Multiply biphenyl substituted zinc(II) porphyrin and phthalocyanine as components for molecular materials

Article abstract of DOI:10.1142/S1088424612501453

The preparation and physico-chemical characteristics of zinc(II) porphyrin and phthalocyanine derivatives with biphenyl units are reported. These compounds have been prepared as components for molecular electronics systems and rotor-based molecular machin

Full text of DOI:10.1142/S1088424612501453

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2012; 16: 1293–1302
DOI: 10.1142/S1088424612501453
Published at http://www.worldscinet.com/jpp/
Multiply biphenyl substituted zinc(II) porphyrin and
phthalocyanine as components for molecular materials
Oriol Penona, Filippo Marsicob, Davide Santuccia, Laura Rodríguezc,
David B. Amabilino*b◊ and Lluïsa Pérez-García*a
a Laboratori de Química Orgànica, Facultat de Farmàcia, and Institut de Nanociència i Nanotecnologia (IN2UB),
Universitat de Barcelona, 08028 Barcelona, Spain
b Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus Universitari de Bellaterra, 08193
Cerdanyola del Vallès, Spain
c Departament de Química Inorgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain
In memory of Christian G. Claessens
Received 2 September 2012
Accepted 27 November 2012
ABSTRACT: The preparation and physico-chemical characteristics of zinc(II) porphyrin and
phthalocyanine derivatives with biphenyl units are reported. These compounds have been prepared
as components for molecular electronics systems and rotor-based molecular machines, where the
biphenyl units can act as paddles because they are oriented quasi-perpendicularly to the plane of the
aromatic macrocycles which would be coordianted through the transition metal ion by an axial ligand.
The minimalist design along with the absence of solubilizing groups leads to a low solubility of the
compounds in organic solvents; the phthalocyanines is only sparingly soluble while the porphyrin is
more easily manipulated, but in any case the concentration of both compounds is sufficient for surface
deposition. The luminescence of the compounds is characteristic of the central unit, although it is clear in
the absorption spectra that the phthalocyanine derivative has a particularly strong tendency to aggregate
non-specifically. The porphyrin forms microcrystals while the phthalocyanines which bears eight biphenyl
units forms amorphous aggregates from 1,2-dichlorobenzene reminiscent of glasses of other biphenyl
derivatives, which is interesting for the preparation of amorphous materials for optics applications.
KEYWORDS: aromatic compounds, organic dyes, p-functional materials, molecular electronics.
and symmetry are often attractive features which lead
to excellent solid state properties because of the lack
INTRODUCTION
The search for novel molecular materials which
might have utility in areas such as molecular electronics
of dilution of the p-functional units by solubilizing
groups, even if the solubility of these apparently simple
[1–7], photovoltaic current generation [8–12], and even
compounds can limit processing possibilities [27]. We
molecular machines [13–19] is leading many researchers
were attracted to 4-substituted biphenyl derivatives
to explore the synthesis and self-assembly of complex
compounds containing p-functional units — among
[28–36] of p-functional units because these groups are
well-defined spatially (that is, their general calamitic
them porphyrins and phthalocyanines — which are often
shape points in a certain direction determined by
at the heart of their function [20–26]. Yet simplicity
their connectivity) and they might aid in electrical
or mechanical transmission of energy. Rubrene is an
inspiration to us in this sense, insofar as it contains phenyl
SPP full member in good standing
substituents attached to an essentially flat aromatic
core to which they are oriented perpendicularly [37].
Although intuition might suggest that the conformation
*Correspondence to: David B. Amabilino, email: amabilino@
icmab.es, tel: +34 93-5801853, fax: +34 93-5805729; Lluïsa
Pérez-García, email: mlperez@ub.edu, tel: +34 93-4035849
Copyright © 2012 World Scientific Publishing Company

1294 O. PENON ET AL.
N
N
N
M
N
N
N
N
M
N
N
N
N
N
1 M = 2H
2 M = 2H
Zn1 M = Zn
Zn2 M = Zn
Formulae
H
O
of these groups could hinder charge transport, rubrene
has excellent electronic properties [38].
