Tetrathiafulvalene porphyrins

Article abstract of DOI:10.1002/chem.200801636

Four tetrathiafulvalene (TTF)-annulated porphyrins 1-4 were synthesized and characterized. All contain a tetraphenylporphyrin (TPP) core onto which four, two, or one TTF subunits were annulated. Absorption and fluorescence spectroscopic studies together w

Full text of DOI:10.1002/chem.200801636

DOI: 10.1002/chem.200801636
Tetrathiafulvalene Porphyrins
Kent A. Nielsen,[a] Eric Levillain,[b] Vincent M. Lynch,[c] Jonathan L. Sessler,*[c] and
Jan O. Jeppesen*[a]
Abstract:
Four
tetrathiafulvalene
of 0.105 to 0.355 V and 0.200 to 0.370 V
for the first and second reduction po-
tential, respectively, compared to the
corresponding processes in the model
compound TPP, 18. The redox poten-
tials for the first oxidation of the TTF
pected for a normal TTF unit. Consid-
erable changes in the second oxidation
potential associated with the TTF sub-
units were seen for 2 (DEox1 =ꢀ0.085)
and 3 (DEox1 =ꢀ0.175). The emission
spectra of 1–4 revealed that the por-
phyrin fluorescence is almost quenched
in the neutral state of the TTF-annulat-
ed porphyrins, a finding that is consis-
tent with substantial electron transfer
taking place from the TTF subunits to
the porphyrin core. Oxidation of the
(TTF)-annulated porphyrins 1–4 were
synthesized and characterized. All con-
tain a tetraphenylporphyrin (TPP) core
onto which four, two, or one TTF sub-
ACHTUNGTRENNUNGunits were annulated. Absorption and
fluorescence spectroscopic studies to-
gether with electrochemical investiga-
tions reveal that interactions between
the porphyrin system and the annulat-
ed TTF units take place in solution.
The annulation of one or more TTF
units to the porphyrin core has a pro-
found effect on the reduction poten-
tials associated with this latter frame-
work, with positive shifts in the range
units are considerably shifted in
4
=
1
(DEox1 =+0.285 V) and
2
(DEox
ꢀ0.140 V), whereas for 1 and 3 these
potentials remain within the region ex-
Keywords:
electrochemistry
·
TTF unit(s) (TTF!TTF +) present in
C
electron transfer · porphyrinoids ·
1–4 leads to the emission intensity
being restored.
supramolecular
chemistry
·
tetrathiafulvalenes
Introduction
ly, therefore, porphyrins and metalloporphyrins have been
incorporated into a large number of electron- and energy-
transfer model systems and have also been used to create ar-
tificial light-harvesting antenna,[3] photosynthetic reaction
centers, photonic wires,[4] and redox switches.[5] Likewise, the
redox-active tetrathiafulvalene[6] (TTF) unit has been the
subject of extensive investigation because it is able to exist
Porphyrins and related tetrapyrrolic macrocycles,[1] classic
“pigments of life”, are found in a large variety of biological
systems (e.g., bacterial photosynthetic system, cyto-
ACHTUNGTRENNUNG
chrome P450, cytochrome C, hemoglobin).[2] Not surprising-
in three different stable redox states (TTF, TTF +, and
TTF2+). Indeed, TTF derivatives[7] have found widespread
use in materials chemistry. Since the first TTF charge trans-
fer (CT) complex with metallic behavior was reported,[8]
[a] Dr. K. A. Nielsen, Prof. J. O. Jeppesen
Department of Physics and Chemistry
University of Southern Denmark
Campusvej 55, 5230 Odense M (Denmark)
Fax : (+45)66-15-87-80
C
AHCTUNGTRENNUNG
a
E-mail: joj@ifk.sdu.dk
huge number of TTF radical-cation salts have been studied,
work that has been stimulated in part by the discovery that
some of the systems in question display organic supercon-
ductivity.[8] During the last few years TTF and its derivatives
have also been used to prepare a number of intriguing mo-
lecular and supramolecular systems, including chemical sen-
sors,[9] charge-separating ligands,[10] artificial muscles,[11] mo-
lecular shuttles,[12] chemical springs,[13] and synthetic
switches.[14] Although there have been some attempts to
combine TTF chemistry with porphyrin chemistry,[15] the
direct combination of these two all-important building
blocks into the same molecular system in which the TTF
[b] Dr. E. Levillain
Chimie et Ingꢀnierie Molꢀculaire dꢁAngers
(CIMA–UMR 6200)
Universitꢀ dꢁAngers–CNRS
2, bd Lavoisier, 49045 Angers Cedex (France)
[c] Dr. V. M. Lynch, Prof. J. L. Sessler
Department of Chemistry and Biochemistry
1 University Station-A5300, The University of Texas at Austin
Austin, TX 78712-0165 (USA)
Fax : (+1)512-471-7550
E-mail: sessler@mail.utexas.edu
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200800xxx.
506
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Chem. Eur. J. 2009, 15, 506 – 516

FULL PAPER
units are directly annulated to the porphyrin core has only
recently been
achieved[16–18] by the Odense and Angers
groups, and only after the development[19] of a fused mono-
pyrrolo-TTF (MPTTF) precursor. However, the chemistry
photophysical features almost impossible to deconvolute.[16]
In the case of the monoTTF-porphyrin appended with p-cy-
anophenyl groups, electrochemical and photophysical inves-
tigations revealed an absence of significant interactions be-
tween its constituent subunits in the ground state. However,
substantial electron transfer from the TTF donor to the por-
phyrin chromophore was observed to occur in the excited
state of the corresponding monoTTF-porphyrin. Thus, pre-
liminary experiments[17] reveal that the emission intensity
can be changed by oxidation of the TTF unit.
To elucidate further the effect of annulating TTF units di-
rectly onto a central porphyrin chromophore, and motivated
by a desire to understand more fully the physical properties
of the resulting systems, we decided to investigate (Figure 1)
a series of neutral TTF-annulated porphyrins containing
four, two, and one TTF units. Here, we describe the synthe-
sis of four different TTF-porphyrins, namely, 1) the
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
of these hybrid systems has yet to be extensively explored.
One of the reasons why compounds containing both por-
phyrin and TTF entities are of interest is that compounds
containing both a chromophore and a redox site incorporat-
ed into a single molecule can act as chemical sensors. In
fact, a multitude of porphyrin systems functionalized with
redox groups,[15e,20] such as ferrocene,[21] have been prepared
with such an objective in mind. In many cases, the utility of
these compounds as chemical sensors has been limited by a
lack of suitable communication between the redox group
and the porphyrin core. Recently, some of us described[16]
the synthesis of tetraTTF-porphyrins, such as 1 depicted in
Figure 1, as well as a monoTTF-porphyrin bearing p-cyano-
AHCTUNGTREGtNNNU etraTTF-porphyrin 1, 2) the bisTTF-porphyrins 2 and 3,
and 3) the monoTTF-porphyrin 4, and present the results of
1
mass spectrometric, H NMR spectroscopic, X-ray crystallo-
graphic, electrochemical, and photophysical studies of these
four systems.
Results and Discussion
Synthesis: The synthesis of the monopyrrolo-tetrathiafulva-
lene (MPTTF) derivative[22] 5, 2,5-bisbenzoylpyrrole[23] (7),
and the MPTTF derivative[19b] 9 have already been reported.
Here, we describe the synthesis of the TTF-porphyrins 1–4
(see Figure 1).
