Simple zwitterionic merocyanines as potential NLO chromophores

Article abstract of DOI:10.1039/b103148c

A suite of zwitterionic pyridylidene-based merocyanines that contain no interconnecting π-bridge between the donor and acceptor rings has been synthesised and their second-order NLO properties evaluated largely by semi-empirical computational methods (MOP

Full text of DOI:10.1039/b103148c

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Simple zwitterionic merocyanines as potential NLO chromophores
A. J. Kay,a A. D. Woolhouse,*a G. J. Gainsford,a T. G. Haskell,a C. P. Wyss,b S. M. Giffin,b
I. T. McKinnieb and T. H. Barnesc
aIndustrial Research Limited, P.O. Box 31 310, Lower Hutt, New Zealand
bDepartment of Physics, University of Otago, P.O. Box 56, Dunedin, New Zealand
cDepartment of Physics, University of Auckland, P.O. Box 92019, Auckland, New Zealand
Received 6th April 2001, Accepted 11th June 2001
First published as an Advance Article on the web 18th July 2001
A suite of zwitterionic pyridylidene-based merocyanines that contain no interconnecting p-bridge between the
donor and acceptor rings has been synthesised and their second-order NLO properties evaluated largely by
semi-empirical computational methods (MOPAC 97/AM1). Contrary to expectation, increasing the degree of
inter-ring twist (h), at least up to 55u, in these new pyridylideneazolone chromophores is found to have little or
no effect on the figure of merit [mb(0)]. An X-ray crystallographic appraisal of one of these chromophores, 14,
reveals however that the twist angle (albeit in the solid state) is greater than that predicted by computation and
that all other features are consistent with the highly zwitterionic nature of these systems. In spite of this, a
combination of factors—insufficient acceptor strength, insufficient extent of conjugation and perhaps
insufficient twist angle, in particular—clearly leads to the low values of the quadratic hyperpolarisabilities. The
trade-off between targeting a more modest b from a minimum of p-conjugating framework between D and A
(and therefore synthetic expediency) and seeking a moderate-to-high dipole moment has therefore resulted in
only low figures of merit for these systems.
Calculations performed on a suite of readily accessible, isoelectronic cyanines, in which the acceptor is a
stabilised cyclopentadienide carbocycle rather than a heterocycle, have revealed the potential that these systems,
exemplified by 27, have as NLO chromophores. Representative polymer-tetherable derivatives of this system
have been prepared as have the corresponding TDI-based polyurethanes.
the normalised molecular hyperpolarisability coefficient b(0)
Introduction
approaches its maximum (ca. 240 6 10230 esu) when h is
between 40–50u. Of the simple (stunted) merocyanine class,
only the quinopyridine system 1 has been studied experiment-
ally as an NLO chromophore and, for the 3,5-di-tert-butyl-
homologue (R ~ R’ ~ H; R@ ~ But), been shown by NMR
spectroscopy to have a tilt angle of 42 ¡ 7u and to possess a
b(0) approaching 230 6 10230 esu.13,14
Organic molecules that give rise to large second-order
nonlinear figures of merit (mb) consist of electron donor and
electron acceptor groups that flank a p-conjugating bridge.1–4
The magnitudes of the nonlinearities depend upon donor and
acceptor strengths and upon the length and effectiveness of the
p-interconnect in the chromophore and are due principally to
the hyperpolarisability term (b) rather than to the dipole
moment term (m). In general, the chromophores that yield these
large nonlinearities are also structurally ‘large’, there being
extensive conjugation between the donor and acceptor
groups.5–7 Not only does this make the molecule less readily
accessible synthetically but, because of this structural complex-
ity, thermal and particularly photochemical stability issues
might therefore preclude any practical application in either
host polymer or backbone polymer matrices.
Recently, we embarked upon a study of the quadratic NLO
properties of some planar Brooker-type merocyanines (e.g. 4
and 5, n ~ 1) and, at the same time, devised a simple method to
render these chromophores polymer-tetherable [R ~ -CH2CH-
(OH)CH2OH].15 This study showed, amongst other things,
that the quinoid acceptor was more effective than any of the
aromatisable heterocyclic acceptor systems investigated.
Nonetheless, with a view to further minimising the structural
Chromophores whose ground states are predominantly
zwitterionic present a class of NLO molecules capable of
yielding large figures of merit.8–11 Theoretically it is possible to
design structurally less complex chromophores, with perhaps
more modest b (and concomitantly lower lCT), but that have
more appreciable dipole moments. In fact, computational
modelling on a number of simple, zwitterionic merocyanines
(e.g. the TICTOID quinopyridines 1, Fig. 1) and merocyanine-
type compounds (e.g. the quinopyrans 2 and analogues8 and
diaminodicyanoquinodimethanes 311,12) has shown that b can
be optimised by way of substantial modifications of the
dihedral angle between each of the ring planes. This twisting
around the central double bond in 1 and 2 leads to charge
separation and this, in turn, leads to aromatic stabilisation of
the resulting pyridinium and pyrylium phenolate rings.
For example,12 in an AM1-optimised structure for 3 (which
closely resembled the structure obtained by crystallography)
Fig. 1 Simple zwitterionic merocyanines.
DOI: 10.1039/b103148c
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This journal is # The Royal Society of Chemistry 2001
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heterocyclic equivalents of the parent 1 because the introduc-
tion of the R and R’ substituents required to bring about the
inter-ring twist should be reasonably achievable in these
systems. Brooker’s group’s pioneering work24 on merocyanines
is the only literature that details the synthesis of this type of
stunted chromophore. Only one example each of chromo-
phores containing the 2(1H)-pyridylidene 9a and 2(1H)- and
4(1H)-quinolylidene donor nuclei 9b and 10 have been reported
and each of these contains only the weak ethylrhodanine
acceptor.
complexity of the chromophore, we were interested in
exploring the syntheses and NLO properties of the ‘simple’
merocyanines (e.g. 5, n ~ 0) that contained the pyridylidene
donor nucleus, reasoning that through the incorporation of a
tilt between the two sp2 connected ring planes, it might be
possible to realise b values comparable to or better than those
observed for the planar chromophores 4 and 5 (n ~ 1) and
perhaps the quinopyridine system 1 (R@ ~ But). We were also
interested in the related pyridinium cyclopentadiene (cyanine)
system 6, which has been reported16–19 before but not in an
NLO capacity; our interest was triggered by the results of a
computational study on selected members of this class of
zwitterionic chromophore.
By employing, in essence, the same chemistry, heterocyclic
acceptors were condensed with the 4-(phenylthio)pyridinium
halides 11–13 to give the respective merocyanines in moderate
yields (Schemes 1–3). In most instances, the 2,3-dihydroxy-
propyl halides were used to directly quaternise the pyridine
nitrogen since we had previously shown that it was unnecessary
to protect this polymer-tethering substituent.15 As the means of
introducing bulky substituents into the donor moiety, the 3,5-
diiodopyridinium nucleus was elected as the target system
principally because of the accessibility and availability of
suitable precursors. To this end also, consideration was given
to the synthesis of the 3,5-bis(trimethylsilyl)pyridinium analo-
gue employing the recently published ‘bromine–magnesium
exchange’ methodology.25 Even though we were able to
prepare the corresponding 4-(phenylthio)methylpyridinium
iodide, attempts to couple heterocycles and to isolate product
cleanly were unsuccessful.
In this paper, we present details of the syntheses of repre-
sentative, polymer-ready, ‘stunted’ merocyanines and cyanines
together with a theoretical estimate of m and b(0) for these
systems.
Results and discussion
In spite of the theoretical interest that the stunted or ‘simple’
merocyanines 1 and the analogous quinopyrans 2 have
generated as potential NLO chromophores,8,20 examples of
them are few and far between. In fact, to our knowledge only
the merocyanine chromophores 7 and 8, that bear substituents
in the 3’ and 5’ positions of the quinone ring, have been
synthesised (electrochemically) and their NLO properties
evaluated.21–23
Consistent with expectation, all of the compounds, 14–24,
Modest figures of merit [mb(0)] in the range 500–700 6 10248
have been measured by EFISH for these chromophores, which
have been described as having twist angles between 40–50u
from proton NMR spin-relaxation rate data on the two sets of
hydrogen atoms ortho to the interconnect. Computational
modelling on systems 1 and 2, on the other hand, implies that
as the twist angle increases from near zero (when R ~ R’ ~ H
in 1) to near 90u, large and sudden enhancements (two orders of
magnitude, for example) in NLO response are to be expected.
Chromophore 1 (R ~ R’ ~ But; R@ ~ H), for example, has a
calculated twist angle of 83u and an impressive mb at 0.65 eV of
about 230 000 6 10248 esu.
In view of the obvious potential that these stunted systems
have, we were interested to explore the synthetic accessibility of
Scheme 1 Syntheses of merocyanines 14–17.
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Table 1 Calculated dipole moment, static field hyperpolarisability and
inter-ring dihedral angle values for chromophores 14–24
b(0)/
mb(0)/
Compound
mg/D
10230 esu
10248 esu
Twist angle/ua
14
15
16a
16b
17
18a
18b
19
20
21
9.62
7.10
7.37
7.35
8.05
11.04
11.20
8.85
1.38
7.71
6.29
8.44
8.15
2.4 (27)b
3.4 (31)b
14.3
23.1
24.1
105.4
105.1
12.1
74.0
104.2
97.4
4.8
16.2
24.5
117.3
30.2
0.22
0.89
0.00
0.00
0.00
44.8
52.5
54.2
4.65
1.72
3.01
0.00
1.91
14.3
1.5
6.7 (20)b
9.3 (16)b
11.0
3.5
2.1
3.9
13.9
22
23
24
3.7
aAverage of the two dihedral angles between the donor–acceptor
moieties. bMeasured values using HRS.
chromophores we describe herein are clearly zwitterionic, as
judged from the small but consistent negative solvatochro-
mism, but the extent of this status is probably only marginal.
