Syntheses and characterizations of Zn (Ⅱ) Phthalocyanines & Naphthopyrans based polymers for improved nonlinear optical properties

Article abstract of DOI:10.1016/j.dyepig.2020.108662

In this paper, four organic polymers of poly [(MMA)_x-co-(NPMA)_y-co-(CPMA)_z] and four zinc phthalocyanine (ZnPc) polymers of poly [(MMA)_x-co-(NPMA)_y-co-(ZnPc)_z] have been successfully synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization, where MMA is methyl methacrylate, NPMA is 3,3-diphenyl-8-methacryloxy-3H-naphtho [2,1-b]pyran, and CPMA is 3,4-dicyanophenyl methacrylate. The components of these polymers have been fully characterized by ¹H and ¹³C NMR, FT-IR, Raman, XPS, UV–Vis, and photoluminescence (PL) spectroscopy. From PL spectra, poly [(MMA)_x-co-(NPMA)_y-co-(ZnPc)_z] polymers display strong fluorescence quenching by the energy transfer (ET) process between NPMA and ZnPc moieties. The third-order nonlinear optical (NLO) properties of poly [(MMA)_x-co-(NPMA)_y-co-(ZnPc)_z] polymers have been investigated by the Z-scan technique, and poly [(MMA)₁₆₈-co-(NPMA)_5.2-co-(ZnPc)_1.2] (Q4) showed the best NLO properties owing to the much stronger ET between NP and ZnPc units. Furthermore, it is essential to obtain doped poly (methyl methacrylate) (PMMA) films for practical application. The poly [(MMA)₁₆₈-co-(NPMA)_5.2-co-(ZnPc)_1.2]/PMMA film exhibited a higher nonlinear absorption coefficient of 61 × 10^?11 m/W and a lower limiting threshold of 0.19 J/cm². The significantly enhanced NLO properties of poly [(MMA)₁₆₈-co-(NPMA)_5.2-co-(ZnPc)_1.2]/PMMA film compared with solution are attributed to the weaker aggregation effect in PMMA film. This research provides a promising molecular design strategy for high performance NLO materials.

Full text of DOI:10.1016/j.dyepig.2020.108662

Journal Pre-proof
Syntheses and Characterizations of Zn (Ⅱ) Phthalocyanines & Naphthopyrans Based
Polymers for Improved Nonlinear Optical Properties
Jihua Wang, Wenyue Dong, Bo Gao, Dajun Liu, Qian Duan
PII:
S0143-7208(20)31359-0
DOI:
https://doi.org/10.1016/j.dyepig.2020.108662
DYPI 108662
Reference:
To appear in: Dyes and Pigments
Received Date: 14 January 2020
Revised Date: 31 May 2020
Accepted Date: 20 June 2020
Please cite this article as: Wang J, Dong W, Gao B, Liu D, Duan Q, Syntheses and Characterizations of
Zn (Ⅱ) Phthalocyanines & Naphthopyrans Based Polymers for Improved Nonlinear Optical Properties,
Dyes and Pigments, https://doi.org/10.1016/j.dyepig.2020.108662.
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Graphical Abstract
Syntheses and Characterizations of Zn ( ) Phthalocyanines &
Naphthopyrans Based Polymers for Improved Nonlinear Optical
Properties

Syntheses and Characterizations of Zn ( ) Phthalocyanines &
Naphthopyrans Based Polymers for Improved Nonlinear
Optical Properties †
Jihua Wanga, Wenyue Donga, Bo Gaoa, Dajun Liub and Qian Duan*a, c
a. School of Materials Science and Engineering, Changchun University of Science and Technology,
Changchun, 130022, China.
b. School of Chemistry and Environmental Engineering, Changchun University of Science and
Technology, Changchun, 130022, China.
c. Engineering Research Center for Opto-electronic Functional Materials, Ministry of Education,
Changchun, 130022, China. E-mail: duanqian88@hotmail.com
Corresponding author: Fax: +86 431 85583015
E-mail: duanqian88@hotmail.com

Abstract
In this paper, four organic polymers of poly[(MMA)x-co-(NPMA)y-co-(CPMA)z]
and
four
zinc
phthalocyanine
(ZnPc)
polymers
of
poly[(MMA)x-co-(NPMA)y-co-(ZnPc)z] have been successfully synthesized by reversible
addition-fragmentation chain transfer (RAFT) polymerization, where MMA is methyl
methacrylate, NPMA is 3,3-diphenyl-8-methacryloxy-3H-naphtho[2,1-b]pyran, and
CPMA is 3,4-dicyanophenyl methacrylate. The components of these polymers have been
fully characterized by 1H and 13C NMR, FT-IR, Raman, XPS, UV-Vis, and
photoluminescence
(PL)
spectroscopy.
From
PL
spectra,
poly[(MMA)x-co-(NPMA)y-co-(ZnPc)z] polymers display strong fluorescence quenching
by the energy transfer (ET) process between NPMA and ZnPc moieties. The third-order
nonlinear optical (NLO) properties of poly[(MMA)x-co-(NPMA)y-co-(ZnPc)z] polymers
have
been
investigated
by
the
Z-scan
technique,
and
poly[(MMA)168-co-(NPMA)5.2-co-(ZnPc)1.2] (Q4) showed the best NLO properties owing
to the much stronger ET between NP and ZnPc units. Furthermore, it is essential to obtain
doped poly(methyl methacrylate) (PMMA) films for practical application. The
poly[(MMA)168-co-(NPMA)5.2-co-(ZnPc)1.2] / PMMA film exhibited a higher nonlinear
absorption coefficient of 61×10-11 m/W and a lower limiting threshold of 0.19 J/cm2. The
significantly enhanced NLO properties of poly[(MMA)168-co-(NPMA)5.2-co-(ZnPc)1.2] /
PMMA film compared with solution are attributed to the weaker aggregation effect in
PMMA film. This research provides a promising molecular design strategy for high
performance NLO materials.
Keywords: phthalocyanine; naphthopyran; RAFT; nonlinear optical property;
2

