Synthesis of a nickel bis(dithiolene) complex with strong near-infrared two-photon absorption

Article abstract of DOI:10.1080/15421400801924979

The diketones 4,4'-di[3,4-bis(n-dodecyloxy)styryl]benzil and 4,4'-di[3,4-bis(n-dodecyloxy)phenylethynyl]benzil have been synthesized from 4,4'-dibromobenzil using Heck coupling with the appropriate styrene and Sonogashira coupling with the appropriate phe

Full text of DOI:10.1080/15421400801924979

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Synthesis of a Nickel
Bis(dithiolene) Complex with
Strong Near-Infrared Two-
Photon Absorption
Jian-Yang Cho a b , Jie Fu c , Lazaro A. Padilha c ,
Stephen Barlow a b , Eric W. Van Stryland c , David J.
Hagan c , Maximilienne Bishop b & Seth R. Marder a b
a School of Chemistry and Biochemistry and Center
for Organic Photonics and Electronics , Georgia
Institute of Technology , Atlanta , Georgia , USA
b Department of Chemistry , University of Arizona ,
Tucson , Arizona , USA
c College of Optics and Photonics: CREOL and
FPCE, Department of Physics , University of Central
Florida , Orlando , Florida , USA
Published online: 31 Aug 2012.
To cite this article: Jian-Yang Cho , Jie Fu , Lazaro A. Padilha , Stephen Barlow ,
Eric W. Van Stryland , David J. Hagan , Maximilienne Bishop & Seth R. Marder
(2008) Synthesis of a Nickel Bis(dithiolene) Complex with Strong Near-Infrared Two-
Photon Absorption, Molecular Crystals and Liquid Crystals, 485:1, 915-927, DOI:
10.1080/15421400801924979
To link to this article: http://dx.doi.org/10.1080/15421400801924979
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Mol. Cryst. Liq. Cryst., Vol. 485, pp. 167=[915]–179=[927], 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400801924979
Synthesis of a Nickel Bis(dithiolene) Complex
with Strong Near-Infrared Two-Photon Absorption
Jian-Yang Cho1,2, Jie Fu3, Lazaro A. Padilha3, Stephen
Barlow1,2, Eric W. Van Stryland3, David J. Hagan3,
Maximilienne Bishop2, and Seth R. Marder1,2
1School of Chemistry and Biochemistry and Center for Organic
Photonics and Electronics, Georgia Institute of Technology, Atlanta,
Georgia, USA
2Department of Chemistry, University of Arizona, Tucson, Arizona, USA
3College of Optics and Photonics: CREOL and FPCE, Department
of Physics, University of Central Florida, Orlando, Florida, USA
The diketones 4,40-di[3,4-bis(n-dodecyloxy)styryl]benzil and 4,40-di[3,4-bis(n-dode-
cyloxy)phenylethynyl]benzil have been synthesized from 4,40-dibromobenzil using
Heck coupling with the appropriate styrene and Sonogashira coupling with the
appropriate phenylalkyne, respectively. Treatment of the distyrylbenzil derivative
with phosphorus pentasulfide followed by nickel(II) chloride gave the correspond-
ing extended nickel bis(dithiolene) derivative which shows strong near-infrared
two-photon absorption with a cross-section of over 440 GM (1 GM ¼ 10ꢀ50 cm4
s
photonꢀ1 moleculeꢀ1) throughout the telecommunications range and a peak
cross-section of 5300 GM at ca. 1.2 lm.
Keywords: dithiolene; nickel; two-photon absorption; Z-scan
INTRODUCTION
The third-order nonlinear optical properties of bis(dithiolene) nickel
complexes such as the dye known as BDN, 1, and dyes of the general
type 2 (Fig. 1) have attracted considerable interest [1–5]. Dyes of type
This research is based upon work supported in part by the National Science Foun-
dation through the STC Program under Agreement Number DMR-0120967 and through
grants CHE-0211419 and ECS-0217932. We also thank DARPA (MORPH program, ONR
N00014-04-0095) and the AFOSR (FA95500410200) for support.
Address correspondence to Stephen Barlow, School of Chemistry and Biochemistry
and Center for Organic Photonics and Electronics, Georgia Institute of Technology,
Atlanta, Georgia 30332-0400, USA. E-mail: stephen.barlow@chemistry.gatech.edu
167=[915]

