Near-infrared absorbing dyes at 1064 nm: Soluble dithiolene nickel complexes with alkylated electron-donating groups as Peripheral substituents

Article abstract of DOI:10.1016/j.dyepig.2016.01.026

Soluble dithiolene nickel complexes are designed and synthesized as near-infrared (NIR) absorbing dyes through the introduction of strong electron-donating groups at the molecular periphery. The resulting complexes are characterized by ¹H/

Full text of DOI:10.1016/j.dyepig.2016.01.026

Accepted Manuscript
Near-Infrared Absorbing Dyes at 1064nm: Soluble Dithiolene Nickel Complexes with
Alkylated Electron-Donating Groups as Peripheral Substituents
Dr. Yingliang Liu, Zhenru Zhang, Xuemei Chen, Shengang Xu, Prof. Shaokui Cao
PII:
S0143-7208(16)00038-3
10.1016/j.dyepig.2016.01.026
DYPI 5080
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 4 August 2015
Revised Date: 1 January 2016
Accepted Date: 5 January 2016
Please cite this article as: Yingliang Liu Zhang Z, Chen X, Xu S, Shaokui Cao Near-Infrared Absorbing
Dyes at 1064nm: Soluble Dithiolene Nickel Complexes with Alkylated Electron-Donating Groups as
Peripheral Substituents, Dyes and Pigments (2016), doi: 10.1016/j.dyepig.2016.01.026.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Near-Infrared Absorbing Dyes at 1064nm: Soluble Dithiolene
Nickel Complexes with Alkylated Electron-Donating Groups as
Peripheral Substituents
Yingliang Liu,* Zhenru Zhang, Xuemei Chen, Shengang Xu, Shaokui Cao*
School of Materials Science and Engineering, Zhengzhou University, Zhengzhou
450052, P. R. China
ABSTRACT
Soluble dithiolene nickel complexes are designed and synthesized as
near-infrared (NIR) absorbing dyes through the introduction of strong
electron-donating groups at the molecular periphery. The resulting complexes are
1
characterized by H/13C-NMR, IR, ESI-MS, UV-vis-NIR, TG, DSC, XPS and
elemental analysis. The identification results are in accord with the chemical structure
of designed dithiolene nickel complexes. The XPS results suggested that the
dithiolene ligands in carbazole-containing nickel complex take a radical monoanion,
which depends on the substituent electron-donating ability to a large extent. The TG
and DSC measurements indicated that the resulting complexes have an excellent
thermal stability and take on a glassy state at low temperature. The laser transmittance
measurement suggested that the optical filters fabricated through static
solution-casting approach with dithiolene nickel complexes as NIR absorbing dyes
could be well applied to the NIR laser protection at 1064 nm.
Keyword: near-infrared; absorbing dye; dithiolene nickel complex; laser protection
1. INTRODUCTION
*
Correspondence to: Dr. Yingliang Liu, liuylxn@sohu.com; Prof. Shaokui Cao, caoshaokui@zzu.edu.cn. Tel.&Fax:
+86-371-6776-3523.

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The near-infrared (NIR) optical filtering will be paid much more attention with
the rapid development of laser applications in biological medicine[1, 2], free-space
optical telecommunication[3], satellite remote sensing[4, 5], night view imaging[6] and
other military fields[7]. Especially, the NIR optical filtering in relation with optical
attenuation and laser protection within biological optical window of 800~1300nm,
which is derived from the total transmittance of blood and water[8], becomes an
important issue[9] in the process of medical imaging[10], NIR medical therapeutics[11]
and NIR-controlled drug release[12-16]. Additionally, the NIR optical filtering is also
specially emphasized in all kinds of military activities because many military lasers
work within the NIR wavelength range, such as the laser at 1064nm[17-20]
.
The optical filtering, which are often applied in laser protections, photographs,
precision instruments, eye-protecting glasses, etc., are usually achieved from
absorbing dyes[19], nonlinear refringence/scattering materials[21], photonic crystals[22,
23], interference/diffraction gratings[24], dichroic/dielectric reflections[25, 26], phase
changes, and so on. One of them, the absorbing dyes are one of the most promising
optical filtering materials suitable for the convenient processing approach, for
example, static casting or injection molding, which will avoid the complicated
fabrication processes of high precision patterns, such as gratings, photonic crystals,
etc. Currently, the well-known dye categories include metal complexes, cyanines,
porphyrins, phthalocyanines, quinoids, azo compounds, etc[17]. Thereamong,
dithiolene metal complexes have been applied to NIR photodetector, dye sensitized
solar cells, field effect transistor, second/third-order optical nonlinearity, Q-switch
dye lasers, antioxidants for polymers and light stabilizers on account of high electron
mobility, superior photostability, air-stability and thermal stability[27, 28]. Due to their
tense and broad absorption in the near-infrared region, dithiolene metal complexes are
also a kind of quite outstanding NIR optical filtering materials. Interestingly, a certain
transmittance in visible light region of dithiolene metal complexes affords the
potential combination of NIR laser protection and visibility in the visible region.
More interestingly, the transparent region of dithiolene metal complexes has the
potential to be red-shifted to the working wavelength of low-light night view devices.

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For example, the NVIS-compatible optical filter in the NIR range of 700-1000nm has
been reported with an aim to filtrate the interferential light of light-emitting device in
martial applications[18]. However, its NIR optical filtering range is not yet in accord
with biological optical window of 800-1300nm, eliminating the disturbance of
heterochromatic light or being used for the laser protection within biological optical
window.
Soluble dithiolene nickel complexes are designed and synthesized in this work as
NIR absorbing dyes through the introduction of strong electron-donating groups at the
molecular
periphery,
such
as
N-(2-ethylhexanyl)carbazol-3-yl,
and N,
N-(2-ethylhexanyl)phenothiazin-3-yl
N-bis[(4-(2-ethylhexyloxy)phenyl]-anilin-4-yl groups, to red-shift the NIR optical
filtering range of dithiolene nickel complexes to biological optical window. The
introduction of N-(2-ethylhexanyl) group is to increase the dye solubility. The
resulting complexes are characterized by 1H/13C-NMR, IR, ESI-MS, UV-vis-NIR and
XPS spectra, together with TG, DSC and CV. The NIR absorbing filters are fabricated
through static solution-casting approach with polystyrene as transparent polymeric
matrix and with dithiolene nickel complexes as NIR absorbing dyes. Their laser
transmittance measurement suggested that the fabricated NIR absorbing filters could
be applied to the NIR optical filtering in biological optical window, especially the
NIR laser protection at 1064nm.
2. Experimental Section
2.1. Reagents: Nickel chloride hexahydrate (NiCl2·6H2O) is bought from AlfaAesar
Chemical Co. Ltd. 1-Bromo-2-ethylhexane, ethanedioyl chloride and phosphorus
pentasulfide are purchased from Aladdin Chemical Co. Ltd. Carbazole, phenothiazine
and N-bromosuccinimide are bought from Zhengzhou alpha chemical Co. Ltd.
4-Iodophenol is from J&K Scientific Ltd. 4-Bromoanilines is from AlfaAesar. Other
reagents and solvents are from Chinese chemical companies. All the reagents are
directly used without further purification. N, N-Dimethyl formamide (DMF) is dried
overnight with anhydrous magnesium sulfate and then refluxed over calcium hydride

