via a syringe for 2 h
at room temperature. After concentration on a rotary evapo-
rator, this solution was loaded onto a silica gel column and
eluted with a mixture of petroleum ether and methylene
chloride (1:1 v/v). This afforded the product as purple solid
(6 mg, 18%). 1H NMR (CDCl3): d (ppm) ꢁ2.59 (s, 2H), 1.84
(s, 12H), 2.65 (s, 6H), 7.18 (s, 2H), 7.25 (s, 2H), 7.28 (s, 6H),
7.39 (t, 4H, J¼7.6 Hz), 7.45 (t, 3H, J¼3.6 Hz), 7.55 (t, 6H,
J¼8.0 Hz), 7.60 (d, 3H, J¼8.0 Hz), 7.67 (d, 3H, J¼8.0 Hz),
7.90 (d, 3H, J¼8.0 Hz), 8.09–8.13 (m, 3H), 8.21–8.25 (m,
3H), 8.67–8.70 (m, 2H), 8.76–8.78 (m, 2H), 8.82 (d, 1H,
J¼4.7 Hz), 8.82 (d, 1H, J¼4.7 Hz), 8.85 (d, 1H, J¼
4.8 Hz), 8.91 (d, 1H, J¼4.7 Hz), 8.94 (d, 1H, J¼4.7 Hz).
MALDI-TOF MS: m/z: 1106 [M+H]+. Anal. Calcd for
C82H66N4: C, 88.93; H, 6.01; N, 5.06. Found: C, 88.78; H,
5.97; N, 5.12.
4.1.2. 2,5-Bis(dodecyloxy)-1,4-bis(4-formylphenylene
vinylene) benzene. OPV3. A suspension of 1,4-bis(bromo-
methyl)-2,5-bis(dodecyloxy)benzene16 (1 g, 1.59 mmol) and
triphenylphosphine (0.87 g, 3.32 mmol) in toluene was
heated at reflux for 10 h. The solvent was then removed
from the resulting solution under reduced pressure. The
resulting residue, along with terephthalaldehyde (0.425 g,
3.17 mmol), was dissolved in methylene chloride (50 mL).
To this solution was added lithium ethoxide solution
(4 mL, 1.0 M in ethanol) dropwise via a syringe at room tem-
perature. The base should be introduced at such a rate that
the transient red-purple color produced upon the addition
of base should not persist. The resulting solution was
allowed to stir for further 10 min after the completion of
base addition. Then this reaction was quenched by aqueous
HCl. The organic layer was separated, washed with water,
and dried over anhydrous sodium sulfate. The residues, after
removal of solvents, contained both E- and Z-isomers. A
solution of this isomer mixture and iodine (500 mg) in
methylene chloride (50 mL) was stirred at room temperature
overnight. The dark brown solution was then diluted with
methylene chloride and washed consecutively with aqueous
Na2S2O3 solution (1.0 M, 2ꢂ75 mL) and water. After con-
centration on a rotary evaporator, this solution was loaded
onto a silica gel column and eluted with methylene chloride.
This afforded 0.78 g of OPV3 as a yellow fluorescent solid.
Yield 70%. 1H NMR (CDCl3): d (ppm) 0.87 (t, 6H,
J¼8.0 Hz), 1.10–1.41 (m, 36H), 1.85–1.92 (m, 4H), 4.08
(t, 4H, J¼8.4 Hz), 7.15 (s, 2H), 7.18 (s, 1H), 7.23 (s, 1H),
7.60 (s, 2H), 7.67 (d, 4H, J¼8.4 Hz), 7.87 (d, 4H,
J¼9.2 Hz), 10.00 (s, 2H). MALDI-TOF MS: m/z: 706
[M+H]+.
4.1.5. P-OPV4. Similar procedure to prepare P-OPV2 was
carried out to afford P-OPV4 as purple solid. Yield: 7 mg
1
(20%). H NMR (CDCl3): d (ppm) ꢁ2.59 (s, 2H), 0.90 (t,
12H, J¼6.0 Hz), 1.25–1.28 (m, 72H), 1.54–1.58 (m, 12H),
1.85–1.91 (m, 8H), 2.63–2.66 (m, 6H), 4.08–4.12 (m, 8H),
7.14–7.18 (m, 8H), 7.22–7.24 (m, 2H), 7.27–7.29 (m, 6H),
7.35–7.39 (m, 4H), 7.44–7.45 (m, 2H), 7.50–7.54 (m,
14H), 7.60–7.68 (m, 8H), 7.89 (d, 2H, J¼7.6 Hz), 8.10 (d,
2H, J¼7.6 Hz), 8.22 (d, 2H, J¼7.9 Hz), 8.47–8.55 (m,
8H), 8.69–8.71 (m, 4H), 8.86–8.87 (m, 4H). MALDI-
TOF MS: m/z: 2253 [M+H]+. Anal. Calcd for
C162H186N4O4: C, 86.35; H, 8.32; N, 2.49. Found: C,
86.27; H, 8.26; N, 2.40.