N
H
Porphyrins and phthalocyanines are p-functional
units that have proven interest as photoconductors [39],
components of photovoltaic devices [40–42], and in
molecular electronics in general [43–48]. In addition,
their C4 symmetries are appealing for both solid state
packing and for components for rotors when the central
metal atom is coordinated orthogonally to the plane of
the macrocyclic ring. Here we report the preparation
of derivatives of these cores with biphenyl units joined
directly to them. The porphyrin 1 and phthalocyanine 2
and their zinc(II) complexes (Zn1 and Zn2) have been
synthesized, fully characterised, their tendency to form
aggregates has been studied, and their photochemical
characteristics established.
AcOH/PhNO2
Propionic acid
140 °C, 1.5 h
3%
120 °C, 1 h
9%
N
N
N
N
M
RESULTS AND DISCUSSION
Synthesis and characterisation
The porphyrin and phthalocyanine derivatives 1
and 2 were prepared by the synthetic routes shown in
Schemes 1 and 2. The porphyrin (Scheme 1) was obtained
by reaction of biphenyl-4-carboxaldehyde with pyrrole
either under the classic conditions in boiling propionic
acid in air or by heating in a mixture of acetic acid and
nitrobenzene [49], with a very recent report using the
BF3 etherate method [50]. Having assayed the former
two methods, that in acetic acid and nitrobenzene proved
to be more effective and substantially easier to work up,
in accord with the cited procedure [49], although the
yield reported previously could not be reproduced. The
1 M = 2H
Zn(OAc)2
>37%
Zn1 M = Zn
Scheme 1.
great advantage of this procedure is that the resulting
porphyrin crystallizes directly from the cooled reaction
mixture. The crystals were washed with EtOH in order to
remove traces of nitrobenzene, to give an overall yield of
9%, compared with a reported 12% for the BF3 etherate
method [50].
Copyright © 2012 World Scientific Publishing Company
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MULTIPLY BIPHENYL SUBSTITUTED ZINC(II) PORPHYRIN AND PHTHALOCYANINE 1295
Cl
N
Cl
N
on the porphyrin periphery since tetraphenyl porphyrins
do not usually show this behavior. Addition of acid
causes the protonation of the porphyrin, which becomes
positivelychargedandadoptsadistortedratherthanplanar
structure, so that the electrostatic repulsion disfavors
aggregation and aids solubilization. As a consequence,
the 1H NMR signals are sharp and well-defined.
OH
HO
B
B
OH
HO
Dioxane
100 °C, 2 h
85%
Pd(PPh3)4, K3PO4
In order to confirm this hypothesis, we tested if
aggregation was concentration dependent. To check
concentration dependency, we prepared a set of samples
of compound 1 ranging from 7 mM to 0.1 mM. From
the spectra recorded it can be concluded that when
concentration diminishes a progressive reduction of the
broadness, was observed, and the appearance, initially
weakly, of the well-defined aromatics signals (Fig. 2).
There is not a continuous shift of the signals, rather a very
broad signal appears centred at approximately 7.5 ppm at
highconcentrations,whichindicativeofarapidaggregation
of non-specific interactions caused by the poor solubility
rather than a particular strong non-covalent interaction.
It is conceivable that the biphenyl units could enter into
edge-on interactions which lead to this aggregation.
N
N
Li, n-hexanol
∆ 12 h
52%
Incorporation of zinc(II) into the centre of 1 to give
the new zinc(II) complex proved surprisingly difficult.
The usual method for preparing the metallated porphyrin
in dichloromethane [51–54] only resulted in partial
metallation of the sample, in spite of the large excesses
of Zn(OAc)2 added (up to 16 equivalents) and the long
reaction times used (up to 76 h). Absorption spectroscopy
and laser desorption-ionization time of flight (LDI-
TOF) mass spectrometry both indicated the presence
of starting material. We surmise that the high tendency
of 1 to aggregate in the solvent is at least partially
responsible for the poor efficiency of the reaction under
these conditions. Subsequently the solvent was changed
to N,N-dimethylformamide, in order to give more energy
to the reaction by increasing the temperature (to 153 °C),
and because of the greater solubility of Zn(OAc)2 that
is insoluble in CH2Cl2 (although this is not usually an
impediment). The reaction time and the number of
equivalents of Zn(OAc)2 required were not optimized,
but no more starting material was found in the reaction
mixture after 24 h as indicated by LDI-TOF MS. The
complete inclusion was also evidenced by the absence
of the N–H band in the IR spectrum, as well as the
characteristic (UV-vis) absorption spectrum (vide infra).
