A simple, novel method for the preparation of polymer-tetherable, zwitterionic merocyanine NLO-chromophores

Article abstract of DOI:10.1039/b008316j

A suite of polymer-ready nonlinear optical merocyanines has been synthesised and characterised. The tethering functionality - a vicinal dihydroxypropyl residue - is introduced onto the donor nitrogen of the chromophore precursor without the need for protection/deprotection steps, thereby giving ready access to potentially high T_g condensation polymer systems. An X-ray crystal structure determination on a representative chromophore 5 confirms the largely zwitterionic nature of these systems and experimental measurements of second-order nonlinear response [β(0)], by hyper-Raleigh scattering, indicate that a pyridylidene donor-quinomethide acceptor combination gives rise to the largest nonlinearity.

Full text of DOI:10.1039/b008316j

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A simple, novel method for the preparation of polymer-tetherable,
zwitterionic merocyanine NLO-chromophores
a
A. J. Kay, A. D. Woolhouse,* G. J. Gainsford, T. G. Haskell, T. H. Barnes,
a
a
a
b
c
I. T. McKinnie and C. P. Wyss
c
a
Industrial Research Ltd., P.O. Box 31 310, Lower Hutt, New Zealand.
E-mail: t.woolhouse@irl.cri.nz
Department of Physics, University of Auckland, Private Bag 92019 Auckland, New Zealand
b
c
Department of Physics, University of Otago, P.O. Box 56, Dunedin, New Zealand
Received 16th October 2000, Accepted 25th January 2001
First published as an Advance Article on the web 2nd March 2001
A suite of polymer-ready nonlinear optical merocyanines has been synthesised and characterised. The tethering
functionality—a vicinal dihydroxypropyl residue—is introduced onto the donor nitrogen of the chromophore
precursor without the need for protection/deprotection steps, thereby giving ready access to potentially high Tg
condensation polymer systems. An X-ray crystal structure determination on a representative chromophore 5
confirms the largely zwitterionic nature of these systems and experimental measurements of second-order
nonlinear response [b(0)], by hyper-Raleigh scattering, indicate that a pyridylidene donor–quinomethide
acceptor combination gives rise to the largest nonlinearity.
there has only been the one high-b zwitterionic chromophore
system—the pyridino-phenolate (Fig. 1, n~0)—that has been
1
. Introduction
1
3,14
In the search for optically nonlinear organic chromophores and
(
x
covalently incorporated into a polymer matrix;
give a low T (co)methacrylate.
albeit to
2)
materials that will find use in photonics applications, a
g
great deal of research has focused upon the molecular
engineering requirements to optimise optical nonlinearities in
push–pull compounds (i.e. molecules that contain electron-
donating and electron-withdrawing substituents flanking a
Here we report a simple and efficient strategy that enables
ready access to potentially high T condensation polymers that
contain the more zwitterionic merocyanine-type chromophores
as mainchain components of the polymer. With pyridylidene
and benzothiazolylidene donor systems, in particular, the
chemistry is achievable without the need for protection/
deprotection of the tethering functionality and polyurethanes,
for example, are easily accessible.
g
1
–3
conjugating p-framework). In realising ever-increasing
values of the first hyperpolarisability b(0) in these systems,
the chromophores have become more extensively and effi-
4
ciently conjugated and structurally elaborate with the
concomitant result of having intense intramolecular charge-
transfer absorption in the visible spectrum. This phenomenon
greatly minimises the optical transparency range of these
chromophores, a fact that is clearly of critical importance, for
example, to the process of successfully interfacing plastic
optical fibres to plastic optoelectronic devices.
2. Results and discussion
Chromophore syntheses
The synthesis of the dihydropyridylidene donor moiety
common to both the stilbazolium and heterocyclic merocya-
nine systems was accomplished by alkylating 4-picoline (4-
methylpyridine) with either 3-iodo- or 3-chloropropane-1,2-
diol to give the N-(dihydroxypropyl)picolinium salts 1a,b as
stable, colourless materials that required no purification prior
to subsequent reaction. Only the picolinium chloride was able
to be purified by recrystallisation. Alkylation with the
isopropylidene 1,2-protected iododiol was successful but
ultimately unnecessary. Our initial attempts to functionalise
4-picoline by alkylation with a symmetrical (protected) diol, 2-
O-tosyl-1,3-O-benzylideneglycerol, for example, were unsuc-
cessful, presumably as a result of steric hindrance to underside
SN2 approach through nonbonded interactions by the 1,3-
dioxane ring oxygens.
As a means of overcoming this dilemma and, at the same
time, seeking synthetic expediency, we became interested in
exploring the possibility of preparing polymers containing
chromophores with increased ground state zwitterionic char-
acter (e.g. Brooker-type merocyanines, n¡1, Fig. 1) reasoning
that acceptable figures of merit mb(0) might be realisable by
CT
trading some b for some m. Hence, by ‘blue-shifting’ l and
increasing the chromophore dipole moment, this would
enhance the figures of merit of such molecules for poled
materials applications that might use any second-order effects.
5
–7
As has been previously recognised, merocyanines of this
type and other amphiphilic systems are classes of NLO
8
–12
chromophores that are known
to have large second-order
hyperpolarisabilties and yet have received comparatively scant
attention from a materials point of view, a fact that is
surprising particularly because stabilisation of the charge-
separated state is relatively easily achieved. To our knowledge,
Condensation of the picolinium salts 1a,b with the 4-
hydroxybenzaldehydes 2a–d was effected in refluxing ethanol
containing stoichiometric amounts of piperidine. The resulting
stilbazolium salts 3a–d were recovered by filtration and
deprotonated by suspension in aqueous ammonia at 70 ‡C
for 30 minutes to give the new merocyanines 4a–d (Scheme 1)
as sparingly soluble, high melting microcrystalline solids. As
such, the syntheses represent no major departure from those
1
5,16
Fig. 1 Limiting ground state geometries of merocyanines.
previously published.
The new merocyanines were, how-
996
J. Mater. Chem., 2001, 11, 996–1002
This journal is # The Royal Society of Chemistry 2001
DOI: 10.1039/b008316j

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Scheme 1 Syntheses of merocyanines 4a–d.