The synthesis of the tetraTTF-annulated porphyrin 1 is
outlined in Scheme 1. The monobenzoyl-MPTTF 5 was ef-
fectively[24] reduced to the corresponding alcohol 6 by using
an excess of NaBH4 and LiBr in a THF/MeOH (3:1) solvent
mixture. However, all attempts to isolate the product 6 by
Figure 1. Structural formulae (Pe=n-C5H11) of the tetraTTF-porphyrin 1,
the bisTTF-porphyrins 2 and 3, and the monoTTF-porphyrin 4.
phenyl substituents in the four meso-positions.[17] In these
systems, the TTF units were annulated directly to the ACTHNUTRGNEUNGC-
bonds of the porphyrin core, giving an annulene-like p-elec-
tron system in which the electronic character was “extend-
ed” by direct conjugation with the TTF units. However, it
turned out that the system wherein the central porphyrin
ring was annulated with four TTF units (compound 1) was
isolated as a mixture of the neutral porphyrin 1 and its cor-
+
C
responding radical-cation porphyrin 1 in a ratio of approx-
imately 4:1; this rendered the 1H NMR spectroscopic and
Scheme 1. Synthesis of the tetraTTF-porphyrin 1 (Pe=n-C5H11).
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507

J. O. Jeppesen, J. L. Sessler et al.
Scheme 2. Synthesis of the bisTTF-porphyrin 2 (Pe=n-C5H11).
column-chromatographic purification failed. Instead, the al-
cohol 6 was subjected to a standard non-acidic workup[25]
and subsequently cyclized into the corresponding porphyri-
nogen (structure not shown) by addition (Scheme 1) of a
catalytic amount of trifluoroacetic acid (TFA) to a CH2Cl2
solution of the alcohol 6. Matrix-assisted laser desorption
time-of-flight (MALDI-TOF) mass spectrometry and TLC
analysis were used to monitor qualitatively the crude, un-
purified, reaction mixture for the disappearance of the start-
ing material 6 and the formation of the presumed porphyri-
nogen product. After 30 min this conversion was deemed
complete, and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone
(DDQ) was added, followed by an immediate addition of
triethylamine (Et3N). This afforded the neutral tetraTTF-
porphyrin 1 as a dark-purple solid in 9% yield after
column-chromatographic purification.[26]
The synthesis of the bisTTF-annulated porphyrin 2 is il-
lustrated in Scheme 2. The two benzoyl groups in 7[23] were
reduced (Scheme 2) by using an excess of NaBH4 and LiBr
in an anhydrous THF/MeOH (3:1) solvent mixture to give
the corresponding diol 8 in quantitative yield. The diol 8
was rather unstable as inferred from TLC analysis. It was,
therefore, used without any purification other than being
subjected to a non-acidic aqueous workup. The bisTTF-an-
nulated porphyrin 2 was obtained as a purple solid in 6%
yield by stirring a mixture of the MPTTF derivative 9, the
diol 8, and a catalytic amount of Et2O·BF3 in anhydrous
CH2Cl2 for 1 h followed by first oxidation with three equiva-
lents of DDQ for 5 s and then treatment with excess Et3N.
The bisTTF-annulated porphyrin 3 was synthesized as
outlined in Scheme 3. Initially, starting from the MPTTF de-
rivative 9,[19b] 2-phenyl-1,3-benzodithiol-2-ylium tetrafluoro-
borate (10), and pyridine (1:3:3), the 2,5-bisbenzoditholyl
functionalized MPTTF 11 was obtained as a yellow solid in
91% yield. Removal of the protecting groups in 11 using an
Scheme 3. Synthesis of the bisTTF-porphyrin 3 (Pe=n-C5H11).
MPTTF 12 in 76% yield. Subsequently, the two carbonyl
groups in 12 were reduced in near-quantitative yield by
using an excess of NaBH4 and LiBr in a solvent mixture
consisting of THF/MeOH (3:1). This afforded the diol 13 as
an unstable solid after a non-acidic aqueous workup.[27]
Treating diol 13 with ten equivalents of 3,4-diethylpyrrole
(14)[28] and a catalytic amount of TFA in anhydrous CH2Cl2
for 1 h, followed by neutralization with Et3N, gave the func-
tionalized MPTTF 15 as a yellow oil in 65% yield after
column chromatography. This compound was used without
any further purification. Finally, the bisTTF-annulated por-
phyrin 3 was synthesized using a 3+1 approach[29] that in-
volved stirring a catalytic amount of TFA, the functionalized
MPTTF 13, and the functionalized MPTTF 15 for 1 h in
CH2Cl2 followed by oxidation with DDQ for 5 s and subse-
quent neutralization with Et3N. This produced the bisTTF-
porphyrin 3 as a purple solid in 13% yield.
The monoTTF-annulated porphyrin 4 was also synthe-
sized using the 3+1 approach[29] as shown in Scheme 4. Stir-
ring the diol 8 dissolved in neat pyrrole (16) with a catalytic
amount of Et2O·BF3 for 1 h, followed by neutralization with
Et3N, gave the tripyrrane[30] 17 as a colorless solid. Cycliza-
tion was accomplished by stirring the functionalized MPTTF
13 and the tripyrrane 17 together with a catalytic amount of
TFA for 30 min in CH2Cl2 followed by oxidation with DDQ
excess of mercury(II) acetate (Hg
ACHTUNGRTEN(NGNU OAc)2) at 1008C in
Me2SO gave the corresponding 2,5-bisbenzoyl functionalized
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Porphyrins
FULL PAPER
peaks were assigned to the two inner-ring NH protons. The
remaining aromatic and aliphatic protons in the TTF-por-
phyrins 1–4 all appeared at the expected chemical-shift
values (see Experimental Section).
X-ray diffraction analysis: Diffraction-grade single crys-
tals[33] of the bisTTF-porphyrin 3 were grown by slow diffu-
sion of a MeOH layer into a CH2Cl2 solution containing 3.
The resulting structure (Figure 2a) revealed a non-planar
solid-state structure (Figure 2b). The distortion from planar-
ity is ascribed to the high degree of peripheral substitution
Scheme 4. Synthesis of the monoTTF-porphyrin 4 (Pe=n-C5H11).
for 5 s and subsequent neutralization with Et3N; this afford-
ed the monoTTF-porphyrin 4 as a purple solid in 9% yield.
Mass-spectrometric
characterization:
High-resolution
matrix-assisted laser-desorption/ionization mass-spectromet-
ric (HiResMALDI-MS) analysis of 1, 2, and 4 produced
peaks with exact masses of m/z 2134.1950, 1374.2235, and
994.2393, respectively, corresponding to the expected molec-
+
ular ions M (calcd masses M + =2134.2022, 1374.2243, and
994.2354, respectively). These were the dominant peaks in
all cases. The HiResMALDI-MS spectrum of 3 gave rise to
a major peak at m/z 1487.4453, corresponding to MH+
(calcd mass MH+ =1487.3579).
C
C
1H NMR spectroscopic studies: The 1H NMR spectra
(300 MHz) of the TTF-porphyrins 1–4 were recorded in
CDCl3 at 298 K and exhibited in all four cases sharp lines.
This finding provides important support for the conclusion
that, in contrast to what proved true previously in the case
of 1,[16] under the present reaction conditions products 1–4
were obtained as the neutral porphyrins (as indicated in
Schemes 1–4) free of any radical species.[31,32]
Figure 2. X-ray crystal structure of the bisTTF-porphyrin 3; a) top view
showing the three co-crystallized CH2Cl2 molecules found per unit of 3,
b) space-filling representation (side view) showing the saddle conforma-
tion, and c) partial packing diagram.
