Synthesis of novel thioxanthone-containing macromolecular photosensitizer and its photocatalytic property

Article abstract of DOI:10.1016/j.polymer.2019.04.063

Aiming to overcome the disadvantages of small molecule photosensitizers, a novel macromolecular photosensitizer was designed and synthesized in this work. Firstly, the functional small molecule photosensitizer 9-oxo-9H-thioxanthene-2-carboxylic acid (TX-C

Full text of DOI:10.1016/j.polymer.2019.04.063

Accepted Manuscript
Synthesis of Novel Thioxanthone-Containing Macromolecular photosensitizer and
Its Photocatalytic Property
Aishun Ding, Yang Chen, Guowei Wang, Yaopeng Zhang, Jianhua Hu, Hao Guo
PII:
S0032-3861(19)30390-8
10.1016/j.polymer.2019.04.063
JPOL 21446
DOI:
Reference:
To appear in:
Polymer
Received Date:
Accepted Date:
25 March 2019
25 April 2019
Please cite this article as: Aishun Ding, Yang Chen, Guowei Wang, Yaopeng Zhang, Jianhua Hu,
Hao Guo, Synthesis of Novel Thioxanthone-Containing Macromolecular photosensitizer and Its
Photocatalytic Property, Polymer (2019), doi: 10.1016/j.polymer.2019.04.063
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ACCEPTED MANUSCRIPT
Graphical Abstract
O
Br
n
O
O
S
O P
OMe
O
P
OMe
S
O
3
3
O
O
PHEMA-TX
Visible Light
Solvent, air, room temperature
O
S
(1) Recyclable use
(2) Easy separation
(3) High yield
O
O
B(OH)2
OH
1

ACCEPTED MANUSCRIPT
Synthesis of Novel Thioxanthone-Containing Macromolecular
photosensitizer and Its Photocatalytic Property
Aishun Ding a #, Yang Chen a #, Guowei Wang a, Yaopeng Zhang b, *, Jianhua Hu a, *, Hao Guo c, d,
*
a
State Key Laboratory of Molecular Engineering of Polymers and Department of Macromolecular
Science, Fudan University, Shanghai 200433, PR China
b
State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of
Materials Science and Engineering, Donghua University, Shanghai, 201620, PR China
c Department of Chemistry, Fudan University, 2005 Songhu Road, Shanghai 200438, PR China
d Academy for Engineering and Technology, Fudan University, 220 Handan Road, Shanghai 200433,
PR China
* Corresponding authors. State Key Laboratory of Molecular Engineering of Polymers and Department
of Macromolecular Science, Fudan University, 2005 Songhu Road, Shanghai 200438, PR China (J. Hu).
State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials
Science and Engineering, Donghua University, 2999 Peopel North Road, Shanghai, 201620, PR China
(Y. Zhang).
Department of Chemistry, Fudan University, 2005 Songhu Road, Shanghai 200438, PR China (H. Guo).
E-mail address: hujh@fudan.edu.cn (J. Hu), Fax: +86-21-31242888; Tel: +86-21-55665280
E-mail address: zyp@dhu.edu.cn (Y. Zhang), Fax: +86-21-67792955; Tel: +86-21-67792954
E-mail address: Hao_Guo@fudan.edu.cn (H. Guo), Fax: +86-21-31249190; Tel: +86-21-31249190
# Aishun Ding and Yang Chen contributed equally to this work.
2