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for 12 hours. Toluene and dioxane are dried overnight with anhydrous magnesium
sulfate and then refluxed over sodium for 4 hours with benzophenone as an indicator.
Dichloromethane is dried by refluxing over phosphorous pentoxide for 4 hours.
1
2.2. Instruments and Characterization: H-/13C-NMR spectra are recorded on
Bruker DPX-400 nuclear magnetic resonance spectrometer using d-chloroform or
d-dimethylsulphoxide solution at room temperature. Infrared (IR) spectra are
measured using Nicolet Protégé 460 Infrared Spectrometer. ESI-MS is performed on
APEX IV fourier transform ion cyclotron resonance mass spectrameter.
Thermogravimetry (TG) is investigated on NETZSCH TG-209 Thermogravimetric
Analyzer at heating and cooling rates of 10oC/min under N2 atmosphere.
Differentionial scanning calorimetry (DSC) is carried out with NETZSCH-DSC-204
Differential Scanning Calorimeter at heating and cooling rates of 10oC/min under N2
atmosphere. Ultraviolet-visible-NIR (UV-vis-NIR) spectra are recorded using the
quartz cuvette with a thickness of 1cm on Agilent Cary5000 Spectrophotometer.
Cyclic voltammetry is carried out on CHI600E electrochemical working station at a
scanning rate of 100mv/s. The transmitted laser power of fabricated optical filters is
measured by an optical powermeter with the NIR lasers (780, 1064 and 1550 nm) as
an incidence light source.
2.3. Synthesis: All the intermediates and dithiolene nickel complexes are synthesized
according to the synthetic route in Scheme 1.
N-(2-Ethylhexyl)-carbazole (1): A 250mL round-bottomed flask is charged with
carbazole (15.1g, 90mmol) and DMF (130mL). NaH (2.59g, 108mmol) is slowly
added when carbazole is completely dissolved. The resulting mixture is stirred for 30
minutes. Then, 2-ethylhexylbromideꢀ20.86gꢁ108mmolꢂis added under argon and
stirred overnight at room temperature. The reaction is quenched with 300 mL of
distilled water and extracted three times with n-hexane (80mL each). Organic
combined fraction is washed with brine and dried over anhydrous MgSO4. The
solvent is removed under reduced pressure and the residue is purified by silica column
chromatography using n-hexane as eluent. N-(2-Ethylhexyl)-carbazole is obtained as a

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colorless viscous liquid in the yield of 90.2%. 1H-NMR (400MHz, CDCl3, δ): 8.12 (d,
J=7.76Hz, 2H), 7.47 (t, J=7.32Hz, 2H), 7.42 (d, J=8.16Hz, 2H), 7.24 (t, J=7.08Hz,
2H), 4.17 (d, J=4.32Hz, 2H), 2.09 (m, 1H), 1.23-1.48 (m, 8H), 0.90 (dt, J=7.40,
7.08Hz, 6H). IR, υmax (KBr, cm-1): 3054 (ArH), 2958 (CH3, υas), 2927 (CH2, υas),
2857 (CH2, υs), 1598, 1571, 1484, 1463 (benzene ring), 1452 (CH3, υas), 1152 (C-N),
748 (o-substitution).
1,2-Bis[N-(2-ethylhexyl)-carbazol-3-yl]ethane-1,2-dione (2): Compound 1 (5.03g,
18mmol) and oxalyl chloride (0.73mL, 7.5mmol) are added in turn into a 100mL
three-necked round-bottomed flask charged with anhydrous CH2Cl2 (20mL). AlCl3
(2.8g, 21mmol) is added slowly to the mixture at 0oC. The reaction mixture is stirred
for 8 hours at ambient temperature and then quenched with ice and concentrated HCl.
After stirring for another one hour, organic layer is separated and aqueous layer is
extracted with dichloromethane. The combined organic layer is washed with distilled
water and dried over anhydrous MgSO4. After evaporating the solvent, the resulting
residue is purified using column chromatography (silica gel, chloroform) to provide a
yellow solid in the yield of 43.1%. 1H-NMR (400 MHz, CDCl3, δ): 8.80 (s, 2H), 8.21
(d, J=7.96Hz, 2H), 8.05 (d, J=7.76Hz, 2H), 7.46 (t, J=7.46Hz, 2H), 7.38 (t, J=8.92Hz,
4H), 7.24 (d, J=7.52Hz, 2H), 4.10 (d, J=7.16Hz, 4H), 2.01 (t, J=5.96Hz, 2H),
1.20-1.38 (m, 16H), 0.87 (t, J=7.32Hz, 6H), 0.83 (t, J=7.00Hz, 6H). 13C-NMR
(101MHz, CDCl3, δ): 195.08 (s) (carbonyl groups), 144.48 (s), 141.54 (s), 127.66 (s),
126.63 (s), 124.79 (s), 123.90 (s), 122.94 (s), 120.73 (s), 120.28 (s), 109.64 (s),
109.15 (s) (carbazole), 47.53 (s), 39.29 (s), 30.88(s), 28.69(s), 24.29(s), 22.93(s),
13.96(s), 10.81(s) (2-ethylhexanyl groups). IR, υmax (KBr, cm-1): 3053 (ArH), 2957
(CH3, υas), 2922 (CH2, υas), 2863 (CH2, υs), 1669 (C=O), 1592, 1507, 1464 (benzene
ring), 1336 (CH2, υs), 1157 (C-N), 833
(m-substitution). ESI-MS (m/z):
[M+1]=613.4.
Bis{1,2-bis[N-(2-ethylhexyl)-carbazol-3-yl]ethylene-1,2-ditholate} nickel complex
(3): Compound 2 (1. 19gꢁ5mmol) is refluxed at 95oC with P2S5 (3.33g, 15mmol) in
20ml of dioxane for 10 hours. The reaction mixture is filtered to remove the excess
P2S5. A solution of NiCl2·6H2O (0.58g, 2.5mmol) in distilled water (3ml) is added to

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the filtrate. The mixture is refluxed at 85oC for 4 hours. After cooling, the reactant is
poured into distilled water (20mL) and extracted for three times with dichloromethane.
The combined organic fraction is washed with brine and dried over anhydrous MgSO4.
The solvent is removed under reduced pressure and the residue is purified by column
chromatography using silica gel and dichloromethane as eluent to give a blackish
green solid in the yield of 40.2%. 1H-NMR (400MHz, CDCl3, δ): 8.48 (s, 4H), 8.02 (d,
J=7.68Hz, 4H), 7.47 (t, J=7.64Hz, 4H), 7.39 (t, J=7.88Hz, 8H), 7.23 (t, J=7.36Hz,
4H), 7.17 (d, J=8.64Hz, 4H), 4.13 (d, J=6.92Hz, 8H), 2.05 (m, 4H), 1.21-1.36 (m,
13
32H), 0.88 (dt, J=7.28, 7.12Hz, 24H). C-NMR (101MHz, CDCl3, δ): 181.80 (s)
(C=C), 141.76 (s), 14161 (s), 133.77 (s), 127.42 (s), 126.32 (s), 123.47 (s), 123.42 (s),
122.01 (s), 121.06 (s), 119.73 (s), 109.60 (s), 108.93 (s) (carbazole), 47.97 (s), 39.74
(s), 31.37 (s), 29.14 (s), 24.76 (s), 23.41 (s), 14.41 (s), 11.25 (s) (2-ethylhexanyl
groups). IR, υmax (KBr, cm-1): 3050 (ArH), 2957 (CH3, υas), 2922 (CH2, υas), 2855
(CH2, υs), 1617, 1591, 1473 (benzene ring), 1336 (CH2, υs), 1268, 1217 (C=C), 1123
(C-N), 902 (m-substitution), 749 (o-substitution). ESI-MS (m/z): [M+1]=1347.6.
Element. Anal. Calcd for C84N4S4H96Ni: C, 74.83; N, 4.16; H, 7.13. Found: C, 74.40;
N, 3.84; H, 7.23.
N-(2-Ethylhexyl)-phenothiazine (4): A 250 mL Schlenk flask is charged with
phenothiazine (18.0g, 90mmol), NaH (2.81g, 117mmol) and 100mL of DMF. The
resulting mixture is stirred for 30 minutes. 2-Ethylhexylbromide (22.7g, 117mmol) is
then added. The mixture is stirred overnight at room temperature. The reaction is
quenched with distilled water and extracted for three times with n-hexane. The
combined organic fraction is washed with brine and dried over anhydrous MgSO4.
The solvent is removed under reduced pressure and the residue is purified by column
chromatography using silica gel and n-hexane as eluent to give
N-(2-ethylhexyl)-phenothiazine as a yellow viscous liquid in the yield of 86.8%.
1H-NMR (400MHz, CDCl3, δ): 7.15 (t, J=7.44Hz, 4H), 6.90 (p, J=7.44Hz, 4H), 3.73
(d, J=6.72Hz, 2H), 1.95 (m, 1H), 1.27–1.47 (m, 8H), 0.88 (m, 6H). IR, υmax (KBr,
cm-1): 3065 (ArH), 2958 (CH3, υas), 2927 (CH2, υas), 2857 (CH2, υs), 1593, 1485,
1458 (benzene ring), 1222 (C-N), 749 (o-substitution).

