Conjugated oligomers and polymers of cis- And trans-platinum(II)-para- and ortho -bis(ethynylbenzene)quinone diimine

Article abstract of DOI:10.1021/om7010563

Three conjugated polymers of the type (-spacer-C≡C-PtL ₂-C≡C-)_n, with spacer = para- and orthobis(diphenyl(tetramethoxy)quinone diimine) and L = PEt₃, were synthesized as the cis- and frans-isomers about the Pt. The three combinations (spacer/PtL₂Cl₂), ortho/trans, para/trans, and para/cis led to polydispersed polymers, which upon fractionation provided more monodispersed materials with Arn ranging from 3600 to 32400 (GPC). The spacer ortho-bis(diphenylethynyl)tetramethoxyquinone diimine reacts with cis-PtL ₂Cl₂ to form small oligomers and a chelate cyclic complex (7), which was used as a model compound. All materials along with the aryl-C≡C-PtL₂- C≡C-aryl models (L = PEt₃; aryl = C₆H₅, 2,4,6-C₆H₂Me₃; 2,4,5-C₆H₂Me₃) were studied by ¹H and ³¹P NMR, IR, UV-vis, TGA, DSC, luminescence spectroscopy, photophysics, and cyclic voltammetry. The UV-vis spectra exhibit an intramolecular low-energy and low-intensity charge transfer band (CT) assigned to π(Ph-C≡C) (for organics) and π/d_xy((Ph-C≡C) ₂Pt) (for organometallics) to the π*(quinone diimine), as demonstrated by comparison with a corresponding amine derivative (i.e., no CT band) and corroborated by DFT and TDDFT. The polymers and 7 are not luminescent at room temperature (solid and solution). However in 2MeTHF at 77 K, the polymers bearing the combination ortho/trans and para/cis as well as the model compound 7 exhibit higher energy phosphorescence (T_n → S ₀) originating from the ππ/d_xy((Ph-C≡C) ₂Pt) excited states. A correlation between the structural parameters (angle made by the PtP₂(C≡C)₂ vs the aryl planes, angle made by the aryl and the quinone diimine planes, molecular weight) with the calculated oscillator strength, absorptivities, and the observed position of the lowest energy absorption bands is demonstrated. Finally, upper energy delayed fluorescence (S_n → S₀) was detected for the polymers and 7 at 77 K and was assigned to T₁-T₁ interactions via aggregation as its intensity varies with the concentration.

Full text of DOI:10.1021/om7010563

Organometallics 2008, 27, 2201–2214
2201
Conjugated Oligomers and Polymers of cis- and trans-Plati-
num(II)-para- and ortho-bis(ethynylbenzene)quinone Diimine
Karl Gagnon,† Shawkat Mohammed Aly,† Anne Brisach-Wittmeyer,† Diana Bellows,†
Jean-François Bérubé,† Laurence Caron,† Alaa S. Abd-El-Aziz,‡ Daniel Fortin,*,† and
Pierre D. Harvey*,†
Département de Chimie, UniVersité de Sherbrooke, Sherbrooke, PQ, Canada J1K 2R1, and Department of
Chemistry, UniVersity of British Columbia, Okanagan, 3333 UniVersity Way, Kelowna, BC, Canada V1V 1V7
ReceiVed October 20, 2007
Three conjugated polymers of the type (-spacer-Ct C-PtL2-Ct C-)n, with spacer ) para- and ortho-
bis(diphenyl(tetramethoxy)quinone diimine) and L ) PEt3, were synthesized as the cis- and trans-isomers
about the Pt. The three combinations (spacer/PtL2Cl2), ortho/trans, para/trans, and para/cis led to polydispersed
polymers, which upon fractionation provided more monodispersed materials with Mn ranging from 3600 to
32400 (GPC). The spacer ortho-bis(diphenylethynyl)tetramethoxyquinone diimine reacts with cis-PtL2Cl2 to
form small oligomers and a chelate cyclic complex (7), which was used as a model compound. All materials
along with the aryl-Ct C-PtL2- Ct C-aryl models (L ) PEt3; aryl ) C6H5, 2,4,6-C6H2Me3; 2,4,5-C6H2Me3)
were studied by 1H and 31P NMR, IR, UV–vis, TGA, DSC, luminescence spectroscopy, photophysics, and
cyclic voltammetry. The UV–vis spectra exhibit an intramolecular low-energy and low-intensity charge transfer
band (CT) assigned to π(Ph-Ct C) (for organics) and π/dxy((Ph-Ct C)2Pt) (for organometallics) to the
π*(quinone diimine), as demonstrated by comparison with a corresponding amine derivative (i.e., no CT
band) and corroborated by DFT and TDDFT. The polymers and 7 are not luminescent at room temperature
(solid and solution). However in 2MeTHF at 77 K, the polymers bearing the combination ortho/trans and
para/cis as well as the model compound 7 exhibit higher energy phosphorescence (Tn f S0) originating from
the ππ*/dxy((Ph-Ct C)2Pt) excited states. A correlation between the structural parameters (angle made by
the PtP2(Ct C)2 vs the aryl planes, angle made by the aryl and the quinone diimine planes, molecular weight)
with the calculated oscillator strength, absorptivities, and the observed position of the lowest energy absorption
bands is demonstrated. Finally, upper energy delayed fluorescence (Sn f S0) was detected for the polymers
and 7 at 77 K and was assigned to T1-T1 interactions via aggregation as its intensity varies with the
concentration.
Chart 1a
Introduction
The use of metal-containing macromolecules have been the
topics of intense research for the past 10 years or so, and
important applications such as semi- and photoconducting and
optical materials, catalysis, and nanomaterials were reported.
Reviews on the topics have indeed flourished at a fast rate during
the past 5 years or so.1,2 Among the building blocks for the
preparation of these novel materials, one finds the well-known
a
R ) alkyl group.
metal-containing fragment bis(ethynylaryl)bis(phosphine)plati-
num(II), Ar-Ct C-PtL2-Ct C-Ar (Chart 1; L ) monophos-
phine), which can be used to prepare innovative conjugated
coordination and organometallic cyclic and acyclic oligomers,
polymers, dendrimers, and star-shaped molecules.3 At the same
time, both the trans- and cis-Ar-Ct C-PtL2-Ct C-Ar units and
alike turn out to be photo- and electroluminescent chromophores,4
and their excited-state characteristics have attracted some attention
from a theoretical point of view.5
* To whom correspondence should be addressed. Tel: 819-821-7092.
Fax: 819-821-8017. E-mail: Pierre.Harvey@USherbrooke.ca.
† Université de Sherbrooke.
‡ UBC Okanagan.
In parallel, quinone diimine is a nonluminescent chromophore
but exhibits electroresponsive properties in acidic solution.6
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10.1021/om7010563 CCC: $40.75
2008 American Chemical Society
Publication on Web 04/18/2008