1
The H NMR spectrum of the monoTTF-porphyrin 4 was
characterized by a 2H singlet at d=8.74 ppm and a 4H AB
system (J=5.0 Hz) at d=8.75 and 8.89 ppm, a feature that
was assigned to the H12,13 and H7,18/8,17 protons (Figure 1), re-
spectively. The resonances for the two inner-ring NH pro-
tons were observed as a broad 2H singlet at d=ꢀ2.94 ppm,
as would be expected given the strong shielding effect of the
conjugated porphyrin p system.
with four ethyl groups, four sulfur atoms (two TTF units),
and four phenyl rings in the meso-positions. The structure
exhibits a saddle-like conformation (Figure 2b), wherein the
pyrrole subunits are substantially tilted and the core atoms
deviate considerably from the mean macrocyclic plane. In
the packing diagram of 3 (Figure 2c), two molecules of 3 are
paired, as reflected in several short S···S interactions in the
solid state.
The 1H NMR spectrum of the bisTTF-porphyrin 2 fea-
tured a singlet, integrating to 4H, at a chemical shift of d=
8.74 ppm; this feature was assigned to the resonances associ-
ated with the H7 protons (Figure 1), whereas the resonances
for the two inner-ring NH protons were observed as a broad
2H singlet at d=ꢀ3.15 ppm.
Electrochemical investigations: Electrochemical studies in-
volving the TTF-porphyrins 1–4 were carried out in a glove
box in THF solution at room temperature using cyclic vol-
tammetry (CV). In these studies the main focus was on oxi-
1
The H NMR spectra of the tetraTTF-porphyrin 1 and the
bisTTF-porphyrin 3 each featured a broad singlet integrat-
ing to 2H at d=ꢀ3.03 and ꢀ2.88 ppm, respectively. These
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J. O. Jeppesen, J. L. Sessler et al.
dation processes involving the TTF unit and reduction pro-
cesses ascribable to the porphyrin core. To facilitate analysis
of the data, the MPTTF derivative 9 and tetraphenylpor-
phyrin (TPP, 18)[34] were studied under conditions analogous
to those used to study the TTF porphyrins 1–4. Deconvolut-
ed voltammograms of these latter species are shown in
Figure 3 and the resulting redox potentials are summarized
in Table 1, along with those for the model compounds
MPTTF 9 and TPP 18. A more detailed discussion of each
TTF-porphyrin follows.
model compound TPP 18. The redox processes at +0.275
(one electron) and +0.500 V (one electron) vs. Fc/Fc+ can
be associated with the first and second oxidation of the TTF
unit, respectively. As compared with the model compound
MPTTF 9, the first and second oxidation processes of 4 are
shifted to more positive potentials (DEox1 =+
ACHUTNGRNEUNG 0.285 and
DEox2 =+0.055 V). The relatively large positive shift ob-
served for the first TTF-centered oxidation in 4 can most
likely be ascribed to the presence of an electron-withdraw-
ing 18 p-annulene porphyrin ring system or by more direct
electronic involvement of the
TTF unit within the delocaliza-
Table 1. Electrochemical data[a] for the TTF-porphyrins 1–4 and for the model compounds 9 and 18, as deter-
tion pathway of the 18 p-annu-
lene system. The second oxida-
tion of 4, however, is close to
that of the model compound
MPTTF 9.[19b] Such an observa-
tion is consistent with little
direct electronic interaction
between the TTF unit and the
porphyrin ring. However, it
could reflect the fact that the
putative interaction is blocked
after the first oxidation.
mined by cyclic voltammetry.
Porphyrin[b]
TTF[b]
2
Compound
Ered2 [V]
Ered1 [V]
Eox1 [V]
ꢀ0.010[c]
Eox [V]
9
18
4
2
3
+0.445[c]
ꢀ2.010[c]
ꢀ1.640[c]
ꢀ1.810[c]
ꢀ1.770[c]
ꢀ1.660[c]
ꢀ1.675[c]
ꢀ1.340[c]
ꢀ1.570[c]
ꢀ1.510[c]
ꢀ1.320[c]
+0.275[c]
+0.500[c]
+0.360[d]
+0.270[d]
ꢀ0.150[c], ꢀ0.020[c]
+0.030[d]
1
+0.080,[e] +0.150,[e] +0.250,[e] +0.400,[e] +0.510[e]
[a] Nitrogen-purged THF, RT; tetrabutylammonium hexafluorophosphate (TBAPF6, 0.1m) and a platinum disk
were used as the supporting electrolyte and working electrode, respectively; potential values in V vs. Fc/Fc+
couple. [b] Unit involved in the observed processes. [c] Reversible and monoelectronic processes. [d] Rever-
sible and dielectronic processes. [e] See text for further details.
BisTTF-porphyrin 2: The CV
of the bisTTF-annulated porphyrin 2 features (Figure 3b)
two one-electron reduction waves at ꢀ1.570 and ꢀ1.810 V
vs. Fc/Fc+, respectively. The oxidation processes associated
with the TTF units in 2 are observed at ꢀ0.150 (one elec-
tron), ꢀ0.020 (one electron), and +0.360 V (two electrons)
vs. Fc/Fc+. In this case, it is important to note that the ratio
of the intensities of the two first-oxidation waves and of the
first reduction wave is consistent with the proposed struc-
ture, namely the presence of two TTF units per porphyrin
ring. It is also noteworthy that the first-oxidation signals for
each of the two TTF units are separated from one another.
Such a finding is best interpreted[35] in terms of intramolecu-
lar interactions taking place between the two TTF units in
the mono-oxidized form of 2 (i.e., 2 +). Compared with the
C
MPTTF model compound 9, the first-oxidation process (i.e.,
2!2 +) of the first TTF unit in 2 is shifted to a more nega-
C
tive potential (DEox1 =ꢀ0.140 V), whereas the first-oxidation
+
C
2C/2+
) of the second TTF unit in 2 only is
process (i.e., 2 !2
slightly shifted (DEox2 =ꢀ0.010 V). We interpret these obser-
vations in terms of an electronic communication between
the two TTF units in 2 that is made possible as the result of
their being annulated directly onto the porphyrin core.
Figure 3. Deconvoluted voltammograms (vs. Fc/Fc+) recorded on THF/n-
Bu4NPF6 (0.1m) solutions of a) the monoTTF-porphyrin 4, b) the
bisTTF-porphyrin 2, c) the bisTTF-porphyrin 3, and d) tetraTTF-porphy-
rin 1 using a platinum electrode with a scan rate of 0.1 Vsꢀ1
.
BisTTF-porphyrin 3: For the bisTTF-annulated porphyrin 3,
+
+
C
C
2C/2+
MonoTTF-porphyrin 4: For the monoTTF-porphyrin 4, the
redox processes (Figure 3a) at ꢀ1.340 and ꢀ1.640 V vs. Fc/
Fc+ can be assigned to the first and second one-electron re-
duction of the porphyrin ring system, respectively. Although
clearly identifiable as being analogous, these reductions are
substantially shifted relative to the first (ꢀ1.675 V vs. Fc/Fc+)
the first-oxidation processes (i.e., 3!3 and 3 !3
)
were observed in the CV (Figure 3c) as a broad peak cen-
tered around +0.030 V. Such an observation is consistent
with the first-oxidation process (i.e., 3!3 +) of the first TTF
C
+
C
2C/2+
) of the
unit and the first-oxidation process (i.e., 3 !3
second TTF unit occurring at different potentials. However,
the separation between these two presumed oxidation pro-
and second (ꢀ2.010 V vs.
Fc/Fc+)
ACHUTGTNRENNGU ACHTUNGTRENNUGN reduction processes of the
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Porphyrins
FULL PAPER
cesses proved too small to be resolved under the conditions
of the experiment. In addition, a comparison between the
oxidation potentials of the related compounds 2 and 3 re-
veals that the first-oxidation processes of compound 3
(+0.030 V) appear at more positive potentials relative to
compound 2 (ꢀ0.150 and ꢀ0.020 V). Taken together, these
results might indicate that the electronic communication be-
tween the two TTF units in compound 3 is much less pro-
nounced than the electronic communication in compound 2.
