Porphyrins fused with strongly electron-donating 1,3-dithiol-2-ylidene moieties: Redox control by metal cation complexation and anion binding

Article abstract of DOI:10.1021/ja404830y

A new class of redox-active free base and metalloporphyrins fused with the 1,3-dithiol-2-ylidene subunits present in tetrathiafulvalene, termed MTTFP (M = H₂, Cu, Ni, Zn), have been prepared and characterized. The strong electron-donating properties of MTTFP were probed by electrochemical measurement and demonstrated that oxidation potentials can be tuned by metalation of the free base form, H₂TTFP. X-ray crystal structures of H ₂TTFP, ZnTTFP, and CuTTFP revealed that a severe saddle-shape distortion was observed with the dithiole rings bent out of the plane toward one another in the neutral form. In contrast, the structure of the two-electron oxidized species (CuTFFP²⁺) is planar, corresponding to a change from a nonaromatic to aromatic structure upon oxidation. A relatively large two-photon absorption (TPA) cross-section value of H₂TTFP ²⁺ (1200 GM) was obtained for the free base compound, a value that is much higher than those typically seen for porphyrins (<100 GM). Augmented TPA values for the metal complexes were also seen. The strong electron-donating ability of ZnTTFP was further enhanced by binding of Cl^- and Br ^- as revealed by thermal electron-transfer between ZnTTFP and Li ⁺-encapsulated C₆₀ (Li⁺@C₆₀) in benzonitrile, which was switched on by the addition of either Cl^- or Br^- (as the tetrabutylammonium salts). The X-ray crystal structure of Cl^--bound ZnTTFP was determined and provided support for the strong binding between the Cl^- anion and the Zn ²⁺ cation present in ZnTTFP.

Full text of DOI:10.1021/ja404830y

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Article
Porphyrins Fused with Strongly Electron Donating 1,3-Dithole-2-ylidene
Moieties. Redox Control by Metal Cation Complexation and Anion Binding
Nathan L. Bill, Masatoshi Ishida, Steffen Bähring, Jong Min Lim, Sangsu Lee,
Christina M. Davis, Vincent M. Lynch, Kent Albin Nielsen, Jan O. Jeppesen,
Kei Ohkubo, Shunichi Fukuzumi, Dongho Kim, and Jonathan L. Sessler
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/ja404830y • Publication Date (Web): 21 Jun 2013
Downloaded from http://pubs.acs.org on June 22, 2013
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Porphyrins Fused with Strongly Electron Donating 1,3-Dithiol-2-
ylidene Moieties. Redox Control by Metal Cation Complexation and
Anion Binding
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Nathan L. Bill,a Masatoshi Ishida,b Steffen Bähring,c Jong Min Lim,b Sangsu Lee,b Christina M. Davis,a
Vincent M. Lynch,a Kent A. Nielsen,c Jan O. Jeppesen,c Kei Ohkubo,d Shunichi Fukuzumi,d,e* Dongho
Kim,b* and Jonathan L. Sesslera,b*
a Department of Chemistry and Biochemistry, University StationꢀA5300, The University of Texas at Austin, Austin, Texas 78712
b Department of Chemistry, Yonsei University, Seoul, 120ꢀ750, Korea
c Department of Chemistry, Physics, and Pharmacy, University of Southern Denmark, Denmark
d Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA, Japan Science and Techꢀ
nology Agency, Suita, Osaka 565ꢀ0871, Japan
e Department of Bioinspired Science, Ewha Womans University, Seoul 120ꢀ750, Korea
ABSTRACT: A new class of redox active free base and metalloporphyrins fused with the 1,3ꢀdithiolꢀ2ꢀylidene subunits present in
tetrathiafulvalene, termed MTTFP (M = H2, Cu, Ni, Zn), have been prepared and characterized. The strong electron donating propꢀ
erties of MTTFP were probed by electrochemical measurement and demonstrated the oxidation potentials can be tuned by metaꢀ
lation of the free base form, H2TTFP. Xꢀray crystal structures of H2TTFP, ZnTTFP, CuTTFP, and the twoꢀelectron oxidized
species (CuTTFP2+) revealed that a severe saddle shape distortion was observed with the dithiole rings bent out of the plane toꢀ
wards one another in the neutral form. In contrast, the structure of CuTTFP2+ is planar, corresponding to a change from a nonꢀ
aromatic to aromatic structure upon oxidation. A relatively large twoꢀphoton absorption (TPA) crossꢀsection value of H2TTFP2+
(1200 GM) was obtained for the free base compound, a value that is much higher than those typically seen for porphyrins (<100
GM). Augmented TPA values for the metal complexes were also seen. The strong electron donating ability of ZnTTFP was further
enhanced by binding of Cl– and Br– as revealed by thermal electronꢀtransfer between ZnTTFP and Li+–encapsulated C60 (Li+@C60)
in benzonitrile, which was “switched on”by the addition of either Cl– or Br– (as the tetrabutylammonium salts). The Xꢀray crystal
structure of Cl–ꢀbound ZnTTFP was determined and provided support for the strong binding between the Cl– anion and the Zn2+
cation present in ZnTTFP.
Recently, we reported that a sterically restricted “rosarin”, a
hexapyrrolic expanded porphyrin, is capable of transitioning
Introduction
Precise control and thorough understanding of the electronꢀ
ic structure and reactivity of redox active molecules is of
significant importance for the development of new catalysts
and chargeꢀseparation devices, among other applications.1ꢀ4
The exceptional optoelectronic and redox properties of porꢀ
phyrins have driven efforts to prepare derivatives with more
than one accessible and wellꢀdefined electronic state (e.g.,
aromatic, nonaromatic, and antiaromatic). In recent years,
this challenge has been met in a number of instances via the
use of soꢀcalled expanded porphyrins, analogues of porphyꢀ
rins containing larger conjugated peripheries or a greater
number of pyrrolic subunits than present in porphyrins.5
However, there remains a need for smaller, electronically
switchable materials that more closely resemble porphyrins.
