Synthesis and non-linear optical properties of new ionic species: Tolan and diphenylbutadiyne with trimethylammonio and dimethylamino groups

Article abstract of DOI:10.1002/poc.870

As new ionic organic species for second-order non-linear optical (NLO) materials, 4-{[4-(dimethylamino)phenyl]ethynyl)phenyltrimethylarnmonium iodide (1a), 4-{[4-(dimethylamino)phenyl]butadiynyl}phenyltri-methylammoniura iodide (2a) and their derivatives

Full text of DOI:10.1002/poc.870

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2005; 18: 468–472
Published online 22 September 2004 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/poc.870
Synthesis and non-linear optical properties of new
ionic species: tolan and diphenylbutadiyne with
trimethylammonio and dimethylamino groups
Hirohito Umezawa,1* Shuji Okada,1 Hidetoshi Oikawa,2 Hiro Matsuda3 and Hachiro Nakanishi1
1Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
2Nanomaterials Laboratory, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan
3National Institute of Advanced Industrial Science and Technology, Central 1, 1-1-1 Higashi, Tsukuba 305-8561, Japan
Received 2 March 2004; revised 3 July 2004; accepted 26 July 2004
ABSTRACT: As new ionic organic species for second-order non-linear optical (NLO) materials, 4-{[4-(dimethyla-
mino)phenyl]ethynyl}phenyltrimethylammonium iodide (1a), 4-{[4-(dimethylamino)phenyl]butadiynyl}phenyltri-
methylammonium iodide (2a) and their derivatives with 4-substituted benzensulfonate instead of iodide were
successfully synthesized. The transparent wavelength region of 1a is wider than that of a typical NLO molecule,
p-nitroaniline (pNA), whereas 2a and pNA have similar transparent regions. The experimental and calculated first
hyperpolarizabilities (ꢀ) of 1a and 2a were found to be about 7 and 11 times, respectively, larger than those of pNA.
Even when the volume factor was taken into account, the cationic part of 1a was found to be a better second-order
NLO material than pNA derivatives. Four second-order NLO-active crystals were found out of 12 salts synthesized.
Copyright # 2004 John Wiley & Sons, Ltd.
KEYWORDS: DAST; second-order non-linear optical materials; anilinium salt; organic ionic crystal; hyper-Rayleigh
scattering
INTRODUCTION
ethenyl}pyridinium p-toluenesulfonate (DAST).5–7 Third,
large first hyperpolarizabilities (ꢀ) are expected owing
to the unconventionally polarized structures caused by
charged ꢁ-conjugation systems. In a previous computa-
tional and experimental study, we clarified that the large
dipole moment difference between the ground and ex-
cited states (Áꢂeg) resulted in stilbazolium with large ꢀ,8
which is proportional to Áꢂeg in the two-level model.9
Owing these advantageous features of ꢁ-conjugated ionic
species for second-order NLO properties, we synthesized
a variety of stilbazolium analogues.10–14
In the present study, we extended the ionic species by
changing the cationic acceptor portion from an N-methyl-
pyridinium ring to an N,N,N-trimethylanilinium ring.