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1,2-Bis[N-(2-ethylhexyl)-phenothiazin-3-yl]ethane-1,2-dione
(5):
Aromatic
1,2-diketone derived from N-(2-ethylhexyl)-phenothiazine, Compound 5, is
synthesized according to the same procedure as Compound 2. The product is
separated by column chromatography and chloroform as eluent to obtain a blackish
1
green solid in the yield of 32.3%. H-NMR (400MHz, CDCl3, δ): 7.72 (d, J=8.52Hz,
2H), 7.71 (s, 2H), 7.16 (t, J=8.24Hz, 2H), 7.00 (d, J=7.60Hz, 2H), 6.97 (t, J=7.52Hz,
2H), 6.88 (d, J=7.92Hz, 4H), 3.77 (d, J=7.04Hz, 4H), 1.91 (m, 2H), 1.36-1.44 (m, 8H),
13
1.25 (m, 8H), 0.86 (m, 12H). C-NMR (101MHz, CDCl3, δ): 192.50 (s) (carbonyl
groups), 151.83 (s), 143.86 (s), 130.24 (s), 129.07 (s), 127.81 (s), 127.51 (s), 1.27.42
(2), 126.03 (s), 124.87 (s), 123.76 (s), 116.64 (s), 115.36 (s) (phonothiazine), 51.46 (s),
36.04 (s), 30.61 (s), 28.52 (s), 23.92 (s), 23.04 (s), 14.01 (s), 10.45 (s) (2-ethylhexanyl
groups). IR, υmax (KBr, cm-1): 3056 (ArH), 2966 (CH3, υas), 2922 (CH2, υas), 2856
(CH2, υs), 1659 (C=O), 1592, 1570, 1547, 1459 (benzene ring), 1192 (C-N), 747
(o-substitution). ESI-MS (m/z): [M+1]=677.3.
Bis{1,2-bis[N-(2-ethylhexyl)-phenothiazin-3-yl]ethylene-1,2-ditholate}
nickel
complex (6): Dithiolene nickel complex derived from phonothiazine, Compound 6, is
synthesized according to the same procedure as Compound 3. The product is purified
by column chromatography using silica gel and dichloromethane as the eluent to give
1
a blackish green solid in the yield of 17.6%. H-NMR (400MHz, CDCl3, δ): 7.40 (s,
4H), 7.16 (t, J=7.08Hz, 4H), 7.12 (d, J=7.64Hz, 4H), 7.01 (d, J=8.44Hz, 4H), 6.96 (t,
J=7.4 Hz, 4H), 6.89 (d, J=8.08Hz, 4H), 6.69 (d, J=8.60Hz, 4H), 3.71 (d, J=6.88Hz,
13
8H), 1.93 (m, 4H), 1.37-1.46 (m, 32H), 1.27 (m, 24H). C-NMR (101MHz, CDCl3,
δ): 179.32 (s) (carbonyl groups), 146.52 (s), 144.90 (s), 135.70 (s), 128.00 (s), 127. 86
(s), 127.67 (s), 127.20 (s), 125.88 (s), 125.22 (s), 122.80 (s), 116.02 (s), 115.32 (s)
(phonothiazine), 51.20 (s), 35.84(s), 30.66 (s), 28.53 (s), 23.98 (s), 23.05 (s), 14.04 (s),
10.53 (s) (2-ethylhexanyl groups). IR, υmax (KBr, cm-1): 3068 (ArH), 2957 (CH3, υas),
2915 (CH2, υas), 2854 (CH2, υs), 1591, 1566, 1559, 1456 (benzene ring), 1336 (CH2,
υs), 1268, 1242 (C=C), 1131 (C-N), 740 (o-substitution). ESI-MS (m/z):
[M+2]=1476.5. Element. Anal. Calcd for C84N4S8H96Ni: C, 68.34; N, 3.80; H, 6.51.
Found: C, 67.82; N, 3.35; H, 6.83.

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1-(2-Ethylhexyloxy)-4-iodobenzene (7): K2CO3 (26.3g, 190mmol) is suspended in
DMF (100mL), followed by the addition of 4-iodophenol (28.0g, 127mmol) and
2-ethylhexylbromide (26.6g, 135mmol). The mixture is refluxed for 51 hours under
the protection of argon. The reaction is quenched with distilled water and extracted
for three times with n-hexane. The combined organic fraction is washed with brine
and dried over anhydrous MgSO4. The solvent is removed under reduced pressure and
the residue is purified by column chromatography using silica gel and n-hexane as
eluent to give a colorless liquid in the yield of 76.7%. 1H-NMR (400MHz, CDCl3, δ):
7.51 (d, J=8.96Hz, 2H), 6.67 (d, J=8.96Hz, 2H), 3.78 (d, J=5.84Hz, 2H), 1.69 (m, 1H),
1.23-1.52 (m, 8H), 0.90 (m, 6H). IR, υmax (KBr, cm-1): 2958 (CH3, υas), 2927 (CH2,
υas), 2872 (CH2, υs), 1586, 1487, 1467 (benzene ring), 1283, 1244 (C-O-C), 1032
(C-O), 819 (p-substitution).
N-Bis[4-(2-ethylhexyloxy)phenyl] phenylaniline (8): The reaction is carried out in a
250mL three-neck round-bottomed flask. Toluene (150mL) is charged to the
round-bottom flask, followed by the addition of Compound 7 (35.6g, 107mmol), CuI
(0.35g, 1.82mmol), 1,10-phenanthroline monohydrate (0.36g, 1.82mmol), aniline
(4.75g, 51mmol), and KOt-Bu (17.1g, 153mmol). The round-bottom flask is flushed
with argon for three times to ensure the removal of air. Then, an argon balloon is
attached to the condenser to maintain the argon atmosphere during the reaction. The
mixture is stirred at 115°C for 4 hours. After cooling to room temperature, the
reaction mixture is quenched with distilled water (150mL) and extracted with toluene
for three times. The combined organic fraction is washed with brine and dried over
anhydrous MgSO4. The solvent is removed under reduced pressure and the residue is
separated by column chromatography and cyclohexane as eluent to obtain the product
as a light yellow solid in the yield of 73.6%. 1H-NMR (400MHz, CDCl3, δ): 7.25 (d,
J=7.48Hz, 2H), 7.13 (d, J=7.24Hz, 4H), 7.06 (d, J=7.64Hz, 2H), 6.93 (d, J=8.80Hz,
5H), 3.93 (d, J=5.12Hz, 4H), 1.84 (m, 2H), 1.39-1.69 (m, 16H), 1.06 (m, 12H).
13C-NMR (101MHz, CDCl3, δ): 155.68 (s), 149.01 (s), 141.07 (s), 128.99 (s), 126.52
(s), 120.93 (s), 120.50 (s), 115.35 (s) (benzene), 70.79 (s), 39.64 (s), 30.73 (s), 29.28
(s), 24.06 (s), 23.22 (s), 14.25 (s), 11.31 (s) (2-ethylhexanyl groups). IR, υmax (KBr,