Of particular interest would be systems that provide for preꢀ
cise, tunable control of the redox potential over a range that
allows for thermal electron transfer interactions with comꢀ
mon donors or acceptors. Also of interest would be simpleꢀ
toꢀprepare porphyrin analogues that allow access to stable 4n
and 4n + 2 πꢀelectron configurations, as well as intermediate
4n +1 radical states.
between its antiaromatic and reduced aromatic electronic
forms via a stable oneꢀelectron oxidized radical state.6 Howꢀ
ever, we are unaware of any tetrapyrrolic species that allow
access to an analogous 4n + 1 πꢀelectron radical oxidation
state and which permit switching between two different
closed shell electronic states under standard laboratory condiꢀ
tions. Such putative tetrapyrrolic species are attractive since,
in principle, their redox properties could be tuned by metaꢀ
lation as observed for normal porphyrins. Further fineꢀtuning
of the redox properties could likewise be achieved by coordiꢀ
nation of an axial ligand to a bound metal center.7
Here we report a new πꢀextended analogue of tetrathiafulꢀ
valene8 (TTF), namely the bis(1,3ꢀdithiolꢀ2ꢀylidene)
quinoidal porphyrin (H2TTFP) and its Cu(II), Ni(II), and
Zn(II) derivatives (MTTFP; M = CuII, NiII, and ZnII). In preꢀ
vious work, we reported TTFꢀbearing porphyrins wherein the
TTF subunits were directly annulated to the porphyrin core.9
MTTFP differs from these earlier systems in that it is a diꢀ
rect “extended”analogue of TTF. As such, it was expected
to combine the desirable optical features of the known, but
not extensively studied, quinoidal porphyrins10 with the redox
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features of the soꢀcalled “exTTF” class of compounds (e.g.,
solid in 27% yield. The zinc(II) (ZnTTFP), copper(II)
9,10ꢀbis(1,3ꢀdithiolꢀ2ꢀylidene)ꢀ9,10ꢀdihydroꢀanthracene).11
As detailed below, this combination permits access to three
stable oxidation states, as well as to the rich metalation chemꢀ
istry of porphyrins. This latter attribute allows the electronic
and redox properties of MTTFP to be tuned without addiꢀ
tional synthetic modification. Additionally, complexation of
either a chloride or bromide anion to a bound metal center
permits fineꢀtuning of the redox properties of the MTTFP.
This, in turn, enables control of electron transfer reactions,
including specifically thermal processes involving transfer of
an electron from ZnTTFP to Li+–encapsulated C60 (Li+@C60)
in benzonitrile (PhCN). This combination of chemical feaꢀ
tures, as well as the separate metalꢀ and anionꢀbased control
of the redox properties is not possible with the previously
reported exꢀTTF systems. Nor, is it attainable with simple
porphyrin derivatives. A further notable feature of the present
system is that, in contrast to unmodified and dithioleꢀfree
quinoidal porphyrins, the MTTFPs reported herein display
relatively large twoꢀphoton absorption (TPA) crossꢀsection
values.
(CuTTFP), and nickel(II) (NiTTFP) complexes were then
obtained in good yields by subjecting the freeꢀbase to standꢀ
ard acetate salt metal insertion.14
A quinoidal structure, such as the one assigned to diketone
2, was assigned to H2TTFP and its metalated derivatives
1
after examination of the H NMR spectrum. Although tauꢀ
tomerization of the exocyclic double bonds would result in a
fully conjugated core, H2TTFP appears to be nonꢀaromatic.
This is consistent with what has been observed in the case of
recently reported alkylidene porphyrins10 and is specifically
supported by the fact that the NꢀH protons within the porphyꢀ
rinoid core resonate at 12.5 ppm (Figure 1; note that the full
spectrum is shown in Figure S1 in the Supporting Inforꢀ
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mation (SI)). In addition, the outer
βꢀCꢀHs of the pyrrolic
rings give rise to signals at 6.5 and 6.9 ppm. Consequently,
1
the H NMR spectrum is strongly indicative of a lack of diaꢀ
tropic ring current, and a corresponding lack of aromaticity in
H2TTFP. A nonꢀaromatic quinoidal core is thus taken to be
the dominant species in solution.
Results and Discussion
Scheme 1. Synthesis of H2TTFP and its Metal Derivatives,
MTTPS
Figure 1. Partial 1H NMR spectra of H2TTFP (top) and
H2TTFP•2PF6 (bottom) recorded in DMSOꢀd6 at 298 K.
Spectroscopic Studies of MTTFP. In the case of MTTFP
(M = Zn, Cu, Ni), evidence for metal complexation came
from highꢀresolution mass spectrometric (HRMS) analyses.
1
The H NMR spectra of the diamagnetic Ni(II) and Zn(II)
complexes revealed spectral patterns and chemical shifts
similar to those for the corresponding βꢀpyrrolic and mesoꢀ
phenyl proton signals of H2TTFP (Figures S3–S5). A lack of
NꢀH proton resonances is consistent with metal coordination
within the macrocyclic core present in H2TTFP. On the basis
of these spectroscopic analyses, the resulting complexes,
ZnTTFP and NiTTFP were also assigned a quinoidal strucꢀ
ture analogous to H2TTFP.
An EPR spectrum of CuTTFP recorded in CH2Cl2 at 298
K is typical of what is expected for a square planar Cu(II)
complex with hyperfine interactions between the d9 configꢀ
ured copper ion and the four magnetically equivalent 14N
atoms of the ligand (Figure 2a). The nearꢀperfect agreement
between the observed and simulated spectra was obtained
with the isotropic g value of g = 2.090 and superꢀhyperfine
splitting of a(Cu) = 91 G, a(N) = 16 G by changing the linꢀ
ewidth (ꢀHmsl) depending on the mI values of Cu (Figures 2b
and 2c). The observed a(Cu) value is smaller than those of
typical Cu(II) porphyrin complexes.15 This difference is asꢀ
cribed to the fact that the unpaired electron density in
CuTTFP is largely centered on the macrocycle and the assoꢀ
ciated orbital has dx2ꢀy2 character. This acts to delocalize ca.
50% of the spin density away from the copper center, as inꢀ
Synthesis of MTTFP. The synthesis of H2TTFP is shown
in Scheme 1. It involves as the key step the triethylphosphiteꢀ
mediated crossꢀcoupling between diketoporphyrinogen 2 and
the known TTF precursor 3.33 The Lindsey group has previꢀ
ously reported the preparation of 2, through a thallium proꢀ
moted oxidation of 5,15ꢀdiphenylporphine (1).12 However, in
our hands, we found that compound 2 was more conveniently
prepared (1 step; 56% yield) by treating 1 with PbO2 in acꢀ
cord with a decades old procedure for the synthesis of xanꢀ
thoporphryinogen.13 Coupling of 2 and 3 then afforded the
desired product H2TTFP, as an intensely colored dark green
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ferred from the theoretical spin density map obtained from
UB3LYP/LanL2DZ calculations (Figure 2d).
tribution involving an intramolecular charge transfer from the
dithiole subunits to the central macrocyclic core (cf. Figure
S7).17 Upon metalation, similar low energy broad absorption
bands are seen (Figure 3) above 650 nm. The order of the
redꢀshift in these energy transitions is as follows: ZnTTFP >
CuTTFP > NiTTFP. In the case of ZnTTFP, a small inꢀ
tense band around 850 nm is typically seen in the UVꢀvis
spectrum. This band is thought to reflect the presence of a
radical cation impurity formed in small amounts under ambiꢀ
ent aerobic conditions. The redox properties and dedicated
formation of this and other oxidized forms of MTTFP are
discussed later on in the text.