Differences between pyridinium and anilinium cations
in electronic resonance structures are shown in Fig. 1,
where the left- and right-hand structures have more
contributions in the ground and excited states, respec-
tively. Although the two structures for pyridinium can be
drawn by just shifting the bonds and charge, those for
anilinium cannot be drawn without generating charge
separation in the ꢁ-conjugated system. This qualitatively
indicates that the excited state of the anilinium cation is
destabilized compared with the pyridinium cation and a
wider HOMO–LUMO gap was expected to break through
the trade-off relationship between absorption cutoff and
ꢀ.15 We selected the dimethylamino group as a typical
donor and tolan (diphenylethyne) and diphenylbutadiyne
In the last two decades, organic non-linear optical (NLO)
materials have been extensively studied owing to their
large optical non-linearity and ultrafast response origi-
nating from their ꢁ-conjugation systems.1–3 For second-
order NLO materials, the typical molecular design was
established to be ꢁ-conjugation systems possessing an
electron donor and acceptor at both ends of the systems,
and non-ionic species such as p-nitroaniline (pNA)
derivatives have mainly been investigated. We started a
series of studies on organic ionic species for second-order
non-linear optics because of their several advantages
compared with non-ionic species. First, they have higher
melting-points and hardness in general due to the
Coulombic intermolecular interaction in crystals. Second,
non-centrosymmetric crystal structures with proper
molecular alignment can be achieved not by direct
modification of the NLO species but by simple exchange
of the counter ion, as demonstrated by Meredith.4
We found that a combination of p-toluenesulfonate with
NLO-active stilbazolium often gave non-centrosymmetric
structures, e.g. 1-methyl-4-{2-[4-(dimethylamino)phenyl]-
*Correspondence to: H. Umezawa, Department of Chemistry and
Biochemistry, Fukushima National College of Technology, 30 Aza
Nagao Taira Kamiarakawa, Iwaki, 970-8034, Japan
E-mail: umezawa@fukushima-nct.ac.jp
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 468–472

SYNTHESIS AND NON-LINEAR OPTICAL PROPERTIES OF NEW IONIC SPECIES
469
EXPERIMENTAL
Iodide salts 1a and 2a were synthesized according to
Fig. 3. 4-Ethynyl-N,N-dimethylaniline (7) was prepared
by the Sonogashira reaction20 of 5 followed by aceto-
nolysis.21 Compounds 5 and 7 were coupled by the
Sonogashira reaction again to give bis[4-(dimethylami-
no)phenyl]ethyne (8). Bis[4-(dimethylamino)phenyl]bu-
tadiyne (9) was synthesized by the oxidative coupling
reaction22 of 7. Careful asymmetric methylation of 8 and
9 with iodomethane gave salts 1a and 2a, respectively.
The iodide anions of 1a and 2a were converted to other
anions such as p-aminobenzenesulfonate, p-toluenesul-
fonate, benzenesulfonate, p-chlorobenzenesulfonate and
p-nitrobenzenesulfonate, as shown in Fig. 4. Details of
the synthetic procedures are described below.
Figure 1. Resonance structures of N-methylpyridinium
and N,N,N-trimethylanilinium with an electron-donationg
group (D)
4-Iodo-N,N-dimethylaniline (5). Into a stirred mixture of
4 (40 g), DMF (100 ml) and NaHCO3 (34 g), iodo-
methane (72 g) was poured dropwise and stirred for
40 h at room temperature and the resulting mixture was
poured into 500 ml of cold water. The precipitate obta-
ined was filtered and dissolved in tetrahydrofuran. Then it
was filtered off and solvent in the filtrate was removed.
Recrystallization of the residual solid from methanol
gave 5 (25 g, 55%) as white crystals, m.p. 79 ꢀC. 1H NMR
(CDCl3), ꢃ 2.92(s, 6H), 6.49 (d, J ¼ 9.0 Hz, 2H), 7.46 (d,
J ¼ 9.0 Hz, 2H). Found: C, 38.71; H, 4.34; N, 5.70%.
Calculated for C8H10NI: C, 38.89; H, 4.08; N, 5.67%.
Figure 2. Structures of 1a, 2a and 3a
skeletons as ꢁ-conjugation systems. 4-{[4-(Dimethyla-
mino)phenyl]ethynyl}phenyltrimethylammonium iodide
(1a), 4-{[4-(dimethylamino)phenyl]butadiynyl}phenyl-
trimethylammonium iodide (2a) (shown in Fig. 2) and
their derivatives with different counter anions were
synthesized to clarify their linear and non-linear optical
properties. X-ray crystallographic analysis of 1a was
also investigated. Although tolan16–18 and diphenylbuta-
diyne19 derivatives have been studied as second-order
NLO materials, they were all non-ionic compounds and
those with an anilinium-type structure were studied here
for the first time.
4-(3-Methyl-3-hydroxy-1-butynyl)-N,N-dimethylaniline
(6). To a mixture of 5 (40 g), dichlorobis(triphenylpho-
sphine)palladium(II) (1.4 g), copper(I) chloride (0.1 g)
and triethylamine (300 ml), 2-methyl-3-butyn-2-ol (23 g)
was added and stirred for 2 days at 80 ꢀC under a nitrogen
atmosphere. Water (300 ml) was added and the mixture
Figure 3. Synthetic procedure for 1a and 2a
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 468–472