168=[916]
J.-Y. Cho et al.
FIGURE 1 Structures of some nickel bis(dithiolene)s discussed in the text.
2 were reported to have large values of the real parts of the third-order
susceptibility, Re(v3), at 1.06 mm, suggesting potential applications in
all-optical switching [3,4], although subsequent studies showed that
these susceptibilities were not purely electronic in origin [5]. Only
one study has addressed the two-photon absorption (2PA) properties
of nickel bis(dithiolenes); this study on films containing 2 was aimed
at demonstrating that the real part of the susceptibility was large com-
pared to the imaginary part at 1.06 mm [4,6], since Im(v3), to which
2 PA is often a major contributor, is detrimental for all-optical switch-
ing, with Re(v3)=Im(v3) being a frequently used figure-of-merit for
these applications [7].
More recently, 2PA has attracted attention as a useful phenomenon
with potential applications for three-dimensional microfabrication,
high-density memory, biological imaging, and photodynamic therapy
[8], rather than merely as a nuisance detrimental to applications
based on exploiting Re(v3). p-Conjugated chromophores with various
structural motifs incorporating p-donors (D) and p-acceptors (A) have
been shown to exhibit high peak 2PA cross-sections, dmax; these
include D-A-D [9–15], A-D-A [9,16–19], D-A [13,20–23], and multipolar
systems [24–26]. Electrochemical measurements indicate that the
nickel bis(dithiolene) moiety has a rather low-lying LUMO and these
properties have been exploited in conducting and superconducting
charge-transfer salts of the type [X]x[M(dmit)2] {X ¼ organic cation,
dmit ¼ 1,3-dithol-2-thione-4,5-dithiolato} [27,28] and in the use of neu-
tral nickel bis(dithiolene)s (such as 1 and 4) in n-channel field-effect

Two-Photon Absorbing Nickel Bis(dithiolene)
169=[917]
transistors [29–31], suggesting they might also be used as acceptors in
conjugated p-systems. Nickel bis(dithiolene)s generally exhibit rather
low-energy one-photon absorption (1 PA) bands, suggesting that two-
photon-allowed states may be sufficiently low-lying for 2 PA in the tel-
ecommunications region (1.3–1.55 mm) of the near-infrared (NIR), in
which range only a few chomophores have been characterized
[15,23,32,33] and where potential applications include optical pulse
suppression [34], all-optical beam stabilization, dynamic-range com-
pression, and the sensitization of photorefractive composites [35,36].
We have recently reported that nickel bis(dithiolene) complexes 3
[37], 4 [31,38,39], and 5 (Fig. 1) show increasingly strong NIR 2PA
with a peak cross-section as high as 5300 GM (1 GM ¼ 10ꢀ50 cm4 s
photonꢀ1 moleculeꢀ1) being observed for 5 [40]. In this article we
describe the synthesis and characterization of the new chromophore
5 in more detail.
RESULTS AND DISCUSSION
Figure 2 shows the synthetic route adopted for the synthesis of 5,
along with the synthesis of some other compounds undertaken in an
unsuccessful attempt to obtain its alkyne-containing analogue, 6.
Intermediate S1 was synthesized from the commercial 3,4-dihydroxy-
benzaldehyde essentially as described as in the literature [41]. During
the course of our work, similar syntheses of S2 [42] and S4–S5 [43]
have been published, although with only minimal characterization of
these intermediates. For S2, both our synthesis and the recently
reported synthesis rely on a Wittig reaction between S1 and methyl
triphenylphosphonium bromide; our synthesis is based on a general
procedure involving potassium carbonate in wet 1,4-dioxane [44],
while Gehringer and co-workers obtained a somewhat higher yield
using more traditional conditions of potassium tert-butoxide in tetra-
hydrofuran [42]. We obtained the dibromovinyl derivative, S4, by
treating S1 with 1 equivalent of carbon tetrabromide and 2 equiva-
lents of triphenylphosphine, following a procedure described for 4-
(2,2-dibromovinyl)-1,2-dimethoxybenzene [45], while Gehringer and
co-workers obtained similar yields using 5 equivalents each of carbon
tetrabromide, triphenylphosphine, and zinc [43]. Treatment with
strong base (n-butyl lithium in our case, lithium di-iso-propylamide
in Gerhringer’s work [43]) leads to formation of the terminal alkyne,
S5. The two diketone precursors, S3 and S6, were obtained as yellow
solids in good yield by coupling commercially available 4,4’-dibromo-
benzil with the terminal alkene or alkyne under Heck or Sonogashira
conditions, respectively [46].

