Nonlinear optical and energy-level modulation of organic alkynes by click chemistry

Article abstract of DOI:10.1016/j.tet.2016.05.035

A series of novel donor–acceptor chromophores have been successfully synthesized in excellent yield by metal-free [2+2] click chemistry, which was effective in the energy-level modulation of organic the π-conjugation aniline derivatives. Meanwhile, struct

Full text of DOI:10.1016/j.tet.2016.05.035

Accepted Manuscript
Nonlinear optical and energy-level modulation of organic alkynes by click chemistry
Zongcheng Miao, Huihui Han, Dong Wang, Hong Gao, Jianming Gu, Huiying Hu
PII:
S0040-4020(16)30420-3
10.1016/j.tet.2016.05.035
TET 27762
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 29 February 2016
Revised Date: 12 May 2016
Accepted Date: 13 May 2016
Please cite this article as: Miao Z, Han H, Wang D, Gao H, Gu J, Hu H, Nonlinear optical and
energy-level modulation of organic alkynes by click chemistry, Tetrahedron (2016), doi: 10.1016/
j.tet.2016.05.035.
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Nonlinear optical and energy-level
modulation of organic alkynes by click
chemistry
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Zongcheng Miaoa, Huihui Hanb, Dong Wangb,*, Hong Gaoc,*, Jianming Gud, Huiying Hue
aXijing University, Xi’an, Shaanxi Province, 710123, PR China
bDepartment of Materials Physics and Chemistry, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing
100083, PR China
cDivision of Material Engineering, China Academy of Space Technology, Beijing, 100094, PR China
dDepartment of Adult Joint Reconstruction, Beijing Jishuitan Hospital, Beijing, 100035, PR China
eDepartment of Obsterics and Gynecology, Peking Union Medical College Hospital, Beijing, 100730, PR China

1
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Tetrahedron
journal homepage: www.elsevier.com
Nonlinear optical and energy-level modulation of organic alkynes by click chemistry
Zongcheng Miaoa, Huihui Hanb, Dong Wangb,*, Hong Gaoc,*, Jianming Gud, Huiying Hue
aXijing University, Xi’an, Shaanxi Province, 710123, PR China
bDepartment of Materials Physics and Chemistry, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083,
PR China
cDivision of Material Engineering, China Academy of Space Technology, Beijing, 100094, PR China
dDepartment of Adult Joint Reconstruction, Beijing Jishuitan Hospital, Beijing, 100035, PR China
eDepartment of Obsterics and Gynecology, Peking Union Medical College Hospital, Beijing, 100730, PR China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A series of novel donor-acceptor chromophores have been successfully synthesized in excellent
yield by metal-free [2+2] click chemistry, which was effective in the energy-level modulation of
organic the π-conjugation aniline derivatives. Meanwhile, structures of all products were fully
characterized by NMR, IR, and MS. UV-vis spectra were enlarged with end-absorptions into the
near infrared region in varying degrees by introducing TCNE, TCNQ, F4-TCNQ click reagents
and correspondingly electrochemical tests revealed that the energy levels of HOMO and LUMO
were effectively tuned. The third order nonlinear optical properties studied at 532/1064 nm with
picosecond Z-scan techniques indicated that almost all products exhibited the high NLO
properties, especially, for dye c5, exhibiting third-order susceptibility χ(3)=1.83×10-7 esu under
laser beam at 1064 nm.
Available online
Keywords:
Nonlinear optical
Energy-level modulation
Click chemistry
2009 Elsevier Ltd. All rights reserved
.
Near infrared absorption
1. Introduction
Both increasing the light absorption intensity and expanding
the light absorption range, which were important to improve
third-order NLO properties, were still the important task.
Fortunately, we found a simple and efficient method for the
synthesis of organic benzene derivatives with great potential
applications for photoelectric materials which can be achieved by
the thermal [2+2] cycloaddition followed by the ring-opening of
click chemistry[27-31]. This approach through linking click
reagent to the π-conjugation bridge of the compound extending
the photo absorption to longer wavelength, and obtaining higher
molar extinction coefficients access to the better third-order NLO
properties[32-35].
The nonlinear optical organic materials have received wide
attention in material science due to their possible applications in
electronic and optoelectronic devices[1-11]. The organic
materials, which were gaining considerable interest as a
promising class of materials, were being used in optical limiting,
optical switching, electronic devices, and nonlinear optical
media[12-15], because of their large nonlinear optical (NLO)
response, chemical stability and process ability. Donor–acceptor
conjugated organic materials containing both electron rich and
electron deficient moieties along the molecule backbone were
known to exhibit the enhanced third-order NLO properties due to
the increase in effective π electron delocalization. Design and
synthesis of the excellent performance of the three order NLO
materials was a hot research topic in recent years. To date, many
kinds of organic NLO materials have been synthesized, such as
D-A push-pull structure of azo compounds, squaric acid,
heterocyclic compounds, tetrathiafulvalene derivatives, schiff
base complex, phthalocyanine compounds and ferrocene
derivatives[16-26]. Among them, complexes with potential NLO
properties, good thermal and photochemical stability, and redox
switching abilities have caused considerable interests. These
studies had focused on the important role of substituents
enhancing third-order NLO properties of such materials.
Here, we designed and synthesized a family of organic
conjugated molecules with great potential applications for
photoelectric materials. Meanwhile, the novel click chemistry
allowed us to efficiently modulate the HOMO-LUMO energy
band gap, leading top-conjugated molecules with tunable
electrochemical properties as well as excellent solubility, which
was beneficial for processing. The differences of the NLO
performance had also been analyzed based on the chemical
structures of the compounds.

