Synthesis and optical characterisation of platinum(II) poly-yne polymers incorporating substituted 1,4-diethynylbenzene derivatives and an investigation of the intermolecular interactions in the diethynylbenzene molecular precursors

Article abstract of DOI:10.1039/b206946f

A series of 1,4-diethynylbenzene (1) derivatives, H-C≡C-R-C≡C-H with R = C₆H₃NH₂ (2), C₆H₃F (3), C₆H₂F₂-2,5 (4), C₆F₄ (5), C₆H₂

Full text of DOI:10.1039/b206946f

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Synthesis and optical characterisation of platinum(II) poly-yne
polymers incorporating substituted 1,4-diethynylbenzene derivatives
and an investigation of the intermolecular interactions in the
diethynylbenzene molecular precursorsy
Muhammad S. Khan,*a Muna R. A. Al-Mandhary,a Mohammed K. Al-Suti,a Timothy C.
Corcoran,a Yaqoub Al-Mahrooqi,a J. Paul Attfield,b Neil Feeder,b William I. F. David,c
c
Kenneth Shankland, Richard H. Friend, Anna Kohler, Elisabeth A. Marseglia,*
d
d
d
¨
Emilio Tedesco,d Chiu C. Tang,e Paul R. Raithby,*f Jonathan C. Collings,g Karl P. Roscoe,g
Andrei S. Batsanov,g Lorna M. Stimsong and Todd B. Marder*g
a
Department of Chemistry, Sultan Qaboos University, P.O. Box 36, Al Khod 123, Sultanate of Oman.
E-mail: msk@squ.edu.om
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, UK CB2 1EW
ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, UK OX11 0QX
Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, UK CB3 0HE
CLRC Daresbury Laboratory, Daresbury, Warrington, UK WA4 4AD
Department of Chemistry, University of Bath, Claverton Down, Bath, UK BA2 7AY.
E-mail: p.r.raithby@bath.ac.uk
b
c
d
e
f
g
Department of Chemistry, University of Durham, South Road, Durham, UK DH1 3LE.
E-mail: Todd.Marder@durham.ac.uk
Received (in Montpellier, France) 15th July 2002, Accepted 27th September 2002
First published as an Advance Article on the web 26th November 2002
=
=
=
A series of 1,4-diethynylbenzene (1) derivatives, H–C C–R–C C–H with R ¼ C H NH (2), C H F (3),
=
6
3
2
6
3
C6H2F2-2,5 (4), C6F4 (5), C6H2(OCH3)2-2,5 (6) and C6H2(OnC8H17)2-2,5 (7) has been synthesised and their
=
=
crystal structures determined by single crystal (2–5) or powder (6, 7) X-ray diffraction. The C CHꢀ ꢀ ꢀp
=
=
C C
=
hydrogen bonds dominating structure 1 are gradually replaced by C C–Hꢀ ꢀ ꢀF ones with the increase of
=
=
=
=
fluorination (3 ! 5), or completely replaced by C CHꢀ ꢀ ꢀN and NHꢀ ꢀ ꢀp
bonds in 2, and C CHꢀ ꢀ ꢀO in 6 and 7.
=
=
=
C C
n
=
=
=
=
The related platinum-based polymers, trans-[–Pt(P Bu ) –C C–R–C C–] (R ¼ as above and C H ,) have been
3 2
n
6 4
prepared and characterised by spectroscopic methods and thermogravimetry, which show that the amino- and
methoxy-derivatives have lowest thermal stability while the fluorinated ones exhibit increasing thermal stability
with increasing fluorination. Optical spectroscopic measurements reveal that substituents on the aromatic spacer
group do not create strong donor–acceptor interactions along the rigid backbone of the organometallic polymers.
than the corresponding polymers, allowing for a detailed
Introduction
structural analysis and, thus, an assessment of the structure–
electronic property relationship.7 There is some evidence that
the solid state arrangement of these molecules represents an
important factor in determining their optical behaviour.5–8
While the p–p stacking interaction between adjacent oligomer
molecules or polymer chains has been identified as a key ‘inter-
chain’ interaction in solids,9 it is possible that hydrogen bond-
The last decade has witnessed a growing interest in the use of
organic semiconductor materials in light-emitting diodes,
lasers, photovoltaic cells and field-effect transistors.1 Conju-
gated polymers have shown considerable promise in this con-
text. The need to optimise their processability and so
enhance their commercial exploitation has prompted several
investigations into the relationship between the chemical and
electronic structure. Of particular interest are a series of
organic poly-yne polymers that have been employed recently
in successful liquid crystal display and photocell technology.2
A number of publications have also been dedicated to the che-
mical and optical characterisation of related tailored organic3
and organometallic4,5 oligomers and polymers.
ˆ
ing can also play an important role in this context.
Hydrocarbon groups are generally poor donors of hydrogen
bonds, but the ethynyl moiety with its acidic H atom is an
exception.10 Furthermore, the concentration of electron den-
sity in the triple bond can act as an acceptor, albeit a rather
weak one, of an H-bond.11 Thus ethynyl groups can form
co-operative H-bonds,12 similarly to OH groups.13 Such a
cooperative effect is evident in the crystal structure14 of 1,4-
diethynylbenzene 1. In order to investigate the effect of various
substituents on the crystalline architecture of these organic
Recently, attention has also been directed toward oligomers,
taken not only as model compounds, but also as potential
materials for device applications.6 They are more crystalline
=
pC Cz H-bonding in competition15 with other intermolecular
poly-yne precursors, particularly the stability of the C CHꢀ ꢀ ꢀ
=
=
=
y Electronic supplementary information (ESI) available: atomic
cooordinates for 6 and 7. See http://www.rsc.org/suppdata/nj/b2/
b206946f/
=
z pC is the midpoint of the C C bond.
=
=
=
C
140
New J. Chem., 2003, 27, 140–149
DOI: 10.1039/b206946f
This journal is # The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2003

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i
Scheme 2 Reagents: (i) Pd(OAc)2 , PPh3 , CuI, Pr2NH/CH2Cl2 ; (ii)
KOH, MeOH/THF, or Bu4NF, THF; (iii) trans-[PtCl2(PnBu3)2], CuI,
iPr2NH/CH2Cl2 . R ¼ C6H4 1, 8; C6H3NH2 2, 9; C6H3F 3, 10;
C6H2F2-2,5 4, 11; C6F4 5, 12; C6H2(OMe)2-2,5 6, 13;
C6H2(OnC8H17)2-2,5 7, 14.
=
=
=
Scheme 1 Compounds HC C–R–C CH.
=
interactions, e.g. X–Hꢀ ꢀ ꢀpC
(X ¼ N, C) and C–Hꢀ ꢀ ꢀY
=
=
C
(Y ¼ N, O, F16), we synthesised a series of amino-, fluoro-
and alkoxy-derivatives of 1,4-diethynylbenzene (2–7, see
Scheme 1) and structurally characterised them by single crystal
and powder X-ray diffraction. The structures of 4 and 5 were
determined at variable temperature, to investigate the sup-
posed effects of the latter on weak hydrogen bonds.17In addi-
tion, these substituted diethynylbenzene ligands have been
incorporated into rigid-rod platinum(II)-containing polymers
and their thermal and opto-electronic properties investigated
systematically.
