Preparation and photophysical properties of a tetraethylene glycol-linked phthalocyanine-porphyrin dyad and triad

Article abstract of DOI:10.1039/c3nj00036b

Treatment of 1,4-bis(tetraethylene glycol)-substituted zinc(ii) phthalocyanine with p-toluenesulfonyl chloride and triethylamine followed by 5-(4-hydroxyphenyl)-10,15,20-triphenylporphyrin and K₂CO₃ resulted in the formation of both a covalently linked phthalocyanine-porphyrin dyad and triad. The photophysical properties of these hetero-arrays were studied in detail using steady-state and time-resolved spectroscopic methods. Upon excitation at the porphyrin moiety, both compounds exhibited predominantly highly efficient excitation energy transfer from the excited porphyrin to the phthalocyanine core. The rate of energy transfer (2.4 × 10¹⁰ s^-1) was more than 20-fold faster than the rate of electron transfer (1.1 × 10⁹ s^-1). When the phthalocyanine core of the dyad and triad was excited either directly or via excitation energy transfer, its singlet excited state underwent charge transfer leading to reduction in the fluorescence quantum yield and fluorescence lifetime. The rate of charge transfer for the triad (2.8 × 10⁸ s^-1) was about two-fold higher than that for the dyad (1.5 × 10⁸ s ^-1) due to the presence of an additional porphyrin moiety in the triad.

Full text of DOI:10.1039/c3nj00036b

NJC
View Article Online
View Journal | View Issue
PAPER
Preparation and photophysical properties of a
tetraethylene glycol-linked phthalocyanine–porphyrin
dyad and triad
Cite this: NewJ.Chem., 2013,
37, 1746
Eugeny A. Ermilov,*ab Xuebing Leng,c Beate Rodera and Dennis K. P. Ng*c
¨
Treatment of 1,4-bis(tetraethylene glycol)-substituted zinc(II) phthalocyanine with p-toluenesulfonyl
chloride and triethylamine followed by 5-(4-hydroxyphenyl)-10,15,20-triphenylporphyrin and K2CO3
resulted in the formation of both a covalently linked phthalocyanine–porphyrin dyad and triad.
The photophysical properties of these hetero-arrays were studied in detail using steady-state and
time-resolved spectroscopic methods. Upon excitation at the porphyrin moiety, both compounds
exhibited predominantly highly efficient excitation energy transfer from the excited porphyrin to the
phthalocyanine core. The rate of energy transfer (2.4 ꢀ 1010 sꢁ1) was more than 20-fold faster than the
rate of electron transfer (1.1 ꢀ 109 sꢁ1). When the phthalocyanine core of the dyad and triad was
excited either directly or via excitation energy transfer, its singlet excited state underwent charge
transfer leading to reduction in the fluorescence quantum yield and fluorescence lifetime. The rate
of charge transfer for the triad (2.8 ꢀ 108 sꢁ1) was about two-fold higher than that for the dyad
(1.5 ꢀ 108 sꢁ1) due to the presence of an additional porphyrin moiety in the triad.
Received (in Montpellier, France)
9th January 2013,
Accepted 14th March 2013
DOI: 10.1039/c3nj00036b
www.rsc.org/njc
non-natural analogues showing the B-band absorption at ca.
350 nm and Q-band absorption at ca. 670 nm. Thus a broad
Introduction
Photoinduced energy and electron transfer are the key processes in
natural photosynthesis, in which sunlight is initially absorbed by
ensembles of light-harvesting chromophores and then efficiently
delivered to the reaction centre where the captured energy is
converted into chemical potential energy.1 There has been
considerable interest in the development of bioinspired mole-
cular systems that can undergo rapid and directional energy
and electron transfer processes.2,3 These properties are crucial
for applications in artificial photosynthesis,4 photovoltaics5
and molecular electronics.6 Among the various classes of
chromophores being employed as the building blocks, porphyrins
(Pors)2,4b,7 and phthalocyanines (Pcs)4b,8 are of particular interest
owing to their high stability and intriguing electronic and
photophysical properties. Pors are naturally occurring pigments
showing a strong B band at ca. 400 nm and a number of weaker
Q bands in the region of 500–600 nm, whereas Pcs are their
range of solar spectrum could be covered when these functional
dyes are coupled together.9 In addition, their photophysical
and redox properties can also be altered readily by changing
the metal centre and the peripheral substituents. These
features enable the interactions between these chromophores
to be systematically tuned.