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cm-1): 3038 (ArH), 2957 (CH3, υas), 2924 (CH2, υas), 2871, 2858 (CH2, υs), 1592,
1507, 1492 (benzene ring), 1271, 1239 (C-O-C), 1034 (C-O), 829 (p-substitution).
1,2-Bis{N-bis[4-(2-ethylhexyloxy)phenyl]amino-4-phenyl}ethane-1,2-dione
(9):
Aromatic 1,2-diketone derived from triphenylamine, Compound 9, is synthesized
according to the same procedure as Compounds 2 and 5. The product is separated by
column chromatography and chloroform as eluent to obtain a yellow solid in the yield
of 41.3%. 1H-NMR (400MHz, CDCl3, δ): 7.72 (d, J=7.48Hz, 4H), 7.08 (d, J=8.84Hz,
8H), 6.88 (d, J=8.92Hz, 8H), 6.79 (d, J=9.0Hz, 4H), 3.83 (d, J=5.68Hz, 8H), 1.72 (m,
13
4H), 1.30-1.55 (m, 32), 0.93 (m, 24H). C-NMR (101MHz, CDCl3, δ): 193.51 (s)
(carbonyl groups), 157.21 (s), 154.10 (s), 138.42 (s), 131.71 (s), 128.01 (s), 124.04 (s),
116.52 (s), 115.57 (s) (triphenylamine), 70.74 (s), 39.43 (s), 30.54 (s), 29.11 (s), 23.88
(s), 23.06 (s), 14.10 (s), 11.15(s) (2-ethylhexanyl groups). IR, υmax (KBr, cm-1): 3043
(ArH), 2966 (CH3, υas), 2931 (CH2, υas), 2864 (CH2, υs), 1661 (C=O), 1592, 1499,
1464 (benzene ring), 1329 (CH2, υs), 1285, 1234 (C-O-C), 1029 (C-O), 825
(p-substitution). ESI-MS (m/z): [M+1]=1057.7.
Bis{1,2-bis{N-bis[4-(2-ethylhexyloxy)phenyl]amino-4-phenyl}ethylene-1,2-dithola
te} nickel complex (10): Dithiolene nickel complex derived from triphenylamine,
Compound 10, is synthesized according to the same procedure as Compounds 3 and 6.
The product is separated by column chromatography and dichloromethane as eluent to
1
obtain a blackish green solid in the yield of 21.3%. H-NMR (400MHz, CDCl3, δ):
7.23 (d, J=8.76Hz, 4H), 7.10 (d, J=8.84Hz, 8H), 6.88 (d, J=8.88Hz, 8H), 6.78 (d,
J=8.76Hz, 4H), 3.84 (d, J=5.68Hz, 8H), 1.74 (m, 4H), 1.34-1.57 (m, 32H), 0.94 (m,
24H). 13C-NMR (101MHz, CDCl3, δ): 180.14 (s) (C=C), 156.72 (s), 149.83 (s),
140.17 (s), 133.96 (s), 130.21 (s), 127.75 (s), 118.48 (s), 115.73 (s) (triphenylamine),
71.10 (s), 39.87 (s), 30.95 (s), 29.52 (s), 24.28 (s), 23.46 (s), 14.50 (s), 11.55 (s)
(2-ethylhexanyl groups). IR, υmax (KBr, cm-1): 3043 (ArH), 2957 (CH3, υas), 2922
(CH2, υas), 2854 (CH2, υs), 1584, 1498, 1456 (benzene ring), 1345 (CH2, υs), 1293,
1233 (C-O-C), 1293, 1233 (C=C), 1038 (C-O), 816 (p-substitution). ESI-MS (m/3z):
[M/3]=745.4. Element. Anal. Calcd for C140N4S4H184O8Ni: C, 75.17; N, 2.51; H, 8.23.
Found: C, 74.75; N, 2.35; H, 8.21.

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Filter fabrication: The NIR optical filters are fabricated by static solution-casting
approach with polystyrene as transparent polymeric matrix and with dithiolene nickel
complexes as NIR absorbing dyes. The specific procedure is given below: Polystyrene
(1.0g) is firstly dissolved in chloroform and then dithiolene nickel complex
(Compounds 3, 6 and 10, 1.0mg) synthesized by us is added into the chloroform
solution of polystyrene. After stirring for 10 minutes, the composite solution is
dropped on the glass substrate. With the solvent being dried spontaneously, a series of
NIR optical filters are achieved respectively denoted as 3@PS for Compound 3,
6@PS for Compound 6 and 10@PS for Compound 10.
3. Results and Discussion
3.1. Synthesis
Dithiolene metal complexes generally conclude homoleptic complexes with a
symmetrical molecular structure and heteroleptic complexes with an unsymmetrical
molecular structure [28]. Heteroleptic dithiolene metal complexes are developed for
nonlinear optical applications due to their noticeable first molecular
hyperpolarizabilities[27], which are derived from the interligand charge transfer of
HOMO-LUMO transition in unsymmetical molecules. As for absorbing dyes without
any requirement of intramolecular hyperpolarization, homoleptic complexes are much
more favored owing to their simple synthetic routes from symmetrical molecular
structures. In view of DFT calculations on substituent effect for dithiolene metal
complexes[18, 27-29], the electron-donating group increases the electron density of
dithiolene moiety resulting in the higher energy levels of HOMO and LUMO. On
account of much more improvement of HOMO, the band gap of dithiolene metal
complexes will be decreased, i.e., the excitation energy of electrons from ligands to
metal plane is reduced. In this case, the NIR absorption range of dithiolene metal
complexes has a potential to be red-shifted through the introduction of
electron-donating groups at the molecular periphery. Besides, the red-shift extent of
NIR absorption range is decided by the electron-donating ability of substituents.
On the basis of molecular design strategy mentioned above, three

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electron-donating
groups,
alkylcarbazole,
alkylphenothiozine
and
dialkyltriphenylamide, are introduced into the molecular periphery of dithiolene
nickel complexes as efficient electron-donating groups while the introduction of alkyl
group is to increase the dye solubility. Carbazole, phenothiazine and triphenylamide,
which are usually contained in organic compounds or conjugated polymers for
organic photoelectronic semiconducting materials to improve the hole-transporting
ability in organic light-emitting diodes, organic solar cells and organic field-effect
transistors, are used to enhance the electron-donating ability of substituents at the
molecular periphery affording the potential red-shift of NIR absorption range to
biological optical window. The specific synthetic route is shown in Scheme 1. First of
all, carbazole, phenothiazine and triphylamide are alkylated by 2-ethylhexylbromide
to increase the molecular solubility, affording Compounds 1, 4 and 8. Then, three
aromatic 1,2-diketones, Compounds 2, 5 and 9, are presented by acylation reaction of
Compounds 1, 4 and 8 with oxalyl chloride. Finally, dithiolene nickel complexes,
Compounds 3, 6 and 10, are synthesized under the action of P2S5 and NiCl2·6H2O.
The alkyl group, 2-ethylhexanyl group, is applied to increase the solubility of
dithiolene nickel complexes in common solvents, which is a necessary issue for
solution-processible molding approaches. As we expected, the resulting dithiolene
nickel complexes have an excellent solubility in common solvents such as toluene,
tetrahydrofuran, dichloromethane, chloroform and dioxane, except for
N,N-dimethylformamide.
1
All the intermediates and target compounds are identified by H/13C-NMR, IR
1
and ESI-MS spectra. All the H/13C-NMR spectra is carefully assigned as shown in
Figures S1-S18 of electronic supporting information (SI). The proton signals of
1
carbazole ring in H-NMR spectra of Compounds 1-3 are illustrated Figure 1a.
Evidently, the singlet proton signal at 8.80 ppm, which is assigned to the protons
marked out by two astisks in the molecular skeleton of Compound 2 in Scheme 1,
1
appears in H-NMR spectrum of Compound 2 compared with Compound 1. It is
1
shifted again to the singlet proton signal at the high field of 8.48 ppm in H-NMR
spectrum of Compound 3. These results indicated the successful introduction of

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carbonyl group into Compound 2 and its transformation in dithiolene nickel molecular
core in Compound 3. The transformation of carbonyl group is further confirmed by
the shift of carbon signal of carbonyl group from 195.08 ppm of Compound 2 to
13
181.80 ppm of Compound 3 in the C-NMR sepctra of Figure 1b. In the process of
ESI-MS measurement of Compound 2, the appearance of [M+1]=613.4 in Figure S19
identifies the chemical structure of 1,2-diketone (M=612.4) instead of single ketone
(M=584.4). The introduction and transformation of carbonyl group is also proved by
the appearance of absorption peak at 1669 cm-1 in the IR spectrum of Compound 2
and by its disappearance in the IR spectrum of Compound 3 in Figure 1c. Finally, the
appearance of [M+1]=1347.6 in the ESI-MS spectrum of Figure S20 definitely
proved
the
successful
preparation
of
Compound
3,
bis{1,2-bis[N-(2-ethylhexyl)-carbazol-3-yl]ethylene-1,2-ditholate} nickel complex.
The measurement results of Compounds 3, 6 and 10 is in accord with their calculation
values of C, N and H.
The changes of chemical shift of proton and carbon adjacent to carbonyl group in
aromatic 1,2-diketones are also similarly found in 1H/13C-NMR spectra of
Compounds 4-6 (1H-NMR: 7.71ppm/singlet in Compound 5 to 7.40ppm/singlet in
13
Compound 6; C-NMR: 192.50ppm in Compound 5 to 179.32ppm in Compound 6;
See. Figures S6-S10) and Compounds 8-10 (1H-NMR: 7.72ppm/doublet in
Compound 9 to 7.23ppm/doublet in Compound 10; 13C-NMR: 193.51ppm in
Compound 9 to 180.14ppm in Compound 10; See. Figures S13-S18). The appearance
and disappearance derived from the introduction and transformation of carbonyl
group are also revealed in the IR spectrum of Compounds 4-6 (1659 cm-1 in
Compound 5, See. Figure S21) and Compounds 8-10 (1661 cm-1 in Compound 9, See.
Figure S22). In addition, the introduction of 1,2-diketone into Compounds 5 and 9 is
respectively verified by the signal of [M+1]=677.3 and [M+1]=1057.7 in the ESI-MS
spectra of Figures S23 and S24. The successful preparation of Compound 6,
bis{1,2-bis[N-(2-ethylhexyl)-phenothiazin-3-yl]ethylene-1,2-ditholate}
nickel
complex, is further proven by the signal of [M+2]=1476.5 in the ESI-MS spectrum of
Figure S25. Due to the large molecular weight of Compound 10, it is very difficult to