470
H. UMEZAWA ET AL.
Figure 4. Counter anion exchanges of 1a and 2a using silver salts of 4-substituted benzenesulfonate
was extracted with diethyl ether (300mlꢁ 3). The organic
phase was dried over Na2SO4 and filtered. Solvent in the
filtrate was removed under reduced pressure. Purification
of the residue on silica gel 60 [eluent: hexane–ethyl
acetate (10:1)] gave 6 (20 g, 71%) as a yellow powder,
m.p. 88ꢀC. 1H NMR (CDCl3), ꢃ 1.60 (s, 6H), 2.04 (s, 1H),
2.96 (s, 6H), 6.61 (d, J ¼ 9.0 Hz, 2H), 7.29 (d, J ¼ 9.0 Hz,
2H). Found: C, 76.70; H, 8.37; N, 6.80%. Calculated for
C13H17NO: C, 76.81; H, 8.43; N, 6.89%.
Bis[4-(dimethylamino)phenyl]butadiyne (9). Copper(I)
chloride (100 mg) was dissolved in 5 ml of acetone
and N,N,N0,N0-tetramethylethylenediamine (116 mg), then
acetone (100 ml) and 7 were added and stirred with
oxygen bubbling for 6 h. The precipitate was filtered
and washed with acetone to give 9 (2.0 g, 84%) as a
1
light-yellow powder, m.p. 216 ꢀC. H NMR (CDCl3),
ꢃ 2.99 (s, 12H), 6.61 (d, J ¼ 8.9 Hz, 4H), 7.39 (d,
J ¼ 8.9 Hz, 4H). Found: C, 82.69; H, 6.71; N, 9.68%.
Calculated for C20H20N2: C, 83.30; H, 6.99; N, 9.71%.
4-Ethynyl-N,N-dimethylaniline (7). To a mixture of 6
(20 g) and toluene (300 ml), potassium hydroxide (20 g)
was added and the mixture was refluxed for 5 h. After
filtration, the solvent was removed under reduced pressure.
Purification of the residue on silica gel 60 [eluent: hexane–
ethyl acetate (20:1)] gave 7 (11 g, 87%) as an orange
4-{[4-(Dimethylamino)phenyl]butadiynyl}phenyltrimethy-
lammonium iodide (2a). A similar procedure to the
synthesis of 1a was performed using 9 instead of 7 to
give 2a as a light-yellow powder in 68% yield, m.p.
244 ꢀC. 1H NMR (CD3OD), ꢃ 3.00 (s, 6H), 3.67 (s, 9H),
6.69 (d, J ¼ 9.0 Hz, 2H), 7.35 (d, J ¼ 9.0 Hz, 2H), 7.73
(d, J ¼ 9.3 Hz, 2H), 7.92 (d, J ¼ 9.3 Hz, 2H). Found: C,
58.45; H, 5.38; N, 5.97%. Calculated for C21H23IN2: C,
58.61; H, 5.39; N, 6.51%.
1
powder, m.p. 56 ꢀC. H NMR (CDCl3), ꢃ 1.57 (s, 1H),
2.97 (s, 7H), 6.62 (d, J ¼ 8.5 Hz, 2H), 7.36 (d, J ¼ 8.5 Hz,
2H). Found: C, 82.48; H, 7.68; N, 9.52%. Calculated for
C10H11N: C, 82.72; H, 7.64; N, 9.65%.
Bis[4-(dimethylamino)phenyl]ethyne (8). To a mixture
of 7 (400 mg), dichlorobis(triphenylphosphine)palladiu-
m(II) (39 mg), copper(I) chloride (3 mg) and triethyla-
mine (25 ml), 5 (680 mg) was added and the mixture was
stirred for 1 day at 80 ꢀC under a nitrogen atmosphere.
After filtration, the solvent was removed under reduced
pressure. Purification of the residue on silica gel [eluent:
hexane–ethyl acetate (10:1)] gave 8 (160 mg, 22%) as a
colorless powder, m.p. 196 ꢀC. 1H NMR (CDCl3), ꢃ 2.97
(s, 12H), 6.65 (d, J ¼ 9.0 Hz, 4H), 7.38 (d, J ¼ 9.0 Hz,
4H). Found: C, 81.32; H, 7.75; N, 10.49%. Calculated for
C18H20N2: C, 81.78; H, 7.63; N, 10.60%.