170=[918]
J.-Y. Cho et al.
FIGURE 2 Synthesis of new diketones with extended conjugation and alkoxy
donors.
Nickel bis(dithiolene)s can be synthesized in a number of ways [47]
including treatment of nickel(II) salts with dithiones, with solvent
molecules presumably acting as in situ reducing agents; we adopted
this approach, initially forming the dithiones in situ by treatment with
phosphorus pentasulfide in 1,4-dioxane, and then adding aqueous
nickel(II) chloride. The product 5 was isolated as a dark green solid
in moderate yield after careful column chromatography. While we
were unable obtain satisfactory combustion analysis for 5, despite
repeated chromatography and attempts at crystallization, the identity
of the compound was clearly established by NMR spectroscopy and
1
mass spectrometry; H NMR spectroscopy suggested that there were

Two-Photon Absorbing Nickel Bis(dithiolene)
171=[919]
no (<1%) conjugated impurities that could contribute to the observed
nonlinear absorption (vide infra). Attempts to prepare 6 in the same
way were unsuccessful; although the product showed the character-
istic visible–NIR absorption spectrum of a nickel bis(dithiolene), with
a low-energy maximum at 939 nm, a broad 1H NMR spectrum with few
resolvable peaks and poor solubility are suggestive of formation of an
oligomerized or polymerized material.
Figure 3 compares the one-photon visible-NIR spectrum of 5 with
that of its analogue 4 which has a less extensive p-system. The charac-
teristic near-IR absorption of nickel bis(dithiolene)s, which has been
assigned to a p-pꢁ absorption delocalized over the core of the complex
[47], occurs at similar energy in the two complexes, corresponding to
photon wavelengths of 960–970 nm. Weak absorptions in the 1.8–
2.3 eV (550–700 nm) range, which have been assigned to d–d transi-
tions [47], are also similar in the two complexes. The most significant
difference between the spectra of 4 and 5 is in the strong UV absorp-
tion of the latter, corresponding to a photon wavelength of 350 nm and
presumably due to transitions localized in the stilbene units of the
ligands.
Figure 3 also shows degenerate 2PA spectra acquired using open-
aperture Z-scan measurements [48,49]. Compounds 4 and 5 show
similar 2 PA profiles, with apparent maxima at state energies of ca.
2.0 eV (the error bars do not allow us to definitively rule out the
possibility that the true maxima occur at slightly higher energy),
FIGURE 3 One-photon (lines) and two-photon (lines and data points) spectra
of 4 (broken lines, filled squares, data taken in chloroform) and 5 (solid lines,
open circles, tetrahydrofuran).

172=[920]
J.-Y. Cho et al.
corresponding to photon energies of ca. 1.0 eV and to photon wave-
lengths of ca. 1.2 mm. However, the cross-sections differ significantly
with peak cross-sections of 1400 and 5300 GM for 4 and 5 respectively.
For 5, d ¼ 2500 GM at the telecommunications wavelength of 1.3 mm
and d exceeds 440 GM throughout the entire telecommunications
range. Figure 3 shows that 2PA-allowed state lies at very similar
energy to the 1PA d–d states; however, the differences in 2 PA spectra
between 4 and 5 (and 3) indicate that there must be considerable
ligand contributions to the 2PA state. For centrosymmetric chromo-
phores such as these complexes, 1PA states are 2PA-forbidden and
vice versa; the cross-section for degenerate 2PA from the ground state,
g, into an excited state, e0, is given by terms of form
l2gel2ee0
d / E2ge0
ð1Þ
2
0
ðEge ꢀ ðEge =2ÞÞ
where the e subscript denotes an intermediate 1 PA-allowed state and
where E and l denote energies and transition dipole moments respect-
0
ively. Thus, the small detuning energies, Ege–(Ege =2), of <0.3 eV
between the virtual states and the intermediate 1 PA states for 4
and 5 are important factors contributing to large d. However, consider-
ation of the energy terms does not explain the difference in cross-
section between 4 and 5, which, according to Eq. (1), must be
dominated by differences in the transition dipole moment terms [50].
One of these transition dipole moment terms, lge, can be determined
from 1 PA spectra using the relation
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
R
ꢀ
ꢀ
eðnÞdn
lge ¼ 0:09584
ð2Þ
ꢀ
nmax
ꢀ1
where nmax and e(n) are in cm and Mꢀ1 cmꢀ1 respectively. Values of
8.0 and 11.2 D are found for 4 and 5 respectively; this difference may
arise from extension of the frontier orbitals, and, therefore, of the 1 PA
transition density, onto the styryl groups of the ligands of 5. Using
Eq. (1) one can see that these values of lge would be expected to lead
to an increase of dmax by a factor of ca. 2 between 4 and 5, whereas
the experimental values of dmax differ by a factor of ca. 4. The tran-
ꢀ
ꢀ
0
sition dipole moments linking the 1 PA and 2 PA states, lee , are less
readily experimentally determined (although, in principle, accessible
through pump-probe measurements). However, if one assumes the
same detuning energies for 4 and 5, and that a single three-level term
with the low-energy 1 PA state as an intermediate state dominates the
2 PA response, the discrepancy between the ratios in the lge and dmax