The most likely explanation for this difference is that the
periphery of compound 3 is substituted with additional four
ethyl groups relative to compound 2. This higher degree of
substitution in compound 3 produces a non-planar structure
as confirmed by its X-ray crystal structure (see above), with
a concomitant reduction in the electronic communication
between the two TTF units in the case of compound 3.
TetraTTF-porphyrin 1: The tetraTTF-annulated porphyrin 1
displays numerous redox processes. Because 1 contains four
TTF units, it was expected that a total of eight electrons
could be removed readily from 1. In fact, the electrochemi-
cal behavior in the oxidative region is rather complex be-
cause all the oxidation waves coalesce and appear within a
sharp potential range. Nevertheless, at least five oxidation
processes (+0.080, +0.150, +0.250, +0.400 and +0.510 V
vs. Fc/Fc+) were observed (Figure 3d). All of these poten-
tials are in the region expected for oxidation of the TTF
units. The two one-electron reduction processes of the por-
phyrin ring system appear (Figure 3d) at higher potentials
(ꢀ1.320 and ꢀ1.660 V vs. Fc/Fc+) than those recorded for
the model system 18.
Figure 4. Absorption (THF, 298 K, c) and emission (THF, 298 K, a)
spectra of a) the model porphyrin TPP 18 and b) the monoTTF-porphy-
rin 4. Excitation was performed at 420 nm (Soret band) for 18 and 4.
Note that the fluorescence intensity is much weaker for 4 than for 18.
Table 2. Photophysical data for TTF-porphyrins 1–4 and for the model
porphyrin 18.
Cpd. Soret band Soret band
Q bands
[nm][a]
Fluorescence
[nm]
[a]
[nm][a]
e [Lmolꢀ1 cmꢀ1
]
4
2
3
1
420
430
441
440
420
186000
625000
261000
696000
460000
520, 610
520, 590
650, 710[b]
680, 740[b]
701, 783[b]
710, 770[b]
483, 538, 605
525, 550
Photophysical studies: The photophysical properties of the
mono-, bis-, and tetraTTF-porphyrins 1–4 and the model
compounds MPTFF 9 and TPP 18 were studied in solutions
of air-equilibrated THF at room temperature. The absorp-
tion spectra of the TTF-porphyrins 1–4 were comparable to
the sum of the spectra of their constituents, as defined by
model compounds 9 and 18. This observation rules out a sig-
nificant interaction between the TTF and porphyrinic chro-
mophores of 1–4 in the ground state. In the visible region of
the absorption spectra, the expected strong Soret bands
appear (Figure 4 and Table 2) at 420, 430, 441, and 440 nm
for 4, 2, 3, and 1, respectively. Based on this progression, it
is evident that the Soret band shifts to longer wavelength as
the porphyrin core becomes more substituted. In addition to
the Soret bands, two or three Q-type bands are seen in the
visible region between 483 and 605 nm (Table 2) and can be
ascribed to the porphyrin core present in the TTF-porphyr-
ins 1–4. Likewise, weak absorptions between 250 and
350 nm are seen in the UV region of the absorption spectra
and reflect the presence of the TTF subunits.
18
512, 546, 590, 648 650, 713[c]
[a] Absorption maxima (THF, 298 K) of 1–4. [b] Emission maxima (THF,
298 K) of 1–4 after addition of the oxidant FeCl3. Note that, compared to
the TPP control, 18, the fluorescence intensity of 1–4 is weak.
[c] Emission maxima (THF, 298 K) of 18. Excitation of the porphyrins
was carried out at their respective Soret bands.
core in 4 is quenched by >90% relative to this latter unsub-
stituted model compound.[36] This observation provides sup-
port for the proposal that substantial electron transfer, from
the TTF donor to the porphyrin acceptor, occurs following
photoexcitation of 4. It was expected that removal of one
+
C
electron from the TTF unit (TTF!TTF
)
in the
AHCTUNGTREGmNNUN onoTTF-porphyrin 4 would prevent the TTF unit from
acting as an electron donor and that consequently, it would
not act to quench the porphyrin emission. The net result
would be a (re)generation of the porphyrin emission. To test
this hypothesis, an oxidation experiment was carried out
that involved the addition of increasing amounts of the
chemical oxidant FeCl3 to a THF solution of 4. It was ob-
served (Figure 5) that the fluorescence intensity increased as
the amount of added FeCl3 increased. This finding thus pro-
vides support for the notion that the porphyrin emission can
indeed be (re)generated, at least in part, by oxidizing the
Diamagnetic porphyrins are well known[1] to display a
strong fluorescence-emission feature in the 600–800 nm
spectral region. However, a comparison of the emission
spectra of the monoTTF-porphyrin 4 (Figure 4b) and TPP
18 (Figure 4a) reveals that the fluorescence of the porphyrin
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511

J. O. Jeppesen, J. L. Sessler et al.
Conclusion
Herein we have reported the clean synthesis of TTF-annu-
lated porphyrins that permits the annulated derivatives 1–4
to be prepared free of any apparent radical impurities. This
finding provides support for the notion that preparative
pathway matters and that the radical impurities seen previ-
ously in the sample of 1, synthesized using the prior proce-
dure, were just that, namely impurities, as opposed to an in-
trinsic feature of the molecule. A single-crystal X-ray dif-
fraction analysis of 3 revealed that the porphyrin macrocycle
adopts a non-planar saddle-like conformation in the solid
state. Photophysical studies carried out in solution show that
in TTF-porphyrins 1–4 there are no significant interactions
between the constituent chromophore subunits in the
ground state. However, substantial electron transfer from
the TTF units to the porphyrin chromophore takes place in
the excited state(s) generated upon photoexcitation of these
four compounds, as evidenced by 1) a greater than 90%
quenching of the fluorescence relative to what is seen in the
model compound TPP 18 and 2) the observation that the
porphyrin emission of 1–4 can be partly (re)generated upon
oxidation of the TTF unit. In the case of the bis-TTF-por-
phyrin 2, electrochemical studies provide support for the
presence of intramolecular interactions between the two
Figure 5. Emission (THF, 298 K) spectra of the monoTTF-porphyrin 4 re-
corded upon addition of increasing amounts of the chemical oxidant
FeCl3. Excitation was performed at 420 nm. The Soret band was omitted
from the plotted spectra for clarity.
+
TTF unit to the corresponding TTF radical cation.[37] The
C
emission maxima of compounds 1–3 together with those for
compounds 4 and 18 are summarized in Table 2. It is evident
that the emission maxima shifts to longer wavelengths as the
porphyrin core becomes more substituted.
Spectroelectrochemical investigations: Spectroelectrochem-
istry[38] has proven to be a very powerful tool for monitoring
the formation of the TTF radical cation (TTF +) and TTF
C
dication (TTF2+) during electrochemical oxidation. In the
case of the bisTTF-porphyrin 2, spectroelectrochemical
analysis (Figure 6) reveals the formation of a species with
two structured absorption bands with maxima at 450 and
810 nm, respectively, as the voltage is stepped from ꢀ0.2 to
+0.3 V; such features are characteristic of a TTF radical
cation.[38] Increasing the voltage further leads (Figure 6) to a
decrease in these bands along with a concomitant increase
in the intensity of the band centered around lmax =680 nm, a
spectral feature that can be assigned to the presence of a
TTF dication. It is thus proposed that the species produced
TTF units in the mono-oxidized form (i.e., 2 +). This finding
C
thus supports the conclusion that following oxidation, the
two TTF units are able to communicate electronically
through the intervening porphyrin core. These systems thus
serve as potential prototypes for molecular transistors or
diodes, in which the extent of through-molecular-device
communication depends on an external output. A further
novel feature of the present series of compounds, especially
1 and 2, is that, by applying appropriate potentials, they can
be made to hold several electrons, or even more effectively,
holes within a small molecular space. This could make them
of interest in charge-storage applications or in catalyst de-
velopment.
is 24+, that is, TTF2+-porphyrin-TTF2+
.