2202 Organometallics, Vol. 27, No. 10, 2008
Gagnon et al.
Chart 2
Along with its reduced form, N,N′-diphenyl-1,4-phenylenedi-
amine, quinone diimine was often investigated in relation with
the well-known conducting polymer polyaniline in its protonated
emaraldine form.7
We now wish to report new conjugated organometallic
polymers exhibiting the general structure (-[ethynylben-
zene-metal-ethynylbenzene]-[quinone diimine]-)n where the
[ethynylbenzene-metal-ethynylbenzene] is the trans- or cis-
PtL2(Ct CC6H4-)2 unit and the [quinone diimine] moiety is
the para- or ortho-substituted bis(ethynylbenzene)-N,N′-tet-
ramethoxyquinone diimine (Chart 2). The photophysical proper-
ties for the ortho/trans- and para/cis-polymers and the mono-
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Chart 3
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to exhibit luminescence arising from upper excited states at 77
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Results and Discussion
Synthesis of the Model Compounds. The model compounds
1 and 2 (Chart 3) were prepared by reacting respectively 2,4,6-
and 2,4,5-trimethylphenylacetylene with the trans-Pt(PEt3)2Cl2
i
complex in the presence of Pr2NH. These derivatives were
selected in order to provide specific structural information about
the trans-PtL2(Ct C)2 segment and for assignment purposes in
the polymers (cis vs trans about Pt using 31P NMR). Similarly,
a study of the electrochemical, optical, and photophysical
properties of these models helps understand the photonic
properties of the polymers.
The X-ray structures for 1 and 2 (Figure 1) reveal the
anticipated trans-geometry in both complexes, which turn out
to be crystallographically centrosymmetric at the Pt atom. Two
different orientations of the aryls with respect to the PtP2(Ct C)2
plane are noted, demonstrating at first glance no obvious
preference for the parallel or perpendicular orientations of the
aryl π-orbitals vs this Pt-containing plane. In 1, the aryl groups
are placed near perpendicular to the PtP2(Ct C)2 plane (83.0°).
This orientation may be induced by steric effects generated by
the two ortho methyl groups of the mesityl residues and the
PEt3 ligands. Noteworthy, this compound appears white as
crystals. In 2, there are fewer steric effects (just one ortho methyl
instead of two). The aryls are oriented more parallel with the
PtP2(Ct C)2 plane (29.8°), which allows a different alignment
of the aryl π-system with respect to the d Pt orbitals. Interest-
ingly, the compound exhibits a yellowish coloration. Again,
steric hindrance between the methyl groups and the PEt3 ligand
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Conjugated Polymers of cis- or trans-PhCt CPt(PEt3)2Ct CPh
Organometallics, Vol. 27, No. 10, 2008 2203
Figure 1. ORTEP representations of 1 (left) and 2 (right). The thermal ellipsoids are represented at 25% probability. The H atoms are not
shown for clarity. Selected bond distances (Å) and angles (deg), 1: Pt-P, 2.288(3); Pt-C, 2.013(9); Ct C, 1.184(13) ; PPtC, 91.3(3); 2:
Pt-P, 2.288(3); Pt-C, 2.047(10); Ct C, 1.148(12); PPtC, 90.6(3).
Scheme 1a
a
Only the anti-geometry is shown for simplicity.
may be the cause for this. A deviation of 6.9° from linearity of
the Ct C-C fragment is also noted, corroborating this hypoth-
esis. The variability in dihedral angle is not uncommon
according to the Cambridge Data Bank. Examples where the
relative angle between the PtP2C2 plane and the aryl group is
nil or almost nil,8 perpendicular or almost perpendicular,9 or
anywhere in between10 are frequent. In these models, the δ value
is about 15 ppm and the J(31P-195Pt) coupling constant
approaches 2400 Hz.
The synthesis of ligand 4 proceeds as indicated in Scheme
1. The precursor 3 is prepared from the condensation of a desired
tetrasubstituted quinone with an ortho-substituted ethynyl(tri-
methylsilane)aniline. The structure determination of 3 was made
by X-ray techniques (Figure 2; top) and reveals the anti-
geometry (3a). Although several X-ray structures of trans-
quinone diphenylimines were reported,11 compound 3a repre-
sents the first example of an ortho-substituted derivative. In
Scheme 1, only the corresponding anti-conformer is presented
for simplicity. After the next synthetic step (i.e., C-Si bond
cleavage), the X-ray structure for the syn-conformer (4b) was
also solved, demonstrating the existence of both conformers,
the anti and syn. The angles between the phenyl rings and the
central quinone average planes are 67.00° for the tetrafluoro-
spacer (anti-conformer) and 88.89° for the tetramethoxy-spacer
(syn-conformer), indicating that in both solids the π-systems
are not well oriented for conjugation.
conformers. These species were unfortunately not separable by
column chromatography despite several attempts.
The C-Si bond cleavage by a base in methanol (i.e.,
methanolate) is accompanied by the substitution of all the
fluoride atoms by methoxy groups, leading to 4, for which an
X-ray structure determination was made (Figure 2a). As stated
in this particular case, the syn-conformation (4b) was observed.
The incorporation of ethoxy substituents instead of methoxy
was also tested (compound 4′; Chart 4, and the obtained
corresponding ortho-derivative was characterized by X-ray
techniques (Figure 3), see Supporting Information for experi-
mental). For 4′, the anti-conformer was observed. The angle
between the phenyl and quinone diimine average plane is 89.98°,
almost completely perpendicular precluding efficient electronic
communication by conjugation. This convenient reaction (C-Si
bond cleavage and F-substitution by RO groups) was attempted
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2204 Organometallics, Vol. 27, No. 10, 2008
Gagnon et al.
Figure 2. (Top) ORTEP representations of 3 (left) and 4 (right). The thermal ellipsoids are represented at 25% probability. The H-atoms
are not shown for clarity. Selected bond distances (Å), 3: Ct C, 1.204(5), CdN, 1.399(14); 4: Ct C, 1.181(13), CdN, 1.273(9). (Bottom)
Redundant relaxed energy scan at the Hartree–Fock level for 3* (without silyl groups) and 4. In these calculations, one-half of the molecule
is fixed and the second half undergoes rotation about the N-Ph bond (θ ) 90° at first).
stability, consistent with the fact that both forms were observed
from X-ray structure determination. The graph exhibits an energy
barrier of 31 kJ/mol for 3* (without silyl groups), a barrier small
enough to observe fluxion at room temperature in solution. For 4,
a barrier of 47 kJ/mol is computed, a larger value stressing evidence
for steric hindrance of the -Ct CH with the OMe groups.
Noteworthy, the energy profile does not exhibit a Gaussian-shaped
curve as observed for the fluoride-based ligand 3* because of a
Figure 3. ORTEP representations of 4′ (right) and the corresponding
cooperative action between one of the OMe groups and the
Chemdraw (left). The thermal ellipsoids are represented at 25%
C6H4Ct CH group upon rotation. At a critical angle, the energy
probability. The H atoms are not shown for clarity. Selected bond
drops drastically after the MeO groups get “out of the way”. These
distances (Å): Ct C, 1.187(13), CdN, 1.269(11).
computations indicate that the barriers to fluxion are low enough
to anticipate fluxion in solution. Maybe for this reason also, the
Chart 4
separation of the syn- from the anti-forms was not possible in this
work.
Ligands 5 and 6 were also prepared in the same manner as
for 3 and 4 (Scheme 2). Both compounds were characterized
by X-ray techniques (Figure 4). These structures reveal the anti-
conformation in both cases and exhibit angles between the
phenyl and quinone diimine mean planes of 55.15° and 69.38°
for 5 and 6, respectively. The smaller interplanar angles indicate
that there is less steric hindrance and so less “torsion” on the
π-system in comparison with the ortho-substituted species.
These X-ray data also reveal that the fluoride substituents induce
even less torsion than the methoxy groups.
to test the facile incorporation of solubilizing chains often
desired for polymers (polymer growth during synthesis, solubil-
ity for characterization, and protecting groups to minimize
interchain interactions in the solid).
Imine formation in 3–6 and 4′ is evidenced by the shorter
CdN distance (ranging from 1.23 to 1.31 Å; X-ray) and the
presence of a broad UV–vis band in the 500–700 nm range,
giving the red to purple color in these materials. This color is
very diagnostic since the most probable side product is the
corresponding reduced diamine, which is white.12
The difficulty in separating the anti- to syn-conformers is now
addressed. Molecular modeling calculations on 4 as well as on
3* (without the silyl groups) were performed to evaluate the
energy barrier for the anti- to syn-conformer interconversion.
The computational results are provided in Figure 2 (bottom). The
calculations predict that the two conformers exhibit almost the same