A substantial number of covalent and non-covalent Por–Pc
systems have been prepared and studied for their photophysical
properties and intramolecular photoinduced processes.9,10
Recently, we have reported two Pc–Por triads in which two
meso-tetraphenylporphyrin (MTPP; M = H2, Zn) rings are linked
to a silicon(IV) phthalocyanine core at the axial positions.11 It
has been found that the triads exhibit both photoinduced
energy and electron transfer processes. The extent depends
on the nature of the metal centre of the Por and the solvent. As
an extension of this work, we report herein a related Pc–Por
dyad and triad in which a zinc(II) phthalocyanine is covalently
linked to one or two metal-free H2TPP via a tetraethylene glycol
chain, including their synthesis and photophysical properties
as studied by various steady-state and time-resolved spectro-
scopic methods. In designing artificial photosynthetic models,
rigid linkers are commonly used to connect the building blocks
with a view to facilitating their electronic interactions and
a
¨
¨
Institut fur Physik, Photobiophysik, Humboldt-Universitat zu Berlin,
Newtonstrasse 15, D-12489 Berlin, Germany
b
¨
´
¨
´
Institut fur Physiologie, CCM, Charite-Universitatsmedizin Berlin, Chariteplatz 1,
D-10117 Berlin, Germany. E-mail: eugeny.ermilov@charite.de;
Fax: +49 30-450-528930
c Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T.,
Hong Kong, China. E-mail: dkpn@cuhk.edu.hk; Fax: +852 2603-5057
c
1746 New J. Chem., 2013, 37, 1746--1752
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013

View Article Online
Paper
NJC
having a better control of the separation and orientation of the
interacting components.12 However, flexible linkers also have
their advantages as conformational changes of the corres-
ponding systems can be induced readily, for example, by
changing the solvents or addition of metal ions, thereby
controlling the intramolecular photoinduced processes.13 This
kind of aliphatic linkers can also enhance the solubility of the
multi-macrocyclic systems. As a result, a flexible tetraethylene
glycol spacer was used in this study.
Results and discussion
The synthetic route used to prepare both the Pc–Por dyad and
triad is shown in Scheme 1. The 1,4-bis(tetraethylene glycol)-
substituted zinc(II) phthalocyanine 1 was prepared readily by
mixed cyclisation of the corresponding phthalonitriles.14 Treat-
ment of this compound with p-toluenesulfonyl chloride (TsCl) in
the presence of triethylamine gave the ditosylate 2 in good yield.
Fig. 1 UV-Vis spectra of the dyad 4, triad 5, H2TPP and Pc
1 in DMF.
The absorbance of the Q-band absorption maximum of the Pc moiety in 1, 4
and 5, and the absorbance of the B-band absorption maximum of H2TPP were
normalised as 1.
Further treatment of compound 2 with two equiv. of hydroxypor- reference compounds H2TPP and Pc 1 are also included. The B- and
phyrin 315 and K2CO3 in N,N-dimethylformamide (DMF) afforded Q-band absorptions of these compounds are listed in Table 1. It
a mixture of dyad 4 (15%) and triad 5 (45%), which was separated can be seen that the absorption positions of the dyad 4 and
and purified readily by column chromatography. Both com- triad 5 are essentially the same as those of the reference
pounds were soluble in a wide range of organic solvents, includ- compounds, showing that the Pc and Por components in these
ing CHCl3, tetrahydrofuran (THF), DMF, toluene and pyridine, hetero-arrays exhibit negligible ground-state interactions.
and were characterised by various spectroscopic methods.
The steady-state fluorescence spectra of these compounds
Fig. 1 shows the UV-Vis spectra of these two compounds were also recorded in DMF and the data are also summarised in
in DMF. For comparison, the absorption spectra of the two Table 1. Upon excitation at 510 nm, where only the Por moiety
Scheme 1 Preparation of Pc–Por dyad 4 and triad 5.
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
New J. Chem., 2013, 37, 1746--1752 1747

View Article Online
NJC
Paper
Table 1 Electronic absorption and fluorescence maxima, fluorescence quantum yields (Ffl) and fluorescence lifetimes (tfl) of the dyad 4, triad 5 and the two reference
compounds H2TPP and Pc 1 in DMF
b
Ffl
tfl (ns)
Q-banda (nm)
lfl (nm)
Por-part excitation
Pc-part excitation
Por-part excitation
Pc-part excitation
Compound
B-band (nm)
H2TPP
Pc 1
Dyad 4
419
339
346, 419
650
689
689
653, 719
697
697
0.11
—
9.72 ꢂ 0.02
—
—
—
0.27 ꢂ 0.01c
2.50 ꢂ 0.01
o0.01d
0.20 ꢂ 0.02c
(31 ꢂ 5) ꢀ 10ꢁ3
1.79 ꢂ 0.01
9.3 ꢂ 0.1
1.79 ꢂ 0.01
0.20 ꢂ 0.02c
Triad 5
346, 419
689
697
o0.01d
0.16 ꢂ 0.02c
(27 ꢂ 3) ꢀ 10ꢁ3
1.46 ꢂ 0.01
9.7 ꢂ 0.1
1.46 ꢂ 0.01
0.15 ꢂ 0.02c
a
b
The lowest-energy band. Relative to H2TPP in DMF (Ffl = 0.11) for Por-part emission and SiPc(OEG)2 in DMF (Ffl = 0.50) for Pc-part emission.
