Synthesis and photophysical properties of a conformationally flexible mixed porphyrin star-pentamer

Article abstract of DOI:10.1071/CH09142

The synthesis of a porphyrin star-pentamer bearing a free-base porphyrin core and four zinc(ii) metalloporphyrins, which are tethered by a conformationally flexible linker about the central porphyrin's antipody, is described. The synthetic strategy is hig

Full text of DOI:10.1071/CH09142

RESEARCH FRONT
Full Paper
CSIRO PUBLISHING
Aust. J. Chem. 2009, 62, 692–699
www.publish.csiro.au/journals/ajc
Synthesis and Photophysical Properties of a Conformationally
Flexible Mixed Porphyrin Star-Pentamer
Toby D. M. Bell,A Sheshanath V. Bhosale,B Kenneth P. Ghiggino,A
Steven J. Langford,B,C and Clint P. WoodwardB
ASchool of Chemistry and Bio21 Institute, The University of Melbourne, Parkville,
Vic. 3010, Australia.
BSchool of Chemistry, Monash University, Clayton, Vic. 3800, Australia.
CCorresponding author. Email: s.langford@sci.monash.edu.au
The synthesis of a porphyrin star-pentamer bearing a free-base porphyrin core and four zinc(ii) metalloporphyrins, which
are tethered by a conformationally flexible linker about the central porphyrin’s antipody, is described.The synthetic strategy
is highlighted by the use of olefin cross metathesis to link the five chromophores together in a directed fashion in high
yield. Photoexcitation into the Soret absorption band of the zinc porphyrin chromophores at 425 nm leads to a substantial
enhancement of central free-base porphyrin fluorescence, indicating energy transfer from the photoexcited zinc porphyrin
(outer periphery) to central free-base porphyrin. Time-resolved fluorescence decay profiles required three exponential
decay components for satisfactory fitting. These are attributed to emission from the central free-base porphyrin and to two
different rates of energy transfer from the zinc porphyrins to the free-base porphyrin.The faster of these decay components
equates to an energy-transfer rate constant of 3.7 × 109 s−1 and an efficiency of 83%, whereas the other is essentially
unquenched with respect to reported values for zinc porphyrin fluorescence decay times. The relative contribution of
these two components to the initial fluorescence decay is ∼3:2, similar to the 5:4 ratio of cis and trans geometric isomers
present in the pentamer.
Manuscript received: 11 March 2009.
Final version: 13 May 2009.
Introduction
mixed pentameric porphyrin array (1) and discuss a prelim-
inary photophysical analysis of this light-harvesting complex
mimic.
The efficient synthesis of multiporphyrin systems, ranging
from dimers to higher oligomers, is sought for applications
in light-harvesting,[1] two-photon absorption spectroscopy,[2]
catalysis[3] and molecular recognition applications,[4] and for
studying hole and energy transfer reactions.[5] Linking of por-
phyrin chromophores by covalent bonds to form stable, multi-
porphyrin architectures has previously been achieved using
several different porphyrin-to-porphyrin coupling techniques,[6]
yet alternative methods suitable for forming regiospecifically
mixed-metal (or metal–free-base) porphyrin architectures and
systems containing sensitive pendant functional groups are still
sought. Our interest in this area also stems from the fact that
multichromophoric systems that undertake a single donor and
acceptor event from an array of potential donors allow what
is termed a redundancy effect to be evaluated.[1f] If, or when,
one of the donors is damaged, another is there to take its place,
maintaining the cycle and facilitating longevity in the device
application.
Results and Discussion
Synthesis of the Star-Burst Pentamer 1
Our previous work in the formation of a porphyrin-C60 dyad and
multiporphyrin arrays using CM demonstrated that 3-butenyl
phenyl and α,β-unsaturated ester olefins are ideal coupling part-
ners. Once the mixed cross-product is formed, it can no longer
be reactivated by the catalyst,[8] thereby trapping out the desired
chromophore bridge with excellent chemo- and stereoselectiv-
ity.The 3-butenyl phenyl groups were also specifically chosen to
minimize olefin isomerization under metathesis conditions.[10]
Porphyrin 2, bearing four meso 4-(3-butenyl)phenyl groups, was
prepared from the reaction of pyrrole with the aldehyde 3[9b]
under Rothemund conditions in 20% yield. The correspond-
ing zinc metallated adduct 4 was subsequently formed using
standard metallation conditions.[11] The mono acryloyl func-
tionalized porphyrin cross partner 5 was prepared according to
a previously reported method in an 8% yield over two steps
(Scheme 1).[7a] Zinc(ii) metallation of 5 was achieved using
Zn(OAc)2 in CH3CN/CHCl3 to give 6 in a 70% yield after purifi-
cation by column chromatography. The substitution of methanol
for acetonitrile as the co-solvent of choice in this case was
Recently, we have been studying the use of olefin cross
metathesis (CM) as a mild coupling technique to prepare
donor–acceptor systems[7] by taking advantage of the differ-
ences in olefin reactivity.[8] Olefin CM has also been found to
be an effective tool for the covalent capture of supramolecu-
lar porphyrinic architectures.[9] Here, we report the extension
of this CM coupling strategy to the synthesis of a star-burst,
© CSIRO 2009
10.1071/CH09142
0004-9425/09/070692

RESEARCH FRONT
Properties of a Mixed Porphyrin Star-Pentamer
693
necessary to avoid any transesterification of the acrolyl ester
functionality.
formation of a highly symmetrical product (Fig. 1). Loss of
the olefinic proton resonances of porphyrins 2 and 6 and the
appearance of two new resonance signals at 6.08 and 6.24 ppm
indicated successful tetracoupling to the central porphyrin 2 had
taken place. Furthermore, the proton resonance signals of the β-
pyrrolic, inner-periphery NH, meso aromatic, and alkyl moieties
were all accounted for in the 1H NMR spectrum, displaying the
expected integration values for the desired mixed pentamer prod-
uct 1. The olefinic resonance signals observed in the 1H NMR
spectrum of 1, at 6.08 and 6.24 ppm were assigned as a mixture
of cis and trans geometric isomers in approximately a 5:4 ratio.