Compared to the parent 1, the amino, fluoro and the alkoxy
derivatives are relatively stable at low temperature in the
absence of light and air; if exposed to either, the initially col-
ourless solids slowly turn off-white, yellow, light brown or light
purple. Long storage times at ambient temperature and under
aerobic conditions led to the formation of some insoluble
material ( < 5%), which was presumed to be a polymerisation
product.
The platinum-containing poly-yne polymers were obtained
by the organometallic polycondensation reaction of the diethy-
nylbenzene derivatives with one equivalent of trans-
[Pt(PnBu3)2Cl2] in CH2Cl2/iPr2NH solution in the presence
of catalytic quantities of CuI (Scheme 2). The resultant poly-
mers were purified by passing through a short alumina col-
umn, and isolated as off-white or yellow solids. The
materials were characterised by spectroscopic techniques.
=
Results and discussion
Synthesis
The substituted 1,4-diethynylbenzene derivatives were syn-
thesised by a sequence of coupling and protodesilylation
reactions. The trimethylsilyl-protected bis(ethynyl) ligand pre-
cursors were synthesised by adopting improved procedures for
the palladium-catalysed coupling of trimethysilylethyne with
dibromo/diiodoaryls18 (Scheme 2). Conversion of the ligand
precursors into their diterminal alkynes 2–7 was accomplished
by smooth removal of the trimethylsilyl protecting groups with
dilute aqueous KOH in MeOH/THF or with Bu4NF in THF.
The products were purified by silica column chromatography
and characterised by elemental analyses and by IR, NMR
(1H and 13C) spectroscopy and mass spectrometry. In order
to obtain the diethynylaryls, isolation of the bis(silylethynyl)
derivatives is unnecessary. Thus, after the coupling reaction
of the dihalide with the terminal alkyne (Scheme 2) was
complete, the solvent was evaporated and the resultant residue
was treated directly with dilute alkali to give the diethynyl
compounds.
The IR spectra showed a single n(C C) stretching frequency
=
at 2095 cmꢁ1 consistent with the trans-arrangement of the
ethynyl groups. The 31P NMR spectrum of each polymer dis-
played the expected singlet signal at approximately d ꢁ138
ppm with JPt-P coupling confirming the trans-configuration
1
of the phosphine ligands. The H NMR spectra of the poly-
mers show the expected resonances corresponding to the sub-
stituted 1,4-diethynylbenzene derivatives. The weight average
molecular weights (Mw) of the polymers indicate a high degree
of polymerisation. The number average molecular weight (Mn)
values are in the range of 74 000 to 95 000 g molꢁ1. These
values correspond to between 95 and 128 repeat units in the
polymer chain. The molecular weights should be viewed with
caution in view of the difficulties associated with utilizing
GPC for rigid-rod polymers. GPC is not a direct measure of
molecular weight but a measure of the hydrodynamic volume.
New J. Chem., 2003, 27, 140–149
141

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Rod-like polymers in solution possess very different hydrody-
namic properties from flexible polymers. Thus, by GPC using
randomly coiled polystyrene standards, the observed average
molecular weights of rigid rod poly-ynes are likely to be
inflated to some extent relative to the actual molecular weights.
However, the lack of discernable resonances that could be
attributed to end groups in the NMR spectra provides support
for the view that there is a high degree of polymerisation in
these poly-ynes.
Crystal structures of 2–7
Structures of compounds 2–5 were determined by single-
crystal X-ray diffraction, and those of the alkoxy derivatives
6 and 7 by powder X-ray diffraction. The molecular structures
of 2–7 (see ESI) are unexceptional; the geometry of the 1,4-
diethynylbenzene moiety is little affected by the substituents,
but the crystal packing and H-bond patterns are significantly
different. Comparison with the structure of 1 is instructive.
=
In it the potential donor (ethynyl H) and acceptor (C C
=
bonds) H-bonding sites are not only congruous (moderately
polar) but also equal in numbers. This favours the formation
of a two-dimensional net of co-operative H-bonds, linking
molecules into a puckered layer (Fig. 1, Table 1). In both
recent studies this layer was described as parallel to the (1 0
0), i.e. bc, plane.14b,c In fact, as can be seen from Fig. 2, it is
parallel to the (1 0 ꢁ2) plane. It is noteworthy that the same
mistake was repeated in the description of three crystal struc-
=
=
4
tures of p-XC H C CH (X ¼ Cl, Br or I), pseudo-isomor-
6
phous with 1.19 There are infinite p–p stacks between
molecules of adjacent layers (related by the a translation), at
normal interplanar separations (d in Table 1).
Introduction of a polar (amino) group in 2 contributes two
additional ‘‘active’’ H atoms, but only one potential acceptor
site (the lone pair of N). The prominent feature of this struc-
ture (Fig. 3) is a ring system of co-operative H-bonds, invol-
ving four molecules. The ring (having crystallographic Ci
symmetry) includes two relatively strong N–Hꢀ ꢀ ꢀpC bonds
=
=
C
ꢂ
˚
=
(Hꢀ ꢀ ꢀp ¼ 2.51 A, N–Hꢀ ꢀ ꢀp ¼ 145 )x and two C CHꢀ ꢀ ꢀN
=
ꢂ
˚
bonds (Hꢀ ꢀ ꢀN ¼ 2.44 A, C–Hꢀ ꢀ ꢀN ¼ 159 ), directed towards
the lone pair of the substantially pyramidalised N atom (the
valent bond angles at N average 116ꢂ). As each molecule par-
ticipates in two such tetrameric systems, this generates a mole-
cular layer, parallel to the crystallographic (1 0 ꢁ2) plane. The
other amino-H atom is involved in a bifurcated interaction
=
with two (crystallographically non-equivalent) C C bonds of
˚
=
two different molecules (Hꢀ ꢀ ꢀp ¼ 2.89 and 2.87 A, N–
Hꢀ ꢀ ꢀp ¼ 128 and 140ꢂ, respectively), belonging to the next
layer. The ethynyl group not involved in the co-operative H-
bonding points almost perpendicularly towards the benzene
ring of one of these molecules (C–H vector/ring plane angle
of 81ꢂ), with the shortest contacts Hꢀ ꢀ ꢀC(4) 3.04 and
Fig. 1 Crystal structures of 1 (a), 3 (b) and 4 (c); projections on the
(1 0 ꢁ2) plane.
20
˚
Hꢀ ꢀ ꢀC(5) 2.98 A typical for van der Waals interactions.
The outcome is a peculiar orientation of molecular planes: nor-
mal to each other but all normal to the layer plane. Molecules
belonging to different layers (as defined by cooperative H-
bonds) are nevertheless engaged in p–p stacking with each
ine atom, notwithstanding its high formal electronegativity, is
known to be very poor H-bond acceptor, and is able to parti-
cipate in them only in the absence of competition from stron-
ger ones, e.g. oxygen.21 However, structures 3, 4 and 5 satisfy
the conditions for the formation of C–Hꢀ ꢀ ꢀF hydrogen bonds,
as pointed out by Desiraju et al. in a study on fluoroben-
zenes:22 they contain only C, H and F atoms, and the H atoms
are bonded to sp2 or sp-hybridised C atoms. Indeed, in 3 and 4
˚
other (interplanar separations of 3.56 A), albeit with consider-
able offset. Unlike all other compounds reported herein, mole-
cule 2 has no crystallographic symmetry and is slightly ‘bent’,
the directions of the two bonds forming an angle of 170.8(2)ꢂ.