For Pc-part emission. For Por-part emission.
c
d
absorbs, both dyad 4 and triad 5 gave an emission band at for Pc 1 and 1.92 eV for H2TPP according to their absorption
697 nm due to the Pc core (Fig. 2a). The fluorescence quantum and fluorescence emission positions), the quenching should be
yield of the Por part was lower than 0.01, which was much lower mainly due to a charge transfer (CT) process.
than that of the reference H2TPP (Ffl = 0.11).16 It clearly
The photoinduced intramolecular processes of these compounds
indicates that an efficient excitation energy transfer (EET) were also investigated by time-resolved fluorescence spectroscopy.
occurs from the excited Por unit(s) to the Pc core both in the The fluorescence decays of the reference compounds Pc 1 and
dyad and triad.
H2TPP were found to be mono-exponential with decay times of
The fluorescence quantum yields of the Pc-part emission 2.50 ns and 9.72 ns respectively (see Table 1). Upon excitation at
were found to be 0.20 and 0.15 for the dyad 4 and triad 5 the Por-part (lex = 532 nm), both dyad 4 and triad 5 gave three
respectively, with respect to bis(oligoethylene glycol)-substi- resolved decay-associated fluorescence (DAF) spectra (see
tuted silicon(IV) phthalocyanine [SiPc(OEG)2] (the average mole- Fig. 3a and c). The one with the shortest lifetime (31 ps for 4
cular weight of OEG = ca. 750) (Ffl = 0.50)11a when the Por-part and 27 ps for 5) has a positive amplitude in the Por-part
was excited. Similar values were obtained when the Pc-part was emission, but became negative at longer wavelengths where
directly excited (see Fig. 2b and Table 1). These values are lower the Pc fluorescence is dominant. The negative amplitude
compared with that of the reference Pc 1 (Ffl = 0.27). Based on indicated an increase in fluorescence intensity. Hence, this
these results, two conclusions can be drawn: (i) the probability decay time could be attributed to the EET process from the
of EET from the initially photoexcited Por unit to the Pc core excited Por to Pc in its ground state. The longest-life decay
in its ground state is close to unity for both dyad 4 and triad 5; spectrum (9.3 ns for 4 and 9.7 ns for 5) with very low amplitude
(ii) for both of these hetero-arrays, there is an additional has a lifetime similar to that of H2TPP and could be assigned to
quenching process for the first excited singlet state of the Pc the Por-part fluorescence decay. The remaining one showed the
moiety, resulting in reduction of its fluorescence quantum yield maximum at 697 nm which could be attributed to the decay of
compared with that of Pc 1. Moreover, the probability of this the first excited singlet state of the Pc moiety. It is worth noting
quenching process is higher for the triad than for the dyad. that this decay follows the order: Pc 1 (2.50 ns) 4 dyad 4
Since the energy transfer for 1Pc* - Por is energetically (1.79 ns) 4 triad 5 (1.46 ns). Moreover, upon direct excitation of
unfavourable (the energy of S0,0 - S1,0 transition is 1.79 eV the Pc moiety at 620 nm, only one DAF spectrum was detected
Fig. 2 Steady-state fluorescence spectra of the dyad 4, triad 5 and H2TPP (or Pc 1) in DMF upon excitation at (a) the Por-part and (b) the Pc-part.
c
1748 New J. Chem., 2013, 37, 1746--1752
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013

View Article Online
Paper
NJC
Fig. 3 DAF spectra of the dyad 4 (a and b) and triad 5 (c and d) upon Por-part (a and c) or Pc-part (b and d) excitation.
for the dyad 4 and triad 5 with decay times of 1.79 and 1.46 ns chromophores was estimated to be ca. 2 nm. Due to the high
respectively (see Fig. 3b and d and Table 1). The shortening of flexibility of the tetraethylene glycol chain between the Por and
the Pc-part fluorescence lifetime is in good agreement with the Pc chromophores in the dyad and triad, the value of the
reduction of the Pc-part fluorescence quantum yield observed orientation factor was taken to be 2/3 as first approximation.
in steady-state measurements.