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detect the signal of monocharged molecular ion (m/z) as above. Fortunately, its signal
of triple charged molecular ion (m/3z=745.4), whose interval of isotopic ion peaks is
approaximately equal to 0.333, is found in its ESI-MS spectrum in Figure 1d. This
result
indicated
the
successful
preparation
of
Compound
10,
bis{1,2-bis{N-bis[4-(2-ethylhexyloxy)phenyl]amino-4-phenyl}ethylene-1,2-ditholate}
nickel complex. The identification results of all the intermediates and target
complexes are entirely in accord with the chemical structures in Scheme 1.
3.2. Thermal property
The thermal property of dithiolene nickel complexes is investigated by
thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The
TG curves in Figure 2a suggested that the onset degradation temperature of
o
o
o
Compounds 3, 6 and 10 is respectively 413.1 C, 339.7 C and 391.3 C, which is
defined as the crosspoint temperature of two tangenthial lines at the onset degradation
stage of TG curves as shown in Figure 2a. Evidently, dithiolene nickel complex
derived from carbazole, Compound 3, bear the best thermal stability compared with
Compounds 6 and 10. Except for that, TG curve of Compound 6 takes on an evident
three-step degradation compared with Compounds 3 and 10. This point is derived
from the introduction of phenothiazine ring, in which the sulphur atom is a main
origination of thermal instability. The instable feature of sulphur atom in the
phenothiazine ring is also shown in the lowest onset degradation temperature of
Compound 6.
The DSC measurement in Figure 2b illustrated that the glass transition
o
temperature of dithiolene nickel complexes is respectively 74.5 C for Compound 3,
67.3 oC for Compound 6 and 93.8 oC for Compound 10. Except for the glass transition
in the DSC curves of Figure 2b, Compound 3 has a recrystallization process at 148.3
oC with the enthalpy change of -26.45 J/g and a melting transition at 243.3 oC with the
enthalpy change of 56.82 J/g and Compound 10 has two melting processes with the
o
o
enthalpy changes of -4.315 J/g at 124.5 C and -5.114 J/g at 142.7 C. These results
indicated that the resulting dithiolene nickel complexes bear a poor crystallinity, even

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taking on a glassy state at low temperature due to the introduction of nonplane
substituents such as phenothiazine, triphenylamide and 2-ethylhexanyl group.
XPS spectra
The chemical state of nickel, sulfur, nitrogen and carbon elements in dithiolene
nickel complexes, Compounds 3, 6 and 10, is characterized in detail by X-ray
photoelectron spectroscopy (XPS) with binding energies calibrated by that of C1s,
which is an excellent tool to describe the chemical state of elements in organic or
inorganic compounds and to provide the basic data about chemical bonds for
theoretical calculation [30, 31]. The full-scale XPS spectrum of Compound 3 in Figure
3a obviously showed the signals of S2p (163 eV), N1s (400 eV), Ni2p (855 eV) and
C1s (285 eV). These signals are also found in the full-scale XPS spectra of
Compounds 6 and 10 (See. Figures S26 and S27). The high-resolved XPS spectra of
Ni2p in Compounds 3, 6 and 10 in Figure 3b showed that there is almost no change
for chemical state of nickel in three dithiolene nickel complexes, suggesting that the
stable binding energies of spin orbit splitting peaks (Ni2p1/2 and Ni2p3/2) with the
approximate intensity ratio of Ip1/2:Ip3/2=1:2. It is speculated that the change of
chemical states might happen in other elements of dithiolene nickel complexes.
Therefore, the high-resolved XPS spectra of sulfur, nitrogen and carbon elements are
also recorded to investigate their specific chemical states, which are involved in the
change of electronic structure of dithiolene nickel complexes caused by the
introduction of electron-donating groups at the molecular periphery.
The high-resolved XPS spectra of S2p in Figure 3c clearly indicated that the
sulphur element in the molecular core of dithiolene nickel complexes takes on two
chemical states at binding energies of 162.6 eV and 163.8 eV, without regard for the
sulphur on phenothiazine ring at binding energy of 165.0 eV. By fitting their
high-resolved XPS spectra (See. Figures S28-S30), the peak of S2p belonging to the
molecular core is respectively divided into two evident individual peaks with different
ratios (Compound 3: 50.7%@163.8eV, 49.3%@162.6eV; Compound 6:
86.7%@163.8eV,
13.3%@162.6eV;
Compound
10:
65.0%@163.5eV;

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35.0%@162.3eV. See. Table S1). This kind of dual-peak phenomenon was also
discovered in other dithiolene nickel complexes approximately at 169 eV and 164
eV[32], even in Langmuir-Blodgett films of dithiolene nickel complex approximately
at 168 eV and 163 eV[33]. The reference [33] thought the high binding energy at 168
eV is caused by the sulfur oxidation, i.e. S-O. Another explanation is that the
existence of high binding energy at 169 eV is a kind of characteristic “satellite”
feature of S2p[32], which is attributed to high oxidization degree and conjugation of
anion moiety in the partially oxidized or charge transition species. The higher the
degree of oxidation or conjugation, the higher is the degree of π-electron
delocalization over the ligand through the π-d interaction, resulting in the more
obvious “satellite” feature. Additionally, the sulphur in the molecular core of
dithiolene nickel complex is proved to a mixture of 0 and -1 by different C-S
stretching bands (1029 cm-1 and 1099 cm-1) in IR spectra of original complex and by
the deconvolution of high-resolved XPS spectrum of S2s in reduced complex at
binding energy of 228 eV[34]
.
Our XPS result of high-resolved S2p is different from the outcoming in the
references [32-34] although the coexistence of [S]0 and [S]-1 in dithiolene nickel
complex is also confirmed. The dual-peak phenomenon appear approximately at low
binding energies of 163.8 eV and 162.6 eV, which might be derived from the strong
electron-donating ability of carbazole, phenothiozine and triphenylamide. Due to the
stronger electron-donating ability of triphenylamide, the binding energies of [S]0 and
[S]-1 are respectively decreased about 0.3 eV from Compounds 3 and 6 to Compound
10. In our case, the sulfur oxidation is definitely excluded due to the absence of O1s at
binding energy of 531 eV in Figure 3a. Simultaneously, the binding energy of
high-resolved N1s in Figure 3d has a minor shift on account of different
electron-donating ability of carbazole, phenothiazine and triphenylamide in
Compounds 3, 6 and 10. Besides, the binding energy of carbon element is
unchangeable in the high-resolved C1s of Figure 3f, in which the shoulder
appearance of C-O in Compound 10 with the content of 4.1% is also resolved out at
binding energy of 286.5 eV by fitting its high-resolved C1s spectrum as shown Figure