2
Tetrahedron
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2. Experimental section
2.1. Instrumental characterization equipments
1H NMR spectra were measured on a Bruker AV 500 NMR
spectrometer (500 MHz) at 20 ºC. Chemical shifts were reported
in ppm downfield from SiMe4, using the solvent’s residual signal
as an internal reference. FT-IR was recorded on a Perkin Elmer
LR-64912C Fourier transform infrared spectrometer. All
MALDI-TOF-MS spectra were measured on a Shimadzu
AXIMA-CFR mass spectrometer. UV-vis spectra were recorded
in a quartz cuvette on a JASCO V-570 spectrophotometer. Cyclic
voltammetric measurements were carried out on a computer-
controlled CHI 660C instrument at RT. Both the first oxidation
potentials (Eox) corresponding to the HOMO levels of the
compounds and the first reduction potentials (Ered) relating to the
LUMO levels of the compounds were measured by cyclic
voltammetry (CV) in CH2Cl2 solution containing 0.1 M
tetrabutylammonium hexafluorophosphate (TBAPF6) as the
supporting electrolyte, glassy carbon as working electrode,
Ag/AgCl as the reference electrode, Pt as the counter electrode
and a standard ferrocene/ferrocenium redox system as the
internal standard. The third order NLO properties such as
nonlinear index of refraction n2 and nonlinear absorption
coefficient β can be measured with high accuracy by a single-
beam Z-scan technique. Test conditions of Z scanning platform
were as follows: for the 532-band laser, DMSO acts a standard
sample and pulse width of 21 ps was applied. The conditions of
focal length, energy and light hole diameter were 400 mm, 0.39
uj and 4.8 mm, respectively. Additionally, for the 1064-band
laser, the standard sample of Silicon sheet was used and pulse
energy decreases from 0.39 uj to 1.2 uj. Moreover, transmission
was reduced from 58 percent to 10 percent, which other
parameters were not changed comparing with the 532-band laser.
Elemental analyses were performed at Flash EA 1112 instrument.
b1 (78%) b2 (60%) b3 (70%) b4 (95%)
c1 (91%) c4 (89%) c7 (93%) c10 (92%)
c2 (92%) c5 (95%) c8 (83%) c11 (96%)
TCNE
TCNQ
F4-TCNQ c3 (97%) c6 (98%) c9 (93%) c12 (89%)
Scheme 2. Synthesis routes of click reaction and yield, Reagents
and conditions: (i) THF, TCNE/TCNQ/F4-TCNQ, 40 °C, 2 h.
2.3. Materials synthesis
4,4'-(Ethyne-1,2-diyl)bis(N,N-dibutylaniline) (b1).
a2 (0.166 g, 0.5 mmol) and a4 (0.137 g, 0.6 mmol) were
dissolved in the mixed solvent of TEA (150 mL) and THF (150
mL). The Pd(PPh3)4 (20.8 mg, 0.018 mmol) and CuI (5.7 mg,
0.03 mmol) were added into the solution after flushing with
bubbling Ar gas for 30 min. The reaction mixture was then
stirred at 40 °C for 10 h under Ar atmosphere. The resulting
mixture was concentrated, rediluted with CH2Cl2, and filtered
through a plug of silica gel. The solvent was removed in vacuo,
and the product was purified by column chromatography (SiO2,
petroleum ether/CH2Cl2=4:1) to give b1 (0.155 g, 78%) as a
1
colorless solid. H NMR (CDCl3, 500 MHz): δ=0.99 (m, 12H),
1.38 (m, 8H), 1.62 (m, 8H), 3.31 (m, 8H), 6.59 (d, J=8.5Hz, 4H),
7.36 (d, J=8.5Hz, 4H) ppm. FT-IR (KBr): υ=2947, 2874, 2200,
1587, 1527, 1441, 1367, 1024, 914, 804, 621, 523 cm-1. MALDI-
TOF-MS (dithranol): m/z: calcd for C30H44N2: 432.35 g/mol,
found: 433.3 g/mol [MH]+. Elemental analysis calcd (%) for
C30H44N2 (432.69): C 83.28, H 10.25, N 6.47; found: C 83.27, H
10.26, N 6.47.
2.2. Synthesis routes
All solvents and reagents, unless otherwise stated, were of
puriss quality and used as received. Materials were synthesized
via the synthetic route presented in Scheme 1. a2 - a4, b1, c3, b2, c6
were synthesized according to the corresponding literature
methods[27-31]. Notice: DMF: dimethyl-formamide, THF:
2,3-bis(4-(dibutylamino)phenyl)buta-1,3-diene-1,1,4,4-tetra
tetrahydrofuran,
TEA:
triethylamine,
TMSA:
carbonitrile (c1).
trimethylsilylacetylene, TCNE: tetracyanoethylene, TCNQ: 2,2'-
(cyclohexa-2,5-diene-1,4-diylidene) dimalononitrile, F4-TCNQ:
b1 (43.2 mg, 0.1 mmol) and click reagent TCNE (12.8 mg, 0.1
mmol) were dissolved in THF (2 mL). After the reaction mixture
was then stirred at 40 °C for 2 h under Ar. The solvent was
removed in vacuo, and the product was purified by column
chromatography (SiO2, CH2Cl2) to give c1 (51.0 mg, 91%) as a
black red solid. 1H NMR (CDCl3, 500 MHz): δ=0.98 (m, 12H),
1.39 (m, 8H), 1.64 (m, 8H), 3.39 (m, 8H), 6.67 (d, J=9.0 Hz, 4H),
7.80 (d, J=8.5 Hz, 4H) ppm. FT-IR (KBr): υ=2922, 2836, 2200,
1649, 1607, 1464, 1343, 1184, 914, 621 cm-1. MALDI-TOF-MS
(dithranol): m/z: calcd for C36H44N6: 560.36 g/mol, found: 561.2
g/mol [MH]+. Elemental analysis calcd (%) for C36H44N6: C
77.10, H 7.91, N 14.99; found: C 77.08, H 7.92, N15.00.