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1.6
1.4
H2TTFP
ZnTTFP
CuTTFP
NiTTFP
1.2
1
0.8
0.6
0.4
0.2
0
300
450
600
750
900
Wavelength (nm)
Figure 3. UV/Vis absorption profiles of the metal derivatives of
H2TTFP recorded in CH2Cl2 including ZnTTFP (red),
CuTTFP (orange), and NiTTFP (blue).
(d)
The excited state dynamics of H2TTFP were further exꢀ
plored by femtosecond (fs) transient absorption (TA) specꢀ
troscopy in toluene. The transient species produced from
H2TTFP by fs laser irradiation at 650 nm exhibited both
broad excited state absorption (ESA) and ground state
bleaching (GSB) features across the entire spectral region as
shown in Figure 4a. The temporal profile of the prominent
GSB signal at 660 nm was fitted to a biexponential function.
This fitting revealed a short time constant of ≈77 ps, as well
as a longer time constant (>500 ps) ascribed to a subsequent
transition to the triplet manifold. Presumably, this latter interꢀ
system crossing reflects the heavy atom effect of the sulfur
atoms.
Figure 2. (a) ESR spectrum of CuTTFP recorded in CH2Cl2 at
298 K, (b) the computer simulated spectrum; a(Cu) = 91 G,
a(4N) = 16 G, DHmsl = 53, 27, 12, and 9.0 G at mi = ꢀ3/2, ꢀ1/2,
1/2 and 3/2, respectively, (c) plot of ꢀHmsl vs mi, and (d) spin
density map obtained from UB3LYP/LanL2DZ calculations.
The TPA spectrum of H2TTFP was also recorded in
CH2Cl2 using the open aperture zꢀscan method (Figure 5a and
5b). This analysis revealed spectral features coincident with
the lowest oneꢀphoton absorption band. The maximum TPA
crossꢀsection value, σ(2) = 1700 GM, was attained upon exciꢀ
tation at 1400 nm. This value is notably larger than those for
analogous (but dithioleꢀfree) quinoidal porphyrins (σ(2) = ca.
500 GM at 1200 nm).16 We propose that the unusual σꢀdonorꢀ
πꢀacceptorꢀσꢀdonor structure of H2TTFP gives rise to the
relatively enhanced nonlinear optical response. The TPA
properties of the metal complexes, MTTFPs (M = Zn, Ni,
The UVꢀvisible spectrum of H2TTFP recorded in CH2Cl2
at 298 K supports the assignment of the system as being nonꢀ
aromatic. For instance, broad absorption bands are seen at
λ
max = 650 nm (
ε ε
= 58000 Mꢀ1), 429 nm ( = 53700 Mꢀ1), and
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317 nm (
ε
= 38700 Mꢀ1) (Figure 3). These spectral features
resemble those of the reported quinoidal porphyrins.16 The
molecular orbitals (MOs), obtained from B3LYP/6ꢀ31G(d)
calculations, provide support for the conclusion that the highꢀ
est occupied MO (HOMO) is mainly localized on the dithiole
subunits. In contrast, the lowest unoccupied MO (LUMO) is
primarily centered within the macrocycle. This is taken as
evidence that the observed optical transition includes a conꢀ
Cu) were also examined (Figure S9). The ZnTTFP (σ(2)
=
1100 GM at 1300 nm), NiTTFP (σ(2) = 510 GM at 1300 nm)
and CuTTFP (σ(2) = 450 GM at 1300 nm) complexes gave
values that were reduced compared to H2TTFP, but still relaꢀ
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tively large with respect to the corresponding metalated
rings bent out of the plane towards one another (cf. Figures
porphryins.18
6aꢀb and Figure S10). A distinct lack of planarity is evident.
Such a finding provides support for the conclusion drawn
from the spectroscopic analyses, namely that the MTTFPs
are nonꢀaromatic.
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Cu
Cu
(b)
(d)
Cu
Cu
Figure 6. Crystal structures of CuTTFP (a) front view and (b)
side views and of CuTTFP•2OTf (c) front view and (d) side
views. The thermal ellipsoids represent 50% probability. The
triflate counteranions of CuTTFP•2OTf and mesoꢀphenyl
groups (in the side views) are omitted for clarity.
The electrochemical properties of H2TTFP and its metalatꢀ
ed counterparts were further analyzed by cyclic voltammetry
(CV) (Figure 7). In the case of the free base, H2TTFP, a reꢀ
dox wave at ꢀ0.01 V (vs Fc/Fc+) was seen. A cathodic/anodic
peak separation of 215 mV was also seen in the case of the
metalꢀfree system. This was taken as initial evidence that a
large conformational change occurs during this redox process.
Shifts in the oxidation potentials were seen upon metalation.
The nickel complex, NiTTFP displayed a nominal shift of ꢀ
0.008 V, making it only slightly easier to oxidize than the
parent compound, H2TTFP. However, the complexes,
CuTTFP and ZnTTFP displayed marked anodic shifts to ꢀ
0.186 V and ꢀ0.245 V, respectively. These findings provide
support for the notion that the oxidation potential of the bisꢀ
dithiole quinoidal porphyrin H2TTPF can be tuned by simple
metal cation complexation.
Insight into the number of electrons being transferred durꢀ
ing the oxidation of H2TTFP and its metalated counterparts
was inferred from the full CV of CuTTFP recorded in
CH2Cl2 (Figure 8 and Figure S14). A reversible oneꢀelectron
feature ascribed to the reduction of CuTTFP is observed at ꢀ
1.580 V whose size is approximately half that of the TTFP
oxidation peaks; on this basis we propose that twice as many
electrons are being transferred (2 e–) in the TTFP oxidation
than in the Cu reduction (1 e–).19
Figure 4. Femtosecond transient absorption spectra and decay
profiles of (a) free base H2TTFP recorded in toluene at 298 K
and (b) H2TTFP•2ClO4 recorded in acetonitrile at 298 K obꢀ
tained following excitation at 650 and 600 nm, respectively.