Two-Photon Absorbing Nickel Bis(dithiolene)
173=[921]
0
suggests a ratio of ca. 1.4 between the values of lee for 5 and 4,
presumably also due to more extensive delocalization of the e ! e0
transition density in 5.
EXPERIMENTAL DETAILS
3,4-Bis(n-dodecyloxy)benzaldehyde (S1)
K2CO3 (50.0 g, 0.362 mol) and 1-bromododecane (90.3 g, 0.362 mol)
were added to a solution of 3,4-dihydroxybenzaldehyde (25.0 g,
0.181 mol) in DMF (400 mL). The reaction mixture was heated at
80ꢂC for 45 h under N2 atmosphere. Water was added and the mixture
was extracted with CH2Cl2. The organic layer was washed with water
and saturated aq. NaCl several times and dried over MgSO4. The sol-
vent was removed under reduced pressure and the product was
further dried under vacuum overnight to give an off-white solid
ꢂ
1
(52.8 g, 62%). mp 69–70 C. H NMR (200 MHz, CDCl3) d 9.80 (s, 1 H),
7.36–7.41 (m, 2 H), 6.92 (d, J ¼ 8.6 Hz, 1 H), 4.03 (q, J ¼ 6.2 Hz, 4 H),
1.81 (m, 4 H), 1.44 (m, 4 H), 1.24 (s, 32 H), 0.85 (t, J ¼ 6.4 Hz, 6 H).
13C{1H} NMR (200 MHz, CDCl3) d 190.92, 154.65, 149.42, 129.85,
126.54, 111.72, 110.93, 69.08, 31.89, 29.58, 29.34, 29.04, 28.96,
25.92, 22.66, 14.07. IR (cmꢀ1): 2916, 2847, 1686, 1672, 1584, 1506,
1277, 1236, 1133, 807, 800. HRMS (FAB) calcd for C31H55O3 (MHþ ),
475.4151; found, 475.4156. Anal. Calcd for C31H54O3: C, 78.43; H,
11.46. Found: C, 78.46; H, 11.72.
3,4-Bis(n-dodecyloxy)styrene (S2)
A mixture of Ph3PMeBr (8.79 g, 24.6 mmol), K2CO3 (3.4 g, 24.6 mmol),
S1 (10.0 g, 21.1 mmol), 1,4-dioxane (25 mL), and H2O (0.3 mL) was
refluxed for 24 h, allowed to cool to room temperature, and extracted
with CH2Cl2. The organic extracts were washed with H2O, dried over
MgSO4, evaporated under reduced pressure, and purified by column
chromatography (silica gel, 2:1 hexanes=CH2Cl2) to give S2 as a white
1
solid (6.53 g, 66%). H NMR (300 MHz, CDCl3) d 6.96 (d, J ¼ 1.9 Hz,
1 H), 6.90 (dd, J ¼ 8.0 Hz, 1.9 Hz, 1 H), 6.80 (d, J ¼ 8.2Hz, 1H), 6.62
(dd, J ¼ 17.3 Hz, 10.7 Hz, 1 H), 5.57 (dd, J ¼ 17.6 Hz, 0.5 Hz, 1 H), 5.11
(d, J ¼ 11.5 Hz, 1 H), 3.98 (q, J ¼ 6.6 Hz, 4 H), 1.74–1.85 (m, 4 H),
1.19–1.50 (m, 36 H), 0.87 (t, J ¼ 6.6 Hz, 6 H). 13C{1H} NMR (75 MHz,
CDCl3) d 149.01, 148.98, 136.44, 130.63, 119.46, 113.44, 111.50,
111.18, 69.24, 32.00, 29.78, 29.72, 29.51, 29.45, 29.38, 29.34, 26.12,
22.78, 14.22. HRMS(EI) calcd for C32H56O2, 472.4280; found, 472.4267.
Anal. Calcd C32H56O2: C, 81.29; H, 11.94. Found: C, 81.36; H, 11.99.