Z-scan
3

1. Introduction
Metal phthalocyanines (MPcs) and their derivatives are a series of macrocyclic
molecules with planar conjugated array of 18-π electrons, and often play a key role in
materials chemistry fields such as electronic devices, catalysts and supramolecules, due to
their unique optical, electronic, spectral and structural properties [1-3]. Especially they
exhibited excellent nonlinear optical (NLO) properties, such as large third-order NLO
coefficient, rapid responsiveness and excellent light/thermal stability [4-6], which could
be widely applied in the fields of optical limiting, solar cells, optical signal processing,
optical switch and information storage [7-10]. In recent years, to further improve the
nonlinear effects of phthalocyanines, different materials were combined with MPcs such
as metallic nanoparticles [11-14], carbon-based materials [15-18] and chromophores
[19,20]. MPc constructed from various of chromophores via covalent bonds have
increasingly gained interest due to their excellent and unique properties, such as simple
functionality, well-defined chemical composition, and tunable structures [21,22].
To our surprise, introduction of chromophores such as azobenzene, carbazole and
benzimidazole benzothiazole to MPcs can improve the optical limiting performance and
enhance the NLO parameters [23-26]. These chromophores which have rigid plane
structure and larger conjugated system make them possess preferable optical performance,
such as photosensitizers, fluorescence probe and nonlinear optical materials. Also, they
could act as energy donors in the presence of acceptors. Due to an energy transfer (ET)
effect between donors and acceptors, the increased rates of intersystem crossing (ISC) to
the triplet state enhance NLO properties of MPc with chromophores. Herein we choose
naphthopyran (NP) as an excellent chromophore and combine NP with MPcs. NP as a
4

special class of chromophore possesses several advantages for the applications in optical
switches, fluorescence modulations, and ophthalmic lenses, for example, absence of
background color, high color density, broad color gamut, good thermal reversibility and
resistance to photochemical fatigue [27-29]. Therefore, NP could act as an outstanding
energy donor due to their unique physical and chemical properties [30-32]. However, to
the best of our knowledge, many materials have been researched on NLO field, and the
NLO properties of NP covalently functionalized with MPcs has few studies so far
[33-36].
Herein, in order to further improve the NLO properties, increase the solubility of
zinc phthalocyanine (ZnPc) in common organic solvents and broaden the application
scope, a series of poly[(MMA)x-co-(NPMA)y-co-(ZnPc)z] polymers were designed and
synthesized. Firstly, the poly[(MMA)x-co-(NPMA)y-co-(CPMA)z] polymers were
synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization
with
the
monomers
of
methyl
and
methacrylate,
3,3-diphenyl-8-methacryloxy-3H-naphtho[2,1-b]pyran,
3,4-dicyanophenyl
methacrylate. After that, the targeted poly[(MMA)x-co-(NPMA)y-co-(ZnPc)z] polymers
were prepared by reacting poly[(MMA)x-co-(NPMA)y-co-(CPMA)z] polymers with zinc
1
acetate and 4-nitrophthalonitrile. The structure of the polymers was characterized by H
and 13C NMR, FT-IR, Raman, XPS and UV-Vis spectroscopy. All the obtained polymers
have excellent solubility in common organic solvents, coupled with good film-forming
property and processability. Among them, poly[(MMA)168-co-(NPMA)5.2-co-(ZnPc)1.2]
polymers show excellent initial transmittance and nonlinear absorption coefficient by
Z-scan test, which illustrates that the nonlinear absorption coefficients increase with the
5

increased ratio of NPMA in the polymers. The enhanced NLO properties demonstrate that
the efficient ET process between NPMAs and ZnPcs played a pivotal role in the
poly[(MMA)168-co-(NPMA)5.2-co-(ZnPc)1.2] polymers, where NPMA acts as an
outstanding energy donor, ZnPc acts as an energy acceptor [37-39]. Furthermore, we also
studied the NLO properties of the poly[(MMA)x-co-(NPMA)y-co-(ZnPc)z] / PMMA
doped films, and the results demonstrate that the NLO properties of the
poly[(MMA)x-co-(NPMA)y-co-(ZnPc)z] / PMMA films are better than that in solution,
which makes them more accessible for practical application.
2. Experimental
2.1 Instruments and parameters
Fourier transform infrared spectra were recorded on a Shimadzu-8400S FT-IR
spectrophotometer. The samples for FT-IR measurement were prepared with KBr plates.
1H NMR and 13C NMR spectra were recorded on a Bruker AVANCE II 500 MHz NMR
spectrometers using tetramethylsilane (TMS) as an internal reference. Matrix-assisted
laser desorption ionization time-of-flight mass (MALDI-TOF MS) spectra were recorded
on Bruker Autoflex III. The UV-Vis absorption spectra were recorded on a Shimadzu
UV-2600 UV-vis spectrophotometer. Photoluminescence (PL) spectra were measured on
a
PerkinElmer LS-55 Fluorescence Spectrometer using appropriate filters.
Thermogravimetric analysis (TGA) was determined by TA5000-2950TGA with a heating
rate of 10 °C/min under the protection of nitrogen. Raman spectra were obtained on
LabRAM HR Evolution HORIBA Scientific spectrometer equipped with the
semiconductor laser of 532 nm generation wavelength, impact power of 0.8 mW and
duration time of 20 s. X-ray photoelectron spectroscope analysis was recorded by
6

