Structural characterisation of a red phthalocyanine

Article abstract of DOI:10.1039/b304173p

Metal 1,4,8,11,15,18,22,25-octakis(hexylsulfanyl)phthalocyanines exhibit a weak absorption band in the 450-600 nm region, leading to novel dyes that include the red lead metallated derivative that has been characterised by X-ray crystallography.

Full text of DOI:10.1039/b304173p

Structural characterisation of a red phthalocyanine
Paul M. Burnham, Michael J. Cook,* Lee A. Gerrard, Martin J. Heeney and David L. Hughes
Wolfson Materials and Catalysis Centre, School of Chemical Sciences and Pharmacy, University of East
Anglia, Norwich, UK NR4 7TJ. E-mail: m.cook@uea.ac.uk; Fax: 44 1603 507773; Tel: 44 1603 593135
Received (in Cambridge, UK) 15th April 2003, Accepted 23rd June 2003
First published as an Advance Article on the web 9th July 2003
Metal 1,4,8,11,15,18,22,25-octakis(hexylsulfanyl)phthalo-
cyanines exhibit a weak absorption band in the 450–600 nm
region, leading to novel dyes that include the red lead
metallated derivative that has been characterised by X-ray
crystallography.
bathochromically shifted Q-band lmax 836 nm, cf. 1, lmax 818
nm.†
Previous reports of arylsulfanyl substituted analogues3
focussed on the near-IR absorption band and gave no indication
of visible region absorptions. Such absorptions clearly arise
from the series 1–4. The weak absorption just to the blue of the
Q-band is a common feature of phthalocyanine electronic
absorptions and can be assigned to a transition to a higher
vibrational level. However, there is also a weak, broad band in
the 450–600 nm region, Fig. 1 (inset). The energies of these two
weak bands are sensitive to the metal centre and give rise to the
variation in the colours of the four phthalocyanine derivatives.
Thus in the solution phase the zinc derivative 2 is brown, the
chloroindium derivative 3 mauve and the copper derivative 4
purple. The lead derivative 1 proves to be a red dye, crystallising
as deep red needle-prisms, mp 144–146 °C, from THF–acetone
and dissolving in various organic solvents to form red
solutions.
Metallated phthalocyanines are commercially important blue/
green dyes and pigments. Their intense colour arises from a
strong and relatively narrow absorption band at ca. 700 nm (the
Q-band) that arises from a p–p* transition.1 The energy of this
transition shows some degree of sensitivity to the central metal
ion. However, substituents, particularly when they are located at
the non-peripheral (1,4,8,11,15,18,22,25) sites of the macro-
cycle, can show a much more marked effect leading to
significant bathochromic shifts. Indeed, examples of near infra-
red absorbing phthalocyanine dyes include derivatives bearing
non-peripheral substituents linked through oxygen atoms (lmax
ca. 760 nm),2 and sulfur (lmax > 800 nm).3 However, there are
no comparable structural modifications which shift the Q-band
as significantly towards the blue.
In a programme designed to investigate phthalocyanine dye
materials with colours other than blue or green, we have
commenced investigation of the effect of substituents and metal
centres on the energies of transitions other than the Q-band.
These include the Soret, N, L and C transitions which normally
occur in the UV spectrum.1 Here we describe the novel
1,4,8,11,15,18,22,25-octakis(hexylsulfanyl)phthalocyanines
1–4 all of which exhibit a visible region transition between
450–600 nm.
A burnished film of 1, i.e. one formed by smearing crystals
onto a glass slide, shows a Q-band at 859 nm. This compares
with lmax 818 nm in the solution phase. The shift to longer
wavelength in the solid state implies a packing dissimilar from,
for example, the columnar packing of the ‘shuttlecock’ shaped
molecules of unsubstituted lead phthalocyanine in its mono-
clinic form.5 X-Ray crystallography of 1 confirmed this. The
room-temperature X-ray structure analysis shows a single,
unique molecule in a triclinic cell; pairs of these molecules lie
about centres of symmetry. The cores of the molecules, i.e. Pb,
the eight N and the thirty-two sp2 C atoms, are well-resolved
and they refined satisfactorily. However, gross disorder was
found in four of the eight hexyl groups, and the refinement was
concluded with rather high R-values, viz. wR2 = 0.271 and R1
= 0.196 for all 12005 reflections; for the 5082 observed
reflections, R1 = 0.094.