1
ever, not purifiable to analytical standard (as is typical ) but
6
Polymer-tetherable chromophores that contain the ben-
zothiazolylidene donor nucleus 16–18 are also directly
accessible, albeit in moderate yields, from the reaction of the
2-methylbenzothiazolium iodide salt 15 with 3,5-dimethoxy-4-
hydroxybenzaldehyde, for example, and with the anilino-
methylene functionalised heterocycles 9 and 10 (Scheme 3). In
our hands the salt 15 could not be obtained pure, so no
attempts were made subsequently to isolate it. Rather, the
crude product was reacted directly with each of the acceptor
precursors in solution in methanol. Whilst chromophore 17
was recovered, after a single crystallisation, as a single
stereoisomer presumed to have the trans interconnect,
1
were characterised adequately by H NMR spectroscopy,
HRMS and UV-vis spectroscopy.
In essentially the same manner the heterocyclic merocyanines
5–7 as well as the indanedione analogue 8 were obtained as
coloured, high melting, microcrystalline solids (Scheme 2) from
the reaction of the picolinium salts 1a,b and piperidine with the
1
7
anilinomethylene functionalised molecules 9–12. The reaction
of the 4-anilinomethylenerhodanine 13 furnished only the
corresponding piperidinomethylene substituted heterocycle 14,
clear testimony to the fact that the rhodanine nucleus is a
weaker electron acceptor than the acceptor systems present in
compounds 9–12.
1
chromophore 18 was clearly not. On the basis of H NMR
Scheme 2 Syntheses of merocyanines 5–8.
J. Mater. Chem., 2001, 11, 996–1002
997

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Scheme 3 Syntheses of merocyanines 16–18.
data, compound 18 is presumed to be a mixture of regioisomers
in which the interconnect stereochemistry is again presumed to
be trans but in which the pyrazolone carbonyl is either syn or
anti to the N-(dihydroxypropyl) residue. Resonances attribu-
table to the olefinic methine protons in compounds 4a–c and 5–
chromophores, the N-methylene AB quartet appears at lower
field than that attributable to the terminal O-methylene AB
system; this clearly must be due to the deshielding effect of a
contiguous pyridinium nitrogen atom.
8
clearly show coupling constants consistent with the trans
Polymer synthesis
stereochemistry (viz. 13–16 Hz), but in compounds 16–18 these
are not discernible.
With the exception of merocyanine 4b, all of the new,
tetherable chromophores are high melting solids and, conse-
quently, their thermal stabilities (T ) are likely to be high also.
In fact, TD values measured by differential scanning calori-
2
metry (10 ‡C min ) on compounds 5 and 6 were found to be
Novel TDI-based polyurethanes containing various of the
functionalised chromophores were synthesised cleanly and in
high yields employing standard condensation polymerisation
2
2
techniques. Whilst no attempt has been made to structurally
characterise these systems, two of the polymers, those that
D
1
contain 5 and 6, recorded high T values at 220 ‡C and 230 ‡C,
g
respectively. In addition, excellent spin-coated thin films of
several of these polymers could be prepared from solutions in
N,N-dimethylacetamide. These are now under investigation.
2
53 ‡C and 275 ‡C, respectively.
All compounds exhibit the negative solvatochromic beha-
1
vior characteristic of zwitterionic stilbazolium merocya-
8
1
9
nines. That the predominant resonance contributors to the
ground states of these chromophores, albeit in the solid state,
are zwitterionic is evidenced from the X-ray crystal structure
parameters for chromophore 5 (Fig. 2). Most significantly, the
chromophore is only 4.2‡ from systemic planarity and the
Nonlinear optical characterisations
The first order hyperpolarisability coefficients of selected
members of the compound sets as measured by hyper-Raleigh
scattering in solution in methanol at 1064 nm are shown in
Table 1. Because of the proximity of the respective absorption
maxima to the second harmonic, the measured nonlinearities
will almost certainly contain contributions from resonance-
‘pyridylidene’ donor ring is pyridinium rather than quinoid as
all bond angles around N1 are between 119 and 121‡.
Remarkably, the C9–C10 bond in the bridging ethylidene
˚
moiety is shortened markedly to 1.33 A from that expected of a
2
5
2
2
enhancement. Table 1 also presents calculated ground state
dipole moments (m) for this suite of molecules from the
semiempirical AM1 procedure contained in the MOPAC 97
package (employing the PRECISE keyword). With respect to
dipole moments calculated for other more zwitterionic
chromophores, these values are perhaps best described as
modest. The extent of intramolecular charge transfer between
donor and acceptor termini is clearly sufficient to produce the
negative solvatochromic behavior but not as great as that
calculated and observed for zwitterionic amino substituted
˚
simple sp –sp carbon–carbon single bond (1.48 A). Negative
charge is considered to be delocalised over the (aryl)isoxazole
1
nucleus. With regard to the H NMR characteristics of all the
2
6
dicyanoquinodimethanes, for example. Within the entire
series, the ‘pyridylidene–quinone’ system clearly yields |b(0)|
values and overall figures-of-merit (i.e. the mb(0) product) that
are larger than those observed for the chromophore systems
that contain the heterocyclic acceptors. Furthermore, because
the extent of conjugation is common to all, it is evident also
Fig. 2 View of the molecular structure of 5 using 30% probability
Atom numbering is non-
standard (IUPAC) but is concurrent with that used in Table 2.
20,21
ellipsoids for non-hydrogen atoms.
998
J. Mater. Chem., 2001, 11, 996–1002

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Table 1 First-order hyperpolarisabilities and calculated dipole moments of selected merocyanines
2
b/10
30
a
esu
230
b
esu
218
m/10
248
mb(0)/10
Chromophore
l
max/nm
Solvent
b(0)/10
esu
esu
4
4
5
6
1
1
a
a
b
452
500
476
501
490
486
Aq. NaOH
Aq. NaOH
Methanol
Methanol
Methanol
Methanol
799
2508
467
1500
v30
153
2420
2741
2205
2432
12
256
9.88
9.33
10.34
7.64
10.03
7.54
24150
26914
22120
23300
120
c
7
8
2422
234
23 b
4
b Values are calculated with respect to a p-nitroaniline reference (b~34610
esu). b(0) calculated using the formula: b~b(0)6(1/lmax) /
2
2
2
2
24 c
{
[(1/lmax )2(4/l )]6[1/lmax )2(1/l )]}. b Assumed to be 30 for this calculation.
that the benzothiazolylidene nucleus is a less effective electron
donor than the pyridylidene nucleus and that the heterocyclic
electron acceptors are less effective than the quinone methide
system.