This was an unexpected result considering that all other hetero
CM-mediated porphyrin modifications previously performed by
our group have given exclusive trans-isomer formation.The poor
cis and trans-isomer selectivity is attributed to a gradual increase
in the steric bulk around the central free-base porphyrin 2 as
the reaction progresses, forcing the catalyst to operate via a
less-favoured stereochemical pathway. Laser desorption mass
spectrometry provided further supporting evidence of the suc-
cessful formation of the mixed porphyrin pentamer 1, with the
observed isotopic pattern closely matching that predicted for the
structure (see Accessory Publication).
In a model reaction, zinc(ii) porphyrin 4 was reacted with an
excess of methyl acrylate in the presence of second-generation
Grubbs’ catalyst (20 mol-%, 5 mol-% per alkene). After
2 days, the corresponding tetrafunctionalized product 7 was
isolated in 63% yield by column chromatography (SiO2, 20:1
CHCl3/acetone) (Scheme 2). In line with our previous work,
only the trans isomer was observed by 1H NMR spectroscopic
analysis for the newly installed acrylate functionality.
With suitable conditions in hand, the zinc(ii) (4-
acryloyloxy)phenylporphyrin (6) and the free-base butenyl func-
tionalized porphyrin (2) were combined in a 6:1 ratio under
metathesis conditions to effect formation of the mixed-porphyrin
pentamer (Scheme 3). A high loading of the second-generation
Grubbs’ catalyst (50 mol-% catalyst present per alkene linkage)
was employed to ensure a short reaction time. Formation of
the pentamer 1 proceeded smoothly, with the complete disap-
pearance of the porphyrin 2 within the first 2 h of the reaction,
as determined by TLC analysis. After 24 h, two major bands
were detected by TLC analysis, one corresponding to the excess
porphyrin acrylate 6 and a second broad porphyrinic band of
significantly lower Rf value. The second band was isolated
by column chromatography (CHCl3/acetone, 50:1) to yield the
desired mixed star pentamer 1 in 84% yield.
Steady-State Spectra
Assessment of the 1H NMR spectrum of 1 revealed rea-
sonably few unique resonance signals, which indicated the
The absorption spectrum of 1 in toluene is shown in Fig. 2
and features a strong absorption band in the blue region of
N
N
M
N
N
Pyrrole
∆, in propionic acid
2
4
M ϭ 2H
Zn(OAc)2
rt, in CH3OH/CHCI3
CHO
M ϭ Zn(II)
3
H3C
H3C
CH3
OH
OH
O
Pyrrole
∆, in propionic acid
N
N
H
Acryloyl chloride, TEA
N
N
M
N
O
N
H
N
N
0ЊC, in THF
H3C
H3C
CHO
CHO
CH3
CH3
8
5
6
M ϭ 2H
M ϭ Zn(II)
Zn(OAc)2
rt, in CH3CN/CHCI3
Scheme 1.
MeO
O
Methyl acrylate (excess)
2nd gen. Grubbs’ cat. (20 mol-%)
rt, under Ar, in CH2Cl2
OMe
O
N
N
N
N
N
Zn
Zn
N
N
N
MeO
O
OMe
7
4
O
Scheme 2.

RESEARCH FRONT
694
T. D. M. Bell et al.
H3C
O
N
N
O
N
H
Zn
N
N
N
H
N
N
H3C
CH3
2
6
2nd gen. Grubbs’ cat.
(50 mol-% per alkene of 2)
rt, under Ar, in CH2CI2
N
Zn
N
N
N
N
N
Zn
N
O
N
O
O
O
N
H
N
N
H
N
O
N
O
N
Zn
N
N
O
O
N
1
N
Zn
N
N
Scheme 3.
β-Pyrrolic H
*
Tolyl methyl
Inner NH
Ar H
Ϫ2
Ϫ3
ppm
-CH2-
Olefin H
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0 ppm
Fig. 1. 400 MHz 1H NMR spectrum (273 K, CDCl3) of the mixed porphyrin pentamer (1) isolated from the cross metathesis reaction.

RESEARCH FRONT
Properties of a Mixed Porphyrin Star-Pentamer
695
(a)
(b)
0.4
0.016
0.3
0.012
0.008
0.004
0.2
0.000
500
550
600
650
0.1
0.0
300
600 650 700 750
500
550
600
400
500
Wavelength [nm]
600
700
Wavelength [nm]
Fig. 3. (a) Corrected emission spectrum of 1 in toluene following excita-
tion at 425 nm.The shortest and longest wavelength maxima can be assigned
to emission from ZnP and FbP chromophores respectively, while the cen-
tral band consists of overlapped emission bands from both chromophores.
(b) Corrected excitation spectra (wavelengths <600 nm) of 1 in toluene
monitoring fluorescence at 615 nm (dashed line) and 730 nm (solid line).
Fig. 2. Absorption spectrum of 1 in toluene. Inset shows the Q-band region
in more detail.
spectrum (the Soret band – absorption to the second singlet
state S2), and a series of weaker absorptions at longer wave-
lengths (the Q-bands – absorption to the first excited singlet
state S1). Expansion of the Q-band region is shown in the inset
of Fig. 2 and absorption maxima are apparent at 515, 553, 601,
and 648 nm. Comparison of the spectra with those of typical
zinc(ii) (ZnP) and free-base (FbP) porphyrins (such as the much-
studied tetraphenyl derivatives)[12] suggests that for 1, up to six
absorption maxima in the Q-band region might be expected,
two associated with the ZnP chromophores, and four due to the
free-base chromophore (the different number of Q-bands for the
two different types of porphyrin arises owing to the higher-order
symmetry resulting from replacement of two protons by a central
ZnII cation). The observation of four Q-band absorption max-
ima suggests that there is significant spectral overlap of the ZnP
and FbP bands, so that all maxima are not fully resolved. This
overlap is also the likely cause of the slightly distorted shape of
the bands in the observed absorption spectrum of 1.