2,2'-(perfluoroc-yclohexa-2,5-diene-1,4-diylidene)
nitrile.
dimalono
2-(1,2-bis(4-(dibutylamino)phenyl)-2-(4-(dicyanomethylene)
cyclohexa-2,5-dien-1-ylidene)ethylidene)malononitrile (c2).
Scheme 1. Synthesis routes of compounds, Reagents and
conditions: (i) DMF, C4H9Br, 130 °C, 20 h; (ii) THF, TEA,
Pd(PPh3)4, CuI, TMSA, 40 °C, 12 h; (iii) THF, methanol, K2CO3,
40 °C, 3 h; (iv) THF, TEA, Pd(PPh3)4, CuI, 80 °C, 8 h; (v)
N,N,N’,N’-tetraethylethylenediamine, toluene, CuCl, 60 °C, 24
h.
b1 (43.2 mg, 0.1 mmol) and click reagent TCNQ (20.4 mg, 0.1
mmol) were dissolved in THF (2 mL). After the reaction mixture
was then stirred at 40 °C for 2 h under Ar. The solvent was
removed in vacuo, and the product was purified by column
chromatography (SiO2, CH2Cl2) to give c2 (58.3 mg, 92%) as a
black red solid. 1H NMR (CDCl3, 500 MHz): δ=0.99 (m, 12H),
1.42 (m, 8H), 1.63 (m, 8H), 3.38 (m, 8H), 6.61 (d, J=9.0 Hz, 2H),
6.72 (d, J=9.0 Hz, 2H), 6.98 (d, J=9.0 Hz, 1H), 7.12 (d, J=9.5 Hz,
1H), 7.27 (d, J=9.5 Hz, 1H), 7.35 (d, J=9.0 Hz, 2H), 7.58 (d,

3
J=9.5 Hz, 1H), 7.75 (d, J=8.5 Hz, 2H) ppm. FT-IR (KBr):
υ=2922, 2833, 1575, 1477, 1391, 1331, 1160, 890, 816, 719 cm-1.
MALDI-TOF-MS (dithranol): m/z: calcd for C42H48N6: 636.39
g/mol, found: 636.0 g/mol [M]. Elemental analysis calcd (%) for
C42H48N6: C 79.21, H 7.60, N 13.20; found: C 79.20, H 7.62, N
13.18.
b2 (37.5 mg, 0.1 mmol) and click reagent TCNQ (20.4 mg,
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0.1 mmol) were dissolved in THF (2 mL). After the reaction
mixture was then stirred at 40 ºC for 2 h under Ar. The solvent
was removed in vacuo, and the product was purified by column
chromatography (SiO2, CH2Cl2) to give c5 (55.0 mg, 95%) as a
1
black red solid. H NMR (CDCl3, 500 MHz): δ=0.92 (m, 3H),
1.02 (m, 6H), 1.37 (m, 4H), 1.43 (m, 4H), 1.67 (m, 6H), 2.66 (m,
2H), 3.40 (m, 4H), 6.71 (d, J=9.0 Hz, 2H), 6.94 (d, J=9.5 Hz,
2H), 7.14 (d, J=9.5 Hz, 2H), 7.30 (d, J=7.0 Hz, 2H), 7.54 (d,
J=9.5 Hz, 2H), 7.63 (d, J=7.0 Hz, 2H) ppm. FT-IR (KBr):
υ=2910, 2850, 2187, 1575, 1391, 1331, 1172, 914, 719, 645 cm-1.
MALDI-TOF-MS (dithranol): m/z: calcd for C39H41N5: 579.34
g/mol, found: 579.60 g/mol [M]. Elemental analysis calcd (%)
for C39H41N5: C 80.79, H 7.13, N 12.08; found: C 80.77, H 7.14,
N 12.09.
2-(2-(4-(Dibutylamino)phenyl)-2-(4-(dicyanomethylene)-2,3,5,6-
tetrafluorocyclohexa-2,5-dien-1-ylidene)-1-(4-
nitrophenyl)ethylidene)malononitrile (c3).
b1 (120 mg, 0.361 mmol) and F4-TCNQ (0.090 g, 0.360 mmol)
were dissolved in THF (2 mL). After the reaction mixture was
then stirred at 40 °C for 2 h under Ar atmosphere. The solvent
was removed in vacuo, and the product was purified by column
chromatography (SiO2, CH2Cl2) to give c3 (0.213 g, 97%) as a
black red solid. 1H NMR (CDCl3, 500 MHz): δ=0.94 (m, 6H),
1.00 (m, 6H), 1.44 (m, 4H), 1.51 (m, 4H), 1.66 (m, 4H), 1.78 (m,
4H), 3.57 (m, 4H), 3.61 (m, 4H), 6.62 (d, J=9.0 Hz, 2H), 6.83 (d,
J=9.5 Hz, 2H), 7.41 (d, J=9.0 Hz, 2H), 7.56 (d, J=9.0 Hz, 2H)
ppm. FT-IR (KBr): υ=2947, 2874, 2187, 1587, 1527, 1441, 1367,
1024, 914, 804, 621, 523 cm-1. MALDI-TOF-MS (dithranol): m/z:
calcd for C42H44N6F4: 708.84 g/mol, found: 709.6 g/mol [MH]+.
Elemental analysis calcd (%) for C42H44N6F4 (708.84): C 71.17,
H 6.26, N 11.86; found: C 71.19, H 6.28, N 11.87.
2-(2-(4-(Dibutylamino)phenyl)-2-(4-(dicyanomethylene)-2,3,5,6-
tetrafluorocyclohexa-2,5-dien-1-ylidene)-1-(4-
pentylphenyl)ethylidene)malononitrile (c6).
b2 (112 mg, 0.3 mmol) and F4-TCNQ (0.082 g, 0.30 mmol)
were dissolved in THF (2 mL). After the reaction mixture was
then stirred at 40 °C for 2 h under Ar atmosphere. The solvent
was removed in vacuo, and the product was purified by column
chromatography (SiO2, CH2Cl2) to give c6 (0.19 g, 98%) as a
1
black red solid. H NMR (CDCl3, 500 MHz): δ=0.92 (m, 3H),
N,N-dibutyl-4-((4-pentylphenyl)ethynyl)aniline (b2).
