NLO chromophores containing dihydrobenzothiazolylidene and dihydroquinolinylidene donors with an azo linker: Synthesis and optical properties

Article abstract of DOI:10.1016/j.dyepig.2013.01.010

We report the synthesis of a series of nonlinear optical chromophores containing either a - dihydrobenzothiazolylidene or dihydroquinolinylidene donor with an azo linker. The results demonstrate the versatility of coupling a diazonium salt to a donoremethylidene nucleus in order to access novel materials with good thermal stabilities and high nonlinear optical responses. From hyper- Raleigh scattering studies it was found that the use of the well-known TCF acceptor yields the best performing chromophores, one of which has a dynamic first hyperpolarizability of 1900 × 10^-30 esu at 800 nm. The results from this study suggest the use of pro-aromatic donors such as dihydrobenzothiazolylidene or dihydroquinolinylidene results in compounds with higher nonlinear optical responses than those containing donors based on either indoline or aniline.

Full text of DOI:10.1016/j.dyepig.2013.01.010

Dyes and Pigments 98 (2013) 82e92
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
NLO chromophores containing dihydrobenzothiazolylidene and
dihydroquinolinylidene donors with an azo linker: Synthesis and
optical properties
,
a
Mohamed Ashraf a, Ayele Teshome b, Andrew J. Kay a , Graeme J. Gainsford ,
*
M. Delower H. Bhuiyan a, Inge Asselberghs b, Koen Clays b
a Photonics, Industrial Research Ltd., P.O. Box 31-310, Lower Hutt 5040, New Zealand
b Department of Chemistry, University of Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
We report the synthesis of
a series of nonlinear optical chromophores containing either a -
Received 4 December 2012
Received in revised form
6 January 2013
Accepted 7 January 2013
Available online 24 January 2013
dihydrobenzothiazolylidene or dihydroquinolinylidene donor with an azo linker. The results
demonstrate the versatility of coupling a diazonium salt to a donoremethylidene nucleus in order to
access novel materials with good thermal stabilities and high nonlinear optical responses. From hyper-
Raleigh scattering studies it was found that the use of the well-known TCF acceptor yields the best
performing chromophores, one of which has a dynamic first hyperpolarizability of 1900 ꢀ 10ꢁ30 esu at
800 nm. The results from this study suggest the use of pro-aromatic donors such as dihy-
drobenzothiazolylidene or dihydroquinolinylidene results in compounds with higher nonlinear optical
responses than those containing donors based on either indoline or aniline.
Keywords:
Nonlinear optics
Chromophore
Hyperpolarizability
Hyper-Raleigh scattering
Azo dyes
Ó 2013 Elsevier Ltd. All rights reserved.
X-Ray crystallography
1. Introduction
typically results in a reduction in the inherent stability or pro-
cessability due to the presence of either open chain double bonds or
Organic molecules and materials possessing large second-order
optical nonlinearities continue to be of interest due to their po-
tential use in optical communications, information storage, optical
switching and photonic imaging and sensing [1,2,3]. The basic
design strategy successfully used by many researchers involves the
attachment of strong donor (D) and acceptor (A) groups at opposing
aryl groups respectively. However, despite the vast range of possi-
bilities, there are some strategies for designing effective NLO ma-
terials that consistently give good results. Among these are the
incorporation of azo linkers into the conjugated interconnect.
Consequently a number of such DepeA systems have been inves-
tigated, with many azo-containing systems showing improved
nonlinear optical performance [12] and thermal stability [13] when
compared to the olefinic analogues. Furthermore, over the past two
decades, azobenzene/azoheterocycle containing polymers have
been the subject of intensive research in optical switching [14], and
digital and holographic storage applications [15]. Thus they repre-
sent a useful class of compound to study as they hold promise for
applications beyond just nonlinear optics.
With the above in mind, we recently described the synthesis
and optical and nonlinear optical properties of a suite of NLO
chromophores containing an indoline donor and azo linker, e.g.1ae
c [16]. It was found that the compounds had dynamic first hyper-
polarizability values, bzzz, of between 210 and 1640 ꢀ 10ꢁ30 esu
when measured at a fundamental wavelength of 800 nm. In par-
ticular the highest value was found for 1c, which contains the very
ends of a
molecules which exhibit large molecular optical nonlinearities.
Over the past two decades a number of different -conjugated
p-conjugated bridge. This results in highly polarizable
p
bridges have been investigated in order determine the extent to
which they impact both the nonlinear optical (NLO) response, as
well as other parameters such as thermal stability, photochemical
stability and processability/solubility. Common conjugated in-
terconnects include olefins [4,5], acetylenes [6], aromatic and het-
eroaromatic rings [7,8,9], oxadiazole systems [10] and azo groups
[11]. Thus, there is often a trade-off to be made, insofar as devel-
oping pushepull polyenes with large first hyperpolarizabilities (b)
* Corresponding author. Tel.: þ64 4 931 3210; fax: þ64 4 931 3306.
E-mail address: a.kay@irl.cri.nz (A.J. Kay).
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.01.010

M. Ashraf et al. / Dyes and Pigments 98 (2013) 82e92
83
well studied “TCF” acceptor system, 4,4,5-trimethyl-3-cyano-
2.2. Measurements and instrumentation
2(5H)-furanylidenepropanedinitrile. Another interesting feature
was that both the static (b0 ¼ 900 ꢀ 10ꢁ30 esu) and dynamic
Melting points were recorded using an EZ-Melt automated
melting point apparatus and are uncorrected. The melting point
values given represent the onset of melting. 1H and 13C NMR
spectra were recorded on a Bruker AVANCE 300 MHz or 500 MHz
spectrometer and proton multiplicities are defined by the usual
notations. Accurate mass measurements were made on a Micro-
mass Q-Tof Premier Mass Spectrometer operating in the positive
ion mode. The UVeVisible (UVeVis) absorption spectra were
recorded by a PerkineElmer Lambda 900 spectrometer at room
temperature. Hyper-Rayleigh scattering (HRS) measurements
were performed at 800 nm in both THF and DMF. Crystal violet
dissolved in methanol was used as an octupolar external reference
(
bzzz ¼ 1640 ꢀ 10ꢁ30 esu at 800 nm) hyperpolarizability values
measured for 1c were significantly higher than an analogous
compound, 2, which contains an aniline e as opposed to indoline e
donor unit (b0 ¼ 343 ꢀ 10ꢁ30 esu and bzzz ¼ 682 ꢀ 10ꢁ30 esu at
800 nm). This was somewhat surprising given the conjugation
length in the indoline systems is shorter by two sp2 hybridised
carbon atoms, and we proposed that it was likely due to the aro-
matic versus non-aromatic nature of the aniline and indoline nuclei
respectively. Based on these results it was a logical progression for
us to explore the effect of replacing the indoline ring in series 1
with other donor units, and in particular pro-aromatic systems.