2200
(a)
(b)
0.6
0.5
0.4
0.3
0.2
0.1
0.0
2000
1800
1600
1400
1200
1000
800
OPA
TPA
980 GM
1400 nm
1300 nm
1700 GM
600
ε
ε
ε
ε
400
1500 GM
1200 nm
200
-30 -20 -10
0
10 20 30
0
Z / mm
400
600
800
Wavelength (nm)
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
7000 (d)
6000
(c)
OPA
TPA
1500 nm
1400 nm
1300 nm
900 GM
400 GM
5000
4000
3000
1200 GM
2000
ε
ε
ε
ε
1000
1100 GM
1200 nm
0
400
600
800
-30 -20 -10
0
10 20 30
Wavelength (nm)
Z / mm
Figure 5. Oneꢀphoton absorption (OPA) and twoꢀphoton absorpꢀ
tion (TPA) spectra of (a) H2TTFP and (c) H2TTFP•2ClO4 with
(b and d) Zꢀscan curves recorded in CH2Cl2 and acetonitrile,
respectively at 298 K.
Crystal Structures and Redox Properties of MTTFP.
Single crystals suitable for Xꢀray diffraction analysis of
H2TTFP (1:1 mixture of CH2Cl2 and acetonitrile), CuTTFP
(CH2Cl2), and ZnTTFP (1:1 mixture of CH2Cl2 and tetrahyꢀ
drofuran) were grown by slow evaporation. In all cases, a
severe saddle shape distortion was seen with the dithiole
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6cꢀd and S15). The bond lengths between the dithiole rings
and the mesoꢀcarbon atom of porphyrin also increased upon
oxidation, as would be expected for the conversion of a
C(sp2)=C(sp2) double bond (average length = 1.364 Å in the
case of CuTTFP) to a single bond (length = 1.48 Å from
CuTTFP•2OTf). These structural features are thus conꢀ
sistent with the proposed aromatic formulation.
The steadyꢀstate UVꢀvis absorption spectrum of
H2TTFP•2PF6, recorded in acetonitrile at 298 K, revealed
features characteristic of a porphyrin (e.g., tetraphenylporꢀ
phyrin). For instance, well resolved Qꢀlike bands and an inꢀ
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tense Soret band at 410 nm (ε
= 121000 Mꢀ1) were seen (Figꢀ
ure 5b). The porphyrinꢀlike MO density distributions of
H2TTFP2+ is in good agreement with the experimental specꢀ
trum (Figure S16 and S17).20 However, differences from
normal porphyrins were revealed in the fs TA spectra of the
dication as recorded in acetonitrile. In particular, an ultraꢀ
short singlet excited state lifetime of 26 ps (with a component
with a prolonged decay profile ascribed to population of the
triplet state) was seen in Figure 4b. This short lifetime21 is
consistent with the nonꢀfluorescent nature of the dication and
is thought to reflect electronic coupling with the dithiole
moieties.
Further underscoring the differences relative to porphyrins
(taken as ostensibly analogous control aromatic systems) is
the relatively large TPA crossꢀsection value of H2TTFP2+.
Specifically, a TPA value of 1200 GM was recorded upon
excitation at 1300 nm (Figures 5c and 5d). These values are
considerably higher than those typically seen for porphyrins
for which TPA values of <100 GM are found.18 These differꢀ
ences are ascribed to the charged dithiole sites that serve to
perturb the intrinsic electronic structure of the central porꢀ
phyrin core present in H2TTFP2+.22
Figure 7. (a) Cyclic voltammograms (CVs) of H2TTFP,
NiTTFP, CuTTFP, and ZnTTFP (E1/2 = ꢀ0.097, ꢀ0.105, ꢀ0.186
and ꢀ0.245 vs ferrocene/ferrocenium couple (Fc/Fc+), respectiveꢀ
ly). All CVs were recorded in CH2Cl2 at 298 K under identical
conditions: 50 mV/s scan rate, 1 mM solution of the compound
under study, 100 mM TBAPF6.
Figure 8. Cyclic voltammogram (CV) showing the first oxidaꢀ
tion and reduction features of CuTTFP (referenced to Fc/Fc+).
The CV was recorded in CH2Cl2 at 298 K: 50 mV/s scan rate, 1
mM solution of the compound under study, 100 mM TBAPF6.
Scheme 2. Stepwise oxidation of H2TTFP.
Chemical Oxidation of H2TTFP. The doubly oxidized
form of H2TTFP could also be prepared by chemical means
(Scheme 2). Specifically, it was found that by dissolving
H2TTFP in CH2Cl2 and adding an excess of crystalline nitroꢀ
syl hexafluorophosphate, the oxidized product could be preꢀ
cipitated from solution in quantitative yield in the form of its
PF6 salt (H2TTFP•2PF6). In a similar fashion, complexes
with other counteranions were easily obtained by altering the
identity of the oxidant used. The conversion of H2TTFP to
H2TTFP2+ gave rise to distinctive spectral changes. In the 1H
NMR spectrum (Figure 1) of the dication, H2TTFP•2PF6, the
NꢀH protons are shifted upfield to –2.8 ppm, while the βꢀ
hydrogens on the porphyrin core are shifted downfield. These
changes are thought to reflect the macrocyclic diamagnetic
ring current of the central tetrapyrrolic unit. The negative
NICS(0) values of −12.1 ppm at the center of the core macꢀ
rocycle of H2TTPF2+ provides further support for the asꢀ
signment of H2TTFP2+ as being aromatic (cf. Figure S13).
The singly oxidized radical cation form, H2TTFP•+, could
be prepared in situ by the careful addition of tris(4ꢀ
bromophenyl)aminium hexachloroantimonate (soꢀcalled
“magic blue”) in CH2Cl2.23 The formation of a species with
an intense absorption band at 930 nm was seen, with a maxꢀ
imal intensity being observed upon the addition of one equiv
of oxidant (Figure 9).24 When less than one molar equivalent
of magic blue is added, a species with an absorption maxiꢀ
mum (λmax) at 760 nm is observed. This peak is thought to
reflect protonation of H2TTFP (for which enhanced acidity is
expected due to the saddleꢀtype distortion of the porphyrinoid
core24) by residual acid present in the oxidant.25 Support for
this suggestion comes from the observation that adding triꢀ
fluoroacetic acid to the freeꢀbase species H2TTFP in the
A single crystal Xꢀray diffraction structure of the doubly
oxidized dication species derived from CuTTFP (i.e.,
CuTTFP•2OTf) revealed a highly planar geometry (Figures
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absence of magic blue likewise gives rise to an analogous
760 nm spectral feature while leading to a decrease of the
original absorption peak at 650 nm (Figure S18). Furtherꢀ
more, chemical oxidation of ZnTTFP (which lacks the basic
pyrrolic sites present in H2TTFP) with magic blue fails to
produce a species with a λmax ≈ 760 nm (Figure S19).