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S31. The data in Table S1 showed a positive relationship between the content of [S]-1
and the binding energy of N1s, indicating that the charge on [S]-1 should come from
nitrogen element on carbazole, phenothiazine and triphenylamide through electron
π-delocalization. This point told us that the introduction of electron-donating groups
has an extraordinary potential to modulate the electronic structure of dithiolene nickel
complexes.
To the best of our knowledge, the chemical state of dithiolene ligand in metal
complexes is still under debate to date[27, 28, 35], such as neutral dithioketone (L),
radical monoanion (L•-) or dianionic dithiolate (L2-) as shown in Scheme 2. Our
XPS results related with the chemical state of S2p in the molecular core support the
existence of radical monoanion [form d] in single dithiolene ligand. In consideration
of unchangeable binding energy at 855.0 eV of high-resolved Ni2p in Figure 3b, the
potential existence of neutral dithioketone (form a) and dianionic dithiolate (form b) is
excluded since the single chemical state of Ni2p and the dual-peak phenomenon of
S2p show the existence of the Ni2+ instead of the coexistence of Ni2+ and Ni0/Ni4+.
According to the ratio of [S]0:[S]-1=1.03 in Compound 3, we know that the molecular
core of dithiolene nickel complex derived from alkylcarbazole only take a radical
monoanion (form d). Compound 6 takes a majority of overall π-electron
delocalization (form c) owing to its ratio of [S]0:[S]-1=6.52. The molecular core of
Compound 10 takes a part of radical monoanion due to its ratio of [S]0:[S]-1=1.86.
These results told us that the chemical state of S2p in dithiolene ligand depends to a
large extent on the electron-donating ability of substituents at the molecular periphery.
3.4. Electrochemical and optical properties
Cyclic voltammetry (CV) is carried out at a scanning rate of 100mv/s to
investigate the electronic structure of dithiolene nickel complexes, especially the
energy level of HOMO and LUMO, with the n-BuNPF6 acetonitrile solution (0.1mol)
as an electrolyte, with platinum carbon electrodes as working electrodes and with
Ag/AgCl as reference electrode. The results indicated that Compounds 3, 6 and 10
exhibit an evident reversible reduction peak and a weak irreversible oxidation peak as

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shown in the CV curve of Compound 10 of Figure 4 (Compound 3: Figure S32;
Compound 6: Figure S33). Based on the fact of reproduced CV curve in different
loops, we deemed that the CV behavior of Compounds 3, 6 and 10 is reversible as a
whole, i.e., the balance of gain and loss electron. Small irreversible oxidation wave is
derived from the electron transportation through a conjugated bridge (-C=C-) from the
donating-electron group at the molecular periphery to the molecular core. The ability
of electron transportation results in the area of small oxidation wave, which is
seemingly different for Compounds 3, 6 and 10 due to the different electron-donating
ability of substituents at the molecular periphery, such as carbazole, phenothiazine
onset
and triphenylamine. The onset reduction potential (
E
) of Compounds 3, 6 and 10
red
is respectively -0.73 V, -0.75 V and -0.79 V, whose energy level of LUMO is
onset
red
calculated with the formula ELUMO =-(
E
+4.44) eV to be -3.71 eV for Compound 3,
-3.69 eV for Compound 6 and -3.65 eV for Compound 10. Similarly, the onset
onset
ox
oxidation potential (
E
) of Compounds 3, 6 and 10 is respectively 0.55 V, 0.85 V
and 0.60 V, whose energy level of HOMO is calculated with the formula
onset
ox
EHOMO =-(
E
+4.44) eV to be -4.99 eV for Compound 3, -5.29 eV for Compound 6
and -5.04 eV for Compound 10. Therefore, their electrochemical band gap (Eegl ) is
calculated with the formula Egel
ELUMO EHOMO to be 1.26 eV for Compound 3, 1.60 eV
=
-
for Compound 6 and 1.39 eV for Compound 10. It is obviously that the as-prepared
dithiolene nickel complexes bear the typical characteristics of low band gap,
suggesting their potentially excellent NIR absorption performance. All the CV data
are summarized in Table 1.
The optical absorption property of dithiolene nickel complexes is measured using
the dichloromethane solution with a concentration of 0.02 mg/mL as shown in the
UV-vis-NIR spectra of Figure 5a. The results suggested that the absorption maximum
(
λmax ) of Compounds 3, 6 and 10 is respectively 1021 nm, 1088 nm and 1168 nm,
where the molar extinction coefficient is calculated with the formula ε=A/bc to be

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5.23×104 L·mol-1·cm-1 for Compound 3, 3.86×104 L·mol-1·cm-1 for Compound 6 and
5.81×104 L·mol-1·cm-1 for Compound 10. Here, ε is denoted to be the molar
extinction coefficient; A is the absorbance; b is the thickness of quartz cuvette; c is the
molar concentration. The absorption onset ( λonset ) wavelength is 1167 nm for
Compound 3, 1295 nm for Compound 6 and 1387 nm for Compound 10. As a result,
the optical band gap ( Egop. ) is calculated with the formula Egop. =1240/λonset eV to be
1.06 eV for Compound 3, 0.96 eV for Compound 6 and 0.89 eV for Compound 10.
All these results showed that the resulting dithiolene nickel complexes have an
excellent NIR absorption performance as menthioned above. All the UV-vis-NIR data
are listed in Table 1.
Evidently, the optical band gap is different from the electrochemical band gap as
shown in Table 1, which is caused by different measurement mechanisms. The
electrochemical energy level is determined through the electron achievement at
LUMO and the losing at HOMO while the optical energy level stems from the photon
excitation/recombination between HOMO and LUMO. As for Compounds 3, 6 and 10,
the photons are basically excitated from aromatic rings, which is proved by the
existence of CKLL Auger electron peak at binding energy of 1225 eV as shown in the
inset of Figure 3a because the Auger electron peak is usually caused by the relaxation
of atoms in excited state with photogenerated holes in the atomic internal electron
shell[31]. Additionally, the dithiolene nickel complex derived from phenothiazine has
the lowest of molar extinction coefficient as shown in Table 1, similarly to the lowest
content of [s]-1, the lowest binding energy of N1s and the lowest HOMO level. The
reason is that the electrons are excitated from HOMO not only in electrochemical
measurement but also in the XPS measurement, even in electron π-delocalization.
Therefore, the content of [S]-1 in the molecular core has a direct relationship with both
the binding energy of N1s and the oxidation potential, even the molar extinction
coefficient. In addition, Compounds 3, 6 and 10 have a strong absorption property in
the near-infrared region between 900 nm and 1300 nm, which is basically in accord
with biological optical window (800~1300nm). This feature can be well applied to the

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NIR optical filtering in biological optical window, even the NIR laser protection at
1064nm.
3.5. Near-infrared optical filter
In light of high molar extinction coefficient in the near-infrared region of
dithiolene nickel complexes, a series of optical filters are fabricated on the glass
substrate by solution-casting the concentrated solutions of polystyrene (PS) and
Compounds 3, 6 and 10 in chloroform. The optical filters are denoted as 3@PS for
Compound 3, 6@PS for Compound 6 and 10@PS for Compound 10. Here, PS is
applied as polymeric matrix with an excellent optical transparency, whose
transmittance is more than 90% in the visible and near-infrared light region as shown
in Figure 5b. Notably, the optical filters are impossibly achieved with
polymethylmethacrylate (PMMA) as a matrix, which is another universal transparent
polymeric matrix for a variety of optical devices, due to the serious fading of
Compounds 3, 6 and 10 in the near-infrared region as shown in Figure S34. This
might be resulted from the degradation action of carbonyl groups in PMMA on
dithiolene nickel complexes, which is found through the poor solubility of
Compounds 3, 6 and 10 in DMF and the considerable blue-shift of absorption maxima
in the DMF solution, for example, the large blue-shift of absorption maximum of
Compound 10 from 1168 nm in dichloromethane to 1025 nm in DMF in Figure S35
while the molar extinction coefficient at the absorption maximum is decreased about
one order of magnitude from 5.81×104 L·mol-1·cm-1 in dichloromethane to 4.53×103
L·mol-1·cm-1 in DMF. Simultaneously, we also make an attempt to fabricate the
optical filters through in-situ bulk polymerization with styrene as a monomer and with
azodiisobutyronitrile (AIBN) as an initiator. Unfortunately, this experiment is also
ended in failure owing to the rapid fading of dithiolene nickel complexes, which
might be derived from the polymerization inhibition of sulphur-containing
compounds on free radicals or the coordination action of vinyl groups with dithiolene
nickel complexes having been applied to the initiators of polymerization reaction of
vinyl monomers[36, 37] and the purification of olelifins[38]. Fortunately, the static