Consequently in this paper we report on the synthesis and prop-
erties on a series of chromophores analogous to 1aec that have
either a benzothiazolylidene (BTZ) or 4-quinolinylidene (QUIN)
donor. Indeed these are particularly useful comparators. The BTZ
ring is structurally very similar to that of indoline, save for the
sulfur atom that will now confer “pro-aromatic” character. Likewise
the QUIN donor has one more double bond than the indoline ring,
but an identical conjugation length to aniline species 2; however
once again the QUIN nucleus is pro-aromatic. In order to ensure
valid comparisons with previously reported compounds we have
retained the azo-phenyl-vinylidene spacer between the donor and
acceptor moieties.
(
bxxx ¼ 338 ꢀ 10ꢁ30 esu at 800 nm). For all of the HRS measure-
ments, a series of dilute solutions were measured and compared
to the reference concentration series. To correct for the differences
in the solvent between the chromophores and the reference
compound, local field correction factors were applied [(n2 þ 2)/3]3
where n is the refractive index of the solvent at the sodium D line,
with n(DMF) ¼ 1.43, n(THF) ¼ 1.41 and n(MeOH) ¼ 1.32. The
calculations of the dynamic first hyperpolarizability were per-
formed by taking the ratio of the slopes of the sample and the
reference compound. For dynamic first hyperpolarizability values
obtained at 800 nm it is necessary to consider the appropriate
tensor components (dipolar versus octupolar geometry) as the
2. Experimental
reference compound crystal violet is octupolar whereas the
chromophores under investigation are dipolar. The static first
hyperpolarizability is derived from the simple two-level model as
previously described [17]. The apparatus and experimental pro-
cedures for the HRS measurements are exactly the same as those
described before [18].
2.1. Reagents and procedures
All reagents were obtained from Aldrich and were used without
further purification. Analytical grade solvents were used and also
without additional purification. Thin-layer chromatography (TLC)
was performed on pre-coated plates (Merck aluminium sheets,
silica gel 60F 254, 0.2 mm). Column chromatography was con-
ducted on Merck silica gel 9385 (230e400 mesh) with the stated
solvent systems.
2.3. Preparation of chromophores
The methods used to prepare the chromophores are shown in
Schemes 1e4. 4-Aminobenzaldehyde and compounds 11b and

84
M. Ashraf et al. / Dyes and Pigments 98 (2013) 82e92
Scheme 1. Methodology used to prepare the donoremethylidene precursor compounds.
11c were prepared according to the literature procedures [19]. As
part of this study we also attempted to obtain X-ray crystallo-
graphic data for the target chromophores, but we were not able
to grow suitable crystals (possibly due to the presence of the N-
decyl group). However we found that when we replaced the N-
decyl group in 12b with a N-pentyl group to give 14 we were able
to grow X-ray quality crystals. The synthesis of 14 is also
described.
2.4.1. 3-Decyl-2-methylbenzothiazolium iodide (6)
M.p. 176.8 ꢂC. (Found: Mþ m/z 290.1156 C18H28NS requires Mþ
m/z 290.1160;
D
¼ ꢁ1.8 ppm). 1H NMR (500 MHz, DMSO-d6):
d 8.52
(d, 1H, J 10 Hz), 8.38 (d, 1H, J 10 Hz), 7.91 (m, 1H), 7.82 (m, 1H), 4.75
(m, 2H), 3.28 (s, 3H), 1.88 (m, 2H), 1.46e1.34 (m, 14H), 0.89 (t, 3H).
13C NMR (75.4 MHz, DMSO-d6):
d 16.46, 19.99, 24.44, 30.25, 30.67,
52.03, 119.62, 127.39, 130.75, 131.74, 132.07, 143.07, 179.59.
2.4.2. 1-Decyl-4-methylquinolinium iodide (8)
M.p. 198.3 ꢂC. (Found: Mþ m/z 284.1600 C20H30N requires Mþ m/
2.4. Preparation of quarternary salts 6 and 8
z 284.1596;
D
¼ 1.9 ppm). 1H NMR (500 MHz, DMSO-d6):
d 9.53 (d,
1H, J 10 Hz), 8.66 (d, 1H, J 10 Hz), 8.58 (d, 1H, J 10 Hz), 8.30 (m, 1H),
8.13 (d, 1H, J 10 Hz), 8.09 (m, 1H), 5.07 (m, 2H), 3.05 (s, 3H), 1.99 (m,
2H), 1.42e1.33 (m, 14H), 0.88 (t, 3H). 13C NMR (75.4 MHz, DMSO-
The appropriate donor moiety, 5 or 7 (250 mmol), was dissolved
in dry acetonitrile (100 mL) to which an iododecane (69.68 g,
260 mmol) was then added. The reaction mixture was heated under
reflux for 3 days in the case of 2-methylbenzothiazole (5) and
overnight with 4-methylquinoline (7). The solvent was removed
under reduced pressure and the residual solid slurried with diethyl
ether. This was collected by filtration, washed 2e3 times with
diethyl ether and dried under vacuum to afford a white solid in
quantitative yield. The products were purified by recrystallization
from ethanol.
d6):
d 16.46, 19.99, 24.44, 30.25, 30.67, 52.03, 119.62, 127.39, 130.75,
131.74, 132.07, 143.07, 179.59.
2.5. Preparation of methylidene donor precursors (3) and (4)
To
a stirred solution of the appropriate quaternary salt
(50 mmol) was added distilled water (100 mL). After all the solid
Scheme 2. Coupling of the diazonium salt of 4-aminobenzaldehyde to the donor-methylidene units.

M. Ashraf et al. / Dyes and Pigments 98 (2013) 82e92
85
Scheme 3. Coupling of acceptor units to aldehyde containing donor-linker systems.
had dissolved, the solution was filtered to remove any traces of
insoluble material. To the filtrate was added dropwise a solution of
NaOH (4 g, 100 mmol) in distilled water (20 mL) and the resulting
mixture was stirred at room temperature for 5 h. To this was added
a further portion of 20% NaOH in water (10 mL) and the solution
stirred for another 2 h. The product, which formed a reddish or
violet oil, was extracted with ether, the solution dried (Na2SO4) and
the solvent removed under reduced pressure. The oily product was
purified by column chromatography using 1:1 dichloromethane:-
light petroleum as eluent.