2,3-Dihydroxy-1-iodopropane
With vigorous stirring, hydriodic acid (57%, 133 mL, 1.0 mol)
was added dropwise to neat glycidol (74.0 g, 1.0 mol) at
ambient temperature. After stirring overnight the mixture was
concentrated and then pumped to dryness under high vacuum.
The crude oily product was purified by flash chromatography
over silica using gradient elution with ethyl acetate–hexane
mixtures (50–100% ethyl acetate) to give the iodopropanediol
Conclusion
This work has shown that tetherable ‘polymer-ready’ zwitter-
ionic merocyanine type NLO chromophores that contain the
pyridyl and benzothiazolyl donor nuclei can be synthesised
without the need for any protection/deprotection steps prior to
polymerisation. This finding now enables ready access to
2
7
(
125 g, 65%) as a colourless solid, mp 46–47 ‡C (lit. mp 48–
1
4
dd, J 10.8, 4.2 Hz, 1H, lower field branch of AB quartet,
9 ‡C). H NMR (D O) d 3.60, m, 3H, -CH(OH)CH I; 3.56,
2
2
-
AB quartet, -CH
CH OH; 3.26, dd, J 10.8, 6.0 Hz, 1H, higher field branch of
2
1
OH. C NMR (D
3
2
2
O) d 71.2 (CH), 65.0
potentially high T condensation polymers (e.g. polyurethanes)
g
(
2)
(
2 2
CH OH), 9.2 (CH I).
that might find use as stable, polable polymer x materials.
Hyper-Raleigh scattering estimates of b(0) for selected
members of this suite indicate that the ‘quinomethide’ acceptor
is more effective than the heterocyclic equivalents and,
furthermore, that the pyridylidene donor is more effective
than the benzothiazolylidene equivalent.
1-(2,3-Dihydroxypropyl)-4-methylpyridinium iodide, 1a
To a stirred solution of 2,3-dihydroxy-1-iodopropane (10.0 g,
4
9.5 mmol) in dry isopropyl alcohol (50 mL) was added
dropwise, freshly distilled 4-methylpyridine (5.07 g,
4.5 mmol) and the resulting mixture refluxed overnight
5
under an atmosphere of nitrogen. The solution was then
cooled and concentrated to afford 1a as a viscous, off-white oil
Experimental
(
12.2 g) that was used as such after the removal of the volatiles
Nuclear magnetic resonance spectra and two-dimensional
correlation data were recorded on a Bruker AVANCE 300
spectrometer and UV-vis absorption spectra were recorded
using an HP 8452A diode array spectrophotometer. Mass
spectra were recorded, unless otherwise stated, in the FAB(z)
mode on a VG Micromass ZAB IF instrument. Elemental
analyses were performed by the Campbell Microanalytical
Laboratory in the Chemistry Department, University of Otago.
Melting points were determined on a Reichert hot-stage
apparatus and are uncorrected. First-order hyperpolarisabil-
ities were measured by hyper-Raleigh scattering at 1064 nm
using a seed-injected Nd:YAG pulsed laser operating at 10 Hz
and producing 10–15 ns pulses. The scattered radiation from
the solution was passed through either a 10 nm FWHM
interference filter centred at 532 nm or through a monochro-
mater to a Philips 56 UVP photomultiplier tube.
1
under high vacuum. H NMR (D
aromatic; 7.98, d, J 6.5 Hz, 2H, aromatic; 4.73, dd, J 13.1,
.0 Hz, 1H, lower field branch of AB quartet, -NCH ; 4.41, dd,
2
O) d 8.81, d, J 6.5 Hz, 2H,
3
2
J 13.1, 8.5 Hz, 1H, higher field branch of AB quartet, -NCH2;
3.87, m, 1H, CHOH; 3.49, dd, J 11.1, 4.9 Hz, 1H, lower field
branch of AB quartet, -CH OH; 3.31, dd, J 11.1, 6.3 Hz, 1H,
higher field branch of AB quartet, -CH
1
2
2
OH; 2.61, s, 3H, CH
C NMR (D O) d 159.2 (C ), 144.8 (CH), 128.2 (CH), 70.6
2
3
.
3
Q
(
2 2 3
CH), 63.2 (CH ), 63.1 (CH ), 21.9 (CH ).
1-(2,3-Dihydroxypropyl)-4-methylpyridinium chloride, 1b
mixture of freshly distilled 4-methylpyridine (10.0 g,
A
1
9
08 mmol) and 2,3-dihydroxy-1-chloropropane (10.0 g,
1 mmol) was heated at 80–100 ‡C for 72 h whilst protected
from moisture by a calcium chloride drying tube. After cooling
a solid formed which was broken up with the aid of a spatula
and then ethyl acetate (20 mL) added. The solid mass was
collected by filtration and washed with ethyl acetate to give 1b
X-Ray crystallography
Single crystals of compound 5 were crystallized from methanol
(
Table 2).
˚
Table 2 Selected geometric parameters for 5 (A, ‡)
Crystal
data. C19
H
18
N
2
O
4
,
M
r
~338.35,
˚
triclinic,
a~7.761(6), b~10.257(7), c~11.119(8) A, a~73.408(12),
N1–C8
N1–C4
N2–C12
N2–O13
C4–C5
C5–C6
C6–C7
C6–C9
C7–C8
C9–C10
1.340 (6)
1.337 (6)
1.318 (6)
1.423 (5)
1.348 (7)
1.401 (6)
1.395 (6)
1.431 (7)
1.354 (7)
1.328 (6)
C10–C11
C11–C12
C11–C14
C14–O13
C8–N1–C4
C8–N1–C3
C5–C6–C9–C10
C6–C9–C10–C11
C9–C10–C11–C12
C9–C10–C11–C14
1.423 (7)
1.418 (6)
1.426 (7)
1.391 (6)
118.7 (5)
119.9 (5)
5.9 (5)
2178.4 (5)
178.9 (6)
23.2 (9)
3
U~796.3(10) A ,
(No. 2);
˚
b~80.744(12),
T~173(2) K,
rc~1.411 g cm , Radiation MoKa, l~0.7107 A, m (Mo
c~70.240(14)‡,
¯
P1
space
group
Z~2,
2
3
˚
2
1
Ka)~0.100 mm , 4056 reflections collected, 2902 unique
(
2
Rint~0.081) used in all calculations. The final wR(F ) (all
data) & R(F) (Iw2s(I)) were 0.172 & 0.072 respectively. CCDC
reference number 1145/276. See http://www.rsc.org/suppdata/
jm/b0/b008316j/ for crystallographic files in .cif format.