Interestingly, a crystallographic appraisal of one of these
chromophores, the pyridylideneisoxazolone 14 (Fig. 2) reveals
quite clearly that, in addition to the conformational flexibility
in the dihydroxypropyl tether, there is considerable benzenoid,
i.e. pyridinium, character in the donor nucleus of the
chromophore system. Bond lengths in the azine ring mimic
the trends observed in N-methylpyridinium iodide26 and not
those in either the cyclopentadienylidene-1,4-dihydropyridine
2527 or the benzylidene-1,4-dihydropyridine 26.28 In precisely
the same manner, the same is true of the bond angles about the
azine nitrogen in 14; all are within the tight range 119.4–120.7u,
which confirms the existence of systemic planarity about the
nitrogen, whereas in 25 the angles are in the range 117–123u.
Scheme 2 Syntheses of merocyanines 18–22.
˚
Furthermore, at 1.436 A, the interconnect between the two
rings in 14 is markedly lengthened when compared to those in
˚
˚
25 (at 1.388 A) and 26 (at 1.360 A) and, as such, clearly implies
that there is considerable charge separation within the
chromophore.
A twist angle of 14.5u is observed in the crystal geometry of
14, compared to that of 0.2u suggested through the application
of the AM1 method.
This particular observation is entirely consistent with the
findings of Ravi et al.29,30 who found that crystallographic
geometries of chromophores belonging to the dicyanodiamino-
quinodimethane system 3 were more benzenoid than was
Scheme 3 Syntheses of doubly-tetherable merocyanines 23,24.
exhibited negative solvatochromic behaviour but to a lesser
degree than their more conjugated homologues.15 No signifi-
cant differences in behaviour were observed between the three
suites of chromophores. However, the extinction coefficients
for the three compounds that would be expected to have the
largest twist angles, namely 18a,b and 19, are an order of
magnitude less than almost all of those for which an angle of
v5u is calculated. This is clearly a result of a much less effective
extent of p-orbital overlap between the rings.
Table 1 presents the results of twist angle (h), ground state
dipole moment (mg) and average static hyperpolarisability [b(0)]
computations on the three suites of chromophores using the
MOPAC97 programme. Structure optimisations were per-
formed using the semi empirical AM1 method with the
PRECISE keyword.
Immediately obvious from this table are the modest figures
of merit [mgb(0)], most particularly when compared to those
reported for the quinopyridines 9a,b, for which values in the
vicinity of 2500 6 10248 esu have been measured by EFISH.21
This is entirely reminiscent of the situation that emerged from a
study15 of the next highest homologues 4 and 5; molecules
containing the quinonoid acceptor, viz. 4 (n ~ 1), consist-
ently exhibited higher figures of merit than those containing
Fig. 2 View of the molecular structure of 14 showing the two
conformations for the C1 and C2 atoms. 30% probability ellipsoids
for non-hydrogen atoms are used.37,38
the heterocyclic acceptors, e.g.
5 (n ~ 1). The stunted
J. Mater. Chem., 2001, 11, 2271–2281
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Table 2 Calculated dipole moment and static hyperpolarisability
values for selected members of the cyanine series 27
otherwise predicted at the AM1 level because the former are the
optimal geometries for those molecules in a strongly polar
crystal environment. From Table 1, it can also be seen that the
measured values of b(0) for 14 and 15 (the only compounds for
which measurements were made) are larger than those
predicted.
Compound
mg/Da
b(0)/10230 esua
mb(0)/10248 esua
The introduction of substituents into each of the rings as a
means of twisting the donor and acceptor rings out of
coplanarity appears to have little real effect on b(0). However,
the larger measured b(0) for compounds 14 and 15 might
suggest that the AM1 derived values are consistently low but,
even with this factor applied to other chromophores, mb(0)
values are still v300 6 10248 esu and much less than that for
the parent quinone system 7, for example. With the exception
of the thiobarbituric acid derivative 22, which has only ortho
carbonyl functionalities and the acyclic dicyanomethylidene
containing compounds 17 and 21, all the chromophore
acceptor systems contain 5-membered heterocyclic rings. As
a consequence, it is conceivable that twist angles of the
magnitude putatively required to maximise b in 6–6 D–A ring
systems might not be as achievable by synthetic manipulation
in 6–5 D–A ring systems.
27a
27b
27c
27d
27e
27f
27g
27h
4.08 (2.46)
7.65 (5.47)
35.9 (3.4)
43.9 (34.7)
51.6 (10.0)
51.2 (25.0)
50.5 (36.4)
49.2 (35.3)
62.1 (7.8)
49.7 (17.1)
146.5 (8.3)
335.8 (189.8)
619.2 (35.4)
1350.1 (329.3)
1095.9 (292.3)
702.6 (294.9)
785.6 (45.1)
917.5 (150.7)
12.00 (3.54)
26.37 (13.17)
21.70 (8.03)
14.28 (8.35)
12.65 (5.78)
18.46 (8.83)
aValues given first are calculations performed without the iodide
counterion, while those in parentheses are for the neutral molecules.
In any event, at the AM1 level, the dipole moment and
hyperpolarisability terms are smaller than expected for
zwitterionic species but are, nonetheless, features which
imply that the extent of charge transfer and/or acceptor
strength are insufficient to produce significant figures of merit
in these stunted systems.
In connection with some of our earlier studies15 on mero-
cyanines 4 and 5 (n ~ 1), we had reason to explore the syntheses
of double salts of 1,3-di(4-pyridyl)propane as a potential means
of gaining access to bridged dimers of 4 and of 5. This search
revealed that such double (methiodide) salts were, in fact,
precursors to stunted donor–acceptor functionalised molecules
belonging to the cyanine class of chromophore.17–19
In view of the fact that this system can be viewed
simplistically as a push–pull azasesquifulvalene chromophore
that is isoelectronic with the stunted merocyanines above
(albeit bearing a pyridinium substituent), we calculated the
ground state dipole moment and static hyperpolarisability data
from optimised AM1 geometries of a number of derivatives of
27 and the results are presented in Table 2. Even though the
system is symmetrical or fluxional, there is an unexpectedly
high ground state dipole moment that increases with increasing
acceptor strength in R. For compound 27d as a positively
charged chromophore (without its counterion), for example,
a dipole moment of 26.4 D is calculated together with a static
hyperpolarisability of 51.2 6 10230 esu. When optimised
in the presence of its counterion, values of 13.2 D and
25.0 6 10230 esu, respectively, are calculated.
Encouraged by the results of our computational study, we
prepared the ‘polymer-tetherable’ cyanines 29a–d as outlined in
Scheme 4. Attempts to prepare the corresponding cyanine from
4,4’-dinitrobenzil were unsuccessful due to the extremely poor
solubility of the requisite dione in methanol. In addition, a blue
solid was obtained from reaction of 28 with 2,7-dinitrophenan-
threnequinone but this has proved to be too insoluble to be
meaningfully characterised. The negative solvatochromic effect
observed for these compounds is a little more pronounced than
it is for the stunted merocyanines above and again suggests that
the chromophore moiety is zwitterionic, the negative charge
being associated with the cyclopentadienyl(ide) system or
further delocalised by the Ar and pyridinium substituents. In
fact, in all but compound 29d, the systemic simplicity of the
cationic chromophore is confirmed from 13C- and 1H-NMR
spectroscopy, thereby attesting to the fluxional nature of the
entire pyridinium–sesquifulvalene nucleus in solution. These
cyanine dyes are, however, known to be protonated on the
central cyclopentadienide ring in strongly acid media.17 With
regard to the NMR spectra of compounds 29a–c, in which the
two pairs of vicinal methylene groups are observed as two
discrete multiplets [at d 4.16 (NCH2) and 3.72 (CH2OH) for 29b
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Scheme 4 Synthesis of polymer-tetherable cyanines 29a–d.
for example] and as a coincident signal at 60.2 ppm (for 29b),
the corresponding signals in compound 29d are all non-
equivalent, appearing as four two-proton multiplets at d 4.21
and 4.00 (NCH2) and d 3.76 and 3.62 (CH2OH). The 13C-NMR
spectrum displays three discrete signals in the ratio 1 : 2 : 1 at
60.6, 60.3 and 60.1 ppm indicating most probably that the two
N-methylenes are no longer equivalent. This indicates that
there is a lack of symmetry in 29d, most likely as a result of
distortion in the phenanthrenyl nucleus caused by its close
proximity to the azine rings.
As NLO materials, molecular salts, in which one ion
possesses a large molecular hyperpolarisability, are known to
exhibit large second-order optical nonlinearities.31,32 Stilbazo-
lium tosylate salts 30 in the solid state, for example, can form
macroscopically polar (i.e. noncentrosymmetric) structures as a
result of alternating cation and anion sheets in the crystal
lattice.31 Analogues containing an ‘internal salt’, e.g. 31, have
also been shown to possess a large permanent dipole moment
(16 D) and an high static nonlinear coefficient b(0) of
37 6 10230 esu. These systems have been considered as
chromophores for inclusion in side-chain polymers and in
LB films.32
As both 30 and 31 crystallise in noncentrosymmetric space
groups (P1 and Pc21b, respectively), we were interested to see
whether or not the same might have been true of a repre-
sentative of the azasesquifulvalene system. Large crystals of
chromophore 29a were prepared, but these showed poor
refinement in the structure analysis. The molecular structure
could not be definitely established even though a space group
and unit cell dimensions could be assigned (P21/c; a ~
side- or main-chain component of the backbone. In addition,
we are interested to see whether or not a satisfactory level of
chromophore alignment can be achieved by electric field poling
and this will be reported in due course.
Utilising standard procedures34 for novel polyurethane
synthesis, we prepared
a polymer of 29c with a 1 : 1
stoichiometry with tolylene diisocyanate (TDI) and purified
it easily twice by redissolution (DMSO–cyclohexanone)–
reprecipitation (MeOH). Whilst we have no molecular weight
data on this and other mainchain cyanine polymers, the
integrity of this particular chromophore in this polymer was
confirmed from UV–vis spectroscopy and an elemental analysis
revealed an almost stoichiometric retention of iodide ion. The
Tg recorded for this polymer was 240 uC.