2.5.1. 3-Decyl-2-methylene-2,3-dihydro-benzothiazole (3)
Dark red oil (60%). (Found: MHþ m/z 290.1961 C18H28NS requires
MHþ m/z 290.1960;
D
¼ 0.5 ppm). 1H NMR (500 MHz, CDCl3):
d 6.81
(t, 1H), 6.73 (d, 1H, J 5 Hz), 6.63 (m, 1H), 6.31 (d, 1H, J 5 Hz), 4.55 (s,
2H), 3.02 (t, 2H), 1.90 (m, 2H), 1.50e1.30 (m, 14H), 0.88 (t, 3H). 13C
Scheme 4. Preparation of compound 14 for X-ray crystallographic studies.

86
M. Ashraf et al. / Dyes and Pigments 98 (2013) 82e92
NMR (75.4 MHz, CDCl3):
29.91, 32.60, 44.66, 53.46, 80.90, 108.14, 117.47, 119.71, 126.87,
132.85, 143.66, 149.28.
d
14.03, 22.53, 27.52, 27.73, 29.17, 29.26,
2.6.2. 4-[(1-Decyl-1H-quinolin-4-ylidenemethyl)-azo]-
benzaldehyde (10)
Dark violet oil (48%). (Found: MHþ m/z 416.2598 C27H34N3O
requires MHþ m/z 416.2596;
CDCl3): d 9.97 (s, 1H), 9.32 (d, 1H, J 5 Hz), 8.21 (m, 2H), 7.84 (d,
D
¼ 0.4 ppm). 1H NMR (500 MHz,
2.5.2. 1-Decyl-4-methylene-1,4-dihydro-quinoline (4)
Dark violet oil (30%). (Found: MHþ m/z 284.1906 C20H30N re-
2H, J 10 Hz), 7.67 (m, 2H), 7.64 (d, 2H, J 10 Hz), 7.24 (m, 1H),
6.80 (d, 1H, J 5 Hz), 4.01 (m, 2H), 1.82 (m, 2H), 1.42e1.22 (m,
quires MHþ m/z 284.1913;
D
¼ ꢁ2.3 ppm). 1H NMR (500 MHz,
CDCl3):
d
7.21 (t, 1H), 6.98 (d, 1H, J 5 Hz), 6.82 (m, 1H), 6.41 (d, 1H, J
14H), 0.88 (t, 3H). 13C NMR (75.4 MHz, DMSO-d6):
d 14.00,
5 Hz), 6.21 (d,1H, J 5 Hz), 5.88 (d,1H, J 5 Hz), 5.38 (d, 2H, J 5 Hz), 4.55
22.12, 26.02, 26.48, 27.00, 28.49, 28.84, 31.21, 46.04, 57.08,
112.18, 112.90, 113.86, 117.32, 119.67, 120.90, 121.62, 122.39,
124.07, 125.82, 127.22, 128.10, 129.65, 130.27, 132.90, 141.59,
191.59.
(m, 2H), 1.94 (m, 2H), 1.50e1.22 (m, 14H), 0.88 (t, 3H). 13C NMR
(75.4 MHz, CDCl3):
d 14.04, 24.11, 26.86, 29.10, 29.30, 29.44, 30.21,
31.78, 49.37, 57.99, 109.23, 109.96, 116.08, 117.04, 119.03, 127.02,
129.04, 132.57, 142.73, 158.03.
2.7. Preparation of chromophores 12aec and 13aec
2.6. Diazotisation: general procedure for preparation of
azo-aldehydes 9 and 10
The appropriate aldehyde 9 or 10 (1.1 eq) and the corresponding
acceptor 11aec (1 eq) were dissolved in methanol (c. 50 mL per
gram of acceptor) and a catalytic quantity of triethylamine added.
The mixture was refluxed for 6 h, and resulted in a change in the
colour of the mixture from either red to purple or dark blue
depending on the acceptors used. The methanol was then removed
under reduced pressure, the residue washed with water and taken
up into dichloromethane and dried (MgSO4). The solvent was
removed at reduced pressure the resulting solid was purified by
column chromatography.
To concentrated sulfuric acid (4 mL) was added 4-amino-
benzaldehyde (0.302 g, 2.5 mmol) and the reaction mixture
cooled to 0e5 ꢂC. A solution of sodium nitrite (206 mg, 3 mmol) in
water (2 mL) was added slowly and the reaction stirred at 0e5 ꢂC
for 30 min. To this was added a solution of either 5 or 7 (2 mmol)
in glacial acetic acid (10 mL), the mixture stirred for an additional
2 h and then poured into water and neutralized with aqueous so-
dium carbonate. The resulting oil was extracted with dichloro-
methane, dried (MgSO4) and concentrated under reduced pressure.
The final product was obtained following purification by column
chromatography by using 1:1 dichloromethane:light petroleum as
an eluent.
2.7.1. 2-{4-[(3-Decyl-3H-benzothiazol-2-ylidenemethyl)-azo]-
benzylidene}-malononitrile (12a)
Brownish-violet solid (61%), purification by column chroma-
tography on silica gel (dichloromethane:petroleum ether 4:1);
m.p. 121.9 ꢂC. (Found: MHþ m/z 470.2380 C28H32N5S requires
2.6.1. 4-[(3-Decyl-3H-benzothiazol-2-ylidenemethyl)-azo]-
benzaldehyde (9)
MHþ m/z 470.2378;
d 7.72 (d, 2H, J 10 Hz), 7.55 (d, 2H, J 10 Hz), 7.42 (d,1H, J 5 Hz),
D
¼ 0.4 ppm). 1H NMR (500 MHz, CDCl3):
Dark red oil (60%). (Found: MHþ m/z 422.2263 C25H32N3OS re-
quires MHþ m/z 422.2266;
D
¼ ꢁ0.7 ppm). 1H NMR (500 MHz,
7.35e7.30 (m, 2H), 7.18 (d, 1H, J 5 Hz), 7.11 (m, 1H), 6.75 (s, 1H),
CDCl3):
d 9.95 (s, 1H), 7.87 (d, 2H, J 10 Hz), 7.72 (d, 2H, J 10 Hz), 7.52
4.01 (m, 2H), 1.82 (m, 2H), 1.42e1.22 (m, 14H), 0.88 (t, 3H). 13C
(s, 1H), 7.38e7.32 (m, 2H), 7.21 (m, 1H), 7.18 (m, 1H), 4.01 (m, 2H),
NMR (75.4 MHz, DMSO-d6): d 13.88, 20.91, 22.02, 25.98, 26.93,
1.82 (m, 2H), 1.42e1.22 (m, 14H), 0.88 (t, 3H). 13C NMR (75.4 MHz,
28.61, 28.83, 31.22, 46.20, 57.20, 78.9, 113.40, 116.80, 118.10,
118.40, 118.82, 119.42, 127.17, 127.50, 127.90, 129.21, 129.38,
130.20, 135.20, 141.77, 146.50, 156.70, 165.00. lmax (DMF) 484,
log10ε 4.37.