Crystal structures of 3 and 4 (Fig. 1) are isomorphous with
that of 1. In each case, the molecule lies at a crystallographic
inversion centre, which means that in 3 the fluorine atom is
disordered, being distributed equally between two positions,
related by this centre. Hydrogen bonding in 1, 3 and 4 is com-
pared in Table 1. The ‘organic’ (i.e. bonded to carbon) fluor-
=
the C CHꢀ ꢀ ꢀp C H-bond of 1 is weakened, or rather replaced
=
by a bifurcated H-bond to both the C C group and the fluor-
=
C
=
=
=
=
ine atom of the same molecule, the C CHꢀ ꢀ ꢀF interaction
=
being the stronger of the two. Thus, the Hꢀ ꢀ ꢀp distance
˚
increases by ca. 0.2 A from that in 1 to that in 4. There is also
a much longer, but probably electrostatically attractive, con-
tact (iii) with another F atom. Comparison of the structure
x All hydrogen bond parameters are calculated for idealized bond
˚
lengths C–H 1.08 A and N–H 1.01 A.
˚
142
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Table 1 Intermolecular interactions in crystals of 1 and its fluorinated
derivatives
Compound
114b
114c
3
4(A) 4(B) 5(A) 5(B) 5(C)
T/K
(i)a Hꢀ ꢀ ꢀp/A
295
2.68
176
125 180 180 120 273 180 150
2.60 2.75 2.87 2.85 2.94 2.93 2.89
175 168 161 160 129 127 127
2.66 2.60 2.58
˚
(i) C–Hꢀ ꢀ ꢀp/ꢂ
˚
(ii) Hꢀ ꢀ ꢀF/A
(ii) C–Hꢀ ꢀ ꢀF/ꢂ
121 122 122
2.86 2.94 2.88 2.49 2.41 2.41
˚
(iii) Hꢀ ꢀ ꢀF/A
(iii) C–Hꢀ ꢀ ꢀF/ꢂ
90
116 117 132 136 134
b
d /A
3.71c 3.53 3.47 3.43 3.41 3.63 3.60 3.59
˚
a
b
See notation in Figs. 1 and 4. Mean interplanar separation in the
c
p–p stack. Probably erratum in the original, cannot be verified as
atomic coordinates are unavailable.
of 4 at different temperatures (180 and 120 K) shows similar
˚
(ca. 0.02 A) thermal expansions of the H-bonds (i) and (ii)
and the interplanar separations (d) in the p–p stack, but a lar-
ger extension of contact (iii). The layers in all three structures
are similarly puckered: the dihedral angles between H-bonded
molecules are 48ꢂ (1), 52ꢂ (3) and 54ꢂ (4).
The increased degree of fluorination in compound 5 gives
rise to completely different crystal packing (Fig. 4). The mole-
cule also possesses crystallographic Ci symmetry, but the prin-
cipal synthon in structure 5 is the pair of inversion-related,
parallel and nearly coplanar molecules, linked by two
=
C CHꢀ ꢀ ꢀF hydrogen bonds (iii), shorter than in 3 and 4 (see
=
Table 1). Thus molecules are linked into an infinite ‘ribbon’,
parallel to the (1 0 ꢁ1) direction. There are no continuous
p–p stacks of molecules, although each molecule has one neigh-
bour contacting it in a p–p fashion. These molecules, related
by an inversion centre, have a longitudinal (parallel to the
Fig. 3 (a) Crystal structure of 2, projected on the (1 0 ꢁ2) plane;
(b) H-bonds and intermolecular contacts. Symmetry transformations:
˚
=
=
=
C C bond) shift of ca. 4.3 A, so that a C C bond of one mole-
=
1
1
(i) 1 ꢁ x, 12 + y, 2 ꢁ z; (ii) 2 ꢁ x, 1 ꢁ y, 1 ꢁ z; (iii) x + 1, 2 ꢁ y, 12 + z;
cule overlaps with the benzene ring of another. The interplanar
(iv) x ꢁ 1, y, z; (v) x, 2 ꢁ y, 12 + z; (vi) 2 ꢁ x, y ꢁ 2, 2 ꢁ z.
1
1 1
˚
˚
separation contracts from 3.63 A at 273 K to 3.59 A at 150 K.
This double ribbon is surrounded on all sides by four other
ribbons, propagating in the same direction but with perpendi-
cular molecular planes. Each ethynyl H atom participates in a
=
Structure 7 contains nearly-flat layers, in which a synthon,
broadly similar to that of structure 5, can be identified: a cen-
rather long inter-ribbon C CHꢀ ꢀ ꢀp
contact (i) (Table 1);
=
=
C C
=
=
trosymmetric pair of molecules, linked by two C CHꢀ ꢀ ꢀO
=
hydrogen bonds. These, however, are much weaker than in
the interaction thus can be interpreted as a very asymmetric
bifurcated H-bond. Structure determinations at 273, 180 and
150 K did not reveal any substantial change, although thermal
expansion in the direction of the strongest H-bond (iii) is
somewhat greater than in other directions.
ꢂ
˚
6 (Hꢀ ꢀ ꢀO ¼ 2.80 A, C–Hꢀ ꢀ ꢀO ¼ 167 ). Probably, the crystal
structure of 7 is dominated by the close packing of (all-trans)
n-alkyl chains, to which the H-bonding pattern has to adjust.
This structure is in good agreement with the structural model
proposed recently for the corresponding polymer.3b
The crystal packing of di-alkoxy derivatives 6 and 7 is shown
in Figs. 5 and 6. Both molecules have crystallographic Ci symme-
try and adopt planar (6) or nearly planar (7) conformations.
Structure 6 comprises puckered layers, parallel to the (1 0 ꢁ2)
plane and broadly similar to those observed in structures 3
Thermal analysis
All the polymer samples exhibited an exotherm coincident with
mass loss due to decomposition. Decomposition onset was
defined as a mass loss of 2%. The peak decomposition tem-
perature was defined as the first inflection point in the thermo-
gravimetic curve, corresponding to a peak in the derivative of
=
and 4, in which the molecules are linked by C CHꢀ ꢀ ꢀO hydrogen
=
ꢂ
˚
=
bonds (Hꢀ ꢀ ꢀO ¼ 2.34 A, C–Hꢀ ꢀ ꢀO ¼ 146 ), while the C CHꢀ ꢀ ꢀ
=
pC interaction between the same molecules is much weaker
=
=
C
ꢂ
˚
than in structures 3 and 4 (Hꢀ ꢀ ꢀp ¼ 3.07 A, C–Hꢀ ꢀ ꢀp ¼ 137 ).
Unlike 1–4, structure 6 contains no p–p stacks, molecules of
adjacent layers contacting in a herring-bone fashion.
Fig. 2 Crystal structure of 1, viewed down the y axis.
Fig. 4 Crystal structure of 5.
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Table 2 Decomposition temperatures (in ꢂC, ꢃ8 ꢂC) from thermal
analysis
Compound
Tdec (onset)
Tdec (peak)
9
10
11
12
13
14
248
300
304a
312
254
310
336
333
337a
345
314
353
a
Estimated from DTA data only.
Fig. 5 Crystal structure of 6.
analogous organic polymers, where T1 emission (phosphores-
cence) is spin-forbidden and cannot be observed. While such
a constant S1–T1 energy gap has been observed for these orga-
nometallic and analogous organic polymers with a variety of
spacers its cause is not yet fully understood.23,25
The emission spectra normalised to the fluorescence peak for
the polymers with one, two and four fluorine substituents
(polymers 10, 11 and 12, respectively) are shown in Fig. 9.