174=[922]
J.-Y. Cho et al.
4,4’-Di[3,4-bis(n-dodecyloxy)styryl]benzil (S3)
S2 (5.78 g, 12.2 mmol), 4,40-dibromobenzil (1.8 g, 4.9 mmol), K2CO3
(3.38 g, 24.5 mmol), nBu4NBr (1.58 g, 4.9 mmol), LiCl (0.21 g,
4.9 mmol), Pd(OAc)2 (0.11 g, 0.49 mmol), and dry DMF (40 mL) were
heated at 100ꢂC under Ar for 60 h, allowed to cool to room temperature,
and extracted with CH2Cl2. The organic extracts were washed with
H2O, dried over MgSO4, evaporated under reduced pressure, and pur-
ified by column chromatography (silica gel, 1:2 to 3:2 CH2Cl2=hexanes)
and recrystallization from CH2Cl2=hexanes to give S2 as a bright yellow
1
solid (4.27 g, 76%). H NMR (300 MHz, CDCl3) d 7.94 (d, J ¼ 8.2 Hz,
2 H), 7.58 (d, J ¼ 8.5 Hz, 2 H), 7.18 (d, J ¼ 16.2 Hz, 2 H), 7.08 (d,
J ¼ 1.9 Hz, 2 H), 7.05 (dd, J ¼ 8.2 Hz, 1.9 Hz, 2 H), 6.96 (d, J ¼ 16.2 Hz,
Hz, 2 H), 6.85 (d, J ¼ 8.2 Hz, 2 H), 4.03 (t, J ¼ 6.6 Hz, 4 H), 4.01 (t,
J ¼ 6.6 Hz, 4 H), 1.76–1.88 (m, 8 H), 1.20–1.53 (m, 72 H), 0.86 (t,
J ¼ 6.6 Hz, 12 H). 13C{1H} NMR (75 MHz, CDCl3) d 193.70, 149.87,
149.12, 144.09, 132.51, 131.28, 130.40, 129.32, 126.39, 124.83, 120.81,
113.29, 111.53, 69.37, 69.15, 32.00, 29.78, 29.73, 29.52, 29.46, 29.38,
29.29, 26.14, 26.11, 22.80, 14.24. MS(EI) m=z 1152 (Mþ ). Anal. Calcd
for C78H118O6: C, 81.34; H, 10.33. Found: C, 81.25; H, 10.35.
Compound 5
S3 (1.0 g, 0.87 mmol), P2S5 (0.58 g, 1.3 mmol), and p-dioxane (20 mL)
were refluxed for 5 h under N2, allowed to cool to 60ꢂC, and filtered
under N2. NiCl2 ꢃ 6H2O (0.103 g, 0.43 mmol) in H2O (1.5 mL) was added
to the filtrate; the resulting mixture was refluxed overnight and then
allowed to cool to room temperature, and extracted with CH2Cl2. The
organic extracts were washed with H2O, dried over anhydrous MgSO4
and evaporated under reduced pressure. The resulting dark green
solid was washed with acetone and MeOH and purified by column
chromatography (silica gel, 1:1 hexanes=CH2Cl2) to give a dark green
1
solid, 5 (0.314 g, 30%). H NMR (300 MHz, CDCl3) d 7.39 (s, 16 H),
6.81–7.11 (m, 20 H), 4.02 (t, J ¼ 6.9 Hz, 8 H), 3.99 (t, J ¼ 6.9 Hz,
8 H), 1.75–1.88 (m, 16 H), 1.16–1.52 (m, 144 H), 0.864 (t, J ¼ 6.6 Hz,
12 H), 0.861 (t, J ¼ 6.6 Hz, 12 H). 13C{1H} NMR (75 MHz, CDCl3) d
180.73, 149.33, 149.13, 140.05, 138.22, 130.10, 129.76, 129.26, 126.16,
125.69, 120.26, 113.51, 111.43, 69.35, 69.21, 32.01, 29.79, 29.73, 29.54,
29.46, 29.35, 26.15, 22.78, 14.24. MS(MALDI) m=z 2426 (Mþ ).
4-(2,2-Dibromovinyl)-1,2-bis(n-dodecyloxy)benzene (S4)
To a well-stirred solution of CBr4 (6.99 g, 21.1 mmol) in dry CH2Cl2 at
0ꢂC was added PPh3 (11.05 g, 42.1 mmol) and S1 (10.0 g, 21.1 mmol).