J. Mater. Chem., 2001, 11, 996–1002
999

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as a moisture sensitive pale-brown solid (17.81 g, 97%).
Recrystallisation (ethanol) gave beige microcrystals, mp 157–
concealed by a broad water signal. Solubility precluded the
1
recording of full C NMR spectral details.
3
1
1
6
5
1
4
58 ‡C. H NMR (d -DMSO) d 8.88, d, J 6.5 Hz, 2H; 7.97, d, J
6
.5 Hz, 2H; 5.66, br s, 1H, -CHOH (exchangeable in D
.20, br s, 1H, -CH OH (exchangeable in D O); 4.77, dd, J
2
O);
4-{2-[1-(2,3-Dihydroxypropyl)pyridin-4(1H)-ylidene]ethylidene}
-2,6-di-tert-butylcyclohexa-2,5-dien-1-one, 4c
2
2
3.0, 3.1 Hz, 1H, lower field branch of AB quartet, -NCH
.47, dd, J 13.0, 8.1 Hz, 1H, higher field branch of AB quartet,
; 3.89, m, 1H, CHOH; 3.47–3.53, m, 1H, lower field
branch of AB quartet, -CH OH; 3.27–3.33, m, 1H, higher field
2
;
From the reaction of the 4-methylpyridinium iodide with 3,5-
di-tert-butyl-4-hydroxybenzaldehyde, 4c was isolated as a pale
green microcrystalline solid (7.09 g, 37%), mp 292–294 ‡C
-
NCH
2
2
z
z
1
3
(Found: MH m/z 384.25274. C H NO requires MH m/z
branch of AB quartet, -CH
-DMSO) d 159.1 (C ), 144.9 (CH), 128.1 (CH), 70.7 (CH),
3.0 (due to 26CH ), 21.7 (CH ). The signal at d 63.0 is able to
2
OH; 2.60, s, 3H, CH
3
.
C NMR
24 35 3
3
4
8
1
2
84.25387 D~2.9 ppm). lmax 538 (H O); 590 (methanol) log10e
(
d
6
Q
1
.70; 618 (DMSO); 630 (pyridine). H NMR (d -DMSO) d
6
2
3
6
.75, d, J 6.0 Hz, 2H; 8.20, d, J 6.0 Hz, 2H; 8.02, d, J 16.1 Hz,
H; 7.54, s, 2H; 7.32, d, J 16.1 Hz, 1H; 5.36, br s, -CHOH; 4.97,
2
be resolved as two separate signals at d 63.1 and 62.9 with D O
as solvent.
2
br s, -CH OH; 4.64, apparent d, J 12.4 Hz, 1H, lower field
branch of AB quartet, -NCH ; 4.30–4.37, m, 1H, higher field
2
branch of AB quartet, -NCH ; 3.91, m, 1H, -CHOH; 3.50, m,
2
General procedure for the preparation of 2,6-disubstituted 4-{2-
1-(2,3-dihydroxypropyl)pyridin-4(1H)-ylidene]ethylidene}
cyclohexa-2,5-dien-1-ones, Brooker’s merocyanines, 4a–d
[
1
higher field branch of AB quartet, -CH
H, lower field branch of AB quartet, -CH OH; 3.35, m, 1H,
2
2
OH; 1.43, s, 18H,
1
3
-
C(CH ) . C NMR (d -DMSO) d 157.6 (C ), 154.0 (C ),
3 3 6 Q Q
To a stirred solution of 1-(2,3-dihydroxypropyl)-4-methyl-
pyridinium iodide 1a (14.75 g, 50 mmol) (or an equimolar
amount of 1b) in absolute ethanol (150 mL) was added the
appropriate 4-hydroxybenzaldehyde 2a–d (50 mmol), and the
mixture heated to reflux. To the mixture was then added
piperidine (4.5 g, 5.2 mL, 53 mmol) at which point an intense
red colour developed. The solution was refluxed overnight,
cooled and the resulting precipitate recovered by filtration
and washed with a little cold ethanol. The precipitate was
then suspended in aqueous ammonia (35%, 400 mL), and
heated to ca. 70 ‡C with stirring for 30 min. The solid was
again recovered by filtration and recrystallised from water, to
which isopropyl alcohol (ca. 20% final volume) was later
added to facilitate crystallisation. The product was pistol
dried at ca. 75 ‡C under high vacuum.
1
1
3
44.9 (CH), 142.9 (CH), 139.6 (C
22.8 (CH), 119.7 (CH), 70.7 (CH), 63.2 (CH
5.0 (C ), 30.8 (CH ) ppm
Q
), 126.7 (C
Q
), 125.9 (CH),
), 62.8 (CH ),
2
2
Q
3
4-{2-[1-(2,3-Dihydroxypropyl)pyridin-4(1H)-ylidene]ethylidene}
-2,6-dibromocyclohexa-2,5-dien-1-one, 4d
From the reaction of the 4-methylpyridinium iodide with 3,5-
dibromo-4-hydroxybenzaldehyde, 4d was isolated as a reddish-
brown microcrystalline solid (12.63 g, 59%), mp 256–258 ‡C
z
z
(
Found: MH m/z 429.94866. C H NO Br requires MH
16 15 3 2
m/z 429.94777 D~2.1 ppm). lmax 448 (H
log10e 4.63; 540 (DMSO); 578 (pyridine). The low solubility of
d in common NMR solvents precluded the acquisition of
2
O); 490 (methanol)
4
1
13
satisfactory H and C NMR data.