This average value of the orientation factor is commonly used
As mentioned above, the observed results could be explained for solutions with uniform distribution of the transition dipole
by two photoinduced processes, namely EET and CT. The moments of the interacting chromophores. As a result, the rate
Dexter exchange EET mechanism was excluded on the basis of FRET was estimated to be 2.4 ꢀ 1010
s
ꢁ1. It is worth noting
of the long separation between the Por and Pc moieties, which that this value is very close to the Por first excited singlet state
prevents the two p-electron clouds from overlapping. Thus, the depopulation rate (3.2 ꢀ 1010
s
ꢁ1) determined by taking the
¨
Forster mechanism was assumed to be responsible for the EET reciprocal value of the fluorescence lifetime of the Por moiety
from the initially photoexcited Por unit to the Pc core in its measured by time-resolved fluorescence spectroscopy (ca. 30 ps).
ground state. By using a well-established procedure,9c the Forster FRET is therefore a dominant pathway of the Por-part fluores-
¨
radius, R0, for Por - Pc fluorescence resonance energy transfer cence quenching.
(FRET) was calculated to be 5.3 nm. The FRET rate, kFRET, was
estimated using the following equation:
To reveal whether the decrease in fluorescence quantum
yield and fluorescence lifetime for the Pc unit in the dyad 4
and triad 5 is due to a photoinduced CT process, the free
energy change of charge separation was calculated by using the
Rehm–Weller equation:17
ꢀ
ꢁ
6
1
R0
R
kFRET
¼
k2
;
(1)
t0
ꢂ
ꢃ
e2
DG0D=A ¼ e EoxdðD=DꢃþÞ ꢁ EredðA=AꢃꢁÞ ꢁ ED=A
ꢁ
where R is the centre-to-centre distance between the energy
donor and acceptor, t0 is the donor fluorescence lifetime in the
absence of acceptor and k2 is the orientation factor, which
depends on the relative orientation of the dipole moments of
the interacting molecules. According to molecular dynamic
1=2
1=2
0;0
4pe0esR
ꢄ
ꢅꢄ
ꢅ
e2
1
1
1
1
ꢁ
þ
ꢁ
;
(2)
ꢃꢁ
rA
ꢃþ
8pe0 rD
eref es
simulations using the HyperChem 5.0 programme package, where DGD0 /A is the change in free energy of charge separation
the centre-to-centre distance between the donor and acceptor with selective excitation of the electron donor D (i.e. Pc) or the
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
New J. Chem., 2013, 37, 1746--1752 1749

View Article Online
NJC
Paper
Table 2 Electrochemical data of the dyad 4, triad 5, Pc 1 and H2TPPa
Por
ET
Pc
CT
indirect approach was used and the ratio between k and k
could be calculated as follows:11a
Compound E1/2 (oxd. 2) E1/2 (oxd. 1) E1/2 (red. 1) E1/2 (red. 2)
À
ꢄ
ÁÀ
Á
ꢅ
1.05b
0.56
–0.95b
–1.10
–1.06
–1.05b
DGD0 ꢁ DG0A DG0D þ DG0A þ 2l
Por
ET
H2TPP
Pc 1
Dyad 4
Triad 5
k
1.10b
1.05b
1.04b
–1.62
¼ exp
;
(3)
Pc
CT
0.57b
0.57b
4kBTl
k
–1.77b
a
where l = lI + lS is the total nuclear reorganisation energy
which can formally be divided into an intramolecular part, lI,
and a contribution from inertial solvent reorganisation, lS,
which is given by eqn (4) according to the classical treatment
of Marcus:18
Recorded with [Bu4N][PF6] as an electrolyte in DMF (0.1 M) at ambient
temperature. Potentials were obtained by cyclic voltammetry with a
scan rate of 100 mV sꢁ1, and are expressed as half-wave potentials (E1/2
in volts relative to the saturated calomel electrode (SCE) unless other-
wise stated. By differential pulse voltammetry.
