Comparative electrochemical and photophysical studies of tetrathiafulvalene-annulated porphyrins and their Znii complexes: The effect of metalation and structural variation

Article abstract of DOI:10.1002/chem.201202727

A series of tetrathiafulvalene (TTF)-annulated porphyrins, and their corresponding Zn^II complexes, have been synthesized. Detailed electrochemical, photophysical, and theoretical studies reveal the effects of intramolecular charge-transfer transitions that originate from the TTF fragments to the macrocyclic core. The incremental synthetic addition of TTF moieties to the porphyrin core makes the species more susceptible to these charge-transfer (CT) effects as evidenced by spectroscopic studies. On the other hand, regular positive shifts in the reduction signals are seen in the square-wave voltammograms as the number of TTF subunits increases. Structural studies that involve the tetrakis-substituted TTF-porphyrin (both free-base and Zn ^II complex) reveal only modest deviations from planarity. The effect of TTF substitution is thus ascribed to electronic overlap between annulated TTF subunits rather than steric effects. The directly linked thiafulvalene subunits function as both π acceptors as well as σ donors. Whereas σ donation accounts for the substituent-dependent charge-transfer transitions, it is the π-acceptor nature of the appended tetrathiafulvalene groups that dominates the redox chemistry. Interactions between the subunits are also reflected in the square-wave voltammograms. In the case of the free-base derivatives that bear multiple TTF subunits, the neighboring TTF units, as well as the TTF⁺ generated through one-electron oxidation, can interact with each other; this gives rise to multiple signals in the square-wave voltammograms. On the other hand, after metalation, the electronic communication between the separate TTF moieties becomes restricted and they act as separate redox centers under conditions of oxidation. Thus only two signals, which correspond to TTF^.+ and TTF²⁺, are observed. The reduction potentials are also seen to shift towards more negative values after metalation, a finding that is considered to reflect an increased HOMO-LUMO gap. To probe the excited-state dynamics and internal CT character, transient absorption spectral studies were performed. These analyses revealed that all the TTF-porphyrins of this study display relatively short excited-state lifetimes, which range from 1 to 20 ps. This reflects a very fast decay to the ground state and is consistent with the proposed intramolecular charge-transfer effects inferred from the ground-state studies. Complementary DFT calculations provide a mechanistic rationale for the electron flow within the TTF-porphyrins and support the proposed intramolecular charge-transfer interactions and π-acceptor effects.

Full text of DOI:10.1002/chem.201202727

DOI: 10.1002/chem.201202727
Comparative Electrochemical and Photophysical Studies of
Tetrathiafulvalene-Annulated Porphyrins and Their ZnII Complexes: The
Effect of Metalation and Structural Variation
Atanu Jana,[a] Masatoshi Ishida,[a] Kyuju Kwak,[a] Young Mo Sung,[a] Dong Sub Kim,[b]
Vincent M. Lynch,[b] Dongil Lee,*[a] Dongho Kim,*[a] and Jonathan L. Sessler*[a, b]
Abstract: A series of tetrathiafulvalene
(TTF)-annulated porphyrins, and their
corresponding ZnII complexes, have
been synthesized. Detailed electro-
chemical, photophysical, and theoreti-
cal studies reveal the effects of intra-
molecular charge-transfer transitions
that originate from the TTF fragments
to the macrocyclic core. The incremen-
tal synthetic addition of TTF moieties
to the porphyrin core makes the spe-
cies more susceptible to these charge-
transfer (CT) effects as evidenced by
spectroscopic studies. On the other
hand, regular positive shifts in the re-
duction signals are seen in the square-
wave voltammograms as the number of
TTF subunits increases. Structural stud-
ies that involve the tetrakis-substituted
TTF–porphyrin (both free-base and
ZnII complex) reveal only modest devi-
ations from planarity. The effect of
TTF substitution is thus ascribed to
electronic overlap between annulated
TTF subunits rather than steric effects.
The directly linked thiafulvalene subu-
nits function as both p acceptors as
well as s donors. Whereas s donation
accounts for the substituent-dependent
charge-transfer transitions, it is the p-
acceptor nature of the appended tetra-
thiafulvalene groups that dominates
the redox chemistry. Interactions be-
tween the subunits are also reflected in
the square-wave voltammograms. In
the case of the free-base derivatives
that bear multiple TTF subunits, the
neighboring TTF units, as well as the
TTF·+ generated through one-electron
oxidation, can interact with each other;
this gives rise to multiple signals in the
square-wave voltammograms. On the
other hand, after metalation, the elec-
tronic communication between the sep-
arate TTF moieties becomes restricted
and they act as separate redox centers
under conditions of oxidation. Thus
only two signals, which correspond to
+
TTF and TTF2+, are observed. The
C
reduction potentials are also seen to
shift towards more negative values
after metalation, a finding that is con-
sidered to reflect an increased
HOMO–LUMO gap. To probe the ex-
cited-state dynamics and internal CT
character, transient absorption spectral
studies were performed. These analyses
revealed that all the TTF–porphyrins
of this study display relatively short ex-
cited-state lifetimes, which range from
1 to 20 ps. This reflects a very fast
decay to the ground state and is consis-
tent with the proposed intramolecular
charge-transfer effects inferred from
the ground-state studies. Complemen-
tary DFT calculations provide a mech-
anistic rationale for the electron flow
within the TTF–porphyrins and support
the proposed intramolecular charge-
transfer interactions and p-acceptor ef-
fects.
Keywords: charge transfer · elec-
trochemistry · photophysics · por-
phyrinoids · tetrathiafulvalenes
Introduction
Porphyrins continue to attract interest within the scientific
community owing to their unique physicochemical and spec-
troscopic properties.[1] They have, for instance, seen wide
use in a variety of research fields, including anion sensing,[2]
photodynamic therapy,[3] optical data-storage technology,[4]
and so on. Over the past decade, a significant attempt has
been made to prepare p-extended or annulated oligopyrrolic
systems that bear an analogy to porphyrins.[5] Typically, this
has been done by increasing the number of pyrrolic or other
heterocyclic rings within the macrocycle,[6] fusing substitu-
ents onto the b position of pyrrole, varying the connectivity
between the pyrrolic subunits,[7] or by adjusting the number
of meso-carbon atoms.[8] Likewise, tetrathiafulvalenes
(TTFs) are well known to be redox-active species that can
[a] Dr. A. Jana, Dr. M. Ishida, K. Kwak, Y. M. Sung, Prof. Dr. D. Lee,
Prof. Dr. D. Kim, Prof. Dr. J. L. Sessler
Department of Chemistry, Yonsei University
Seoul 120 749 (South Korea)
Fax : (+1)512-471-7550
E-mail: dongho@yonsei.ac.kr
dongil@yonsei.ac.kr
[b] D. S. Kim, Dr. V. M. Lynch, Prof. Dr. J. L. Sessler
Department of Chemistry and Biochemistry
The University of Texas at Austin
1 University Station-A5300
Austin, TX 78712-0165 (USA)
E-mail: sessler@cm.utexas.edu
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202727.
338
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Chem. Eur. J. 2013, 19, 338 – 349

FULL PAPER
exist as any of three different stable redox states, namely,
served intramolecular charge-transfer events. The experi-
mental results detailed herein are supported by theoretical
calculations.