4-{2-[1-(2,3-Dihydroxypropyl)pyridin-4(1H)-ylidene]ethylidene}
cyclohexa-2,5-dien-1-one, 4a
2
-Anilinomethylideneindane-1,3-dione, 12
2
8
Indane-1,3-dione (4.38 g, 30 mmol) and N,N’-diphenylforma-
midine (6.48 g, 33 mmol) were stirred together at 120 ‡C for
From the reaction of the 4-methylpyridinium iodide with 4-
hydroxybenzaldehyde, 4a was isolated as bright red platelets
2
0 min, and the mixture then allowed to cool to room
z
(
10.57 g, 78%), mp 227–229 ‡C (Found: MH m/z 272.12813.
temperature to give a green–black paste. To this was added
isopropyl alcohol (50 mL) and the resultant slurry refluxed for
10 min and then cooled, whereupon a dark-green precipitate
formed. This was collected by filtration and washed with
isopropyl alcohol (3615 mL) to give 2-anilinomethylidenein-
dane-1,3-dione 12 as an olive-green powder (6.61 g, 88%).
z
16 3
C H17NO requires MH m/z 272.12867 D~1.8 ppm). lmax
4
(
56 (H O); 490 (methanol) log e 4.57; 578 (DMSO); 574
2 10
1
pyridine). H NMR (D
2
O) d 8.34, d, J 6.3 Hz, 2H; 7.80, d, J
.3 Hz, 2H; 7.61, d, J 13.2 Hz, 1H; 7.47, d, J 8.4 Hz, 2H; 6.91,
6
d, J 13.2 Hz, 1H; 6.70, d, J 8.4 Hz, 2H; 4.52, d, J 13.5 Hz, 1H,
lower field branch of AB quartet, -NCH ; 4.27, dd, J 13.5,
2
Recrystallisation (1 : 1 ethanol–isopropyl alcohol) gave yellow–
z
9
1
.0 Hz, 1H, higher field branch of AB quartet, -NCH
2
; 4.08, m,
H, -CHOH, 3.63–3.65, m, 2H, -CH OH. Solubility precluded
green microcrystals, mp 200–201 ‡C (Found: MH
m/z
250.08501. C H NO requires MH m/z 250.08626 D~5.0
z
2
1
6
21
2
1
3
the recording of complete, meaningful C NMR data. Micro-
analytical data were inconsistent with the expected formula and
NMR spectra consistently confirmed the presence of both
water and propan-2-olate of crystallization.
1
ppm). H NMR (d
6
-DMSO) d 8.31, s, 1H; 7.76, s, 4H; 7.58–
13
7
6
.60, m, 2H; 7.41–7.46, m, 2H; 7.21–7.26, m, 1H. C NMR (d -
DMSO) d 144.7 (CH), 139.8 (C
1
1
Q
), 139.4 (C
30.0 (CH), 126.0 (CH), 121.7 (CH), 121.7 (C
06.0 (CQ).
Q
), 134.4 (CH),
Q
), 118.7 (CH),
4
-
-{2-[1-(2,3-Dihydroxypropyl)pyridin-4(1H)-ylidene]ethylidene}
2,6-dimethoxycyclohexa-2,5-dien-1-one, 4b
General procedure for the preparation of chromophores 5–8 and
the piperidinomethylene substituted rhodanine 14
From the reaction of the 4-methylpyridinium iodide with 3,5-
dimethoxy-4-hydroxybenzaldehyde, 4b was isolated as a dark
green microcrystalline solid (10.43 g, 63%), mp 170–172 ‡C
To a stirred solution of the 4-methylpyridinium iodide 1a
(5.0 g, 16.9 mmol) (or an equimolar amount of 1b) in ethanol
(25 mL) was added the appropriate N-phenylamino sub-
stituted acceptor 9–13 (16.9 mmol). The mixture was then
refluxed under nitrogen for 5 min and then piperidine
(1.70 g, 2.0 mL, 20 mmol) was added and the resulting
solution refluxed overnight under an atmosphere of nitro-
gen. After cooling the brightly coloured solid was recovered
by filtration and washed with a little cold methanol. A
further concentration and cooling of the mother liquors
afforded more of the desired product. These materials were
pistol dried and were generally suitable for use without
(
6
C
5
Found: C, 61.2; H, 6.5; N, 4.0. C18
H
21NO
5
?H
2
O requires C,
m/z 332.14939.
requires MH m/z 332.14980 D~1.2 ppm). lmax
2
O); 558 (methanol) log10e 4.64; 640 (DMSO); 654
z
1.7; H, 6.9; N, 4.0%. Found: MH
z
18 5
H21NO
02 (H
1
(
pyridine). H NMR (d -DMSO) d 7.70, d, J 5.7 Hz, 2H; 7.58,
6
d, J 14.7 Hz, 1H; 7.27, d, J 5.7 Hz, 2H; 6.79, s, 2H; 6.42, d, J
4.7 Hz, 1H; 4.18, d, J 13.2 Hz, 1H, lower field branch of AB
quartet -NCH ; 3.91, m, 1H, higher field branch of AB quartet
NCH ; 3.77, s, 6H, -OCH ; remaining methine and methylene
1
2
-
2
3
resonances of the N-(dihydroxypropyl) substituent were
1
000 J. Mater. Chem., 2001, 11, 996–1002

View Article Online
2-{2-[1-(2,3-Dihydroxypropyl)pyridin-4(1H)-ylidene]ethylidene}-
indane-1,3-dione, 8
further purification. Analytical samples were obtained by
recrystallisation from methanol.
From the reaction of 1a with 2-anilinomethylideneindane-1,3-
dione 12, the product was isolated as a red–brown micro-
4
-{2-[1-(2,3-Dihydroxypropyl)pyridin-4(1H)-ylidene]ethylidene}
z
crystalline solid (3.06 g, 56%), mp 258–260 ‡C (Found: MH
-
3-phenylisoxazol-5(4H)-one, 5
z
m/z 324.12441. C19
4
H17NO requires MH m/z 324.12304
From the reaction of 1a with 4-anilinomethylidene-3-phenyl-
isoxazol-5(4H)-one 9, the product was isolated as an orange
microcrystalline solid (3.40 g, 61%), mp 253–255 ‡C (Found:
D~4.2 ppm). lmax 476 (H
2
O); 502 (methanol) log10e 4.85; 524
acetonitrile); 524 (DMSO); 530 (acetone); 534 (pyridine) log10
(
e
1
5
1
5
1
4
6
.05. H NMR (d -DMSO) d 8.06, d, J 7.1 Hz, 2H; 7.67, d, J
5.0 Hz, 1H; 7.40–7.52, m, 6H; 7.21, d, J 15.0 Hz, 1H; 5.30, d, J
.4 Hz, 1H, -CHOH; 4.92, t, J 5.4 Hz, 1H, -CH OH; 4.32, dd, J
3.5, 2.9 Hz, 1H, lower field branch of AB quartet, -NCH
.05, dd, J 13.5, 8.1 Hz, 1H, higher field branch of AB quartet,
; 3.79, m, 1H, -CHOH; 3.42–3.49, m, 1H, lower field
branch of AB quartet, -CH OH; 3.26–3.32, m, 1H, higher field
z
z
MH
39.13448 D~0.4 ppm). lmax 446 (H
log10e 4.52; 500 (acetonitrile); 500 (DMSO); 514 (acetone); 518
m/z 339.13435.
