Synthesis and hyperpolarizabilities of high temperature triarylamine-polyene chromophores

Article abstract of DOI:10.1016/j.tetlet.2005.03.140

The synthesis and hyperpolarizabilities of a series of push-pull chromophores containing bis-(4-methoxyphenyl)-amine donor and efficient acceptors bridged with ring locked polyene are presented. The chromophores are readily soluble in common organic solvents and exhibit high thermal decomposition temperatures (highest T_d = 330°C). Molecular hyperpolarizabilities (β) of the chromophores were measured by Hyper Rayleigh Scattering (HRS) at 1604 nm (highest β = 20,000 × 10 ^-30 esu). These chromophores can be used to develop electro-optic (EO) materials due to their large optical nonlinearities, good absorption characteristics, high thermal decomposition temperatures, and excellent solubility with organic solvents and polymeric materials.

Full text of DOI:10.1016/j.tetlet.2005.03.140

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 3913–3916
Synthesis and hyperpolarizabilities of high temperature
triarylamine-polyene chromophores
S. Suresh,a Huseyin Zengin,a Bryan K. Spraul,a Takafumi Sassa,b
Tatsuo Wadab and Dennis W. Smith, Jr.a,*
aDepartment of Chemistry, Clemson University, Center for Optical Materials Science and Engineering Technologies
(COMSET), Clemson, SC 29634, USA
bSupramolecular Science Lab., RIKEN, 2-1, Hirosawa, Wako 351-1098, Japan
Received 23 February 2005; revised 19 March 2005; accepted 21 March 2005
Available online 12 April 2005
Abstract—The synthesis and hyperpolarizabilities of a series of push–pull chromophores containing bis-(4-methoxyphenyl)-amine
donor and efficient acceptors bridged with ring locked polyene are presented. The chromophores are readily soluble in common
organic solvents and exhibit high thermal decomposition temperatures (highest Td = 330 ꢀC). Molecular hyperpolarizabilities (b)
of the chromophores were measured by Hyper Rayleigh Scattering (HRS) at 1604 nm (highest b = 20,000 · 10À30 esu). These
chromophores can be used to develop electro-optic (EO) materials due to their large optical nonlinearities, good absorption
characteristics, high thermal decomposition temperatures, and excellent solubility with organic solvents and polymeric materials.
ꢁ 2005 Elsevier Ltd. All rights reserved.
Organic nonlinear optical (NLO) chromophores with
enhanced thermal and chemical stability and a high
hyperpolarizability are of interest for photonic applica-
tions.1 Quantum mechanical calculations have helped
to identify polyene and thiophene based chromophores
with the highest nonlinearity.2 Recently, we have re-
ported the synthesis of heterocyclic bridged triarylamine
chromophores with high hyperpolarizability (b).3 Here,
we report the synthesis and hyperpolarizabilities of ring
locked polyene and polyene–thiophene derived chro-
mophores 7–12 with the same triarylamine donor. The
chromophores are soluble in common organic solvents,
show good thermal stability, and adequate absorption
behavior. The synthesis, thermal, linear, and nonlinear
optical properties are discussed.
The rigid isophorone bridge also causes crystallization
and solubility problems. Usage of bulky protected
donor groups,6 attachment of floppy side chains,7
attachment of bulky groups to the acceptor,8 and use
of dendritic structures9 are methods sought for minimiz-
ing these interactions. It has also been recognized that
the addition of aromatic rings in the donor may impose
a quinoidal bonding pattern and help prevent unfavor-
able organization of the chromophores.11 Also the use
of diarylamino electron donor substituents in extended
donor–acceptor substituted chromophores results in
significant improvement in thermal stability compared
to the alkyl amino substituted derivatives.3,10
Molecules with 4-(N,N-di-p-anisylamino)phenyl moie-
ties as the electron donor have shown long-lived charge
separation and have been used in multiphoton absorb-
ing materials.12 In the present study, triarylamine do-
nors are bridged to powerful acceptors via ring locked
polyenes and polyene linked thiophene moieties to
give chromophores 7–12 (Fig. 1). The triarylamine
polyene aldehyde 5 was synthesized in five steps as
shown in Scheme 1. Ullmann coupling of 4-iodoanisole
with aniline yielded N,N-bis(4-methoxyphenyl)-N-phen-
ylamine (1) in 65% yield. A Vilsmeier–Haack reaction of
Ring locked phenyltetraene-bridged chromophores
(CLD)4 and analogues in general exhibit high b values
and electro-optic (EO) devices derived from them have
shown commercial promise. Due to their high ground
state dipole moment induced head to tail interactions,
noncentrosymmetric alignment remains a challenge.5
Keywords: Triarylamine chromophores; Hyperpolarizability.
*
1
provided 4-[bis-(4-methoxyphenyl)amino]benzalde-
Corresponding author. Tel.: +86 46565020; fax: +86 46566613;
e-mail: dwsmith@clemson.edu
hyde (2) in 78% yield.3 Condensation of 2 with
0040-4039/$ - see front matter ꢁ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.03.140