1.04 (m, 6H), 1.36 (m, 4H), 1.48 (m, 4H), 1.67 (m, 2H), 1.75 (m,
4H), 3.68 (m, 2H), 3.60 (m, 4H), 6.86 (d, J=9 Hz, 2H), 7.33 (d,
J=8 Hz, 2H), 7.38 (d, J=9 Hz, 2H), 7.53 (d, J=8 Hz, 2H) ppm.
FT-IR (KBr): υ=2935, 2850, 2200, 1601, 1379, 1012, 816, 645,
559 cm-1. MALDI-TOF-MS (dithranol): m/z: calcd for
C39H37F4N5: 651.30 g/mol, found: 652.4 g/mol [MH]+. Elemental
analysis calcd (%) for C39H37F4N5 (651.30): C 71.87, H 5.72, N
10.75; found: C 71.89, H 5.71, N 10.74.
a4 (0.137 g, 0.6 mmol) and 1-bromo-4-pentylbenzene (0.113 g,
0.5 mmol) were dissolved in the mixed solvent of TEA (150 mL)
and THF (150 mL). The solution was flushed with bubbling Ar
gas for 30 min. Then the Pd(PPh3)4 (20.8 mg, 0.018 mmol) and
CuI (5.7 mg, 0.03 mmol) were added. The reaction mixture was
then stirred at 80 °C for 10 h under Ar atmosphere. The resulting
mixture was concentrated, rediluted with CH2Cl2, and filtered
through a plug of silica gel. The solvent was removed in vacuo,
and the product was purified by column chromatography (SiO2,
petroleum ether/CH2Cl2=7:1) to give b2 (0.135 mg, 60%) as a
N,N-dibutyl-4-((4-nitrophenyl)ethynyl)aniline (b3).
a4 (229.2 mg, 1.0 mmol) and 1-bromo-4-nitrobenzene (200.9
mg, 1.0 mmol) were dissolved in the mixed solvent of 25 mL
TEA and 25 mL THF. After the solution was flushed with
bubbling Ar for 30 min, Pd(PPh3)4 (23.1 mg, 0.02 mmol) and CuI
(7.6 mg, 0.04 mmol) were added. The reaction mixture was then
stirred at 80 ºC for 12 h under an Ar atmosphere. The resulting
mixture was concentrated, rediluted with CH2Cl2, and filtered
through a plug of silica gel. The solvent was removed in vacuo
and the product was purified by column chromatography (SiO2,
petroleum ether/CH2Cl2=4:1) to give b3 (245.0 mg, 70%) as a red
1
yellow oil liquid. H NMR (CDCl3, 500 MHz): δ=0.94 (m, 3H),
1.00 (m, 6H), 1.39 (m, 8H), 1.68 (m, 6H), 2.65 (m, 2H), 3.33 (m,
4H), 6.62 (d, J=9.0 Hz, 2H), 7.17 (d, J=7.5 Hz, 2H), 7.40 (d,
J=9.0 Hz, 2H), 7.45 (d, J=7.5 Hz, 2H) ppm. FT-IR (KBr):
υ=2935, 2850, 2200, 1601, 1503, 1367, 1184, 112, 792, 731, 535
cm-1. MALDI-TOF-MS (dithranol): m/z: calcd for C27H37N:
375.29 g/mol, found: 376.2 g/mol [MH]+. Elemental analysis
calcd (%) for C27H37N (375.29): C 86.34, H 9.93, N 3.73; found:
C 86.35, H 9.94, N 3.74.
1
solid. H NMR (CDCl3, 500 MHz): δ=0.97 (m, 6H), 1.37 (m,
2-(4-(dibutylamino)phenyl)-3-(4pentylphenyl)buta-1,3-diene-
1,1,4,4tetracar-bonitrile (c4).
4H), 1.56 (m, 4H), 3.29 (m, 4H), 6.58 (d, J=11.0 Hz, 2H), 7.38
(d, J=11.0 Hz, 2H), 7.58 (d, J=11.0 Hz, 2H), 8.17 (d, J=11.0 Hz,
2H) ppm. FT-IR (KBr): υ=2960, 2850, 2187, 1587, 1489, 1331,
1190, 809, 731, 509 cm-1.MALDI-TOF-MS (dithranol): m/z:
calcd for C22H26O2N2: 350.20 g/mol, found: 351.1 g/mol [MH]+.
Elemental analysis calcd (%) for C22H26O2N2: C 75.40, H 7.48, N
7.99; found: C75.39, H 7.50, N 7.99.
b2 (37.5 mg, 0.1 mmol) and click reagent TCNE (12.8 mg, 0.1
mmol) were dissolved in THF (2 mL). After the reaction mixture
was then stirred at 40 ºC for 2 h under Ar. The solvent was
removed in vacuo, and the product was purified by column
chromatography (SiO2, CH2Cl2) to give c4 (44.8 mg, 89%) as a
1
black red solid. H NMR (CDCl3, 500 MHz): δ=0.92 (m, 3H),
2-(4-(dibutylamino)phenyl)-3-(4-nitrophenyl)buta-1,3-diene-
1.04 (m, 6H), 1.36 (m, 4H), 1.43 (m, 4H), 1.63 (m, 2H), 1.67 (m,
4H), 2.70 (m, 2H), 3.40 (m, 4H), 6.69 (d, J=9.0 Hz, 2H), 7.35 (d,
J=8.0 Hz, 2H), 7.70 (d, J=8.0 Hz, 2H), 7.80 (d, J=9.0 Hz, 2H)
ppm. FT-IR (KBr): υ=2935, 2850, 2187, 1613, 1477, 1343, 1184,
816 cm-1. MALDI-TOF-MS (dithranol): m/z: calcd for C33H37N5:
503.30 g/mol, found: 504.2 g/mol [MH]+. Elemental analysis
calcd (%) for C33H37N5: C 78.69, H 7.40, N 13.90; found: C
78.68, H 7.43, N 13.89.