The phthalocyanine 2 was prepared in two steps from
4-biphenylboronic acid and 4,5-dichlorophthalonitrile
using palladium tetrakis(triphenylphosphine) as coupling
reagent (Scheme 2). The intermediate 1,2-dicyano-4,5-bis-
biphenylbenzene showed the characteristic spectroscopic
signals expected for this kind of compound in the NMR
spectrum, especially the singlet at 7.92 ppm corresponding
to the protons in the central phenyl ring, as well as the
CN band in the IR spectrum at 2229 cm-1. Formation
of the phthalocyanine from this dinitrile proceeded
smoothly by reacting it with lithium in hexanol. The
N
N
N
N
N
N
M
N
N
2 M = 2H
Zn(OAc)2
95%
Zn2 M = Zn
Scheme 2.
While the mass and IR spectra of 1 are in total accord
with its structure, the 1H NMR spectrum of the porphyrin
(at 300 MHz in CDCl3 at a concentration of 1.16 × 10-2
M and at room temperature) exhibits broad signals of
very low intensity compared with that expected given
the concentration. Increasing the temperature at which
the spectrum was recorded only achieved a marginal
improvement. Addition of 1.5% CF3COOD by volume
to the CDCl3 solution (which results in deuteration
of the basic pyrrolic nitrogen atoms) causes a clear
improvement in the intensity and resolution of the signals
as well as a slight shift of some of the resonances (Fig. 1).
These observations could be a result of aggregation of
the porphyrins under these experimental conditions,
presumably favored by the biphenyl substituents present
Copyright © 2012 World Scientific Publishing Company
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1296 O. PENON ET AL.
but which is an empirical fact. The product
does not show better solubility than its free base
precursor, but the absorption and LDI-TOF
spectra confirm its identity.
Optical microscopy of solids
In order to investigate the capacity of the
compounds to form ordered solid state materials
which might be interesting for opto-electronic
applications, theporphyrinsandphthalocyanines
were precipitated from solution. The porphyrins
can be dissolved in hot chloroform, toluene
and dioxane, and crystallized upon cooling.
The largest and most well–defined solid was
obtained from chloroform from which rhombic
crystals precipitate (Fig. 3 for compound 1). The
crystals have well-defined edges in the main,
and are clearly birefringent when observed with
a polariser at different angles with respect to the
sample. The crystals also show the fluorescence
characteristic of the porphyrins in the solid state.
When the porphyrins were crystallised from
either dioxane or toluene (in which they are
slightly less soluble than in chloroform) smaller
and less well-defined crystallites were formed.
The solubilization of the phthalocyanines
2 and Zn2 is considerably more challenging
than the biphenyl-substituted porphyrins.
The only solvent found which provided
sufficient solubility of these compounds in
order to attempt a crystallisation process was
1,2-dichlorobenzene. The compounds were
apparently well-dissolved near the boiling
point of the solvent, but when the solutions
were allowed to cool a flocculent apparent
solid was observed at the solvent-air interface.
When the suspension was cast onto glass
and was observed with a polarising optical
microscope, blobs of amorphous material
containing very small crystallites were
Fig. 1. 1H NMR spectra of 1 in CDCl3 at a concentration of 1.16 × 10-2 M and
at room temperature (top) and below in CDCl3/CF3COOD (98.5/1.5) under
otherwise identical conditions. The peak at d = 7.25 ppm corresponds to the
residual signal of chloroform in CDCl3
Fig. 2. 1H NMR spectra (300 MHz) in CDCl3 of compound 1 at two different
concentrations: 7 mM (top), and 0.1 mM (bottom). The peak at d = 7.25
ppm corresponds to the residual signal of chloroform in CDCl3
observed. Figure 4 shows one of these regions, wherein
the amorphous majority of the material has solid lumps
with sizes below 5 µm in all cases.
product was purified by repeated washings with acetic
acid, methanol, and dichloromethane. Compound 2 is a
green microcrystalline powder that is largely insoluble in
all common solvents at room temperature. We could not
identify a solvent which permitted recording of the 1H NMR
spectrum of the molecule. The LDI-TOF mass spectrum of
2 clearly indicates the authenticity of the compound. The
characteristic (UV-vis) absorption bands of the free base
phthalocyanine are observed clearly, although a broad band
corresponding to an aggregate was present. The preparation
of the zinc(II) phthalocyanine was successfully achieved by
heating the free base compound with an excess of zinc(II)
acetate. Curiously, no difficulties were encountered in
the incorporation of the metal ion despite the apparently
strong tendency of the molecules to aggregate, in apparent
contradiction to the observations made for the porphyrin
Photochemical characterisation
The absorption spectra of the porphyrins show the two
characteristic bands, one at around 420 nm (Soret band,
with an extinction coefficient e around 105 M-1.cm-1) and
less intense bands between 500 and 650 nm (Q-bands,
with lower extinction coefficient values of ca, 103-104
M-1.cm-1) [55, 56]. The Soret band of 1 is located at ca.