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ABSTRACT
Aiming to overcome the disadvantages of small molecule photosensitizers, a novel macromolecular
photosensitizer was designed and synthesized in this work. Firstly, the functional small molecule
photosensitizer 9-oxo-9H-thioxanthene-2-carboxylic acid (TX-COOH) and precursor poly(2-
hydroxyethyl methacrylate) (PHEMA) was individually synthesized. Then, the macromolecular
photosensitizer PHEMA-TX was realized by an optimized reaction procedure between PHEMA and
TX-COCl, which was previously prepared by acyl chlorination of TX-COOH. The modification
efficiency was calculated as 64 %. Finally, the photocatalytic reaction using the as-synthesized
PHEMA-TX was investigated based on three substrates of tris(4-methoxyphenyl)phosphane,
methyl(phenyl)sulfane, (4-methoxyphenyl)boronic acid. The results showed that the photocatalyst
PHEMA-TX can be easily separated, recovered by a simple precipitation, and reused 7 times without
significant loss of the catalytic activity. The excellent photocatalytic property, easy separation, and
recyclability of PHEMA-TX were comprehensively confirmed, which contributed great potential of this
novel macromolecular photosensitizer in future application.
Keywords
Thioxanthone, photosensitizer, recyclability, photooxidation, photocatalysis
3

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1. Introduction
Visible light, as an economical green energy, has received much attention from researchers. [1-6] In
most cases, small molecule compounds are used as photosensitizers.[7, 8] Although the small molecule
photosensitizers have good catalytic property in the reaction, they always have some disadvantages,
such as difficult separation from the reactants, hard recycling or increasing of cost, etc. In order to solve
these problems, some alternative methods had been developed. For example, in recent years, the
macromolecular photosensitizers were designed and synthesized by linking photosensitive groups onto
polymeric chains.[9, 10] Comparing with the small molecule photosensitizers, macromolecular
photosensitizers have an especial advantage. That is, the macromolecular photosensitizers can be easily
separated from the reactant and recycling used, which greatly decreased the cost and simplify the
producing technology. Thus, the macromolecular photosensitizers had attracted much attentions from
the researchers and had been widely used in medical, biological and hydrogel fields.[11-15]
Up to now, a library of small molecule photosensitizers had been developed and used in
photocatalytic reactions. The examples included the typical organic dyes of methylene blue, riboflavin
and related aza heterocycles, fluorescein, Eosin Y, Eosin B, and rose red (RB),[16-22] as well as the
infrequently used phenoxazines (such as Nile Red) and phenothiazine scaffolds,[23] larger aromatic
systems (such as hydrazine or perylene and boron dipyrromethene derivatives),[24-26] transition metal
ligands (such as CuI-phenanthroline derivatives).[27] In recent years, some novel photocatalysts, such
as Ru(II) or Ir(III) polypyridyl complexes, aryl aldehyde ketones,[28] thioxanthone[29-31] and its
derivatives were developed and found potential application in many fields. Among all the above
photosensitizers, the thioxanthone and its derivatives are especially attracting more and more attentions
due to its excellent photocatalytic property.[32] Besides of its function as catalyst for small molecules
compounds, the thioxanthone and its derivatives can also be used as photosensitizers in free radical
polymerization.[33-36] However, the study on macromolecular photosensitizeds with thioxanthone is
still rather limited. On one hand, the functionalization of thioxanthone is always difficult. On the other
hand, the introduced functional group might affect the photocatalytic property.[37, 38]
Considering the excellent properties of thioxanthone and the current limitation on macromolecular
thioxanthone, a novel methodology was developed in this work to immobilize the TX groups on
macromolecules (Scheme 1). Firstly, a thioxanthone derivative of 9-oxo-9H-thioxanthene-2-carboxylic
acid (TX-COOH) containing a carboxyl group was synthesized, and precursor poly(2-hydroxyethyl
methacrylate) (PHEMA) was obtained by an electron transfer atom transfer radical polymerization
(AGET ATRP) procedure. Subsequently, the TX groups were attached onto PHEMA to give PHEMA-
TX by an optimized synthetic procedure. The photocatalytic property of PHEMA-TX was finally
4