1,1,4,4-tetr-acarbonitrile (c7).
b3 (35.0 mg, 0.1 mmol) and click reagent TCNE (12.8 mg, 0.1
mmol) were dissolved in THF (2 mL). After the reaction mixture
was then stirred at 40 ºC for 2 h under Ar. The solvent was
removed in vacuo, and the product was purified by column
chromatography (SiO2, CH2Cl2) to give c7 (44.5 mg, 93%) as a
1
black red solid. H NMR (CDCl3, 500 MHz): δ=1.02 (m, 6H),
1.43 (m, 4H), 1.66 (m, 4H), 3.45 (m, 4H), 6.74 (d, J=9.0 Hz, 2H),
7.79 (d, J=9.0 Hz, 2H), 7.89 (d, J=8.5 Hz, 2H), 8.39 (d, J=8.5 Hz,
2H) ppm. FT-IR (KBr): υ=2922, 2862, 2200, 1587, 1477, 1331,
1172, 902, 719 cm-1. MALDI-TOF-MS (dithranol): m/z: calcd
for C28H26 N6O2: 478.21 g/mol, found: 478.9 g/mol [MH]+.
2-(2-(4-(dibutylamino)phenyl)-2-(4-(dicyanomethylene)
cyclohexa-2,5-dien-1-ylidene)-1-(4-pentylphenyl)
ethylidene)malononitrile (c5).

4
Tetrahedron
Elemental analysis calcd (%) for C28H26N6O2: C 70.28, H 5.48,
1160, 1184, 1098, 926, 790, 523 cm-1. MALDI-TOF-MS
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N 17.56; found: C 70.25, H 5.49, N 17.53.
(dithranol): m/z: calcd for C38H44N6: 584.36 g/mol, found: 584.6
g/mol [M]. Elemental analysis calcd (%) for C38H44N6: C 78.05,
H 7.58, N 14.37; found: C 78.06, H 7.59, N 14.35.
2-(2-(4-(dibutylamino)phenyl)-2-(4-(dicyanomethylene)cyclohexa
-2,5-dien-1-ylidene)-1-(4-nitrophenyl)ethylidene)malononitrile
(c8).
2-(1,4-bis(4-(dibutylamino)phenyl)-1-(4-(dicyanomethylene)
cyclohexa-2,5-dien-1-ylidene)but-3-yn-2-ylidene)malononitrile
(c11).
b3 (35.0 mg, 0.1 mmol) and click reagent TCNQ (20.4 mg, 0.1
mmol) were dissolved in THF (2 mL). After the reaction mixture
was then stirred at 40 ºC for 2 h under Ar. The solvent was
removed in vacuo, and the product was purified by column
chromatography (SiO2, CH2Cl2) to give c8 (47.1 mg, 83%) as a
b4 (45.6 mg, 0.1 mmol) and click reagent TCNQ (20.4 mg, 0.1
mmol) were dissolved in THF (2 mL). After the reaction mixture
was then stirred at 40 ºC for 2 h under Ar. The solvent was
removed in vacuo, and the product was purified by column
chromatography (SiO2, CH2Cl2) to give c11 (63.4 mg, 96%) as a
1
black red solid. H NMR (CDCl3, 500 MHz): δ=1.00 (m, 6H),
1.43 (m, 4H), 1.63 (m, 4H), 3.39 (m, 4H), 6.69 (d, J=8.5 Hz, 2H),
6.98 (d, J=10.0 Hz, 2H), 7.22 (d, J=9.0 Hz, 2H), 7.24 (d, J=7.0
Hz, 2H), 7.32 (d, J=9.5 Hz, 2H), 7.51 (d, J=10.0 Hz, 2H), 7.81 (d,
J=8.5 Hz, 2H), 8.32 (d, J=8.5 Hz, 2H) ppm. FT-IR (KBr):
υ=2922, 2850, 2187, 1575, 1503, 1379, 1331, 890, 707 cm-1.
MALDI-TOF-MS (dithranol): m/z: calcd for C34H30N6O2: 554.24
g/mol, found: 555.1 g/mol [MH]+. Elemental analysis calcd (%)
for C34H30N6O2 (555.1): C 73.63, H 5.45, N 15.15; found: C
73.60, H 5.47, N 15.14.
1
black solid. H NMR (CDCl3, 500 MHz): δ=0.99 (m, 12H), 1.43
(m, 8H), 1.60 (m, 4H), 1.65 (m, 4H), 3.36 (m, 4H), 3.43 (s, 4H),
6.60 (d, J=8.5 Hz, 2H), 6.74 (d, J=9.0 Hz, 2H), 7.26 (m, 2H),
7.41 (d, J=9.0 Hz, 4H), 7.41 (m, 2H) ppm. FT-IR (KBr): υ=2919,
2850, 2187, 2120, 1575, 1391, 1331, 1172, 1098, 890 cm-1.
MALDI-TOF-MS (dithranol): m/z: calcd for C44H48N6: 660.39
g/mol, found: 660.1 g/mol [M]. Elemental analysis calcd (%) for
C44H48N6: C 79.96, H 7.32, N 12.72. found: C 79.98, H 7.32, N
12.70.
2-(2-(4-(dibutylamino)phenyl)-2-(4-(dicyanomethylene)-2,3,5,6-
tetrafluorocy-clohexa-2,5-dien-1-ylidene)-1-(4-nitrophenyl)
ethylidene)malononitrile (c9).