422 nm (S0 → S2 transition), and is red-shifted by 1 nm
in the Zn(II) complex. The four less intense Q-bands
(S0 → S1 transition) are observed at 517, 554, 593 and
647 nm for the free-base porphyrin, at virtually identical
positions for other tetraaryl porphyrins [57–59]. The
Copyright © 2012 World Scientific Publishing Company
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MULTIPLY BIPHENYL SUBSTITUTED ZINC(II) PORPHYRIN AND PHTHALOCYANINE 1297
Fig. 4. Transmission optical microscope images of
2
precipitated from 1,2-dichlorobenzene, top image with parallel
polarizers and bottom image with crossed polarizers. The scale
bars corresponds to 30 µm
Fig. 3. Optical microscope images of 1 crystallized from
chloroform, A and B transmission images with a bottom
polarizer at the positions indicated by the arrows above the
scale bar, C is a transmission image with crossed polarisers,
and D is a reflection fluorescence image with GFP filter. In all
cases the scale bar corresponds to 10 µm
Fig. 5. Normalized emission spectra of 1 (solid line) and Zn1
(dotted line) in dichloromethane solution at 1 × 10-6 M (298 K)
lowest energy bands disappear for the metalloporphyrins
and this lower number of electronic absorption bands
is attributed to an increase in the molecular symmetry
upon complex formation (the protons in the free
base porphyrin are localised on the timescale of the
spectroscopy). Additionally, an absorption band is
observed with maximum at 254 nm corresponding to
the p–p* transitions associated with the phenyl groups
(pendant “arms”) of the porphyrins.
Excitation of diluted dichloromethane solutions
of compounds 1 and Zn1 results in the characteristic
porphyrin emission bands. The emission spectra were
recorded at 298 K and at 77 K. Two bands were observed
in the red region which are weaker and blue-shifted
for the metalloporphyrin with respect to the free-base
system (Fig. 5). The emission spectra are dominated
by S1 → S0 fluorescence [60]. The shorter-wavelength
feature is the Q(0,0) band and the longer-wavelength
feature is the Q(0,1) vibronic satellite (Table 1). The
same emission was observed when the samples were
excited at the Soret and the different Q-bands. The
lowest energy emission band increases in intensity for
the metallated porphyrins. No emission was observed in
any case when the samples were excited in the phenyl
absorption band. Low temperature experiments (77 K)
Copyright © 2012 World Scientific Publishing Company
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1298 O. PENON ET AL.
Table 1. Absorption and emission data of the free-base porphyrin and phthalocyanine and their corresponding Zn(II)-complexes at
1 × 10-6 M and at 298 K (in dichloromethane for 1 and Zn1 and THF for 2 and Zn2)
Compounds Absorption maximum nm
Emission maximum
nm (298 K)
t (singlet, ns)
F
kr (× 10-6, s-1)
knr (× 10-6, s-1)
(e × 10-3, M-1.cm-1)
1
254 (119.2), 422 (531.2),
517 (27.3), 554 (23.4), 593
(17.6), 647 (20.3)
654, 717
5.36
0.079
14.7
172
Zn1
247 (138.2), 423 (496.9),
547 (37.9), 587 (26.1)
599, 652
1.72
0.037
21.5
560
2
686, 717*
695*
723, 761, 808
3.80
2.63
0.065
0.043
24.9
11.4
355
252
Zn2
700, 721sh, 776
*The absorption coefficients are not given for these compounds because of the high state of aggregation makes it impossible to attain
a reliable value.
resulted in the same emission bands which were slightly
sharper than the room temperature spectra. The excitation
collected at both emission maxima match well with the
corresponding absorption spectrum, which proves the
involvement of the porphyrin ring at the origin of the
emission (Fig. 6).
Solid-state experiments displayed broad emissions one
order of magnitude lower in intensity than those recorded
in solution for the free ligands and non-emissive metallated
derivatives. This effect arises from concentration
quenching, as reported for similar derivatives [54, 55].