In like manner, each of the multiply-tetherable chromo-
phores 16b, 23 and 24 (Schemes 1 and 3) was found to form,
very cleanly, stoichiometric polyurethanes with TDI. Tg values
are again high at 234 uC for 23 and 243 uC for 16b. However, as
these new materials are genuine mainchain polymer systems we
envisage the need to further space and/or crosslink these types
of chromophore elements using the triethanolamine methodol-
ogy,35 for example.
˚
˚
˚
9.120 A, b ~ 24.34 A, c ~ 9.659 A, a ~ c ~ 90u, b ~ 96u;
z ~ 4); this cell has been confirmed by X-ray powder
diffraction studies which show that other phases may be
present. With a space group of P21/c, the packing motif
would be clearly centrosymmetric, an outcome that, if general
for this class of compound, effectively precludes the use of them
as NLO elements in the crystalline state. With respect to the
position of the organic cation, the iodide ion is localised at a
pyridinium terminus, the nearest neighbour in fact being the
oxygen of the pyridinium hydroxyethyl substituent.
Finally, we believe there is scope to study the preparation of
non-centrosymmetric crystals of derivatives of 27 and this
In an earlier crystallographic study of the N,N’-dimethyl
(bromide) analogue of 27, namely 32, in which one of the azine
rings is present as a 2- rather than as a 4-substituent, Ammon
and Erhardt33 found no evidence for the existence of a tripolar
structure, i.e. a bis(pyridiniumyl)cyclopentadienide; rather,
that the compound is a hybrid of two monopolar cationic
c
forms that exists in the centrosymmetric P1¯ space group.
Even though only computational findings suggested non-
linear optical behaviour in these cyanine systems, we were
interested to explore the possibility of synthesising a polymer
containing this genuinely ionic NLO chromophore as either a
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Crystal data. C17H16N2O4, Mr ~ 312.32, triclinic, a ~
˚
7.987(2), b ~ 10.300(3), c ~ 10.806(3) A, a ~ 118.308(4),
3
˚
b ~ 106.121(4),c ~ 94.752(4)u,U ~ 727.3(4) A ,T ~ 158(2) K,
space group P1 (No. 2); Z ~ 2, rc ~ 1.426 g cm23, radiation
¯
MoKa, l ~ 0.71073 A, m (Mo Ka) ~ 0.103 mm21, 8989
˚
reflections collected, 2897 unique (Rint ~ 0.0217) used in all
calculations. The final wR(F2) (all data) and R(F) (I w 2s(I))
were 0.112 and 0.0392 respectively. Selected bond lengths and
angles are given in Table 3.
CCDC reference number 164244. See http://www.rsc.org/
suppdata/jm/b1/b103148c/ for crystallographic files in .cif or
other electronic format.
should be readily achieved by incorporating a chiral substituent
onto one of the pyridinium N atoms; this will form the basis of
our future studies. Thus, while polymers derived from 28 may
yet prove unsuitable for spin-coating and ‘utilisation’ due to
the tendency of ionic polymers to promote hole-burning on
poling, non-centrosymmetric crystals of large b(0) organic salts
are known to have high second harmonic generation
efficiencies.36
3-(p-Hydroxyphenyl)rhodanine
4-Aminophenol (10.9 g, 0.1 mol) was dissolved in aqueous
NaOH (1 M, 100 mL) and the solution refluxed for 10 min and
then allowed to cool. Bis(carboxymethyl) trithiocarbonate
(22.6 g, 0.1 mol) was added and the mixture refluxed overnight.
After cooling, the resulting solid was recovered by filtration,
washed with water (3 6 100 mL), suspended in methanol–
isopropanol (propan-2-ol) (1 : 1) (150 ml) and the mixture
refluxed for 10 min before being cooled and filtered. The solid
was dried in air to give the hydroxyphenyl rhodanine as a beige
powder (14.4 g, 64%). Recrystallisation (methanol) gave beige
crystals, mp 237.5–241 uC (dec.) (Found: C, 48.13; H, 3.01; N,
6.31. C9H7NO2S2 requires C, 47.98; H, 3.13; N, 6.22%)
(Found: MH2 m/z 223.98396; C9H7NO2S2 requires MH2 m/z
223.98345; D ~ 2.3 ppm). 1H NMR (d6-DMSO) d 9.80 (s,
1H, -OH), 7.02 (d, J 8.7 Hz, 2H), 6.86 (d, J 8.7 Hz, 2H), 4.35 (s,
2H). 13C NMR (d6-DMSO) d 204.3 (CQ), 174.5 (CQ), 158.3
(CQ), 130.1 (CH), 126.8 (CQ), 116.1 (CH), 37.0 (CH2).
Experimental
1H and 13C NMR spectra were recorded on a Bruker
AVANCE 300 MHz spectrometer. 1H NMR multiplicities
are defined by the usual notation and coupling constants are in
hertz. The assignments of resonances were made with the aid of
DEPT, 1H–1H COSY and 13C–1H HSQC experiments and
heteronuclear multiple bond connectivity (HMBC) experi-
ments. UV–vis absorption spectra were recorded on an
Hewlett-Packard 8452A diode array spectrophotometer.
Accurate mass measurements were made on a PE Biosystems
Mariner operating in the electrospray mode and used in
preference to microanalytical data since these were consistently
marred by the retention of variable amounts of solvent of
crystallisation.
1-(2-Hydroxyethyl)-3-methyl-1H-pyrazol-5(4H)-one
To a stirred solution of ethyl acetoacetate (10.0 g, 58 mmol) at
0–5 uC was added dropwise over 10 min 2-hydroxyethylhydra-
zine (5.0 g, 60 mmol) and then acetic acid (1 mL). [The addition
of the hydrazine results in a vigorous reaction and the addition
should be done at such a rate so as to minimise sudden
elevations in the reaction temperature.] The mixture was then
stirred together for 1 h at 100 uC, cooled and, while still slightly
warm, diluted with ether (30 mL) and triturated to give a tarry
brown syrup (14.4 g) that was used as such in subsequent
reactions; all attempts to crystallise the product failed. 1H
NMR (CDCl3) d 3.72–3.84 (m, 4H, -NCH2 and -CH2OH), 3.17
(s, 2H, -CH2-), 2.04 (s, 3H, -CH3). 13C NMR (CDCl3) d 173.3
(CQ), 156.7 (CQ), 61.5 (CH2), 47.5 (CH2), 42.1 (CH2), 17.3
(CH3). NMR spectroscopy indicated significant impurities to
be present in the crude tar, and while suitable for use without
further purification it was presumed to be only 75% pure.
Confirmation of the proposed structure was obtained by
Thin layer chromatography was performed on Merck
Alufoilen 60 F254 analytical plates and flash chromatography
performed over Riedel-de Haen silica gel S (230–400 mesh).
Measurements of the first hyperpolarisability were measured
at the University of Otago using the hyper-Raleigh scattering
technique with a fundamental wavelength of 1064 nm (seed-
injected Nd:YAG pulsed laser; energy 20–25 mJ, width 70 ps,
repetition rate 2 kHz) and with a series of concentrations
(c 1–5 mM) in 0.2 micron-filtered methanol. Scattered SH light
was detected by interference filtration and shown to have a
quadratic dependence upon I2 (1064).
X-Ray crystallography
Single crystals of compound 14 were crystallized from an
acetone–hexane mixture.
˚
Table 3 Selected geometric parameters for chromophore 14 (A, u)
O(3)–C(14)
O(13)–C(14)
N(1)–C(8)
C(4)–C(5)
C(6)–C(11)
C(7)–C(8)
C(12)–C(15)
C(3)–N(1)–C(4)
C(4)–C(5)–C(6)
C(6)–C(11)–C(12)
C(12)–C(11)–C(14)
O(3)–C(14)–O(13)
O(13)–C(14)–C(11)
C(4)–N(1)–C(3)–C(2A)
C(11)–C(6)–C(7)–C(8)
C(5)–C(6)–C(11)–C(14)
C(7)–C(6)–C(11)–C(14)
1.245(2)
1.3859(16)
1.3589(17)
1.3674(18)
1.4359(17)
1.3698(18)
1.494(2)
119.62(13)
120.89(13)
130.83(13)
104.97(11)
118.67(12)
107.12(13)
94.4(2)
O(13)–N(2)
N(1)–C(4)
N(2)–C(12)
C(5)–C(6)
C(6)–C(7)
C(11)–C(12)
N(2)–O(13)–C(14)
C(5)–C(6)–C(7)
C(6)–C(11)–C(14)
C(11)–C(12)–C(15)
O(3)–C(14)–C(11)
C(3)–N(1)–C(4)–C(5)
C(5)–C(6)–C(11)–C(12)
C(7)–C(6)–C(11)–C(12)
C(6)–C(11)–C(14)–O(3)
C(12)–C(15)–C(16)–C(17)
N(2)–C(12)–C(15)–C(20)
1.4455(19)
1.3605(17)
1.3166(17)
1.419(2)
1.4207(17)
1.435(2)
109.58(10)
115.88(11)
124.01(13)
130.82(11)
105.9(3)
2176.29(13)
210.6(2)
171.37(14)
3.9(3)
2176.48(13)
251.07(18)
2179.79(13)
163.55(13)
214.5(2)
2276
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(CH), 132.1 (CH), 131.4 (CH), 126.0 (CQ), 123.1 (CH), 70.9
(CH), 62.9 (CH2), 62.6 (CH2).
reacting the crude tar with N,N’-diphenylformamidine to give
the expected anilinomethylidene derivative as shown below.