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studied by using three characteristic substrates. Furthermore, the recyclability and separation ability of
this novel photocatalyst were also investigated.
O
O
Br
n
COOH
O
O
S
O
OH
TX-COOH
PHEMA
O
O
Br
n
O
S
O
O
P
OMe
S
O P
OMe
O
O
3
3
PHEMA-TX
O
S
Visible Light
Solvent, air, room temperature
(1) Recyclable use
O
(2) Easy separation
(3) High yield
O
B(OH)2
OH
Scheme 1. The synthetic procedure of macromolecular photosensitizer and its photocatalytic reaction.
2. Materials and methods
2.1 Materials
2-Hydroxyethyl methacrylate (HEMA, 97 %, Energy chemical) was passed over a column of basic
alumina to remove inhibitor prior to use. 2-Mercaptobenzoic acid (97 %, Energy chemical), 4-
iodobenzoic acid (97 %, Energy chemical), copper (99 %, Energy chemical), anhydrous potassium
carbonate (K2CO3, 99%, Sinopharm Chemical Reagent Co., Ltd.), ethyl 2-bromoisobutyrate (EBiB,
98%, Energy chemical), cupric bromide (CuIIBr2, 99 %, Aldrich), 2,2'-bipyridine (Bpy, 98 %, Energy
chemical), stannous octoate (Sn(Oct)2, 97%, Energy chemical), thionyl chloride (SOCl2, 99 %,
Sinopharm Chemical Reagent Co., Ltd.), 4-dimethylaminopyridine (DMAP, 98 %, Energy chemical),
dicyclohexylcarbodiimide (DCC, 98 %, Energy chemical), concentrated sulfuric acid (95 %, Sinopharm
Chemical Reagent Co., Ltd.), tris(4-methoxyphenyl)phosphane (97 %, Energy chemical),
5

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methyl(phenyl)sulfane (97 %, Energy chemical), (4-methoxyphenyl)boronic acid (97 %, Energy
chemical), N,N-diisopropylethylamine (i-Pr2Net, 99 %, Energy chemical), methanol (AR), 2-butanolne
(AR), triethylamine (Et3N, AR), N,N-dimethylformamide (DMF, AR), dimethyl carbonate (AR) were
used as recieved. All other chemicals were purchased from Sinopharm Chemical Reagent Co., Ltd. And
used as received unless otherwise specified.
2.2 Synthesis of 9-oxo-9H-thioxanthene-2-carboxylic acid (TX-COOH)
According to the literature,[39] the diphenylsulfide-2,4'-dicarboxylic acid was firstly prepared
(Scheme 2). Into a 250 mL round-bottomed flask, thiosalicylic acid (4.622 g, 29.9 mmol) was firstly
added and dissolved in DMF (100 mL). Then, the 4-iodobenzoic acid (7.443 g, 30.0 mol), K2CO3
(12.494 g, 90.4 mmol) and Cu powder (384 mg, 6.0 mmol) was sequentially added. After the mixture
was refluxed for 36 h, water (300 mL) was added and the mixture was filtered to remove the Cu powder.
The filtrate was carefully acidified with concentrated HCl (37 %) to pH < 1 and the product was
precipitated. After the washing of the precipitate with water, the product was dried at 100 oC to give the
white powder of diphenylsulfide-2,4'-dicarboxylic acid (6.995 g, 85%).
Subsequently, the as-synthesized diphenylsulfide-2,4'-dicarboxylic acid (4.002 g, 14.6 mmol) and
concentrated sulfuric acid (76 mL) were charged into a 250 mL dry three-necked flask. After the
reaction was stirred at room temperature for 33 h, 90 mL of boiling water was added and the reaction
o
was continued for another 1 h at 100 C. The mixture was then cooled down to room temperature and
the crude product 9-oxo-9H-thioxanthene-2-carboxylic acid was precipitated from the mixture. The
precipitate was filtrated and washed with water for three times. The 9-oxo-9H-thioxanthene-2-
carboxylic acid was obtained with the yield of 48 % (1.792 g). 1H NMR (400 MHz, DMSO) δ 13.37 (s,
1H), 8.96 (s, 1H), 8.46 (d, J = 6.4 Hz, 1H), 8.19 (d, J = 6.0 Hz, 1H), 8.02 – 7.73 (m, 3H), 7.61 (s, 1H).
COOH
O
COOH
COOH
SH
S
COOH
Cu, K2CO3
DMF
H2SO4
I
COOH
S
TX-COOH
Scheme 2. The synthetic procedure for TX-COOH.
2.3 Synthesis of precursor poly(2-hydroxyethyl methacrylate) (PHEMA)
According to our previous work[40] and literatures,[41-43] the precursor PHEMA was synthesized
by an electron transfer atom transfer radical polymerization (AGET ATRP) procedure (Scheme 3).
Typically, the monomer HEMA (40.0 mL, 330 mmol), initiator EBiB (0.1602 g, 0.8 mmol), catalytic
Ⅱ
complex of Cu Br2 (0.1862 g, 0.8 mmol) and Bpy (0.2587 g, 1.6 mmol), mixture solvent of 2-butanone
6