0
TTF , TTF +, and TTF2+. Not surprisingly, therefore, consid-
C
erable effort has been devoted to incorporating TTF moiet-
ies into supramolecular hybrid architectures, including TTF–
calixpyrroles,[9] TTF–cyclophanes,[10] TTF–catenanes,[11] and
hybrid TTF–porphyrins.[12] These latter systems are particu-
larly attractive because they contain both a redox active site
and a chromophore. In fact, an initial study reported not
just the synthesis of various TTF-substituted porphyrins that
contain TTF subunits fused to the b-pyrrolic positions, but
also the results of preliminary spectroelectrochemical and
photophysical studies.[12c] However, to the best of our knowl-
edge, a systematic analysis of the electrochemical and pho-
tophysical behavior of TTF–porphyrins as a function of
structure (i.e., number and placement of TTF subunits;
metalated versus free base) has not been carried out so far.
Herein, we report the one-pot synthesis of several TTF-
annulated porphyrins (n-H2: n=1–4; see below) along with
their corresponding ZnII complexes (n-Zn: n=1–4). The
Results and Discussion
Synthesis: As outlined in Scheme 1, four different b-annulat-
ed TTF–porphyrins, n-H2 (n=1–4), were synthesized from
the known TTF-annulated pyrrole (PrS-TTF-pyrrole), pyr-
role, and pentafluorobenzaldehyde by means of a conven-
Scheme 1. Synthesis of TTF–porphyrins.
tional acid-catalyzed pyrrole–aldehyde condensation reac-
tion. The condensation of pyrrole, PrS-TTF-pyrrole, and
pentafluorobenzaldehyde with a set, varied molar ratio in
the presence of a catalytic amount of BF3·OEt2 in anhydrous
CH2Cl2, followed by gradual addition of 2,3-dichloro-5,6-di-
cyano-1,4-benzoquinone (DDQ), afforded the TTF-annulat-
ed porphyrins shown in Scheme 1. The various mixtures that
were obtained from differing ratios of starting materials
were then subjected to several rounds of silica gel chromato-
graphic separation. The products, isolated as different frac-
tions, were then further subjected to recycling preparative
HPLC-GPC (gel-permeation chromatography) to effect
final purification.
The ZnII complexes of each of the isolated free-base
TTF–porphyrins, n-Zn (n=1-4) were then obtained by treat-
ing them with ZnACHTUNRGTNE(UNG OAc)2·2H2O in CHCl3/MeOH and heat-
ing at reflux for 30 min. Column chromatography over silica
gel, followed by GPC separation, gave the purified metallo-
porphyrin in good yields. All the compounds were character-
ized by NMR spectroscopy, MALDI-TOF mass spectrome-
try, and elemental analysis. Freshly prepared and recrystal-
lized samples were used for the photophysical and electro-
chemical studies.
availability of this series of compounds has permitted a de-
tailed analysis of the electrochemical features of TTF-substi-
tuted porphyrins and their excited-state behavior, as well as
an analysis of the structural determinants that regulate their
spectroscopic and electrochemical features. As detailed
below, monotonic variations were seen in the redox proper-
ties, intramolecular charge-transfer character, and detailed
excited-state dynamics as a function of TTF substitution.
Moreover, dramatic differences between the free-base and
ZnII complexes were seen. In the present case, four elec-
tron-deficient pentafluorophenyl groups were attached to
the meso positions to enhance the intrinsic charge-transfer
character. As with the electron-rich TTF substituents, the
presence of the electron-deficient pentafluorophenyl groups
is thought to play an important role in regulating the ob-
1
NMR spectroscopic studies: The H NMR spectra for all the
compounds were recorded at room temperature in CDCl3.
The resonance for the inner NH protons in each of the free-
base porphyrins appeared as a broad signal in the range of
d=ꢀ2.84 to ꢀ3.03 ppm; these signals disappeared upon zinc
insertion, as expected. In addition, three sets of sharp signals
in the aliphatic region were observed for each compound, as
would be expected given the presence of the propyl substitu-
Chem. Eur. J. 2013, 19, 338 – 349
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339

D. Lee, D. Kim, J. L. Sessler et al.
ent. The protons on the methylene attached to the sulfur
atom were found to resonate at lower field than those fur-
ther along the propyl chain. For example, in the case of the
mono-TTF derivative 1-H2, a triplet at d=1.08 ppm, a
sextet at 1.78 ppm, and a triplet at 2.89 ppm were seen. Res-
onance features that corresponded to the two b protons of
the pyrrole located trans to the TTF–pyrrole were also seen
at d=8.81 ppm. Signals at d=8.93 and 9.01 ppm, respective-
ly, ascribed to the four b protons of the two pyrrole subunits
located cis to the TTF–pyrrole, were also seen.
In the corresponding ZnII complex (1-Zn), resonances at
d=8.91 ppm (2H) and 8.99 ppm (4H) were observed, which
are reflective of the b-pyrrolic protons.
In the case of the bis-TTF–porphyrin 2-H2, it is notewor-
thy that two sets of signals at d=8.69 and 8.76 ppm, respec-
tively, were seen that are ascribed to the four chemically dis-
tinct pyrrolic protons that arise from the cis-like substitution
pattern. Were compound 2-H2 characterized by a trans-like
substitution pattern (for the TTF moieties), a single b-H res-
onance peak would be expected. Since this was not ob-
served, we propose a cis-like configuration for 2-H2. In fact,
trace quantities of what was considered to be the trans-like
isomer were observed in the reaction mixture. However, this
latter putative product could not be isolated in clean form.
A singlet peak at d=8.83 ppm was seen in the spectrum
of the tris-TTF–porphyrin 3-H2; this feature is assigned to
the two chemically equivalent b-pyrrolic protons. No signals
ascribable to b-pyrrolic protons are observed in the case of
the tetrakis-TTF–porphyrin 4-H2, which is in line with what
would be expected for such a structure.
Figure 1. Single-crystal X-ray structure of the tetrakis-TTF–porphyrin (4-
H2) and the ZnII complex (4-Zn): a,c) top views and b,d) side views, re-
spectively. Solvent molecules and meso-aryl substituents are omitted for
clarity in the side views. The thermal ellipsoids are scaled to the 50%
probability level.
The tetrakis-TTF–porphyrinatozinc(II) complex (4-Zn) is
also characterized by an overall near-planar geometry. How-
ever, the two trans-like TTF fragments are oriented in oppo-
site directions (Figure 1c and d).
Electrochemical studies: As a free standing entity, the
redox-active tetrathiafulvalene (TTF) subunit can exist as
any of three different stable redox states, namely, TTF0,
TTF +, and TTF2+. The present series of porphyrins defines
C
a matched set of congeners that differ in terms of the
number of TTF fragments annulated at the b positions. The
effect that this variation in substitution pattern has on the
redox properties of the resulting systems could thus be ex-
plored (Figure 2 and Table 1). Towards this end, electro-
chemical analyses were carried out under an argon atmos-
phere in CH2Cl2 solution containing 0.1m tetra-n-butylam-
monium hexafluorophosphate (TBAPF6) as the supporting
electrolyte. Square-wave voltammograms of the starting
PrS-TTF-pyrrole and the reference porphyrin meso-tetra-
kis(pentafluorophenyl)porphyrin (as its free base and zinc
complex, P-H2 and P-Zn, respectively) were recorded under
identical experimental conditions as used for the analysis of
the TTF–porphyrins (see Figure S34 in the Supporting Infor-
mation). PrS-TTF-pyrrole gives rise to two well-separated
oxidation waves, each of which corresponds to a one-elec-
tron process. The first oxidation potential at +0.284 V
(versus Fc/Fc+) is ascribed to the formation of the radical
In the case of all the ZnII complexes, the inner NH sig-
ꢀ
nals are absent as expected, whereas the signals in the ali-
phatic region arising from the propyl groups do not undergo
any significant shift.