DMSO-d6):
d 13.88, 22.02, 25.92, 26.48, 27.00, 28.60, 28.84, 31.21,
45.97, 57.20, 112.21, 117.32, 119.67, 121.62, 122.45, 124.07, 125.79,
127.97, 129.65, 130.27, 130.86, 132.00, 132.90, 141.69, 191.59.
Table 1
Linear, nonlinear optical and thermal properties of the compounds prepared in this study. For comparative purposes data obtained for 1aec and 2 in earlier studies are also
given [16,22]. Dynamic first hyperpolarizability bzzz values were determined at a fundamental wavelength of 800 nm; static hyperpolarizability bzzz,0 values were obtained
using the two level model. Calculated dipole moments and the corresponding figures of merit are also included.
Compound
Solvent
lmax (nm)
Log10ε
bzzz (10ꢁ30 esu)
bzzz,0 (10ꢁ30 esu)
m
b (calc) (10ꢁ18 esu)
8.3
m
(calc).bzzz (10ꢁ48 esu)
Td ꢂC
12a
THF
DMF
THF
477
484
556
569
637
e
4.35
4.37
4.79
4.76
4.86
e
370 ꢃ 20
320 ꢃ 25
800 ꢃ 30
600 ꢃ 30
1900 ꢃ 100
e
100 ꢃ 5
95 ꢃ 5
3071
2656
5760
4320
26600
e
221.2
12b
12c
13a
13b
13c
1a
380 ꢃ 15
300 ꢃ 15
1100 ꢃ 50
e
7.2
232.8
248.1
215.2
220.0
230.5
230.0
245.0
270.0
e
DMF
THF
14.0
10.2
8.5
DMFa
THF
539
550
520
564
572
e
4.89
4.85
4.79
5.02
4.57
e
840 ꢃ 25
680 ꢃ 25
600 ꢃ 40
960 ꢃ 30
1280 ꢃ 60
e
450 ꢃ 10
290 ꢃ 10
230 ꢃ 15
480 ꢃ 20
650 ꢃ 30
e
8568
6936
5100
8160
20096
e
DMF
THF
DMF
THF
15.7
7.1
DMFa
THF
540
549
525
534
590
601
e
4.95
4.69
4.79
4.67
4.75
5.04
e
710 ꢃ 20
550 ꢃ 25
695 ꢃ 25
650 ꢃ 25
1060 ꢃ 55
1640 ꢃ 155
682
320 ꢃ 10
260 ꢃ 10
290 ꢃ 10
280 ꢃ 10
570 ꢃ 30
900 ꢃ 85
343
5014
3905
3892
3640
13356
20664
e
DMF
THF
DMF
THF
DMF
DMSO
1b
5.6
1c
12.6
e
2
a
These two compounds were not stable in DMF.
MOPAC (CS Chem Draw Pro), AM1 Level using PRECISE keyword.
b

M. Ashraf et al. / Dyes and Pigments 98 (2013) 82e92
87
2.7.2. 5-{4-[(3-Decyl-3H-benzothiazol-2-ylidenemethyl)-azo]-
benzylidene}-3-(4-hydroxy-phenyl)-2-thioxo-thiazolidin-4-one
(12b)
Violet solid (63%), purification by column chromatograpþhy on
silica gel (dichloromethane); m.p. 221.6 ꢂC. (Found: MH m/z
629.2073C34H37N4O2S3
D
requires
MHþ
m/z
629.2079;
¼ ꢁ1.0 ppm). 1H NMR (500 MHz, CDCl3)
d 7.79 (s, 1H), 7.73 (d, 2H,
J 10 Hz), 7.70 (s, 1H), 7.54 (d, 2H, J 10 Hz), 7.53 (s, 1H), 7.36 (m, 1H),
7.22 (m, 2H), 7.15 (d, 1H, J 5 Hz), 7.13 (d, 2H, J 10 Hz), 6.97 (d, 2H, J
10 Hz), 4.00 (m, 2H), 1.82 (m, 2H), 1.44e1.24 (m, 14H), 0.88 (t, 3H).
13C NMR (75.4 MHz, DMSO-d6):
d 13.90, 22.04, 25.95, 26.87, 28.63,
28.85, 28.88, 31.24, 45.70, 53.30, 110.92, 111.74, 115.75, 119.28,
120.04, 120.33,120.90, 122.23, 123.63, 125.61, 126.06,127.01, 129.69,
129.90, 132.09, 132.32, 132.58, 141.73, 155.10, 158.10, 163.66, 167.05,
193.70. lmax (DMF) 569, log10ε 4.76.
2.7.3. 2-[3-Cyano-4-(2-{4-[(3-decyl-3H-benzothiazol-2-
ylidenemethyl)-azo]-phenyl}-vinyl)-5,5-dimethyl-5H-furan-2-
ylidene]-malononitrile (12c)
Brown solid (63%), purification by column chromatography on
silica gel (dichloromethane:methanol 9:1); m.p. 201.4 ꢂC. (Found:
MHþ m/z 603.2900C36H39N6OS requires MHþ m/z 603.2906;
D
¼ ꢁ1.0 ppm). 1H NMR (500 MHz, CDCl3)
d 7.74 (s, 1H), 7.68 (m,
1H), 7.62 (d, 2H, J 10 Hz), 7.56 (d, 2H, J 10 Hz), 7.40 (m, 1H), 7.25 (m,
1H), 7.19 (d, 2H, J 5 Hz), 6.95 (d, 1H, J 15 Hz), 4.07 (m, 2H), 1.85 (m,
2H), 1.79 (s, 6H), 1.48e1.28 (m, 14H), 0.88 (t, 3H). 13C NMR
(75.4 MHz, DMSO-d6):
d 13.88, 22.02, 25.33, 25.92, 27.04, 28.61,
28.83, 30.58, 30.82, 31.22, 45.97, 53.33, 96.91, 98.92, 111.20, 112.06,
112.21, 112.86, 113.08, 119.80, 120.44, 122.44, 123.37, 124.08, 125.86,
127.23, 131.46, 138.59, 141.71, 147.41, 147.76, 164.24, 175.02, 177.02.
lmax (THF) 637, log10ε 4.86.