Conjugated Polymers of cis- or trans-PhCt CPt(PEt3)2Ct CPh
Organometallics, Vol. 27, No. 10, 2008 2205
Scheme 2
Figure 4. ORTEP representations of 5 (left) and 6 (right). The thermal ellipsoids are represented at 25% probability. The H atoms are not
shown for clarity. Selected bond distances (Å); 5: Ct C, 1.193(8), CdN, 1.296(9); 6: Ct C, 1.190(8), CdN, 1.274(6).
Scheme 3
Synthesis of the Cyclic Model Compound 7 and Reaction
with cis-Pd(PEt3)2Cl2. 4 reacts with cis-Pt(PEt3)2Cl2 in the
presence of a base and CuI to form complex 7 and another small
oligomer, 7′ (GPC), as verified by 31P NMR of the crude product
(Scheme 3).
Figure 5. ORTEP representation 7. The thermal ellipsoids are
represented at 25% probability. H atoms are not shown for clarity.
Selected bond distances (Å) and angles (deg): Pt-C, 1.928(30),
Pt-P, 2.308(13), Ct C, 1.31(4), CdN, 1.27(5); PPtC ) 87.2(9).
After separation, complex 7 was characterized by X-ray
crystallography (Figure 5). The starting Pt-containing complex
in its cis-geometry turns out to be well adapted to coordinate
ortho-ligand 4, in its syn-conformation. This compound repre-
sents a rare example where the cis-geometry about the Pt(II)
atom was used. Indeed, the trans-geometry is more often
encountered (as indicated in refs 26 to 28), but some examples
of cis-coordination also exist.13 The presence of ring stress is
noted in complex 7, as evidenced by the deviation of the quinone
diimine NdC6(OMe)4dN ring from planarity. The angle formed
by the CdN axis and quinone diimine C6-skeleton planes is
7.79°. The separable complex 7 (by column chromatography)
also represents a model compound for cis-Pt-containing materi-
als (polymers) readily identifiable from the 31P NMR signature
(δ ) 8.7 ppm and 1J(31P-195Pt) ) 2225 Hz (in CD2Cl2)). The
π-plane angle between the quinone diimine and phenyl rings is
61.40°. GPC indicated that the separated oligomers were
primarily composed of very small oligomers of 2 and 3 units
long.
The oligomers may also consist of a mixture of compounds
with anti- and syn-ligands of the precursor,11b where the anti-
form promotes polymerization, whereas the syn-form promotes
the chelation. The presence of oligomers is also consistent with
other literature works on Pt(II)-containing trimers, tetramers,
and higher oligomers.14,15
Attempts were also made to generate Pd-containing com-
plexes and polymers analogous to 7 and 7′. cis-Pd(PEt3)2Cl2
reacts with 4 in the presence of CuI with the possibility of C-C
coupling occuring (Scheme 4). The compounds 8 and 9 were
characterized by X-ray techniques (Figure 6), and other oligo-
mers were also detected in the GPC traces (n ) 2, 3).
Compound 8 is formed by C-C coupling as anticipated. The
reaction mechanism should proceed through a Pd-containing
(12) The corresponding diamines for ligand 3 (cis and trans) were
isolated and characterized by X-ray crystallography as reaction side products.
The crystals were colorless, the CdN distance ranging form 1.39 to 1.41
Å. The angles made by the peripheral aryls vs central aryl were 51.53° and
63.97° for the trans-conformer and 49.84° for the syn-conformer, respec-
tively. This shows that crystal-packing forces could also participate in the
π-torsion angles, since we find more than 10° torsion angle difference in a
same crystal packing. However, in this case it is an amine instead of an
imine bound to the quinone ring, allowing for free rotation on both sides
of the nitrogen.
(13) (a) Johnson, C. A., Jr.; Baker, B. A.; Berryman, O. B.; Zakharov,
L. N.; O’Connor, M. J.; Haley, M. M. J. Organomet. Chem. 2006, 691,
413–421. (b) Johnson, C. A., Jr.; Haley, M. M.; Rather, E.; Han, F.;
Weakley, T. J. R. Organometallics 2005, 24, 1161–1172.
(14) Vincente, J.; Chicote, M.-T.; Alvarez-Falcon, M. M.; Jones, P. G.
Chem. Commun. 2004, 2658–2659.
(15) Lee, S. J.; Luman, C. R.; Castellano, F. N.; Lin, W. Chem. Commun.
2003, 2124–2125.

2206 Organometallics, Vol. 27, No. 10, 2008
Gagnon et al.
Scheme 4
Figure 6. ORTEP representations of 8 (left) and 9 (right). The thermal ellipsoids are represented at 25% probability. The H atoms are not
shown for clarity. Selected bond distances (Å) and angles (deg), 8: Ct C, 1.204(8), CdN, 1.278(6); 9: Pd-P, 2.297(6); Pd-Cl, 2.341(6),
Ct C, 1.204(8), CdN, 1.278(6); PPdCl, 89.3(2), PPdC, 92.0.
Scheme 5
precursor with a structure similar to that of 7, where the
macrocycle exhibits the appropriate cis-orientation for C-C
coupling. It is reasonably anticipated that the existence of this
macrocycle precursor stems from ligand 4b (syn-conformer) and
cis-Pd(PEt3)2Cl2. Moreover, the characterization of compound
8 corroborates the presence of the syn-conformer for spacer 4,
while the anti-conformer is evidenced by the structure of the
binuclear complex 9. The latter complex is interesting because
a cis/trans isomerization took place, which is rare but not
unprecedented.16 This isomerization was not observed for the
Pt-containing materials. Interestingly, 9 also represents a model
for the Pt-containing polymers built upon an ortho-substituted
spacer and a trans-metallic fragment (noted as ortho/trans). On
the basis of this structure, the synthesis of ortho/trans polymers
is possible from the extension at the chloro positions.
For 9, the interplanar angle between the phenyl and quinone
planes is 84.78°. The imine functions are also evidenced by
the short NdC distances (1.28 Å). This rather large angle (∼85°)
makes conjugation difficult through the π-orbitals. The angle
made by the aryl and the Pt(PEt3)2(CC)2 planes is 81.47°.
Syntheses of the Oligomers and Polymers. The syntheses
of polymers 10-12 proceed the same way as mentioned for 7
(Scheme 5). The nature of the coordination geometry about the
Pt atom is confirmed by 31P NMR by comparison with the
diagnostic chemical shifts of the model compounds 1 and 2 for
polymers 10 and 12 (δ is in the 15 ppm range) and compound
7 for polymer 11 (δ is in the 8.5 ppm range). Similarly, the 1:1
ratio of ligand and Pt-containing starting material in the
(16) Cross, R. J.; Davidson, M. F. Inorg. Chim. Acta 1985, 97, L35–
L36.