The emission spectrum of 1 in toluene is provided in Fig. 3a.
With excitation at 425 nm, where ZnP and FbP absorb strongly,
the spectrum shows features characteristic of both these chromo-
phores.The emission maxima of Zn tetraphenylporphyrin (TPP)
in toluene occur at 598 and 647 nm, and for FbTPP, which emits
further to the red, maxima in toluene are at 649 and 717 nm.[12a]
Three emission bands are present (at 608, 654, and 721 nm) in
the emission spectrum of 1 and can be assigned as follows:
the band with a maximum at 608 nm is a higher-energy ZnP
emission band, the peak at 721 nm is the lower-energy FbP
emission band and the central band is a combination of the lower-
energy ZnP band and the higher-energy FbP band. The relative
intensity of the zinc porphyrin emission, however, is attenuated
(i.e. quenched) considerably when compared with the free-base
porphyrin (cf. comparison of intensity at 608 and 721 nm),
particularly considering that there are four ZnP chromophores
compared with a single FbP species. The quantum yield of fluo-
rescence with excitation at 425 nm was determined to be 0.034.
Excitation spectra of 1 are presented in Fig. 3b. The flu-
orescence excitation spectrum obtained monitoring at 615 nm
(Fig. 3b dashed line), where only the ZnP chromophores emit,
and the spectrum obtained by monitoring at 730 nm, where emis-
sion is dominated by FbP, are quite similar. If the ZnP and FbP
chromophores were emitting independently, then the excitation
spectra would reflect the different absorption spectra of the two
species. The quenched ZnP emission and the large contribu-
tion of ZnP absorption to the excitation spectrum of FbP imply
that absorption by the peripheral ZnP chromophores is lead-
ing to emission from the central FbP chromophore, confirming
that significant excitation energy transfer (EET) from the ZnP
chromophores to the central FbP is occurring.
Time-Resolved Fluorescence Measurements
To investigate further the possibility of EET being operative
in 1, time-resolved fluorescence decay profiles were recorded
using the time-correlated single-photon counting method at
15-nm wavelength intervals from 595 to 700 nm and at 720 nm.
The decay profiles displayed a significant wavelength depen-
dence that is most pronounced for the extreme cases of 595
and 720 nm, where emission is dominated by ZnP and FbP,
respectively. These two emission decay profiles are shown in
Fig. 4.
Based on the typical spectral characteristics of fluorescence
emission from ZnP and FbP chromophores, contributions from
both porphyrin species are expected over the wavelength range
studied. In addition, the two decay profiles shown in Fig. 4 are
clearly decaying over different time-scales. Based on literature
fluorescence lifetimes,[7b,13] decay components with decay time
constants in the ranges of 10–12 ns (for FbP) and 1.4–1.7 ns
(for ZnP) might reasonably be expected. Fitting the decay pro-
files with one or two exponential decay components did not
yield satisfactory fits at all wavelengths – three components
were required. The extracted decay constants showed very lit-
tle variation across the nine decay profiles, which could, indeed,
be fitted globally with quite satisfactory results in terms of both
the local and global χ2 fitting parameters (global χ2 = 1.21) and
the randomness of the residuals for each profile. The residuals
for the two decay profiles at the extremes of the measurement
range are shown in the inset to Fig. 4. The values of the global

RESEARCH FRONT
696
T. D. M. Bell et al.
70
60
50
40
30
20
10
0
10000
8000
6000
4000
4
2
0
Ϫ2
Ϫ4
270 ps
1.63 ns
10.2 ns
595 nm
40
60
20
30
50
4
2
0
Ϫ2
Ϫ4
Time [ns]
720 nm
2000
595 nm
0
720 nm
10
20
30
40
Time [ns]
50
60
600
620
640
660
680
700
720
Wavelength [nm]
Fig. 4. Fluorescence decay profiles of 1 in toluene with detection wave-
lengths of 595 and 720 nm. Fitting functions (solid lines) to the profiles and
an instrument response function (IRF – dashed line) are also shown.The inset
shows the residuals of the fits to the decay profiles resulting from a global
fitting of nine decay profiles recorded over the emission spectrum.The fitting
function comprised three exponential decay components convolved with the
IRF (see text).
Fig. 5. Pre-exponential factors (i.e. contributions to initial intensity) of the
three exponential decay components as a function of detection wavelength
for 1 in toluene. The pre-exponential factors were obtained from global
fitting of nine decay profiles over the range of 595–720 nm.
the inverse sixth power of the distance (R) between the donor
and acceptor chromophores,
fluorescence decay times for two of the decay components are
1.6 and 10.2 ns, indicating that fluorescence attributable to each
of the porphyrin species (ZnP and FbP, respectively) is present.