2.7.4. 2-{4-[(1-Decyl-1H-quinolin-4-ylidenemethyl)-azo]-
benzylidene}-malononitrile (13a)
Dark brown solid (50%), purification by column chromatogþraphy
on silica gel (dichloromethane); m.p. 115.2 ꢂC. (Found: MH m/z
464.2690 C30H34N5 requires MHþ m/z 464.2688;
D
¼ 0.4 ppm). 1H
NMR (500 MHz, CDCl3):
d 8.45 (m, 1H), 8.21(m, 2H), 7.86 (d, 2H, J
10 Hz), 7.78 (m, 3H), 7.38 (m, 3H), 6.62 (d, 1H, J 5 Hz), 4.01 (m, 2H),
1.84 (m, 2H), 1.42e1.22 (m, 14H), 0.90 (t, 3H). 13C NMR (75.4 MHz,
Fig. 1. a and b: UVevis absorption spectra of chromophores 12aec and 13aec in THF.
DMSO-d6):
d 13.88, 20.87, 21.58, 22.02, 26.01, 26.83, 28.61, 28.96,
31.22, 55.80, 78.20, 113.08, 115.98, 117.98, 118.08, 118.92, 119.42,
127.21, 127.48, 127.90, 128.20, 128.50, 129.10, 129.30, 130.20, 135.28,
141.77, 146.48, 156.65, 165.20. lmax (DMF) 550, log10ε 4.85.
Table 2
Crystallographic and structure refinement data for 14.
Asymmetric unit
C58 H60 N4 O8S6
m
, mmꢁ1
2.81
Moiety formula
MW
2(C29 H26 N4 O2 S3).4H2O
1189.50
123(2)
1.54184
Limiting indices
ꢁ13 ꢄ h ꢄ 13, ꢁ17 ꢄ k ꢄ 18, 0 ꢄ l ꢄ 20
Crystal size (mm)
Theta range deg.
Reflections collected
No of unique data
Rint
0.28 ꢀ 0.17 ꢀ 0.04
3.2e75.5
8656
Temperature (K)
ꢀ
Wavelength (A)
Crystal system,
Space group
Triclinic
4647
0.24
0.166000, 3.505400
0.512, 0.896
10
772
79.145(10)
1.02
0.094, 4647
0.319
1,23 and ꢁ0.44
P-1
Refinement method
Full matrix least-squares on F2
P1, P2 coefficients of weighting schemea
Absorp. Coeff. range
Restraints
ꢀ
a, A
11.7058(13)
15.675(2)
17.281(2)
68.779(13)
69.883(12)
2768.1(6)
2
ꢀ
b, A
ꢀ
c, A
No. of parameters
a
g
, deg.
, deg.
b, deg.
Goodness-of-fit on F2
R1b,c/data number
wR2c i (all data)
3
ꢀ
Volume, A
Z
P, Mg mꢁ3
1.427
Largest diff. peak and
hole (e Aꢁ3
)
a
Weight, w ¼ 1/[
s
2(Fo2) þ (P1 ꢀ P)2] where P ¼ (Max(Fo2, 0) þ 2 ꢀ Fc2)/3.
b
Intensities 2.0 times their standard deviations (from counting statistics).
c
R1 ¼ SjjFoj ꢁ Fcjj/SjFoj; wR2 ¼ S[w(F2o ꢁ Fc2)2]/S[(wFo2)2]]1/2
.

88
M. Ashraf et al. / Dyes and Pigments 98 (2013) 82e92
Table 3
(s, 1H), 7.92 (d, 2H, J 10 Hz), 7.68 (d, 2H, J 10 Hz), 7.42 (s, 1H), 7.37e
7.33 (m, 2H), 7.21 (m, 1H), 7.18 (m, 1H), 4.30 (m, 2H), 1.79 (m, 2H),
1.40e1.30 (m, 4H), 0.88 (t, 3H). 13C NMR (75.4 MHz, DMSO-d6):
ꢀ
Selected bond distances (A) in 14 and related compound 1b [16].
Bond
A
B
Average 1b
d
13.75, 21.87, 28.45, 30.61, 45.70, 48.31,111.29,114.98,117.71,126.58,
N2eN3
1.312(8)
1.301(8)
1.404(9)
1.443(9)
1.348(11)
1.753(8)
1.760(8)
1.635(7)
1.347(8)
1.288(8)
1.347(10)
1.394(9)
1.450(10)
1.330(11)
1.723(8)
1.752(8)
1.638(8)
1.334(8)
1.318(11)
1.388(11)
1.412(12)
1.462(13)
1.409(13)
1.718(11)
1.763(11)
1.597(11)
1.423(12)
C
13eN2
129.32, 129.62, 130.79, 131.12, 134.51, 136.84, 139.86, 168.84, 192.04.
N3eC14
C
C
17eC20
20eC21
2.8.3. 3-(4-Hydroxy-phenyl)-5-{4-[(3-pentyl-3H-benzothiazol-2-
ylidenemethyl)-azo]-benzylidene}-2-thioxo-thiazolidin-4-one (14)
Reddish-brown solid (58%), Purified by column chromatogþraphy
on silica gel (dichloromethane); m.p. 227.3 ꢂC. (Found: MH m/z
S2eC21
S2eC22
C
C
22eS3
27eO2
559.1299 C29H27N4O2S3 requires MHþ m/z 559.1296;
D
¼ 0.5 ppm).
1H NMR (500 MHz, CDCl3)
d 9.89 (s, 1H), 7.95 (s, 1H), 7.90 (m, 1H),
7.78 (s, 1H), 7.69 (m, 3H), 7.59 (d, 2H, J 10 Hz), 7.52 (m, 1H), 7.38 (m,
1H), 7.16 (d, 2H, J 10 Hz), 6.89 (d, 2H, J 10 Hz), 4.30 (m, 2H), 1.79 (m,
2H), 1.40e1.30 (m, 4H), 0.88 (t, 3H). 13C NMR (75.4 MHz, DMSO-d6):
2.7.5. 5-{4-[(1-Decyl-1H-quinolin-4-ylidenemethyl)-azo]-benzyl}-
3-(4-hydroxy-phenyl)-2-thioxo-thiazolidin-4-one (13b)
Brownish-pink solid (51%), Purification by column chromatog-
raphy on silica gel (dichloromethane:methanol 4.5:0.5); m.p.