X-ray crystallography: Single crystals suitable for X-ray dif-
fraction analysis were grown by the slow diffusion of hex-
anes into a solution of the tetrakis-TTF–porphyrin (4-H2)
and its corresponding ZnII complex (4-Zn) in CHCl3, respec-
tively. The solid-state structure of 4-H2 revealed a slightly
distorted geometry for the porphyrin core (Figure 1a and b).
This distortion presumably reflects the presence of four ster-
ically hindered pentafluorophenyl groups in the meso posi-
tions, which are in close proximity of eight bulky sulfur
atoms from the four TTF-annulated pyrroles. In many ex-
amples of dodeca-substituted porphyrins reported previous-
ly, for example, the b-octaethyl-substituted meso-phenyl por-
phyrin, a severely distorted core plane with a saddle shape
is seen.[13] This leads to small dihedral angles between the
meso-aryl rings and the porphyrin core (approximately 30–
408). In 4-H2, the corresponding angle is approximately 908,
which reflects substituents that lie nearly perpendicular to
the porphyrin core. Presumably, this difference originates in
the smaller steric influence of the adjacent b-sulfur atom
compared to an ethyl group. In the event, the core of 4-H2
(as defined by the mean plane) retains a near-planar geome-
try.
cation (TTF +), whereas the second oxidation feature, which
C
corresponds to the generation of the dication (TTF2+), is lo-
cated at about 0.661 V. The square-wave voltammogram of
reference P-H2 exhibited no oxidation wave in the corre-
sponding oxidation scan, as seen in the case of PrS-TTF-pyr-
role; instead, two signals appear at ꢀ1.481 and ꢀ1.055 V, re-
spectively, upon reduction. These latter features are thought
to correspond to two one-electron reduction processes that
involve the porphyrin core. Little change in the redox be-
havior was seen upon metalation and conversion to P-Zn.
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Tetrathiafulvalene-Annulated Porphyrins
FULL PAPER
unit present in the periphery. Microelectrode analysis (see
Figure S35 in the Supporting Information), which allowed
the number of electrons associated with each redox process
to be inferred, are consistent with these assignments. In the
case of the ZnII complex, 1-Zn, little shift in the peak posi-
tions or the peak intensity in the square-wave voltammo-
grams was seen.
For the free-base form of the bis-TTF–porphyrin, 2-H2,
redox processes at ꢀ1.538 and ꢀ1.205 V (versus Fc/Fc+), re-
spectively, were observed. These processes are ascribed to
the two-electron reduction of the porphyrin core, whereas
the redox processes centered at +0.102, +0.318, +0.441,
and +0.723 V, respectively, are thought to reflect four one-
electron oxidation processes centered on the two TTF units.
On the basis of the NMR spectroscopic analyses, the two
TTF subunits in 2-H2 are in a cis-like orientation (see
above). As the result of this arrangement, electronic com-
munication between the two neighboring redox subunits
might be expected. For instance, the formation of a TTF
radical cation (produced as the result of the first oxidation
process) could render the oxidation of the second TTF
moiety energetically less favorable. The same could be true
for the processes that lead to the formation of the TTF dica-
tions. To the extent this interaction was appreciable: four
distinct oxidation waves would be seen, as indeed is expect-
ed by experimental results.
In the case of the ZnII complex of the bis-substituted mac-
rocycle 2-Zn, there is a slight negative shift in the reduction
peaks relative to the metal-free form. This is consistent with
reduction of the porphyrin core being relatively more diffi-
cult after metal-ion complexation. In contrast to what was
seen in the case of the metal-free form, only two relatively
intense peaks were seen in the oxidative scan. Together,
these peaks are ascribed to the full four-electron oxidation
of the two TTF moieties. The lack of electrochemical wave
splitting, as seen for the metal-free form, is consistent with
the notion that inter-TTF coupling is greatly reduced upon
metalation.
The free-base form of the tris-TTF-porphyrin, 3-H2, dem-
onstrated electrochemical behavior similar to that of the bis-
substituted derivative. Two redox features are seen at
ꢀ1.185 and ꢀ0.963 V (versus Fc/Fc+) and are ascribed to
two single-electron reduction processes that involve the por-
phyrin core. Poorly resolved redox features are also seen at
ꢀ0.123, +0.022, +0.164, and +0.258 V in the oxidation
region. It is likely that this multiplicity of signals reflects the
existence of multiple interactions between the neighboring
TTF units. However, the exact extent and nature of these in-
teractions remain difficult to assess and hard to quantify.
In contrast to the free-base system, the ZnII complex, 3-
Zn, exhibits two similarly sized features that correspond to
the net removal of six electrons from the three noninteract-
ing TTF substituents. This occurs by means of a tris-radical
cation intermediate under conditions of oxidation. In the re-
duction process, there is a negative shift in the two reduction
waves relative to the metal-free form. Thus, in accord with
what was observed for the bis derivative, reduction of the
Figure 2. a) Square-wave voltammograms for free-base forms of the
mono, bis, tris, and tetrakis-TTF–porphyrin of this study; b) overlay plots
of all the free-base macrocycles and c) their ZnII complexes.
In the case of the free-base form of the mono-TTF-por-
phyrin, 1-H2, the redox processes seen at ꢀ1.625 and
ꢀ1.257 V versus Fc/Fc+ are due to one-electron reduction
processes that involve the porphyrin core. Likewise, the
redox processes seen at +0.124 and +0.466 V, respectively,
are ascribed to the two-electron oxidation of the single TTF
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D. Lee, D. Kim, J. L. Sessler et al.
Table 1. Redox formal potentials (V versus Fc/Fc+)[a] for the free-base forms of TTF-
porphyrins and their ZnII complexes, as determined by square-wave voltammograms.[a]
TTF subunits increases (see Figure S43 and
Table S3 in the Supporting Information).
E2red [V]
E1red [V]
E1ox [V]
E2ox [V]
E3ox [V]
E4ox [V]
In the case of the ZnII complexes, the reductive
peaks also shift to more positive values (see Fig-
ure S37 in the Supporting Information) in analogy
to the free-base derivatives as the number of TTF
moieties increases. However, in contrast to the
free-base systems, a big change in the oxidative
region as a function of substituent number is not
seen; thus, apart from the expected increase of
signal intensity as the number of TTF substituents
increases, the electrochemical features of 4-Zn re-
semble those of the other ZnII complexes in the
present series. The gradual increase in the peak in-
tensity observed near the oxidative region as the
number of annulated TTF moieties increases (Fig-
ure 2b and c) provides support for the intuitively
reasonable expectation that more electrons are
being transferred at the same redox potential in the case of
the more highly substituted systems. This is true for the
free-base compounds as well as their metalated derivatives.