General procedure for counter anion exchanges. To a
methanolic solution of iodide 1a or 2a (10 mmol), a
methanolic solution of the silver salt of benzenesulfo-
nates b–f (10 mmol) were added. The silver iodide pre-
cipitated in the resulting mixture was filtered off. The
solvent of the filtrate was removed under reduced pres-
sure and recrystallization from methanol gave 1b–1f and
2b–2f in 50–80% yield.
Measurements. Melting-points were determined using a
differential scanning calorimeter (Perkin-Elmer pyres
diamond DSC). The chemical structures of the com-
1
pounds obtained were confirmed by H NMR spectro-
4-{[4-(Dimethylamino)phenyl]ethynyl}phenyltrimethylamm-
onium iodide (1a). Into a mixture of 8 (1.3 g) and
chloroform (100 ml), iodomethane (3 g) was poured
dropwise and stirred for 4 days at room temperature.
Then precipitate was collected by filtration and recrys-
tallized from methanol to give 1a (1.0 g, 56%) as a light-
scopy (JEOL Lambda 400) and elemental analysis
(IMRAM, Tohoku University). UV–visible absorption
spectra in methanolic solution were recorded on a Jasco
V-570 spectrophotometer. Hyper-Rayleigh scattring
(HRS) measurements23 for 1a and 2a were performed
by using a nanosecond Nd:YAG laser (Coherent Infinity
40–100) at 1064 nm. These measurements were executed
in the methanolic solution and pNA was used as an
external standard,24 whose ꢀ value at 1064 nm in metha-
nol is 3.45 ꢁ 10ꢂ 29 esu.9 The ꢀ values obtained were
corrected to ꢀ at zero frequency (ꢀ0,expt) according to the
1
yellow powder, m.p. 208 ꢀC. H NMR (CD3OD), ꢃ 2.99
(s, 6H), 3.67 (s, 9H), 6.72 (d, J ¼ 9.1 Hz, 2H), 7.36 (d,
J ¼ 8.6 Hz, 2H), 7.68 (d, J ¼ 9.1 Hz, 2H), 7.88 (d,
J ¼ 8.6 Hz, 2H). Found: C, 56.09; H, 5.63; N, 6.86%.
Calculated for C19H23IN2: C, 56.17; H, 5.71; N, 6.89%.
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 468–472

SYNTHESIS AND NON-LINEAR OPTICAL PROPERTIES OF NEW IONIC SPECIES
471
two-level model. The ꢀ values at zero frequency (ꢀ0,calc
)
ꢅmax ("max) of 1 and 2 are about double those of pNA
because of the increased number of ꢁ-electrons in the
conjugation system for 1 and 2.
were also obtained together with Áꢂeg by the semi-
empirical molecular orbital (MO) calculation using MO-
PAC94 PM3 (CAChe version 4.1.1) for their optimized
structures. SHG activities of crystals were confirmed by
irradiation with the Nd:YAP laser beam at 1079 nm from
an Elmas L-100. This was conducted only for qualitative
purposes to remove the centrosymmetric crystals from
further investigation. X-ray crystallographic analysis was
performed using a Mac Science MXC3 diffractometer
Since the ꢅcutoff values of the related compounds are
shorter than 532 nm, their ꢀ values could be properly
evaluated by the HRS method using a Nd:YAG laser beam
at 1064 nm. The ꢀ0,expt values obtained for 1a and 2a
were 1.14 ꢁ 10ꢂ 28 and 1.06 ꢁ 10ꢂ 28 esu, respectively,
which are about seven times larger than those of pNA. By
MO calculations, we also obtained ꢀ0,calc and Áꢂeg
values, which are summarized in Table 1 together with
the experimental values mentioned above. The ꢀ0,calc
values of 1 and 2 are about 11 times larger than those
of pNA, and a similar tendency was verified by the
experimental results. According to the two-level model,
ꢀ is proportional to Áꢂeg, f and Eeg ꢂ 3, where f is
oscillator strength and Eeg is excitation energy from the
ground state to the excited state. Since f is considered to
be roughly proportional to "max and Eeg is inversely
proportional to ꢅmax, we can estimate the enhancement
factors of ꢀ values of 1 and 2 from the values in Table 1.