210.2 ꢂC. (Found: MHþ m/z 623.2376 C36H39N4O2S2 requires MHþ
d
13.80, 18.82, 21.84, 27.00, 28.13, 41.80, 46.41, 51.12, 61.67, 63.23,
110.93, 112.76, 115.28, 119.73, 120.57, 122.98, 124.62, 126.06, 127.55,
129.72, 132.29, 149.46, 158.11, 162.64, 167.08, 193.79. X-ray quality
crystals were grown by slow evaporation from a mixture 1:1
mixture of methanol and chloroform.
m/z 623.2382;
D
¼ ꢁ1.0 ppm). 1H NMR (500 MHz, CDCl3)
d 9.22 (d,
1H, J 5 Hz), 7.82 (s, 1H), 7.73 (d, 2H, J 10 Hz), 7.70 (s, 1H), 7.54 (d, 2H, J
10 Hz), 7.53 (s, 1H), 7.36 (m, 1H), 7.22 (m, 2H), 7.15 (d, 1H, J 5 Hz),
7.13 (d, 2H, J 10 Hz), 6.97 (d, 2H, J 10 Hz), 6.62 (d, 1H, J 5 Hz), 4.00 (m,
2H), 1.82 (m, 2H), 1.44e1.24 (m, 14H), 0.88 (t, 3H). 13C NMR
3. Results and discussion
(75.4 MHz, DMSO-d6):
d 14.02, 22.04, 26.00, 26.87, 28.28, 28.65,
3.1. Synthesis
28.90, 31.24, 45.66, 53.32, 110.88, 111.68, 116.02, 119.28, 120.04,
120.30, 120.90, 122.19, 123.58, 125.61, 125.98, 127.01, 129.70, 129.90,
132.09, 132.26, 132.58, 141.73, 155.10, 158.10, 163.72, 166.98, 193.68.
lmax (DMF) 564, log10ε 5.02.
The synthetic methodology used to prepare chromophores
12aec and 13aec is shown in Schemes 1e3. In line with our pre-
vious work using indoline based chromophores, the diazonium salt
of 4-aminobenzaldehyde was coupled to the methylidene analogue
of the donor unit e in this case compounds 3 and 4 e to give the key
aldehyde containing synthons 10 and 11. The success of these
diazonium coupling reactions is presumably assisted by the strong
electron donating ability of the donor rings, and confirms the utility
of this methylidene-diazonium method as a means to easily build
such “donor-linker” units. It is worth noting that compounds 3 and
4 were in turn prepared by dehydrohalogenation of the quarternary
salts of 6 and 8 using 20% aqueous NaOH at room temperature
(Scheme 1) and these molecules can be considered direct analogous
of Fischer’s base, which we successfully used to prepare a suite of
indoline containing compounds. The final chromophores were then
readily accessible via the condensation of the appropriate acceptor
system, 11aec with 10 or 11. The final products were all obtained as
2.7.6. 2-[3-Cyano-4-(2-{4-[(1-decyl-1H-quinolin-4-
ylidenemethyl)-azo]-phenyl}-vinyl)-5,5-dimethyl-5H-furan-2-
ylidene]-malononitrile (13c)
Green solid (54%), Purification by column chromatography on
silica gel (dichloromethane:methanol 4:1); m.p. 196.8 ꢂC. (Found:
MHþ m/z 597.3300 C38H41N6O requires MHþ m/z 597.3306;
D
¼ ꢁ1.0 ppm). 1H NMR (500 MHz, CDCl3)
d 7.89 (d, 2H, 10 Hz), 7.82
(m, 1H), 7.68 (m, 1H), 7.62 (m, 5H), 7.58 (d, 1H, J 15 Hz), 7.28 (d, 1H, J
5 Hz), 7.01 (d, 1H, J 15 Hz), 6.64 (d, 1H, J 5 Hz), 4.07 (m, 2H), 1.85 (m,
2H), 1.80 (s, 6H), 1.48e1.28 (m, 14H), 0.88 (t, 3H). 13C NMR
(75.4 MHz, DMSO-d6):
d 12.98, 22.22, 24.99, 25.92, 27.14, 28.61,
28.86, 30.48, 30.98, 31.10, 45.93, 53.33, 96.85, 98.92, 100.12, 104.98,
106.22, 111.20, 112.06, 112.21, 112.98, 113.10, 119.80, 120.44, 122.44,
123.37, 124.08, 126.02, 127.23, 131.46, 138.63, 141.90, 147.41, 147.76,
163.96, 175.12, 177.02. lmax (THF) 572, log10ε 4.57.
2.8. Synthesis of N-pentyl derivative 14
Compound 14 and its precursors were prepared using exactly
the same methodology described above. Thus compounds 3,6 and 9
were replaced with their N-pentyl analogues.
2.8.1. 2-Methylene-3-pentyl-2,3-dihydro-benzothiazole
Starting from 2-methyl-3-pentyl-benzothiazoliumiodide [20].
Purified by column chromatography using 1:1 dichloromethane:light
petroleum as eluent. Deep red oil (50%). (Found: MHþ m/z 220.1155
C13H18NS requires MHþ m/z 220.1160;
(500 MHz, CDCl3): d 6.81 (m, 1H), 6.73 (d, 1H, J 5 Hz), 6.63 (t,1H), 6.31
D
¼ ꢁ2.3 ppm). 1H NMR
(d,1H, J5 Hz), 4.50 (s, 2H), 4.30(m, 2H),1.79 (m, 2H),1.40e1.30(m, 4H),
0.88 (t, 3H). 13C NMR (75.4 MHz, CDCl3):
d
13.77, 21.96, 29.12, 31.84,
54.90, 88.03, 113.56, 117.21, 120.79, 127.26, 133.36, 148.01, 160.05.
2.8.2. 4-[(3-Pentyl-3H-benzothiazol-2-ylidenemethyl)-azo]-
benzaldehyde
Red oil (55%). (Found: MHþ m/z 352.1484C20H22N3OS requires
MHþ m/z 352.1484;
D
¼ 0.0 ppm).1H NMR (500 MHz, CDCl3):
d
10.00
Fig. 2. Structure of molecule B in 14 (with 20% probability ellipsoids) [26].

M. Ashraf et al. / Dyes and Pigments 98 (2013) 82e92
89
coloured solids that were readily purified by column chromatog-
raphy, and this was no doubt aided by the inclusion of the decyl
groups on the donor nitrogen atoms which are essential for pre-
aromatic group in the linker between the donor and acceptor as
this will result in a loss of aromatic stabilisation energy should the
ground state be zwitterionic.
paring dyes that are sufficiently soluble in organic solvents. The
chromophores were fully characterised by NMR, high resolution
mass spectrometry and UVevis data. A feature to note is that NMR
data indicate that all of 12aec and 13aec exist as a single isomer
and that the rotational isomerisation sometimes present when
asymmetrical acceptors are used (e.g. 11b,c) is not observed [21].
In order to assess the likely stability of the chromophores their
thermal decomposition temperatures (Td) were measured and the
results are presented in Table 1. Pleasingly, all of the compounds
studied have acceptable thermal stabilities as their Td’s are all
higher than 215 ꢂC, and this confirms their suitability for poling at
high temperatures, i.e. up to 180 ꢂC. Among all of the chromophores
12c is the best performed with a Td of 248 ꢂC, although this is some
22 ꢂC less than its indoline analogue (1c, Td 270 ꢂC). Moreover,
combining the results of this study with our previous work there is
a clear improvement in thermal stability in going from the quino-
line to benzothiazole to indoline donor systems.