Compound
PrS-TTF-pyrrole
P-H2
P-Zn
1-H2
1- Zn
2-H2
2-Zn
3-H2
3-Zn
–
–
+0.284
–
–
+0.661
–
–
–
–
–
–
–
–
–
–
ꢀ1.481
ꢀ1.528
ꢀ1.625
ꢀ1.638
ꢀ1.538
ꢀ1.692
ꢀ1.185
ꢀ1.523
ꢀ1.015
ꢀ1.501
ꢀ1.055
ꢀ1.117
ꢀ1.257
ꢀ1.253
ꢀ1.205
ꢀ1.235
ꢀ0.963
ꢀ1.229
ꢀ0.754
ꢀ1.189
+0.124
+0.178
+0.102
+0.148
ꢀ0.123
+0.174
+0.452
+0.223
+0.466
+0.434
+0.318
+0.468
+0.022
+0.479
+0.618
+0.529
–
–
+0.441
–
+0.164
–
+0.798
–
+0.723
–
+0.258
–
–
–
4-H2
4-Zn
[a] Measurements were carried out in CH2Cl2 containing 0.1m TBAPF6 as the support-
ing electrolyte under an Ar atmosphere and with platinum as the working and counter
electrodes, respectively. A silver quasi-reference electrode was used. Potentials are in
V versus the Fc/Fc+ couple recorded under the conditions of analysis. The scan rate
was 0.02 Vsꢀ1
.
porphyrin core becomes much difficult after ZnII complexa-
tion.
In the case of the tetrakis-TTF–porphyrin 4-H2 and its
corresponding ZnII complex, 4-Zn, the same porphyrin-core
reduction features as seen earlier were noted in the case of
this fully substituted system. In contrast to what is seen
during reduction, the oxidative region contains three well-
resolved signals one of which is twice the size of the others.
The number of electrons involved in the redox processes
was inferred from microelectrode experiments (see Fig-
ure S35 in the Supporting Information). Here it is estimated
that a total of eight electrons are transferred over the course
of oxidation. Consistent electrochemical features are seen in
the tetrakis-TTF-annulated ZnII complex, 4-Zn; two signals
associated with porphyrin reduction, and two well-resolved
relatively intense signals are seen in the oxidative region.
Again, this is consistent with the suggestion that all the TTF
moieties behave independently after complexation.
From an inspection of Figure 2a, it is apparent that as the
number of TTF moieties increases, reduction of the porphyr-
in core becomes more facile (i.e., the square-wave voltam-
mogram peaks shift towards more positive values). We as-
cribe the observed electrochemical shifts to electronic ef-
fects. The compounds of this study bear TTF substituents
that are directly fused to the b-pyrrolic positions. This, we
suggest, allows for an expansion of the effective p-orbital
framework by means of partial rehybridization of the thia-
fulvalene sulfur atoms, from sp3, which dominates, to sp2,
and overlap with the resulting nonhybridized p orbital. To
the extent that this occurs, it would allow for the increased
electron density that arises from reduction to be delocalized
onto the sulfur atoms that are directly bound to the b-pyr-
rolic positions, thus accounting for the shifts to more posi-
tive potential that are seen as the number of TTF substitu-
ents increases. In fact, DFT calculations reveal that the
LUMOs for all the derivatives considered in this study bear
electron density on the sulfur atoms that are directly attach-
ed to the b-pyrrolic positions. Moreover, a gradual decrease
in the HOMO–LUMO separation occurs as the number of
Steady-state absorption and fluorescence studies: Append-
ing TTF subunits to the porphyrin core, as has been per-
formed in the present study, affects both the ground- and ex-
cited-state optical properties. In the case of the mono-TTF–
porphyrin, there is a long tail that originates from 650 to
1100 nm, which is ascribed to an internal charge-transfer
(CT) transition from the TTF moieties to the polypyrrolic
macrocycle. To understand the determinants of this charge-
transfer spectral feature, detailed steady-state spectroscopic
measurements of 1-H2 with two reference compounds,
namely, P-H2 and the PrS-TTF-pyrrole subunit, were car-
ried out. These studies revealed the lack of any CT band
beyond 600 nm in the case of both the references; however,
a significant CT band was observed in the case of 1-H2 (see
Figure 3a). This implies that even the presence of a single
TTF subunit is sufficient to introduce a detectable level of
CT character in the case of this class of compounds.
The photoinduced CT events that occur upon irradiation
of TTF-annulated porphyrins were also studied by steady-
state fluorescence spectroscopy. In the case of the reference
porphyrins, P-H2 and P-Zn, strong emission features are ob-
served in CH2Cl2 (Figure 3b). In contrast, the emission in-
tensity of 1-H2 and 1-Zn was quenched effectively with a
quantum yield of less than 0.01. This latter observation is
consistent with what would be expected for molecules that
undergo intramolecular charge-transfer transitions.[12b,14] The
degree of charge transfer is presumably enhanced in the
case of the more TTF-substituted analogues. In fact, no ob-
servable fluorescence was seen for any of the porphyrins 2,
3, or 4, either in their free-base forms or as the correspond-
ing ZnII complexes.
The relative intensity of the CT phenomenon increases
with the degree of TTF functionalization. As a result, the
CT-related features become particularly prominent in the
case of the tetrakis-TTF–porphyrin, 4-H2 (Figure 4). A care-
342
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Chem. Eur. J. 2013, 19, 338 – 349

Tetrathiafulvalene-Annulated Porphyrins
FULL PAPER
Figure 4. UV/Vis-NIR spectra of the TTF–porphyrins considered in this
study: a) free-base forms and b) their corresponding ZnII complexes, as
recorded in CH2Cl2.
Figure 3. a) UV/Vis-NIR spectra of two reference compounds PrS-TTF-
pyrrole and P-H2 along with that for the simplest representative com-
pound among the TTF–porphyrin series of this report, 1-H2; b) fluores-
cence spectra of P-H2, P-Zn, 1-H2, and 1-Zn. All spectra were recorded
in CH2Cl2.
B3LYP/6-31G* level. All calculated conformations of the
core planes for the free-base derivatives and their ZnII com-
plexes were found to be nearly planar. These findings are
consistent with the available X-ray diffraction data. The sys-
tems were then analyzed in accord with the Gouterman
four-orbital model used to describe the electronic features
of ordinary porphyrins. By using such an analysis, the molec-
ular orbitals (MOs) of the mono-TTF-substituted derivatives
1-H2 and 1-Zn were characterized by electron-density distri-
butions expected for CT molecules. In particular, in all
cases, the HOMO is mainly located on the TTF fragments,
whereas the HOMOꢀ1, HOMOꢀ2, LUMO, and LUMO+1
are predominantly centered on the macrocyclic core
(Figure 5). Energy levels that originate from local TTF frag-
ments are seen above the MOs that reflect dominant contri-
butions from the porphyrin cores in all derivatives (see Fig-
ures S40–S42 in the Supporting Information for other enti-
ties). On this basis, we assign the CT band observed in the
NIR region (650–1100 nm) to a HOMO-to-LUMO (or an-
other degenerate pair of LUMO+1) electronic transition.
ful observation of the absorption spectra revealed modest
redshifts in the absorption maxima (lmax) as the number of
TTF fragments increased (e.g., the lmax of 1-H2 (421 nm) is
shifted by 17 nm in the case of 4-H2 (438 nm)). Meanwhile,
the lower-energy specteral features ascribed to the proposed
intramolecular CT effect become more pronounced as the
number of annulated TTF units increases monotonically
from 1-H2 to 4-H2 (Figure 4). This trend also holds for the
corresponding ZnII complexes. However, as is typical of ZnII
complexes of porphyrins, the metalated forms displayed
Soret bands that are more intense than those of the respec-
tive free-base derivatives, as well as a smaller number of Q
bands.