Compounds 1–4 were prepared in a convenient three step
synthesis from dicyanohydroquinone according to Scheme 1.†
Fig. 1 shows the UV to near-IR spectra for the four compounds.
The series exhibits, as expected, the Q-band shifted into the near
infra-red and the lmax is clearly metal dependent. In contrast to
the corresponding metallated 1,4,8,11,15,18,22,25-octaalkyl
derivatives,4 the chloroindium derivative, 3, shows the most
To improve the resolution, intensity data were measured at
140 K. The cell is now twice as large and there are two
independent molecules in the asymmetric unit, i.e. four in the
¯
triclinic cell with P1 symmetry.‡ The two molecules, denoted as
Scheme 1 Reagents and conditions: i Triflic anhydride, 2,6-lutidine,
CH2Cl2, 220 °C to RT, 65%. ii Hexanethiol, K2CO3, DMSO, RT, 70%. iii
M(OAc)2 or InCl3, DBU, PeOH, reflux, 15–55% depending upon M.
Fig. 1 Absorption spectra of compounds 1–4 in THF between 350–1000 nm
and, inset, expansion of 400–600 nm region.
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1A and 1B, are very similar in dimensions, orientation and in the
arrangements of the hexyl side-chains (Table 1 and Fig. 2). The
two lead atoms Pb(1) and Pb(2) in 1A and 1B respectively are
each four-coordinate, and lie 1.339(4) and 1.306(4) Å out of the
square planes of four nitrogen atoms; mean Pb–N distances are
2.406(10) and 2.391(8) Å in the two molecules.
There are significant differences in the tilt of the benzenoid
ring groups which define the saddle-shape patterns of the cores
of the molecules. The angles between the normals of opposite
benzenoid groups in molecule 1A are 19.0(4) and 24.1(4)°,
whereas the corresponding angles in molecule 1B are 13.9(4)
and 14.4(4)°. The hexyl side-chains are much better resolved at
low temperature, but two chains in each molecule still show
disorder, with alternative sites for some of the carbon atoms in
the chain. All eight of the hexylsulfanyl groups in each molecule
lie approximately in the plane of the core of that molecule. The
hexyl groups on the sulfur atoms S(7), S(17), S(27) and S(37)
are all well-resolved and have all-trans conformations; the
carbon atoms all lie close to the core plane with their hydrogen
atoms directed out of that plane. Of the other hexyl groups,
those on S(14) and S(24) show disorder; those on S(34) are
ordered but show two gauche links in the chain. The
conformations of the S(4) hexyl groups show the major
difference between the two molecules 1A and 1B. In 1A, the
hexyl chain is all-trans, whereas in 1B, there are gauche
conformations about S(4)–C(41) and C(42)–C(43). In all cases,
the pairs of hexyl groups on adjacent S atoms, e.g. those on S(7)
and S(14), lie approximately parallel.
Fig. 3 Packing of molecules in crystals of 1 viewed down the c axis.
Molecules lie in sheets, as in the top layer of the diagram; the lower two
layers show pairs of Pb-phthalocyanine cores about centres of symmetry,
1
1
1
1
e.g. 1A and 1AA about (2, 2, 2), and 1BB and 1BÚ about (22, 1, 0). The minor
differences in the projections of the 1A and 1B molecules may be
discerned.
The overall packing arrangements (Fig. 3) show pairs of
molecules linked about centres of symmetry with short
distances between the molecules, viz. the Pb…N(30A), …S(27A)
and …S(34A) distances are 3.292(8), 3.371(3) and 3.484(3) Å
between the 1A and 1AA molecules, correspondingly 3.254(8),
3.444(4) and 3.448(3) Å between pairs of 1B molecules. The
pairs of molecules are stacked parallel to the a axis in the
crystal, with the 1A molecules forming stacks about y = 0.5 and
the 1B molecules about y = 0.0 and 1.0.
In summary, we have identified a series of differently
coloured metallated phthalocyanines having non Q-band ab-
sorptions in the 450–600 nm region. The lead derivative is red
and has been characterised by X-ray crystallography.
We thank the EPSRC national mass spectroscopy service
centre, Swansea, for MS data.