Two-Photon Absorbing Nickel Bis(dithiolene)
175=[923]
The resulting mixture was stirred for 1 h at ambient temperature. The
reaction mixture solidified during the time. The solid was dissolved in
CH2Cl2, washed with H2O, and dried over anhydrous MgSO4. The sol-
vent was removed under reduced pressure to give an off-white solid.
The product was further purified by column chromatography (silica
gel, 2:1 hexanes=CH2Cl2) to give a yellowish white solid (11.37 g,
1
86%). H NMR (300 MHz, CDCl3) d 7.37 (s, 1 H), 7.17 (d, J ¼ 2.2 Hz,
1 H), 7.04 (dd, J ¼ 8.5 Hz, 0.6 Hz, 1 H), 6.82 (d, J ¼ 8.5 Hz, 1 H),
3.983 (t, J ¼ 6.6 Hz, 2 H), 3.976 (t, J ¼ 6.9 Hz, 2 H), 1.75–1.85 (m,
4 H), 1.20–1.50 (m, 36 H), 0.87 (t, J ¼ 6.6 Hz, 6 H). 13C{1H} NMR
(75 MHz, CDCl3) d 149.37, 148.37, 136.38, 127.67, 121.85, 113.51,
112.72, 86.90, 69.29, 69.00, 32.00, 29.78, 29.70, 29.51, 29.45, 29.26,
26.09, 22.78, 14.24. HRMS(EI) calcd for C32H54O2Br2, 628.2491; found,
628.2472. Anal. Calcd for C32H54O2Br2: C, 60.95; H, 8.63; Br, 25.34.
Found: C, 60.92; H, 8.62; Br, 25.48.
1,2-Bis(n-dodecyloxy)-4-ethynyl-benzene (S5)
A solution of S4 (9.0 g, 14.3 mmol) in 150 mL of dry THF was cooled
to ꢀ78ꢂC under Ar. nBuLi (11.4 mL of 2.5 M solution in hexanes,
28.5 mmol) was added dropwise to the mixture and the resulting
mixture was stirred at ꢀ 78ꢂC for 1 h, allowed to warm up to room
temperature and stirred at room temperature for additional 4 h. The
reaction was quenched with a saturated aq. NH4Cl and extracted with
Et2O. The organic layer was dried over anhydrous MgSO4. The solvent
was removed under reduced pressure and the product was further
purified by column chromatography (silica gel, hexanes, then 50:1 hex-
1
anes=CH2Cl2) to give a white solid (4.38 g, 65%). H NMR (300 MHz,
CDCl3) d 7.04 (dd, J ¼ 8.2 Hz, J ¼ 1.9 Hz, 1H), 6.97 (d, J ¼ 1.9 Hz,
1 H), 6.77 (d, J ¼ 8.2 Hz, 1 H), 3.97 (t, J ¼ 6.6 Hz, 2 H), 3.95 (t,
J ¼ 6.6 Hz, 2 H), 2.96 (s, 1 H), 1.74–1.84 (m, 4 H), 1.20–1.50 (m,
36 H), 0.87 (t, J ¼ 6.6 Hz, 6 H). 13C{1H} NMR (75 MHz, CDCl3) d
149.87, 148.45, 125.36, 116.91, 113.93, 112.91, 83.92, 75.39, 69.18,
69.05, 32.00, 29.78, 29.73, 29.70, 29.48, 29.45, 29.22, 26.08, 22.78,
14.22. HRMS-EI (m=z): [M]þ calcd for C32H54O2, 470.4124; found,
470.4113. Anal. Calcd for C32H54O2,: C, 81.64; H, 11.56. Found: C,
81.36; H, 11.70.
4,4’-Di[3,4-bis(n-dodecyloxy)phenylethynyl]benzil (S6)
A Schlenk tube was charged with Pd(PhCN)2Cl2 (29.4 mg, 7.7 ꢄ 10ꢀ2
mmol), CuI (10 mg, 5.1 ꢄ 10ꢀ2 mmol), anhydrous 1,4-dioxane (30 mL),
PtBu3 (0.31 g of 10 wt% solution in hexanes, 1.5 ꢄ 10ꢀ1 mmol), iPr2NH