The relative intensity of phosphorescence increases strongly
with the fluorine content.
the TG data. This peak usually preceded the peak of the
exotherm in the DTA data. The decomposition exotherms
were broad with multiple peaks, and the thermogravimetic
curve suggests a stepwise process. The results are shown in
Table 2 and Fig. 7. Polymers 9 and 13 exhibited the lowest
onset decomposition temperatures, while the fluorinated poly-
mers 10–12 exhibited increasing decomposition temperatures
with increasing fluorination. Polymer 14 also exhibited one
of the highest decomposition temperatures, since the octyloxy
groups likely encourage stronger interchain van der Waals
bonding.
Conclusions
Optical spectroscopy
A number of substituted derivatives of 1,4-diethynylbenzene
with electron donating and accepting substituents have been
studied, and their structural characterisation performed by
both single-crystal and powder X-ray diffraction. An interest-
ing result of this work has been the ability to obtain compar-
able structural information from conventional techniques
(single crystal) and from powder X-ray diffraction.
The effect of the substitution of the aromatic spacer group on
the electronic structure of the platinum(II) poly-yne polymers
has been investigated. The absorption and emission spectra
taken at room temperature from thin films of polymers 8, 12
and 13 are shown in Fig. 8. The first absorption band of poly-
mer 8 peaking at 3.26 eV (380 nm) has its origin mostly in the
p–p* transitions of the conjugated polymer backbone and is
associated with the first singlet excited state denoted S1 .23 Sub-
stitution by fluorine or by methoxy groups leads to a weak red
shift of 0.05 eV (6 nm) and 0.15 eV (20 nm), respectively, indi-
cating only slightly more conjugated backbones. Substitution
with less than four fluorines, as in 10 and 11, leads to a corre-
spondingly smaller red shift (not shown here).
The emission spectra consist of two bands. The band just
below the onset of absorption at 3 eV is emission from the
S1 state (fluorescence). The band below 2.5 eV has been well
characterised for the polymer 8 and other aromatic/hetero-
aromatic spacers by time-resolved luminescence measurements
and is assigned to emission from the triplet excited state T1
(phosphorescence).8,24 Substitution of the aromatic ring shifts
the energy of the T1 emission by about the same amount as the
S1 emission, so that the S1–T1 energy difference remains con-
stant. This can be used to accurately fine-tune the energy of
the T1 state for energy harvesting purposes25 particularly in
The packing analysis of the structures of the polymer pre-
cursors has also thrown light on the co-presence of weak
hydrogen bonding in model compounds of polymers that are
of technological interest. In summary the ethynylenic moiety
provides a good hydrogen bond donor and acceptor, which
is able to compete in terms of intermolecular interactions
and as structure defining synthons, with more electronegative
=
atoms, such as nitrogen. C CHꢀ ꢀ ꢀp
hydrogen bonds dom-
=
=
C C
=
inate the crystal structure of 1, and are gradually replaced by
=
C C–Hꢀ ꢀ ꢀF ones with the increase of fluorination (3 ! 5), as
=
has been noted previously,19 or completely replaced by
=
=
=
C CHꢀ ꢀ ꢀN and NHꢀ ꢀ ꢀp
bonds in 2, and C CHꢀ ꢀ ꢀO in 6
=
=
=
C C
and 7. However, it is hard to judge, based solely on geometri-
cal measurements, the relative strength of the C–Hꢀ ꢀ ꢀF interac-
tions in these derivatives. A C–Hꢀ ꢀ ꢀpC bond in 1 has been
=
=
C
Fig. 7 Simultaneous thermogravimetric (TG) curve (above) and dif-
ferential thermal analysis (DTA) curve (below) for 10. The onset and
peak decomposition temperatures, as defined in the text, are marked.
Fig. 6 Crystal structure of 7.
144
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performed on a Hewlett-Packard 5890 Series II/5971A MSD
instrument equipped with an HP 7673A autosampler and a
fused silica column (30 m ꢄ 0.25 mm ꢄ 0.25 mm, cross-linked
5% phenylmethyl silicone). The following operating conditions
were used: injector, 260 ꢂC; detector, 280 ꢂC; oven temperature
was ramped from 70ꢂ to 260 ꢂC at the rate of 20 ꢂC minꢁ1
;
helium (UHP grade) was used as the carrier gas; toluene
(BDH, 99.7%) was used as an internal integration standard.
Synthesis of 1,4-diethynylbenzene derivatives
1,4-Diethynyl-2-aminobenzene 2. Coupling. To an ice-cooled
solution of 1,4-dibromo-2-aminobenzene (3.01 g, 12 mmol)
in diisopropylamine/THF (75 cm3, 1:4 v/v) under nitrogen
were added CuI (29 mg, 0.15 mmol), Pd(OAc)2 (27 mg, 0.12
mmol) and PPh3 (157 mg, 0.60 mmol). The solution was stirred
for 0.5 h, trimethylsilylethyne (2.95 g, 30 mmol) was then
added over 10 min to the vigorously stirred solution; during
the addition a white precipitate formed. The suspension was
stirred for 30 min in an ice-bath before being warmed to room
temperature. After reacting for 30 min at room temperature
the mixture was heated to 80 ꢂC for 20 h when TLC, GC
analysis and IR spectroscopy indicated that all the starting
material had been consumed and the coupling reaction was
completed. After being cooled to room temperature, the
mixture was filtered to eliminate the ammonium salt and the
solvent mixture was removed in vacuo.
Fig. 8 Absorption and luminescence spectra of the platinum-
containing poly-yne polymers 8, 12 and 13 taken from thin films at
room temperature with excitation at 3.4 eV.
estimated being of ca. 4 kJ mol .
ꢁ1 26 When alkoxy substituents
are present, C–Hꢀ ꢀ ꢀO interactions occur, but the presence of
long alkyl chains in the structure can impede the formation
of these short contacts.
The substituted 1,4-diethynyl benzene ligands have also been
incorporated into rigid-rod Pt(II) polymers and their thermal
and opto-electronic properties investigated. The substituents
on the aromatic spacer have a major effect on the thermal sta-
bility of the polymeric complexes but their electronic proper-
ties are affected only to a minor extent.
Protodesilylation. The solid residue was dissolved in THF (50
cm3) with stirring. Methanol (15 cm3) and aqueous KOH
(1.50 g, 27 mmol in 5 cm3 water) were added at room tempera-
ture to the stirred solution. The reaction mixture was stirred
for 2 h. The completion of the desilylation reaction was veri-
fied by TLC, GC analysis and IR spectroscopy. The mixture
was filtered and the solvent was removed under reduced pres-
sure to leave a yellow residue. This residue was dissolved in the
minimum amount of dichloromethane and subjected to col-
umn chromatography on silica using hexane–dichloromethane
(2:1 v/v) as eluent to afford a pale yellow solid. Recrystalliza-
tion from hexane with activated charcoal yielded pale yellow
Experimental
General
All reactions were performed under a dry nitrogen atmosphere
using standard Schlenk or glove box techniques. Solvents were
pre-dried and distilled before use by standard procedures.27 All
chemicals, except where stated otherwise, were obtained from
Sigma Aldrich and checked for purity by GC/MS prior to
use. 1,4-Diiodo-2,5-bis(octyloxy)benzene was prepared by
adaptation of the literature method.28
micro-crystals (0.62 g, 76% yield). IR (CH2Cl2): n/cmꢁ1 2108
1
=
=
=
(–C C–), 3300 (C CH), 3428 (–NH–). H NMR (250 MHz,
=
=
=
=
CDCl ): d 3.12 (s, 1H, C C–H), 3.50 (s, 1H, C C–H), 4.70
=
3
(br s, 2H, NH2), 7.21 (d, 2H, ar), 7.73 (dd, 1H, ar). 13C
NMR spectra were recorded on Bruker WM-250 or AM-400
1
spectrometers in CDCl3 and the H and 13C{1H} were refer-
=
NMR (100.6 MHz, CDCl ): d 78.2, 80.6, 83.1, 84.0 (C C),
=
3
107.2 (C1), 117.5 (C3), 121.4 (C4), 123.0 (C6), 132.2 (C5),
148.0 (C2). EI mass spectrum: m/z 141 (M+). Found: C,
85.03; H, 4.94; N, 9.90; Calc. for C10H7N: C, 85.08; H. 5.00;
N, 9.92%.