The fractional contributions of the three decay components
to the initial amplitude of each decay profile (i.e. the pre-
exponential factors) over the detection wavelength range are
given in Fig. 5. The components with decay times of 1.63
and 10.2 ns show wavelength-dependence characteristics con-
sistent with the steady-state emission spectra of ZnP and FbP,
respectively, with the 10.2-ns component contributing more sig-
nificantly at longer wavelengths. The third component shows a
similar dependence on detection wavelength to the 1.63-ns com-
ponent but has a much shorter decay time constant of 270 ps,
suggesting that it, too, originates from the ZnP chromophores
but is quenched.The data in Fig. 5 are also replotted in theAcces-
sory Publication (Fig.A2a) in terms of the relative total intensity
of light emitted by each decay time component as a function of
detection wavelength. Confirmation that the decay components
arise from the two different porphyrins present is obtained by
normalizing these values to the total steady-state emission of the
pentamer over the emission wavelength range. These are plot-
ted in Figs A2b and c and clearly show spectral characteristics
consistent with an assignment of FbP for the 10.2-ns component
and ZnP for the 1.63-ns and 270-ps components.
The observation from the star-burst pentamer 1 of a quenched
fluorescence lifetime component originating from ZnP in the
time-resolved fluorescence decay profiles provides additional
evidence that an efficient non-radiative EET process is occur-
ring from some of the peripheral ZnPs to the central FbP. EET
from ZnP to FbP is an energetically favourable process (the S1
state of FbP is estimated to lie 0.15 eV lower in energy than
ZnP based on steady-state absorption and emission spectra).
The decay lifetime of 270 ps corresponds to a rate constant of
3.7 × 109 s−1 for EET and an 83% quenching efficiency of the
ZnP fluorescence. The efficiency (E) for the transfer of energy
from a photoexcited donor chromophore to an acceptor chromo-
phore via an induced dipole–dipole interaction is dependent on
R06
R60 + R6
E =
,
(1)
where R0 (the Förster critical transfer distance) is the distance at
which 50% of the excitation energy is transferred. R0 is depen-
dent on the spectral overlap (J) of donor emission and acceptor
absorption (with units of nm4 M−1 cm−1), the donor fluores-
cence quantum yield (ΦD), the index of refraction of the medium
(η), and a geometrical factor (κ2) that accounts for the relative
orientation of the two interacting transition dipoles. R0 is given
(in Å) by:[14]
R0 = [8.79 × 10−5J(λ)ΦDη−4κ2]1/6
.
(2)
Using spectra recorded in toluene for ZnTPP and FbTPP
and assuming a random orientation (κ2 = 0.67) for the transition
dipoles of the ZnP and FbP, Eqn 2 predicts a critical distance of
22.5 Å for energy transfer from ZnTPP to FbTPP. From Eqn 1,
it can be calculated that 83% efficiency occurs at a separation of
17.1 Å for this value of R0.The values of the pre-exponential fac-
tors for the two decay components of ZnP at 615 nm (where there
is negligible FbP emission) imply that 40% of all ZnP chromo-
phores are not undergoing EET. Interestingly, the ratio of 3:2 for
quenched:unquenched ZnP emission from the pentamer is quite
similar to the cis:trans isomeric ratio of 5:4 determined by NMR
studies. This raises the possibility that one geometric isomer, the
cis-isomer, is undergoing EET while EET in the trans-isomer is
inefficient. Molecular modelling based on a simple molecular
mechanics approach gives the minimum energy centre-to-centre
separation for ZnP to FbP in the cis-isomer to be 17 Å and for the
trans-isomer to be 22 Å. This difference, although significant, is
not sufficient on its own to effectively ‘switch off’ EET in the
trans-isomer. As calculated above, 83% efficiency for EET can
be expected at 17.1 Å, consistent with the experimental result on
the ‘active’ isomer; however, at 22 Å, EET should still be 53%
efficient for the other isomer.

RESEARCH FRONT
Properties of a Mixed Porphyrin Star-Pentamer
697
The other important factor that will affect the relative EET
efficiencies for the two isomers is the relative orientation of the
interacting transition dipoles of the ZnP and FbP chromophores.
The calculations above are based on a random orientation for
which κ2 = 0.67. However, κ2 can take values from 0 to 4 and,
clearly, the efficiency of EET is particularly adversely affected
as κ2 tends to zero. κ2 is given by:[14]
Photophysical Measurements
Samples for photophysical measurements were prepared using
spectroscopic grade toluene used as received from Aldrich and
degassed by multiple freeze–pump–thaw cycles. Steady-state
absorption spectra were recorded on a Cary 50 (Varian) spec-
trophotometer, whereas emission and excitation spectra were
obtained on a Cary Eclipse (Varian) fluorimeter. Fluorescence
emission decay profiles were recorded using the time-correlated
single-photon counting method with excitation provided by the
frequency-doubled output (425 nm) of a mode-locked amplified
Ti:sapphire laser (Coherent Mira). The system was cavity-
dumped to provide a pulse repetition rate of 500 KHz and
fluorescence was detected by a multichannel plate photomulti-
plier (Eldy) and recorded by a photon counting card (Edinburgh
Instruments). The time-resolved fluorescence instrumentation
has been described extensively elsewhere.[7b]
κ2 = [D ·A − 3(D · R)(A · R)]2,
(3)
where D, A and R are unit vectors in the directions of the transi-
tion dipoles for the donor, the acceptor, and the line connecting
the centres of the donor and the acceptor, respectively. It is appar-
ent that κ2 tends to zero for orthogonal arrangements of D and
A and, should one of the isomers adopt a conformation where
this is the case, it would exhibit very little EET. A factor mitigat-
ing this possibility is the flexibility of the linker, which would
be expected to lead to significant conformational freedom for
each isomer. Another potential complication is the possibility
of energy-hopping between the four ZnP chromophores of each
pentamer. This would allow an excitation on a poorly oriented
ZnP to hop to one where EET is favoured. One way to determine
if the observed complexity in photophysical behaviour arises
from the presence of geometric isomers and, if so, which isomer
is EET active and which is not, would be to study samples with
differing cis:trans ratios, or ideally, isomerically pure samples.
These intriguing possibilities are currently being investigated
and will be reported subsequently.