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(58 mL) and methanol (38 mL) were sequentially added into a 250 mL Schlenk flask. After the flask
was purged with argon for 30 min, the reducing agent of SnOct2 (0.2844 g, 0.7 mmol) dissolved in a
mixture solvent of 2-butanone (2.0 mL) and methanol (2.0 mL) was charged into the flask to trigger the
polymerization. After the mixture was stirred at 60 oC for 40 h, the crude product was precipitated into a
large amount of water. The obtained PHEMA was further dried under vacuum to a constant weight at 60
oC. 1H NMR (400 MHz, DMSO, δ, ppm, TMS): 0.78 (m, -CH2C(CH3)-), 1.23-2.13 (m, -CH2C(CH3)-),
3.42-4.05 (m, HOCH2CH2-). Mn,GPC = 27,800, Mw/Mn = 1.55.
O
O
O
CuBr2, Bpy, SnOct2
Br
n
O
O
Br
OH
n
O
O
2-Butanone/Methanol (v:v = 3:2), 60 oC
O
OH
PHEMA
Scheme 3. The synthetic procedure for PHEMA.
2.4 Synthesis of PHEMA-TX-1 hanging with TX groups (Route A)
The PHEMA-TX-1 hanging with TX groups was prepared by reaction between PHEMA and TX-
COCl (Scheme 4). Firstly, the TX-COOH was transformed into TX-COCl as the following procedure.
In a dry 100 mL Schlenk flask, under argon atmosphere, TX-COOH (0.343 g, 1.34 mmol) was refluxed
with SOCl2 (0.3 mL) in anhydrous dichloroethane (10 mL). After 4 h, the mixture was concentrated
under vacuo and the residue was stripped twice with anhydrous dichloroethane (10 mL). Subsequently,
the residue was dissolved in 5 mL anhydrous DMF and transferred into another dry 100 mL Schlenk
flask containing precursor PHEMA (0.3487 g) which was previously dried by azeotropic distillation
procedure with 30 mL toluene. Anhydrous Et3N (2.0 mL) was syringed into the flask and used as acid-
binding agent. The system was set into an ice bath (0 oC) and allowed to warm to room temperature, the
reaction was continued for 60 h. The product was precipitated into a mixture of water and methanol
(water: methanol = 2:1) with three times. The obtained PHEMA-TX-1 was further dried under vacuum
1
to a constant weight at 60 oC. H NMR (400 MHz, DMSO, δ, ppm, TMS): 0.78 (m, -CH2C(CH3)-),
1.23-2.13 (m, -CH2C(CH3)-), 3.47-4.16 (m, TXOCH2CH2-), 7.58-9.01 (m, Ar-H). Mn,GPC = 84,800,
Mw/Mn = 1.47.
7