The absorption maxima of the BTZ compounds 12b and 12c in
THF are red shifted by 36 nm and 65 nm respectively when com-
pared to the corresponding QUIN compounds 13b and 13c. It is well
established that a reduction in the energy difference between the
ground and excited states typically corresponds to an increase in
the molecular hyperpolarizability,
b; thus for these four compounds
it would be expected that the two compounds containing the BTZ
donor would give the superior NLO response. However, contrary to
this trend, compound 12a with benzothiazole donor and malono-
nitrile acceptor units shows on average a 64 nm hypsochromic shift
in its absorption maxima when compared to QUIN compound 13a.
While the reason for this reversal in absorption maxima is not
immediately obvious, it does imply that the ground state of 12a is
more charge separated than 13a. This in turn will be due to a com-
bination of factors such as the relative strength of the donore
acceptors units, the aromatic stabilisation energy of a benzothia-
zole versus quinoline ring system and the number of carbon atoms
between the donor nitrogen atoms and that of dicyanomethylidene
acceptor unit (i.e. 11 for 12a and 13 for 13a). Furthermore, the
comparatively high energy absorption maxima seen for 12a also
suggests that it will have the lowest molecular hyperpolarisability.
It should also be noted that the spectra obtained in THF (Fig.1) show
no evidence of H- or J-aggregation, as the absorption bands show
none of the high or low energy shoulders typically associated with
such phenomena. This is important as the polarity of THF (ε ¼ 7.5) is
similar to that of the polymers in which these chromophores would
ultimately need to be deployed (ε 1e9). Such polymers include
amorphous polycarbonate, polyimides and polyurethanes. Hence,
on this basis, it would appear that all of the chromophores will
exhibit little, if any, aggregation when incorporated into host
polymers. This in turn suggests they will respond well to poling and
better retain a non-centrosymmetric alignment post-poling.
3.2. Linear optical properties
The UVevisible spectra of all chromophores were recorded in
DMF and THF, and the data is summarised in Table 1. Furthermore,
for illustrative purposes, the spectra obtained in THF are shown in
Fig. 1a and b. For chromophores 12a,b and 13a,b there is a slight
bathochromic shift in the absorption maxima on changing from
THF to the more polar DMF, and such positive solvatochromism
indicates the chromophores have only a small degree of charge
separation in the ground state, and cannot be considered zwitter-
ionic. This needs to be considered alongside the fact that the use of
pro-aromatic donors such as BTZ, QUIN and pyridinylidene in
combination with the TCF acceptor is known to result in chromo-
phores that display high degrees of negative solvatochromism e.g.
15e17 [21]. Furthermore, X-ray crystallographic studies on ana-
logues of 16 and 17 confirms their zwitterionic nature due to the
bond order observed across the corresponding molecular back-
bones [23]. As UVevis data for 12c and 13c in DMF could not be
obtained e these compounds decompose in this solvent e it can
only be assumed that the acceptor units deployed in 12a,b and
13b,c are insufficiently powerful to induce a reversal in bond order
across the conjugated system. Furthermore, the low degree of
charge separation is probably also due to the presence of an
3.3. Quadratic nonlinear optical properties
The second-order NLO polarizability (or first hyperpolarizability
b), the static first hyperpolarizability bzzz,0 and the calculated dipole
moments of all the compounds under investigation are listed in
m
Table 1. It should be noted that there is no fluorescence contribution
from the compounds. From the values given in Table 1 it is evident
that most of the bzzz and bzzz,0 values are in general agreement with

90
M. Ashraf et al. / Dyes and Pigments 98 (2013) 82e92
Table 4
ꢀ
Hydrogen bond geometries (A, deg.) for 14.
DdH.A
DdH
H.A
D.A
DdH.A
Symmetrya
O2BeH2B...O2A
0.84
1.83
2.542(7)
142
1 ꢁ x, ꢁy, ꢁ1 ꢁ z
x, y, 1 þ z
O1WeH1WA...O2B
O1WeH1WB...O2W
O2WeH2WA...O2B
O3WeH3WA...N3B
O3WeH3WB...O2A
O4WeH4WA...S3B
O4WeH4WB...O3W
C6AeH6AA...O4W
C8AeH8AB...O4W
C9BeH9BB...S3B
C18AeH18A...O1B
C18BeH18B...O1A
C20AeH20A...O1B
C20BeH20B...O1A
C25BeH25B...O3W
0.93(10)
0.93(10)
0.92(10)
0.93(6)
0.93(12)
0.94(5)
0.9(2)
0.95
0.95
0.99
0.95
0.95
1.89(10)
1.88(10)
1.76(10)
2.05(7)
2.03(13)
2.71(13)
2.04(19)
2.57
2.43
2.84
2.41
2.42
2.794(10)
2.775(10)
2.663(10)
2.939(10)
2.899(11)
3.477(11)
2.777(15)
3.426(14)
3.409(17)
3.758(10)
3.259(11)
3.294(11)
3.215(11)
3.298(11)
3.270(13)
164(10)
163(10)
165(10)
160(11)
155(11)
139(16)
136(14)
151
171
154
149
153
1 ꢁ x, ꢁy, 1 ꢁ z
x, y, 1 þ z
x, y, z
1 ꢁ x, ꢁy, ꢁz
1 ꢁ x, 1 ꢁ y, ꢁz
1 ꢁ x, 1 ꢁ y, 1 ꢁ z
1 ꢁ x, 1 ꢁ y, 1 ꢁ z
1 ꢁ x, 1 ꢁ y, 1 ꢁ z
2 ꢁ x, 1 ꢁ y, ꢁz
1 ꢁ x, ꢁy, ꢁz
1 ꢁ x, ꢁy, ꢁz
1 ꢁ x, ꢁy, ꢁz
1 ꢁ x, ꢁy, ꢁz
1 ꢁ x, 1 ꢁ y, ꢁz
0.95
0.95
0.95
2.33
2.40
2.42
155
159
149
a
Symmetry to bring the A atom into contact.
the data obtained from the linear optical properties. Thus the
compounds with the lowest energy absorption maxima in THF (12c
and 13c) also have the highest dynamic and static hyper-
polarizabilities. This supports the two-level model equation insofar
as a red-shift in absorption maxima is associated with lower ab-
calculated dipole moment values, this suggests these compounds
are likely to have high figures of merit of approximately 5,000e
25,000 ꢀ 10ꢁ48 esu, where the figure of merit is simply the prod-
uct of the dipole moment and first hyperpolarizability, viz. m.b.
sorption energy and this in turn enhances the
b value [17].