Conjugated Polymers of cis- or trans-PhCt CPt(PEt3)2Ct CPh
Organometallics, Vol. 27, No. 10, 2008 2207
Table 1. Molecular Weight Determination of the Polymers 10–12a
0.2 electron based upon a comparison of the peak height. The
purity was checked by H NMR. A chemically reversible but
1
c
polymer
Mn
Mw
PD
electrochemically irreversible reduction wave was also noted.
The cathodic and anodic peaks for this reduction process are
very broad.
10b
11b
12b
7′d
32 400 (38)
16 800 (20)
6600 (8)
68400
17300
10000
4400
2.1
1.0
1.5
1.2
3600 (4)
The CVs for 1 and 2 show a series of irreversible oxidation
peaks in the same window as for trans-PhCt CPt(PEt3)2Ct CPh,
but two differences are observed. First, the number of peaks
increased in the 1–1.5 V window, and the peaks are shifted to
lower potentials. Both observations are due to the methyl group
donating inductive effect, rendering the phenyl groups easier
to oxidize. This is well exemplified by the shift of the 1.17 V
peak (of trans-PhCt CPt(PEt3)2Ct CPh) down to 1.11 and 1.06
V vs SCE for 1 and 2, respectively. The presence of peaks at
1.42 and 1.46 V for 1 and 2 may also arise from a shift of a
higher potential peak (presumably above the 1.5 V limit used
for the comparison molecule, trans-PhCt CPt(PEt3)2Ct CPh).
Coulometry for 2 reveals that the number of transferred electrons
is 1.1, 1.4, and 1.1 ( 0.2 for the peaks located at 1.06, 1.46,
and 1.70 V, respectively, consistent with their relative height
and that observed for trans-PhCt CPt(PEt3)2Ct CPh. 1 and 2
exhibit broad and ill-defined irreversible reduction peaks.
Fractional numbers of transferred electrons were also noted for
the reductions and were not studied further. All in all, 1 and 2
exhibit multiple irreversible waves in the 0.9–1.82 V range and
are used for assignment purposes with the polymers.
a GPC against monodispersed polystyrene standards. b Measured after
fractionation, which consisted of precipitation by diethyl ether. c The
values in brackets are the average number of units in the chain obtained
by dividing Mn by the molecular weight of a repetitive unit. d Portion
separated from the reaction presented in Scheme
chromatography.
3 by column
polymers is confirmed by 1H NMR (using the integrated signals
for Me vs Et). Stand-alone films were obtained for 10 (SI) and
11. The striking feature is the polydispersitity of the crude
polymers based on the GPC traces, in which small oligomers
all the way to large polymers are detected, notably for 10 and
11. Fractionation is performed by precipitating the polymers
10–12 out of a concentrated CH2Cl2 solution using diethyl ether
as the poor solvent. For comparison purposes, the fractions of
oligomers separated for the reaction of Scheme 3, which are
noted as “oligomer 7′ (anti-ortho-cis)”, were also investigated.
These oligomers and precipitated polymers 10–12 exhibited Mn
ranging from 3600 to 32 400 (Table 1). From this analysis, we
observe that the molecular weight has a tendency to get higher
with more linear building-block ligands. The trend is that both
Mn and Mw vary as cis < trans and ortho < para and may
reflect the steric hindrance and geometry twist effects. Also,
this steric hindrance may slow the growth process of the
polymer. No attempt was made to increase the Mn, Mw, and
PD parameters, as this was not the purpose of this work.
The bis(ethynylbenzene)quinone diimine compounds 3 and
5 exhibit two sets of reduction waves only in the -0.37 to -1.20
V range. The peaks of 3 are found irreversible. For 5, the peak
at -0.48 V appears reversible. The peak at -0.96 V shows a
very slow electron transfer. Hence, these model compounds
exhibit low potential reduction peaks, totally consistent with
the assignment for being an electron acceptor.
The thermal stability was >300 °C in all 3 cases (SI), whereas
the small oligomers (primarily composed of dimers and trimers
separated from compound 7 using column chromatography)
exhibited weight loss between 100 and 200 °C. For polymers
10 and 11, a glass transition was detected at ∼147 °C (SI) and
at 142 °C, respectively.
Compound 7 exhibits three irreversible peaks resembling that
of 1 and 2, allowing one to assign the oxidation to the
PhCt CPt(PEt3)2Ct CPh unit. A quantity of 1.0 ( 0.2 for both
peaks at 1.00 and 1.42 V are transferred, again consistent with
the findings for 1 and 2. Polymers 10-12 exhibit two or three
peaks on the oxidation side, but the signals are ill-defined and
located at lower potentials, consistent with an extended conju-
gated polymer where the wave widths are associated with
polydispersity. Compound 7 and polymer 11 exhibit irreversible
ill-defined reduction peaks and were not investigated further.
Analysis of the Frontier Orbitals and UV–Vis Spectra.
An earlier report on the bimolecular charge transfer interactions
between 7,7,8,8-tetracyanoquinodimethane (TCNQ) and a series
of trans-Pt(PR3)2(Ct CR′)2 complexes (R ) Me, Et, Pr, Bu; R′
) H, CH2dCH, MeCt C, Ph) exists.22 The purple 1:1 adducts
exhibit an absorption in the 506–555 nm range in the UV–vis
spectra similar to our polymers. The authors deduced that the
electron was donated from the alkynyl fragment to the TCNQ
unit. These findings provide interesting clues for the investigated
systems.
Electrochemical Oxidation Properties of the Oligomers
and Polymers. N,N′-Diphenylquinone diimine exhibits oxida-
tion processes in its protonated form only.6b–d,17,18 PhCt CH
exhibits an irreversible, large oxidation wave in the CVs (cyclic
voltammograms; 1.5-2.0 V vs Ag/AgCl).19 This irreversibility
is due to the presence of a radical-type polymerization process
forming polyphenylacetylene.19 The CV of the ligands, model
compounds, and polymers (SI) and the observed oxidation and
reduction peaks are reported in Table 2. The CV of trans-
PhCt CPt(PEt3)2Ct CPh was also studied and compared well
with the literature.20,21 This compound exhibits an irreversible
oxidation peak at ∼1.2 V vs Ag/AgCl, and 1.43 ( 0.21 electron
was transferred in a benzene/acetonitrile mixture.21 This ir-
reversible oxidation peak was also observed by us at 1.17 V vs
SCE in acetonitrile (+0.1 M TBAPF6) with 1.1 ( 0.2 transferred
electron. We do not have an explanation for this small difference
except that a weak irreversible peak was also noted at 0.97 V
vs SCE (also seen in the other samples) corresponding to about
The UV–vis spectra and MO descriptions (DFT and TDDFT)
of the parent compounds trans-PhCt CPt(PR3)2Ct CPh (R )
Et, Bu, Ph) to the models 1 and 2 were previously studied
throughout the literature.4k,23–25 Only a brief account of the
relevant information is provided below. The complexes exhibit
(17) Ueda, F.; Mikai, K.; Harada, I.; Nakajima, T.; Kawagoe, T
Macromolecules 1990, 23, 4925–4928.
(18) Turovska, B.; Stradins, J.; Glezer, V.; Lokmane, E.; Sarule, E.;
Freimanis, J. Zinatnu Akademijas Vestis, Kimijas Serija 1989, 108–15.
(19) Garcia-Canadas, J.; Lafuente, A.; Rodriguez, G.; Marcos, M. L.;
Gonzalez Velasco, J. J. Electroanal. Chem. 2004, 565, 57–64.
(20) Kershman, J. R.; Paris, K. E.; Stamey, J. A.; Pyati, R J. Electroanal.
Chem. 2006, 597, 87–94.
(22) Masai, H.; Sonogashira, K.; Hagihara, N. J. Organomet. Chem.
1972, 34, 397–404.
(23) Wong, C.-Y.; Che, C.-M.; Chan, M. C. W.; Han, J.; Leung, K.-H.;
Philips, D. L.; Wong, K.-Y.; Zhu, N. J. Am. Chem. Soc. 2005, 127, 13997–
14007.
(21) Kondrachova, L.; Paris, K. E.; Sanchez, P. C.; Vega, A. M.; Pyati,
R.; Rithner, C. D. J. Electroanal. Chem. 2005, 756, 287–294.
(24) Batista, E. R.; Martin, R. L. J. Phys. Chem. A 2005, 109, 9856–
9859.