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O
O
Br
O
n
Br
n
O
O
O
O
O
S
COOH
O
COCl
O
OH
SOCl2
O
S
S
O
O
Et3N, DMF, rt
DCE, reflux
TX-COOH
TX-COCl
PHEMA-TX-1
Scheme 4. The synthetic procedure for PHEMA-TX-1.
2.5 Synthesis of PHEMA-TX-2 hanging with TX groups (Route B)
Alternatively, using DMAP and DCC as catalyst, the direct esterification between PHEMA and TX-
COOH was performed for PHEMA-TX-2. The detailed procedure was shown in (Scheme 5). The
PHEMA (0.3490 g) dried by azeotropic distillation with 50 mL toluene, TX-COOH (0.343 g, 1.34
mmol), DMAP (0.033 g, 0.27 mmol), and DCC (1.117 g, 5.36 mmol) were sequentially added into the
flask and dissolved in 20 mL DMF. The mixture was stirred under room temperature for 36 h. The crude
product was concentrated in vacuo and precipitated into a large amount of mixture solvent of water and
methanol (water: methanol = 2:1) with three times. The obtained PHEMA-TX-2 was further dried under
o
1
vacuum to a constant weight at 60 C. H NMR (400 MHz, DMSO, δ, ppm, TMS): 0.78 (m, -
CH2C(CH3)-), 1.23-2.13 (m, -CH2C(CH3)-), 3.47-4.16 (m, TXOCH2CH2-), 7.58-9.01 (m, Ar-H). Mn,GPC
= 63,100, Mw/Mn = 1.52.
O
O
Br
Br
O
n
n
O
O
O
O
S
COOH
O
O
OH
O
S
O
O
DMAP, DCC, DMF, rt
PHEMA-TX-2
TX-COOH
Scheme 5. The synthetic procedure for PHEMA-TX-2.
2.6 Photocatalytic reaction of tris(4-methoxyphenyl)phosphane
Using PHEMA-TX-1 as catalyst, the tris(4-methoxyphenyl)phosphane (1a) was transformed into
tris(4-methoxyphenyl)phosphine oxide (2a) (Scheme 6). Typically, 1a (352 mg, 1.0 mmol), PHEMA-
TX-1 (0.52 mg, 0.001 mmol, 19 μL stock solution prepared by dissolving 56 mg PHEMA-TX-1 in 2.0
mL of DMF), CH3OH (30 mL) were added into to a 100 mL round bottom flask equipped with a
magnetic stirrer. The reaction was triggered by irradiation of a 23 W household lamp at room
temperature under air atmosphere. The photocatalytic reaction was monitored by TLC (eluent:
8

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petroleum ether/ethyl acetate = 20/1) and finished after 8 h. The solution was concentrated under vacuo
and the mixture was again dissolved in 5 mL of ethyl acetate (EA). The PHEMA-TX-1 was precipitated
in EA and recovered for the second cycle of photocatalytic reaction. The NMR yield of 2a in the first
1
cycle was 99 % as determined by H NMR analysis of the crude reaction mixture using
dibromomethane as internal standard. Subsequently, using the recovered PHEMA-TX-1 as catalyst, the
following cycles of reactions were performed using the same procedure as above. The result was shown
1
in Scheme 6. H NMR (400 MHz, CDCl3) δ 7.57 (dd, J = 9.4, 9.4 Hz, 6H), 6.95 (d, J = 8.0 Hz, 6H),
3.83 (s, 9H).
OMe
OMe
PHEMA-TX-1, visible light (23 W)
O
P
MeO
P
MeO
CH3OH, air (1atm), rt
OMe
OMe
2a
1a
Scheme 6. The photocatalytic reaction of 1a.
2.7 Photocatalytic reaction of methyl(phenyl)sulfane
Using PHEMA-TX-1 as catalyst, the methyl(phenyl)sulfane (1b) was transformed into
methyl(phenyl)sulfoxide (2b) (Scheme 7). Typically, 1b (0.12 mL, 1.0 mmol), PHEMA-TX-1 (0.52 mg,
0.001mmol, 19 μL, prepare a solution of 56 mg of PHEMA-TX-1 with 2 mL of DMF), CH3OH (5 mL)
were added into a 25 mL round bottom flask equipped with a magnetic stirrer. The reaction was
triggered by irradiation of a purple LED lamp at room temperature under air atmosphere. The
monitoring procedure and the final purification operation were similar as those for the above 2a. The
1
NMR yield of 2b in the first cycle was 99 % as determined by H NMR analysis of the crude reaction
1
mixture using dibromomethane (1 mmol) as internal standard. The result was shown in Scheme 7. H
NMR (400 MHz, CDCl3) δ 7.65 (d, J = 5.6 Hz, 2H), 7.52 (d, J = 5.6 Hz, 3H), 2.72 (s, 3H).
O
S
PHEMA-TX-1, purple LED
CH3OH, air (1atm), rt
S
2b
1b
Scheme 7. The photocatalytic reaction of 1b.
2.8 Photocatalytic reaction of (4-methoxyphenyl)boronic acid
9