3.4. X-ray crystallography
Also from Table 1 it is seen that the three compounds containing
a TCF acceptor (1c, 12c and 13c) undoubtedly have superior non-
linear optical responses, thus reinforcing the consistently high
performance of NLO molecules containing this moiety. Fur-
thermore, with the exception of 12a, there is little difference in NLO
response between those compounds containing either a dicyano-
methylidene or hydroxyphenylrhodanine acceptor; again this is
entirely consistent with the expected trends obtained from the
linear absorption data. There is no definitive trend when comparing
the various donor units as the highest NLO response (in THF only) is
clearly found for the BTZ derivative 12c while for the other two
types of acceptor the QUIN donor, on average, is preferable. In
addition, both the linear and second-order NLO properties of
compounds with a QUIN donor (13a,b) can be more readily tuned
by varying the dielectric constant of the surrounding medium than
compounds with either a BTZ or IND donor unit (12a,b and 1a,b). In
the latter compounds there is a smaller shift in the absorption
maxima but its impact on the static first molecular hyper-
polarizability is generally not significant.
We have managed to obtain adequate X-ray crystallographic
data for compound 14; Table 2 contains the refinement data
whereas Table 3 contains a summary of key bond lengths. The
crystals contained water solvent of crystallization (Table 2). The
asymmetric unit of 14 contains two independent copies (labeled A
& B) of the compound (Fig. 2 shows molecule B) and four water
solvate molecules. In molecule A, the butyl atom chain adopts two
conformations for the last 3 atoms (10-C12). Excluding the terminal
It is also evident that regardless of the acceptor system used, for
the most part, the new compounds reported here have superior
static and dynamic hyperpolarizabilities when compared to the
known aniline containing chromophore 2 (Table 1). However, there
is no obvious trend when comparing 12aec and 13aec with their
indoline analogues 1aec. Thus, while 1a,b exhibit the second
highest hyperpolarizabilities when compared to 12a,b and 13a,b,
the use of TCF as acceptor results in 12c and 13c being clearly su-
perior to 1c. As the TCF containing compounds consistently give the
highest values this is perhaps the most important comparison and
confirms the efficacy of using either a BTZ or QUIN donor. From
Table 1 it is also seen that there is a reasonable correlation between
the polarity of the solvent used and the magnitude of the
b value,
and with the exception of 1c and 13b, a decrease in solvent polarity
results in an increase in the dynamic and static hyperpolarisability.
As noted above, this is an encouraging trend as utilisation of the
chromophores would ultimately require their deployment in non-
polar environments such as hosteguest polymer matrices. Fur-
thermore, for the most part, the values of the dynamic
hyperpolarizability bzzz are between of 500e1000 ꢀ 10ꢁ30 esu at
800 nm which is a very respectable range. Coupled with the
Fig. 3. Crystal packing of 14 [27]; some of the main attractive contacts are shown as
dotted lines (see Table 4). Atom H3A is H3WA. Symmetry (i): 1 ꢁ x, 1 ꢁ y, 1 ꢁ z.

M. Ashraf et al. / Dyes and Pigments 98 (2013) 82e92
91
[4] Marder SR, Cheng LT, Tiemann BG, Friedli AC, Blanchard-Desce M, Perry JW,
et al. Large first hyperpolarizabilities in pushepull polyenes by tuning of the
bond length alternation and aromaticity. Science 1994;263:511e4.
[5] Blanchard-Desce M, Runser C, Fort A, Barzoukas M, Lehn JM, Bloy V, et al.
Large quadratic hyperpolarizabilities with donoreacceptor polyenes func-
tionalized with strong donors. Comparison with donoreacceptor diphe-
nylpolyenes. Chemical Physics 1995;199:253e61.
[6] Cheng LT, Tam W, Stevenson SH, Meredith GR, Rikken G, Marder SR. Exper-
imental investigations of organic molecular nonlinear optical polarizabilities.
1. Methods and results on benzene and stilbene derivatives. Journal of
Physical Chemistry 1991;95:10631e43.
4-hydroxyphenyl ring, the molecules are approximately planar,
with both lying parallel to the (2,ꢁ2,1) plane. The terminal 4-
hydroxyphenyl rings make angles of 67.1(4)ꢂ (in A) and 65.9(4)ꢂ
(B, Fig. 2) to the 5-membered thioxo rings (S1,C20eC22,N4). The
root mean square bond and angle fits betweenꢂthe two molecules,
ꢀ
excluding the butyl atoms, are 0.018 A and 1.33 [24]. These similar
dimensions (Table 3) confirm that within the limited resolution
provided by the analysis there are no significant deviations be-
tween the two copies, or with a previously reported compound (1b)
[16]. The molecules are not exactly superimposable with molecule
A twisting further from planarity around the central C14eC19 ring:
the interplanar angles with the 5-membered thioxo rings are
15.9(4)ꢂ and 10.1(4)ꢂ respectively (molecules A & B). The molecular
contents are bound together via a comprehensive set of Oe
H...O(water & hydroxyl), O(water)eH...N(azo), O(water)eH...S, and
CeH...O(carbonyl & water) interactions (Table 4; Fig. 3 shows the
conventional hydrogen bonding set of these interactions). There are
bifurcated interactions involving two acceptors, the hydroxyl atom
O2B and water O4W. Molecules lying “side by side” are linked by
weaker CeH...O(]C) interactions completing R12(6), R12(7) and
R22(10) ring motifs [25] The overall packing is thus based on a full 3-
dimensional interaction set through the water solvate molecule
interactions. Lastly it needs to be noted that the molecules of 14 are
packed centrosymmetrically in the crystal structure, meaning that
the crystals will not exhibit a macroscopic NLO response. Rather 14
e and presumably all the other chromophores e will need to be
incorporated into polymeric films and subjected to poling in order
to have the desired macroscopic response.
[7] Cheng LT, Tam W, Marder SR, Stiegman AE, Rikken G, Spangler CW. Exper-
imental investigations of organic molecular nonlinear optical polarizabilities.
2. A study of conjugation dependences. Journal of Physical Chemistry 1991;
95:10643e52.
[8] Rao VP, Cai YM, Jen AKY. Ketene dithioacetal as a
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nucleus can be readily extended. Linear absorption studies show
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Hyper-Raleigh scattering results once again show that the TCF
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indoline donor, and this is most likely a reflection of the pro-
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have acceptable thermal stabilities and this confirms their suit-
ability for high temperature poling in order to examine their mac-
roscopic NLO response. These studies are currently underway.
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This work has been supported by the New Zealand Ministry for
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the University of Leuven (GOA/2006/03).
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