ESCALAB MK II X-ray Instrument using an Al Kα source. The particle diameters were
determined using dynamic light scattering (DLS) with WYATT Technology DynaPro
NanoStar detector. Number-average molecular weights (Mn) and the polydispersity index
(PDI: Mw/Mn) were determined using gel permeation chromatography (GPC) in THF, and
calibrated with polystyrene standards on the instrument equipped with Waters 1100 pump,
Waters 2414 RID detector and Styragel HR 4 THF 7.8×300 mm columns. The Z-scan
measuring instrument was purchased from Suzhou micronano laser photon technology
Co., Ltd. All Z-scan measurements were performed using a frequency doubled Nd:YAG
laser. The second harmonic of a Q-switched Nd: YAG laser (1064 nm, 7 ns) was used as
the laser source with a repetition rate of 10 Hz. The sample solutions were placed in a
cuvette (internal dimensions: 2 mm×10 mm×5.5 mm, 0.7 mL) and a path length of 2 mm.
2.2 Materials
2,2′-Azobis(2-methyylpropionitrile) (AIBN) purchased from Sinopharm Chemical
Reagent Co. was recrystallized three times from ethanol and dried under vacuum before
use. Methyl methacrylate (MMA) purchased from Shanghai Macklin Biochemical Co.,
Ltd was distilled at reduced pressure. 1,4-dioxane purchased from Aladdin Reagent
Company was distilled prior to use. S-1-dodecyl-S'-(α,α'-dimethyl-α"-acetic
acid)trithiocarbonate (DDMAT) and 4-hydroxyphthalonitrile were synthesized according
to previous literature [40,41]. Trimethylsiylacetylene, n-butyllithium in hexanes (2.2
mol/L),
diphenyl
ketone,
2,6-naphthalenediol,
benzyl alcohol,
methacryloyl
chloride,
and
para-toluenesulfonate
(PTSA),
zinc acetate
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) were purchased from Aladdin Reagent
Company and used as received. All other chemicals were purchased from Sinopharm
7

Chemical Reagent Co. and were used as received. The dialysis bags were purchased from
MYM Biological Technology Company Limited with MwCO 5000D. The synthetic
routes of the monomers and the corresponding polymers were presented in Scheme 1 and
2, respectively. All reactions were performed under N2 atmosphere.
2.3 Synthesis of monomers and polymers
Scheme 1. Synthetic routes of monomer CPMA and NPMA.
Synthesis of 3,4-dicyanophenyl methacrylate (CPMA).
4-Hydroxyphthalonitrile (1153 mg, 8.0 mmol) and triethylamine (1.1 mL, 8.0 mmol)
were added into 15 mL THF and the mixture was cooled down to 0 °C. Methacryloyl
chloride (0.82 mL, 8.4 mmol) in CH2Cl2 (DCM) (15 mL) was dropped into the reaction
mixture. After stirring for 24 h, the mixture was extracted with DCM. The organic phase
was collected and washed with water, and then dried with anhydrous sodium sulfate. The
pure CPMA was obtained by column chromatography on silica gel (ethyl acetate:
petroleum ether=1: 4) as 1419 mg white powder with a yield of 83%. 1H NMR (500 MHz,
DMSO-d6, 25 °C) (δ, ppm): 8.25(d, J= 8.8 Hz, 1H, Ar-H), 8.16(d, J= 2.2 Hz, 1H, Ar-H),
8

7.86(dd, J= 8.6 Hz, J= 2.1 Hz, 1H, Ar-H), 6.34 (s, 1H, CH2=C), 6.00(s, 1H, CH2=C),
13
2.02(s, 3H, CH3). C NMR (125 MHz, CDCl3, 25 °C) (δ, ppm): 164.2, 154.1, 135.0,
134.6, 129.6, 127.2, 127.0, 117.3, 115.0, 114.6, 112.9, 18.2. FT-IR (KBr, cm-1) νmax: 3112
(Ar, C-H), 3054 (C=C-H), 2237 (C≡N), 1736 (C=O), 1634 (C=C), 1601, 1570, 1488,
1455 (Ar, C-C), 1380 (CH3), 1243, 1132 (C-O). MALDI-TOF-MS m/z: calc. for
C12H8N2O2 [M-H] +: 213.1; found 213.0.
Synthesis of 1,1-diphenyl-2-yn-1-ol (M1)
Trimethylsiylacetylene (1.2 mL, 8.0 mmol) and n-butyllithium in hexanes (3.7 mL,
8.0 mmol) were added into anhydrous THF (15 mL) at -10 °C via syringe nitrogen
atmosphere. After stirring for 1 h, diphenyl ketone (1385 mg, 7.6 mmol) was added and
the reaction mixture was stirred for another 4 h. A methanol solution (10 mL) of KOH
(898 mg, 16 mmol) was added into the above solution, and the solution was warmed to
room temperature for 0.5 h and the mixture was neutralized with acetic acidand extracted
with DCM. The organic solution was washed with brine and dried with anhydrous
sodium sulfate. The pure M1 was obtained by column chromatography on silica gel
(ethyl acetate: petroleum ether=1: 20) as 1459 mg slight yellow solid with a yield of 92%.
1H NMR (500 MHz, DMSO-d6, 25 °C) (δ, ppm): 7.53(m, 4H, Ar-H), 7.33(m, 4H, Ar-H),
7.24(m, 2H, Ar-H), 6.80(s, 1H, OH), 3.80(s, 1H, C≡CH). 13C NMR (125 MHz, CDCl3,
25 °C) (δ :
, ppm): 144.3, 128.3, 127.9, 125.9, 86.3, 75.6, 74.3. FT-IR (KBr, cm-1) νmax
3554 (O-H), 3275 (≡C-H), 3083, 3060, 3026 (Ar, C-H), 2116 (C≡C), 1597, 1489, 1449
+
(Ar, C-C), 1097 (C-C), 1052 (C-O). MALDI-TOF-MS m/z: calc. for C15H12O [M-H] :
209.1; found 209.1.
Synthesis of 6-hydroxynaphthalen-2-yl methacrylate (M2)
9