Electron paramagnetic resonance (EPR) spectroscopic
analysis of H2TTFP•+ (930 nm absorption band) revealed
features at g┴ = 2.001 and g// = 2.006 at 77 K,26 thus supportꢀ
ing assignment of this oxidized species to the radical cation.
Such readily accessible 4n + 1 πꢀelectron radical cation speꢀ
cies are not attainable with either simple quinoidal porphyꢀ
rins or the anthraceneꢀderived exTTF species reported earlier.
The behavior of MTTFP also stands in contrast to what is
seen for the previously reported TTF porphyrins, where TTFꢀ
centered, but not porphyrinoid 4n+1 πꢀelectron, radicals may
be observed9
ing ZnTTFP and Li+@C60 resulted in thermal electron transꢀ
fer from ZnTTFP to Li+@C60. This is evidenced by the genꢀ
eration of spectral features ascribable to ZnTTFP•+
(λmax
=
•–
865 nm) and Li+@C60
(λmax = 1035 nm) as seen in Figure
10a.28 The 1:1 stoichiometry of electron transfer between
ZnTTFP and Li+@C60 in the presence of TBACl was conꢀ
firmed by a Job plot (Figure S22). The formation of
•–
ZnTTFP•+ and Li+@C60 was further confirmed by EPR
spectral analyses, which revealed a superposition of signals
corresponding to both species (Figure S23). The yield of the
electronꢀtransfer products increased with increasing concenꢀ
tration of Li+@C60. The electronꢀtransfer equilibrium conꢀ
stant (Ket), determined from the titration shown in Figure 10b,
is 0.53.
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(a)
The stability of H2TTFP•+ proved to be highly dependent
on the choice of solvent. In contrast to what was seen in pure
CH2Cl2, in polar solvents, such as acetonitrile, PhCN or mixꢀ
tures of these solvents in CH2Cl2, the spectral features correꢀ
sponding to H2TTFP•+ were not observed (Figure S20). This
is ascribed to disproportionation of the radical cation
+
•
H2TTFP . Disproportionation leads to formation of the
closed shell neutral and dication forms of H2TTFP, respecꢀ
tively, in analogy to what was found in the exTTFs.27 An
alternative explanation, involving dimerization to form a
closed shell, EPR silent dimer (e.g., [(H2TTFP)2] 2+), is ruled
out on steric grounds; the large mesoꢀphenyl groups are exꢀ
pected to preclude the necessary intermolecular contact.
Wavelength, nm
(b)
[Li+@C60], M
Figure 10. (a) UV/vis absorption changes in electron transfer
from ZnTTFP (10 ꢁM, black) to Li+@C60 (final: red) in the
presence of 1.0 mM TBACl in PhCN at 298 K. (b) Plot of
absorbance at 460 nm vs the concentration of Li+@C60.
Figure 9. (a) UV/vis/NIR absorption spectra of H2TTFP recordꢀ
ed in CH2Cl2 at 298 K in the presence of increasing quantities of
magic blue up to one molar equivalent; [H2TTFP] = 10 ꢁM.
–
Inset shows the EPR spectrum of H2TTFP•+ (as the SbCl6 salt)
prepared via the addition of 1 equiv of magic blue. (b) Spin denꢀ
sity map of H2TTFP•+ obtained at the UB3LYP/6ꢀ31G(d) level.
Fine Redox Control of ZnTTFP by Anion Binding. The
strong electron donor ability of ZnTTFP is further enhanced
by axial coordination of chloride anion, Cl– as shown via its
use as an external donor in a thermal electron transfer reacꢀ
tion. In these experiments, Li+–encapsulated C60 (Li+@C60)
was chosen as the electron acceptor, because Li+@C60 has a
oneꢀelectron reduction potential (i.e., 0.13 V (vs SCE)),
which is slightly less positive than that of ZnTTFP (cf. Figꢀ
ure 7).28 No evidence of electron transfer from ZnTTFP to
Li+@C60 was seen in PhCN at 298 K. Specifically, addition
of tetraꢀnꢀbutylammonium perchlorate (TBAClO4: 1.0 mM)
to a PhCN solution of ZnTTFP and Li+@C60 resulted in no
change in the optical features (Figure S21). However, addiꢀ
tion of chloride anion as TBACl to a PhCN solution containꢀ
Figure 11. (a) Cyclic voltammogram (CV) of ZnTTFP (0.10
mM) recorded in the presence of TBAPF6 (100 mM) in PhCN.
(b) CV of ZnTTFP in the same solvent after the addition of
TBAClO4 (20 mM). (c) CV of ZnTTFP recorded under identical
conditions after addition of TBACl (20 mM).
The negative shift in the (twoꢀelectron) oxidation potential
(Eox) of ZnTTFP induced by binding of Cl– was confirmed
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by CV measurements, as shown in Figure 11. The Eox value
plex ZnTTFP can ligate an axial ligand, thereby allowing the
electronic properties to be tuned via two different modes
(metal complexation and anion coordination). In the case
where Cl– or Br– was bound to the zinc center of ZnTTFP,
the electron donor ability of the complex was further enꢀ
hanced and this fineꢀtuning makes possible electron transfer
from ZnTTFP to Li+@C60. Upon addition of pyridine to the
chloride complex, back electron transfer took place, demonꢀ
strating the necessity of the Znꢀhalide bond for the forward
reaction, as well as the versatility of the system.
The salient features of the MTTFPs, namely access to
three distinct 4n + y (y = 0, 1, 2) πꢀelectron configurations,
fineꢀtuning of the redox features through metal coordination
and anion complexation, thermal electron transfer to Li+@C60,
and high TPA values, are not observed in the case of either
other easyꢀtoꢀaccess tetrapyrrolic derivatives (including
quinoidal porphyrins and TTFꢀporphyrins) or the anthraceneꢀ
derived exTTF systems. We thus think that present systems
may have a role to play in advancing our understanding of
how modifications of relatively simple structures can be
translated into potentially useful properties and electronic
applications.
of ZnTTFP in the presence of TBAPF6 in PhCN was deterꢀ
mined to be 0.21 V vs SCE. The Eox value remained the same
after the addition of TBAClO4. However, the addition of
TBACl resulted in a cathodic shift of the Eox value to 0.13 V
vs SCE. Since the Ered value of Li+@C60 is 0.13 V vs SCE,
electron transfer from ZnTTFP to Li+@C60 becomes therꢀ
modynamically feasible as the result of the complexation of
the Cl– anion to ZnTTFP. The binding of Cl– to ZnTTFP
was confirmed via a single crystal Xꢀray diffraction analysis.
The resulting structure, shown in Figure 12, reveals that the
Cl– is coordinated to the Zn2+ center present in ZnTTFP.