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Using PHEMA-TX-1 as catalyst, the (4-methoxyphenyl)boronic acid (1c) was transformed into 4-
methoxyphenol (2c) (Scheme 8). Typically, 1c (152 mg, 1.0 mmol), PHEMA-TX-1 (5.16 mg, 0.01
mmol, 214 μL, prepare a solution of 56 mg of PHEMA-TX-1 with 2 mL of DMF), i-Pr2NEt (330 μL, 2
mmol), and dimethyl carbonate (5 mL) were added into a 25 mL round bottom flask equipped with a
magnetic stirrer. The reaction was also triggered by irradiation of a purple LED lamp at room
temperature under air atmosphere. The monitoring procedure and the final purification operations were
1
similar as that for the above 2a. The NMR yield of 2c in the first cycle was 99 % as determined by H
NMR analysis of the crude reaction mixture using dibromomethane (1 mmol) as internal standard. The
result was shown in Scheme 8. 1H NMR (400 MHz, CDCl3) δ 6.81-6.73 (m, 4 H), 5.44 (br s, 1H), 3.76
(s, 3H).
O
O
PHEMA-TX-1, purple LED
i-Pr2NEt, DMC, air (1atm), rt
OH
B(OH)2
2c
1c
Scheme 8. The photocatalytic reaction of 1c.
2.5 Characterization
The apparent molecular weight (MW) and molecular weight distribution (Mw/Mn) of polymers
was analyzed by size exclusion chromatography (SEC) measurement, which was performed in LiBr-
o
added N,N-dimethylformamide (DMF) ([LiBr] = 14 mM) at 55 C with an elution rate of 1.0 mL/min
on an Agilent 1260 equipped with a G1310B pump, a G1362A refractive index detector, and a G1314F
variable wavelength detector. Two 5 μm LP gel columns (500 Å, molecular range 500 - 1.2 × 105 Da
1
and 200 - 1.0 × 106 Da) were calibrated using poly(methyl methacrylate) (PMMA) standards. H
Nuclear Magnetic Resonance (NMR) spectra were recorded on a Bruker (400 MHz) spectrometer in
CD3Cl3 or DMSO-d6 at 298 K.
3. Results and discussion
3.1 Synthesis and characterization of PHEMA-TX
According to the literature,[38] the TX-COOH was prepared from thiosalicylic acid and 4-
iodobenzoic acid. The structure of TX-COOH was confirmed by 1H NMR spectrum as shown in Figure
1. The characteristic resonance signal on phenyl can be clearly attributed at 6.96-9.10 ppm. According
to our previous work[39] and literatures,[40-42] the precursor PHEMA was synthesized by AGET
10