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solution-casting approach is successful applied to fabricate the NIR optical filters
from Compounds 3, 6 and 10 with PS as polymeric matrix. The transmittance spectra
of optical filters are investigated and illustrated in Figure 5b. The results indicated
that all the optical filters have an extraordinary ultraviolet absorption property,
together with an NIR filtering region (See. Table S2, 885-1135 nm for 3@PS,
947-1214 nm for 6@PS and 986-1305 nm for 10@PS) and an transparent region (See.
Table S2, 472-848 nm for 3@PS, 522-896 nm for 6@PS and 497-925 nm for
10@PS). These results suggested that 3@PS, 6@PS and 10@PS have the potential
application in the NIR optical filtering performance within biological optical window,
especially the NIR laser protection at 1064 nm.
3.6. Near-infrared laser protection
The performance of NIR laser protection is detailedly investigated by the laser
transmittance measurement of NIR optical filters fabricated from dithiolene nickel
complexes at the wavelength of common NIR lasers, such as 780, 1064 and 1550 nm.
Their curves of transmitted laser power versus incidence laser power are illustrated in
Figure 6 and the laser transmittances are summarized in Table S3. The results in
Figure 6a showed that the transmitted laser powers at 780nm of 3@PS, 6@PS and
10@PS are respectively 67.5%, 25.8% and 46.0%, which are less than their
transmittances of 78.5%, 71.8% and 62.2% in the UV-vis-NIR spectra of Figure 5a.
The measurement of transmitted laser power at 1064 nm in Figure 6b indicated that
all the NIR optical filters have a low optical laser transmittance, which is respectively
5.7% for 3@PS, 9.7% for 6@PS and 8.3% for 10@PS. Their optical densities (OD)
are calculated with the formula OD=lg(1/T) to be 1.24 for 3@PS, 1.01 for 6@PS and
1.08 for 10@PS, here, T is the laser power transmittance. It is believed that their
optical density at 1064nm has a large potential to be further improved with the
increase of dye-doping concentration. In addition, their transmitted laser powers at
1550nm are more than 80% as shown in the inset of Figure 6b. Obviously, the
resulting dithiolene nickel complexes possess an excellent NIR laser protection
performance at 1064nm. Other applications of these NIR absorbing dyes are under

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research in our laboratory.
4. Conclusion
Soluble dithiolene nickel complexes are designed and synthesized as NIR
absorbing dyes through the introduction of strong electron-donating groups at the
1
molecular periphery. The resulting complexes are characterized by H/13C-NMR, IR,
ESI-MS, UV-vis-NIR and XPS spectra, together with TG, DSC and CV. The
identification results are in accord with their chemical structures. The TG and DSC
measurement indicated that the dithiolene nickel complexes have an excellent thermal
stability, even taking on a glassy state at low temperature. The XPS results suggested
that the dithiolene ligands in carbazole-containing nickel complex take a radical
monoanion, depending to a large extent on the electron-donating ability of
substituents at the molecular periphery. The content of [S]-1 in the molecular core has
a direct relationship with both the binding energy of N1s and the oxidation potential,
even the molar extinction coefficient because the electrons are excitated from HOMO
not only in electrochemical measurement but also in the XPS measurement, even in
electron π-delocalization. The NIR optical filters could be fabricated through static
solution-casting approach with polystyrene as transparent polymeric matrix and with
dithiolene nickel complexes as NIR absorbing dyes. The laser transmittance
measurement suggested that the fabricated NIR absorbing filters bear a good NIR
optical protection performance at 1064 nm.
Acknowledgements: This work is supported by the National Natural Science
Foundation of China (NSFC, U1304212 and 21274133) and the Development
Foundation for Distinguished Junior Researchers at Zhengzhou University (No.
1421320043).
1
Supporting Information: H/13C-NMR spectra of Compounds 1-10 in Figures
S1-S18; ESI-MS spectra of Compounds 2, 3, 5, 9 and 6 in Figures S19, S20, S23-S25;
Full-scale XPS spectra of Compounds 6 and 10 in Figure S26 and S27; Fitted XPS

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spectra of high-resolved S2p of Compounds 3, 6 and 10 in Figure S28-S30; XPS data
of fitted core-level S2p, N2s and C1s in Table S1; Fitted high resolution XPS spectra
of C1s of Compound 10 in Figure S31; CV curves of Compounds 3 and 6 in Figure
S32 and S33; Transmittance spectra of Compounds 3, 6 and 10 with PMMA as a
matrix in Figure S34; UV-vis-NIR spectra of Compound 10 with a concentration of
0.02mg/mL in dichloromethane and DMF in Figure S35; Filtering and transparent
regions of optical filters in Table S2; Laser transmittance of optical filters at 780nm,
1064nm and 1550nm in Table S3.
References:
[1] Hou CY, Duan YR, Zhang QH, Wang HZ, Li YG. Bio-applicable and
electroactive near-infrared laser-triggered self-healing hydrogels based on
graphene networks. J Mater Chem 2012; 22: 14991-6.
[2] Wu JL, Chen FC, Chuang MK, Tan KS. Near-infrared laser-driven polymer
photovoltaic devices and their biomedical applications. Energ Environ Sci 2011;
4: 3374-8.
[3] Maggio S, Zhang QN, Zhao ZX. Free-space optical backplane prototype for
telecommunication equipment in the petabit/s range. Bell Labs Tech J 2013; 18:
285-91.
[4] Bigo S. Multiterabit/s DWDM terrestrial transmission with bandwidth-limiting
optical filtering. IEEE J Sel Top Quant 2004; 10: 329-40.
[5] Sargent RB, O’Brien NA. Dielectric materials for thin-film-based optical
communications filters. MRS Bull 2003; 28: 372-6(+344).
[6] Simi C, Dixon R, Schlangen M, Winter E, Lasota C. Night Vision Imaging
Spectrometer (NVIS) processing and viewing tools. Proc SPIE 2001; 4381:
118-28.
[7] Kobrinski H, Cheung KW. Wavelength-tunable optical filters: Applications and
technologies. IEEE Commun Mag 1989; 27: 53-63.
[8] Valery VT. Handbook of Coherent-Domain Optical Methods (2nd
ED)-Biomedical Diagnostics, Environmental Monitoring, and Materials Science:

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Fourier Transform Light Scattering of Tissues, Springer Science+Business Media
New York, 2013. ISBN: 978-1-4614-5175-4 (Print), 978-1-4614-5176-1
(Online).
[9] Huang ZL, Chen SH, Lv CH, Huang Y, Lai JJ. Infrared characteristics of VO2
thin films for smart window and laser protection applications. Appl Phys Lett
2012; 101: 191505 (1-4).
[10]Pansare VJ, Hejazi S, Faenza WJ, Prud’Homme RK. Review of long-wavelength
optical and NIR imaging materials: Contrast agents, fluorophores, and
multifunctional nano carriers. Chem Mater 2012; 24: 812-27.
[11]Luo SL, Zhang EL, Su YP, Cheng TM, Shi CM. A review of NIR dyes in cancer
targeting and imaging. Biomaterials 2011; 32: 7127-38.
[12]Zhao LZ, Peng JJ, Huang Q, Li CY, Chen M, Sun Y, Lin QN, Zhu LY, Li FY.
Near-Infrared Photoregulated Drug Release in Living Tumor Tissue via
Yolk-Shell Upconversion Nanocages. Adv Funct Mater 2014, 24, 363-71.
[13]Yang JP, Shen DK, Zhou L, Li W, Li XM, Yao C, Wang R, El-Toni AM, Zhang
F, Zhao DY. Spatially confined fabrication of core-shell gold
nanocages@Mesoporous silica for near-infrared controlled photothermal drug
release. Chem Mater 2013; 25: 3030-7.
[14]Cao J, Huang SS, Chen YQ, Li SW, Li X, Deng DW, Qian ZY, Tang LP, Gu YQ.
Near-infrared light-triggered micelles for fast controlled drug release in deep
tissue. Biomaterials 2013; 34: 6272-83.
[15]Chang YT, Liao PY, Sheu HS, Tseng YJ, Cheng FY, Yeh CS. Near-Infrared
light-responsive intracellular drug and sirna release using au nanoensembles with
oligonucleotide-capped silica shell. Adv Mater 2012; 24: 3309-14.
[16]Kuo TR, Hovhannisyan VA, Chao YC, Chao SL, Chiang SJ, Lin SJ, Dong CY,
Chen CC. Multiple release kinetics of targeted drug from gold nanorod embedded
polyelectrolyte conjugates induced by near-infrared laser irradiation. J Am Chem
Soc 2010; 132: 14163-71.