2208 Organometallics, Vol. 27, No. 10, 2008
Gagnon et al.
Table 2. Observed Electrochemical Wavesa
compound
oxidation
reduction
-0.62/-1.06b
trans-Ph-Ct C-PtEt2-C’C-Ph
0.97 (ir), 1.17 (ir)
∼1.0 (ir), 1.11 (ir)
1.42 (ir), 1.82 (ir)
0.90 (ir), 1.06 (ir)
1.46 (ir), 1.70 (ir)
1.06 (ir) weak
1
-0.32 (ir), -1.74 (ir)
2
-1.09 (ir)
3
5
7
10
11
12
-0.58 (ir), -1.15/-1.09
-0.58/-0.37b, -1.20/-0.72b
0.77 (ir) 1.00 (ir), 1.42/1.25b
0.67 (ir), 1.16/1.01b
0.60 (ir), 0.96 (ir), 1.26 (ir)
0.51 (ir), 0.68 (ir), 1.12 (ir)
-1.06 (ir.)
a Volts vs SCE; ir ) irreversible (i.e., no return wave). b Electrochemically irreversible as the difference between the anodic and cathodic waves
exceeds 60 mV.
strong lowest energy absorption bands between 320 and 340
nm. For example, for R ) Ph, these are found at 330 (sh; ꢀ )
43 600) and 337 nm (ꢀ ) 44 900 M-1 cm-1).23 Reported DFT
results (B3LYP) for trans-PhCt CPt(PBu3)2Ct CPh indicated
that the HOMO is composed of conjugated π-orbitals, which
include contribution from the Pt(dxy) orbital, while the LUMO
consists of the ligand π* orbitals only.4k Thus the lowest energy
excitation is a mixture of ππ* and MLCT (metal-to-ligand
charge transfer). This assignment is corroborated by the differ-
ence in band shape between the complex (broad) and the free
ligand (as PhCt CH; narrow absorption). However, a recent
computational report (TDDFT) pointed out that this first
excitation is a mixture between two contributions, which are
ππ* (59%), similar to that described above (i.e., with a MLCT
character), and LMCT (32%; also primarily ππ*). These two
transitions arise from two different vertical but nearly degener-
ated excitations (difference only 0.04 eV; ꢀg f ꢀu* and ꢀu f
ꢀg*, where ꢀg and ꢀu and ꢀg* and ꢀu* are π- and π*-orbitals,
respectively, and the “g” orbitals include the Pt(dxy) orbital).
This more recent analysis better corroborates our results and
our experimental observations for 1 and 2. It is not clear whether
the strong absorptions are MLCT or LMCT since the LUMO
implies the complete molecules including the ligands and the
metal.
The nature of the frontier MOs is addressed by DFT, and the
transition energies and oscillator strength are addressed by
TDDFT. The crystal structure data of 1, 2, 4, 6, and 7 were
used as input files for all calculations. The frontier MO drawings
are shown in Figure 7.
Figure 7. Representations of the relevant frontier MOs for 1 and 2.
Table 3. UV-Vis Data for Model Compounds and Polymers 10–12a
compound or polymer
λmax in nm (ε in M-1 cm-1
)
1
2
4
6
270 (43 600), 312 (sh), 322 (20 000)
266 (154 000), 286 (sh), 330 (118 000)
240 (38 800), 318 (48 500), 476 (3440)
260 (23 400), 320 (38 900), 480 (4200)
266 (25 381), 314 (41 200), 514 (2100)
240 (38 300), 310 (40 000), 510 (2500)
350 (59 300), 560 (13 700)
The HOMO for 1 and 2 exhibits atomic contributions
spreading from the aryl π-system to the π-systems of the
ethynyls to the Pt d-orbitals. However the LUMOs for 1 and 2
differ greatly. For 1, the electronic density is primarily
concentrated about the Pt d and π Ct C with almost no
contribution on the mesityl residue. Conversely, the LUMO for
2 exhibit an electronic density spreading from the Pt d-orbitals
to the π-system of the aryl group, indicating a longer electronic
delocalization. All in all, the orientation of the aryl groups with
respect to the PtP2(Ct C)2 plane (83.0° for 1 and 29.8° for 2
defined as A1 in Chart 4) clearly plays an important role in the
nature of the LUMO. Figure 7 also shows representations for
the relevant HOMO-1 and HOMO-2 for 1. The HOMO-1
is composed of the π-system of the ethynylaryl fragments with
some contribution of the lone pair of the P atoms. No
contribution is computed for the Pt metal. The HOMO-2 is
composed primarily of the π-systems of the ethynyl linkers and
the Pt d-orbitals.
7
7′
10
11
12
330 (28 300), 540 (5900)
265 (28 000), 314 (40 200), 535 (2700)
a In 2 MeTHF at 298 K.
Four electronic transitions are possible from the MOs
presented in Figure 7 (3 for compound 1 and 1 for compound
2). These are all MLCT transitions, consistent with previous
finding for the trans-PhCt CPt(PBu3)2Ct CPh complex. The
computed oscillator strength for the HOMO f LUMO transition
for 2 is 0.70, and the calculated wavelength is 314 nm (the
experimental value is 330 nm (ꢀ ) 118 000 M-1 cm-1); Table
3). In 1, the HOMO f LUMO transition exhibits an oscillator
strength of 0.02, meaning that this contribution to the intensity
is minimal. On the other hand, the HOMO-2 f LUMO
transition exhibits a calculated oscillator strength of 0.13 and a
(25) Cooper, T. M.; Krein, D. M.; Burke, A. R.; McLean, D. G.; Rogers,
J. E.; Stagle, J. E. J. Phys. Chem. A 2006, 110, 13370–13378.