2,6-Naphthalenediol (1281 mg, 8.0 mmol) and triethylamine (1.1 mL, 8.0 mmol) in
THF (15 mL) were cooled down to 0 °C. Methacryloyl chloride (0.82 mL, 8.4 mmol) in
DCM (15 mL) was dropped into the reaction mixture. The solution was stirred for 24 h.
The product was extracted with DCM and the organic solution was washed with water
and dried with anhydrous sodium sulfate. The pure M2 was obtained by column
chromatography on silica gel (ethyl acetate: petroleum ether=1: 6) as 683 mg white
powder with a yield of 37%. 1H NMR (500 MHz, DMSO-d6, 25 °C) (δ, ppm): 9.79(s, 1H,
OH), 7.77(t, J= 8.8 Hz, 2H, Ar-H), 7.58(d, J= 2.2 Hz, 1H, Ar-H), 7.23(dd, J= 8.8 Hz, J=
2.3 Hz, 1H, Ar-H), 7.17(d, J= 2.2 Hz, 1H, Ar-H), 7.13(dd, J= 8.8 Hz, J= 2.3 Hz, 1H,
Ar-H), 6.31(s, 1H, CH2=C), 5.92(s, 1H, CH2=C), 2.03(s, 3H, CH3). 13C NMR (125
MHz, CDCl3, 25 °C) (δ, ppm): 166.9, 153.4, 146.6, 135.8, 132.5, 129.2, 128.6, 127.8,
121.4, 118.6, 118.5, 109.5, 18.5. FT-IR (KBr, cm-1) νmax: 3427 (O-H), 2962, 2929 (CH3,
C-H), 1718 (C=O), 1637 (C=C), 1606, 1524, 1436, 1390 (Ar, C-C), 1228, 1210 (C-O).
MALDI-TOF-MS m/z: calc. for C14H12O3 [M-H] +: 229.1; found 229.1.
Synthesis of 3,3-diphenyl-8-methacryloxy-3H-naphtho[2,1-b]pyran (NPMA)
A mixture of 6-hydroxynaphthalen-2-yl methacrylate (1141 mg, 5.0 mmol),
1,1-diphenyl-2-yn-1-ol (1250 mg, 6.0 mmol) and PTSA (114 mg,0.60 mmol) in
anhydrous DCM solution (10 mL) was stirred at room temperature for 48 h. The reaction
mixture was extracted with DCM and the organic solution was washed with water and
dried with anhydrous sodium sulfate. The pure NPMA was obtained by column
chromatography on silica gel (DCM: petroleum ether=2: 3) as 1312 mg white powder
with a yield of 62%. 1H NMR (500 MHz, DMSO-d6, 25 °C) (δ, ppm): 8.17(d, J= 9.2 Hz,
1H, CH=C), 7.80(d, J= 8.9 Hz, 1H, Ar-H), 7.64(d, J= 2.3 Hz, 1H, Ar-H), 7.51(m, 5H,
10

Ar-H), 7.35(m, 6H, Ar-H), 7.26(t, J= 7.3 Hz, 2H, Ar-H), 6.64(d, J= 10.0 Hz, 1H, CH=C),
6.32(s, 1H, CH2=C), 5.92(s, 1H, CH2=C), 2.03(s, 3H, CH3). 13C NMR (125 MHz,
CDCl3, 25 °C) (δ, ppm): 166.1, 150.4, 147.0, 144.7, 135.9, 129.6, 129.4, 128.2,
128.1, 127.8, 127.6, 127.3, 127.0, 122.8, 121.8, 119.5, 119.2, 114.3, 82.6, 18.5.
FT-IR (KBr, cm-1) νmax: 3061, 3029 (Ar, C-H), 2957, 2927 (CH3, C-H), 1730 (C=O),
1636, 1619 (C=C), 1594, 1516, 1448 (Ar, C-C), 1232, 1224, 1159, 1131 (C-O).
MALDI-TOF-MS m/z: calc. for C29H22O3 [M-H] +: 419.2; found 419.3.
1
The H NMR, 13C NMR, FT-IR and MS spectra of the above molecules were
showed in supplementary information (Fig. S1-S4).
Scheme 2. Synthetic routes of P1 P5 (up) and Q1 Q5 (down).
11

Synthesis of poly[(MMA)161-co-(CPMA)1.5] (P1)
MMA (1.06 mL, 10 mmol), CPMA (12.8 mg, 0.06 mmol), DDMAT (36.4 mg, 0.1
mmol), AIBN (3.3 mg, 0.2 mmol) were added into 1,4-dioxane (5 mL). The mixture
system was degassed by three freeze-pump-thaw cycles and then was filled with nitrogen.
The polymerization was carried out at 65 °C for 10 h and then the solvent was evaporated
under reduced pressure. The polymer was dissolved in THF (3 mL) and then isolated by
precipitation in cold n-hexane for three times. After drying under vacuum at ambient
temperature for 24 h, the P1 was obtained as 428 mg white power with a yield of 41%.
Synthesis of poly[(MMA)167-co-(NPMA)1.5-co-(CPMA)1.3] (P2)
MMA (1.06 mL, 10 mmol), NPMA (50.2 mg, 0.12 mmol), CPMA (12.8 mg, 0.06
mmol), DDMAT (36.4 mg, 0.1 mmol) and AIBN (3.3 mg, 0.02 mmol) were added to
1,4-dioxane (5 mL), and the mixture was heated for 10 h at 65 °C. The solvent was
evaporated under reduced pressure. The polymer was dissolved in 3 mL THF and isolated
by the precipitation for three times in cold n-hexane. Finally, the product was dried for 24
h under vacuum at room temperature and 436 mg white power of P2 was obtained with a
yield of 39%.
The
preparation
of
poly[(MMA)169-co-(NPMA)2.8-co-(CPMA)1.3]
(P4)
(P3),
and
poly[(MMA)170-co-(NPMA)5.5-co-(CPMA)1.4]
poly[(MMA)168-co-(NPMA)6.8-co-(CPMA)1.5] (P5) were similar to that of P2 with
different NPMA amounts of (100.4 mg, 0.24 mmol), (150.7 mg, 0.36mmol) and (200.9
mg, 0.48mmol), respectively.
Synthesis of poly[(MMA)167-co-(ZnPc)1.1] (Q1)
P1 (200 mg), zinc acetate (Zn(CH3COO)2) (10 mg), 4-nitrophthalonitrile (27 mg)
12