In an attempt to analyze in more detail the characteristics
of the emission processes, the fluorescence lifetimes were
measured in solution. The time-correlated single photon
counting technique was used upon excitation of the samples
at 370 nm and the results are summarized in Table 1. The
recorded lifetime of the metallated compound is shorter
than that of the free-base molecule because of the heavy
metal effect, i.e. metallation of the porphyrin quenches
the fluorescence. The fluorescence quantum yield of the
free-base compound 1 is also about the double than the
corresponding to the metallated species Zn1. (Table 1).
Radiative, kr, and non-radiative knr, decay constants
(Table 1) were calculated assuming that the emissive
state is formed with unitary efficiency in each case when
excited directly into the porphyrins at 420 nm and taking
into account that:
kr = F / t and knr = 1/t–kr
Fig. 6. Absorption spectra of 1 and 2 (top) and normalized
It is observed that non-radiative constants (knr) are one
order of magnitude higher than the corresponding kr, as
observed in other porphyrins [61].
excitation spectrum of 1 in dichloromethane solution (bottom,
1 × 10-6 M, lem = 422 nm)
The absorption spectra of the free-base phthalocyanine
2 and the corresponding zinc(II)-complex were recorded
in THF at a concentration 1 × 10-6 M and the results
are summarized in Table 1. The absorption spectra
of both compounds are poorly resolved. The Soret
(~370 nm) and the Q-bands (~690 and 715 nm) could
be identified and are in the expected regions for these
compounds [62–66] although they are buried under broad
transitions, characteristic of the presence of aggregated
phthalocyanines [62–67].
The phthalocyanine compounds are not very soluble
in most solvents but THF seemed to be a good choice
since the increased solvent polarity improved the spectral
resolution. This solvent proved to be a good candidate in
other works [62–66]. Decreasing the concentration did
not eliminate aggregates, and a very broad absorption
Copyright © 2012 World Scientific Publishing Company
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MULTIPLY BIPHENYL SUBSTITUTED ZINC(II) PORPHYRIN AND PHTHALOCYANINE 1299
Fig. 8. Normalized excitation spectra of 2 (solid line, lem = 762
nm) and Zn2 (dashed line, lem = 723 nm) in approximately 1 ×
10-6 M THF solution
the shoulder around 720 nm observed in the metallic
compound increases in intensity (Fig. 7).
The excitation spectra reproduce the absorption
spectra of the molecules without the broad aggregate
band observed in the absorption spectra. This observation
indicates that the species responsible for the emission are
the isolated solvated molecules (Fig. 8).
Fluorescence quantum yields are summarized in
Table 1. The lifetime is in the order of 2–4 ns as observed
for other similar complexes [65] and is shorter for Zn2
than for 2, which could be due to the heavy atom effect as
in the case of the porphyrins. As there, the knr constant is
one order of magnitude greater for the metallic complex.
CONCLUSION
The synthesis of oligo-biphenyl derivatives of zinc(II)
porphyrin and phthalocyanines has been achieved with
relative ease, and although the compounds show the
expected low solubility in organic solvents, they are
sufficiently dispersed to allow the characterisation of their
photophysical properties and the concentration levels
will allow the study of their binding and adsorption to
surfaces. The processing of the phthalocyanines product
Fig. 7. Absorption spectra of the phthalocyanines (top) and
is a particular challenge at the present time, presumably
because of the increased number of biphenyl units and
the intrinsically lower solubility of phthalocyanines
when compared with tetraaryl porphyrins, and the surface
assembly of this compound is an attractive prospect,
since surface-based rotors are an area of great interest
[68–69], and although the solubility is low it is sufficient
to allow surface deposition.
It is remarkable that the phthalocyanines does not
seem to precipitate from solution, but forms a disordered
state, similar to layers of oligoethyleneoxide-substituted
phthalocyanines on mica [70] which in turn reminds us
of layers of porphyrins on the same surface [71, 72]. The
bulk disordered state requires further investigation, but
normalized emission spectra of 2 (solid line) and Zn2 (dashed
line) in approximately 1 × 10-6 M THF solution at room
temperature (middle) and at 77 K (bottom). lexc = 680 nm
band persisted even at very low concentration. Emission
spectra were recorded in ca. 1 × 10-6 M THF solutions
at RT and 77 K (lexc = 680 nm, Fig. 7). A very intense
emission band is observed for both compounds, with
clear maxima located at 723 and 700 nm (with a shoulder
at ca. 720 nm) for the free base phthalocyanine and for
the metal-complex respectively. As observed with the
porphyrins, the emission of the zinc(II)-derivative is blue-
shifted with respect to its metal-free parent. Emission
experiments at 77 K display similar features, although
Copyright © 2012 World Scientific Publishing Company
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1300 O. PENON ET AL.
some biphenyl derivatives do show glass-like behavior
[73]. We are presently exploring these possibilities,
because the amorphous state can be advantageous for
optics applications.