enced to solvent resonances. Infrared spectra were recorded
as CH2Cl2 solutions, in a NaCl cell, on a Perkin-Elmer 1710
FT-IR spectrometer, mass spectra on a Kratos MS 890 spec-
trometer by the electron impact (EI) technique. Microanalyses
were performed in the Department of Chemistry, University of
Cambridge. Column chromatography was performed in
Kieselgel 60 (240–400 mesh) silica gel. GC/MS analyses were
1,4-Diethynyl-2-fluorobenzene 3. Coupling. To a solution of
1,4-dibromo-2-fluorobenzene (2.5 g, 10 mmol) in diisopropyla-
mine/THF (100 cm3, 1:4 v/v) at reflux under nitrogen was
added a catalyst mixture of CuI (24 mg, 0.13 mmol), Pd(OAc)2
(22 mg, 0.10 mmol) and PPh3 (131 mg, 0.50 mmol). Trimethyl-
silylethyne (2.45 g, 25 mmol) was then added over the course of
10 min to the vigorously stirred solution; during the addition a
white precipitate formed. The reaction mixture was stirred at
reflux for 8 h and the completion of the reaction was verified
by TLC, GC analysis and IR spectroscopy. The reaction mix-
ture was allowed to cool to room temperature and the ammo-
nium iodide precipitate was filtered off. The yellow filtrate was
evaporated to dryness.
Protodesilylation. Removal of the trimethylsilyl protecting
groups was accomplished as for the synthesis of 2 described
above. Compound 3 was obtained as an off-white solid in
82% yield. Good quality crystals were obtained by sublimation
(15 mmHg, ice-water cooled). IR (CH2Cl2): n/cmꢁ1 2107
1
=
=
=
(–C C–) and 3300 (–C C–H). H NMR (250 MHz, CDCl ):
=
3
Fig. 9 Room temperature thin-film luminescence spectra of plati-
num-containing poly-yne polymers 10, 11 and 12 normalised to the
peak of the S1 emission and shown on a logarithmic scale.
=
=
=
d 3.21 (s, 1H, C C–H), 3.38 (s, 1H, C C–H), 7.22 (d, 2H,
=
ar) and 7.46 (d, 1H, ar). 13C NMR (100.6 MHz, CDCl3):
New J. Chem., 2003, 27, 140–149
145

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1
3
=
d 77.1, 80.2, 81.8, 84.1 (C C), 111.51 (C ), 119.02 (C ), 124.36
382 (M+). Found: C, 81.52; H, 10.04; Calc. for C26H38O2 :
C, 81.63; H, 10.01%.
=
(C4), 128.10 (C6), 134.20 (C5) and 162.65 (C2). EI mass spec-
trum: m/z 144 (M+). Found: C, 83.29; H, 3.58. Calc. for
C10H5F: C, 83.32; H, 3.50%.
Polymer preparations. The synthesis of polymer 8 has been
reported previously.30 The polymers 9–14 were synthesized
by the general procedure outlined below for 9.
1,4-Diethynyl-2,5-difluorobenzene 4. Similar coupling and
protodesilylation procedures as in 3 were adopted using 1,4-
dibromo-2,5-diflurobenzene (2.72 g, 10 mmol) to give 4 as
off-white solid in 95% yield. Good quality crystals were
obtained by sublimation (15 mmHg, ice-water cooled). IR
n
=
=
=
trans-[Pt(P Bu ) (–C C–C H (NH )–C C)–] 9. CuI (10
=
3 2
6
3
2
n
mg) was added to a mixture of trans-[Pt(PnBu3)2Cl2] (0.670 g,
1.0 mmol) and 1,4-diethynyl-2-amimobenzene (0.141 g, 1.0
mmol) in CH2Cl2/iPr2NH (50 cm3, 1:1 v/v). The yellow solu-
tion was stirred at room temperature over a period of 15 h,
after which all volatile components were removed under
reduced pressure. The residue was dissolved in dichloro-
methane and filtered through a short alumina column. After
removal of solvent by rotary evaporator, an off-white solid
of polymer 9 was obtained in 85% yield (0.750 g). Further pur-
ification can be accomplished by precipitating the polymer
(CH2Cl2) n/cmꢁ1: 2107 (–C C–) and 3299 (–C C–H). 1H
NMR (250 MHz, CDCl ): d 3.41 (s, 2H, C CH), 7.24 (d,
=
=
=
=
=
=
3
13
=
=
2H, ar), C NMR (100.6 MHz, CDCl ): d 75.7, 85.5 (C C),
3
112.8 (C1,4), 120.2 (C3,6), 158.9, (C2,5). EI mass spectrum:
m/z 162 (M+). Found C, 74.11; H, 2.45; Calc. for C10H4F2 :
C, 74.08; H. 2.49%.
1,4-Diethynyl-2,3,5,6-tetrafluorobenzene 5. Coupling17e,28
.
from dichloromethane solution in methanol. IR (CH2Cl2):
1,4-Diiodo-2,3,5,6-tetrafluorobenzene (4.02 g, 10 mmol) and
trimethylsilylethyne (2.45 g, 25 mmol) were reacted in diiso-
propylamine/THF (100 cm3, 1:4 v/v) in the presence of cata-
lytic amounts of CuI (24 mg), Pd (OAc)2 (22 mg) and PPh3
(131 mg). The coupling reaction was completed after 1 h of
reflux. The crude product was worked up, as before, to yield
a pale-yellow residue.
1
n/cmꢁ1 2094 (–C C–). H NMR (250 MHz, CDCl ): d 0.87
=
=
3
(t, 18H, CH3), 1.40 ((sex, 12H, CH2), 1.65 (brs, 12H, CH2),
2.25 (m, 12H, PCH2), 4.18 (s, 2H, NH2), 6.58 (d, 2H, ar),
7.12 (d, IH, ar). 31P{1H} NMR (101.3 MHz, CDCl3): d
ꢁ138.08, JPt-P ¼ 2330 Hz. Found: C, 55.17; H, 8.14; Calc.
for (C34H59NP2Pt)n : C, 55.26; H. 8.05%. GPC (THF):
Mn ¼ 94 700 g molꢁ1 (n ¼ 128), Mw ¼ 151 500 g molꢁ1, poly-
dispersity ¼ 1.6.