)
b
ꢀ
ꢁꢀ
ꢁ
e2
1
1
1
1
1
lS ¼
ꢁ
þ
ꢁ
(4)
4pe0 n2 es
2rA
2rD
R
electron acceptor A (i.e. Por), E1/2 is the half-wave reduction
ꢃꢁ
ꢃþ
+
potential of the donor (D/Dꢃ ) or acceptor (A/Aꢃꢁ) couple in
volts, ED0,/0A is the energy of S0,0 - S1,0 transition of the donor or
acceptor, R is the separation between the donor and acceptor
moieties, es and eref are the dielectric constants of the solvents
in which the spectroscopic and electrochemical measurements
where n is the refractive index of the solvent used. By using the
ꢃ
ꢃ
+
following parameters: rA
ꢁ
= 4.3 Å, rD
= 4.6 Å, R = 20 Å, es = 37,
Por
ET
k
n = 1.43 and lI = 0.3 eV,19 the ratio
was calculated to be 8.9,
Pc
CT
k
ꢃ
ꢃ
ꢁ
were performed, respectively, rD
+
and rA
are the effective radii
resulting in kPEoTr = 1.1 ꢀ 109 sꢁ1. This value is significantly lower
compared to the above estimated rate of FRET (2.4 ꢀ 1010
s
ꢁ1).
of the radical cation and anion, respectively, e0 is the vacuum
permittivity and e is the charge of the transferred electron.
Since the spectroscopic and electrochemical studies were per-
formed in the same solvent (i.e. DMF), the last term in eqn (2)
e2
This further supports that FRET is a dominant process in
depopulation of the first excited singlet state of the Por moiety
for both dyad 4 and triad 5.
vanishes. Moreover, the contribution of
term is negli-
4pe0eSR
gibly small due to the high polarity of the solvent used as
well as the long separation between the donor and acceptor
moieties (20 Å as estimated by using the HyperChem 5.0
programme package).
The electrochemical potentials of the dyad 4 and triad 5,
as well as the reference compounds Pc 1 and H2TPP, were
studied by cyclic voltammetry and differential pulse voltam-
metry. The data are compiled in Table 2. According to these
Conclusion
In summary, we have prepared a novel Pc–Por dyad and triad
and studied in detail their photophysical properties. Upon
Por-part excitation, both compounds exhibit competitive photo-
induced excitation energy and electron transfer processes. The
probability of FRET was found to be more than one order of
magnitude higher than that of electron transfer. When the first
excited singlet state of the Pc-part is populated either directly or
via FRET, it undergoes transition to the charge-separated state
resulting in reduction of the fluorescence quantum yield as well
as shortening of the fluorescence lifetime of the Pc moiety for
both the hetero-arrays.
oxd
+
data, E (D/Dꢃ ) = 0.57 V and E1re/2d(A/Aꢃꢁ) = ꢁ1.06 V for the dyad 4.
1/2
By substituting the energies of S0,0 - S1,0 transition ED0,0 (1.79 eV)
and EA0,0 (1.92 eV), the values of DGD0 (for Pc-part excitation) and
DGA0 (for Por-part excitation) were determined to be ꢁ0.16
and ꢁ0.29 eV respectively. The values for the triad 5 were
virtually the same. Thus photoinduced CT is thermodynam-
ically favourable both upon Pc- and Por-part excitation for both
the hetero-arrays.
Experimental
General procedure
The rate of CT upon initial excitation of the Pc moiety of the
Pc
dyad 4, (k
)
, was calculated by using the results of the DAF
CT dyad
All the reactions were performed under an atmosphere of
nitrogen. Toluene and THF were distilled from sodium and
sodium benzophenone ketyl respectively. The electrolyte
[Bu4N][PF6] was recrystallised from THF three times prior to
use. Electronic absorption and fluorescence spectroscopic spec-
tra were measured in DMF (Sigma-Aldrich, spectroscopic
grade). All other solvents and reagents were used as received.
À
Á
1
dyad
1
Pc
CT
measurements as
k
¼
ꢁ
¼ 1:5 ꢀ 108 sꢁ1
,
t0ZnPc
dyad
t
Pc
dyad
Pc
where t
and t0ZnPc are the fluorescence lifetimes of the
Pc-part fluorescence of the dyad (1.79 ns) and of the reference
Pc 1 (2.5 ns) respectively. The corresponding value for the triad
Pc
5, (k
)
, was found to be 2.8 ꢀ 108 sꢁ1. Since there is one
CT triad
Pc
1
Compounds 114 and 315 were prepared as described. H NMR
additional Por unit in the triad 5, it is expected that (k
)
CT triad
Pc
should be approximately two-fold faster than (k
the values obtained are in good agreement.
Estimation of the electron transfer (ET) rate upon excitation
of the Por moiety, kPEoTr, is more complicated because this
process competes with the FRET. Nevertheless, the following
)
. Hence
spectra were recorded on a Bruker DPX 300 spectrometer
(300 MHz). Deuterated solvents were used as the lock and
residual non-deuterated solvents as the internal references.
Mass spectra were measured on a Thermo Finnigan MAT 95
XL mass spectrometer.