The charge separated species induced by the presence of
chloride can be reverted to the neutral form via the addition
of excess pyridine; presumably this reflects competitive bindꢀ
ing to the zinc center and displacement of the Cl– ligand
(Figure S24). In this “molecular switch”, the thermal elecꢀ
tron transfer from ZnTTFP to Li+@C60 is“turned on” via
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the addition of chloride and is “turned off”upon treatment
with excess pyridine. This provides an additional level of
control over a process that is not reflected in the chemistry of
either exTTFs or quinoidal porphyrins.
Cl-
•
Experimental Section
Li+@C60
[Zn(Cl)TTFP]+
•
[Li@C60
]
ZnTTFP
Pyridine
Materials and General Methods. All chemicals were obꢀ
tained from Acros chemicals or TCI America in reagent
grade purity and used without further purification unless othꢀ
erwise noted. PhCN was distilled over P2O5 immediately
before use, collecting the middle 50%. Proton (400 MHz) and
13Carbon (100 MHz) NMR spectra were measured using a
As would be expected, complexation of Br– to ZnTTFP
also appears to be facile. This is evidenced by the fact that
the addition of TBABr to a premixed PhCN solution of
ZnTTFP and Li+@C60 also results in electron transfer from
ZnTTFP to Li+@C60 in analogy to what is seen for Cl– (Figꢀ
ure S25).
Varian 400/54/ASW instrument. Chemical shifts (δꢀscale) are
reported in ppm relative to residual solvent and internal
standard signals (DMSOꢀd6: 2.50 ppm and acetoneꢀd6: 2.05
1
(a)
(b)
ppm for H, and CD3Cl: 77.2 ppm, and CD3CN: 1.3 ppm for
13C). UVꢀVisꢀNIR spectra were recorded on a Cary 5000
spectrometer in a 1 cm quartz cuvette. HRMS were recorded
on an Agilent 6530 Accurate Mass QTOF/LCꢀMS (ESI) and
a Ionospec 9.4 FTꢀICR (MALDI).
TBA+
Zn
TBA+
Cl-
Cl-
Zn
Electrochemical Measurements. All electrochemical
measurements were carried out using a CVꢀ50 electrochemiꢀ
cal analyzer in dichloromethane (CH2Cl2) at 298 K using 0.1
M TBAPF6 as the supporting electrolyte. A glassy carbon
working electrode was used, as well as a platinum wire counꢀ
ter electrode and an Ag/AgCl or Ag/AgNO3 reference elecꢀ
trode. The working electrode was routinely polished using
standard polishing procedures.
EPR Measurements. The EPR spectra were recorded on a
JEOL Xꢀband spectrometer (JESꢀRE1XE) under nonꢀ
saturating microwave power conditions (1.0 mW) operating
at 9.2 GHz. The magnitude of the modulation was chosen to
optimize the resolution and the signal to noise ratio (S/N) of
the observed spectrum (modulation width, 20 G; modulation
frequency, 100 kHz). The g values were calibrated using an
Mn2+ marker.
Femtosecond Transient Absorption Measurements. The
femtosecond timeꢀresolved transient absorption (TA) specꢀ
trometer consisted of NIR optical parametric amplifier (OPA)
system (Quantronix, Pallitra) pumped by a Ti:sapphire reꢀ
generative amplifier system (Quantronix, IntegraꢀC) operatꢀ
ing at 1 kHz repetition rate and an optical detection system.
The generated OPA output signals had a pulse width of ~ 100
Figure 12. Two views of the single crystal Xꢀray diffraction
structure of ZnTTFP•TBACl at 50% thermal ellipsoids probaꢀ
bility level. The solvent of crystallization and the hydrogen atꢀ
oms are omitted for clarity.
Conclusion
In conclusion, we have synthesized a new class of quinoidal
porphyrin analogues (MTTFP) capable of existing in three
distinct oxidation states each separated by oneꢀelectron.
When subject to twoꢀelectron oxidation, aromatization is
induced. This leads to conversion from a saddleꢀshaped
nonaromatic species to a planar aromatic dicationic porphyrin,
which exhibits a relatively large TPA crossꢀsection value.
The redox potentials of MTTFP may be tuned by metalation,
with the associated electrochemical analyses revealing that
MTTFP should be capable of acting as a strong electron
donor. A particular advantage of these systems is that they
are readily metalated and as demonstrated by the zinc comꢀ
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Density Functional Theory (DFT) Calculations. Theoretical
fs in the range of 480ꢀ700 nm which were used as pump
pulses. White light continuum (WLC) probe pulses were
generated using a sapphire window (3 mm of thickness) by
focusing of small portion of the fundamental 800 nm pulses.
The time delay between pump and probe beams was carefully
controlled by making the pump beam travel along a variable
optical delay (Newport, ILS250). Intensities of the spectrally
dispersed WLC probe pulses are monitored by two miniature
spectrographs (OceanOptics USB2000+). To obtain the timeꢀ
resolved transient absorption difference signal (ꢀA) at a speꢀ
cific time, the pump pulses were chopped at 25 Hz and abꢀ
sorption spectra intensities were saved alternately with or
without the pump pulse. Typically, 6000 pulses were used to
excite the samples to obtain the TA spectra at a particular
delay time. The polarization angle between pump and probe
beam was set at the magic angle (54.7°) in order to prevent
polarizationꢀdependent signals. Crossꢀcorrelation fwhm in
pumpꢀprobe experiments was less than 200 fs and chirp of
WLC probe pulses was measured to be 800 fs in the 400ꢀ
1200 nm region. To minimize chirp, all reflection optics were
used in the probe beam path and a 2 mm path length quartz
cell was employed. After the TA experiments, the absorption
spectra of all compounds were carefully checked so as to
avoid artifacts arising from, e.g., photoꢀdegradation or photoꢀ
oxidation of the samples in question.
calculations were performed with the Gaussian09 program suite
using a supercomputer (KISTI, IBM).29 All optimized structures
were obtained using the density functional theory (DFT) calculaꢀ
tions with Becke’s threeꢀparameter hybrid exchange functionals
and the LeeꢀYangꢀParr correlation functional (B3LYP) employꢀ
ing the 6ꢀ31G(d) basis set for all atoms.30 The global ring centers
for the NICS(0) values were designated at the nonꢀweighted
mean centers of the macrocycles. The NICS(0) value was obꢀ
tained with gauge independent atomic orbital (GIAO) method
based on the optimized geometries. To simulate the groundꢀstate
absorption spectra, the timeꢀdependent (TD) DFT calculation
was employed with (U)B3LYP/6ꢀ31G(d) level. In the specific
case of dication, 12+, the Handy and coꢀworkers’ of longꢀrange
corrected TDꢀCAMB3LYP/6ꢀ31G(d) level calculations31 that
gives rise to the consistent transitions for charged derivatives
were carried out.