Protodesilylation. A similar procedure to that for 4 was
adopted to obtain an off-white solid in 82% yield. Good qual-
ity crystals were obtained by sublimation (15 mmHg, ice-water
n
=
=
=
trans-[Pt(P Bu ) (–C C–C H F–C C)–] 10. Off-white solid
=
cooled). IR (CH2Cl2) n/cmꢁ1: 2106 (–C C–) and 3297 (–C C–
3 2
6
3
n
=
=
=
=
(82% yield). IR (CH2Cl2): n/cmꢁ1 2095 (–C C). H NMR (250
1
=
=
H). H NMR (250 MHz, CDCl ): d 3.72 (s, 2H, C CH). 13C
1
=
=
3
MHz, CDCl3): d 0.82 (t, 18H, CH3), 1.38 (sex, 12H, CH2), 1.58
(brs, 12H, CH2), 2.29 (m, 12H, PCH2), 7.38 (d, 2H, ar), 7.28
(d, IH, ar). 31P{1H} NMR (101.3 MHz, CDCl3): d ꢁ138.50,
JPt-P ¼ 2330 Hz. Found: C, 55.15; H, 7.74; Calc. for
(C34H57P2FPt)n : C, 55.05; H. 7.76%. GPC (THF):
Mn ¼ 94 650 g molꢁ1 (n ¼ 128), Mw ¼ 160 900 g molꢁ1, poly-
dispersity ¼ 1.7.
NMR (100.6 MHz, CDCl ): d 68.4, 91.5 (C C), 104.5 (C1,4),
=
=
3
147.5 (C2,3,5,6). EI mass spectrum: m/z 198 (M+). Anal.
Found: C, 60.71; H, 1.04; Calc. for C10H2F4 : C, 60.63; H,
1.02%.
1,4-Diethynyl-2,5-bis(methoxy)benzene 6. Coupling29. Similar
coupling procedures as in 5 were adopted using 1,4-diiodo-2,5-
bis(methoxy)benzene (3.90 g, 10 mmol) to produce the crude
trimethylsilylethynyl compound.
n
=
=
=
trans-[Pt(P Bu ) (–C C–C H F –C C)–]
11. Off-white
=
3 2
6
2
2
n
solid (78% yield). IR (CH2Cl2): n/cmꢁ1 2094 (–C C–). 1H
=
=
Protodesilylation. The solid residue was dissolved in THF (50
cm3) and a solution of tetrabutylammonium fluoride (1.1 M,
2 equiv.) was added. The reaction mixture was stirred for
5 min at ambient temperature when TLC, GC analysis and
IR spectroscopy indicated that all the starting material had
been consumed and the desilylation reaction was completed.
The reaction mixture was chromatographed on a small silica
gel column using THF as eluent. The solvent was removed
in vacuo and the crude product was recrystallized in methanol
to yield an off-white solid in 86% yield. IR (CH2Cl2): n/cmꢁ1
NMR (250 MHz, CDCl3): d 0.77 (t, 18H, CH3), 1.34 (sex,
12H, CH2), 1.52 (brs, 12H, CH2), 2.20 (m, 12H, PCH2), 7.28
(d, 2H, ar). 31P{1H} NMR (101.3 MHz, CDCl3): d ꢁ138.50,
JPt-P ¼ 2330 Hz. Found: C, 53.65; H, 7.44; Calc. for
(C34H56P2F2Pt)n : C, 53.74; H. 7.43%. GPC (THF):
Mn ¼ 88 230 g molꢁ1 (n ¼ 116), Mw ¼ 158 810 g molꢁ1, poly-
dispersity ¼ 1.8.
n
=
=
=
trans-[Pt(P Bu ) (–C C–C F –C C–] 12. Off-white solid
=
3 2
6
4
n
(72% yield). IR (CH2Cl2): n/cmꢁ1 2095 (–C C–). 1H NMR
=
=
2107 (–C C–) and 3299 (–C C–H). 1H NMR (250 MHz
=
=
=
=
(250 MHz, CDCl3): d 0.75 (t, 18H, CH3), 1.38 (sex, 12H,
CH2), 1.58 (brs, 12H, CH2), 2.20 (m, 12H, PCH2). 31P{1H}
NMR (101.3 MHz, CDCl3): d ꢁ138.50, JPt-P ¼ 2330 Hz.
Found: C, 51.36; H, 6.79; Calc. for (C34H54P2F4Pt)n : C,
=
CDCl ): d 3.33 (s, 2H, C C–H), 3.92 (s, 6H, OCH ), 7.19 (s,
=
3
3
2H, ar). 13C NMR (100.6 MHz, CDCl3): d 69.89 (OCH3),
=
=
79.96, 82.57 (C C), 113.41 (C1,4), 117.89 (C3,6), 154.14 (C2,5).
EI mass spectrum: m/z 186 (M+). Found: C, 77.46; H, 5.43;
51.31; H. 6.84%. GPC (THF): Mn ¼ 82 500
g
molꢁ1
(n ¼ 103). Mw ¼ 156 770 g molꢁ1, polydispersity ¼ 1.9.
Calcd for C12H10O2 : C, 77.40; H, 5.41%.
n
=
=
=
1,4-Diethynyl-2,5-bis(octyloxy)benzene 7. Coupling. Similar
coupling procedures as in 5 were adopted using 1,4-diiodo-
2,5-bis(octyloxy)benzene (5.87 g, 10 mmol) to produce the
crude trimethylsilylethynyl compound.
trans-[Pt(P Bu ) (–C C–C H (OCH ) –C C–] 13. Light
=
3 2
6
4
3 2
n
yellow solid (85% yield). IR (CH2Cl2): n/cmꢁ1 2095 (–C C–).
=
=
1H NMR (250 MHz, CDCl3): d 0.86 (t, 18H, CH3), 1.38 (sex,
12H, CH2), 1.58 (brs, 12H, CH2), 2.20 (m, 12H, PCH2), 3.70
(s, 6H, OCH3), 7.10 (s, 2H, ar). 31P{1H} NMR (101.3 MHz,
CDCl3): d ꢁ138.10, JPt-P ¼ 2330 Hz. Found: C, 55.22; H,
8.03; Calc. for (C36H62P2O2Pt)n : C, 55.16; H. 7.97%. GPC
Protodesilylation. Similar desilylation procedures as in 6 were
adopted to obtain a pale yellow solid in 79% yield. IR
(CH2Cl2): n/cmꢁ1 2107 (–C C–) and 3299 (–C C–H). 1H
=
=
=
=
NMR (250 MHz CDCl3): d 0.86 (t, 6H, CH3), 1.26, 1.40 (both
(THF): Mn ¼ 74 100 g molꢁ1 (n ¼ 95), Mw ¼ 111 200 g molꢁ1
, polydispersity ¼ 1.5.
,
=
m, 20H, CH ), 1.78 (m, 4H, CH ), 3.32 (s, 2H, C C–H), 3.95
=
2
2
(t, 4H, OCH2), 6.93 (s, 2H, ar). 13C NMR (100.6 MHz,
n
=
=
=
=
CDCl3): d 14.29 (CH3), 22.85, 26.09, 29.31, 29.42, 29.48,
trans-[Pt(P Bu ) (–C C–C H (OC H ) –C C–] 14. Light
3 2
6
4
8
17 2
n
yellow solid (90% yield). IR (CH2Cl2): n/cmꢁ1 2095 (–C C–).