Conjugated Polymers of cis- or trans-PhCt CPt(PEt3)2Ct CPh
Organometallics, Vol. 27, No. 10, 2008 2209
Figure 8. HOMO and LUMO for ligand 6 (methyl groups not shown).
wavelength of 314 nm (the experimental value is 322 nm (ꢀ )
20 000 M-1 cm-1)). The relative amplitude of the oscillator
strengths for 1 and 2 corroborates well the observed absorp-
tivities. These computations, again, stressed the importance of
the angle made by the aryl group and the PtP2(Ct C)2 planes
(A1). For comparison purposes, the geometry optimizations of
1 and 2 were performed and the positions of the associated
MLCT bands were calculated (SI). The calculated A1 and λmax
are 73.9° and 61.7° and 327 and 331 nm for 1 and 2,
respectively. Despite the large change in A1 value (29.8° (X-
ray) vs 61.7° (optimized geometry)) for 2, these red-shifted
calculated λmax values still agree with the experimentals (327
vs 322 for 1 and 331 vs 330 nm for 2), illustrating the good
electronic “communication” of the ethynyl bridge.
these values fit with the experimental spectra in the sense that
these values are located in the tail of the band.
The frontier MOs for the model compound trans-(ligand
6)-Pt(PEt3)2-(ligand 6) representing a segment of polymer 10
is investigated. The geometry of this model was first optimized
prior to MO analysis (Figure 9). The angle A2 between the
phenyl rings and quinone average plane is 49.75°, obviously
deviating from coplanarity. This effect is induced by methoxy
streric contacts with the phenyl groups. This angle is 10° less
than that observed in the X-ray structure of the ligand alone
(6). However, this angle is also much less (∼35°) than in the
structure of model complex 9 (84.78°) built from an ortho-
substituted ligand and supports the tendency stated above that
the ortho-ligands induce more twist to the π-system than does
the para-ligands. The angle A1 between the Pt(PEt3)2(Ct C)2
plane and the phenyl rings in 9 is 81.47°, which is closer to
model complex 1 (83.0°) than 2 (29.8°).
The frontier MOs are presented in Figure 9. The HOMO is
composed of C(px) and N(px) atomic orbitals extending from
one ethynyl residue to the other, including some Pt(dxy) orbital,
securing contact all across the chain, even though the planes
deviate from planarity. This MO bears close similarities with
those described above (i.e., ꢀg and ꢀu). The LUMO is composed
of C(px) and N(px) primarily localized in the quinone diimine
segment. Thus, the computed lowest energy transitions are also
CT excitations (PhCt CPt(PEt3)2Ct CPh f quinone diimine).
The resemblance of the UV–vis spectra of ligands 4 and 6 with
that of the polymers 10-12 and compound 7 strongly supports
this assignment. TDDFT calculations predict that the 0–0
absorption is placed at 660 nm (with an oscillator strength of
2.10), which appears reasonable considering that the observed
CT absorption spreads from 450 to 700 nm. Also, the computed
oscillator strength appears a little more than 1 order of
magnitude larger than that computed for 6 above (0.09). This
observation is consistent with the effect of the angle A2 between
the phenyl and quinone diimine average planes on the absorp-
tivity (Table 4). For example, the angle A2 (49.8°) computed
for the optimized trans-(ligand 6)-Pt(PEt3)2-(ligand 6) com-
plex, representing a fragment of polymer 10, is smaller than
that observed for the compound 6 (X-ray; 69.4°). Experimen-
tally, the measured absorptivity of the CT band of polymer 10
is ∼3-fold larger (13 700) than that found in ligand 6 (4200
M-1 cm-1).
The para-substituted ligand 6 was analyzed by TDDFT (using
the available X-ray data) as a representative example of the
isolated ligand, and the frontier MOs are shown in Figure 8.
The HOMO is composed of all C(px) and N(px) atomic orbitals
extending from one ethynyl residue to the other, with the
exception of the methyl groups, stressing the obvious conjuga-
tion across the ligand, despite the angle of 69.4° made by the
phenyl groups and the quinone diimine ring (defined as A2 in
Chart 4). Conversely, the LUMO exhibits an enhanced electronic
density over the quinone diimine segment and shows a decrease
in atomic contribution on the ethynylphenyl side arms (i.e.,
practically nil). Hence, DFT calculations predict a lowest energy
electronic transition corresponding to a charge transfer process
(CT), ethynylphenyl f quinone diimine.
The computed HOMO f LUMO transition wavelength is
554.8 nm and compares reasonably with the observed low-
energy band spreading from 400 to 600 nm (λmax ) 480 nm; ꢀ
) 4200 M-1 cm-1). The computed oscillator strength is 0.09,
suggesting that the electronic transition is of weak intensity,
probably because of the 69.38° twist between the phenyl groups
and the quinone diimine ring (A2). This observation corroborates
well the observed low absorptivity (ꢀ ) 4200 M-1 cm-1; Table
3). Two other absorptions are observed at 260 and 320 nm.
Prior to discussing the computational results for a model
compound for polymer 10, it is important to state that no X-ray
data are available for any polymers. Instead, geometry optimiza-
tion is necessary, and in order to make appropriate comparisons,
the optimized geometry and TDDFT computations for 4, 6, and
7 were also performed (SI). All in all, some differences in
geometry (angles A1 and A2 vary from 5° to 20°) as well as
calculated 0–0 position and oscillator strengths are noted (SI).
The general trend is that the computed 0–0 position is
systematically red-shifted for the optimized geometry, but these
0–0 positions do not exceed the tail of the observed CT
absorption nor induce a change in the observed relative trend.
So, the CT assignment remains unchanged whether one uses
the X-ray or optimized geometry for analysis. Similarly, the
incorporation of solvent molecules (here THF instead of
2MeTHF) also induces a small red-shift of the calculated CT
0–0 positions (SI; 20 nm for 6 and 30 nm for 7), but again
Complex 7 was also investigated by DFT methods using the
X-ray data. The similarity in shape of the UV–vis spectra to
the polymers and ligands strongly suggests that the lowest
energy excited states are CT states as well. The MO representa-
tions for the frontier MOs, notably LUMO, HOMO-1, and
HOMO, are available in the Supporting Information. Both filled
orbitals exhibit the usual C(px) and N(px) contributions all across
the conjugated loop. The HOMO also exhibits some Pt(dxy)
contributions, stressing the obvious similarity with the model
compounds and ligand 6 computed above. The LUMO exhibits
atomic contributions (also C(px) and N(px)) mainly localized

2210 Organometallics, Vol. 27, No. 10, 2008
Gagnon et al.
Figure 9. Frontier MOs for the model compound trans-(ligand 6)-Pt(PEt3)2-(ligand 6). The respective MO energies are from bottom to
top: –0.181, –0.176, –0.097, –0.096 (degenerated), –0.018, –0.016 au, respectively.
Table 4. Comparison of the Calculated and Experimental Absorption Maximum with the Structural Parameters A1 and A2 Presented in Chart
4 Using X-ray Data, and Comparison of λmax Absorption with the Molecular Weighta
calcd 0–0 position in nm (oscillator strength)
crystal geometry
exptl λmax in nm
nature of the
excited state
compound or polymer
A2 (°)
A1 (°)
(
in M-1 cm-1
)
1
2
4b
83.0
29.8
314 (0.13)
314 (0.70)
536 (0.0006)
516 (0.001)
412 (0.012)
539 (0.09)
524 (0.03)
442 (0.001)
551 (0.04)
483 (0.02)
322 (20 000)
330 (118 000)
476 (3440)
MLCT
MLCT
CT
88.9
69.4
6
480 (4200)
CT
7
61.4
49.8
67.9
82.7
514 (2100)
CT
CT
10
560 (13 700)
compound
4
6
7
12
11
10
Mw or M (g/mol) λmax absorption (nm)
426.5
426.5
4400
476
480
514
535
540
560
10 000
17 300
68 400
a All angles are from X-ray data, except for 10 (DFT; also see Supporting Information).
on the quinone diimine residue. Thus, the computed lowest
energy excitation is also a CT transition despite the cis-geometry
of the metal. In this case, the ring stress makes the parameter
A2 (61.4°) less adequate for efficient CT process (i.e., less
allowed) than polymer 10 for example. Indeed, TDDFT predicts
that the HOMO f LUMO absorption band should be placed at
551 nm, a calculated value that is blue-shifted in comparison
with that computed for 10 (660 nm). Moreover, a small oscillator
strength of 0.04 is computed (in comparison with 2.1 for 10).
These comparisons corroborate the observed values (λmax ) 514
nm and ꢀ ) 2100 M-1 cm-1 for complex 7, and λmax ) 560
nm and ꢀ ) 13 700 M-1 cm-1 for polymer 10).