T. Jiu et al. / Tetrahedron 63 (2007) 232–240
239
3. (a) Diesenhofer, J.; Michel, H. Angew. Chem., Int. Ed. Engl.
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4.1.6. P-OPV2-Zn. To a solution of P-OPV2 (11 mg,
0.01 mmol) in 25 mL of THF solution was added
Zn(CH3COO)2$2H2O (43 mg, 0.13 mmol) and stirred for
2 h. This solution was loaded onto a silica gel column and
eluted with methylene chloride. This gave the product as
4. (a) Ferri, A.; Polzonetti, G.; Licoccia, S.; Paolesse, R.; Favretto,
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1
purple solid. H NMR (CDCl3): d (ppm) 1.84 (s, 12H),
2.63 (s, 6H), 7.11–7.12 (m, 4H), 7.18 (s, 3H), 7.28 (s, 4H),
7.39 (t, 4H, J¼7.6 Hz), 7.45 (d, 3H, J¼4.5 Hz), 7.51–7.52
(m, 14H), 7.56 (t, 2H, J¼8.0 Hz), 7.60 (d, 2H, J¼8.0 Hz),
7.67 (d, 2H, J¼8.0 Hz), 7.90 (d, 2H, J¼7.2 Hz), 8.23 (d,
2H, J¼7.2 Hz), 8.79 (d, 2H, J¼4.5 Hz), 8.95 (d, 2H,
J¼4.5 Hz). MALDI-TOF MS: m/z: 1169 [M+H]+. Anal.
Calcd for C82H64N4Zn: C, 84.12; H, 5.51; N, 4.79. Found:
C, 83.92; H, 5.52; N, 4.86.
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4.1.7. P-OPV4-Zn. Similar procedure to prepare P-OPV2-
Zn was carried out to afford P-OPV4-Zn as purple solid.
1H NMR (CDCl3): d (ppm) 0.79–0.82 (m, 12H), 1.18–1.21
(m, 72H), 1.77 (s, 12H), 1.80–1.82 (m, 8H), 2.56 (s, 6H),
3.99 (t, 8H, J¼6.0 Hz), 7.05–7.09 (m, 8H), 7.17–7.18 (m,
8H), 7.21 (s, 4H), 7.27–7.32 (m, 4H), 7.37–7.40 (m, 4H),
7.44–7.47 (m, 14H), 7.52–7.54 (m, 4H), 7.60–7.62 (m,
4H), 7.81–7.83 (m, 4H), 8.16–8.18 (m, 4H), 8.72 (d, 4H,
J¼4.5 Hz), 8.89 (d, 4H, J¼4.5 Hz). MALDI-TOF MS:
m/z: 2315 [M+H]+. Anal. Calcd for C162H184N4O4Zn:
C, 83.99; H, 8.01; N, 2.42. Found: C, 83.86; H, 7.95; N,
2.35.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (20531060, 10474101, 20418001,
20571078, and 20421101) and the Major State Basic
Research Development Program (2006CB300402).
6. (a) Xue, C.; Luo, F.-T. J. Org. Chem. 2003, 68, 4417; (b)
Jørgensen, M.; Krebs, F. C. J. Org. Chem. 2004, 69, 6688; (c)
Dudek, S. P.; Sikes, H. D.; Chidsey, C. E. D. J. Am. Chem.
Soc. 2001, 123, 8033.
Supplementary data
7. Jiang, B.; Jones, W. E., Jr. Macromolecules 1997, 30,
5575.
Fluorescence emission decay of P-OPVn (n¼2, 4) and P-
OPVn-Zn (n¼2, 4), fluorescence excitation spectra, CV of
P-OPV2 and P-OPV4, and the synthesis route of porphyrin
bisphosphonium salts. Supplementary data associated with
this article can be found in the online version, at
doi:10.1016/j.tet.2006.10.029.
8. Laha, J. K.; Dhanalekshmi, S.; Taniguchi, M.; Ambroise, A.;
Lindsey, J. S. Org. Process Res. Dev. 2003, 7, 799.
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