=
=
=
31.99 (all CH ), 69.84 (OCH ), 79.98, 82.60 (C C), 113.45
=
2
2
(C1,4), 117.92 (C3,6), 154.18 (C2,5). EI mass spectrum: m/z
1H NMR (250 MHz, CDCl3):
d 0.84 (t, 24H, CH3),
146
New J. Chem., 2003, 27, 140–149

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Table 3 Crystal data for 2–7
2
3
4(A)
4(B)
5(A)
5(B)
5(C)
6
7
Formula
Mw/g molꢁ1
T/K
C
10H7N
C10H5F
144.14
180
C10H4F2
162.13
180
C10H2F4
198.12
273
C12H10O2
186.20
290
C26H38O2
380.55
290
141.17
180
120
0.71073
180
1.54178
150
0.71073
˚
l/A
Crystal system
1.54178
monoclinic
P21/c
5.919(2)
12.030(4)
11.026(3)
90
1.54178
monoclinic
P21/c
3.878(1)
5.947(1)
15.800(5)
90
1.54178
monoclinic
P21/c
3.8535(7)
5.906(1)
16.221(5)
90
1.54178
monoclinic
P21/c
6.1510(6)
11.524(1)
5.8204(7)
90
1.2996
monoclinic
P21/c
1.54178
triclinic
¯
P1
Space group
˚
a/A
˚
3.828(1)
5.887(1)
16.204(4)
90
6.112(1)
11.463(2)
5.764(1)
90
6.109(2)
11.456(4)
5.751(2)
90
9.1718(1)
6.04823(7)
9.54469(1)
90
7.6769(8)
11.682(2)
6.926(2)
104.29(1)
96.637(8)
99.671(9)
586.0(2)
1
b/A
˚
c/A
a/ꢂ
b/ꢂ
g/ꢂ
104.17(2)
90
93.46(3)
90
95.23(3)
90
95.21(1)
90
98.71(1)
90
99.27(2)
90
99.35(2)
90
107.428(1)
90
3
˚
V/A
761.2(4)
4
0.57
363.7(2)
2
0.77
367.6(2)
2
1.03
363.7(1)
2
0.12
397.1(2)
2
1.42
398.6(1)
2
1.45
397.1(2)
2
0.16
505.17(1)
2
0.67
Z
m/mmꢁ1
Refls. total
Refls. unique
Rint
0.51
1043
959
920
460
510
466
4764
966
753
691
510
506
4179
907
243a
—
70a
—
0.031
777
0.026
369
0.026
431
0.020
902
0.040
601
0.059
333
0.023
807
Refls., I > 2s(I)
wR(F2)
0.136
0.050
0.122
0.045
0.073
0.028
0.106
0.034
0.129
0.043
0.072
0.035
0.085
0.031
0.070b
0.045c
0.031b
0.024c
R[I > 2s(I)]
a
b
Total number of inequivalent reflections in the powder pattern; Rwp for the Rietveld fits; Rp for the Rietveld fits.
c
˚
1.22–1.38 (m, 32H, CH2), 1.62 (m, 16H, CH2), 2.20 (m, 12H,
PCH2), 3.75 (t, 4H, OCH2), 6.82 (s, 2H, ar). 31P{1H} NMR
(101.3 MHz, CDCl3): d ꢁ138.10, JPt-P ¼ 2330 Hz. Found: C,
61.36; H, 9.29; Calc. for (C50H90P2O2Pt)n: C, 61.26; H.
Daresbury Synchrotron Radiation Source (l ¼ 1.2996 A)
using a flat plate geometry, that for 7 on a Stoe powder
X-ray diffractometer equipped with a linear PSD, using Cu-
ꢀ
˚
Ka radiation (l ¼ 1.5406 A) from a sealed-tube source. Both
diffraction patterns were indexed using the DICVOL91
program34 and each structure solved using the DASH suite
of programs.35 The structure solution details are summarised
in Table 4.
It was clear from the space groups and lattice parameters
that the molecules in both structures lie at crystallographic
inversion centres and have no translational degree of freedom.
The trial structures were subjected to an optimisation in which
torsion angles were the only internal degrees of freedom, and
limits on the external degrees of freedom were derived from
the Euclidean normalisers of the relevant space groups,36 while
the molecule was anchored on a dummy atom lying at the ori-
gin of the unit cell. Structure solutions were deemed to have
been obtained when the w2 figure of merit fell below a predeter-
mined value.
9.25%. GPC (THF): Mn ¼ 94 850 (n ¼ 97)
g
molꢁ1
,
Mw ¼ 151 750 g molꢁ1, polydispersity ¼ 1.6.
Molecular weight measurements. Molar masses were deter-
mined by gel permeation chromatography (GPC) using two
PL Gel 30 cm, 5 micron mixed C columns at 30 ꢂC running
in THF at 1 cm3 minꢁ1 with a Roth Mocel 200 high precision
pump. A DAWN DSP (Wyatt Technology) Multi-Angle Laser
Light Scattering (MALLS) apparatus with 18 detectors and
auxiliary Viscotek model 200 differential refractometer/visco-
meter detectors was used to calculate the molecular weights
(referred to GPC LS).
X-Ray crystallography
Single crystal diffraction. X-Ray quality crystals of 2 were
obtained by the diffusion of hexane into a concentrated solu-
tion of CH2Cl2 , at room temperature, those of 3, 4 and 5 by
sublimation (see above). Crystal data and experimental details
are listed in Table 3. Diffraction experiments for 2, 3, 4(A) and
5(B) were carried out on a Stoe 4-circle diffractometer, for 5(A)
on a Rigaku AFC6S 4-circle diffractometer, both using gra-
Finally, the fractional coordinates obtained at the end of the
simulated annealing runs were verified by Rietveld refinements
using the GSAS program.37 In both cases, the scale factor, cell
constants, and parameters describing a linear interpolated
background function and the diffraction peak shape were var-
ied. The highly-resolved synchrotron powder pattern of 6 con-
tained sufficient data for the atomic coordinates and isotropic
ꢀ
˚
phite-monochromated Cu-Ka radiation (l ¼ 1.54178 A); for
4(B) and 5(C) on a SMART 3-circle diffractometer with a
1K CCD area detector, using graphite-monochromated Mo-
Table 4 Structure solution details for 6 and 7
ꢀ
˚
Ka radiation (l ¼ 0.71073 A). In all cases, crystals were
cooled with Cryostream (Oxford Cryosystems) open-flow N2
gas cryostat. Absorption corrections were performed for 3
and 4 (A and B) by a semi-empirical method, based on c-
scans. The structures were solved by direct methods using
the SHELXS-86 program31 (or SIR9232 for 5) and refined
by full-matrix least squares against F2, using SHELXL-97
software.33
6
7
Data range used/degrees
5–40
74
7–34
66
Number of intensities extracted
w2 for Pawley profile fit
Number of atoms in model, excluding dummy
7.67
12
2.94
33
Internal degrees of freedom
1
8
Initial simulation temperature (w2 units)
Final simulation temperature (w2 units)
Initial w2 for intensities
300
280
3740
63.1
18.17
100
4.5
CCDC reference numbers 196099–196102. See http://
www.rsc.org/suppdata/nj/b2/b206946f/ for crystallographic
data in CIF or other electronic format.
1825.6
24.4
5.61
Final w2 for intensities
w2 for Rietveld profile fit of SA model
(refine scale + ITF only)
Powder diffraction. X-Ray diffraction experiment for a poly-
crystalline sample of 6 was carried out on Station 2.3 of the
New J. Chem., 2003, 27, 140–149
147

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W. Clegg and C. Viney, Chem. Commun., 1999, 2493; ( f ) M.