7.98 (d, J = 6 Hz, 8H, H2’,6’), 7.67 (t, J = 6 Hz, 8H, H3’,5’),
7.55 (t, J = 6 Hz, 4H, H4’). MS (LDI TOF): m/z 919.2
calcd. for (C68H46N4)+ 918.3 [M]+. UV-vis (CH2Cl2): lmax
,
nm 423, 518, 554, 593, 649. IR (ATR): n, cm-1 3317
(NH). Elemental analysis; found C, 88.60; H, 5.32; N,
6.34, expected C, 88.86; H, 5.04; N, 6.10. Method B. A
mixture of acetic acid (20 mL) and nitrobenzene (15 mL)
was heated to reflux, then pyrrole (190 µL, 2.74 mmol)
and biphenyl-4-carboxaldehyde (0.5 g, 2.74 mmol) were
added, all in air. The solution became dark immediately.
After 1 hour, the reaction was cooled down and filtered,
and the crystals that had formed were washed with EtOH
(3 × 8 mL) to give 4 as a purple solid (0.215 g, 8.5%).
The sample was characterized as for method A.
EXPERIMENTAL
General
The starting materials were purchased commercially
and were used without further purification. Thin-layer
chromatography (TLC) was performed on aluminium
plates coated with Merck Silica gel 60 F254. Developed
plates were air-dried and scrutinized under a UV lamp.
Silica gel 60 (35–70 mesh, SDS) was used for column
chromatography. Mass spectrometry was performed
on a LC/MSD-TOF mass spectrometer from Agilent
Technologies. The samples were deposited directly onto a
non-polished stainless steel sample plate from solution. 1H
and 13C NMR spectra were recorded using the deuterated
solvent as lock and tetramethylsilane as internal reference.
Zinc(II)
5,10,15,20-tetrakis(4-biphenyl)porphyrin
(Zn1). Method A. A solution of 1 (95 mg, 0.1 mmol)
in CH2Cl2 (28 mL) was heated to reflux under an argon
atmosphere. Zn(OAc)2 (64 mg, 0.4 mmol) dissolved in
a 1:1 mixture of MeOH (9 mL) and CH2Cl2 (9 mL) was
added dropwise, and the whole was refluxed for 72 h. The
mixture was extracted with a saturated solution of NaHCO3
(2 × 15 mL) and brine (2 × 15 mL). The organic phase was
evaporated under reduced pressure and the crude product
purified by column chromatography (CH2Cl2/EtOAc 95:5)
to give Zn1 as a purple solid (51 mg, 52%). mp > 350 °C.
1H NMR (300 MHz, CDCl3, 25 °C): d, ppm 9.07 (s, 8H,
pyr.), 8.31–7.45 (m, 36H, arom.). MS (LDI TOF): m/z 982.5
Photophysical experiments
Absorption spectra were recorded on a Cary 100 scan
388 Varian UV spectrometer at 298 K and fluorescence
emission spectra on
a Horiba-Jobin-Yvon SPEX
calcd. for (C68H44N4Zn)+ 982.4 [M]+. UV-vis (CH2Cl2): lmax
,
Nanolog-TM at 298 K and 77 K. The values of quantum
yieldweredeterminedat298Kwithrespectto[Ru(bipy)3]
Cl2 in water as standard reference (F = 0.042) [74]. The
fluorescence decays were obtained using a home-built
equipment that has been described elsewhere [75] and
were analyzed using the method of modulating functions
implemented by Striker et al. [76] and on an Edinburgh
Instruments LifeSpec-II spectrometer based on the time
correlated single photon counting (TCSPC) technique,
equipped with a PMT detector, double subtractive
monochromator and 635 nm picosecond pulsed diode
lasers source as excitation (decay fittings were done with
F900 software from Edinburgh Instruments).