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ATRP of HEMA monomer using CuIIBr2 / Bpy as catalyst system and Sn(Oct)2 as reducing agent. The
apparent molecular weight of PHEMA was calibrated as 27,800 g/mol by SEC instrument using PMMA
1
as calibration (Figure 2). From Figure 1 for H NMR spectrum of PHEMA, the characteristic
resonance signals for methylene protons (HOCH2CH2-) can be clearly discriminated at 3.42-4.05 ppm,
and signal for methyl protons (-CH2C(CH3)-) can be observed at 0.78 ppm.
h
O
S
g
e
a
d
COOH
b
c
f
a-g
(TX-COOH)
H2O
DMSO
h
e
O
b
d
Br
a
O
n
c
c
O
g
a,c,d,e
g
h
OH
h
O
f,b
f,b
(PHEMA)
f
e
O
d
c
b
Br
n
a
O
i
j
c
O
f
S
k
l
g
h
O
O
h-n
h-n
g
g
a,c,d,e
m
n
O
O
(PHEMA-TX)
e
d
O
b
Br
n
a
O
i
j
c
c
O
S
k
l
g
h
O
O
f
m
n
f,b
a,c,d,e
O
O
(PHEMA-TX after 3 cycles)
14
12
10
8
6
4
2
0
Chemical shift (ppm)
Figure 1. 1H NMR spectra for TX-COOH, PHEMA and PHEMA-TX in DMSO-d6.
Subsequently, the TX-COOH was attached onto PHEMA. Two synthetic routes were adopted to
optimize the methodology. In route A, the PHEMA-TX-1 was prepared by reaction between PHEMA
and TX-COCl, which was previously prepared from TX-COOH and SOCl2. The high activity of TX-
COCl to hydroxyl groups guaranteed the high modification efficiency of TX onto PHEMA. Comparing
with the GPC curves of precursor PHEMA, one can observe that the GPC curve of PHEMA-TX-1
11

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obviously shift to the higher molecular weight region (84,800 g/mol) (Figure 2). By comparing the
integral areas at aromatic region (8.18-8.22 ppm) and peak at 3.58 ppm (peak g), the modification
efficiency can be calculated as 64 %.
Figure 2. The GPC traces of PHEMA and PHEMA-TX.
Because the preparation of TX-COCl was always complicated and should be carefully operated,
an alternative route B was adopted using DMAP and DCC as catalyst and PHEMA-TX-2 was obtained.
Although the SEC curve of PEHMA-TX-2 shift to the higher molecular weight region (63,100 g/mol),
the low modification efficiency of 18.5% was obtained. The reason can be reasonably attributed to the
bulky substituent group of TX and low activity of carboxyl group. Thus, in the following photocatalytic
reactions, the PHEMA-TX-1 was used.
3.2 Study on PHEMA-TX based photocatalytic reaction
Using PHEMA-TX-1 as catalyst, the photocatalytic reaction and its recycling ability was
systematically
studied.
Three
typical
substrates
of
tris(4-methoxyphenyl)phosphane,
1
methyl(phenyl)sulfane, (4-methoxyphenyl)boronic acid were selected. The yield was determined by H
NMR analysis of the crude reaction mixture using dibromomethane as internal standard, respectively.
For the reactant of tris(4-methoxyphenyl)phosphane (1a), it can be completely consumed in 8 h
and the NMR yield of the corresponding product tris(4-methoxyphenyl)phosphine oxide (2a) was 99 %
1
in the first cycle of photocatalytic reaction. From H NMR spectrum for 1a, the resonance signal of
protons on phenyl group can be attributed at 6.90 ppm and 7.32 ppm. After the photocatalytic reaction,
1
from H NMR spectrum for 2a, the resonance signal of protons shift to 6.95 ppm and 7.57 ppm,
12