Preparation of 5,10,15,20-Tetra(4-(3-butenyl)phenyl)-
21H,23H-porphine 2
A solution of 4-(3-butenyl)benzaldehyde (500 mg, 3.121 mmol)
and pyrrole (210 mg, 3.121 mmol) was stirred in propionic acid
(15 mL) and refluxed for 3 h. The solution was allowed to cool
and the purple precipitate collected, washed with methanol until
fresh washings were clear and dried in a cool oven (60◦C)
to give the title compound 2 (130 mg, 20%) as a microcrys-
talline purple solid. δH (300 MHz, CDCl3) −2.74 (bs, 2H, inner
NH), 2.69 (apparent q, 8H, CH2), 3.07 (t, J 7.1, 8H, CH2),
5.19 (m, 8H, alkene H), 6.08 (m, 4H, alkene H), 7.57 (ABq,
J 7.7, 8H, ArH), 8.12 (ABq, J 7.7, 8H, ArH), 8.84 (s, 8H,
β-pyrrolic H). δC (75 MHz, CDCl3) 35.6, 35.9, 112.2, 115.4,
120.3, 127.0, 134.8, 138.4, 140.0, 141.5, 147.8. m/z (HR-
ESIMS, +ve, dichloromethane (DCM)/MeOH) Calc. 831.4427.
Found 831.4427 [M + H]+.
Conclusion
We have been able to demonstrate that selective olefin CM
can be effectively applied to the coupling of porphyrin tectons,
producing multiporphyrin assemblies in high yield with regio-
selective control of metallation sites. The work conducted has
also shown that olefin CM can be employed to couple dissimilar
porphyrins, both chemo- and stereoselectively, as demonstrated
by the formation of a mixed porphyrin pentamer. Steady-state
and time-resolved fluorescence studies on the pentamer have
shown that significant excitation energy transfer occurs between
the peripheral zinc(ii) porphyrins and the central free-base por-
phyrin with a rate constant of 3.7 × 109 s−1.The results also raise
the possibility that control of the EET process can be imposed
by geometric isomer configurations in the porphyrin array.
Preparation of 5,10,15,20-Tetrakis(4-(3-butenyl)
phenyl)porphyrinato Zinc(II) 4
To a solution of 2 (54.3 mg, 0.06 mmol) in chloroform (5 mL),
saturated zinc acetate in methanol (5 mL) was added and stirred
at reflux for 3 h in darkness. On completion, the reaction mixture
was quenched with water (25 mL) and transferred to sepa-
rating funnel. The organics were extracted with chloroform
(3 × 20 mL), washed with water, dried (MgSO4), filtered, and
solvent removed under vacuum to give 4 (54.3 mg, 93%) as
a microcrystalline purple solid. Mp >350◦C. δH (300 MHz,
CDCl3) 2.69 (apparent q, 8H, CH2), 3.07 (t, J 7.1, 8H, CH2), 5.18
(m, 8H, alkene H), 6.07 (m, 4H, alkene H), 7.56 (ABq, J 7.7, 8H,
ArH), 8.12 (ABq, J 7.7, 8H, ArH), 8.95 (s, 8H, β-pyrrolic H). δC
(75 MHz, CDCl3) 35.6, 35.9, 115.4, 126.8, 132.1, 134.7, 138.5,
140.6, 141.3, 150.5. m/z (HR-ESIMS, +ve, DCM/MeOH) Calc.
915.3376. Found 915.3377 [M + Na]+.
Experimental
All chemicals were used as supplied from Aldrich. Solvents
were obtained as AR grade reagents and were used as received
with the following exceptions. Tetrahydrofuran was stored
over Na wire and benzophenone and was distilled before
use. Dichloromethane used in reaction was predried over 4-Å
sieves, then distilled from CaH. Low resolution-electrospray
ionization mass spectrometry (LR-ESIMS) were recorded on
a Micromass Platform II API QMS-quadrupole electrospray
mass spectrometer. High resolution-ESIMS (HR-ESIMS) were
recorded on a Bruker BioApex 47e Fourier-transform mass
spectrometer. Laser desorption ionisation mass spectrometry
(LDI-MS) were recorded on anApplied BiosystemsVoyager-DE
Preparation of 5-(4-Hydroxy)phenyl-10,15,20-tris(4-tolyl)-
21H,23H-porphine 8
A solution of (4-hydroxy)benzaldehyde (0.68 g, 5.57 mmol),
p-tolualdehyde (2.00 g, 16.65 mmol), and pyrrole (1.50 g,
22.30 mmol) was refluxed in propionic acid (150 mL) for 3 h.
The solution was allowed to cool overnight and the H2TTP by-
product was removed by suction filtration. Propionic acid was
removed from the filtrate by rotary evaporation to leave a black
solid. The solid was taken up in ethyl acetate, passed through
a short silica plug (SiO2, ethyl acetate), and solvent removed
under vacuum. Further purification of the crude mixture was
1
STR Biospectrometry workstation. H and 13C NMR spectra
were recorded using a Bruker DPX 300 MHz spectrometer
(300 MHz, 1H; 75 MHz, 13C) or a Bruker DRX 400 MHz
spectrometer (400 MHz, 1H; 100 MHz, 13C) as solutions in
CDCl3. Chemical shifts (δ) were calibrated against the residual
solvent peak.