2-(1,4-bis(4-(dibutylamino)phenyl)-1-(4-(dicyanomethylene)-
2,3,5,6-tetrafluor-ocyclohexa-2,5-dien-1-ylidene)but-3-yn-2-
ylidene)malononitrile (c12).
b3 (35.0 mg, 0.1 mmol) and click reagent F4-TCNQ (27.6 mg,
0.1 mmol) were dissolved in THF (2 mL). After the reaction
mixture was then stirred at 40 ºC for 2 h under Ar. The solvent
was removed in vacuo, and the product was purified by column
chromatography (SiO2, CH2Cl2) to give c9 (58.2 mg, 93%) as a
b4 (45.6 mg, 0.1 mmol) and click reagent F4-TCNQ (27.6 mg,
0.1 mmol) were dissolved in THF (2 mL). After the reaction
mixture was then stirred at 40 ºC for 2 h under Ar. The solvent
was removed in vacuo, and the product was purified by column
chromatography (SiO2, CH2Cl2) to give c12 (64.4 mg, 89%) as a
1
black red solid. H NMR (CDCl3, 500 MHz): δ=1.02 (m, 6H),
1
1.44 (m, 4H), 1.73 (m, 4H), 3.59 (m, 4H), 6.85 (d, J=12 Hz, 2H),
7.31 (d, J=11.5 Hz, 2H), 7.77 (d, J=10.5 Hz, 2H), 8.33 (d, J=11.0
Hz, 2H) ppm. FT-IR (KBr): υ=2935, 2850, 2175, 1379, 1330,
1170, 1024, 950, 840, 755 cm-1. MALDI-TOF-MS (dithranol):
m/z: calcd for C34H26F4N6O2: 626.21 g/mol, found: 627.10 g/mol
[MH]+. Elemental analysis calcd (%) for C34H26F4 N6O2: C 65.17,
H 4.18, N 13.41; found: C 65.15, H 4.18, N 13.40.
black solid. H NMR (CDCl3, 500 MHz): δ=0.99 (m, 6H), 1.04
(m, 6H), 1.40 (m, 4H), 1.46 (m, 4H), 1.61 (m, 4H), 1.75 (m, 4H),
3.37 (m, 4H), 3.59 (m, 4H), 6.61 (d, J=9.0 Hz, 2H), 6.82 (d,
J=8.5 Hz, 2H), 7.36 (d, J=8.5 Hz, 2H), 7.45 (d, J=6 Hz, 2H) ppm.
FT-IR (KBr): υ=2972, 2862, 2187, 2139, 1601, 1539, 1367,
1184, 1098, 926, 719, 743 cm-1. MALDI-TOF-MS (dithranol):
m/z: calcd for C44H44F4N6: 732.36 g/mol, found: 733.5 g/mol
[MH]+. Elemental analysis calcd (%) for C44H44F4N6: C 72.11, H
6.05, N 11.47; found: C 72.09, H 6.06, N 11.46.
4,4'-(buta-1,3-diyne-1,4-diyl)bis(N,N-dibutylaniline) (b4).
To a solution of a4 (458.4 mg, 2.0 mmol) in toluene (3 mL),
CuCl (97.9 mg, 1.0 mmol) and N, N, N’, N’-
tetramethylethylenediamine (0.8 mL, 5.5 mmol) was added, and
the mixture was stirred at 60 ºC for 24 h. The mixture was
concentrated, rediluted with CH2Cl2, and filtered through a plug
of silica gel. The solvent was removed in vacuo, and the resulting
product was purified by column chromatography (SiO2,
petroleum ether/CH2Cl2=4:1) to give b4 (424.4 mg, 93%) as a
yellow solid. 1H NMR (CDCl3, 500 MHz): δ=0.98 (m, 12H), 1.38
(m, 8H), 1.58 (m, 8H), 3.29 (m, 8H), 6.55 (d, J=6.5 Hz, 4H), 7.36
(d, J=9.0 Hz, 4H) ppm. FT-IR (KBr): υ=2972, 2862, 2187, 2139,
1601, 1539, 1367, 1184, 1098, 926, 719, 743 cm-1. MALDI-TOF-
MS (dithranol): m/z: calcd for C32H44N2: 456.35 g/mol, found:
457.6 g/mol [MH]+. Elemental analysis calcd (%) for C32H44N2: C
84.16, H 9.71, N 6.13; found: C 84.17, H 9.70, N 6.14.
3. Results and discussion
The reacting aromalkyne molecules b1-b4 were shown in
Scheme 1, were synthesized according to the literature
methods[27]. All the compounds were fully characterized by
NMR, IR, and MS spectra from which the chemical structures
were verified. Compounds (b1-b4) have good solubility in
common organic solvents. Synthesis of donor-acceptor
chromophores c1-c12 was achieved through introducing in amine-
substituted aromatic precursors by the high-yielding [2+2] click
reactions using TCNE, TCNQ, and F4-TCNQ as acceptor
molecules. As it was shown in Scheme 2, the click reaction was
high yield from 83% to 95%, could be fulfilled under ambient
temperature, and enhancement of temperature to 40 ºC was just
for higher efficiency. In the previous studies[31-35], it has been
proved that the [2+2] click reaction has high yield and near to
100%. In this paper, the equimolar mixtures of alkynyl and click
reagent were used, but a certain kind of compound should be
residual. Here we selected the column chromatography to purify
the products and to remove the trace amount of residual
compounds. However, losing parts of products in purified
process influence on the data of yields, and all the yields would
be lower than 100%. In addition, b4 has the diacetylene and it
was difference from b1 – b3. In the reference [36-43], it was
proved that only one alkyne in the diacetylene can be reacted
with the electron-withdrawing click reagents. In this paper,
because it was symmetrical chemical structure for b4, any one of
2-(4-(dibutylamino)phenyl)-3-((4-(dibutylamino)phenyl)ethynyl)
buta-1,3diene-1,1,4,4-tetracarbonitrile (c10).