3,5-Diiodo-4-hydroxypyridine
4-Anilinomethylidene-1-(2-hydroxyethyl)-3-methyl-1H-pyrazol-
5(4H)-one
This was prepared employing a slight modification to the
previously reported method.39 To a solution of 4-hydroxy-
pyridine (15.0 g, 0.158 mol) in water (200 mL) was added a
solution of sodium hydroxide (40.0 g, 1 mol) and sodium
acetate trihydrate (200.0 g, 1.47 mol) in water (500 mL). The
solution was stirred and heated to boiling and then powdered
iodine (106 g, 0.417 mol) was added. The solution was acidified
with acetic acid (50%) and then neutralised with aqueous
sodium hydroxide (40%) and these steps repeated. The
acidifications and neutralisations were made at the boiling
point of the reaction mixture and each procedure was
conducted over about 20 minutes. The final (third) acidification
was made until free iodine was just precipitated. This was
removed by boiling and the precipitated 3,5-diiodo-4-hydroxy-
pyridine recovered by filtration, washed thoroughly with
boiling water and dried to give the product as an off-white
powder (47.8 g, 87%), mp 315 uC (dec.) (lit.39 317 uC (dec.)). 1H
NMR (d6-DMSO) d 8.28 (s, 2H). 13C NMR (d6-DMSO) d
170.8 (CQ), 143.3 (CH), 86.8 (CQ).
Crude 1-(2-hydroxyethyl)-3-methyl-1H-pyrazol-5(4H)-one (14.4 g)
and N,N’-diphenylformamidine (14.9 g, 76 mmol) were stirred
together at 120 uC for 1 h, and the mixture then allowed to cool
to room temperature. To this was added firstly isopropanol
(30 mL) and then water dropwise until a solid had formed. The
resultant brown solid was collected by filtration and recrys-
tallised (1 : 1 water–ethanol) to give brown-red needles (10.89 g,
58%), mp 117–119 uC (Found: MHz m/z 246.12279; C13H15-
N3O2 requires MHz m/z 246.12370; D ~ 23.7 ppm). 1H NMR
(CDCl3) d 7.90 (s, 1H), 7.40–7.45 (m, 2H), 7.20–7.25 (m, 3H),
3.92–4.00 (m, 4H, -NCH2 and -CH2OH), 2.23 (s, 3H, -CH3).
13C NMR (CDCl3) d 166.9 (CQ), 147.5 (CQ), 143.6 (CH), 138.9
(CQ), 130.4 (CH), 126.2 (CH), 117.7 (CH), 102.5 (CQ), 62.4
(CH2), 47.9 (CH2), 12.9 (CH3).
3-tert-Butylisoxazol-5(4H)-one
To a solution of ethyl pivaloylacetate (18.0 g, 0.105 mol) in
ethanol (250 mL) was added a solution of hydroxylamine
hydrochloride (7.92 g, 0.114 mol) in water (150 mL) followed
by sodium acetate trihydrate (14.4 g, 0.105 mol). The mixture
was refluxed for 1 h, cooled and concentrated and the resulting
solid extracted with ether (3 6 150 mL). The ether extracts
were pooled, dried (Na2SO4) and concentrated to give an off-
white solid. A single recrystallisation from an ethyl acetate–
hexane mixture afforded the isoxazolone as colourless needles
(8.81 g, 60%), mp 110–111 uC (Found: MHz m/z 142.08561;
C7H11NO2 requires MHz m/z 142.08625; D ~ 4.5 ppm). 1H
NMR (CDCl3) d 1.24 (s, 9H), 3.42 (s, 2H). 13C NMR (CDCl3) d
176.0 (CQ), 174.1 (CQ), 35.1 (CQ), 33.7 (CH2), 27.9 (CH3).
4-Chloro-3,5-diiodopyridine
To a mixture of dry 3,5-diiodo-4-hydroxypyridine (40 g,
0.121 mol) in phosphoryl chloride (120 mL) was added
phosphorus pentachloride (40 g, 0.192 mol) and the resultant
slurry stirred at 100–110 uC for 16 h while protected from
atmospheric moisture by a calcium chloride drying tube. The
solution was then cooled and poured in small portions into
water (1 L). Following each addition of the chlorinating mix-
ture there followed a short induction period (ca. 1–2 min),
after which considerable heat was generated: care was taken
to ensure that the temperature of the aqueous solution did not
rise above 70 uC. The hydrolysis step required 2–3 h in total.
Once the mixture had cooled to room temperature it was
chilled to ca. 5 uC and partially neutralised via the cautious
addition of 30% aqueous sodium hydroxide (500–750 mL),
after which a white precipitate formed in abundance. This was
collected by filtration, suspended in water (500 mL) and the
slurry made slightly basic to litmus. The solid was collected by
filtration and washed thoroughly with water to give 4-chloro-
3,5-diiodopyridine as a white powder (42.2 g, 96%), mp 174–
176 uC (pentan-2-ol) (lit.40 175 uC). 1H NMR (d6-DMSO) d
8.81 (s, 2H). 13C NMR (d6-DMSO) d 157.3 (CH), 150.3 (CQ),
99.1 (CQ).
3-tert-Butyl-1-phenyl-1H-pyrazol-5(4H)-one
A
mixture of ethyl pivaloylacetate (19.2 g, 0.112 mol),
phenylhydrazine (12.5 g, 11.4 mL, 0.116 mol) and acetic acid
(2 mL) was stirred for 1 h at 100 uC. The mixture was then
cooled and, while still slightly warm, diluted with ether (30 mL)
and then triturated with a glass rod. After cooling to 230 uC,
the pale yellow solid was recovered by filtration and washed
with cold ether (2 6 15 mL). Recrystallisation from isopro-
panol containing a few drops of ether afforded chunky
colourless crystals (13.12 g, 54%), mp 117–119 uC (Found: C,
71.92; H, 7.45; N, 12.89. C13H16N2O requires C, 72.19; H, 7.46;
N, 12.95%) (Found: MHz m/z 217.13291; C13H16N2O requires
MHz m/z 217.13354; D ~ 2.9 ppm). 1H NMR (CDCl3), d
7.80–7.83 (m, 2H), 7.27–7.32 (m, 2H), 7.05–7.10 (m, 1H), 3.35
(s, 2H), 1.18 (s, 9H). 13C NMR (CDCl3) d 171.2 (CQ), 167.0
(CQ), 138.7 (CQ), 129.1 (CH), 125.3 (CH), 119.2 (CH), 39.3,
(CH2), 35.3 (CQ), 28.5, (CH3).
3,5-Diiodo-4-(phenylthio)pyridine
To a cooled (ice–water), stirred solution of 4-chloro-3,5-
diiodopyridine (40 g, 0.11 mol) in triethylamine (150 mL) was
added portion wise over 5 min neat thiophenol (15 g, 14 mL,
0.136 mol). The mixture was refluxed overnight, cooled and
then diluted with water (150 mL) and stirred for 30 min. The
precipitated solid was recovered by filtration,{ washed with
plenty of water and then recrystallised from an acetone–
methanol (1 : 1) mixture to give the (phenylthio)pyridine as
off-white microcrystals (38.5 g, 80%), mp 111–112.5 uC. A
further 5–7 g of product was recovered from the mother liquor
(Found: C, 30.38; H, 1.54; N, 3.15. C11H7I2NS requires C,
30.09; H, 1.61; N, 3.19%) (Found: MHz m/z 439.8454;
C11H7I2NS requires MHz m/z 439.84615; D ~ 1.7 ppm). 1H
NMR (d6-DMSO) d 8.99 (s, 2H), 7.32–7.37 (m, 2H), 7.23–7.28
(m, 1H), 7.04–7.07 (m, 2H). 13C NMR (d6-DMSO) d 157.7
1-(2,3-Dihydroxypropyl)-4-(phenylthio)pyridinium iodide, 11
A solution containing 4-(phenylthio)pyridine (2.0 g, 10.7 mmol)
and 1-iodo-2,3-dihydroxypropane (2.2 g, 10.9 mmol) in ethanol
(10 mL) was refluxed for 4 hours then cooled and concentrated
to a yellow oil. Trituration with ethyl acetate afforded 1-(2,3-
dihydroxypropyl)-4-(phenylthio)pyridinium iodide as a hygro-
scopic, off-white solid (3.95 g, 94%) which was used as such
without further purification. 1H NMR (D2O) d 8.36 (d, J
6.8 Hz, 2H), 7.56–7.66 (m, 5H), 7.48 (d, J 6.7 Hz, 2H), 4.61 (dd,
J 3.0, 13.8 Hz, 1H, lower field branch of AB quartet, -NCH2),
4.34 (dd, J 8.8, 13.7 Hz, 1H, higher field branch of AB quartet,
-NCH2), 4.07–4.14 (m, 1H, -CHOH), 3.65 (d, J 5.1 Hz, 2H,
-CH2OH). 13C NMR (D2O) d 165.4 (CQ), 143.3 (CH), 135.9
{Due to the presence of a thick oil filtration may require 5–6 hours until
completion.
J. Mater. Chem., 2001, 11, 2271–2281
2277

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2H), 8.00 (d, J 7.3 Hz, 2H), 7.32 (apparent t, J 7.86 Hz, 2H),
(CH), 150.6 (CQ), 134.4 (CQ), 130.0 (CH), 127.7 (CH), 127.0
(CH), 108.3 (CQ).
7.01 (apparent t, J 7.3 Hz, 1H), 5.26 (d, J 5.4 Hz, 1H, -CHOH),
4.90 (t, J 5.3 Hz, 1H, -CH2OH), 4.26 (dd, J 2.8, 13.5 Hz, 1H,
lower field branch of AB quartet, -NCH2), 3.98 (dd, J 8.0,
13.5 Hz, 1H, higher field branch of AB quartet, -NCH2),
3.77–3.78 (m, 1H; -CHOH), 3.41–3.48 (m, 1H, lower field
branch of AB quartet, -CH2OH), 3.26–3.33 (m, 1H, higher field
branch of AB quartet, -CH2OH), 2.38 (s, 3H, CH3). 13C NMR
(d6-DMSO) d 165.2 (CQ), 149.1 (CQ), 147.0 (CQ), 141.4 (CH),
140.8 (CQ), 128.7 (CH), 122.6 (CH), 117.9 (CH), 114.7 (CH),
97.4 (CQ), 70.9 (CH), 63.2 (CH2), 60.4 (CH2), 18.5 (CH3).