RESEARCH FRONT
698
T. D. M. Bell et al.
performed by flash chromatography (SiO2, CHCl3) to elute any
residual H2TTP; then the solvent system polarity was increased
(CHCl3/MeOH, 20:1), eluting the desired product 8 (320 mg,
8.5%) as a purple solid after solvent removal. Mp >350◦C. δH
(400 MHz, CDCl3) −2.74 (bs, 2H, inner NH), 2.71 (s, 9H, CH3),
7.17 (ABq, J 8.5, 2H, ArH), 7.55 (ABq, J 7.8, 6H, ArH), 8.06
(ABq, J 8.5, 2H, ArH), 8.10 (ABq, J 7.8, 6H, ArH), 8.86 (s,
8H, β-pyrrolic H). δC (100 MHz, CDCl3) 21.7, 113.9, 119.8,
120.3, 127.6, 134.7, 135.1, 135.9, 137.5, 139.6, 155.6. m/z (HR-
ESIMS, +ve, DCM/MeOH) Calc. 673.2967. Found 673.2957
[M + H]+.
Ar environment. Degassed CH2Cl2 (15 mL) and methyl acrylate
(20 mg, 0.225 mmol) were added via syringe and the mixture
was left to stir at room temperature for 3 days in darkness.
After this time, the solvent was removed by rotary evapora-
tion and the crude material was run through a short plug of
silica (CHCl3/acetone, 20:1). The porphyrinic material was fur-
ther purified by preparative TLC (SiO2, CHCl3), giving the title
compound as a red-purple solid 7 (8 mg, 63%). Mp >350◦C. δH
(300 MHz, CDCl3) 2.86 (apparent q, 8H, CH2), 3.14 (t, J 7.5, 8H,
CH2), 3.80 (s, 12H, CO2CH3), 6.02 (dt, J 15.8, 1.5, 4H, alkene
H), 7.23 (dt, J 15.8, 6.8, 4H, alkene H), 7.29 (ABq, J 8.7, 8H,
ArH), 8.13 (ABq, J 8.7, 8H,ArH), 8.86 (m, 8H, β-pyrrolic H). δC
(100 MHz, CDCl3) 34.3, 34.6, 51.7, 121.1, 122.0, 126.7, 132.1,
134.8, 140.2, 141.0, 148.6, 150.5, 167.3. m/z (LR-ESIMS, +ve)
Calc. 1125.4. Found 1125.5 [M + H]+.
Preparation of 5-(4-Acryloyloxy)phenyl-10,15,20-tris
(4-tolyl)-21H,23H-porphine 5
The porphyrin 8 (150.0 mg, 0.297 mmol) and triethylamine
(0.1 mL, 0.74 mmol) were combined in freshly distilled THF
(50 mL) under an Ar environment. The solution was cooled
to 0◦C and a THF solution of acryloyl chloride (0.20 mL in
10 mL) was added dropwise over a 15-min period. The reac-
tion mixture was stirred at room temperature for 24 h and
then quenched with water (20 mL). The THF was removed by
rotary evaporation and the reaction mixture was transferred to
a separating funnel. The product was extracted with chloroform
(3 × 50 mL), washed with saturated NaHCO3 (3 × 50 mL), then
water (1 × 50 mL), dried (MgSO4), filtered, and solvent removed
by rotary evaporation. Further purification was performed by
column chromatography (SiO2, hexane/CHCl3, 1:1), giving
the desired product 5 (180 mg, 84%) as a pink-purple solid.
Mp >350◦C. δH (400 MHz, CDCl3) −2.74 (bs, 2H, inner NH),
2.71 (s, 9H, CH3), 6.15 (dd, J 10.4, 1.1, 1H, alkene H), 6.52
(dd, J 17.3, 10.4, 1H, alkene H), 6.79 (dd, J 17.3, 1.1, 1H,
alkene H), 7.56 (m, 8H, ArH), 8.11 (ABq, J 7.9, 6H, ArH),
8.25 (ABq, J 8.5, 2H, ArH), 8.88 (m, 8H, β-pyrrolic H). δC
(100 MHz, CDCl3) 118.8, 120.0, 120.5, 127.7, 128.4, 133.0,
134.7, 135.5, 137.6, 139.5, 140.2, 150.7, 164.9. m/z (HR-
ESIMS, +ve, DCM/MeOH) Calc. 727.3068. Found 727.3061
[M + Na]+.
Preparation of the Mixed Tetra Zinc(II) Porphyrin
Pentamer 1
The porphyrins 6 (21.5 mg, 27.2 µmol) and 2 (3.8 mg,
4.5 µmol) were combined with second-generation Grubbs’ cat-
alyst (7.7 mg, 9.1 µmol) in CH2Cl2 (10 mL, degassed) under an
Ar atmosphere and left to stir at room temperature in darkness.
The reaction was monitored by TLC, with a new spot appear-
ing at lower Rf value. After 24 h, the solvent was removed by
rotary evaporation and column chromatography was performed.
Excess 6 was collected first (SiO2, CHCl3), then the solvent sys-
tem changed (CHCl3/acetone, 50:1) and the desired pentamer 1
eluted asthe second band as a pink-red solid (14.7 mg, 84%) after
rotary evaporation. Mp >350◦C. δH (400 MHz, CDCl3) −2.66
(bs, 2H, inner NH), 2.69 (bs, 36H, CH3), 2.80 (apparent q, 4H,
CH2), 2.90 (apparent q, 4H, CH2), 3.09 (t, J 7.6, 4H, CH2), 3.19
(t, J 7.6, 4H, CH2), 6.08 (d, J 15.7, 2H, alkene H), 6.24 (m, 2H,
alkene H), 7.40–7.63 (m, 36H,ArH and alkene H (hidden)), 8.10
(m, 24H, ArH), 8.22 (m, 8H, ArH), 8.97 (m, 40H, β-pyrrolic H).
δC (100 MHz, CDCl3) 21.7, 34.4, 119.8, 119.9, 121.6, 127.0,
127.5, 132.0, 132.2, 132.4, 134.6, 135.0, 135.4, 140.5, 150.4,
150.7, 150.8, 165.0. m/z (LDI-MS, no matrix) Calc. 3880.16.
Found 3880.05.