Experimental Section
General methods: All reactions were carried out under an atmosphere of
anhydrous nitrogen or argon unless otherwise stated. THF was distilled
from sodium-benzophenone immediately prior to use or dried by passage
through two columns of activated alumina. MeOH was distilled from Mg
and I2. CH2Cl2 was distilled from CaH2 immediately prior to use. DMF
and MeCN were allowed to stand over molecular sieves (4 ꢃ) for at least
three days before use. Benzoylchloride was distilled under reduced pres-
sure. CDCl3 was purchased in bottles from Cambridge Isotope Inc., and
stored over K2CO3 to remove the small amount of acid contained in this
solvent. Lithium bromide was dried overnight at approximately 2008C in
vacuo. All other reagents were obtained from commercial sources and
used as received. The MPTTF derivatives 5[22] and 9[19b] were prepared ac-
cording to literature procedures. Analytical thin layer chromatography
(TLC) was performed on Merck DC-Alufolien Kiselgel60 F254 0.2-mm
thickness precoated TLC plates, which were inspected by UV light prior
to development with iodine vapor. Column chromatography was per-
formed using Merck Kiselgel60 (0.040–0.060 mm, 230–400 mesh ASTM).
Melting points (M.p.) were determined by using a Bꢄchi melting-point
Figure 6. UV/Vis/NIR spectroelectrochemistry of the bisTTF-porphyrin 2
recorded in THF at 298 K.
512
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Chem. Eur. J. 2009, 15, 506 – 516

Porphyrins
FULL PAPER
apparatus or a Mel-TempII melting-point apparatus; in both cases the
values reported are uncorrected. 1H NMR spectra were recorded by
using a Gemini-300BB instrument at 300 MHz at 298 K, using the deuter-
ated solvent to achieve locking and TMS or the residual solvent as an in-
ternal standard. 13C NMR spectra were recorded at 75 MHz at 298 K,
using broad-band decoupling. The chemical shifts are given in ppm rela-
tive to TMS. Infrared (IR) spectra were recorded by using a Perkin–
Elmer580 spectrophotometer. High-resolution Fourier transform matrix-
assisted laser-desorption/ionization mass spectrometry (HiRes-FT-
MALDI-MS) was performed by using an IonSpec4.7 tesla Ultima Fouri-
er Transform mass spectrometer, utilizing a 2,5-dihydroxybenzoic acid
(DHB) matrix. Absorption spectra were recorded at RT by using a Shi-
madzu UV-1601PC instrument. Cyclic voltammetry was carried out in a
three-electrode cell equipped with a platinum millielectrode and a plati-
num wire counter-electrode. A silver wire served as a quasi-reference
electrode, and its potential was checked against the ferrocene/ferricinium
couple (Fc/Fc+) before and after each experiment. The concentration of
the examined compounds was ꢁ0.4 mm and the electrolytic media con-
sisted of THF and contained 0.1m nBu4NPF6. All experiments were per-
formed at RT in a glove box containing anhydrous, oxygen-free (1 ppm)
argon. Electrochemical experiments were carried out by using an EGG
PAR 273A potentiostat with positive-feedback compensation. On the
basis of repetitive measurements, absolute errors on potentials were
found to be around 5 mV. The setup used for the UV-visible and fluores-
cence spectroelectrochemical experiments has been described previous-
ly.[38] The conversion time of the cell was less than 1 s at 20 mm and less
than 100 s at 200 mm. Elemental analyses were performed by Atlantic Mi-
crolab, Inc., Atlanta, Georgia.
pyrrole (8) as a colorless solid that proved sufficiently pure for further
use as described below.
BF3·OEt2 (ꢁ10 mL) was added to a solution of the MPTTF derivative 9
(0.31 g, 0.70 mmol) and 2,5-bis(hydroxymethylphenyl)pyrrole (8) (0.20 g,
0.70 mmol) in anhydrous CH2Cl2 (100 mL), causing a color change from
yellow to brown. The reaction mixture was stirred for 1 h at RT. This was
followed by the addition of DDQ (0.24 g, 1.05 mmol) in one portion,
which caused the reaction mixture to become black. After stirring for 5 s,
Et3N (ꢁ0.1 mL) was added and the entire mixture was immediately fil-
tered through a pad of alumina (40 mL), which was washed with CH2Cl2
(ꢁ100 mL) until the filtrate was colorless. The combined organic filtrates
were washed with H2O (2ꢅ50 mL) and dried (MgSO4). Concentration in
vacuo gave a black solid that was purified by column chromatography
(silica gel: cyclohexane/CH2Cl2 3:1). The black band (Rf =0.2) was col-
lected and concentrated. This afforded compound 2 (29 mg, 6%) as an
analytically pure, purple solid. M.p. 264–2668C. Recrystallization from
CH2Cl2/MeOH gave
2
as small purple needles. 1H NMR (CDCl3,
300 MHz): d=ꢀ3.15 (s, 2H), 0.93 (t, J=7.1 Hz, 12H), 1.27–1.48 (m,
16H), 1.64 (p, J=7.2 Hz, 8H), 2.81 (t, J=7.4 Hz, 8H), 7.75–7.84 (m,
8H), 7.84–7.94 (m, 4H), 8.00–8.07 (m, 8H), 8.74 ppm (s, 4H); 13C NMR
(CDCl3, 75 MHz): d=14.1, 22.4, 29.6, 30.8, 36.4, 106.9, 118.9, 123.9, 127.9,
128.3, 128.5, 129.4, 133.5, 138.8, 140.5, 142.2, 145.9 ppm; IR (KBr): n˜ =
2954, 2926, 2855, 1630, 1474, 1441, 1062, 797, 750, 700 cmꢀ1; UV/Vis
(THF, 298 K): lmax (e)=430 nm (625000 Lmolꢀ1 cmꢀ1); HiRes-FT-
MALDI-MS: m/z: calcd for C72H70N4S12+: 1374.2243; found: 1374.2235;
elemental analysis calcd (%) for C72H70N4S12 (1376.15): C 62.84, H 5.13,
N 4.07, S 27.96; found: C 62.93, H 5.13, N 4.18, S 27.82.
Compound 11: The MPTTF derivative 9 (0.59 g, 1.32 mmol) and 2-
benzyl-1,3-benzodithiolium tetrafluoroborate (10) (1.04 g, 3.3 mmol)
were dissolved in a mixture of anhydrous CH2Cl2 (5 mL) and MeCN
(15 mL) before anhydrous pyridine (0.26 g, 0.27 mL, 3.3 mmol) was
added to the brown solution. This produced a dark-brown solution. The
reaction mixture was stirred for 20 min at RT (after approximately
10 min a yellow precipitate was formed), whereupon CH2Cl2 (200 mL)
was added and the mixture was washed with first H2O (100 mL), then a
saturated aqueous solution of NaHCO3 (2ꢅ100 mL), and finally H2O
(100 mL). After being dried (MgSO4), concentration gave a yellow solid,
which was purified by column chromatography (silica gel: cyclohexane/
CH2Cl2 2:1). The yellow band (Rf =0.45) was collected and concentrated
to give compound 11 (1.08 g, 91%) as an analytically pure yellow solid.