1-(2,3-Dihydroxypropyl)-3,5-diiodo-4-(phenylthio)pyridinium
chloride, 12
A mixture of 3,5-diiodo-4-(phenylthio)pyridine (5.0 g, 11.4 mmol)
and a-chloroglycerol (15.0 g, 73.7 mmol) was stirred at 120 uC
for 16 h after which time the resulting orange oil was added
dropwise to a stirred volume of acetone (400 mL), whereupon a
sticky orange-yellow solid precipitated. This was recovered by
filtration and recrystallised (ethanol) to give 1-(2,3-dihydroxy-
propyl)-3,5-diiodo-4-(phenylthio)pyridinium chloride as air
sensitive bright yellow microcrystals (3.68 g, 59%), mp 173.5–
175 uC. 1H NMR (d6-DMSO) d 9.42 (s, 2H), 7.35–7.45 (m, 3H),
7.25–7.28 (m, 2H), 5.56 (d, J 5.8 Hz, 1H, -CHOH), 5.05 (t, J
5.5 Hz, 1H, -CH2OH), 4.67 (dd, J 2.6, 12.6 Hz, 1H, lower field
branch of AB quartet, -NCH2), 4.33–4.40 (m, 1H, higher field
branch of AB quartet, -NCH2), 3.95 (m, 1H, -CHOH), 3.48–
3.57 (m, 1H, lower field branch of AB quartet, -CH2OH), 3.38–
5-[1-(2,3-Dihydroxypropyl)pyridin-4(1H)-ylidene]-3-ethyl-
rhodanine, 16a. Isolated as described above and purified by
recrystallisation from an acetone–hexanes mixture to give
orange rosettes (1.72 g, 55%), mp 220–222 uC (Found: MHz
m/z 313.06793; C13H16N2O3S2 requires MHz m/z 313.06751;
D ~ 1.3 ppm). lmax 454 (H2O); 460 (methanol) log10e 4.79; 462
(acetonitrile); 466 (DMSO) log10e 4.78; 464 (acetone); 470
1
(pyridine). H NMR (d6-DMSO) d 8.22–8.25 (m, 1H), 7.81–
3.46 (m, 1H, higher field branch of AB quartet, -CH2OH). 13
C
7.85 (m, 2H), 6.42–6.45 (m, 1H), 5.19 (br s, 1H, -CHOH), 4.85
(br s, 1H, -CH2OH), 4.15 (dd, J 3.0, 13.6 Hz, 1H, lower field
branch of AB quartet, -NCH2), 4.00 (q, J 7.0 Hz, 2H,
-NCH2CH3), 3.89 (dd, J 7.9, 13.6 Hz, 1H, higher field
branch of AB quartet, -NCH2), 3.74 (m, 1H, -CHOH), 3.42
(dd, J 4.9, 10.9 Hz, 1H, lower field branch of AB quartet,
-CH2OH), 3.26 (dd, J 6.5, 10.9 Hz, 1H, higher field branch of
NMR (d6-DMSO) d 161.7 (CQ), 151.6 (CH), 133.1 (CQ), 130.3
(CH), 129.8 (CH), 128.4 (CH), 105.5 (CQ), 70.7 (CH), 63.4
(CH2), 63.0 (CH2).
General procedure for the preparation of pyridylidene-
functionalised heterocycles
AB quartet, -CH2OH), 1.14 (t, J 7.0 Hz, 3H, -NCH2CH3). 13
C
To a solution of 1-(2,3-dihydroxypropyl)-4-(phenylthio)pyri-
dinium iodide (3.89 g, 0.01 mol) and the appropriate hetero-
cyclic acceptor (0.01 mol) in ethanol (50 mL) was added
triethylamine (1.5 mL, 1.09 g, 0.01 mol). The mixture was
then refluxed for 1 h, cooled and the resulting chromophores
isolated as outlined below. Reactions with the diiodopyridi-
nium chloride analogue were performed in like stoichiometric
manner at the 2.0 mmol scale and at reflux for 16 h. In all
instances the crude condensation product was recovered by
filtration of the cooled reaction liquor.
NMR (d6-DMSO) d 185.6 (CQ), 162.9 (CQ), 143.7 (CQ), 141.2
(CH), 140.6 (CH), 113.6 (CH), 113.3 (CH), 88.1 (CQ), 70.8
(CH), 63.2 (CH2), 60.0 (CH2), 38.9 (CH2), 12.6 (CH3).
5-[1-(2,3-Dihydroxypropyl)pyridin-4(1H)-ylidene]-3-(p-hydroxy-
phenyl)rhodanine, 16b. Isolated as a crude precipitate that
was purified by crystallisation from an acetone–hexane mixture
to give bright orange microcrystals (1.55 g, 41%), mp 273–
274 uC (Found: MHz m/z 377.06321; C17H16N2O4S2 requires
MHz m/z 377.06243; D ~ 2.1 ppm). lmax 454 (H2O); 460
(methanol) log10e 4.88; 464 (acetonitrile); 466 (DMSO) log10e
4.91; 464 (acetone); 470 (pyridine). 1H NMR (d6-DMSO) d 9.68
(s, 1H, ArOH), 8.15–8.18 (m, 1H), 7.80–7.84 (m, 2H), 7.00 (d, J
8.7 Hz, 2H), 6.84 (d, J 8.7 Hz, 2H), 6.46–6.50 (m, 1H), 5.22 (d,
J 5.3 Hz, 1H, -CHOH), 4.87 (t, J 5.4 Hz, 1H, -CH2OH), 4.14
(dd, J 2.8, 13.6 Hz, 1H, lower field branch of AB quartet,
-NCH2), 3.88 (dd, J 7.9, 13.6 Hz, 1H, higher field branch of AB
quartet, -NCH2), 3.74 (m, 1H, -CHOH), 3.39–3.47 (m, 1H,
lower field branch of AB quartet, -CH2OH), 3.23–3.32 (m, 1H,
higher field branch of AB quartet, -CH2OH). 13C NMR (d6-
DMSO) d 187.5 (CQ), 163.6 (CQ), 157.7 (CQ), 143.6 (CQ), 141.2
(CH), 140.5 (CH), 130.1 (CH), 128.6 (CQ), 115.7 (CH), 113.4
(CH), 113.2 (CH), 88.2 (CQ), 70.9 (CH), 63.2 (CH2), 59.9
(CH2).
4-[1-(2,3-Dihydroxypropyl)pyridin-4(1H)-ylidene]-3-phenyl-
isoxazol-5(4H)-one, 14. Isolated by flash chromatography over
silica using gradient elution of an acetone–hexane mixture
(70–100%) and isolated as a yellow solid. Recrystallisation
from acetone afforded bright yellow microcrystals (87 mg, 9%),
mp 247–250 uC (Found: MHz m/z 313.11871; C17H16N2O4
requires MHz m/z 313.11828; D ~ 1.4 ppm). lmax 370 (H2O);
382 (methanol) log10e 4.45; 384 (10% aqueous acetonitrile); 394
1
(DMSO) log10e 4.50; 400 (acetone); 404 (pyridine). H NMR
(d6-DMSO) d 8.01 (d, J 7.2 Hz, 2H), 7.52–7.55 (m, 4H), 7.42–
7.45 (m, 3H), 5.21 (d, J 5.4 Hz, 1H), 4.87 (t, J 5.4 Hz, 1H), 4.23
(dd, J 2.9, 13.5 Hz, 1H, lower field branch of AB quartet,
-NCH2), 3.94 (dd, J 8.2, 13.5 Hz, 1H, higher field branch of AB
quartet, -NCH2), 3.71–3.73 (m, 1H, -CHOH), 3.37–3.44 (m,
1H, lower field branch of AB quartet, -CH2OH), 3.21–3.29 (m,
1H, higher field branch of AB quartet, -CH2OH). 13C NMR
(d6-DMSO) d 174.0 (CQ), 162.3 (CQ), 149.4 (CQ), 141.9 (CH),
133.0 (CQ), 129.6 (CH), 129.3 (CH), 128.8 (CH), 115.2 (CH),
85.6 (CQ), 70.7 (CH), 63.2 (CH2), 60.9 (CH2).
[1-(2,3-Dihydroxypropyl)pyridin-4(1H)-ylidene]dicyanomethane,
17. Malononitrile (0.22 g, 3.3 mmol) was added to a solution
of sodium ethoxide [prepared from sodium metal (0.08 g,
3.3 mmol)] in ethanol (10 mL) and the mixture stirred for
30 min after which time 1-(2,3-dihydroxypropyl)-4-(phe-
nylthio)pyridinium iodide (1.30 g, 3.34 mmol) was added.
The solution was refluxed for 1 h, and then cooled to
–18 uC. The resulting solid was recovered by filtration,
washed with water (10 mL) and then isopropanol (10 mL) to
give a pale yellow powder (0.32 g, 44%). Recrystallisation from
ethanol afforded light tan microcrystals, mp 183–184.5 uC
(Found: C, 60.81; H, 5.07; N, 19.14. C11H11N3O2 requires C,
60.82; H, 5.10; N, 19.35%) (Found: MHz m/z 218.09261;
C11H11N3O2 requires MHz m/z 218.09240; D ~ 0.9 ppm). lmax
374 (H2O–acetone; 20 : 1); 378 (methanol) log10e 4.24; 376
(acetonitrile); 378 (DMSO) log10e 4.27; 376 (acetone); 380
4-[1-(2,3-Dihydroxypropyl)pyridin-4(1H)-ylidene]-3-methyl-1-
phenylpyrazol-5(4H)-one, 15. Isolated in the manner described
for the isoxazolone analogue and purified by recrystallisation
from an acetone–hexane mixture to give bright yellow crystals
(214 mg, 22%), mp 242–245 uC (Found: C, 66.33; H, 6.02; N,
12.73. C18H19N3O3 requires C, 66.44; H, 5.89; N, 12.92%)
(Found: MHz m/z 326.15083; C18H19N3O3 requires MHz m/z
326.14992; D ~ 2.8 ppm). lmax 378 (H2O); 390 (methanol)
log10e 4.37; 392 (10% aqueous acetonitrile); 412 (DMSO)
log10e 4.39; 404 (10% aqueous acetone); 418 (pyridine). 1H
NMR (d6-DMSO) d 8.82 (br s, 2H), 8.08 (apparent d, J 8.3 Hz,
1
(pyridine). H NMR (d6-DMSO) d 7.86 (d, J 7.0 Hz, 2H), 6.83
2278
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-CHOH), 4.95 (t, J 5.4 Hz, 1H, -CH2OH), 4.53 (dd, J 2.1,
(d, J 7.0 Hz, 2H), 5.23 (d, J 5.1 Hz, 1H, -CHOH), 4.87 (t, J
5.2 Hz, 1H, -CH2OH), 4.19 (dd, J 2.4, 13.5 Hz, 1H, lower field
branch of AB quartet, -NCH2), 3.92 (dd, J 8.0, 13.5 Hz, 1H,
higher field branch of AB quartet, -NCH2), 3.72 (m, 1H,
-CHOH), 3.36–3.44 (m, 1H, lower field branch of AB quartet,
-CH2OH), 3.22–3.27 (m, 1H, higher field branch of AB quartet,
-CH2OH). 13C NMR (d6-DMSO) d 155.7 (CQ), 141.4 (CH),
118.9 (CQ), 112.6 (CH), 70.8 (CH), 63.1 (CH2), 60.2 (CH2), 43.5
(CQ).