and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) (8 μL) were added to benzyl alcohol
(BnOH) (40 mL), and the mixture was heated for 30 h at 150 °C. Then the solution was
successively dialyzed with N,N-dimethylformamide (DMF) and ultrapure water,
respectively. Finally, 173 mg greenish Q1 was obtained after drying for 2 days under
vacuum.
Synthesis of poly[(MMA)173-co-(NPMA)1.4-co-(ZnPc)1.1] (Q2)
P2 (200 mg), Zn(CH3COO)2 (10 mg), 4-nitrophthalonitrile (27 mg), and DBU (8 μL)
were added to BnOH (40 mL) , and the mixture was heated for 30 h at 150 °C. For
removing the unreacted phthalocyanine small molecules from the polymer, the crude
product was on dialysis (MwCO 5000D) in DMF for 5 days. Through the detection of the
dialysis solution Fig. S5), the free phthalocyanine molecules were completely removed
from the polymer. Then the polymer was on dialysis (MwCO 5000D) in water for 4 days,
and 168 mg greenish Q2 was obtained after drying for 2 days under vacuum.
The
preparation
of
poly[(MMA)172-co-(NPMA)2.6-co-(ZnPc)1.2]
(Q4)
(Q3),
and
poly[(MMA)168-co-(NPMA)5.2-co-(ZnPc)1.2]
poly[(MMA)169-co-(NPMA)6.5-co-(ZnPc)1.0] (Q5) were similar to that of Q2.
2.4 NLO parameters
The measured quantity in open-aperture Z-scan experiments of polymers were the
normalized transmittance, given by eqn (1) for a Gaussian pulse [42,43].
∞
-
τ 2
1


dτ
T(z) =
ln 1+ q0 (z)e
∫


−∞
π
q0 (z)
(1)
where
q0 (z) = β
eff I00Leff / (1+ z2 / z0 )
2
(2)
The nonlinear absorption coefficient (βeff) could be obtained from the equation. I00 is
13

the intensity of the beam at the focus. z and z0 are the sample position with respect to the
input intensity and the Rayleigh length, respectively. Leff is the effective thickness of the
sample and is given by using eqn (3)
α
L
1− e−
Leff
=
α
(3)
where α is the linear absorption coefficient and L is the thickness of the sample.
The imaginary component of the third order optical susceptibility (Im [χ(3)]) is
directly proportional to βeff via eqn (4).
n2ε0cλβeff
3
(

) 
Im χ
=


2π
(4)
where c and n are the speeds of the light in vacuum and the linear refractive index,
respectively. ε0 is the permittivity of free space and λ is the wavelength of the laser light.
3. Results and discussion
3.1 Synthesis and characterization
Firstly, the CPMA and NPMA were synthesized, as shown in Scheme 1.
Subsequently, the P1 P5 polymers were synthesized by RAFT polymerization using
DDMAT as the chain-transfer agent and AIBN as the initiator (Scheme 2). In the end, the
bluish green Q1 Q5 polymers were prepared through macrocyclization reaction from
P1 P5 polymers with 4-nitrophthalonitrile and Zn(CH3COO)2 (Scheme 2). Both the
1
13
CPMA and NPMA monomers were characterized by FT-IR, H and C NMR spectra.
The analysis data are presented in experimental section (2.3) and found to be satisfactory.
The composition of P1 P5 was calculated based on the ratio of the protons on the
1
aromatic ring of CPMA and the protons on the pyran ring of NPMA in their H NMR
spectra, along with the values of Mn, Mw and PDI (Mw/Mn) of P1 P5. Furthermore, the
14

composition of Q1 Q5 was calculated based on the ratio of the protons on the aromatic
1
ring of ZnPc and the protons on the pyran ring of NPMA in their H NMR spectra, as
listed in Table 2, along with the values of Mn, Mw and PDI (Mw/Mn) of Q1 Q5. The
detailed spectra of FT-IR and 1H NMR of polymers were shown in Fig. S6 and Fig. S7.
Table 1. Characterization data of P1 P5.
b
c
c
Polymers
xa
ya
za
Mn
Mn, GPC
Mw, GPC
PDIc
P1
P2
P3
P4
P5
161
167
169
170
168
0
1.5
1.3
1.3
1.4
1.5
16400
17600
18200
19400
19900
17900
18200
18500
19900
20500
30600
32000
31800
32900
33600
1.71
1.75
1.72
1.66
1.64
1.5
2.8
5.5
6.8
a Composition of MMA (x), NPMA (y) and CPMA (z) were characterized by 1H NMR spectroscopy. b
c
Absolute molecular weight was characterized by 1H NMR. Apparent molecular weight and
polydispersity index (PDI) were characterized by GPC relative to polystyrene standard.
Table 2. Characterization data of Q1 Q5.
b
c
c
Polymers
xa
ya
za
Mn
Mn, GPC
Mw, GPC
PDIc
Q1
Q2
167
173
172
168
169
0
1.1
1.1
1.2
1.2
1.0
17600
18800
19300
20000
20500
14800
17500
17400
17900
18100
26000
31100
30600
30800
30900
1.76
1.78
1.76
1.72
1.70
1.4
2.6
5.2
6.5
Q3
Q4
Q5
a
1
b
Composition of MMA (x), NPMA (y) and ZnPc (z) were characterized by H NMR spectroscopy.
Absolute molecular weight was characterized by 1H NMR. c Apparent molecular weight and PDI were
characterized by GPC relative to polystyrene standard.
15