M.p. 172–1758C. Recrystallization from CH2Cl2/MeOH gave compound
11 as yellow needles. 1H NMR (CDCl3, 300 MHz): d=0.90 (t, J=7.1 Hz,
6H), 1.25–1.42 (m, 8H), 1.60 (p, J=7.2 Hz, 4H), 2.76 (t, J=7.4 Hz, 4H),
7.01–7.08 (m, 4H), 7.14–7.20 (m, 4H), 7.19–7.25 (m, 6H), 7.64–7.71 (m,
4H), 8.58 ppm (brs, 1H); 13C NMR (CDCl3, 75 MHz): d=14.0, 22.2, 29.4,
30.7, 36.2, 53.4, 120.9, 121.6, 122.6, 122.9, 125.4, 126.5, 127.3, 128.2, 128.6,
Compound 1: Powdered sodium borohydride (0,76 g, 20.0 mmol) was
added in small portions over a period of 30 min to a stirred solution of
the MPTTF derivative 5 (0.55 g, 1.0 mmol) and anhydrous lithium bro-
mide (1.74 g, 20.0 mmol) in anhydrous THF (60 mL) and anhydrous
MeOH (20 mL) at RT, causing a slow color change from orange to
yellow. After stirring for 1 h at RT, H2O (200 mL) was added and the
mixture was extracted with CH2Cl2 (2ꢅ100 mL). The combined organic
phases were washed with H2O (100 mL) and dried (MgSO4). Concentra-
tion in vacuo gave a yellow solid containing the alcohol 6, which was dis-
solved in anhydrous CH2Cl2 (50 mL) before trifluoroacetic acid
(ꢁ10 mL) was added causing a slow color change to brown. The reaction
mixture was stirred for 30 min at RT. This was followed by the addition
of DDQ (0.17 g, 0.75 mmol) in one portion to yield a black reaction mix-
ture. After stirring for 5 s, Et3N (ꢁ0.1 mL) was added and the entire
mixture was immediately filtered through a pad of alumina (40 mL),
which was washed with CH2Cl2 (ꢁ100 mL) until the filtrate was color-
less. The combined organic filtrates were washed with H2O (2ꢅ100 mL)
and dried (MgSO4). Concentration in vacuo gave a black solid that was
purified by column chromatography (silica gel: cyclohexane/CH2Cl2 7:2).
The black band (Rf =0.2) was collected and concentrated to give com-
pound 1 (49 mg, 9%) as an analytically pure, purple solid. M.p. 276–
2808C. Recrystallization from CH2Cl2/MeOH gave 1 as small purple nee-
dles. 1H NMR (CDCl3, 300 MHz): d=ꢀ3.03 (s, 2H), 0.94 (t, J=7.0 Hz,
24H), 1.27–1.59 (m, 32H), 1.65 (p, J=7.2 Hz, 16H), 2.82 (t, J=7.4 Hz,
16H), 7.80–7.92 (m, 16H), 7.96–8.03 ppm (m, 4H); 13C NMR (CDCl,
75 MHz): d=14.1, 22.4, 29.6, 30.9, 36.5, 117.4, 127.9, 129.5, 130.8, 132.9,
138.9 ppm, four signals are overlapping or missing; IR (KBr): n˜ =2954,
2926, 2855, 1630, 1456, 1441, 1053, 882, 767, 755, 698 cmꢀ1; UV/Vis (THF,
298 K): lmax (e)=440 nm (696000 Lmolꢀ1 cmꢀ1); HiRes-FT-MALDI-MS:
m/z: calcd for C100H110N4S24+: 2134.2022; found: 2134.1950; elemental
analysis calcd (%) for C100H110N4S24 (2137.55): C 56.19, H 5.19, N 2.62, S
36.00; found: C 56.41, H 5.19, N 2.69, S 36.16.
129.1, 137.2, 138.3 ppm; IR (KBr): n˜ =2954, 2926, 2855, 1444, 1259, 1207,
+
1118, 740, 693 cmꢀ1; HiRes-FT-MALDI-MS: m/z: calcd for C44H41NS10
:
903.0446; found: 903.0438; elemental analysis calcd (%) for C44H41NS10
(904.46): C 58.43, H 4.57, N 1.55, S 35.45; found: C 58.61, H 4.57, N 1.44,
S 35.69.
Compound 12: Mercury(II) acetate (3.14 g, 9.84 mmol) was added in one
portion to a yellow solution of compound 11 (1.48 g, 1.64 mmol) in
Me2SO (100 mL) producing a dark-green mixture. The reaction mixture
was stirred at 1008C for 1.5 h (after approximately 10 min, the reaction
mixture became red), whereupon the reaction mixture was treated with
an aqueous solution of potassium iodide (10% solution in H2O, 200 mL)
and extracted with CH2Cl2 (4ꢅ100 mL). The organic phases were com-
bined, filtered through a layer of Celite (50 mL), washed with first an
aqueous solution of potassium iodide (10% solution in H2O, 100 mL),
followed by a saturated aqueous solution of NaHCO3 (100 mL), and then
finally H2O (100 mL). After drying (MgSO4), concentration in vacuo
gave a dark solid, which was purified by column chromatography (silica
gel: CH2Cl2/cyclohexane 3:1). The dark-purple band (Rf =0.3) was col-
lected and concentrated providing compound 12 (0.82 g, 76%) as a pure,
Compound 2: Powdered sodium borohydride (1.29 g, 34 mmol) was
added in small portions over a period of 30 min to a stirred solution of
compound 7 (0.47 g, 1.7 mmol) and anhydrous lithium bromide (1.47 g,
17 mmol) in anhydrous THF (60 mL) and anhydrous MeOH (20 mL) at
RT. After stirring for 1 h at RT, H2O (200 mL) was added and the mix-
ture was extracted with CH2Cl2 (2ꢅ100 mL). The combined organic
phases were washed with H2O (2ꢅ100 mL) and dried (MgSO4). Evapora-
tion of the solvent gave (quantitative) the 2,5-bis(hydroxymethylphenyl)-
1
dark-purple solid. M.p. 55–608C; H NMR (CDCl3, 300 MHz): d=0.90 (t,
J=6.9 Hz, 6H), 1.23–1.42 (m, 8H), 1.61 (p, J=7.3 Hz, 4H), 2.78 (t, J=
7.3 Hz, 4H), 7.48–7.58 (m, 4H), 7.60–7.68 (m, 2H), 7.75–7.84 (m, 4H),
Chem. Eur. J. 2009, 15, 506 – 516
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513

J. O. Jeppesen, J. L. Sessler et al.
9.83 ppm (brs, 1H); 13C NMR (CDCl3, 75 MHz): d=13.9, 22.1, 29.4, 30.6,
36.2, 113.5, 117.0, 126.1, 127.5, 128.2, 129.1, 130.4, 133.1, 136.4,
184.3 ppm; IR (KBr): n˜ =2954, 2926, 2855, 1620, 1493, 1463, 1446, 1317,
color change from purple to yellow. After stirring for 1 h at RT, H2O
(200 mL) was added and the mixture was extracted with CH2Cl2 (2ꢅ
100 mL). The combined organic phases were washed with H2O (100 mL)
and dried (MgSO4). Evaporation of the solvent gave the MPTTF diol 13
as a yellow solid in quantitative yield. This latter product was then dis-
solved in anhydrous CH2Cl2 (50 mL) together with the tripyrrane 17 (pre-
pared as described above). Trifluoroacetic acid (ꢁ10 mL) was then
added, which produced a slow color change from yellow to brown. The
reaction mixture was stirred for 30 min at RT, followed by addition of
DDQ (86 mg, 0.38 mmol) in one portion, which caused the reaction mix-
ture to become black. After stirring for 5 s, Et3N (ꢁ0.1 mL) was added
and the entire mixture was immediately filtered through a pad of alumina
(40 mL), which was washed with CH2Cl2 (ꢁ100 mL) until the filtrate was
colorless. The combined organic filtrates were washed with H2O (2ꢅ
50 mL) and dried (MgSO4). Concentration in vacuo gave a black solid
that was subjected to column chromatography (silica gel: cyclohexane/
CH2Cl2 2:1). The black band (Rf =0.25) was collected and concentrated
to afford compound 4 (35 mg, 9%) as an analytically pure, purple solid.