Table 1 Selected molecular dimensions in complex 1. Bond lengths are in
Å, angles in degrees. E.s.d.s are in parentheses
Molecule 1A
Molecule 1B
with Pb(1)
with Pb(2)
Pb(n)–N(1)
Pb(n)–N(11)
Pb(n)–N(21)
Pb(n)–N(31)
2.409(7)
2.427(8)
2.380(9)
2.406(7)
2.370(7)
2.411(9)
2.392(9)
2.393(8)
Notes and references
† Selected data: 1 lmax (THF) 818 nm. Anal. found C, 58.29; H, 6.65; N,
6.65; C80H112N8S8Pb requires C, 58.25; H, 6.84 and N, 6.79. 2 lmax (THF)
781 nm. Anal. found C, 63.84; H, 7.43; N, 7.37; C80H112N8S8Zn requires C,
63.73; H, 7.49 and N, 7.43. 3 lmax (THF) 836 nm. Anal. found C, 60.66; H,
7.11; N, 6.84; C80H112N8S8InCl requires C, 60.33; H, 7.09 and N, 7.04. 4
lmax (THF) 783 nm. Anal. found C, 63.39; H, 7.53; N, 7.31;
N(1)–Pb(n)–N(11)
N(21)–Pb(n)–N(1)
N(31)–Pb(n)–N(1)
N(21)–Pb(n)–N(11)
N(31)–Pb(n)–N(11)
N(21)–Pb(n)–N(31)
72.2(3)
112.5(3)
71.5(3)
71.7(3)
112.2(3)
72.4(3)
72.7(3)
113.9(3)
72.8(3)
72.2(3)
113.8(3)
72.9(3)
C
80H112N8S8Cu requires C, 63.73; H, 7.48 and N, 7.43.
¯
‡ Crystal data: C80H112N8PbS8, M = 1649.4. Triclinic, space group P1
(no. 2), a = 11.252(1), b = 22.306(8), c = 31.546(6) Å, a = 93.41(3), b
= 91.73(1), g = 90.84(1)°, V = 7899(3) Å3. Z = 4, Dc = 1.387 g cm23
Mean Pb–N
Mean N–Pb–N(cis)
Mean N–Pb–N(trans)
2.406(10)
71.9(2)
112.3(2)
2.391(8)
72.7(2)
113.85(5)
,
F(000) = 3432, T = 140(1) K, m(Mo–Ka) = 24.0 cm21, l(Mo–Ka) =
0.71069 Å. Intensity data recorded on a Rigaku R-Axis IIc image plate
diffractometer equipped with a rotating anode X-ray source and graphite
monochromator. Total no. of reflections recorded, to qmax = 25.5°, was
24489 with 16497 unique (Rint = 0.073); 9571 ‘observed’ with I > 2sI. The
non-hydrogen atoms, except in the disordered parts of the side-chains and
for three atoms which went “non-positive-definite”, refined with aniso-
tropic thermal parameters. Hydrogen atoms included in idealised positions
(except in the disordered areas) and their Uiso values set to ride on the Ueq
Displacement of Pb from N4 plane
Angles between opposite C6 rings
1.339(4)
19.0(4)
24.1(4)
1.306(4)
13.9(4)
14.4(4)
values of the parent carbon atoms. Final R-factors: wR2 = 0.145 and R1
=
0.110 for all 16497 reflections weighted w = [s2(Fo2) + (0.0648P)2]21 with
2
P = (Fo2 + 2Fc )/3; for ‘observed’ data only, R1 = 0.055. Final difference
peaks (to ca. 0.75 e Å23) close to the Pb atoms. CCDC 208895. See http://
www.rsc.org/suppdata/cc/b3/b304173p/ for crystallographic data in .cif
format.
1 M. J. Stillman and T. Nyokong, in, Phthalocyanines: Properties and
Applications, ed. C. C. Leznoff and A. B. P. Lever, VCH, New York,
1989.
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J. Chem. Soc., Perkin Trans. I, 1988, 2453.
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Abstr., 1986, 105, 70242); T. Oguchi and S. Aihara, Eur. Pat. Appl.,
1992, EP 519423 (Chem. Abstr., 1992, 117, 61660).
Fig. 2 View of molecule 1A, with Pb(1) in its core. Hydrogen atoms, and the
disorder in two of the hexyl chains, have been omitted for clarity.
Differences between 1A and 1B are outlined in the text.
4 A. Auger, W. J. Blau, P. M. Burnham, I. Chambrier, M. J. Cook, B. Isare,
F. Nekelson and S. M. O’Flaherty, J. Mater. Chem., 2003, 13, 1042.
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