Theoretical calculations: Quantum mechanical calculations
were carried out in an effort to explain the electrochemical
behavior, charge-transfer character, and the optical proper-
ties of the TTF–porphyrins under investigation at the
Chem. Eur. J. 2013, 19, 338 – 349
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343

D. Lee, D. Kim, J. L. Sessler et al.
Figure 5. Molecular orbital energy diagrams for the mono-TTF–porphyr-
in (1-H2) and its ZnII complex (1-Zn) of this study.
Time-dependent (TD)-DFT (B3LYP/6-31G*) simulations
of the electronic spectra of the TTF-substituted porphyrins,
n-H2, considered in this study were also carried out. The
TD-DFT stick spectra obtained from this analysis are in
good agreement with the experimental spectra (see
Figure 6). In fact, the CT-based transitions that involve the
TTF-dominated MOs are seen to give rise to the broad
bands observed in the NIR region of the experimentally de-
termined steady-state absorption spectra (see Tables S4–S11
in the Supporting Information). Upon increasing the
number of TTF moieties in the molecules, the transition en-
ergies decrease and the oscillator strength (f) of each transi-
tion becomes larger.
In addition, the theoretical analyses revealed that there is
a gradual reduction in the energy gap between the HOMO
and LUMO as the number of TTF moieties increases (i.e.,
in moving from 1-H2 to 4-H2; see Figure S43 in the Sup-
porting Information). This decrease is attributed to the sta-
bilization of the LUMOs that result from an effective ex-
pansion of the p framework through interaction with the ap-
pended sulfur atoms. As noted above, this decrease is fully
consistent with the electrochemical results, namely, the ob-
served positive shifts in the reduction peaks seen in the
square-wave voltammograms.
Figure 6. Comparison between the theoretically predicted UV/Vis-NIR
transitions for the mono-, bis-, tris-, and tetrakis-TTF–porphyrins and
their corresponding ZnII complexes and the experimental spectra.
tion processes are shifted towards more negative values as
noted in the electrochemical studies.
Another noteworthy feature to emerge from the calcula-
tions is that the MO features of the free-base forms beyond
the TTF-dominant HOMO levels are less well ordered than
those of the corresponding ZnII complexes (i.e., n-H2 versus
n-Zn: n>2). In fact, in many cases, the orbitals of the ZnII
complexes are degenerate. This is reflected in the splitting
of the oxidation waves that was observed in the case of the
free-base forms in the square-wave voltammogram experi-
ments (see Figure S43 in the Supporting Information).
Calculation of Gibbs energy for determination of electron-
transfer driving force: As noted above, the steady-state
spectroscopic results are readily rationalized in terms of var-
ious intramolecular photoinduced electron-transfer (PET)
processes. This rationalization is supported by the DFT cal-
culations and by consideration of the relevant thermody-
namic driving force (Gibbs energy) for charge separation.
The energies in question (DGCS) were calculated using the
following expression [Eq. (1)]:[15]
The calculated HOMO–LUMO energy gaps (DE [eV]) of
the ZnII complexes, n-Zn, are larger than those of the corre-
sponding free-base forms. This finding is attributed to both
stabilization of the HOMOs and destabilization of the
LUMOs (see Table S3 in the Supporting Information). A
consequence of these differences is that reduction of the
porphyrin core becomes more difficult, and various reduc-
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Chem. Eur. J. 2013, 19, 338 – 349

Tetrathiafulvalene-Annulated Porphyrins
FULL PAPER
Â
Ã
eref eS
DGCS ¼ e E1oxðTTF=TTFꢁþÞ ꢀ E1redðPor=Porꢁꢀ
Þ
ꢀ
ꢁꢀ
ꢁ
e2
e2
1
1
1
1
ð1Þ
ꢀDE0ꢀ0
ꢀ
ꢀ
þ
þ
4pe0eSRCC 8pe0 rþ rꢀ
1
+
C
in which here Eox(TTF/TTF ) is the first oxidation potential
1
Cꢀ
of the TTF moiety, Ered (Por/Por ) is the first reduction po-
tential of the porphyrin core, DE0–0 is the energy gap for the
0–0 (S0!S1) transition between the lowest excited state and
the ground state of the porphyrin, r+ and rꢀ are the effective
ionic radii of the radical cation and the radical anion, re-
spectively, and RCC is the center-to-center distance between
TTF and porphyrin core. The symbols e0, es, and eref repre-
sent the vacuum permittivity, and the dielectric constant of
the solvent used in photochemical studies, and electrochemi-
cal studies, respectively. To calculate the DGCS value for 1-
H2, the electrochemical results were used (for data, see
Table 1), as determined in CH2Cl2 (es =8.93). The value of
RCC was estimated from the center-to-center distance
(7.5 ꢁ) between the TTF moiety and porphyrin core calcu-
lated from the optimized structure of 1-H2. All the electro-
chemical and photophysical measurements were taken by
using CH2Cl2 as solvent, hence the values of eref and es are
the same. Therefore, the last term of Equation (1), which is
directly related to the solvent, will be ꢂzeroꢃ. By taking all
the parameters into account, the estimated DGCS value of
ꢀ0.902 eV leads us to suggest that the electron transfer
from the TTF moiety to the porphyrin core is thermody-
namically feasible in the studied solvent. In the case of 1-
Zn, the DGCS value of ꢀ0.887 eV is likewise large enough to
allow the electron flow from the TTF fragment to the core
thermodynamically. According to these energies of two de-
rivatives, the other higher-substituted derivatives could show
sufficient driving-force energies like those of the mono de-
rivatives. Due to the lack of emission character of the other
derivatives, the higher-substituted derivatives (n-H2 and n-
Zn; n> 2), respectively, could not be calculated.
Figure 7. Transient-absorption spectra of metal-free TTF-porphyrins and
their ZnII complexes, as recorded in toluene.
Femtosecond transient-absorption spectra: To determine the
effect, if any, that the number of TTF substituents has on
the photophysical properties of the basic porphyrin core, we
determined the femtosecond transient absorption (TA)
decay profiles for both the metal-free and ZnII-metalated
forms of compounds 1–4.
In carrying out this study, we tuned the excitation wave-
length in such a way that it matched the respective Q bands
to avoid potential complications that arise from internal
conversion from the S2 to S1 state. The transient-absorption
decay profiles that correspond to the excited absorption sig-
nals were recorded at the magic angle, as shown in the
insets of Figure 7. The resulting fitted parameters along with
other photophysical data are summarized in Table 2.