12.9 Hz, 1H, lower field branch of AB quartet, -NCH2), 4.23
(dd, J 8.8, 12.9 Hz, 1H, higher field branch of AB quartet,
-NCH2), 3.89 (m, 1H, -CHOH), 3.46–3.53 (m, 1H, lower field
branch of AB quartet, -CH2OH), 3.31–3.39 (m, 1H, higher field
branch of AB quartet, -CH2OH). 13C NMR (d6-DMSO) d
184.1 (CQ), 163.9 (CQ), 149.7 (CH), 140.6 (CQ), 130.8 (CH),
119.1 (CH), 110.9 (CQ), 98.1 (CQ) 70.8 (CH), 63.4 (CH2), 61.7
(CH2).
4-[1-(2,3-Dihydroxypropyl)-3,5-diiodopyridin-4(1H)-ylidene]-3-
phenylisoxazol-5(4H)-one, 18a. Purified by recrystallisation
from ethanol to give an orange-yellow microcrystalline
powder (0.28 g, 25%), mp 223.5–225 uC (Found: MHz m/z
564.90888; C17H14I2N2O4 requires MHz m/z 564.91159;
D ~ 4.8 ppm). lmax 432 (H2O); 456 (methanol) log10e 3.51;
466 (10% aqueous acetonitrile); 492 (DMSO) log10e 3.71; 490
[1-(2,3-Dihydroxypropyl)-3,5-diiodopyridin-4(1H)-ylidene]di-
cyanomethane, 21. Purified by recrystallisation from ethanol to
give yellow platelets (0.39 g, 49%), mp 263–264 uC (Found:
MHz m/z 469.88491; C11H9I2N3O2 requires MHz m/z
469.88571; D ~ 1.7 ppm). lmax 404 (H2O–acetone; 20 : 1); 410
(methanol) log10e 4.16; 410 (acetonitrile); 412 (DMSO) log10e
4.22; 412 (acetone); 416 (pyridine). 1H NMR (d6-DMSO) d 8.53
(s, 2H), 5.24 (d, J 5.6 Hz, 1H, -CHOH), 4.85 (t, J 5.4 Hz, 1H,
-CH2OH), 4.23 (dd, J 2.6, 13.3 Hz, 1H, lower field branch of
AB quartet, -NCH2), 3.96 (dd, J 8.4, 12.3 Hz, 1H, higher field
branch of AB quartet, -NCH2), 3.73–3.75 (m, 1H, -CHOH),
3.38–3.46 (m, 1H, lower field branch of AB quartet, -CH2OH),
3.24–3.31 (m, 1H, higher field branch of AB quartet, -CH2OH).
13C NMR (d6-DMSO) d 154.8 (CQ), 149.5 (CH), 119.6 (CQ),
83.2 (CQ), 70.6 (CH), 63.2 (CH2), 59.9 (CH2). One quaternary
carbon signal, -C(CN)2, not observed.
1
(5% aqueous acetone); 510 (pyridine). H NMR (d6-DMSO) d
9.05 (s, 1H), 9.01 (s, 1H), 7.27–7.36 (m, 3H), 7.16–7.19 (m, 2H),
5.43 (d, J 5.7 Hz, 1H, -CHOH), 4.94 (t, J 5.4 Hz, 1H,
-CH2OH), 4.52 (dd, J 2.6, 13.0 Hz, 1H, lower field branch of
AB quartet, -NCH2), 4.23 (dd, J 8.7, 13.0 Hz, 1H, higher field
branch of AB quartet, -NCH2), 3.86–3.88 (m, 1H, -CHOH),
3.45–3.52 (m, 1H, lower field branch of AB quartet, -CH2OH),
3.33 (m, 1H, higher field branch of AB quartet, -CH2OH). 13
C
NMR (d6-DMSO) d 171.1 (CQ), 161.8 (CQ), 160.6 (CQ), 150.2
(CH), 149.8 (CH), 134.3 (CQ), 128.9 (CH), 128.8 (CH), 126.3
(CH), 99.1 (CQ), 98.8 (CQ), 91.9 (CQ), 70.6 (CH), 63.4 (CH2),
61.9 (CH2).
5-[1-(2,3-Dihydroxypropyl)-3,5-diiodopyridin-4(1H)-ylidene]-
1,3-diethyl-2-thiobarbituric acid, 22. Isolated by concentrating
the crude product mixture to dryness and then stirring the
residual solids in hot acetone–hexanes (1 : 1). The resulting
precipitate was collected by filtration and washed with hot
hexanes to give an orange-yellow powder (119 mg, 10%).
Recrystallisation (isopropanol) afforded bright orange micro-
crystals, mp 265–266 uC (Found: MHz m/z 603.92656;
C16H19I2N3O4S requires MHz m/z 603.92586; D ~ 0.7 ppm).
lmax 414 (H2O); 438 (methanol) log10e 3.93; 458 (acetonitrile);
448 (DMSO) log10e 3.94; 462 (acetone); 468 (pyridine). 1H
NMR (d6-DMSO) d 9.19 (s, 2H), 5.48 (d, J 5.7 Hz, 1H,
-CHOH), 4.97 (t, J 5.4 Hz, 1H, -CH2OH), 4.61–4.64 (m, 1H,
lower field branch of AB quartet, -NCH2), 4.44 (q, J 6.4 Hz,
4H, -NCH2CH3), 4.32 (dd, J 9.0, 12.8 Hz, 1H, higher field
branch of AB quartet, -NCH2), 3.91 (m, 1H, -CHOH), 3.47–
3.54 (m, 1H, lower field branch of AB quartet, -CH2OH), 3.35–
3.39 (m, 1H, higher field branch of AB quartet, -CH2OH), 1.19
(t, J 6.7 Hz, 6H, -NCH2CH3). 13C NMR (d6-DMSO) d 176.3
(CQ), 166.4 (CQ), 156.8 (CQ), 150.2 (CH), 130.2 (CQ), 103.0
(CQ), 70.7 (CH), 63.5 (CH2), 62.6 (CH2), 41.6 (CH2), 13.1
(CH3).
4-[1-(2,3-Dihydroxypropyl)-3,5-diiodopyridin-4(1H)-ylidene]-
3-tert-butylisoxazol-5(4H)-one, 18b. Purified by recrystallisa-
tion from methanol to give orange platelets (0.21 g, 19%), mp
278–280 uC (Found: C, 32.29; H, 3.35; N, 4.87. C15H18-
I2N2O4?½H2O requires C, 32.57; H, 3.46; N, 5.06%) (Found:
MHz m/z 544.94108; C15H18I2N2O4 requires MHz m/z
544.94289; D ~ 3.3 ppm). lmax 448 (H2O); 486 (methanol)
log10e 2.81; 488 (10% aqueous acetonitrile); 554 (DMSO) log10e
3.09; 556 (5% aqueous acetone); 550 (pyridine). 1H NMR
(d6-DMSO) d 9.28 (s, 1H), 9.23 (s, 1H), 5.51 (d, J 5.7 Hz, 1H,
-CHOH), 4.98 (t, J 5.4 Hz, 1H, -CH2OH), 4.59 (dd, J 2.4,
12.8 Hz, 1H, lower field branch of AB quartet, -NCH2), 4.31–
4.35 (m, 1H, higher field branch of AB quartet, -NCH2), 3.92
(m, 1H, -CHOH), 3.40–3.43 (m, 1H, lower field branch of AB
quartet, -CH2OH), 3.32–3.37 (m, 1H, higher field branch of AB
quartet, -CH2OH), 1.09 (9H, -CH3). 13C NMR (d6-DMSO) d
195.0 (CQ), 167.3 (CQ), 166.2 (CQ), 150.0 (CH), 149.7 (CH),
105.9 (CQ), 105.7 (CQ), 93.0 (CQ), 70.6 (CH), 63.4 (CH2), 62.6
(CH2), 33.4, (CQ), 30.2, (CH3).
4-[1-(2,3-Dihydroxypropyl)-3,5-diiodopyridin-4(1H)-ylidene]-
3-tert-butyl-1-phenylpyrazol-5(4H)-one, 19. Obtained as a red
powder, which on filtration and exposure to air gradually
changed to a crimson, glassy-like solid (0.624 g, 50%) (Found:
MHz m/z 619.99386; C21H23I2N3O3 requires MHz m/z
619.99017; D ~ 6.0 ppm). lmax 536 (3 : 1; H2O–DMSO); 536
(methanol) log10e 2.99; 542 (49 : 1; acetonitrile–DMSO); 548
(DMSO) log10e 3.05; 542 (49 : 1; acetone–DMSO); 558 (49 : 1;
1-(2-Hydroxyethyl)-4-(phenylthio)pyridinium iodide, 13
A mixture of 4-(phenylthio)pyridine (5.61 g, 0.03 mol) and
2-iodoethanol (5.16 g, 0.03 mol) in solution in isopropanol
(15 mL) was refluxed for 3 days, after which time it was cooled
and concentrated to give a yellow oil. This was triturated with
ether (15 mL) and then cooled until a solid mass had formed.