CT dyad
c
1750 New J. Chem., 2013, 37, 1746--1752
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013

View Article Online
Paper
NJC
Electronic absorption and steady-state fluorescence
spectroscopy
3.40–3.55 (m, 8H, OCH2), 2.50 (s, 6H, CH3). 13C1{H} NMR: d
153.3, 153.1, 153.0, 152.6, 150.5, 145.9, 139.1, 138.8, 138.7
133.4, 131.1, 130.7, 129.9, 128.6, 126.9, 126.6, 126.0, 123.3,
123.0, 116.0, 71.4, 71.1 71.0, 70.8, 70.7, 69.8, 69.3, 68.9, 64.2.
HRMS (FAB) calcd for C62H61N8O14S2Zn (MH+): 1269.3035;
found: 1269.3026.
The ground-state absorption spectra were recorded using a
commercial spectrophotometer Shimadzu UV-2501PC. Steady-
state fluorescence spectra were measured in quartz cells (1 cm
thickness) using a combination of a cw-Xenon lamp (XBO 150)
and a monochromator (Lot-Oriel, bandwidth 10 nm) for excita-
tion and a polychromator with a cooled CCD matrix as the
detector system (Lot-Oriel, Instaspec IV).20 For determination of
Dyad 4 and triad 5. A mixture of 2 (0.20 g, 0.16 mmol),
5-(4-hydroxyphenyl)-10,15,20-triphenylporphyrin (3) (0.20 g,
0.32 mmol) and K2CO3 (0.5 g, 3.62 mmol) in DMF (5 mL) was
stirred at 80 1C overnight. The volatiles were removed under
reduced pressure, and then the residue was chromatographed
on a silica gel column using CHCl3–CH3OH (10 : 1, v/v) as the
eluent to give 4 as a blue-green solid (38 mg, 15%) and 5 as
a blue solid (157 mg, 45%). Dyad 4: 1H NMR (pyridine-d5): d
9.62–9.71 (m, 6H, Pc-Ha), 9.01 (s, 8H, Por-Hb), 8.38–8.54 (m, 6H,
Ph), 8.05–8.28 (m, 8H, Pc-Hb and p-C6H4), 7.70–7.86 (m, 9H,
Ph), 7.64 (s, 2H, Pc-Hb), 7.35 (d, J = 8.4 Hz, 2H, p-C6H4), 5.08 (br.
s, 2H, OCH2), 4.62 (br. s, 2H, OCH2), 4.47 (br. s, 2H, OCH2),
4.22–4.34 (m, 4H, OCH2), 4.11 (br. s, 2H, OCH2), 3.68–4.02 (m,
20H, OCH2), ꢁ2.53 (s, 2H, NH). HRMS (FAB) calcd for
the fluorescence quantum yields, solutions of H2TPP16 and
11a
SiPc(OEG)2
in DMF were used as the references (Ffl = 0.11
and 0.50 respectively).
Time-resolved fluorescence spectroscopy
Excited-state lifetimes and DAF spectra were measured using a
time-correlated single photon counting (TCSPC) technique in
combination with scanning of the detection wavelength as
described previously.11b The light of a Nd:VO4 laser (Cougar,
Time Bandwidth Products) operating at 60 MHz at a wavelength
of 532 nm and producing pulses with a duration of 12 ps was
used directly for excitation of the Por-part of the samples or to
synchronously pump a dye laser (Model 599, Coherent) tuned
to 620 nm for the Pc-part excitation. Fluorescence was detected
at the magic polarisation angle (54.71) relative to excitation with
a thermo-electrically cooled micro-channel plate (R3809-01,
Hamamatsu). Detection wavelength was chosen using a computer-
controlled monochromator (77200, Lot-Oriel). Electrical signals
were processed by a PCI TCSPC controller card (SPC630, Becker &
Hickl). The instrument response function was 42 ps as measured
at an excitation wavelength using Ludox. The data were analysed
by a home-made programme described previously.11b Decay
times and time shifts were linked through all measurements of
one scan sampled every 3 nm.
C
92H77N12O10Zn (MH+): 1573.5172; found: 1573.5181. UV-Vis
(DMF) [lmax nm (log e)]: 346 (4.98), 419 (5.69), 515 (4.00), 689
1
(5.28). Triad 5: H NMR (pyridine-d5): d 9.80 (d, J = 7.5 Hz, 2H,
Pc-Ha), 9.64 (d, J = 7.5 Hz, 2H, Pc-Ha), 9.52–9.55 (m, 2H, Pc-Ha),
9.06 (s, 16H, Por-Hb), 8.36–8.41 (m, 12H, Ph), 8.11–8.26 (m, 8H,
Pc-Hb and p-C6H4), 7.96–7.99 (m, 2H, Pc-Hb), 7.72–7.80 (m, 18H,
Ph), 7.50 (s, 2H, Pc-Hb), 7.28 (d, J = 8.4 Hz, 4 H, p-C6H4), 4.93
(t, J = 4.5 Hz, 4H, OCH2), 4.50 (t, J = 4.5 Hz, 4H, OCH2),
4.16–4.22 (m, 8H, OCH2), 3.82–3.96 (m, 8H, OCH2), 3.70–3.78
(m, 8H, OCH2), ꢁ2.52 (s, 4H, NH). HRMS (FAB) calcd
for C136H105N16O10Zn (MH+): 2186.7519; found: 2186.7501.