C
19
H
18
2
N O
4
requires MH
m/z
3
2
O); 476 (methanol)
2
2
;
1
(
2
1
pyridine) log10e 4.84. H NMR (d
6
-DMSO) d 8.07, d, J 7.1 Hz,
H; 7.48–7.59, m, 6H; 7.43, d, J 7.0 Hz, 2H; 7.04, d, J 14.7 Hz,
H; 5.28, d, J 5.5 Hz, 1H, -CHOH; 4.91, t, J 5.4 Hz, 1H,
-
NCH
2
2
1
3
-
quartet, -NCH
CH OH; 4.32, dd, J 13.4, 2.9 Hz, 1H lower field branch of AB
2
2 6
branch of AB quartet, -CH OH. C NMR (d -DMSO) d 190.3
2
; 4.05, dd, J 13.4, 8.1 Hz, 1H, higher field
(
C ), 155.8 (C ), 142.3 (CH), 135.4 (CH), 132.0 (CH), 119.6
Q Q
branch of AB quartet, -NCH ; 3.77, m, 1H, -CHOH; 3.45, m,
2
Q
(CH), 118.3 (CH), 109.0 (C ), 108.2 (CH), 70.9 (CH), 63.2
1
higher field branch of AB quartet, -CH OH. C NMR (d6-
H, lower field branch of AB quartet, -CH
2
OH; 3.26, m, 1H,
(
CH ), 60.9 (CH ).
2 2
1
3
2
Q Q Q
DMSO) d 174.1 (C ), 162.4 (C ), 155.1 (C ), 142.5 (CH), 137.0
5
-Piperidinomethylidene-3-ethylrhodanine, 14
(
(
(
CH), 131.6 (C ), 129.4 (CH), 129.1 (CH), 128.3 (CH), 118.5
Q
CH), 107.8 (CH), 90.4 (C
CH2).
Q
), 70.8 (CH), 63.2 (CH
2
), 61.0
From the reaction of 1a with 5-anilinomethylidene-3-
ethylrhodanine 13, or its 5-acetanilido-equivalent, the
product was isolated as purple plates (2.85 g, 66%), mp
1
requires MH m/z 257.07820 D~7.0 ppm). H NMR (d
DMSO) d 7.69, s, 1H; 4.00, q, J 7.1 Hz, 2H; 3.53, br s, 4H;
1
1
z
54–155 ‡C (Found: MH m/z 257.08000. C H N OS
1
1
16
2
2
z
1
4
-
-{2-[1-(2,3-Dihydroxypropyl)pyridin-4(1H)-ylidene]ethylidene}
3-methyl-1-phenylpyrazol-5(4H)-one, 6
6
-
1
.62, br s, 6H; 1.13, t, J 7.1 Hz, 3H. C NMR (d
3
6
-DMSO) d
From the reaction of 1a with 4-anilinomethylidene-3-methyl-1-
phenylpyrazol-5(4H)-one 10, the product was isolated as a red
89.2 (C ), 167.3 (C ), 144.7 (CH), 86.3 (C ), 40.8 (CH ),
2
Q
Q
Q
z
2 2 3
26.3 (CH ), 23.4 (CH ), 12.4 (CH ). One piperidinomethy-
powder (4.21 g, 71%), mp 276–278 ‡C (Found: MH m/z
z
lene carbon signal not observed due to line broadening
3
52.16527. C20
ppm). lmax 462 (H
acetonitrile); 520 (DMSO); 524 (acetone); 534 (pyridine)
21 3 3
H N O requires MH m/z 352.16612 D~2.4
1
arising from N– C coupling.
4
13
2
O); 488 (methanol) log10e 4.88; 516
(
1
log10e 4.88. H NMR (d
2
5
6
-DMSOzD
H; 7.92, d, J 7.1 Hz, 2H; 7.60, d, J 14.5 Hz, 1H; 7.14–7.48, m,
H; 6.98, m, 1H; 4.24, dd, J 13.5, 3.0 Hz, 1H, lower field branch
; 3.97, dd, J 13.5, 8.4 Hz, 1H, higher field
branch of AB quartet, -NCH ; 3.77, m, 1H, -CHOH; 3.45, dd,
2
O) d 8.05, d, J 7.8 Hz,
General procedure for the preparation of the (benzothiazol-
ylidene)ethylidene functionalised chromophores, 16–18
A mixture of 2-methylbenzothiazole (3.0 g, 20.0 mmol) and
2
of AB quartet, -NCH
2
,3-dihydroxy-1-iodopropane (4.0 g, 20.0 mmol) was stirred
2
under an atmosphere of nitrogen at 100 ‡C for 16 h. The
resulting mixture, which was presumed to contain 10 mmol of
the requisite salt 15, was cooled and diluted with a small
volume of methanol. With stirring was then added a solution of
either the N-phenylamino heterocycles, 9 or 10, or 3,5-
dimethoxy-4-hydroxybenzaldehyde, 2b, (10.0 mmol) in metha-
nol (30 ml) followed by triethylamine (2.1 ml, 15.0 mmol). The
mixture was refluxed for 16 h and then cooled. After the
addition of hexane (30 ml) the solution was cooled to –20 ‡C
for several hours and the precipitate recovered by filtration,
washed with hot water and then recrystallised from either
ethanol or an isopropyl alcohol–methanol mixture.
J 11.1, 4.8 Hz, 1H, lower field branch of AB quartet, -CH
3
2
OH;
.28, dd, J 11.1, 6.3 Hz, higher field branch of AB quartet,
1
OH; 2.18, s, 3H. C NMR (d
3
-
CH
2
6
-DMSO) d 154.8 (C
Q
),
),
1
1
6
41.6 (CH), 141.0 (C ), 137.5 (CH), 128.6 (CH), 122.3 (CH),
Q
17.4 (CH), 105.8 (CH), 104.5 (C
Q 2
), 70.9 (CH), 63.2 (CH
0.4 (CH ), 13.2 (CH ). One quaternary carbon signal not
3
2
1
4
13
N– C
observed due to line broadening arising from
coupling. Furthermore, as the signal to noise ratio for the
1
3
C measurements is low one CH carbon signal is not observed.