176=[924]
J.-Y. Cho et al.
(0.9 mL, 6.1 mmol), 4,40-dibromobenzil (0.94 g, 2.6 mmol), and S5 (3.0 g,
6.4 mmol) under Ar atmosphere. The reaction mixture was stirred at
room temperature for 48 h. The reaction mixture was diluted with
CH2Cl2 and filtered through Celite. The solvent was removed under
reduced pressure to give a yellowish brown solid. The product was pur-
ified by column chromatography (silica gel, 2:1 to 1:1 hexanes=CH2Cl2)
to give a yellow solid. The solid was recrystallized from CH2Cl2=
hexanes to give a yellow solid (2.39 g, 82%). 1H NMR (300 MHz,
CDCl3) d 7.93 (d, J ¼ 8.5 Hz, 4 H), 7.60 (d, J ¼ 8.5 Hz, 4 H), 7.11 (dd,
J ¼ 8.5 Hz, 1.9 Hz, 2 H), 7.03 (d, J ¼ 1.9 Hz, 2 H), 6.82 (d, J ¼ 8.5 Hz,
2 H), 4.00 (t, J ¼ 6.6 Hz, 4 H), 3.99 (t, J ¼ 6.6 Hz, 4 H), 1.76–1.86 (m,
8 H), 1.20–1.51 (m, 72 H), 0.86 (t, J ¼ 6.6 Hz, 12 H). 13C{1H} NMR
(75 MHz, CDCl3) d 193.09, 150.22, 148.60, 131.67, 131.45, 130.54,
129.75, 125.33, 116.51, 114.16, 112.94, 94.91, 87.16, 69.26, 69.08,
32.00, 29.78, 29.75, 29.70, 29.46, 29.26, 29.22, 26.09, 22.80, 14.24.
MS(EI) m=z 1148 (Mþ ). Anal. Calcd for C78H114O6: C, 81.62; H,
10.01. Found: C, 81.54; H, 10.05.
Nonlinear Optical Measurements
Solution 2 PA spectra were measured using the open-aperture Z-scan
technique [48,49]. A Ti:sapphire regenerative amplification system
(CPA2010, CLARK-MXR), providing laser pulses at 775 nm with
140 fs duration (FWHM) at a 1 kHz repetition rate, was used to pump
an optical parametric amplifier (OPA) systems (TOPAS, Light Conver-
sion), which was used to tune the wavelength and attenuate the out-
put energy to 10–300 nJ. For regions close to the 1 PA resonance
(close to the 2 PA peak of the present compounds), where linear
absorption is important, the open-aperture Z-scan cannot separate
the pure 2 PA from 1 PA followed by excited-state absorption. Accord-
ingly, we performed time-resolved analysis via pump and probe
measurements at these wavelengths; this allows us to separate those
effects due to the difference in the response time and to establish that
the Z-scan signal does indeed represent 2 PA; these measurements are
described in more detail elsewhere [40].
CONCLUSION
Heck and Sonogashira coupling can be used to synthesize the dike-
tones 4,40-di[3,4-bis(n-dodecyloxy)styryl]benzil and 4,40-di[3,4-bis(n-
dodecyloxy)phenylethynyl]benzil respectively from 4,40-dibromobenzil
and the appropriate styrene and phenylalkyne derivatives. The distyr-
ylbenzil derivative can be converted to the corresponding extended

Two-Photon Absorbing Nickel Bis(dithiolene)
177=[925]
nickel bis(dithiolene) derivative through reaction with phosphorus
pentasulfide followed by nickel(II) chloride, while under the same con-
ditions the di(phenyleythynyl)benzil gives an ill-defined polymeric
material. The extended nickel bis(dithiolene) shows strong 2PA
throughout the telecommunications region of the NIR which, coupled
with the good photostability of this class of compounds [47] suggests
possible applications in optical pulse supression, all-optical beam sta-
bilization, and dynamic-range compression in this wavelength range.
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