3914
S. Suresh et al. / Tetrahedron Letters 46 (2005) 3913–3916
O
O
O
N
N
O
N
S
O
8
7
N
NC
O
O
CN
O
N
N
O
10
O
O
O
9
NC
O
CN
NC
CN
NC
CN
O
O
N
N
S
12
O
NC
11
CN
CN
CN
Figure 1. Triarylamine derived chromophores 7–12.
All intermediates and chromophores were isolated as
pure compounds as evidenced by 1H NMR, 13C
NMR, and high resolution MS or MALDI-TOF. The
electron acceptors 13 and 14 were prepared as reported
previously.15,16 Diethyl thienylmethyl phosphonate was
prepared from 2-methylthiophene using a standard pro-
cedure.17 Di-iso-propyl cyanomethyl phosphonate was
chosen for the synthesis of 4 to favor the formation of
the trans isomer from which 5 was isolated with a 8:2,
E:Z ratio. The highly conjugated aldehyde 5 was stable
at cold temperature over long periods of time.
O
O
O
O
N
(ii)
(i)
N
NH2
2
CHO
(iii)
1
O
O
O
O
O
O
N
N
N
(v)
(iv)
The electronic absorption and thermal stability of the
chromophores are summarized in Table 1. As expected
the increase of acceptor strength induces a bathochro-
mic shift of the kmax. For example, the powerful tricy-
anofuran (TCF) acceptor (9) resulted in a ꢀ40 nm red
shift over the diethylthiobarbiturate acceptor (8). Simi-
larly an increase in conjugation using thiophene (12)
has increased the absorption wavelength by 20 nm with
the same type of donor–acceptor groups. Chromophore
11 gave the lowest absorption due to the presence of the
weak dicyanovinyl electron acceptor.
O
CHO
5
CN
4
3
Scheme 1. Synthesis of parent aldehyde 5. Reagents and conditions: (i)
CuI, 4-iodoanisole; (ii) DMF, POCl3; (iii) isophorone, Na, EtOH; (iv)
n-BuLi, Di-iso-propylcyanomethyl phosphonate; (v) DIBAL-H,
CH2Cl2.
The decomposition temperature, Td, of the chromoph-
ores was measured by thermal gravimetric analysis
(TGA) in N2, with a heating rate of 10 ꢀC/min. The
chromophores exhibit Td ranging from 179 to 330 ꢀC.
Compounds containing the dicyano acceptor have lower
Td values compared to others. An extension of conjuga-
tion has decreased the Td values as expected.
isophorone in basic conditions produced ketone 3 in
65% yield.13 Reaction of 3 with di-iso-propyl cyano-
methyl phosphonate gave 4 (97%) and successive reduc-
tion using DIBAL-H gave aldehyde 5 in 85% yield.14
Knoevenagel condensation of 5 with different acceptors
gave chromophores 7–12 as shown in Scheme 2.18 Chro-
mophore 11 was synthesized by the condensation of 2
with 13 in basic conditions. Condensation of 5 with
diethyl thienylmethyl phosphonate (TMP) followed by
lithiation and treatment with DMF gave aldehyde 6 in
80% yield (7:3, E:Z). Knoevenagel condensation of 6
with 14 gave chromophore 12 in 66% as shown in
Scheme 2.
Additional tests on thermal stability for selected chro-
mophores were performed by dispersing them into
highly thermally stable perfluorocyclobutyl (PFCB) aro-
matic ether polymers19 and heating them at 200 ꢀC for
45 min under N2 atmosphere. Chromophore 9 exhibited
good thermal stability as the UV–visible spectra of the