5
-
-{2-[1-(2,3-Dihydroxypropyl)pyridin-4(1H)-ylidene]ethylidene}
1,3-diethyl-2-thiobarbituric acid, 7
4-{2-[3-(2,3-Dihydroxypropyl)-1,3-benzothiazol-2(3H)-
ylidene]ethylidene}-2,6-dimethoxycyclohexa-2,5-dien-1-one, 16
From the reaction of 1a with 5-anilinomethylidene-1,3-diethyl-
-thiobarbituric acid 11, the product was isolated as an orange–
2
red microcrystalline solid (4.91 g, 77%), mp 233–236 ‡C
From the reaction of 15 with 3,5-dimethoxy-4-hydroxybenzal-
dehyde 2b, the initially isolated solid was suspended in
isopropyl alcohol–triethylamine (5 : 1; 30 mL) and stirred at
ca. 60 ‡C for 30 min, cooled and then collected by filtration to
give an orange–red powder (1.53 g, 40%). Recrystallisation
z
z
(
Found: MH m/z 378.14906. C18
m/z 378.14875 D~0.8 ppm). lmax 452 (H
log10e 4.77; 496 (acetonitrile); 490 (DMSO); 500 (acetone); 510
H
23
N
3
O
4
S requires MH
2
O); 482 (methanol)
1
(
pyridine) log10e 4.99. H NMR (d
6
-DMSO) d 8.27, d, J 6.1 Hz,
H; 8.05, d, J 15.4 Hz, 1H; 7.62, d, J 6.1 Hz, 2H; 7.58, d, J
5.4 Hz, 1H; 5.34, d, J 4.6 Hz, 1H, -CHOH; 4.94, br s, 1H,
OH; 4.44–4.46, m, 5H, -NCH CH and lower field branch
of AB quartet –NCH ; 4.10–4.17, m, 1H, higher field branch of
AB quartet, –NCH ; 3.82, m, 1H, -CHOH; 3.35–3.45, m, 2H,
2
1
(ethanol) gave orange–red microcrystals, mp 262–264 ‡C
z
(decomp.) (Found: MH m/z 388.12065. C20
H
21NO
5
S requires
O); 594
(methanol) log10e 4.96; 566 (acetonitrile); 594 (DMSO) log10
z
28
-
CH
2
2
3
MH m/z 388.12132 D~1.7 ppm). lmax 566 (H
2
2
e
1
4.99; 586 (acetone); 584 (pyridine). H NMR (d -DMSO) d
6
2
higher and lower field branches of AB quartet, -CH
2
OH; 1.17,
8.42, d, J 7.8 Hz, 1H; 8.12–8.19, m, 2H; 7.74–7.87, m, 3H; 7.35,
s, 2H; 5.39, br s, 1H, -CHOH; 5.16, br s, 1H, -CH OH; 4.89–
1
t, J 6.0 Hz, 6H, -NCH CH . C NMR (d -DMSO) d 176.4
3
2
3
6
2
(
(
(
C
Q
), 160.7 (C
CH), 112.6 (CH), 95.1 (C ), 70.8 (CH), 63.2 (CH ), 61.5
Q
), 156.5 (C
Q
), 143.2 (CH), 140.5 (CH), 119.8
2
5.00, m, 2H, -NCH ; 3.99, br s, 1H, -CHOH; 3.88, s, 6H,
1
-OCH ; 3.60–3.64, m, 2H, -CH OH. C NMR (d -DMSO) d
3
Q
2
3
2
6
CH
2
), 42.1 (CH
2
), 12.9 (CH
3
).
172.9 (C
Q
), 149.6 (CH), 148.6 (C
Q
), 142.2 (C
Q Q
), 141.7 (C ),
J. Mater. Chem., 2001, 11, 996–1002
1001

View Article Online
1
1
5
29.4 (CH), 128.3 (CH), 127.9 (C ), 124.9 (C ), 124.5 (CH),
Q
STA 1500 instrument operating from ambient to 320 ‡C at
Q
2
1
17.3 (CH), 111.5 (CH), 108.5 (CH), 70.3 (CH), 63.4 (CH
6.8 (CH ), 52.4 (CH ).
2
),
10‡ min
.
3
2
Acknowledgements
4-{2-[3-(2,3-Dihydroxypropyl)-1,3-benzothiazol-2(3H)-
ylidene]ethylidene}-3-phenylisoxazol-5(4H)-one, 17
This work was funded by the New Zealand Foundation for
Research, Science and Technology
From the reaction of 15 with 4-anilinomethylidene-3-phenyl-
isoxazol-5(4H)-one 9, the product was isolated as a micro-
crystalline orange solid (1.14 g, 29%), mp 240–241 ‡C (Found:
References
z
MH
z
m/z 395.10696. C H N O S requires MH
m/z
2
1
18
2
4
1
2
3
L. R. Dalton, A. W. Harper, R. Ghosen, W. H. Steier, M. Ziari,
H. Fetterman, Y. Shi, R. V. Mustacich, A. K.-Y . Jen and K. J.
Shea, Chem. Mater., 1995, 7, 1060.
S. R. Marder, L.-T. Cheng, B. G. Tieman, A. C. Friedli, M.
Blanchard-Desce, J. W. Perry and J. Skindhoj, Science, 1994, 263,
3
95.10601 D~2.4 ppm). lmax 472 (99:1 H
2
O–acetone); 486
(
4
7
-
3
methanol) log e 4.86; 492 (acetonitrile); 496 (DMSO) log e
10 10
1
.80; 496 (acetone); 502 (pyridine). H NMR (d
6
-DMSO) d
.96, d, J 7.1 Hz, 1H; 7.40–7.71, m, 10H; 5.26, br s, 1H,
OH; 4.30–4.43, m, 2H, -NCH
.97, br s, 1H, -CHOH; 3.53, m, 1H, lower field branch of AB
OH; 3.32, m, 1H, higher field branch of AB
5
11.
D. R. Kanis, M. A. Ratner and T. J. Marks, Chem. Rev., 1994,
4, 195.