Conjugated Polymers of cis- or trans-PhCt CPt(PEt3)2Ct CPh
Organometallics, Vol. 27, No. 10, 2008 2211
Figure 10. Fluorescence (right) and absorption spectra (left) of 2
in degassed 2MeTHF at 298 K. λexc ) 322 nm.
Figure 11. Transient absoption spectrum for 2 in 2MeTHF at 77
K in the 600–800 nm window recorded 150 µs after the laser pulse.
The excitation wavelength is 355 nm.
The comparison of the λmax going from spacers 4 and 6 to
compound 7 to the oligomers and polymers 7′ and 10-12
reveals a trend. When the π-system extends, the absorption band
is red-shifted. The trend follows that of the molecular weight
(Tables 1 and 4b), 4 ) 6 < 7 < 12 < 11< 10 with λmax ) 476,
480, 514, 535, 540, 560 nm, respectively. This comparison
demonstrates the conjugation along the polymer backbone.
Moreover, the values of the absorption coefficient are clearly a
function of the π-orbitals’ alignment (parameters A1 for the
MLCT and A2 for CT); the more aligned the π-orbitals, the
more intense the absorption bands are. To our knowledge, such
detailed analysis of the structural parameters of the polymer
chain on the optical properties is unprecedented.
recorded, and the transient band was seen at about 725 nm,
similar to that of compound 2.
Both 1 and 2 are phosphorescent in 2MeTHF at 77 K (Figure
12). The emission bands show the typical vibronic progression
known for this class of compounds.4k The assignment for the
phosphorescence for 1 and 2 is MLCT on the basis of the MO
description of Figure 7 and the TDDFT described above. The
photophysical data are summarized in Table 5. Compounds 1
and 2 exhibit τP’s of ∼85 and 50 µs, respectively, longer than
that for the trans-PhCt CPt(PBu3)2Ct CPh (35.0 ( 1.3 µs in
2MeTHF at 77 K; this work). This trend follows the number of
methyl groups located at the ortho-positions (τP varies as 2 >
1 > 0) and may reflect the relative ease for the aryl groups to
rotate about the Pt-Ct C-Ar axis. This motion may contribute
to the nonradiative relaxation to the ground state. A weak
fluorescence was also detected for 1 at ∼405 nm, but its weak
intensity prevented accurate measurements of τF and ΦF. We
also proposed a MLCT fluorescence.
Photophysical Properties. For all compounds and polymers,
no emission is detected in solution and in the solid state at 298
K, except for the compounds 1 and 2 and spacers 4 and 6. On
the other hand, all compounds and polymers except 10 exhibit
luminescence in 2MeTHF at 77 K.
1. Model Compounds 1 and 2. The trans-PhCt CPt-
(PBu3)2Ct CPh compound exhibits fluorescence with a 0–0
localized at 346 nm at room temperature in methylcyclohexane
with a fluorescence quantum yield (ΦF) < 0.0006.4n In this
work, the weak fluorescence for this compound is also detected
at the same spectral position using 2MeTHF as the solvent.
Similarly, a weak fluorescence with a 0–0 peak at 356 nm was
also detected for 2 in degassed 2MeTHF at 298 K (Figure 10).
These two λmax are blue-shifted with respect to Pt(dppe)(Ct C-
p-C4H4R)2 (λmax ) 450 nm; dppe ) Ph2PCH2CH2PPh2; R )
Me, Ct CH),4g which exhibit the dppe-directed cis-conforma-
tion. The fluorescence lifetime (τF) for 2 is <0.1 ns, the detection
limit of our instrument, consistent with the weak intensity.
2. Spacers 4 and 6. These spacers are fluorescent at 298
and 77 K in 2MeTHF and also phosphorescent at 77 K in
2MeTHF (Figure 13). These emissions are assigned on the basis
of the small Stokes shift observed at 77 K and the short emission
lifetimes for the short wavelength luminescence, and the large
Stokes shift and longer lifetime for the long wavelength features
(the data are available in Table 5). The 298 K fluorescence of
spacer 6 is very broad and red-shifted (445 nm) with respect to
the 77 K spectrum (365 nm), and the excitation spectra
reasonably matched the absorption feature at 300 nm in both
cases. We have no explanation for this difference except to
suspect that a change in conformation in the excited state is at
the origin of this phenomenon. The fluorescence lifetimes for
4 and 6 at 298 K were too short to be measured on our
instrument (i.e., <0.1 ns).
No phosphorescence is detected at 298 K for trans-
PhCt CPt(PBu3)2Ct CPh,4n 1 and 2, but the triplet excited states
can still be accessible from T1-Tn absorption. For the former
compound, the reported T1-Tn band is located in the 400–650
nm range with a 0–0 peak placed at ∼645 nm. The transient
lifetime is 590 ( 150 ps.4n Our instrument limit (laser pulse
width of 13 ns) did not allow us to reach this time scale, so the
study was performed at 77 K, a temperature where the triplet
excited-state lifetime is long enough.
Spacer 4 exhibits a single fluorescence and single phospho-
rescence band at 77 K, suggesting that either the syn- and anti-
isomers emit at the same wavelength or one is more luminescent
than the other. The fact that a double exponential is observed
in the decay traces indicates that indeed both isomers may be
detected.
Figure 11 exhibits the transient absorption located at 735 nm
for 2 resembling that of trans-PhCt CPt(PBu3)2Ct CPh. The
former species exhibits a triplet lifetime of 48 ( 5 µs, a lifetime
that compares favorably to that of the phosphorescence below
49.9 ( 0.3 µs, confirming the triplet nature of the transient
species, so it is a T1-Tn absorption. For better comparison, the
transient spectrum of trans-PhCt CPt(PBu3)2Ct CPh were
The striking feature is that the observed emissions at both
temperatures are blue-shifted with respect to the CT absorption
(ethynylphenyl f quinone diimine) of the spacer. No emission
was detected all the way down to 850 nm, the limit of our
instrument using excitation going from 300 to 550 nm. This
observation indicates that both the fluorescence and the phos-
phorescence arise from upper excited states in these conjugated

2212 Organometallics, Vol. 27, No. 10, 2008
Gagnon et al.
Figure 12. Phosphorescence spectra (in blue) of 1 (left) and 2 (right) in 2MeTHF at 77 K. The absorption (black) and excitation spectra
(red) superimpose well.
Table 5. Photophysical Data at 77 K
λem (nm)
compound
F ) fluorescence, P ) phosphorescence
τF (ns) and τP(µs)
ΦP ((10%)
ΦF ((10%)
6
365(F), 436(P), 466sh(P)
τF ) 0.78 ( 0.02
0.15
0.59
τP ) 25 ( 2
b
b
4
373(F), 420sh(P), 455sh(P)
τF ) 0.51 ( 0.04
τP ) 1.1 ( 0.2 (85%)
and 11.6 ( 0.6 (15%)
aτP ) 85.2 ( 0.5
c
1
2
7
7′
11
405(F), 440(P), 470(P), 482(P)
446(P), 478(P), 493(P), 510sh(P)
370(F), 444(P), 450sh(P), 475(P)487sh(P)
400(F), 438(P), 450sh(P), 470(P), 480(P), 500sh(P)
395(F), 465(P)
0.38
0.17
0.13
0.033
τP ) 49.9 ( 0.3
-
aτP ) 40.1 ( 5.6
c
τP ) 125 ( 4
0.031
aτP ) 40.2 ( 3.4 (80%) and 92.7 ( 3.4 (20%)
0.0003
0.0033
12
420sh(F), 444sh(P), 455(P), 488(P), 503(P) 523sh(P)
τP ) 80.1 ( 3.8
0.030
a Either too weak to be measured or too short-lived for our instrument (τF < 0.1 ns). b The fluorescence and phosphorescence quantum yields are not
measured. Since the phosphorescence is very weak, the value was placed in the column of the fluorescence. c The weak fluorescence signal was strongly
covered by the phosphorescence, so that it was not possible to accurately measure ΦF.
Figure 13. Phosphorescence spectra (in blue) of 6 (up) and 4 (down) in 2MeTHF at 298 K (left) and 77 K (right). The fluorescence and
phosphorescence are indicated with F and P, respectively, for the 77 K spectra. On some occasions, the excitation spectra did not match
perfectly the absorptions.
molecules (i.e., Sn f S0 and Tn f S0), violating Kasha’s rule.
Such a property is relatively rare and may be due to poor
π-orbital overlaps between the ethynylbenzene and the quinone
diimine fragment, as deduced from the large interplanar angle.
In other words, despite conjugation the spacers act independently
in the excited state, somewhat corroborating the highly localized
LUMO and LUMO+n seen for 6, 7, and trans-(ligand
6)-Pt(PEt3)2-(ligand 6). Also, even considering that the
fragments are not electronically communicating by conjugation
(if this were the case) such as dyads, the lack of emission
quenching by either singlet or triplet electron or energy transfers
is also unusual.