ACCEPTED MANUSCRIPT
[17]Yang XB, Zhang SX, Yang B, Wang CY, Ding ST, Wang AB. Research progress
on near-infrared absorbing croconaine dyes for 1064nm laser protection. J Funct
Mater 2013; 44: 3235-8.
[18]Miao QQ, Gao JX, Wang ZQ, Yu H, Luo Y, Ma TL. Synthesis and
characterization of several nickel bis(dithiolene) complexes with strong and broa
near-IR absorption. Inorg Chim Acta 2011, 376, 619-627.
[19]Men JF, Chen ZH, Cheng HF, Chu ZY. Night vision imaging system (NVIS)
compatibility of cyanine dye-based NIR absorbing filter. Acta Optica Sinica
2008; 28: 1783-7.
[20]Wakita J, Kawamata S, Murano T, Fukamachi H, Hayasaka S. "Night view
system" with pedestrian detection using near-infrared light. 15th World Congress
on Intelligent Transport Systems and ITS America Annual Meeting 2008; 7:
4459-68.
[21]Morris JB, Fiddy MA, Pommet DA. Nonlinear filtering applied to single-view
backpropagated images of strong scatterers. J Opt Soc Am A 1996; 13: 1506.
[22]Hamed AB, Mahdi HK, Farhad M. WDM and DWDM optical filter based on 2D
photonic crystal Thue-Morse structure. Optik 2013; 124: 4416-20.
[23]Debnath K, Welna K, Ferrera M, Deasy K, Lidzey DG, O’Faolain L. Highly
efficient optical filter based on vertically coupled photonic crystal cavity and bus
waveguide. Opt Lett 2013; 38: 154-6.
[24]Yu JH, Han YQ, Huang HK, Li HZ, Hsiao VKS, Liu WP, Tang JY, Lu HH,
Zhang J, Luo YH, Zhong YC, Zang ZG, Chen Z. All-optically reconfigurable and
tunable fiber surface grating for in-fiber devices: A wideband tunable filter. Opt
Express 2014; 22: 5950-61.
[25]Bruno B, Fabien L, Michel C, Michel L. Manufacturing of an absorbing filter
controlled by a broadband optical monitoring. Opt Express 2008; 16: 12008-17.
[26]Shou CH, Luo ZY, Wang T, Shen WD, Rsengarten G, Wei W, Wang C, Ni MJ,
Cen KF. Investigation of a broadband TiO2/SiO2 optical thin-film filter for hybrid
solar power systems. Appl Energ 2012; 92: 298-306.

ACCEPTED MANUSCRIPT
[27]Paola D, Luca P, Davide E, Mercuri ML, Angela S. Square-planar d8 metal
mixed-ligand dithiolene complexes as second order nonlinear optical
chromophores: structure/property relationship. Coordin Chem Rev 2010; 254:
1434-47.
[28]Benedicte GDB, Kathleen IMCC, Fabienne A, Bui TT, Lydie V. Neutral d8 metal
bis-dithiolene complexes: synthesis, electronic properties and applications.
Coordin Chem Rev 2010; 254: 1457-67.
[29]Soras G, Psaroudakis N, Manos MJ, Tasiopoulos AJ, Liakos DG, Mousdis GA.
Synthesis, experimental and theoretical investigation of a new type nickel
dithiolene comoplex. Polyhedron 2013; 62: 208-17.
[30]Sarma DD, Santra PK, Mukherjee S, Nag A. X-ray photoelectron spectroscopy:
A unique tool to determine the internal heterostructure of nanoparticles. Chem
Mater 2013; 25: 1222-32.
[31]Seah MP. Reference data for Auger electron spectroscopy and X-ray
photoelectron spectroscopy combined. Appl Surf Sci 1999; 144: 161-7.
[32]Liu SG, Liu YQ, Zhu DB. Preparation and spectral properties of new molecular
conductors based on anion salt. Synthetic Met 1997; 89: 187-91.
[33]Yang DD, Sun Y, Guo Y, Da DA. X-ray photoelectron spectroscopy of nickel
dithiolene complex Langmuir-Blodgett films. Appl Surf Sci 1999; 148: 196-204.
[34]Kambe T, Sakamoto R, Hoshiko K, Takada K, Miyachi M, Ryu JH, Sasaki S,
Kim J, Nakazato K, Takata M, Nishihara H. π-Conjugated nickel bis(dithiolene)
complex nanosheet. J Am Chem Soc 2013; 135: 2462-5.
[35]Schrauzer GN, Mayweg VP. Coordination compounds with delocalized ground
states. Bisdithioglyoxalnickel and related complexes. J Am Chem Soc 1965; 20:
3585-92.
[36]Li D, Mohamed FS, Yang XZ, Alak A, Harrison DJ, Fekl U, Brothers EN, Hall
MB. The mechanism of alkene addition to a nickel bis(dithiolene) complex: The
role of the reduced metal complex. J Am Chem Soc 2012; 134: 4481-4.

ACCEPTED MANUSCRIPT
[37]Fan YB, Hall MB. How electron flow controls the thermochemistry of the
addition of olefins to nickel dithiolenes: Predictions by density functional theory.
J Am Chem Soc 2002; 124: 12076-7.
[38]Wang K, Stiefel EI. Toward separation and purification of olefins using dithiolene
complexes: An electrochemical approach. Science 2001; 291: 106-9.

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Figrues and Tables
N
N
N
N
H
N
C2O2Cl2
2-Ethylhexyl bromide
(1) P2S5
O
O
S
S
N
S
N
N
Ni
S
AlCl3/CH2Cl2
(2) NiCl2
NaH/DMF
C
C
*
*
*
1
2
5
3
N
N
S
S
H
N
C2O2Cl2
(1) P2S5
O
O
2-Ethylhexyl bromide
S
S
S
S
S
N
N
S
N
S
Ni
AlCl3/CH2Cl2
(2) NiCl2
NaH/DMF
C
C
S
S
S
*
N
N
4
6
O
O
O
OH
aniline
1,10-Phenanthroline
O
O
O
2-Ethylhexyl bromide
K2CO3/DMF
*
*
*
C2O2Cl2
N
C
C
N
N
AlCl3/CH2Cl2
CuI, KOt-Bu, PhMe
I
*
O
O
I
O
7
8
9
O
N
O
N
(1) P2S5
(2) NiCl2
S
S
O
S
S
O
SRC
Ni
O
O
N
O
N
O
10
Scheme 1. Synthetic route of dithiolene nickel complexes.

ACCEPTED MANUSCRIPT
c
Compound 3
Compound 2
1669
Compound 1
4000
3000
2000
1000
Wavenumbers (cm-1)
Figure 1. a) Proton signals of carbazole ring in 1H-NMR spectra of Compounds 1-3;
b) Carbon signals of carbazole and ethylene in 13C-NMR spectra of Compounds 2 and
3; c) IR spectra of Compounds 1-3; d) Signals of triple charged molecular ion in the
ESI-MS spectra of Compound 10.
b
Tonset
Endo
a
100
80
Compound 3
Tg
Compound 6
Compound 10
Compound 3
60
Compound 10
40
Compound 6
600
50
100
150
200
250
200
400
Temperature (°C
800
Temperature (oC)
)
Figure 2. TG (a) and DSC (b) curves of Compounds 3, 6 and 10.
100000
80000
60000
40000
20000
0
a
Compound 3
Compound 6
Compound 10
b
20000
15000
10000
Ni2p
Ni2p
Compound 3
Compound 6
Compound 10
C1s
7000
6000
5000
4000
Ni2p3/2
Ni2p1/2
1280
1200
1120
N1s
CKLL
Ni2p
Compound 3
S2s
S2p
1200 1000 800 600 400 200
Binding Energy / eV
0
880
870
860
850
Binding Energy / eV