UV-Vis (DMF) [lmax nm (log e)]: 346 (5.13), 419 (6.01), 515
(4.49), 689 (5.27).
Acknowledgements
Electrochemical measurements
We thank The Chinese University of Hong Kong for a Research
Fellowship to X. Leng and the DFG for financial support (grant
no. ER 588/1-1).
These were carried out using a BAS CV-50W voltammetric
analyser. The cell comprised inlets for a platinum-sphere work-
ing electrode, a platinum-plate counter electrode and a silver-
wire pseudo-reference electrode. Typically, a 0.1 M solution of
[Bu4N][PF6] in DMF containing the sample was purged with
nitrogen for 15 min, then the voltammograms were recorded at
ambient temperature with a scan rate of 100 mV sꢁ1. Potentials
were referenced to SCE using ferrocene as an internal standard
(E1/2 = +0.38 V vs. SCE).21
References
1 V. Balzani, A. Credi and M. Venturi, ChemSusChem, 2008,
1, 26.
2 (a) M. R. Wasielewski, Acc. Chem. Res., 2009, 42, 1910;
(b) N. Aratani, D. Kim and A. Osuka, Acc. Chem. Res., 2009,
42, 1922; (c) S. Fukuzumi and K. Ohkubo, J. Mater. Chem.,
2012, 22, 4575; (d) J. Yang, M.-C. Yoon, H. Yoo, P. Kim and
D. Kim, Chem. Soc. Rev., 2012, 41, 4808.
3 R. Ziessel and A. Harriman, Chem. Commun., 2011, 47, 611.
4 (a) D. G. Nocera, Acc. Chem. Res., 2012, 45, 767; (b) G. Bottari,
O. Trukhina, M. Ince and T. Torres, Coord. Chem. Rev., 2012,
256, 2453.
Pc 2. A mixture of 1 (0.50 g, 0.52 mmol), TsCl (1.0 g,
5.2 mmol) and triethylamine (10 mL) in CH2Cl2 (50 mL) was
stirred at room temperature overnight. The volatiles were
removed under reduced pressure, and then the residue was
chromatographed on a silica gel column using CHCl3–CH3OH
(15 : 1, v/v) as the eluent to give the product as a green solid
1
(0.56 g, 85%). H NMR (DMSO-d6): d 9.25–9.38 (m, 4H, Pc-Ha),
9.22 (d, J = 7.2 Hz, 2H, Pc-Ha), 8.15–8.25 (m, 6H, Pc-Hb), 7.69 (d,
J = 7.5 Hz, 4H, ArH), 7.58 (s, 2H, Pc-Hb), 7.36 (d, J = 7.5 Hz, 4H,
ArH), 4.83 (t, J = 4.5 Hz, 4H, OCH2), 4.35 (t, J = 4.5 Hz, 4H,
OCH2), 3.85–4.05 (m, 8H, OCH2), 3.60–3.75 (m, 8H, OCH2),
5 (a) Y. Lin, Y. Li and X. Zhan, Chem. Soc. Rev., 2012, 41, 4245;
(b) A. Mishra and P. Bauerle, Angew. Chem., Int. Ed., 2012,
51, 2020.
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
New J. Chem., 2013, 37, 1746--1752 1751

View Article Online
NJC
Paper
6 V. Balzani, A. Credi and M. Venturi, Chem.–Eur. J., 2008,
14, 26.
7 (a) J.-Y. Liu, M. E. El-Khouly, S. Fukuzumi and D. K. P. Ng, 12 (a) D. Holten, D. F. Bocian and J. S. Lindsey, Acc. Chem. Res.,
(b) S. Tannert, E. A. Ermilov, J. O. Vogel, M. T. M. Choi,
¨
D. K. P. Ng and B. Roder, J. Phys. Chem. B, 2007, 111, 8053.
Chem.–Eur. J., 2011, 17, 1605; (b) M. K. Panda, K. Ladomenou
and A. G. Coutsolelos, Coord. Chem. Rev., 2012, 256, 2601;
2002, 35, 57; (b) A. Satake and Y. Kobuke, Org. Biomol.