Unlike the other TTF–porphyrins in the present series, 1-
H2 and 1-Zn show relatively different excited-state dynamic
behavior. In the TA spectra, these two compounds show
reasonably longer transient components, which arise solely
as a result of their weak fluorescence behavior. This phe-
nomenon can be rationalized by theory. From the molecular
orbital diagrams, it is clear that the number of HOMOs
gradually increases as the number of TTF substituents in-
creases; presumably, these substituents contribute effectively
to the main electronic transitions between the HOMO and
HOMOꢀ1 to the LUMO and LUMO+1 (see Figure 5 and
the Supporting Information). On the basis of these results,
we assume that the electronic transitions between the TTF
unit and the porphyrin core are less efficient in the case of
1-H2 and 1-Zn than other compounds, and that the relative-
ly unique photophysical properties of these two cases re-
flects this weaker charge-transfer transition.
Except for the special case of 1-H2 and 1-Zn, all com-
pounds show two fast transient-absorption decay features.
As can be seen from an inspection of Table 2, the excited-
state lifetimes of all other TTF-substituted porphyrins are
very short, generally ranging from 1 to 20 ps. From previous
studies of charge-transfer effects,[14] we infer that these fast
decay profiles reflect efficient internal charge-transfer deac-
tivation pathways that are presumed to be operative in the
Chem. Eur. J. 2013, 19, 338 – 349
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345

D. Lee, D. Kim, J. L. Sessler et al.
Table 2. Photophysical data[a] and transient absorption[b] decay time constants as de-
termined at the so-called magic angles for all the TTF–porphyrins of this study.[a]
Experimental Section
Compound
labs [nm]
e [mꢀ1 cmꢀ1] at Soret
lfl [nm]
Ffl
ts [ps]
Materials: 2,3,4,5,6-Pentafluorobenzaldehyde, DDQ, and
BF3·OEt2 were purchased from Aldrich Chemical Co. and
were used as received without further purification. PrS-TTF-
pyrrole was synthesized using a literature procedure.[16] All
solvents were acquired from local commercial companies and
dried before use following standard literature methods. All re-
actions were carried out under an argon atmosphere unless
noted otherwise. Chromatographic separations were per-
formed by means of column chromatography and using 100–
200 mesh silica gel obtained from Merck. Recycling prepara-
tive GPC-HPLC experiments were performed using a JAI
LC-908 apparatus with preparative JAIGEL-1H and 2H col-
umns and CHCl3 as eluent.
band
1-H2
1-Zn
2-H2
421, 511, 542,
587
427, 547, 575
467523
519834
381210
647,
713
593,
645
–
ꢂ
0.01
ꢂ
4, 112,
long
2, 8, long
0.01
–
429, 515, 547,
575
432, 547, 575
431, 519, 554,
606
438, 547, 577
438, 526, 560,
606
2.6, 20
2-Zn
3-H2
412193
332012
–
–
–
–
1.5, 7
1.2, 13
3-Zn
4-H2
346438
283175
–
–
–
–
1.2, 6
1, 10
Instruments: 1H (500 MHz) and 13C (125 MHz) NMR spectra
4-Zn
443, 547, 581
297667
–
–
1, 5
were recorded using
a Bruker DPX-500 spectrometer in
[a] These values were recorded in CH2Cl2 for both the metal-free and ZnII complexes
at room temperature. [b] TA measurements were carried out in solutions in toluene at
room temperature. For the first three sets of compounds (namely, 1 to 3) the excita-
tion wavelength was 510 nm for the free bases and 540 nm for ZnII complexes, respec-
tively; for compound 4-H2, the excitation wavelength was 560 nm, and for 4-Zn it was
580 nm, respectively.
CDCl3 at 298 K using either residual solvent signals or tetra-
methylsilane as internal standards. Elemental analyses were
performed using
a Thermo Finnigan Elemental Analyzer.
MALDI-TOF mass spectra were recorded using a Bruker Mi-
croflex 2 LRF 20 spectrometer with dithranol (1,8,9-trihydrox-
yantharacene) as a matrix. UV/Vis-NIR spectra were record-
ed using a Varian Cary 50 spectrophotometer in dry CH2Cl2
at 298 K. Square-wave voltammogram measurements were
carried out using an electrochemical workstation (model
case of both the free base and ZnII complexes of 1–4. Fur-
thermore, these fast excited-state lifetimes are reduced in
magnitude in a monotonic fashion upon going from 1 to 4;
we take this as an indication that the charge-transfer effects
become more pronounced as the number of TTF substitu-
ents increases.
660B, CH Instruments) with a Pt working electrode (diameter 0.4 mm), a
Pt wire counter electrode, and a Ag wire quasi-reference electrode in
CH2Cl2 that contained 0.1m TBAPF6 under an Ar atmosphere. Ferrocene
(Fc) was added as an internal reference for the Ag quasi-reference elec-
trode. Potentials are reported versus the Fc/Fc+ couple. Square-wave vol-
tammogram scanning was conducted with a pulse amplitude of 50 mV
and a potential increment of 4 mV at a frequency of 30 Hz. The concen-
tration of all the entities was maintained at 1.0ꢄ10ꢀ3 m in CH2Cl2. In a
few representative cases, cyclic voltammetry was also performed using a
25 mm-diameter Pt microelectrode to quantify the number of electrons in-
volved in the redox processes.
Conclusion
Femtosecond transient-absorption measurements: A dual-beam femto-
second time-resolved transient absorption spectrometer was used for this
study. It consisted of a self-mode-lock femtosecond Ti:sapphire laser (Co-
herent, MIRA), a Ti:sapphire regenerative amplifier (Clark MXR, CPA-
1000) pumped by a Q-switched Nd:YAG laser (ORC-1000), a pulse
stretcher/compressor, an optical parametric generation (OPG) and opti-
cal parametric amplification (OPA) system, and an optical detection
system.[17] The amplified pulses were color-tuned by the optical paramet-
ric amplification technique. The resulting laser pulses had a pulse width
of approximately 150 fs and an average power of 5–30 mW at a 1 kHz
repetition rate in the range of 550–700 nm. The pump beam was focused
to a 1 mm diameter spot, and laser fluence was adjusted to less than ap-
proximately 1.0 mJcm2 by the use of a variable neutral-density filter. The
fundamental beam that remained in the OPG-OPA system was focused
onto a flowing water cell to generate a white-light continuum, which was
again split into two parts: one part of the white-light continuum was
overlapped with the pump beam at the sample to probe the transient,
whereas the other part of the beam was passed through the sample with-
out overlapping the pump beam. The time delay between pump and
probe beams was controlled by making the pump beam travel along a
variable optical delay. The two white continuum beams were sent to a
15 cm focal-length spectrograph (Acton Research) through optical fibers
and then detected by use of dual 512-channel photodiode arrays (Prince-
ton Instruments). The intensity of the white light that reached each 512-
channel photodiode array was processed to calculate the absorption dif-
ference spectrum at the desired time delay between the pump and probe
pulses. To obtain the time-resolved transient-absorption difference signal
at a specific wavelength, the monitoring wavelength was selected by
using an interference filter. By chopping the pump pulses at 43 Hz, the
modulated probe pulses as well as the reference pulses could be detected
by using two separate photodiodes. The output current was amplified by
In conclusion, we have reported a series of TTF-annulated
porphyrins that may be obtained by means of a one-pot pro-
cedure that involves a careful mixing of different pyrroles
with an electron-withdrawing aldehyde (C6F5CHO). The ef-
fects of adding synthetically an increasing number of TTF
substituents are reflected in the charge-transfer (CT) behav-
ior, electrochemical properties, and excited-state dynamics
of the systems in question. A clear dependence on the
number of TTF subunits is seen, with this effect being gener-
ally more substantial in the case of the metal-free forms
than in the corresponding zinc(II) complexes. In particular,
splitting was seen in the TTF-centered oxidation waves in
the square-wave voltammogram for the metal-free porphyr-
ins, but not the Zn-containing species. These findings, which
are fully supported by theoretical analyses, leads us to spec-
ulate that these two general classes of derivative (metal-free
versus zinc-containing) could ultimately find different uses.