S. Suresh et al. / Tetrahedron Letters 46 (2005) 3913–3916
3915
O
O
O
O
O
O
N
N
N
(vi)
(vii)
(viii)
5
12
6
A
S
S
A
O
O
O
CN
A
CN
CN
NC
CN
N
N
CN
CN
O
S
14
13
Scheme 2. Synthesis of chromophores 7–12 (in Fig. 1). Reagents and conditions: (vi) and (viii) acceptor, Et3N; (vii) TMP, t-BuOK, THF, n-BuLi,
DMF. Compounds 7–10 were synthesized from 5 [A = CN–CH2–CN (7), diethyl thiobarbiturate (8), TCF (9), and 13 (10)]. Compound 11 was
synthesized from 2 (A = 13). Compound 12 was synthesized from 6 (A = 14).
b value of 20,000 · 10À30 esu placing it among the high-
est recorded values to date.
Table 1. Thermal, linear, and nonlinear optical properties of 7–12
Chromophore kmax Td
(nm)a (ꢀC)b
b (10À30 esu) b0 (10À30 esu)c
7
550
627
670
585
515
690
267
272
330
258
230
179
—
—
Acknowledgements
8
9
20,000
2000
700
4000
700
We thank the Defense Advanced Research Projects
Agency (DARPA), D.S. thanks the National Science
Foundation (NSF) (CAREER Award DMR-9985160)
and South Carolina EPSCoR for financial support. D.
W. Smith is a Cottrell Scholar of Research Corporation.
10
11
12
400
—
a kmax measured in CHCl3.
b Td is the onset temperature of TGA in N2 with a scanning rate of
10 ꢀC/min.
c Oudar–Chemla method.
References and notes
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Finally, b values for chromophores 7–12 were evaluated
using Hyper Rayleigh Scattering (HRS) at 1604 nm20
and the results are shown in Table 1. All the values were
obtained by the external reference method as previously
described.3 For chromophore 9, the linear absorption of
the second harmonic was corrected using BeerÕs law.21
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In summary, we have accomplished the efficient synthe-
sis of a series of chromophores (7–12) based on ring
locked polyene–thiophene as electron bridge and dime-
thoxy triarylene amine as electron donor. The good
thermal stability and the solubility of the chromophores
are demonstrated. Chromophore 9 exhibited the highest
9. Ma, H.; Chen, B.; Sassa, T.; Dalton, L. R.; Jen, A. K.-Y.
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3916
S. Suresh et al. / Tetrahedron Letters 46 (2005) 3913–3916
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added TCF (1.2 equiv) and catalytic amount of Et3N.
The dark reaction mixture was heated to reflux for 3 h
and monitored by TLC. After complete disappearance of
aldehyde, the reaction mixture was cooled to room
temperature, poured onto ice cold water, and extracted
with excess CH2Cl2. The combined organic layer was
washed with water, dried (MgSO4), and concentrated in
vacuo. The residue was purified by chromatography
(CH2Cl2) to afford (65%) green solid. 1H NMR
(300 MHz, CDCl3) d 8.08 (t, 16.4 Hz, 1H), 7.39 (d,
2H), 7.08 (d, 4H), 6.86–6.79 (m, 8H), 6.37 (s, 1H), 6.32
(d, 7.7 Hz, 1H), 6.24 (d, 14.6 Hz, 1H), 3.80 (s, 6H),
2.41 (s, 2H), 2.32 (s, 2H), 1.25 (s, 6H), 0.96 (s, 6H). 13C
NMR (75.5 MHz, CDCl3) d 178.0, 174.0, 156.4, 154.0,
151.2, 148.3, 145.1, 140.0, 132.3, 130.8, 128.3, 127.4,
126.1, 119.0, 116.5, 114.7, 113.0, 112.2, 98.7, 96.3, 56.0,
48.1, 41.7, 39.5, 32.0, 29.7, 28.4, 26.5. HR-MS m/z:
660 (M+).
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of aldehyde 5 (1 equiv) in dry CH2Cl2 (10 mL/g) was
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