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Synthetic Procedures
5,15-Dioxo-10,20-diphenylporphodimethene (2):
5,15ꢀDiphenylporphyrin (1) (0.77 g, 1.66 mmol) was dissolved
in a mixture of chloroform (100 mL) and acetic acid (20 Ml). A
solution of PbO2 (4.0 g, 16.7 mmol) was added and the reaction
mixture was stirred for 5 h open to air, whereafter the mixture
was slowly poured into a saturated aqueous sodium bicarbonate
solution (300 mL) to quench the acetic acid and the organic and
aqueous phase were separated. The organic phase was passed
through a short plug of celite to remove residual lead salts. The
aqueous layer was extracted twice with dichloromethane (2 x
100 mL) and the two organic fractions were also passed through
the celite. The celite was washed thoroughly with dichloroꢀ
methane until the filtrate was colorless. The combined organic
filtrates were evaporated and the residue purified by column
chromatography over silica gel using 30% hexꢀ
anes/dichloromethane as the eluent. The dark yellow band was
collected affording .46g (56% yield) of 2 as a black solid. The
black crystalline solid could be further purified by recrystallizing
from hot toluene. The 1H NMR spectral data matched that reꢀ
Two-Photon Absorption Experiments. Twoꢀphoton abꢀ
sorption (TPA) spectra were measured in the NIR region
using the openꢀaperture Zꢀscan method with 130 fs pulses
from an optical parametric amplifier (Light Conversion,
TOPAS) operating at a repetition rate of 2 kHz generated
from a Ti:sapphire regenerative amplifier system (Spectraꢀ
Physics, HurricaneꢀX). The NIR beam was divided into two
parts. One was monitored by a GeꢀPIN photodiode (New
Focus) as an intensity reference, and the other was used for
the transmittance measurement. After passing through a 10
cm focal length lens, the laser beam was focused and passed
through a 1 mm quartz cell. Since the position of the sample
cell could be controlled along the laser beam direction (z
axis) using the motorꢀcontrolled delay stage, the local power
density within the sample cell could be simply controlled
under constant laser intensity. The transmitted laser beam
from the sample cell was then detected by the same photodiꢀ
ode as used for reference monitoring. The onꢀaxis peak intenꢀ
sity of the incident pulses at the focal point, I0, ranged from
40 to 60 GW cmꢀ2. For a Gaussian beam profile, the nonlineꢀ
ar absorption coefficient can be obtained by curve fitting of
the observed openꢀaperture traces T(z) with the following
equation:
ported previously:30 (CDCl3, 298 K)
7.17 (d, J = 4.4Hz, 4H, βꢀH), 7.35ꢀ7.45 (m, 10H, PhꢀH), 13.85
δ 6.2ꢀ2.6 (br s, 4H, βꢀH),
(br s, 2H, NꢀH) ppm.
ExTTF-Porphyrin (H2TTFP):
To a mixture of 5,15ꢀdioxoꢀ10,20ꢀdiphenylporphodimethene (2)
100 mg, 0.203 mmol) and 4,5ꢀbis(methylthio)ꢀ1,3ꢀdithioleꢀ2ꢀ
thione (3)33 (100 mg, 0.444 mmol) in a dried 100 mL round botꢀ
tom flask was added freshly distilled triethylphosphite (3 ml)
and the reaction mixture was heated slowly to 90 °C under a
nitrogen atmosphere. After stirring the reaction mixture for 1 h at
90 °C, another 100 mg (0.444 mmol) aliquot of 3 was added to
the reaction mixture. The mixture was stirred for additional 1 h
affording a dark green solution. After cooling to room temperaꢀ
ture, the reaction mixture was filtrated using a fine fritted glass
filter to give a dark green solid as a “first crop”. The remaining
filtrate was poured into cold methanol (100 mL) and the resultꢀ
ing precipitate was collected by filtration to yield a “second
crop”. The first crop obtained in this way proved sufficiently
pure to be used in further reactions. The second crop was puriꢀ
fied by column chromatography over silica gel (to remove the
product of the homocoupling of 3) using 30% hexꢀ
anes/dichloromethane as the eluent; this provided analytically
α
0l
β
I0 (1− e−
)
T(z) = 1−
2 2α
0[1+ (z z0 )2 ]
where α0 is the linear absorption coefficient, l the sample
length, and z0 the diffraction length of the incident beam. After
the nonlinear absorption coefficient has been obtained, the TPA
cross section σ(2) of one solute molecule (in units of GM,
where 1 GM = 10ꢀ50 cm4 s photonꢀ1 moleculeꢀ1) can be deterꢀ
mined by using the following relationship:
10−3 (2)NAd
σ
β
=
pure H2TTFP (total yield, 102 mg, 27%).
hν
1
where NA is the Avogadro constant, d is the concentration of
Rf = 0.3. H NMR: (acetoneꢀd6, 298 K)
δ
2.48 (s, 12H, SꢀCH3),
ꢀH), 6.90 (d, J = 4.3 Hz, 4H, ꢀH), 7.55
(m, 10H PhꢀH) 12.59 (s, 2H, NH); 13C NMR (CDCl3, 298 K):
6.61 (d, J = 4.3 Hz, 4H,
β
β
the compound in solution, h is the Planck constant, and
the frequency of the incident laser beam.
ν is
δ
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19.1, 114.1, 117.9, 127.4, 127.9, 128.5, 129.6, 130.9, 138.0,
140.0, 141.7, 152.3. HRMSꢀPositiveꢀESI: m/z 849.04578.
Calcd.: 849.04654. MP > 300 °C.
All data were collected on a Rigaku ACFꢀ12 with a Saturn
724+ CCD and a Rigaku SCXꢀMini diffractometer with a Merꢀ
cury 2 CCD using a graphite monochromator with MoKa radiaꢀ
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tion (λ = 0.71075 Å). The data were collected at 100 K using a
Oxidation of H2TTFP to H2TTFP•2PF6
Rigaku XStream low temperature device. Details of crystal data,
data collection and structure refinement for each analyzed samꢀ
ple are listed in Table S1ꢀS25 in SI. D\In all cases, the data reꢀ
duction were performed using the Rigaku Americas Corporaꢀ
tion’s Crystal Clear version 1.40.34 Each structure was solved by
direct methods using SIR9735 and refined by fullꢀmatrix leastꢀ
squares on F2 with anisotropic displacement parameters for the
nonꢀH atoms using SHELXLꢀ97.36 The contributions to the scatꢀ
tering factors due to the solvent molecules were removed by use
of the utility SQUEEZE37 in PLATON98.38 Structure analysis
was aided by use of the programs PLATON98 as incorporated
into WinGX.39 The hydrogen atoms on carbon were calculated in
ideal positions with isotropic displacement parameters set to
1.2xUeq of the attached atom (1.5xUeq for methyl hydrogen
atoms). Definitions used for calculating R(F), Rw(F2) and the
goodness of fit, S, are given in SI.40 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
Xꢀray Crystallography (1992).41 All figures were generated usꢀ
ing SHELXTL/PC.42 Details of the structures and their refineꢀ
ment may be obtained from the Cambridge Crystallographic
Data Centre by referencing CCDC 931728 for H2TTFP, 931726
for CuTTFP, 931727 for CuTTFP•2OTf 931725 for ZnTTFP,
0001834 for ZnTTFP(TBACl).