The solid was recovered by filtration and washed thoroughly
with ether to afford 1-(2-hydroxyethyl)-4-(phenylthio)pyridi-
nium iodide as a beige solid (10.57 g, 98%) which was
acceptable for use without further purification. Recrystallisa-
tion from a methanol–isopropanol mixture gave the salt as off-
white microcrystals, mp 166–167.5 uC (Found: C, 43.48; H,
3.82; N, 3.87. C13H14INOS requires C, 43.46; H, 3.93; N,
1
pyridine–DMSO). Due to poor resolution H and 13C NMR
spectra were not helpful and therefore are not reported here.
2-[1-(2,3-Dihydroxypropyl)-3,5-diiodopyridin-4(1H)-ylidene]-
indane-1,3-dione, 20. Purified by recrystallisation from ethanol
to give an orange powder (0.09 g, 8%), mp 235–237 uC (Found:
C, 37.10; H, 2.88; N, 2.36. C17H13I2NO4 requires C, 37.19; H,
2.39; N, 2.55%) (Found: MHz m/z 549.89899; C17H13I2NO4
requires MHz m/z 549.90069; D ~ 3.1 ppm). lmax 432 (H2O);
444 (methanol) log10e 3.96; 468 (acetonitrile); 464 (DMSO)
log10e 4.14; 470 (acetone); 476 (pyridine). 1H NMR (d6-DMSO)
d 9.02 (s, 2H), 7.33–7.43 (m, 4H), 5.44 (d, J 5.7 Hz, 1H,
1
3.90%); H NMR (CDCl3) d 8.85 (d, J 7.1 Hz, 2H), 7.58–7.63
(m, 5H), 7.38 (d, J 7.1 Hz, 2H), 4.88 (t, J 4.8 Hz, 2H), 4.13 (br s,
1H), 4.05 (m, 2H). 13C NMR (CDCl3), d 165.1 (CQ), 143.6
(CH), 135.9 (CH), 132.2 (CH), 131.5 (CH), 125.7 (CQ), 122.8
(CH), 62.3 (CH2), 61.1 (CH2).
J. Mater. Chem., 2001, 11, 2271–2281
2279

View Online
hasten solidification. Isopropanol was then added, and the
5-[1-(2-Hydroxyethyl)pyridin-4(1H)-ylidene]-3-(p-
hydroxyphenyl)rhodanine, 23
product collected by filtration and washed with isopropanol to
give a beige solid (25.9 g, 96%) that was suitable for use without
further purification. The product could not be recrystallised
from common alcohols. 1H NMR (d6-DMSO) d 8.93 (d, J
6.4 Hz, 4H), 8.10 (d, J 6.4 Hz, 4H), 5.09 (br s, 2H, -CH2OH),
4.63 (t, J 4.7 Hz, 4H), 3.85 (t, J 4.7 Hz, 4H), 3.14 (t, J 7.6 Hz,
4H), 2.12 (quintet, J 7.6 Hz, 2H). 13C NMR (d6-DMSO) d
161.8 (CQ), 144.8 (CH), 127.7 (CH), 62.7 (CH2), 60.3 (CH2),
34.3 (CH2), 28.9 (CH2).
A
mixture of 1-(2-hydroxyethyl)-4-(phenylthio)pyridinium
iodide (3.59 g, 0.01 mol), 3-(p-hydroxyphenyl)rhodanine (2.25 g,
0.01 mol) and triethylamine (1.01 g, 0.01 mol) in ethanol (50 mL)
was refluxed for 16 h and then cooled. The resulting precipitate
was collected by filtration and washed with a little cool ethanol
to give a deep orange powder (2.58 g, 75%). Recrystallisation
from an acetone–hexane mixture gave orange microcrystals,
mp w 320 uC (Found: C, 55.20; H, 3.99; N, 8.08. C16H14N2O3S2
requires C, 55.47; H, 4.07; N, 8.09%) (Found: MHz m/z
377.06321; C16H14N2O3S2 requires MHz m/z 377.06243;
D ~ 2.1 ppm). lmax 454 (H2O); 460 (methanol) log10e 4.83;
462 (acetonitrile); 466 (DMSO) log10e 4.85; 464 (acetone), 470
General procedure for the preparation of bridged cyanine dyes
29a–d
To a stirred solution of 1,1’-bis(2-hydroxyethyl)-4,4’-trimethyl-
enedipyridinium diiodide (5.42 g, 0.01 mol) and the appro-
priate a-diketone (0.01 mol) in hot methanol (50 mL) was
added dropwise piperidine (1.70 g, 0.02 mol). The mixture was
then refluxed for 16 h, cooled, and the crude product collected
by filtration and washed with a little ethanol. The crude
products, which were generally suitable for use after drying in a
vacuum at 110 uC, were purified by a single recrystallisation.
1
(pyridine). H NMR (d6-DMSO) d 9.67 (s, 1H, ArOH), 8.16–
8.19 (m, 1H), 7.84–7.88 (m, 2H), 7.00 (d, J 8.7 Hz, 2H), 6.85 (d, J
8.7 Hz, 2H), 6.47–6.50 (m, 1H), 5.06 (t, J 5.1 Hz, 1H, -CH2OH),
4.04 (t, J 4.9 Hz, 2H, -NCH2), 3.67–3.72 (m, 2H, -CH2OH). 13
C
NMR (d6-DMSO) d 187.5 (CQ), 163.6 (CQ), 157.7 (CQ), 143.6
(CQ), 140.8 (CH), 140.1 (CH), 130.1 (CH), 128.6 (CQ), 115.7
(CH), 113.6 (CH), 113.4 (CH), 88.2 (CQ), 60.5 (CH2), 59.4
(CH2).
1-(2-Hydroxyethyl)-4-{4,5,6,7-tetrahydro-1-[1-(2-hydroxyethyl)-
pyridin-4(1H)-ylidene]-1H-inden-3-yl}pyridinium iodide, 29a. From
cyclohexane-1,2-dione, green-black needles (MeOH) (3.50 g, 71%),
mp 223–225 uC (Found: M( 2 I)z m/z 363.20557; C23H27IN2O2
requires M( 2 I)z m/z 363.20671; D ~ 3.1 ppm). lmax 504 (H2O);
534 (methanol) log10e 4.84; 528 (acetonitrile); 530 (DMSO) log10e
4-[1-(2-Hydroxyethyl)pyridin-4(1H)-ylidene]-1-(2-
hydroxyethyl)-3-methylpyrazol-5(4H)-one, 24
A
mixture of 1-(2-hydroxyethyl)-4-(phenylthio)pyridinium
iodide (1.1 g, 3.0 mmol), crude 1-(2-hydroxyethyl)-3-methyl-
1H-pyrazol-5(4H)-one (0.7 g, 4.9 mmol) and triethylamine
(0.5 g, 4.9 mmol) in ethanol (20 mL) was refluxed for 16 h,
cooled and concentrated to dryness. The product was dissolved
in water (25 mL) and the solution reconcentrated with stirring
under high vacuum to the point where ca. 80% solvent had been
removed and a yellow-orange solid had formed. This solid was
recovered by filtration and washed with water (3 6 10 mL) and
dried. Concentration of the filtrate, followed by trituration
with acetone afforded a further crop of solid. Recrystallisation
from a methanol–acetone mixture gave bright yellow micro-
crystals (145 mg, 18%), mp 223–225 uC (Found: C, 55.31; H,
6.77; N, 14.86. C13H17N3O3?H2O requires C, 55.51; H, 6.81; N,
14.93%) (Found: MHz m/z 264.13391; C13H17N3O3 requires
264.13427; D ~ 1.4 ppm). lmax 378 (H2O–methanol; 20 : 1);
390 (methanol) log10e 4.23; 408 (acetonitrile); 414 (DMSO)
log10e 4.27; 412 (acetone), 422 (pyridine). 1H NMR (d6-DMSO)
d 7.97 (apparent s, 4H), 5.12 (br s, 2H, 2 6 -CH2OH), 4.11 (br
s, -NCH2), 3.67–3.72 (m, 4H, -NCH2 and -CH2OH), 3.54–3.58
(m, 2H, -CH2OH), 2.25 (s, 3H, -CH3). 13C NMR (d6-DMSO) d
165.5 (CQ), 149.0 (CQ), 144.1 (CQ), 140.8 (CH), 114.5 (CH),
97.1 (CQ), 60.6 (CH2), 59.6 (CH2), 47.0 (CH), 18.2 (CH3).
1
4.82; 534 (acetone); 542 (pyridine). H NMR (d6-DMSO) d 8.10
(d, J 7.1 Hz, 4H), 7.61 (d, J 7.1 Hz, 4H), 7.53 (s, 1H), 5.13 (t, J
4.9 Hz, 2H, -CH2OH), 4.20 (t, J 4.7 Hz, 4H, -NCH2), 3.75–3.78
(m, 4H, -CH2OH), 2.73 (s, 4H), 1.73 (s, 4H). 13C NMR
(d6-DMSO) d 151.0 (CQ), 141.7 (CH), 127.6 (CQ), 122.8 (CQ),
120.5 (CH), 118.4 (CH), 60.5 (CH2), 59.9 (CH2), 27.1 (CH2), 23.7
(CH2).
1-(2-Hydroxyethyl)-4-{3-[1-(2-hydroxyethyl)pyridin-4(1H)-
ylidene]-4,5-diphenylcyclopenta-1,4-dien-1-yl}pyridinium iodide,
29b. From benzil, bronze microcrystals (MeOH) (2.23 g, 38%),
mp 281–289 uC (partial) (Found: C, 62.03; H, 5.03; N, 4.69.