CHOH; 5.00, br s, 1H, -CH
2
2
;
9
quartet -CH
2
4
5
L. R. Dalton, Opt. Eng., 2000, 39, 589.
1
3
quartet, -CH OH. C NMR (d -DMSO) d 172.9 (C ), 169.6
6
2
Q
M. Szablewski, P. R. Thomas, A. Thornton, D. Bloor, G. H.
Cross, J. M. Cole, J. A. K. Howard, M. Malagoli, F. Meyers, J.-
L. Bredas, W. Winseleers and E. Goovaerts, J. Am. Chem. Soc.,
(
(
(
C
Q
), 162.3 (C
CH), 128.3 (CH), 128.0 (CH), 125.6 (CH), 125.1 (C
Q
), 142.8 (CH), 142.4 (C
Q
), 130.2 (CH), 129.4
Q
), 123.2
),
1997, 119, 3144.
CH), 114.9 (CH), 96.5 (CH), 95.7 (C ), 69.5 (CH), 63.9 (CH
Q
2
6
7
A. Fort, C. Rusner, M. Barzoukas, C. Combellas, C. Suba and
A. Thiebault, Proc. SPIE, 1994, 2285, 5.
H. Ikeda, T. Sakai and K. Kawasaki, Chem. Phys. Lett., 1991,
179, 551.
5
2
0.7 (CH ).
4-{2-[3-(2,3-Dihydroxypropyl)-1,3-benzothiazol-2(3H)-
ylidene]ethylidene}-3-methyl-1-phenylpyrazol-5(4H)-one, 18
8
9
G. L. Gaines, Angew. Chem., Int. Ed. Engl., 1987, 26, 341.
I. R. Girling, P. V. Golinsky, N. A. Cade, J. D. Earls and I. R.
Peterson, Opt. Commun., 1985, 55, 289.
From the reaction of 15 with 4-anilinomethylidene-3-methyl-1-
phenylpyrazol-5(4H)-one 10, the product was isolated as a
10 F. Pan, M. S. Wong, V. Gramlich, C. Bosshard and P. Gunther,
J. Am. Chem. Soc., 1996, 118, 6315.
11 G. J. Ashwell, E. J. C. Dawney, A. P. Kuzzynski, M. Szablewski,
I. M. Sandy, M. R. Bryce, A. M. Grainger and M. Hasan, J. Chem.
Soc., Faraday Trans., 1990, 86, 1117.
microcrystalline red–brown solid (1.55 g, 38%), mp 244–245 ‡C
z
(
Found: MH
m/z 408.13854. C H N O S requires
22 21 3 3
4
08.13764 D~2.2 ppm). lmax 482 (99 : 1 H
2
O–acetone); 488
(
4
methanol) log10e 4.84; 492 (acetonitrile); 500 (DMSO) log10
e
.83; 494 (acetone); 502 (pyridine). Both H and C NMR
1
1
2
3
C. L. Honeybourne, J. Phys., Appl. Phys., 1990, 23, 245.
C. Combellas, M. A. Petit, A. Thiebault, G. Froyer and D.
Bosc, Makromol. Chem., 1992, 193, 2445.
1
13
spectra were clearly consistent with the appearance of
structural isomers of 18; these are assumed to be the
compounds that contain the pyrazolone carbonyl syn and
anti to the benzothiazolyl ring nitrogen.
14 D. Bosc, G. Froyer, M. Petit, A. Thiebault and C. Combellas,
Fr. Pat. FR2, 681 321, 1991.
15
16
17
A. P. Phillips, J. Org. Chem., 1949, 14, 302.
I. Gruda and F. Bolduc, J. Org. Chem., 1984, 49, 3300.
E. H. Rodd and G. E. Watts, British Patent 366 964; Chem.
Abstr., 1933, 27, 2040; E. H. Rodd and G. E. Watts, U. S. Patent
2 032 502; Chem. Abstr., 1936, 30, 2768.
General procedure for the preparation of chromophore: toluene-
2,4-diisocyanate condensation polymers
1
8
A. Botrel and A. L. Beuze, J. Chem. Soc., Faraday Trans., 1985,
80, 1235.
19 M. Niedbalska and I. Gruda, Can. J. Chem., 1990, 68, 691.
To a stirred solution of anhydrous chromophore (10 mmol) in
DMSO (20 mL) maintained at 80 ‡C under an atmosphere of
nitrogen was added, in a single portion via syringe, toluene-2,4-
diisocyanate (1.74 g, 1.43 mL, 10 mmol). This mixture was
stirred at 80 ‡C for 16 h, and then cooled and filtered through
an MSI glass fibre filter (1.0 micron). The filtrate was added
dropwise to a vigorously stirred volume of methanol (100 mL).
The coloured precipitate was recovered by filtration and/or
centrifugation and washed thoroughly with hot methanol
before being dried under vacuum. Polymers were purified by
redissolution in a minimum volume of warm N,N-dimethyl-
acetamide and reprecipitation in methanol. This purification
procedure was repeated once more to give the polymers as fine,
coloured powders in yields of 30–60% after vacuum drying. In
preparation for spin-coating, the polymers were dissolved in
dimethylacetamide optimally at 10–20% w/v and expressed
through a 0.2 micron syringe filter onto glass or ITO-glass
slides.
2
0
C. K. Johnson, Oak Ridge National Laboratory, ORTEP II,
Report ORNL-5138, 1976.
L. J. Farrugia, J. Appl. Cryst., 1999, 32, 837.
N. P. Wang, T. M. Leslie, S. Wang and S. T. Kowel, Chem.
Mater., 1995, 7, 185.
2
2
1
2
23 M. C. Flipse, R. de Jonge, R. H. Woudenberg, A. W. Marsman,
C. A. van Walree and L. W. Jenneskens, Chem. Phys. Lett., 1995,
245, 297.
24
25
26
J. L. Oudar and D. S. Chemla, J. Chem. Phys., 1977, 66, 2664.
K. Clays and A. Persoons, Rev. Sci. Instr., 1992, 63, 297.
M. Ravi, M. Szablewski, N.-A. Hackman, G. H. Cross,
D. Bloor, A. E. Goeta and J. A. K. Howard, New J. Chem., 1999,
23, 841.
27 L. W. Hessel, O. E. Van Lohuizen and P. E. Verkade, Recueil,
954, 73, 842.
All solutions used for the measurements of absorption spectra for
a–d and 16 contained 1% piperidine. This was necessary to ensure
1
28
4
that the species in solution were the neutral molecules and not the
corresponding conjugate acids that readily form due to protona-
tion by solvent of the quinonoid oxygen atoms of these
chromophores.
For compounds 5 and 6, the resulting polyurethanes had T
values at 220 ‡C and 230 ‡C when measured on a Rheometrics
g
1002
J. Mater. Chem., 2001, 11, 996–1002