Preparation of 5-(4-Acryloyloxy)phenyl-10,15,20-tris
(4-tolyl)porphinato Zinc(II) 6
Accessory Publication
The porphyrin 5 (75 mg, 103.1 µmol) was dissolved in chloro-
form (10 mL) and combined with saturated Zn(OAc)2 in aceto-
nitrile (5 mL) under anAr atmosphere. The reaction mixture was
stirred at room temperature 24 h in darkness. After this time, the
solvent was removed by rotary evaporation and redissolved in
chloroform, washed with water (3 × 50 mL), dried (MgSO4),
filtered, and solvent volume reduced. Further purification was
performed by column chromatography (SiO2, CHCl3) to give
the desired product 6 (57 mg, 70%) as a pink-purple solid. Mp
>350◦C. δH (400 MHz, CDCl3) 2.71 (s, 9H, Ar CH3), 6.15 (dd,
J 10.4, 1.2, 1H, alkene H), 6.24 (dd, J 17.3, 10.4, 1H, alkene H),
6.53 (dd, J 17.3, 1.2, 1H, alkene H), 7.55 (m, 8H, ArH), 8.11
(ABq, J 7.9, 6H, ArH), 8.24 (ABq, J 8.6, 2H, ArH), 8.97 (m,
8H, β-pyrrolic H). δC (100 MHz, CDCl3) 21.6, 119.6, 119.7,
121.3, 121.4, 127.4, 128.2, 131.8, 132.0, 132.2, 132.8, 134.4,
135.2, 137.2, 139.9, 140.6, 150.1, 150.4, 150.5, 164.7. m/z (HR-
ESIMS, +ve) Calc. 788.2124. Found 788.2123 [M]+.
Figures showing relative fraction of light emitted by each flu-
orescence decay component for 1 as a function of detection
wavelength, the weighted by total steady state emission of 1
at each wavelength in toluene are available from the Journal’s
website.
Acknowledgements
The present research was supported by the Australia Research Council’s
Discovery Grant Scheme (DP0878220). CPW thanks the Monash University
Faculty of Science for support through a Dean’s post-graduate scholarship.
TDMB thanks the University of Melbourne for the award of the Faculty of
Science Centenary Fellowship. Assistance from Sheryll Yap in carrying out
the photophysical measurements is also acknowledged.
References
[1] (a) S. Prathapan, T. E. Johnson, J. S. Lindsay, J. Am. Chem. Soc. 1993,
115, 7519. doi:10.1021/JA00069A068
Preparation of Tetra Methylacrylate-Functionalized
Zinc(II) Butenyl Porphyrin 7
(b) D. Kim, A. Osuka, Acc. Chem. Res. 2004, 37, 735.
doi:10.1021/AR030242E
The porphyrin 4 (10 mg, 11.2 µmol), and second-generation
Grubbs’ catalyst (1.9 mg, 2.2 µmol) were combined under an
(c) Y. Nakamura, N. Aratani, A. Osuka, Chem. Soc. Rev. 2007, 36,
831. doi:10.1039/B618854K

RESEARCH FRONT
Properties of a Mixed Porphyrin Star-Pentamer
699
(d) H. Imahori, J. Phys. Chem. B 2004, 108, 6130. doi:10.1021/
JP038036B
(e) A. Lyubimtsev, Z. Iqbal, M. Hanack, Aust. J. Chem. 2008, 61, 273.
doi:10.1071/CH07449
[6] For a comprehensive overview of porphyrin covalent linkage methods,
see the following reviews and references therein. (a) A. K. Burrell,
D. L. Officer, P. G. Pileger, D. C. W. Reid, Chem. Rev. 2001, 101,
2751. doi:10.1021/CR0000426
(f) A. C. Benniston, A. Harriman, Mater. Today 2008, 11, 26.
doi:10.1016/S1369-7021(08)70250-5
[2] (a) K. S. Kim, J. M. Lim, A. Osuka, D. Kim, J. Photochem. Photobiol.
Chem. 2008, 1, 13.
(b) M. O. Senge, J. Richter, J. Porphyr. Phthalocyanines 2004, 8, 934.
(c) S. Horn, K. Dahms, M. O. Senge, J. Porphyr. Phthalocyanines
2008, 12, 1053.
[7] (a) S. J. Langford, M. J. Latter, C. P. Woodward, Org. Lett. 2006, 8,
2595. doi:10.1021/OL060867N
(b) T. D. M. Bell, K. P. Ghiggino, A. Haynes, S. J. Langford,
C. P. Woodward, J. Porphyr. Phthalocyanines 2007, 11, 455.
[8] A. K. Chatterjee,T.-L. Choi, D. P. Sanders, R. H. Grubbs, J.Am. Chem.
Soc. 2003, 125, 11360. doi:10.1021/JA0214882
[9] (a) P. C. M. van Gervan, J.A.A.W. Elemans, J.W. Gerritsen, S. Speller,
R. J. M. Nolte, A. E. Rowan, Chem. Commun. 2005, 3537
(b)J. M. Bakker, S. J. Langford, M. J. Latter, K.A. Lee, C. P.Woodward,
Aust. J. Chem. 2005, 58, 757. doi:10.1071/CH05262
(c) C. Ikeda, A. Satake, Y. Kobuke, Org. Lett. 2003, 42, 1121.
(d) A. Satake, M. Yamamura, M. Oda, Y. Kobuke, J. Am. Chem. Soc.