nm 426, 552, 594. Elemental analysis; found C, 82.88; H,
4.79; N, 5.87, expected C, 83.13; H, 4.51; N, 5.70. Method
B. A solution of 1 (100 mg, 0.109 mmol) in DMF (30 mL)
was heated to reflux under an argon atmosphere. Zn(OAc)2
(68 mg, 0.435 mmol) dissolved in DMF (20 mL) was added
dropwise and the whole was refluxed for 24 h. Then the DMF
was evaporated and CH2Cl2 (50 mL) was added. The solution
was extracted with a saturated solution of NaHCO3 (2 × 15
mL) and brine (2 × 15 mL). The organic phase was evaporated
under reduced pressure and the crude product purified by
washing with acetone (3 × 8 mL) to give 8 as a purple solid
(40 mg, 37%); the sample was characterized as for method A.
1,2-dicyano-4,5-bis(4-biphenyl)benzene. A mixture
of 4,5-dichlorophthalonitrile (500 mg, 1.52 mmol),
4-biphenylboronic acid (663 mg, 3.35 mmol) and
palladium tetrakis(triphenylphosphine) (116 mg) in
dioxane (15 mL) was combined with K3PO4 (2.12 g, 10
mmol) in water (4 mL) under nitrogen and the whole was
heated at 100 °C for 2 h. The product was purified by
column chromatography on silica gel using ethyl acetate-
hexane as eluent, yielding the pure compound as a white
solid (55 mg, 85%). The solid was crystallised from
chloroform-hexane to afford the product as transparent
colourless crystals which are fluorescent. MS (LDI TOF):
m/z 432.4 calcd. for (C32H20N2)- 432.2 [M]-. 1H NMR (250
MHz, CDCl3): d, ppm 7.92 (s, 2H), 7.65–7.55 (m, 8H),
7.53–7.36 (m, 6H), 7.27 (d, 4H). 13C NMR (63 MHz,
CDCl3): d, ppm 145.8, 141.8, 140.2, 136.9, 136.0, 130.3,
129.3, 128.3, 127.7, 127.4, 115.9, 114.8. IR (ATR): n,
Synthesis
5,10,15,20-tetrakis(4-biphenyl)porphyrin
(1).
Method A. Propionic acid (14 mL) was heated to
reflux, then pyrrole (190 µL, 2.74 mmol) and biphenyl-
4-carboxaldehyde (0.5 g, 2.74 mmol) were added, all in
air. The solution became dark immediately. After 1.5 h
the reaction was allowed to cool down and was filtered.
The solid was dissolved in CH2Cl2 and extracted with a
solution of 10% Na2CO3 in H2O (2 × 15 mL). The organic
phase was evaporated under reduced pressure and the
crude product purified by column chromatography
(CH2Cl2/EtOAc 95:5) to give 1 as a purple solid (75
1
mg, 3%). mp > 350 °C. H NMR (300 MHz, CDCl3/
CF3COOD (98.5/1.5), 25 °C): d, ppm 8.78 (s, 8H, pyr.),
8.67 (d, J = 9 Hz, 8H, H2,6), 8.29 (d, J = 9 Hz, 8H, H3,5),
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 1300–1302

MULTIPLY BIPHENYL SUBSTITUTED ZINC(II) PORPHYRIN AND PHTHALOCYANINE 1301
cm-1 3032 (w), 2229 (w, CN), 1601 (m), 1589 (m), 1480
7 Babu SS, Prasanthkumar S and Ajayaghosh A.
Angew. Chem. Int. Ed. 2012; 51: 1766–1776.
8 Nelson J. Curr. Opinion Solid State Mater. Sci.
2002; 6: 87–95.
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2011; 23: 682–732.
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ton J, Gorodetsky AA, Palma M, Bullard Z, Kramer
T, Delongchamp D, Fischer D,. Kymissis I, Toney
MF and Nuckolls C. Adv. Func. Mater. 2012; 22:
1167–1173.
11 Li C and Wonneberger H. Adv. Mater. 2012; 24:
613–636.
12 Mishra A and Baeuerle P. Angew. Chem. Int. Ed.
2012; 51: 2020–2067.
13 Balzani V, Credi A, Raymo FM and Stoddart JF.
Angew. Chem. Int. Ed. 2000; 39: 3349–3391.
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(m), 1447 (w), 1406 (w), 1366 (w), 1269 (w), 1190 (w),
1114 (w), 1075 (w), 1006 (w), 923 (m), 841 (s), 769 (s),
734.5 (s), 698 (s). Elemental analysis; found C, 88.74; H,
4.73; N, 6.53, expected C, 88.86; H, 4.66; N, 6.48.