Fig. 1. (a) The FT-IR spectra of P4 and Q4; (b) The Raman spectrum of Q4.
The macrocyclization of P1 P5 polymers were characterized by FT-IR and Raman
spectra.
In
order
to
confirm
the
formation
of
ZnPc
in
the
poly[(MMA)x-co-(NPMA)y-co-(ZnPc)z] polymers, tetranitro zinc phthalocyanine
(ZnPcTN) as a model compound was synthesized according to previous literature
procedures [44,45]. The absorption band of -NO2 group in ZnPcTN appears at 1522 cm-1
and the absorption band of C≡N group in ZnPcTN at 2234 cm-1 disappeared absolutely
(Fig. S8). From Fig. 1 (a), the FT-IR absorption spectrum of P4 has a weak band at 2234
cm-1, which should correspond to the C≡N stretching vibration of the CPMA units. After
the macrocyclization reaction, the C≡N stretching vibration absorption disappeared and
the typical -NO2 absorption band from the ZnPc units appeared at 1527 cm-1 in the FT-IR
spectrum of Q4. To further identify the ZnPc formation, the Q4 was characterized by
Raman spectroscopy. As shown in Fig. 1 (b), the Raman spectrum of Q4 shows
characteristic peaks of ZnPc at 594, 678, 847, 936, 1025, 1107, 1341, 1410, 1515 and
1597 cm-1. The Raman spectrum absorption values of ZnPc fragments of Q4 were similar
to that of phthalocyanines as previous reports [46-48] Moreover, in order to confirm the
presence of Zn in the cavity of phthalocyanine, the Q4 was characterized by XPS. As
16

presented in Fig. S9, the XPS fine spectrum of Zn 2p electrons has two strong peaks
centered at 1045.6 and 1022.5 eV, respectively. The former one should be from the
electrons of Zn 2p1/2, while the latter one comes from the Zn 2p3/2 electrons [49-51]. The
binding energy of Zn atoms (in Zn 2p3/2 electron state) was 1022.5 eV, indicating the Zn
(II) state in Q4. These data indicate that the ZnPc units have been covalently linked onto
the side chains of the Qn polymers (n = 1 5).
Fig. 2. The 1H NMR spectra of (a) P4 and (b) Q4 in CDCl3.
1
In order to confirm the composition of the polymers, H NMR spectra were carried
1
out, and Fig. 2 shows the H NMR spectra of P4 and Q4. From Fig. 2 (a), the
characteristic peaks of the CPMA and NPMA in P4 were noted for aromatic proton at
7.96 ppm and for pyran ring proton at 6.28 ppm, respectively. To confirm the chemical
shift of ZnPc in the poly[(MMA)x-co-(NPMA)y-co-(ZnPc)z] polymers, the ZnPcTN as a
1
model compound was characterized by H NMR. The chemical shifts of the aromatic
protons on ZnPcTN locate at 8.49, 8.25 and 7.87 ppm (Fig. S10). After the
macrocyclization, it is found that the typical chemical shift of CPMA unit disappeared,
and a new characteristic peak of the ZnPc appears at 8.02 ppm in the 1H NMR spectra of
Q4 (Fig. 2 (b)). In addition, the polymers were characterized by 13C NMR to further
confirm the composition of polymers, as shown in Fig. S11 for P4, Q4 and ZnPcTN. The
17

chemical shift of nitrile carbon at 104.61 ppm (Fig. S11 (a), (c)) disappears completely
after the macrocyclization and a new chemical shift of phthalocyanine carbon appears at
119.25 ppm (Fig. S11 (b), (d)). As far as the 13C NMR spectra are concerned, the
chemical shifts of the carbon marked as ‘a’ of P4, Q4 and ZnPcTN locate at 151.50 ppm
(Fig. S11 (a), (c)), 150.46 ppm (Fig. S11 (b), (d)) and 151.11 ppm (Fig. S11 (e)),
respectively. All these NMR data indicate that the CPMA units in P1 P5 are completely
converted into the ZnPc units of Q1 Q5 during the macrocyclization reactions.
Fig. 3. The GPC traces of P4 and Q4.
1
Absolute molecular weights of Q1
Q5 that determined by H NMR increase
significantly comparing to that of the corresponding P1 P5 (Table 2). But the GPC
measurements suggest that Q1 Q5 have a longer elution time than the corresponding P1
P5, that is, the Mn, GPC values of Q1 Q5 are lower than the corresponding P1 P5. For
example, Q4 exhibited a longer elution time and lower Mn, GPC (14.67 min, Mn, GPC
=
17900) compared to P4 (14.28 min, Mn, GPC= 19900) in GPC experiments (Fig. 3). These
phenomena may be attributed to the strong polarity and small steric hindrance of the
18

nitrile groups of P1 P5 which make them more easily to aggregate. Meanwhile, the
ZnPc units on Q1 Q5 with a small polarity as well as a large steric hindrance results in
a difficulty for aggregation [52-53]. Moreover, the grain diameter of the P4 and Q4 in
DMF solution also showed obvious change (Fig. S12). The grain diameter of P4 and Q4
are 5.3 nm and 10.6 nm, respectively. The bigger grain diameter could be assigned to the
high rigidity and large steric hindrance of phthalocyanine ring on the Q4.
3.2 Photophysical properties
Fig. 4. The UV-vis absorption spectra of P4 and Q4 in DMF solutions (5×10-5 mol/L).
The optical properties of P1
P5 and Q1
Q5 were investigated by UV-vis
absorption spectra in diluted DMF solution (5×10-5 mol/L). As presented in Fig. 4, P4
present the absorption bands at 348 and 363 nm which should be attributed to the
absorption of NPMA units. After the macrocyclization, a new absorption band at 695 nm
appears in the UV-Vis absorption spectrum of Q4, which could be assigned to the Q-band
of ZnPc.
19