For instance, the metal-free forms allow access to a number
of presumably addressable redox states, which means that
these compounds could find eventual application in the area
of information storage. In contrast, the zinc complexes
transfer multiple electrons at the same redox potential. Ac-
cordingly, they might find use in the construction of, for ex-
ample, chemical batteries or molecular capacitors. Studies
designed to test some of these possibilities are in progress.
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Chem. Eur. J. 2013, 19, 338 – 349

Tetrathiafulvalene-Annulated Porphyrins
FULL PAPER
using a homemade fast preamplifier, and then the resultant voltage sig-
nals of the probe pulses were gated and processed by using a boxcar
averager. The resultant modulated signal was measured by a lock-in am-
plifier and then fed into a personal computer for further signal process-
ing.
from a CH2Cl2/hexanes mixture generally afforded pure crystalline prod-
ucts.
Compound 1-H2: Yieldꢃ5%; 1H NMR (500 MHz, CDCl3, 298 K, TMS):
d=ꢀ3.03 (brs, 2H), 1.08 (t, J=7.3 Hz, 6H), 1.74 (sextet, J=7.2 Hz, 4H),
2.89 (t, J=7.3 Hz, 4H), 8.81 (s, 2H), 8.93 (d, J=4.5 Hz, 2H), 9.01 ppm
(d, J=4.0 Hz, 2H); 13C NMR (125 MHz, CDCl3, 298 K, TMS): d=13.2,
23.3, 38.5, 101.7, 104.4, 114.2, 115.3, 117.9, 128.1, 128.7, 134.3, 136.6,
137.5, 138.7, 139.5, 141.3, 143.5, 144.4, 145.6, 147.6 ppm; MALDI-TOF-
MS: m/z calcd for C54H22F20N4S6: 1299.1; found: 1299.7; elemental analy-
sis calcd (%) for C54H22F20N4S6: C 49.92, H 1.71, N 4.31, S 14.81; found:
C 49.83, H 1.84, N 4.52, S 14.44.
Compound 2-H2: Yieldꢃ3%; 1H NMR (500 MHz, CDCl3, 298 K, TMS):
d=ꢀ2.98 (brs, 2H), 1.01 (t, J=7.3 Hz, 12H), 1.78 (sextet, J=7.2 Hz,
8H), 2.81 (t, J=7.5 Hz, 8H), 8.69 (brs, 2H), 8.76 ppm (brs, 2H);
13C NMR (125 MHz, CDCl3, 298 K, TMS): d=12.1, 22.2, 37.5, 101.2,
104.0, 112.0, 113.9, 114.1, 115.4, 127.1, 127.2, 132.9, 136.2, 138.6, 142.1,
DFT calculations: Quantum mechanical calculations were performed by
the Gaussian 09 program suite.[18] All calculations were carried out by the
density functional theory (DFT) method with Beckeꢃs three-parameter
hybrid exchange functional and the Lee–Yang–Parr correlation function-
al (B3LYP);[19] a basis set of 6-31G* was employed for all atoms. The X-
ray crystallographic structures were used as initial geometries for geome-
try optimization and the peripheral propyl groups were replaced with
methyl groups to reduce the computational cost. To simulate the steady-
state absorption spectra, the time-dependent (TD)-DFT calculations at
the B3LYP/6-31G* levels were employed on the basis of the optimized
structures.
X-ray structure determination: Crystals of 4-H2 and 4-Zn grew as small,
black prisms by slow evaporation from CHCl3 in the presence of hexane.
The data were collected using a Rigaku AFC12 diffractometer using a
Saturn 724+CCD and a graphite monochromator with MoKa radiation
(l=0.71073 ꢁ). A total of 1360 (for 4-H2) and 1860 (for 4-Zn) frames of
data were collected by using w scans with a scan range of 0.58 and a
counting time of 24 (for 4-H2) and 29 s (for 4-Zn) per frame. The data
were collected at 100 K using a Rigaku XStream low-temperature device.
Details of crystal data, data collection, and structure refinement are
listed in the Supporting Information (Tables S1 and S2, respectively).
Data reduction were performed using Crystal Clear version 1.40 software
from the Rigaku Americas Corporation.[20] The structure was solved by
direct methods using SIR97[21] and refined by full-matrix least-squares on
F2 with anisotropic displacement parameters for the non-hydrogen atoms
using SHELXL-97.[22] Structure analysis was aided by use of the pro-
grams PLATON98[23] and WinGX.[24] The hydrogen atoms were calculat-
ed in ideal positions with isotropic displacement parameters set to 1.2Ueq
of the attached atom (1.5Ueq for methyl hydrogen atoms). The function,
144.2, 145.7, 148.3 ppm; MALDI-TOF-MS: m/z calcd for C64H34F20N4S12
1623.7; found: 1624.1; elemental analysis calcd (%) for C64H34F20N4S12: C
47.34, H 2.11, N 3.45, S 23.70; found: C 47.57, H 2.40, N 3.27, S 23.48.
:
Compound 3-H2: Yieldꢃ1%; 1H NMR (500 MHz, CDCl3, 298 K, TMS):
d=ꢀ2.85 (brs, 2H), 1.10 (t, J=7.3 Hz, 18H), 1.75 (sextet, J=7.2 Hz,
12H), 2.88 (t, J=7.5 Hz, 12H), 8.83 ppm (s, 2H); 13C NMR (125 MHz,
CDCl3, 298 K, TMS): d=14.3, 24.4, 39.6, 102.8, 105.5, 114.4, 115.9, 116.3,
128.8, 128.8, 135.5, 138.7, 139.8, 142.6, 146.1, 148.8 ppm; MALDI-TOF-
MS: m/z calcd for C74H46F20N4S18: 1948.3; found: 1948.8; elemental analy-
sis calcd (%) for C74H46F20N4S18: C 45.62, H 2.38, N 2.88, S 29.62; found:
C 45.31, H 2.52, N 2.79, S 29.56.
Compound 4-H2: Yieldꢃ12%; 1H NMR (500 MHz, CDCl3, 298 K,
TMS): d=ꢀ2.84 (brs, 2H), 1.11 (t, J=7.7 Hz, 24H), 1.76 (sextet, J=
7.6 Hz, 16H), 2.90 ppm (t, J=7.5 Hz, 16H); 13C NMR (125 MHz, CDCl3,
298 K, TMS): d=12.1, 22.4, 37.5, 99.9, 111.5, 111.7, 111.9, 127.1, 136.8,
139.3, 141.9, 144.3, 146.7 ppm; MALDI-TOF-MS: m/z calcd for
C84H58F20N4S24: 2272.9; found: 2273.1; elemental analysis calcd (%) for
C84H58F20N4S24: C 44.39, H 2.57, N 2.46, S 33.86; found: C 44.35, H 2.69,
N 2.38, S 33.78.