Freebase H2TTFP (20 mg, 0.024 mmol) was dissolved in a minꢀ
imal amount of dichloromethane (2 mL). Crystalline NOPF6 (≈
45 mg, 0.257 mmol) was quickly weighed and added in excess
and the reaction was stirred for 15 min. A precipitate was immeꢀ
diately noticeable. After 15 min, the residual solvent proved to
be nearly colorless, and at this time the solvent and precipitate
were decanted from the leftover solid NOPF6. The solution was
filtered and the solids washed with water and dichloromethane
until the filtrate was colorless. The solid material was dried unꢀ
der vacuum at RT to give pure H2TTFP2+•2PF6. 1H NMR
(DMSOꢀd6, 298 K):
7.92 (m, 6H, PhꢀH), 8.24 (dd, J = 1.45, 7.75), 8.99 (br s, 4H,
H), 9.68 (br s, 4H,
ꢀH). 13C NMR (CDCl3, 125 MHz, 298 K):
δ ꢀ2.75 (s, 2H, NH), 3.11 (s, 12H, SꢀCH3),
β
ꢀ
β
δ
19.4, 125.9, 127.0, 128.4, 131.3, 134.3, 134.5, 141.4, 148.9,
152.0, 155.5 HRMSꢀPositiveꢀESI: z = 1, m/z 849.04693, calcd.:
849.04654. z =2, m/z 425.02727. Calcd.: 425.02691 MP > 300
°C.
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General Metalation Procedure for H2TTFP
Compound H2TTFP (20 mg, 0.024 mmol) was dissolved in
dichloromethane (50 ml) and excess metal acetate, M(OAc)2
(100 mg) dissolved in MeOH (1 mL ) was added. The solution
was stirred for 1 h or until all of H2TTFP was consumed, as
judged by TLC analysis. After removal of the solvent, the resiꢀ
due was purified by column chromatography over silica gel to
give the target complexes,:
ASSOCIATED CONTENT
1
ZnTTFP. Eluent dichloromethane; Rf = 0.8, (87% yield) H
Supporting Information. Characterization data for all
new compounds and Xꢀray crystallographic data tables.
This material is available free of charge via the Internet at
http://pubs.acs.org.
NMR (DMSOꢀd6, 400 MHz, 298 K):
6.40 (d, J = 4.2 Hz, 4H, ꢀH), 6.85 (d, J = 4.2 Hz, 4H,
(m, PhꢀH). 13C NMR (CDCl3, 125 MHz, 298 K):
19.0 116.3,
δ
2.43 (s, 12H, SꢀCH3),
β
β
ꢀH), 7.47
δ
117.8, 127.1, 127.5, 128.0, 130.7, 131.6, 139.5, 141.7, 155.7.
HRMSꢀPositiveꢀMALDI: m/z 909.9524, Calcd.: 909.9522. This
compound was further analyzed by a single crystal Xꢀray diffracꢀ
tion analysis. MP > 300 °C.
CuTTFP. Eluent 30% hexanes/dichloromethane; Rf = 0.9,
(73% yield). As noted in the main text, the EPR spectrum of this
complex is consistent with the proposed structure. A clean HPLC
chromatogram of this paramagnetic species was also obtained.
HRMSꢀPositiveꢀMALDI: m/z 908.9516. Calcd.: 908.9527. This
compound was further analyzed by a single crystal Xꢀray diffracꢀ
tion analysis. MP > 300 °C.
AUTHOR INFORMATION
Corresponding Authors
sessler@cm.utexas.edu (JLS); dongho@yonsei.ac.kr
(DK); fukuzumi@chem.eng.osakaꢀu.ac.jp (SF)
ACKNOWLEDGMENT
Support is acknowledged from the U.S. National Science
Foundation (CHEꢀ1057904 to J.L.S.), the Robert A. Welch
Foundation (Fꢀ1018 to J.L.S.), JSPS (No. 20108010 to
S.F), the World Class University (WCU) program (R32ꢀ
2012ꢀ000ꢀ10217ꢀ0 to D.K, R31ꢀ2008ꢀ000ꢀ10010ꢀ0 to
S.F.) of the Ministry of Education, Science and Technoloꢀ
gy, the Villum Foundation (to J.O.J.), and The Danish
Natural Science Reasearch Council (FNU, Project No. 11ꢀ
106744 to J.O.J.).
1
NiTTFP. Eluent dichloromethane; Rf = 0.9, (82% yield). H
NMR (DMSOꢀd6, 400 MHz 298K):
δ
2.46 (s, 12H, SꢀCH3), 6.65
(d, J = 4.5 Hz, 4H,
β
ꢀH), 6.89 (d, J = 4.5 Hz, 4H, βꢀH), 7.52 (m,
10H, PhꢀH). 13C NMR could not be taken due to precipitation
from DMSOꢀd6 upon standing over several hours. HRMSꢀ
PositiveꢀMALDI: m/z 903.9587. Calcd.: 903.9584. MP > 300
°C.
Preparation of ZnTTFPꢀTBACl
For absorption and CV studies, ZnTTFPꢀTBACl was prepared
in situ by the addition of 1.2 molar equivalents of tetrabuꢀ
tylammonium chloride to ZnTTFP in PhCN. ZnTTFPꢀTBACl
can be isolated as its crystalline salt by the addition of 3 molar
equivalents of tetrabutylammonium chloride to ZnTTFP in
dichlormethane followed by slow diffusion of hexanes at 277 K
for several days.
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MeS
SMe
S
S
S
S
Cl
S
S
S
S
S
S
N
N
N
N
Zn
S
S
M2+
Cl
NH
N
N
S
S
Ph
Ph
S
S
Ph
S
S
HN
By Cation
Complexation
By Anion
Binding
N
N
N
N
M
Li
S
S
Ph
M = H2, Ni, Cu, Zn
Li+@C60
MeS
SMe
MTTFP
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