Chem., 2007, 5, 1679.
(c) R. Jono and K. Yamashita, J. Phys. Chem. C, 2012, 13 (a) D. I. Schuster, S. MacMahon, D. M. Guldi, L. Echegoyen and
116, 1445. S. E. Braslavsky, Tetrahedron, 2006, 62, 1928; (b) L. Flamigni,
¨
´
8 (a) J.-Y. Liu, E. A. Ermilov, B. Roder and D. K. P. Ng, Chem.
Commun., 2009, 1517; (b) E. A. Ermilov, J.-Y. Liu, D. K. P. Ng
A. M. Talarico, B. Ventura, C. Sooambar and N. Solladie, Eur. J.
Inorg. Chem., 2006, 2155; (c) M. E. El-Khouly, J. Hasegawa,
A. Momotake, M. Sasaki, Y. Araki, O. Ito and T. Arai,
J. Porphyrins Phthalocyanines, 2006, 10, 1380; (d) T. D. M. Bell,
K. P. Ghiggino, A. Haynes, S. J. Langford and C. P. Woodward,
J. Porphyrins Phthalocyanines, 2007, 11, 455; (e) A. Takai,
M. Chkounda, A. Eggenspiller, C. P. Gros, M. Lachkar,
J.-M. Barbe and S. Fukuzumi, J. Am. Chem. Soc., 2010, 132, 4477.
¨
and B. Roder, Phys. Chem. Chem. Phys., 2009, 11, 6430;
(c) G. Bottari, G. de la Torre, D. M. Guldi and T. Torres,
Chem. Rev., 2010, 110, 6768.
9 (a) P.-C. Lo, X. Leng and D. K. P. Ng, Coord. Chem. Rev.,
2007, 251, 2334; (b) J.-Y. Liu, P.-C. Lo and D. K. P. Ng, Struct.
Bond., 2010, 135, 169; (c) E. A. Ermilov, R. Menting, J. T.
¨
F. Lau, X. Leng, B. Roder and D. K. P. Ng, Phys. Chem. Chem. 14 J.-Y. Liu, X.-J. Jiang, W.-P. Fong and D. K. P. Ng, Org. Biomol.
Phys., 2011, 13, 17633; (d) R. Menting, J. T. F. Lau, H. Xu, D. Chem., 2008, 6, 4560.
K. P. Ng, B. Roder and E. A. Ermilov, Chem. Commun., 2012, 15 P. Osswald, C.-C. You, V. Stepanenko and F. Wu¨rthner,
¨
¨
48, 4597; (e) R. Menting, D. K. P. Ng, B. Roder and
Chem.–Eur. J., 2010, 16, 2386.
E. A. Ermilov, Phys. Chem. Chem. Phys., 2012, 14, 14573.
10 (a) P. D. Harvey, in The Porphyrin Handbook, ed.
16 P. G. Seybold and M. Gouterman, J. Mol. Spectrosc., 1969,
31, 1.
K. M. Kadish, K. M. Smith and R. Guilard, Academic Press, 17 D. Rehm and A. Weller, Isr. J. Chem., 1970, 8, 259.
San Diego, 2003, vol. 18, pp. 63–250; (b) S. Fukuzumi, in 18 R. A. Marcus, J. Chem. Phys., 1956, 24, 966.
Handbook of Porphyrin Science, ed. K. M. Kadish, K. M. Smith 19 (a) I. R. Gould, D. Ege, J. E. Moser and S. Farid, J. Am. Chem.
and R. Guilard, World Scientific, 2010, vol. 10, pp. 183–243;
(c) P. D. Harvey, C. Stern and R. Guilard, in Handbook of
Soc., 1990, 112, 4290; (b) I. R. Gould, R. H. Young,
R. E. Moody and S. Farid, J. Phys. Chem., 1991, 95, 2068.
¨
Porphyrin Science, ed. K. M. Kadish, K. M. Smith and 20 O. Korth, T. Hanke, I. Ru¨ckmann and B. Roder, Exp. Tech.
R. Guilard, World Scientific, 2011, vol. 11, pp. 1–179. Phys., 1995, 41, 25.
11 (a) E. A. Ermilov, S. Tannert, T. Werncke, M. T. M. Choi, 21 R. T. Boere, K. H. Moock and M. Parvez, Z. Anorg. Allg.
´
¨
D. K. P. Ng and B. Roder, Chem.Phys., 2006, 328, 428;
Chem., 1994, 620, 1589.
c
1752 New J. Chem., 2013, 37, 1746--1752
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013