M.p. 264–2658C. Recrystallization from CH2Cl2/MeOH then provided 4
in the form of small purple needles. 1H NMR (CDCl3, 300 MHz): d=
ꢀ2.94 (s, 2H), 0.93 (t, J=7.1 Hz, 6H), 1.26–1.47 (m, 8H), 1.64 (p, J=
7.1 Hz, 4H), 2.82 (t, J=7.3 Hz, 4H), 7.67–7.84 (m, 10H), 7.84–7.94 (m,
2H), 8.02–8.10 (m, 4H), 8.14–8.23 (m, 4H), 8.74 (s, 2H), 8.75 and
8.89 ppm (AB q, J=5.0 Hz, 4H); 13C NMR (CDCl3, 75 MHz): d=14.1,
22.4, 29.6, 30.8, 36.4, 118.2, 121.0, 126.9, 127.9, 128.0, 128.2, 128.2, 128.7,
129.3, 139.6, 134.1, 134.6, 140.8, 142.0 ppm, seven signals overlapping or
missing; UV/Vis (THF, 298 K): lmax (e)=420 nm (186000 Lmolꢀ1 cmꢀ1);
HiRes-FT-MALDI-MS: m/z: calcd for C58H50N4S6+: 994.2354; found:
994.2393; elemental analysis calcd (%) for C58H50N4S6 (995.44): C 69.98,
H 5.06, N 5.63, S 19.33; found: C 69.56, H 5.32, N 5.64, S 19.03.
1278, 734, 710 cmꢀ1
(2700 Lmolꢀ1 cmꢀ1);
;
UV/Vis (CHCl3, 298 K): lmax (e)=539 nm
HiRes-FT-MALDI-MS: m/z: calcd for
C32H33NO2S6+: 655.0830; found: 655.0804; elemental analysis calcd (%)
for C32H33NO2S6 (656.01): C 58.59, H 5.07, N 2.14, S 29.33; found: C
58.75, H 5.08, N 2.09, S 29.44.
Compound 3: Powered sodium borohydride (0.23 g, 6.1 mmol) was added
in small portions over a period of 30 min to a stirred solution of the
MPTTF derivative 12 (0.26 g, 0.40 mmol) in anhydrous THF (50 mL) and
anhydrous MeOH (25 mL) at RT, causing a color change from dark-
purple to yellow. After stirring for 1 h at RT, CH2Cl2 (100 mL) was
added and the mixture was washed with H2O (3ꢅ100 mL) before being
dried (MgSO4). Evaporation of the solvent gave the bis(hydroxymethyl-
phenyl)-MPTTF 13 as a yellow solid in quantitative yield. This product
was used without further purification.
The bis(hydroxymethylphenyl)-MPTTF 13 (0.13 g, 0.20 mmol) and 3,4-di-
ethylpyrrole (14) (0.25 g, 2.0 mmol) were dissolved in anhydrous CH2Cl2
(5 mL) and trifluoroacetic acid (ꢁ10 mL) was added causing a color
change from yellow to brown. The reaction mixture was stirred for 1 h at
RT, whereupon Et3N (1 drop) and CH2Cl2 (50 mL) were added. The mix-
ture was then washed with H2O (2ꢅ50 mL) before being dried (MgSO4).
Concentration in vacuo gave a yellow solid that was purified by column
chromatography (silica gel: hexanes/CH2Cl2 2:1). The yellow band (Rf =
0.15) was collected and concentrated to give compound 15 (0.11 g, 65%)
as a yellow oil, a product that was used immediately for the next step.
The bis(hydroxymethylphenyl)-MPTTF 13 (0.13 g, 0.20 mmol) and com-
pound 15 (0.11 g, 0.13 mmol) were dissolved in anhydrous CH2Cl2
(5 mL), whereupon trifluoroacetic acid (ꢁ10 mL) was added; this caused
a color change from yellow to brown. The reaction mixture was stirred
for 1 h at RT, followed by the addition of DDQ (34 mg, 0.15 mmol) in
one portion, which caused the reaction mixture to become black. After
stirring for 5 s, Et3N (ꢁ0.1 mL) was added, and the entire mixture was
immediately filtered through a pad of alumina (40 mL), which was
washed with CH2Cl2 (ꢁ100 mL) until the filtrate was colorless. The com-
bined organic filtrates were washed with H2O (2ꢅ50 mL) and dried
(MgSO4). Concentration in vacuo gave a black solid that was subjected
to column chromatography (silica gel: hexanes/CH2Cl2 1:1). The black
band (Rf =0.3) was collected and concentrated to give compound 3
(25 mg, 13%) as an analytically pure, purple solid. M.p. 232–2348C. Re-
crystallization from CH2Cl2/MeOH gave 3 as small purple needles suita-
ble for X-ray analysis. 1H NMR (CDCl3, 300 MHz): d=ꢀ2.88 (s, 2H),
0.72 (t, J=7.3 Hz, 12H), 0.87 (t, J=7.1 Hz, 12H), 1.25–1.40 (m, 16H),
1.56 (p, J=7.4 Hz, 8H), 2.63 (q, J=7.4 Hz, 8H), 2.73 (t, J=7.4 Hz, 8H),
7.70–7.80 (m, 8H), 7.80–7.90 (m, 4H), 8.10–8.18 ppm (m, 8H); UV/Vis
(THF, 298 K): lmax (e)=441 (261000 Lmolꢀ1 cmꢀ1); HiRes-FT-MALDI-
MS: m/z: calcd for C80H86N4S12+H+: 1487.3574; found: 1487.4453; ele-
Acknowledgements
This work was supported by Lundbeckfonden, the Strategic Research
Council in Denmark through the Young Researchers Programme (proj-
ect 2117-05-0115), and the Danish Natural Science Research Council
(SNF, project #21-03-0268) through the SONS Programme of the Europe-
an Science Foundation. This work was also funded by the European
Commission, Sixth Framework Programme, and the US National Science
Foundation (NSF grant no. CHE 0749571 to J.L.S.)
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mental analysis calcd (%) for C80H86N4S12·1= CH2Cl2 (1488.36): C 63.16,
2
H 5.73, N 3.66, S 25.14; found: C 63.31, H 5.79, N, 3.50, S 24.10.
Compound 4: Powdered sodium borohydride (0.30 g, 8.0 mmol) was
added in small portions over a period of 30 min to a stirred solution of
compound 7 (0.11 g, 0.4 mmol) and anhydrous lithium bromide (0.69 g,
8.0 mmol) in anhydrous THF (30 mL) and anhydrous MeOH (10 mL) at
RT. After stirring for 1 h at RT, H2O (200 mL) was added and the mix-
ture was extracted with CH2Cl2 (2ꢅ100 mL). The combined organic
phases were washed with H2O (2ꢅ100 mL) and dried (MgSO4). Evapora-
tion of the solvent gave 2,5-bis(hydroxymethylphenyl)pyrrole (8) as a col-
orless oil. This oil was dissolved in neat pyrrole (20 mL) and then
Et2O·BF3 (ꢁ10 mL) was added. The resulting reaction mixture was
stirred for 1 h at RT, whereupon Et3N (ꢁ0.05 mL) was added and the re-
maining pyrrole was removed by using an oil pump. This provided the tri-
pyrrane 17 as a colorless semi-solid that proved sufficiently pure for fur-
ther use (see below).