Conjugated Polymers of cis- or trans-PhCt CPt(PEt3)2Ct CPh
Organometallics, Vol. 27, No. 10, 2008 2213
Figure 14. Phosphorescence spectra (in blue) of 7, 7′, 11, and 12 in 2MeTHF at 77K. The absorption (black) and excitation spectra (red)
superimpose somewhat.
Attempts were made to measure the triplet–triplet absorption
spectra, notably associated with the CT states (as the τP values
were large enough at 77 K), but were unsuccessful. The presence
of N2 bubbles in the Dewar assembly were due to the presence
of high-energy laser-induced large light scatterings. No signal
could be detected.
3. Model Compound 7 and Oligomers and Polymers 7′
and 10-12. These materials are not luminescent at 298 K in
the solid state or in solution. However at 77 K using 2MeTHF
as the solvent, two emissions attributable to fluorescence and
phosphorescence (MLCT) similar to that of compounds 1 and
2 and platinum-acetylide oligomers of the type Ph(-Ct C-
Pt(PEt3)2-Ct C-C4H4-)nH23 were observed for 7, 7′, 11, and
12 (Figure 14), whereas no emission was observed for polymer
10.26 The τF values turned out to be shorter than the limit of
our instrument (<0.1 ns). The spectra were measured at low
concentrations, where no change in the spectral and photo-
physical properties occurred.
suggested by the LUMO (Figure 9) makes the trans-PhCt
CPt(PEt3)2Ct CPh fragment and quinone diimine residue act as
two weakly interacting chromophores in the excited states. Thus,
this behavior provides the possibility of upper excited-state
fluorescence and phosphorescence (Sn f S0 and Tn f S0) arising
from the trans-PhCt CPt(PEt3)2Ct CPh unit. This property is
common to all investigated materials (7, 7′, 11, and 12). The only
exception is polymer 10, for which no reliable emission is detected.
To our knowledge, such a phenomenon is unprecedented in
conjugated polymers.
Moreover, one can also preclude the presence of efficient
triplet–triplet energy transfer (from the cis- or trans-PhCt
CPt(PEt3)2Ct CPh unit to the quinone diimine fragment), as the
τP’s for the donor (here the cis- or trans-PhCt CPt(PEt3)2Ct CPh
chromophore assigned on the basis of the absorption and phos-
phorescence maxima) remain little affected in the polymers. This
observation is consistent with the conclusion that these units do
not communicate efficiently in the excited states.
During the course of this investigation, delayed fluorescence
was observed readily, detected from time-resolved spectroscopy
in the µs time scale (SI), where both the phosphorescence and
fluorescence decay at the same rate with delay times (i.e., the
fluorescence/phosphorescence intensity ratio is constant). An
investigation of the steady-state emission spectra vs concentra-
tion (SI) showed that the fluorescence/ phosphorescence intensity
ratio was indeed a function of the latter, first suggesting the
presence of aggregations at 77 K, but also allowing one to assign
the mechanism of delayed fluorescence to T1 + T1 f S1 + S0.
The presence of aggregation also explains why no linear
correlation between the intensity of the delayed fluorescence
and the square of the concentration was observed.
Several striking features are noticed. First, the magnitude of
ΦP follows that of Mn reported in Table 1 (ΦP; 7′ (0.033) > 12
(0.030) > 11 (0.0033) > 10 (ΦP < 0.0001)). This trend is con-
sistent with an increase in nonradiative deactivation rates as the
molecular size increases via the well-known “loose bolt” effect
(higher density of vibrational levels through which nonradiative
relaxation can take place).27 On the other hand, the measured τP’s
for 7′, 11, and 12 (ranging from 40 to 125 µs) are of the same
order of magnitude as the mononuclear model compounds 1, 2,
and 7 (40–85 µs). This phenomenon is explained by the fact that
the decay traces are dominated by the most intense emission arising
from the longest lived species, which is of very low molecular
weight. This polydispersity is responsible for these observed
photophysical properties.
The most notable feature is the lack of low-energy emission
below the CT (500–650 nm) for the oligomers and polymers.
On the basis of the study of spacers 4 and 6, this behavior is
related to the properties of the spacers. Despite conjugation
detected by UV–vis spectroscopy and corroborated by DFT
calculations, the lack of communication in the excited state as
Conclusion
A novel class of organometallic conjugated polymers were
prepared and characterized in detail. These new materials are
built upon two chromophores, the cis- and trans-PhCt CPt-
(PEt3)2Ct CPh unit and the quinone diimine, often used as a
building block for models of polyaniline. The key feature in this
work is that the structural parameter A2 (Chart 4), directed by
intramolecular steric interactions, controls or explains the variation
of the Mn (and Mw) and the CT absorptivities in the title polymers.
Incidentally, the position of the CT band is also a function of Mn
and, thus, is indirectly a function of the angle A2. Despite the
(26) A weak emission was observed for 10, but this emission spectrum
did not resemble that for the others shown in Figure 14, and the excitation
spectrum did not match the absorption one, despite the change of emission
and excitation wavelength. This emission is most likely due to impurities.
(27) Turro, N. J. Modern Molecular Photochemistry; Benjamin/Cum-
mings: Menlo Park, 1978.

2214 Organometallics, Vol. 27, No. 10, 2008
Gagnon et al.
obvious conjugation in the ground state, the two chromophores
do not communicate efficiently in the excited states. This property
provides the possibility of observing localized excited states. For
this reason, upper excited-state emission arising from the cis- or
trans-PhCt CPt(PEt3)2Ct CPh units is detected. This interesting
phenomenon may well be associated with the large interplanar
angles between the -Ct CPh residue and the quinone diimine An
unpublished geometry optimization by DFT calculations performed
on the protonated (+ 4 H+) model compound trans-(ligand
6)-Pt(PEt3)2-(ligand 6) (where the H+ are placed on the N atoms)
shows that the structure of the resulting compound is totally planar
and delocalized. In addition, the protonated versions of ligands 2,
3, 4, and 5 in the presence of acids exhibit reversible oxidation
waves. On the basis of these observations, the reported polymers
in this work may be potential candidates for the design of novel
conducting polymers resembling that of an organometallic version
of polyaniline. Future works in this area are in progress.
Acknowledgment. This work was supported by the
Natural Science and Engineering Research Council of
Canada (NSERC). The authors thank Dr. Frédéric Brisach,
Mr. Smail Dahmane, and Dr. Regina Zamojska for the
measurements of several preliminary UV–vis spectra, of the
DSC traces, and of TGA traces, respectively.
Supporting Information Available: Synthesis of 4′, cyclic
voltammograms for the model compounds PhCt CPt(PEt3)2Ct CPh,
1-3, 5, 6, and 10-12, TGA traces for the polymers 7′ and 10-12,
DSC trace for polymer 10 in the 80–180 °C window, picture of
stand-alone polymer 10, frontier MOs for the cyclic compound 7,
time-resolved spectra of 1, 2, 7, 7′, 11, and 12, crystal data and
structure refinements for 1-9 and 4′, and experimental section. This
materialisavailablefreeofchargeviatheInternetathttp://pubs.acs.org.
OM7010563