Fig. 5. The PL spectra of Q1 Q5 in DMF solutions (5×10-5 mol/L).
The fluorescence emission properties of the Q1 Q5 polymers were investigated by
PL spectra in DMF (Fig. 5). Under the excitation of 646 nm, Q1 Q5 exhibit the PL
emission peaked at 698 nm. With increasing NPMA ratio in the polymer, the PL
intensities gradually decrease. This PL phenomenon probably stems from the effective
interaction
of
ET
from
NPMA
units
to
ZnPc
units
in
poly[(MMA)x-co-(NPMA)y-co-(ZnPc)z] polymers. Among them, the fluorescence
intensity of Q5 was slightly less than Q4. This phenomenon was attributed to the
following two reasons. On the one hand, the concentration of NPMA groups in Q4 and
Q5 was not much different. On the other hand, the ET between NPMA groups and ZnPc
groups gradually reached saturation with increasing NPMA ratio in the polymer and
resulted in the observation of the fluorescence intensity with fewer changes.
3.3 NLO properties
The open aperture Z-scan technique was used to test the NLO properties of Q1 Q5.
The βeff value was an important parameter for estimating the suitability of materials, since
20

it measured the degree of nonlinear absorptivity. Generally, the size of βeff value
depended on strength of the reverse saturable absorption (RSA) properties. These RSA
mechanisms result in positive nonlinear absorption coefficients and decreased
transmittance when the NLO materials were tested by Z-scan technique.
The NLO constants of Q1 Q5 in 3×10-4 mol/L DMF solutions from the Z-scan
experiments are listed in Table 3. The Q1 Q5 in this work revealed significant NLO
performance in comparison to those of the reported NLO materials (Table 3) [54-60].
Meanwhile, it also clearly revealed that Q4 had the best NLO character among Q1 Q5,
which could be attributed to the cooperation between the inherent NLO properties of the
modest ZnPc groups and the much stronger ET of NPMA groups. And the ET process
could occur as following. The NPMA molecules could absorb energy and reach the first
excited singlet state. The NPMA molecules on the first excited singlet state transported
energy to ZnPc molecules and got back to the ground state. Therefore, more ZnPc
molecules could easily reach the excited triplet state through intersystem crossing (ISC).
It is noteworthy that the Im[χ
(3)] value obtained for Q5 showed a distinct decrease, which
could be attributed to the ET between NPMA groups and ZnPc groups might reach
saturation with the increasing concentration of NPMA groups, causing the enhanced NLO
properties tending to be constant. As well the inherent NLO properties declined with the
decrease concentration of ZnPc groups. The result of the combined effect of the above
factors led to the degradation of the NLO properties of Q5. Besides, the decrease ZnPc in
Q5 might due to the strong steric effect of NPMA groups and the complicated
entanglement ability of Q5, resulting in the macrocyclization reaction of phthalonitriles
on P5 more difficult.
21

Table 3. Summary of the NLO properties of Q1 Q5 compared to literature data.
Sample
Q1a, b
Details
Transmittance βeff (m/W) Im[χ(3)] (esu) Reference
532 nm, 7 ns,
10 Hz
0.64
0.63
0.62
0.64
0.67
11.5×10-11
13×10-11
40×10-11
45×10-11
23×10-11
3.78×10-12
4.27×10-12
13.2×10-12
14.8×10-12
7.56×10-12
This work
This work
This work
This work
This work
532 nm, 7 ns,
10 Hz
Q2 a, b
Q3 a, b
Q4 a, b
Q5 a, b
532 nm, 7 ns,
10 Hz
532 nm, 7 ns,
10 Hz
532 nm, 7 ns,
10 Hz
Rhenium
iminopyridine
complex
532 nm, 30
ps, 10 Hz
—
—
8.2×10-12
3.2×10-12
1.60×10-13
6.16×10-14
[54]
[55]
Zinc
532 nm, 30
ps, 10 Hz
iminopyridine
complex
Difluoroboradi
-azaindacene
derivatives
532 nm, 30
ps, 10 Hz
—
1.9×10-11
4.01×10-13
[56]
532 nm, 30
ps, 10 Hz
Zinc complex
ZnPc
—
—
—
—
8×10-12
—
4.4×10-12
5.61×10-12
5.57×10-14
[57]
[58]
[59]
[60]
355 nm, 16
ps, 10 Hz
355 nm, 16
ps, 10 Hz
DMF solvent
—
800 nm, 80
fs, 80 MHz
saturable
saturable
CuPc
absorption
absorption
a Peak intensity for each independent Z-scan measurement was ~18 μJ. The excitation source was 7 ns
laser pulses of 532 nm wavelength. b c = 3×10-4 mol/L.
22

Fig. 6. The open aperture Z-scan tests of P4 and Q4 in DMF solutions (3×10-4 mol/L).
Fig. 6 presents the open aperture Z-scan tests of P4 and Q4 in DMF. As the position
of the polymers changed in the Z-scan test, it reveals that the transmittance of P4 has no
change, but that of Q4 gradually decreases from 1.00 to 0.82 as the Z value changes from
-50 mm to 0 mm. As the Z value is further increased to 50 mm, the transmittance of Q4
mounts up to 1.00 again. This evolvement of the transmittance of Q4 could be attributed
to the RSA effect, thus indicating that the NPMA and CPMA units have no RSA behavior
in P4.
23