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Powdered sodium borohydride (0.29 g, 7.6 mmol) was added in small por-
tions over
a period of 30 min to a stirred solution of 12 (0.25 g,
0.38 mmol) and anhydrous lithium bromide (0.66 g, 7.6 mmol) in anhy-
drous THF (60 mL) and anhydrous MeOH (20 mL) at RT, causing a
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during the reaction. In addition, TLC analysis revealed the presence
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porphyrin units have been reported so far; see for instance: a) P. A.
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[25] A 1H NMR spectroscopic examination carried out revealed spectral
features consistent with the proposed complete reduction of the car-
bonyl group in 5 and the formation of the corresponding alcohol 6.
Although the alcohol 6 can be handled for a few hours, significant
decomposition is seen within one day.
[26] Some of us have previously reported (ref. [16]) that the tetraTTF-
annulated porphyrin 1 can be synthesized by stirring the MPTTF de-
rivative 9, benzaldehyde, and a catalytic amount of p-toluenesulfoic
acid (PTSA) in THF at RT for 18 h followed by DDQ oxidation.
However, this method gives rise to a mixture of the neutral porphy-
Chem. Eur. J. 2009, 15, 506 – 516
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www.chemeurj.org
515

J. O. Jeppesen, J. L. Sessler et al.
+
C
rin 1 and the corresponding radical-cation porphyrin 1 in a ratio of
[I>2s(I)]=0.0891, wR2 =0.1437, GOF=1.836. The data were col-
lected by using a Nonius Kappa CCD diffractometer. A total of 467
frames of data were collected using w-scans with a scan range of 18
and a counting time of 124 seconds per frame. Data reduction was
performed using DENZO-SMN (DENZO-SMN 1997). Z. Otwinow-
ski, W. Minor, Methods Enzymol. 2007, 276 307–326). The structure
was solved by direct methods using SIR97 (SIR97, a program for
crystal structure solution: A. Altomare, M. C. Burla, M. Camalli,
G. L. Cascarano, C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni,
G. Polidori, R. Spagna, J. Appl. Crystallogr. 1999, 32, 115–119) and
refined by full-matrix least-squares on F2 with anisotropic displace-
ment parameters for the non-H atoms using SHELXL-97 (G. M.
Sheldrick, SHELXL97, Program for the Refinement of Crystal
Structures, University of Gçttingen, Germany, 1994). The hydrogen
atoms on carbon were calculated in ideal positions with isotropic-
displacement parameters set to 1.2ꢅUeq of the attached atom (1.5ꢅ
Ueq for methyl hydrogen atoms). The hydrogen atoms on the pyrrole
nitrogen atoms, N2 and N4, were observed in a DF map and refined
with isotropic-displacement parameters. The anisotropic-displace-
ment parameters for the four pentyl-group carbon atoms were re-
strained to be approximately isotropic in the final stages of the re-
approximately 4:1. Unfortunately, in our hands this mixture proved
impossible to separate by any means. The H NMR spectrum of this
1
porphyrin mixture recorded in CDCl3 at 298 K featured only very
broad peaks, an observation consistent with the presence of radicals
or slow tumbling resulting from aggregation in solution. The radical-
cation nature of the porphyrin mixture was confirmed (ref. [16]) by
quantitative electron paramagnetic resonance (EPR) spectroscopy.
This porphyrin mixture (1 and 1 +) was isolated as a stable pitch-
C
black residue after column-chromatographic purification over silica
gel using CH2Cl2/MeOH (19:1) as the eluent. Attempts to obtain
the neutral tetraTTF-porphyrin 1 by chemical reduction of this radi-
cal mixture (1+1 +) proved unsuccessful (ref. [16]). The big differ-
C
ence in color and eluent (cyclohexane/CH2Cl2 7:2) used for the
column-chromatographic purification of the neutral tetraTTF-por-
phyrin 1 reported here compared to the radical mixture of tet-
raTTF-porphyrins (1+1 +) reflects the different physical properties
C
of these ostensibly similar tetraTTF-porphyrin products. Note the
high stability of both the neutral product 1, whose synthesis is de-
tailed in this report, and the radical-cation porphyrin mixture pre-
pared earlier. Unfortunately, as noted above, efforts to interconvert
these ostensibly similar materials proved unsuccessful.
2
2
finement. The function, ꢀw(jFoj ꢀjFc j )2, was minimized, in which
2
2
[27] A color change from deep-purple to yellow took place during the
reduction, an observation that we take as indicative that the starting
material 12 is being converted to the product 13. Based on TLC
analysis, it was inferred that the diol 13 was unstable; therefore, no
specific purification of this species was attempted.
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w=1/[(s(Fo))2+
ACHTUNGTRENNUNG
to 0.155, with R(F) equal to 0.0891 and a goodness of fit, S,=1.87.
Definitions used for calculating R(F), Rw(F2), and the goodness of
2
2
fit, S, gave the following: Rw(F2)={ꢀw(jFoj ꢀjFc j )2/ꢀw(jFoj)4}1/2, in
G
which w is the weight given to each reflection. R(F)={ꢀ(jFojꢀjFcj)/
ꢀjFo j} for reflections with Fo >4(s(Fo)). S=[ꢀw(jFoj ꢀjFc j )2/
(nꢀp)]1/2, in which n is the number of reflections and p is the
number of refined parameters. The data were checked for secondary
extinction effects, but no correction was applied. Neutral atom-scat-
tering factors and values used to calculate the linear-absorption co-
efficient are from the International Tables for X-ray Crystallogra-
phy: International Tables for X-ray Crystallography, Vol. C, Tables
4.2.6.8 and 6.1.1.4 (Ed.: A. J. C. Wilson), Kluwer Academic Press,
Boston, 1992. CCDC 697641 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif
2
2
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[31] Further support for this conclusion comes from the finding that no
radical signals could be seen using conventional EPR spectroscopy.
[32] As a result of the presumed presence of an oxidized radical species
(i.e., 1 +), the 1H NMR spectrum of a sample of 1 obtained using
[36] G. Zhang, D. Zhang, X. Guo, D. Zhu, Org. Lett. 2004, 6, 1209–1212.
C
+
C
the previously published procedure (ref. [16]) featured broad lines.
[33] X-ray crystal-structure determination of 3: Crystals of the bisTTF-
porphyrin 3, suitable for X-ray diffraction, were grown by slow dif-
fusion of a MeOH layer into a CH2Cl2 solution containing 3. Crys-
[37] Attempts to reverse the process (i.e., TTF !TTF) through the ad-
dition of chemical reductants proved unsuccessful.
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¯
tallographic data: C83H92Cl6N4S12, Mr =1743.03, triclinic, P1, dark-
brown plates, crystal size=0.42ꢅ0.40ꢅ0.06 mm3, Z=2, a=
13.3526(2), b=16.2106(3), c=21.3553(4) ꢃ, a=93.017(1), b=
92.291(1), g=111.631(1)8, V=4282.16(13) ꢃ3, T=153 K, l=
Received: August 7, 2008
Revised: October 10, 2008
0.71073, 1calcd =1.352 gcmꢀ3, m(MoKa)=0.539 mmꢀ1, F
ACTHNUTRGENNUG ACHUTTGNREN(NUGN 000)=1824, q
range=2.94 to 27.508, reflections=30910, parameters=19182, R1
Published online: November 26, 2008
516
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ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 506 – 516