2,3,9,10,16,17,23,24-octakis(4-biphenyl)
phthalocyanine (2). Under an argon atmosphere, hexanol
(260 µL) and lithium metal (3.7 mg, 0.53 mmol) were
stirred for 2 h at 100 °C to generate lithium hexanoate.
1,2-dicyano-4,5-bis(4-biphenyl)-benzene (100 mg, 0.23
mmol) was added as a solid and the mixture was heated
at 160 °C for 12 h. Glacial acetic acid (5 mL) was added,
and the mixture was filtered and washed with acetic acid
(5 mL), methanol (10 mL) and dichloromethane (20 mL).
The solid was boiled in toluene and filtered three times,
and then washed with dichloromethane to leave a deep
green solid 52%. mp > 350 °C. MS (LDI TOF): m/z 1730.8
calcd. for (C128H82N8)+ 1730.7 [M]+. UV-vis (THF): lmax
,
nm 686, 717. Elemental analysis; found C, 88.93; H, 4.77;
N, 6.30, expected C, 88.76; H, 4.77; N, 6.47.
2,3,9,10,16,17,23,24-octakis(4-biphenyl)
phthalocyaninatozinc(II) (Zn2). Phthalocyanine 2 (18
mg, 10 µmol) was suspended in DMF with a large excess
of zinc(II) acetate (32 mg, 0.2 mmol) and the mixture
was stirred at 100 °C for 24 hours under argon. Once at
room temperature, the mixture was filtered and the solid
was washed sequentially with water, acetonitrile, ethyl
acetate, and chloroform; then, it was dried in vacuum, to
give Zn2 in 95% yield. mp > 350 °C. MS (LDI TOF): m/z
1793.6 calcd. for (C128H80N8Zn)+ 1793.1 [M]+. UV-vis
(THF): lmax, nm 695. Elemental analysis; found C, 85.24;
H, 4.67; N, 6.02, expected C, 85.63; H, 4.49; N, 6.24.
16 Durot S, Reviriego F and Sauvage JP. Dalton Trans.
2010; 39: 10557–10570.
17 Lemouchi CS, Vogelsberg L, Zorina S, Simonov P,
Batail S, Brown MA and Garcia-Garibay M. J. Am.
Chem. Soc. 2011; 133: 6371–6379.
18 von Delius M and Leigh DA. Chem. Soc. Rev. 2011;
40: 3656–3676.
19 Coskun A, Banaszak M, Astumian RD, Stoddart JF
and Grzybowski BA. Chem. Soc. Rev. 2012; 41: 19–30.
20 Leclere P, Surin M, Viville P, Lazzaroni R, Kilbin-
ger AFM, Henze O, Feast WJ, Cavallini M, Bis-
carini F, Schenning APHJ and Meijer EW. Chem.
Mater. 2004; 16: 4452–4466.
Acknowledgements
21 Wu JS, Grimsdale AC and Mullen K. J. Mater.
Chem. 2005; 15: 41–52.
22 Gomar-Nadal E, Puigmartí-Luis J and Amabilino
DB. Chem. Soc. Rev. 2008; 37: 490–504.
23 Gonzalez-Rodriguez D and Schenning APHJ.
Chem. Mater. 2011; 23: 310–325.
24 Metri N, Sallenave X, Plesse C, Beouch L, Aubert
PH, Goubard F, Chevrot C and Sini G. J. Phys.
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This work was supported by the DGR, Catalonia
(Project 2009 SGR 158), the MINECO, Spain (projects
CTQ2010-16339,
TEC2008-06883-C03-02
and
TEC2011-29140-C03-02). We thank Dr. João Carlos
Lima from Universidade Nova de Lisboa and Dr.
Fernando Bozoglián from the ICIQ for the help on
lifetime measurements.
25 Yuan WZ, Mahtab F, Gong Y, Yu Z-Q, Lu P, Tang
Y, Lam JWY, Zhu C and Tang BZ. J. Mater. Chem.
2012; 22: 10472–10479.
26 HayashiY, Obata N, Tamaru M, Yamaguchi S, Mat-
suo Y, Saeki A, Seki S, Kureishi Y, Saito S, Yama-
guchi S and Shinokubo H. Org. Lett. 2012; 14:
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