b4 (45.6 mg, 0.1 mmol) and click reagent TCNE (12.8 mg, 0.1
mmol) were dissolved in THF (2 mL). After the reaction mixture
was then stirred at 40 ºC for 2 h under Ar. The solvent was
removed in vacuo, and the product was purified by column
chromatography (SiO2, CH2Cl2) to give c10 (53.7 mg, 92%) as a
1
black solid. H NMR (CDCl3, 500 MHz): δ=0.99 (m, 12H), 1.42
(m, 8H), 1.67 (m, 8H), 3.41 (m, 8H), 6.62 (d, J=9.0 Hz, 4H), 6.69
(d, J=9.0 Hz, 4H), 7.47 (d, J=8.5 Hz, 4H), 7.82 (d, J=9.0 Hz, 4H)
ppm. FT-IR (KBr): υ=2922, 2836, 2223, 2127, 1587, 1515, 1343,

5
alkyne groups was reacted with the click reagents, the products
would be same. All the newly prepared products were in high
purity, which was confirmed by NMR, IR, and MS spectra.
Moreover, they were stable at ambient temperature under air and
reasonably soluble in common organic solvents, such as CH2Cl2,
acetone, and acetonitrile, which was beneficial for processing.
Furthermore, no special purification process was necessary
because of the absence of byproducts. Therefore, this kind of
reaction satisfied most of the requirements of click chemistry,
and it could be classified as a new metal-free click chemistry that
further improved optoelectronic properties of organic materials.
significantly to larger value. In addition, the introduction of the
ACCEPTED MANUSCRIPT
strong electron-withdrawing group (-NO2) managed to extend
photo absorption to a longer wavelength region and the
maximum absorption was red-shifted significantly to larger value
comparing with other compounds under the same conditions.
3.1. UV–vis absorption
The normalized UV-vis absorption spectra were shown in Fig.
1. The spectral shapes and positions were very similar to the
reported click products[27-35]. Most of the prepared products
showed intense CT bands with end-absorptions reaching into the
near infrared region. Aromoalkyne b1-b4 reacting with different
click reagents TCNE, TCNQ, and F4-TCNQ yielded click
compounds c1-c12, respectively (Scheme 2). Throughout the click
reaction, the colors of compounds were changed, and the images
of solution samples were shown in Fig. 1. For example, the color
was nearly colorless for b1 solution, was red for c1 solution (with
TCNE moiety), was black red for c2 solution (with TCNQ
moiety), and was black brown for c3 solution (with F4-TCNQ
moiety). The color got darker from b1, c1, c2, and c3, and it was
suggested that the UV-vis absorption spectra would be different
obviously. For example, the maximum absorption of b1 was 341
nm, and was red-shifted significantly to 480 nm, 684 nm and 830
nm for c1, c2, and c3. For the other series, the similar phenomena
were observed and the results were shown in Fig.1 (b-d). The
reasons were dramatically facilitated by the elongation of
conjugation lengths of molecular backbones and enhancement of
electron affinities via introduction of strong electron-withdrawing
substitutes[31].
Table 1. Optical properties of all products
εb
(10-3M-
1cm-1)
1.8
εb
(10-3M-
1cm-1)
1.6
2.5
2.9
3.6
2.1
2.2
2.4
a
c
a
c
Mate λmax
Eg
Mate λmax
Eg
rial
(nm)
(eV)
rial
(nm)
(eV)
b1
c1
c2
c3
b2
c4
c5
c6
341
480
686
832
342
480
696
863
3.16
1.95
1.33
1.06
3.23
1.93
1.24
1.00
b3
c7
c8
430
469
723
890
357
534
706
856
2.13
1.64
1.13
0.91
2.93
1.60
1.20
0.95
3.1
3.2
3.5
1.2
1.4
1.6
3.3
c9
b4
c10
c11
c12
2.6
aAbsorption spectra were measured in CH2Cl2 solution (5×10-5
M).
bε was the molar extinction coefficient at the absorption peak of
λmax with maximum wavelength).
cBand gap estimated from the onset wavelength of optical
absorption in CH2Cl2 solution.
For the c3, c6, c9, and c12, the same click reagent (F4-TCNQ)
was used, and the main difference was the substituted group,
such as R1. The UV-vis absorption spectra were shown in Fig. 1
(e), and it can be proved that the spectra were influenced by the
substituted group. The red-shifted order was c3, c12, c6, and c9.
Although the substituted group was similar for c3, and c12, the
conjugation length of c12 was larger than that of c3, and the
intramolecular charge transferred over a longer conjugation
length along the molecular backbones, so the CT bands were red
shifted form 832 nm to 856 nm. The introduction of the weak
electron donating group (-C5H11) broke molecular symmetry and
make electronic adjacent circulating ability easier, so compared
with c12 the maximum absorption peak of c6 were red-shifted
Fig. 1. UV-vis absorption spectra of compounds in CH2Cl2 at RT
(the inset photographs were the images of solutions).

6
Tetrahedron
3.2. Electrochemical Properties
c3
0.35
--
-0.45
-1.23
-0.98
-0.65
-0.33
-1.25
-0.7
-5.15
--
-5.58
-5.11
-5.20
--
-5.64
-5.11
-5.20
--
-5.70
-5.11
-5.20
-4.35
-3.57
-3.82
-4.15
-4.47
-3.55
-4.10
-4.20
-4.53
-3.57
-4.05
-4.22
-4.50
0.80
--
1.76
0.96
0.73
--
1.54
0.91
0.67
--
1.65
0.89
0.70
ACCEPTED MANUSCRIPT
b2
c4
To evaluate the possibility of electron transfer, the CV of
0.78
0.31
0.4
--
0.84
0.31
0.4
--
compounds were tested, and some CV curves were shown in Fig.