2008, 130, 6314. doi:10.1021/JA801129A
(b) K. Ogawa, Y. Kobuke, J. Photochem. Photobiol. Chem. 2006, 7,
1. doi:10.1016/J.JPHOTOCHEMREV.2006.03.001
(c) S. Easwaramoorthi, S. J.Y. Jang, Z. S.Yoon, J. M. Lim, C.-W. Lee,
C.-L. Mai, Y.-C. Liu, C.-Y. Yeh, J. Vura-Weis, M. R. Wasielewski,
D. Kim, J. Phys. Chem. A 2008, 112, 6563. doi:10.1021/JP801626S
[3] (a) C. G. Oliveri, S. T. Nguyen, C. A. Mirkin, Inorg. Chem. 2008, 47,
2755. doi:10.1021/IC702150Y
(b) M. L. Merlau, M. P. Meija, S.-T. Nguyen, J. T. Hupp, Angew.
Chem. Int. Ed. 2001, 40, 4239. doi:10.1002/1521-3773(20011119)
40:22<4239::AID-ANIE4239>3.0.CO;2-E
(c) Z. Clyde-Watson, A. Vidal-Ferran, L. J. Twyman, C. J. Walter,
D.W. J. McCallien, S. Fanni, N. Bampos, R. S.Wylie, J. K. M. Sanders,
N. J. Chem. 1998, 22, 493. doi:10.1039/A709199K
(e) K.-T.Youm, S.T. Nguyen, J.T. Hupp, Chem. Commun. 2008, 3375.
doi:10.1039/B800063H
(d) V. F. Slagt, P. W. N. M. van Leeuwen, J. N. H. Reek, Angew. Chem.
Int. Ed. 2003, 42, 5619. doi:10.1002/ANIE.200352525
[4] (a) R. Paolesse, F. Mandoj, A. Marini, C. Di Natale, in Encyclopedia
of Nanoscience and Nanotechnology (Ed. H. S. Nalwa) 2004, Vol. 9,
p. 21 (American Scientific: Valencia, CA).
[10] It has been reported that the allyl ether functionality is prone to
isomerization under metathesis conditions; see R. G. E. Coumans,
J.A.A. W. Elemans, P.Thordason, R. J. M. Nolte,A. E. Rowan,Angew.
Chem. Int. Ed. Engl. 2003, 42, 650. doi:10.1002/ANIE.200390179
[11] J.W. Buchler, inThe Porphyrins (Ed. D. Dolphin) 1978,Vol. 1A, p. 389
(Academic: New York, NY).
(b) G. D. Fallon, S. J. Langford, M. A.-P. Lee, E. Lygris, Inorg. Chem.
Commun. 2002, 5, 715. doi:10.1016/S1387-7003(02)00550-6
(c) M. U. Winters, E. Dahlstedt, H. E. Blades, C. J. Wilson,
M. J. Frampton, H. L. Anderson, J. Am. Chem. Soc. 2007, 129, 4291.
doi:10.1021/JA067447D
(d) L. Flamigni, V. Heitz, J.-P. Sauvage, Struct. Bond. 2006, 121, 217.
doi:10.1007/430_018
(e) M. Fujitsuka, D. Won Cho, N. Solladié, V. Troiani,
H. Qiu, T. Majima, J. Photochem. Photobiol. A 2007, 188, 346.
doi:10.1016/J.JPHOTOCHEM.2006.12.034
[12] (a) P. G. Seybold, M. Gouterman, J. Mol. Spectrosc. 1969, 31, 1.
doi:10.1016/0022-2852(69)90335-X
(b) D. J. Quimby, F. R. Longo, J. Am. Chem. Soc. 1975, 97, 5111.
doi:10.1021/JA00851A015
(c) F. R. Hopf, D. G. Whitten, in Porphyrins and Metalloporphyrins
(Ed. K. M. Smith) 1975, p. 667 (Elsevier: Amsterdam).
(d) M. Gouterman, in The Porphyrins (Ed. D. Dolphin) 1978, Vol. 3,
p. 1 (Academic: New York, NY).
(f) C. G. Oliveri, S. T. Nguyen, C. A. Mirkin, Inorg. Chem. 2008, 47,
2755. doi:10.1021/IC702150Y
[13] (a) L. Pekkarinen, H. Linschitz, J. Am. Chem. Soc. 1960, 82, 2407.
doi:10.1021/JA01495A001
[5] (a) P.Thamyongkit,A. Z. Muresan, J. R. Diers, D. Holten, D. F. Bocian,
J. S. Lindsey, J. Org. Chem. 2007, 72, 5207. doi:10.1021/JO070593X
(b) M. Hoffmann, C. J. Wilson, B. Odell, H. L. Anderson, Angew.
Chem. Int. Ed. 2007, 46, 3122. doi:10.1002/ANIE.200604601
(c)W. J.Youngblood,T.A. Moore,A. L. Moore, D. Gust,T. E. Mallouk,
J. Am. Chem. Soc. 2009, 131, 926. doi:10.1021/JA809108Y
(d) A. Satake, J. Tanihara, Y. Kobuke, Inorg. Chem. 2007, 46, 9700.
doi:10.1021/IC7010056
(b) A. T. Gradyushko, M. P. Tsvirko, Opt. Spectrosc. (USSR) 1971,
31, 291.
(c) O. Ohno, Y. Kaizu, H. Kobayashi, J. Chem. Phys. 1985, 82, 1779.
doi:10.1063/1.448410
[14] (a) T. Förster, Naturwiss. 1946, 33, 166. doi:10.1007/BF00585226
(b) T. Förster, Ann. Phys. 1948, 437, 55. doi:10.1002/ANDP.
19484370105
(e) R. F. Kelley, S. J. Lee, T. M. Wilson, Y. Nakamura, D. M. Tiede,
A. Osuka, J. T. Hupp, M. R. Wasielewski, J. Am. Chem. Soc. 2008,
130, 4277. doi:10.1021/JA075494F
(f) H. Kai, S. Nara, K. Kinbara, T. Aida, J. Am. Chem. Soc. 2008, 130,
6725. doi:10.1021/JA801646B