Fig. 7. Photographs of PMMA films with Q4 (a c), Q1 (d) and P4 (e) as dopants and the
doping concentrations are 5.3×10-5 mol/L (a), 7.5×10-5 mol/L (b, d and e) and 10.1×10-5
mol/L (c), respectively.
Table 4. NLO properties of the selective polymer / PMMA films.
Sample
Q4a
Q4a
c
(mol/L) (×10-5) Transmittance βeff (m/W) (×10-11) Im
[
χ(3)] (esu) (×10-12)
5.3
7.5
0.83
0.66
0.52
0.68
0.87
14
61
80
34
0
5.1
22.1
28.9
12.3
0
Q4a
10.1
7.5
Q1a
P4a
7.5
a Peak intensity for each independent Z-scan measurement was ~18μJ; The excitation source was 7 ns
laser pulses of 532 nm wavelength.
For the practical application, the method of the film prepared in this paper is solution
casting technology. Fig. 7 shows photographs of the PMMA films formed by doping Q1,
Q4 and P4 into the host material PMMA, and the NLO parameters of them were
measured, listed in Table 4. Three type of PMMA films based on Q4 were fabricated with
the concentrations of 5.3 × 10-5 mol/L, 7.5 × 10-5 mol/L and 10.1 × 10-5 mol/L,
respectively. The results in Table 4 demonstrate that Q4 had the strong nonlinear
absorption coefficient Im[
χ
(3)] of 22.1×10-12 esu, with a high initial transmittance 0.66
(3)] value of the Q1 /
with the doping concentration of 7.5×10-5 mol/L. However, the Im[
χ
PMMA films and P4 / PMMA films was 12.3×10-12 esu and 0.0 ×10-12 esu, respectively,
with the doping concentration of 7.5×10-5 mol/L. The Z-scan tests of the P4 / PMMA and
Q4 / PMMA films were shown in Fig. 8. The results of P4 / PMMA film revealed that
NPMA and CPMA units have no RSA behavior in PMMA film.
24

Fig. 8. The Open aperture Z-scan tests of P4 / PMMA and Q4 / PMMA films (7.5 × 10-5
mol/L).
Fig. 9. The OL performance (a) and the nonlinear transmittance (b) of Q1 / PMMA and
Q4 / PMMA films.
In addition, the OL properties of Q1 / PMMA film and Q4 / PMMA film were
shown in Fig. 9. From Fig. 9 (a), the solid black line indicates a hypothetical linear
response, and both the polymer / PMMA films show linear absorption at low input
fluence and nonlinear absorption at high input fluence. Therefore, the polymer / PMMA
films achieved OL and RSA properties at high input fluence. Fig. 9 (a) revealed that the
25

initial threshold of Q1 / PMMA film and Q4 / PMMA film were 0.11 J/cm2 and 0.06
J/cm2, respectively. From Fig. 9 (b), the dash black line indicates 50% of the initial
transmittance and the transmittance decreases with increasing input fluence. The Q1 /
PMMA film showed limiting threshold was 0.41 J/cm2, minimum transmittance was 0.39,
dynamic range was 2.56; and the Q4 / PMMA film showed that limiting threshold was
0.19 J/cm2, minimum transmittance was 0.31, dynamic range was 3.23. The results
indicate that the OL properties of Q4 / PMMA film were better than the Q1 / PMMA film.
The improved OL properties of Q4 / PMMA film may be attributed to the stronger ET
from NPMA to ZnPc. For the need of practical application in laser field, the laser damage
threshold was an important parameter for NLO materials. General, damage threshold was
optical fluence level below which no optical damage occurs in certain materials. The laser
damage threshold of Q4 / PMMA was 8.14 J/cm2. And the Q4 / PMMA revealed
satisfactory laser damage threshold for promising application in practice. In order to
process at optimum temperature. Thermal-stability is a crucial parameter for the practical
application. The thermal stability of Q4 /PMMA was evaluate by TGA. As showed in Fig.
S13, Q4 /PMMA possessed good stability below 220 °C, and the maximum degradation
temperature (the temperature at 50% weight loss) was 388 °C. The thermal stability could
be attributed to the incorporation of NPMA and ZnPc, which act as barriers to inhibit the
mobility of PMMA chains during pyrolysis. From the above, the excellent thermal
stability ensured Q4 /PMMA could be processed at high temperature.
26

Fig. 10. The Open aperture Z-scan of (a) Q4 in MMA solution and (b) PMMA film with
the concentration of 7.5×10-5 mol/L.
As show in Fig. 10, the Z-scan test was performed for Q4 in MMA solution and
PMMA film at 7.5×10-5 mol/L. the βeff values were found to be 5.5×10-11 m/W and
61×10-11 m/W for Q4 / MMA solution and Q4 / PMMA film, respectively. It is worthy to
note that the βeff values of Q4 / MMA solution was much smaller than those from the Q4 /
PMMA films with the similar doping concentration (Table 4). According to the previous
reports, the higher βeff value in PMMA film probably might be attribute to the weaker
aggregation effect in PMMA film than MMA solution, therefore, the more effective
component of Q4 in PMMA film could accomplish RSA process [61]. In addition, the
triplet-triplet annihilation (TTA) effect could also improve the NLO properties and more
populations in the first excited triplet state could accomplish RSA in PMMA film [62,63].
4. Conclusions
In this paper, P1 P5 polymers containing naphthopyran and phthalonitrile units
were synthesized by RAFT polymerization and further used to prepare Q1 Q5 polymers
containing the ZnPc units by the macrocyclization reaction with the presence of zinc
27

acetate and 4-nitrolphthalonitrile. The effects of different ratios of NPMA units in Q1
Q5 on their optical properties have been investigated by UV-vis absorption and PL
spectra. With the increasing ratio of NPMA units in Q2 Q5, the fluorescence decay
becomes stronger, indicating the ET process becomes more intense. The NLO properties
of Q series polymers were investigated by using the Z-scan technique at 532 nm, and Q4
shows strong nonlinear absorption coefficient and high initial transmittance. Such results
reveal that the ET process might play an essential role in the enhancement of NLO
properties of the Q4. In addition, the enhanced NLO responses were obtained when Q4
was doped in PMMA film with a concentration of 7.5×10-5 mol/L. At last, the Q4 /
PMMA film obtains a strong nonlinear absorption coefficient (βeff = 61×10-11 m/W) and
high initial transmittance (0.66). All in all, the Q4 / PMMA film exhibits improved NLO
properties if compared with solution, which makes it more accessible to apply. Our study
provides a promising molecular design strategy for obtaining high performance NLO
materials.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This work was financially supported by the Jilin Science & Technology Department
(grant number 20190303069SF, 20170101107JC). Natural Science Foundation of China
(grant number 51803013); Jilin Association for Science and Technology (grant number
192011).
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photophysical and nonlinear optical properties of reduced graphene oxide-metal(II) phthalocyanine
28