2 (a). The data were listed in Table 1, such as onset
oxidation/reduction potentials, band gaps, LUMO and HOMO
levels. According to the data, it was clear that the band gaps and
energy levels were affected by the chemical structures, such as
the substituted groups and clicked moieties. It was suggested that
the parental choice would be increased, such as the band gaps
(from 0.9 to 3.1). For the band gaps, some interesting phenomena
can also be observed from Fig. 2 (b). If the compounds have the
same substituted groups and different clicked moieties, the band
gaps became smaller with the introduction of click reagent
(TCNE, TCNQ, F4-TCNQ) for all the series. The reasons were
dramatically facilitated by the elongation of conjugation lengths
of molecular backbones and enhancement of electron affinities
via introduction of strong electron-withdrawing substitutes[31].
If the compounds have the same clicked moieties and different
substituted groups, a broadly decreasing trend for band gap was –
N(C4H9)2, –C5H11, -NO2. The introduction of the weak electron
donating group (-C5H11) broke molecular symmetry and make
electronic adjacent circulating ability easier, and the introduction
of the strong electron-withdrawing group (-NO2) managed to
decrease the band gaps too. In short, depending on the difference
click reagent and the difference of the terminal group, both the
HOMO levels and the LUMO levels were regulated in varying
degrees, which was in result of the enlargement of the absorption
spectrum and the corresponding CT bands strongly
bathochromically shifted with an end-absorption, and
photoelectric properties of organic materials further was
improved.
c5
c6
b3
c7
c8
-0.6
c9
-0.27
-1.23
-0.75
-0.58
-0.3
b4
c10
c11
c12
0.9
0.31
0.4
aOnset potentials determined from cyclic voltammograms in
CH2Cl2/Bu4NPF6 at a scan rate of 40 mV/s.
bBand gap calculated from the energy level of cyclic
voltammograms.
3.3. Nonlinear optics Properties
Z-scan experiments were utilized to evaluate the applications
of NLO enhancements via fictionalization of click reagents and
the results were shown in Fig. 3. The NLO parameters were
summarized in Table 2, which included with nonlinear
absorption coefficient (β), nonlinear index (n) and third-order
nonlinear susceptibility. The study indicated that the compounds
without clicked moieties did not exhibit any NLO response. After
the clicked functional methods, the compounds have strong third-
order NLO properties through modification of the different click
chemistry. The third-order NLO properties relied on strong
partnerships with chemical structures. When using 532 pulses,
materials, having end group of the amyl (–C5H11), showed a
prominent nonlinear properties comparing with other
compounds, which non-linear absorption coefficient of c5 shows
higher magnitude of 10-11 and nonlinear index value was 100
times that of other materials under the same conditions. To our
surprise, the NLO properties of b2 derivatives were better than
those of other compounds. Comparing to b1, b2 lacks a strong
electron donating group. Comparing to b3, b2 lacks a strong
electron withdrawing group. Comparing to b4, b2 has the shorter
conjugated
structure.
Usually,
the
strong
electron
donating/withdrawing and the conjugated structures are the key
factors for enhancing NLO properties. We suspect that the
unusual phenomenon may be due to electronic cloud distribution.
The abilities of π-electron delocalization and intramolecular
charge transfer are the foundation for enhancing NLO properties.
The strong electron donating/withdrawing could improve abilities
of π-electron delocalization, but hinder transfer abilities. When
using 1064 pulses, it was attractive that these material,
functionalized by click reagent of F4-TCNQ, had pretty high non-
linear absorption coefficient (10-7) and nonlinear index(10-13),
and that of these numbers were obviously larger than that of
these irradiated by 532 pulses. Automatically, comparing with
using 532 pulses, these materials also showed amazing third-
order nonlinear susceptibility when using 1064 pulses. From the
UV-vis absorption spectra, the products with F4-TCNQ moieties
were potentially facilitated at long wavelength. It was suggested
that the existence of strong electron-withdrawing substitutes
caused that the negative charge located on the click moieties, and
the products were easier excitated using 1064 pulses.
Fig. 2. Cycle voltammograms of clicked derivatives c1, c4, c7 and
c10 at RT.
Table 3. NLO properties of all the products
Table 2. Electrochemical properties of all products
a
a
b
NLO (532 nm)
NLO (1064 nm)
N
Energy level
Eox
Ered
Eg
χ(3)
10-13
esu
--
β
χ(3)
10-7
esu
--
Material
Mate
rial
β
N
10-19
m2/W
--
a
a
(eV)
(eV)
(eV)
EHOMO
ELUMO
10-12
m/W
--
10-13
m/W
--
10-7
m2/W
--
b1
c1
c2
--
-1.28
-1.08
-0.71
--
-5.52
-5.09
-3.52
-3.72
-4.09
--
1.80
1.00
0.72
0.29
b1
c1
-1.8
-7.0
4.02
--
--
--

7
Acknowledgments
c2
c3
b2
c4
c5
0.3
1.3
--
-8.5
20.5
1.5
1.7
--
-10.5
128.5
0.86
1.31
--
10.5
72.64
--
-3.3
--
--
--
--
5.5
--
--
--
--
1.83
--
ACCEPTED MANUSCRIPT
This work was supported by the National Key Basic Research
Program of China (No. 2014CB931804), Natural Science Basic
Research Plan in Shaanxi Province of China (No. 2013JQ8043).
--
--
5×10-
c6
9.1
0
6.64
10-5
10-5
References and notes
6
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b3
c7
c8
--
--
-3.2
1.7
1.7
--
--
1.6
--
--
--
--
--
-3.3
--
0
--
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1.69
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-0.5
1.96
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1.13
0.37
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We addressed the significance of third-order NLO properties
in the compounds obtained by click chemistry. It was found that
the introduction of the click reagents improved optical
performance can make the electron cloud arrange, renewably,
which UV-vis spectra were enlarged with end-absorptions into
the near infrared region in varying degrees and energy level has
been adjusted appropriately. Z-scan measurements to evaluate the
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derivative compounds modulated by click reagents have excellent
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8
Tetrahedron
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ACCEPTED MANUSCRIPT
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