C31H29IN2O2?½H2O requires C, 62.32; H, 5.06; N, 4.68%)
(Found: M( 2 I)z m/z 461.22131; C31H29IN2O2 requires
M( 2 I)z m/z 461.22236; D ~ 2.3 ppm). lmax 484 (H2O); 516
(methanol) log10e 4.85; 508 (acetonitrile); 510 (DMSO) log10e
1
4.86; 512 (5% aqueous acetone); 520 (pyridine). H NMR (d6-
DMSO) d 8.06 (d, J 7.0 Hz, 4H), 7.06–7.23 (m, 14H), 5.10 (t, J
5.0 Hz, 2H, -CH2OH), 4.15 (t, J 4.60 Hz, 4H, -NCH2), 3.70–
3.75 (m, 4H, -CH2OH). 13C NMR (d6-DMSO) d 152.4 (CQ),
141.8 (CH), 139.4 (CQ), 132.0 (CQ), 130.9 (CH), 128.3 (CH),
126.2 (CH), 122.3 (CQ), 120.8 (CH), 119.0 (CH), 60.2
(2 6 CH2).
3,3’-Dinitrobenzil
This was prepared as previously described,41 mp 130–131 uC
1
(lit.41 132 uC). H NMR (CDCl3) d 8.86 (s, 2H), 8.55–8.57 (m,
2H), 8.39 (d, J 7.8 Hz, 2H), 7.81 (dd, J 8.0 Hz, 2H). 13C NMR
(CDCl3) d 189.9 (CQ), 149.0 (CQ), 135.8 (CH), 134.1 (CQ),
130.9 (CH), 129.7 (CH), 125.3 (CH).
1-(2-Hydroxyethyl)-4-{3-[1-(2-hydroxyethyl)pyridin-4(1H)-
ylidene]-4,5-bis(3-nitrophenyl)cyclopenta-1,4-dien-1-yl}pyridi-
nium iodide, 29c. From 3,3’-dinitrobenzil, orange-brown
microplates (H2O–MeOH; 1 : 1) (4.27 g, 63%), mp w 300 uC
(Found: C, 53.76; H, 4.06; N, 8.15. C31H27IN4O6?½H2O
requires C, 54.15; H, 4.10; N, 8.15%) (Found: M( 2 I)z m/z
551.19196; C31H27IN4O6 requires M( 2 I)z m/z 551.19251;
D ~ 1.0 ppm). lmax 472 (H2O); 496 (methanol) log10e 4.85; 492
(acetonitrile); 494 (DMSO) log10e 4.87; 496 (acetone); 504
(pyridine). 1H NMR (d6-DMSO) d 8.18 (d, J 6.8 Hz, 4H), 8.02–
8.04 (m, 2H), 7.84 (s, 2H), 7.69 (s, 1H), 7.49–7.53 (m, 4H), 7.33
(d, J 6.8 Hz, 4H), 5.13 (br s, 2H, -CH2OH), 4.22 (br s, 4H,
-NCH2), 3.74 (br s, 4H, -CH2OH). 13C NMR (d6-DMSO) d
152.3 (CQ), 147.8 (CQ), 142.4 (CH), 140.6 (CQ), 137.8 (CH),
130.0 (CH), 129.6 (CQ), 125.1 (CH), 121.8 (CQ), 121.3
(2 6 CH), 119.8 (CH), 60.6 (CH2), 60.3 (CH2).
1,1’-Bis(2-hydroxyethyl)-4,4’-trimethylenedipyridinium diiodide,
28
A mixture of 4,4’-trimethylenedipyridine (9.9 g, 0.05 mol) and
2-iodoethanol (21.5 g, 0.125 mol) in ethanol (50 mL) was
refluxed for 16 h and then cooled. The solution was
concentrated in vacuum to give a dark olive oil which was
washed by successively shaking with ether, ethyl acetate and
acetone and decanting off the supernatant liquid each time.
The residual green-brown oil was allowed to stand in a
stoppered flask for 48 h after which time the product had begun
to solidify as small ‘flowers’; the mixture was triturated to
2280
J. Mater. Chem., 2001, 11, 2271–2281

View Online
S. R. Marder, L. T. Chen, B. G. Tiemann, A. C. Friedli,
M. Blancharde-Desce, J. W. Perry and J. Skindhoj, Science, 1994,
263, 511.
I. D. L. Albert, T. J. Marks and M. A. Ratner, J. Am. Chem. Soc.,
1998, 120, 11174.
C. Rusner, A. Fort, M. Barzoukas, P. Boy, C. Combellas, C. Suba
and A. Thiebault, Nonlinear Opt., 1995, 9, 195.
7
1-(2-Hydroxyethyl)-4-{1-[1-(2-hydroxyethyl)pyridin-4(1H)-
ylidene]-9H-cyclopenta[l]phenanthren-11-yl}pyridinium iodide,
29d. From 9,10-phenanthraquinone, bronze microcrystals
(H2O–i-PrOH; 1 : 1) (1.81 g, 31%), mp w 300 uC (Found: C,
61.07; H, 4.54; N, 4.63. C31H27IN2O2?H2O requires C, 61.60;
H, 4.84; N, 4.63%). No parent ion was observed for this
compound; instead an ion corresponding to C31H28IN2O3 was
observed. lmax 530 (H2O); 554 (methanol) log10e 4.96; 562
(acetonitrile); 564 (DMSO) log10e 4.95; 566 (acetone); 576
(pyridine). 1H NMR (d6-DMSO) 9.56 (s, 1H), 8.20 (d, J 5.8 Hz,
2H), 8.15 (d, J 7.5 Hz, 4H), 7.95 (d, J 6.2 Hz, 2H), 7.42
(apparent t, J 7.3 Hz, 2H), 7.21 (apparent t, J 7.2 Hz, 2H), 7.01
(d, J 7.3 Hz, 2H), 6.74 (br s, 2H), 5.10 (br s, 1H, -CH2OH), 5.00
(br s, 1H, -CH2OH), 4.21 (br s, 2H, -NCH2), 4.00 (br s, 2H,
-NCH2), 3.76 (br s, 2H, -CH2OH), 3.62 (br s, 2H, -CH2OH).
13C NMR (d6-DMSO) d 152.1 (CH), 147.3 (CQ), 146.9 (CQ),
145.8 (CQ), 142.1 (CH), 141.9 (CH), 128.1 (CH), 123.0 (CH),
121.2 (CH), 120.8 (CQ), 116.5 (CQ), 116.3 (CH), 112.0 (CQ),
60.6 (CH2), 60.3 (2 6 CH2), 60.1 (CH2).
8
9
10 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. Wenseleers and E. Goovaerts, J. Am. Chem. Soc., 1997, 119,
3144.
11 P. Gangopadhyay, M. Ravi and T. P. Radhakrishnan, Indian
J. Chem. Sect. A, 2000, 39, 106.
12 M. Ravi, D. N. Rao, S. Cohen, I. Agranat and T. P.
Radhakrishnan, Chem. Mater., 1997, 9, 830.
13 G. Baquat, P. Bassoul, C. Combellas, J. Simon, A. Thiebault and
F. Tournilhac, Adv. Mater., 1990, 2, 311.
14 C. Combellas, M. A. Petit and A. Thiebault, Makromol. Chem.,
1992, 193, 2445.
15 A. J. Kay, A. D. Woolhouse, G. J. Gainsford, T. G. Haskell,
T. H. Barnes, I. T. McKinnie and C. P. Wyss, J. Mater. Chem.,
2001, 11, 996.
16 H. L. Ammon and W. D. Erhardt, J. Org. Chem., 1980, 45, 1914.
17 A. R. Katritzky, W. Q. Fan and Q. L. Li, J. Heterocycl. Chem.,
1988, 25, 1311.
18 A. R. Katritzky, D. S. Liang and W. Q. Fan, J. Heterocycl. Chem.,
1988, 25, 1315.
Polymer from reaction of tolylene 2,4-diisocyanate and 1-(2-
hydroxyethyl)-4-{3-[1-(2-hydroxyethyl)pyridin-4(1H)-ylidene]-
4,5-bis(3-nitrophenyl)cyclopenta-1,4-dien-1-yl}pyridinium iodide
19 A. R. Katritzky, W. Q. Fan, X. S. Jiao and Q. L. Li, J. Heterocycl.
Chem., 1988, 25, 1321.
20 I. D. L. Albert, T. J. Marks and M. A. Ratner, J. Am. Chem. Soc.,
1997, 119, 3155.
To a stirred solution of dry 29c (3.87 g, 5.71 mmol) in DMSO
(15 mL) at 80 uC and under a nitrogen atmosphere was
added dropwise toluene-2,4-diisocyanate (993 mg, 820 mL,
5.71 mmol). The mixture was then stirred at 80 uC for a further
16 h, cooled and the viscous liquid filtered through a plug of
glass wool into a stirred volume of methanol (150 mL). The
precipitate was collected by filtration and washed thoroughly
with volumes of hot methanol, water and then methanol again
to afford a brown powder (3.29 g). This was dissolved in a
minimum volume of DMSO–cyclohexanone (1 : 1) and filtered
through a glass frit into a stirred volume of methanol (300 mL)
whereupon the solid rapidly reprecipitated. After collecting the
solids, the dissolution–precipitation procedure was repeated
and the final product collected by filtration, washed with
100 mL portions of boiling water, then boiling methanol, and
dried in vacuum at 100 uC to give a chocolate-brown powder
(1.77 g, 37%) (Found: C, 52.62; H, 3.92; N, 9.56; I 16.65.
C39H33IN6O8 requires C, 55.72; H, 3.96; N, 10.00; I 15.10%).
lmax 494 (DMSO).
21 A. Fort, C. Runser, M. Barzoukas, C. Combellas, C. Suba and
A. Thiebault, Proc. SPIE – Int. Soc. Opt. Eng., 1994, 2285, 2.
22 A. Fort, L. Mager, J. Muller, C. Combellas, G. Mathey and
A. Thiebault, Opt. Eng., 1999, 12, 339.
23 An earlier report by these authors13 contains an X-ray crystal
structure determination on chromophore 7 that reveals a twist
angle of 11u.
24 L. G. S. Brooker, G. H. Keyes, R. H. Sprague, R. H. VanDyke,
E. VanLare, G. VanZandt and F. L. White, J. Am. Chem. Soc.,
1951, 73, 5326.
25 F. Trecourt, G. Breton, V. Bonnet, F. Mongin, F. Marsais and
G. Queguiner, Tetrahedron, 2000, 56, 1349.
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Acknowledgements
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