Biswas, P. Nguyen, T. B. Marder and L. R. Khundkar, J. Phys.
Chem. A, 1997, 101, 1689; (g) P. Nguyen, G. Lesley, T. B. Marder,
I. Ledoux and J. Zyss, Chem. Mater., 1997, 9, 406.
U-factors of all non-hydrogen atoms to be refined indepen-
dently while the H atom positions were restrained to idealised
positions, giving an excellent fit with the final w2 ¼ 5.32. The
powder diffraction pattern of 7 contained an amorphous com-
ponent at 2y > 34ꢂ, therefore only the data below this limit
were used in the solution and subsequent Rietveld refinement.
The refinement of atomic coordinates being unstable, these
were fixed and an overall isotropic U-factor was refined, giving
a good fit with the final w2 ¼ 2.24.
4
D. Beljonne, H. F. Wittman, A. Kohler, S. Graham, M. Younus,
J. Lewis, P. R. Raithby, M. S. Khan, R. H. Friend and J. L.
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1998, 37, 3036; N. Chawdhury, A. Ko¨hler, R. H. Friend, M.
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Raithby, M. Younus, A. J. P. White, D. J. Williams, N. N. Payne,
L. Yellowlees, D. Beljonne, N. Chawdhury and R. H. Friend,
Organometallics, 1998, 17, 3034; J. Lewis, P. R. Raithby and
W.-Y. Wong, J. Organomet. Chem., 1998, 556, 219; M. S. Khan,
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M. Younus, P. R. Raithby, T. C. Corcoran, M. R. A.
Al-Mandhary and M. S. Khan, J. Chem. Phys., 1999, 110, 4963.
K. Mullen and G. Wegner, Electronic Materials: The Oligomer
Approach, Wiley-VCH, New York, 1998.
U. H. F. Bunz, V. Enkelmann, L. Kloppenburg, D. Jones, K. D.
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Mater., 1999, 11, 1416.
SHELXTL software38 was used for analysing the geometry
and for graphical presentation of all structures (1–7).
Optical measurements. Thin films of the Pt(II) poly-ynes 8–13
and were spun from dichloromethane solution on quartz sub-
strates using a conventional photoresist spin-coater. Films
were typically 100–150 nm in thickness as measured on a Dek-
tak profilometer. The optical absorption was measured with a
Hewlett-Packard ultraviolet-visible (UV-VIS) spectrometer.
Photoluminescence (PL) was measured with the sample in a
continuous-flow helium cryostat, excitation being provided
by the UV lines (334–365 nm) of a continuous wave (cw) argon
ion laser. Typical intensities used were a few mW mmꢁ2. The
emission spectra were recorded using a spectrograph with an
optical fiber input, coupled to a cooled charge coupled device
(CCD) array (Oriel Instaspec IV).
5
6
7
Thermal analysis. Thermal analysis (differential thermal ana-
lysis, DTA, and thermogravimetry, TG) of 2–7 was performed
simultaneously in a Stanton-Redcroft model STA-780 Simul-
taneous Thermal Analyser under flowing N2 . Sample masses
were ꢅ1 mg packed with ꢅ2 mg Al2O3 in open Inconel cruci-
bles. The reference crucible contained Al2O3 . Samples were
heated at 10 ꢂC minꢁ1 to 465 ꢂC. The thermocouple readings
were calibrated using a series of DTA standard materials:
KNO3 , In, Sn, Ag2SO4 , and K2SO4 as well as Pb and Al
as secondary standards, using the same heating rates as the
samples.
8
9
F. Wittmann, R. H. Friend, M. S. Khan and J. Lewis, J. Chem.
Phys., 1994, 101, 2693.
J. Cornil, D. A. dos Santos, X. Crispin, R. Silbey and J. L. Bredas,
J. Am. Chem. Soc., 1998, 120, 1289.
10 G. R. Desiraju, J. Chem. Soc., Chem. Commun., 1990, 454; P. J.
Langley, J. Hulliger, R. Thaimattam and G. R. Desiraju, New
J. Chem., 1998, 22, 1307; J. M. A. Robinson, D. Philp, B. M.
Kariuki and K. D. M. Harris, Chem. Commun., 1999, 329.
11 T. Steiner, J. Chem. Soc., Chem. Commun., 1995, 95; D. Philp and
J. M. A. Robinson, J. Chem. Soc., Perkin Trans. 2, 1998, 1643.
12 S. Kumar, K. Subramanian, R. Srinivasan, K. Rajagopalan,
A. M. M. Schreurs, J. Kroon, G. Koellner and T. Steiner,
J. Mol. Struct., 1998, 448, 51.
13 T. Steiner, B. Lutz, J. van der Maas, N. Veldman, A. M. M.
Schreurs, J. Kroon and J. A. Kanters, Chem. Commun., 1997,
191.
Acknowledgements
14 (a) N. A. Ahmed, A. I. Kitaigorodsky and M. Sirota, Acta Crys-
tallogr., Sect. B, 1972, 28, 2875; (b) J. M. A. Robinson, B. M.
Kariuki, R. J. Gough, K. D. M. Harris and D. Philp, J. Solid
State Commun., 1997, 134, 203; (c) H.-C. Weiss, D. Bla¨ser, R.
Boese, B. M. Doughan and M. M. Haley, Chem. Commun.,
1997, 1703.
15 T. Steiner, E. B. Starikov and M. Tamm, J. Chem. Soc., Perkin
Trans. 2, 1996, 67.
16 V. R. Vangala, A. Nangia and V. M. Lynch, Chem. Commun.,
2002, 1304.
17 T. Steiner, J. Chem. Soc., Chem. Commun., 1994, 101.
18 (a) S. Thorand and N. Krause, J. Org. Chem., 1998, 63, 8551; (b)
M. S. Khan, M. R. A. Al-Mandhary, M. K. Al-Suti, A. K.
Hisahm, P. R. Raithby, B. Ahrens, M. F. Mahon, L. Male,
E. A. Marseglia, E. Tedesco, R. H. Friend, A. Ko¨hler, N. Feeder
and S. J. Teat, J. Chem. Soc., Dalton Trans, 2002, 1358; (c) R.
Ziessel, J. Suffert and M.-T. Youinou, J. Org. Chem., 1996, 61,
6535; (d ) P. Nguyen, Z. Yuan, L. Agocs, G. Lesley and T. B.
Marder, Inorg. Chim. Acta, 1994, 220, 289; (e) M. S. Khan,
A. K. Kakkar, N. J. Long, J. Lewis, P. R. Raithby, P. Nguyen,
T. B. Marder, F. Wittman and R. H. Friend, J. Mater. Chem.,
1994, 4, 1227; ( f ) M. Moroni, J. Le Moigne, T. A. Pham and
J.-Y. Bigot, Macromolecules, 1997, 30, 1964.
We thank Mr. Jon P. Wright (Department of Chemistry, Uni-
versity of Cambridge) for helpful discussions during indexing
and Rietveld refinement of the data on compounds 6 and 7.
M. S. K. gratefully acknowledges Sultan Qaboos University
Research Grant No. IG/SCI/CHEM/02/02, EPSRC (U.K.)
for a Visiting Fellowship and Sultan Qaboos University for
a research leave. A. K. thanks Peterhouse, Cambridge for a
Research Fellowship and the Royal Society for a University
Research Fellowship. We also acknowledge the EPSRC grant
GR/L52581 (J. P. A.) and GR/L92761 (P. R. R.) and for a
studentship (to J. C. C.).
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