Among the three parameters, the Áꢂeg values of 1 and 2
˚
with an Mo Kꢄ source (ꢅ ¼ 0.71073 A) for a crystal of 1a
grown in methanolic solution by the slow evaporation
method. Cell parameters were determined from the ob-
served setting angles of 22 preliminary reflections. The
crystal structure was determined by the direct method and
refined by full-matrix least-squares procedures using the
CRYSTAN program. Non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were attached to their
parent atoms by fixed bond lengths and idealized bond
angles and were refined isotropically.
RESULTS AND DISCUSSION
are about three to four times larger than those of pNA, the
"
3
values are about double, and the ꢅmax values are
max
The UV and visible absorption spectra of iodide salts 1a
and 2a in methanol are shown in Fig. 5 together with
those of pNA in methanol. The longest absorption max-
imum wavelength (ꢅmax) of 1a is 21 nm shorter than that
of pNA, whereas 2a has a 7 nm longer ꢅmax compared
with pNA. However, the absorption cutoff wavelength
(ꢅcutoff) of 2a is shorter than that of pNA. Hence the new
ionic species 2 can be used in the same wavelength range
as pNA derivatives irrespective of the extended ꢁ-con-
jugation system of 2. Cation 1 has the wider transparent
region than pNA. The corresponding pyridinium analo-
gue to 1a, i.e. 1-methyl-4-[4-(dimethylamino)pheny-
lethynyl]pyridinium iodide (3a), has a ꢅmax in methanol
at 450 nm which is the 102 nm longer than the ꢅmax of 1a.
Hence the wider HOMO–LUMO gap of 1a than that of
3a was confirmed. The molar absorption coefficients at
almost the same. Hence the largest contribution to en-
hancing the ꢀ values of 1 and 2 comes from Áꢂeg. This
result is the same as for stilbazolium derivatives studied
previously.8
Since the bulk NLO property expresses performance in
a unit volume, ꢀ divided by the molecular volume is a
good index to estimate the bulk property. Actually, 1a
and 2a occupy a larger volume in crystals than pNA, and
it is better to take this factor into accout. In the present
study, the molecular shapes are linear and ꢀ divided by the
molecular length is also valid for comparison. The
calculated molecular lengths (L) of pNA, 1 and 2 are
˚
about 6.7, 15.9 and 18.7 A, respectively. Using ꢀ0,calc and
L, the ꢀ0,calc/L ratios for pNA, 1 and 2 were calculated as
1, 4.5 and 4.2, respectively. In actual crystals, cations 1
and 2 accompany counter anions, and the ratios become
lower owing to the counter anion volume. However, when
a counter anion possessing a smaller volume than the
cation is selected, the ratios become no less than half of
the calculated values above. From these results, the order
of bulk NLO property was estimated to be 1 > 2 > pNA.
Hence 1 is a better ionic species for second-order NLO
materials. The ꢁ-conjugation elongation effect of the
Table 1. Values related to optical properties
Experimental values
Calculated values
ꢅmax
"
ꢀ0,expt
ꢀ0,calc Áꢂeg
max
(nm) (104 l molꢂ1 cmꢂ1) (10ꢂ30 esu) (10ꢂ30 esu) (D)
1a
2a
pNA 369
348
376
3.3
3.1
1.6
114
106
15.7
88.5
98.0
8.38
19.5
26.1
6.05
Figure 5. UV and visible absorption spectra of pNA (dotted
curve), 1a ( dot-dashed curve) and 2a (solid curve) in
methanol
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 468–472

472
H. UMEZAWA ET AL.
Table 2. Crystallographic data for 1a
angle between the polar b axis and the long axis of the
cation is unfortunately about 89.9 ꢀ, with the result that
the second-order NLO coefficient of the single crystal is
close to zero.
In conclusion, we found that tolan derivatives 1 with
trimethylammonio and dimethylamino groups are
organic ionic species with better second-order NLO pro-
perties than pNA. Further research to optimize the polar
alingment of the cations and investigation of cation modi-
fication are in progress to improve the optical properties
of the anilinium salts.
Formula
C19H23N2I
406.3
Monoclinic
P21
Formula weight
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
ꢀ( ꢀ)
19.80(1)
8.017(5)
5.876(5)
96.13(6)
927.57(1)
2
˚
V (A3)
Z
Dx (mg mꢂ3
)
1.454
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R
0.037
wR
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Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 468–472