2
2
Sw(jFoj ꢀjFc j )2, was minimized, for which w=1/{[s(Fo)]2 +(0.0724P)2 +
2
2
(4.386P)} and P=(jFo j +2jFc j )/3, Rw(F2) was refined to 0.123, with
R(F) equal to 0.0452 and a goodness of fit, S=1.15. Definitions used for
calculating R(F), Rw(F2), and S are described in the literature.[25] The
data were checked for secondary extinction effects but no correction was
necessary. Neutral atom scattering factors and values used to calculate
the linear absorption coefficient are from the International Tables for X-
ray Crystallography (1992).[26] All figures were generated using
SHELXTL/PC.[27]
Preparation of the ZnII complexes of TTF–porphyrins: Complexation of
ZnII was achieved by subjecting the porphyrins in question to treatment
with ZnACHTNUGTRENUNG(OAc)2·2H2O in CHCl3/MeOH (1:1) while heating at reflux for
30 min under Ar. After washing with plenty of water, the reaction mix-
ture was dried over MgSO4. After filtration and evaporation, the metalat-
ed products were obtained in a crude form. After silica gel column chro-
matographic purification (generally involving several purification cycles),
analytically pure products were isolated in almost quantitative yield.
Compound 1-Zn: 1H NMR (500 MHz, CDCl3, 298 K, TMS): d=1.09 (t,
J=7.7 Hz, 6H), 1.74 (sextet, J=7.8 Hz, 4H), 2.88 (t, J=7.5 Hz, 4H), 8.91
(d, J=5.5 Hz, 2H), 8.99 ppm (d, J=8 Hz, 4H); 13C NMR spectra
(125 MHz, CDCl3, 298 K, TMS): d=13.1, 23.2, 38.4, 101.8, 104.7, 115.2,
116.5, 117.5, 131.9, 132.1, 136.1, 137.2, 138.8, 139.3, 141.1, 145.3, 147.8,
150.4 ppm; MALDI-TOF-MS: m/z calcd for C54H20F20N4S6Zn: 1362.5;
found: 1362.7; elemental analysis calcd (%) for C54H20F20N4S6Zn: C
47.60, H 1.48, N 4.11, S 14.12; found: C 47.53, H 1.42, N 4.05, S 14.24.
Compound 2-Zn: 1H NMR (500 MHz, CDCl3, 298 K, TMS): d=1.09 (t,
J=7.3 Hz, 12H), 1.75 (sextet, J=7.4 Hz, 8H), 2.85 (t, J=7.5 Hz, 4H),
8.83 (s, 2H), 8.91 ppm (s, 2H); 13C NMR (125 MHz, CDCl3, 298 K,
TMS): d=13.2, 23.3, 38.5, 102.5, 105.4, 113.8, 114.9, 116.9, 118.5, 132.1,
132.5, 138.7, 140.0, 141.3, 143.6, 145.6, 147.6, 150.7 ppm; MALDI-TOF-
MS: m/z calcd for C64H32F20N4S12Zn: 1687.1; found: 1687.6; elemental
analysis calcd (%) for C64H32F20N4S12Zn: C 45.56, H 1.91, N 3.32, S 22.81;
found: C 45.67, H 1.88, N 3.27, S 22.72.
Compound 3-Zn: 1H NMR (500 MHz, CDCl3, 298 K, TMS): d=1.08 (t,
J=7.5 Hz, 18H), 1.73 (sextet, J=7.5 Hz, 12H), 2.88 (t, J=7.5 Hz, 12H),
8.75 ppm (s, 2H); 13C NMR (125 MHz, CDCl3, 298 K, TMS): d=14.2,
24.7, 38.5, 103.2, 105.2, 115.1, 116.2, 117.2, 131.9, 132.2, 137.2, 138.5,
141.2, 145.5, 147.4, 150.4 ppm; MALDI-TOF-MS: m/z calcd for
C74H44F20N4S18Zn: 2011.7; found: 2011.6; elemental analysis calcd (%) for
C74H44F20N4S18Zn: C 44.18, H 2.20, N 2.79, S 28.69; found: C 43.98, H
2.13, N 2.68, S 28.55.
CCDC-885518 and -885519 contain the supplementary crystallographic
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.
Synthesis of TTF–porphyrins: TTF–porphyrins under investigation were
synthesized by mixing pyrrole, PrS-TTF-pyrrole, and pentafluorophenyl
aldehyde in an appropriate ratio in anhydrous CH2Cl2. The solution was
degassed for 15 min by bubbling with argon before a catalytic amount of
BF3·OEt2 was added. The reaction mixture was then stirred for 2 h at
room temperature. Treatment with DDQ (2.2 equiv) for 15 min, followed
by neutralization with NEt3, gave mixtures that contained various TTF–
porphyrins. The individual ratios of two different pyrrole precursors were
used to favor the formation of TTF–prophyrins that bore a different
number of PrS-TTF units annulated to the b positions. For instance, if
the stoichiometric ratio of unsubstituted pyrrole were low (and that of
the PrS-TTF-pyrrole precursor was correspondingly greater), formation
of 4-H2 was favored. Reversing this ratio favored the formation of 1-H2
and P-H2. Therefore, when the goal was to make 1-H2 in preference, a
3:1:4 ratio of pyrrole, PrS-TTF-pyrrole, and pentafluorobenzaldehyde
was employed. To obtain 2-H2 and 3-H2 instead, a ratio of 1:1:2 was
used; whereas for making 4-H2, only PrS-TTF-pyrrole and pentafluoro-
benzaldehyde were used. Purification was then effected by column chro-
matography (often multiple rounds were required to obtain pure materi-
al) and by HPLC-GPC (see Figure S5 in the Supporting Information for
partial GPC trace of different porphyrin fractions). Recrystallization
Chem. Eur. J. 2013, 19, 338 – 349
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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347

D. Lee, D. Kim, J. L. Sessler et al.
Compound 4-Zn: 1H NMR (500 MHz, CDCl3, 298 K, TMS): d=1.08 (t,
J=7.7 Hz, 24H), 1.73 (sextet, J=7.5 Hz, 16H), 2.88 ppm (t, J=7.7 Hz,
16H); 13C NMR (125 MHz, CDCl3, 298 K, TMS): d=13.2, 23.3, 38.5,
101.43, 113.4, 114.7, 115.8, 128.1, 138.1, 140.5, 141.9, 145.6, 147.5 ppm;
MALDI-TOF-MS: m/z calcd for C84H56F20N4S24Zn: 2336.3; found:
2336.8; elemental analysis calcd (%) for C84H56F20N4S24Zn: C 43.18, H
2.42, N 2.40, S 32.94, found: C 43.25, H 2.33, N 2.58, S 32.87.
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Acknowledgements
The authors thank the National Science Foundation (grant no. CHE
1057904 to J.L.S. and grant no. 0741973 for the X-ray diffractometer) and
the Robert A. Welch Foundation (grant F-1018 to J.L.S.) for financial
support. J.L.S., D.L., and D.K. thank the WCU (World Class University)
program of Korea (R32-2010-10217-0) for financial support.
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Received: July 30, 2012
Published online: November 23, 2012
Chem. Eur. J. 2013, 19, 338 – 349
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