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1
respectively. The H NMR results clearly confirmed that 1a was completely converted into 2a (Figure
3). After the first cycle, the catalyst PHEMA-TX-1 can be recovered by simple precipitation in EA and
directly used for the second cycle. The following cycles of reactions were performed using the same
procedure. It could be reused seven times without significant loss of the catalytic activity. From the
seventh cycle, a slightly yield decreasement was observed (Figure 4).
a
a
c
c
Tris(4-methoxyphenyl)phosphane (1a
)
MeO
OMe
b
b
c
c
P
b
b
a
b
c
b
c
c
b
OMe
a
a'
a'
c'
b'
c'
Tris(4-methoxyphenyl)phosphine oxide (2a)
b' b'
O
P
MeO
OMe
c'
c'
b'
a'
b'
c'
b'
c'
OMe
a'
c'
b'
8
7
6
5
4
3
2
1
0
Chemical shift (ppm)
Figure 3. 1H NMR spectra of 1a and 2a in CDCl3.
Figure 4. Recycling experiments of the photocatalytic reaction of 1a.
13

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For the reactant of methyl(phenyl)sulfane (1b), the first cycle of photocatalytic reaction was
finished in 12 h and the NMR yield of the corresponding product methyl(phenyl)sulfoxide (2b) was
99 %. From Figure 5, the high conversion of 1b can be confirmed by the complete shift of resonance
signal of methyl groups (-CH3) from 2.40 ppm (before the photocatalytic reaction) to 2.72 ppm (after
the photocatalytic reaction). Additionally, the protons on phenyl group completely shift from 7.25-7.35
ppm to 7.52-7.65 ppm. Similarly, after the first cycle, the catalyst PHEMA-TX-1 can be recovered by
simple precipitation in EA and was directly used for the second cycle. The following cycles of reactions
1
were performed using the same procedure. H NMR (Figure 1) and GPC (Figure 2) of PHEMA-TX-1
were still identical to the freshly prepared ones after 3 cycles. The catalyst could be reused seven times
without significant loss of the catalytic activity. From the seventh cycle, a slightly yield decreasement
was observed (Figure 6).
Methyl(phenyl)sulfane (1b)
b
S
f
a
a
e
c
b-f
d
Methyl(phenyl)sulfoxide (2b)
O
S
b'
d'
f'
a'
e'
c'
a'
b'-f'
8
7
6
5
4
3
2
1
0
Chemical shift (ppm)
Figure 5. 1H NMR spectra of 1b and 2b in CDCl3.
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Figure 6. Recycling experiments of the photocatalytic reaction of 1b.
For the reactant of (4-methoxyphenyl)boronic acid (1c), in the first cycle of photocatalytic
reaction, the reaction time for the complete conversion was 8.5 h and the NMR yield was 99 %. Again,
1
the high conversion of substrate was confirmed by H NMR spectrum. Before the photocatalytic
reaction, the resonance signal of protons on phenyl groups can be observed at 7.0 ppm and 8.20 ppm.
Notably, after the photocatalytic reaction, one can observed that the signal completely shift to 6.78 ppm
(Figure 7). After the first cycle, the catalyst PHEMA-TX-1 can be recovered by simple precipitation in
EA and directly used for the second cycle. The following cycles of reactions were performed using the
same procedure. It could be reused seven times without significant loss of the catalytic activity. From
the seventh cycle, a slightly yield decreasement was observed (Figure 8).
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(4-Methoxyphenyl)boronic acid (1c)
b
c
a
O
B(OH)2
b
c
a
b
c
4-Methoxyphenol (2c)
a'
c'
b'
d'
OH
O
a'
b' c'
b' c'
d'
9
8
7
6
5
4
3
2
1
0
Chemical shift (ppm)
Figure 7. 1H NMR spectra of 1c and 2c in CDCl3.
Figure 8. Recycling experiments of the photocatalytic reaction of 1c.
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From the above three photocatalytic reactions, we can draw a conclusion that the designed
photocatalyst PHEMA-TX in this work has an excellent photocatalytic property and recyclability. The
slight loss of the catalytic activity from the seventh cycle, might be attributed to the loss of PHEMA-TX
during the recover procedure and the possible side reaction on the functional group of TX.
4. Conclusion
In summary, the functional TX groups were immobilized on precursor PHEMA and the novel
macromolecular photosensitizer PHEMA-TX was prepared. In order to introduce high content of TX
groups onto PHEMA, two modification routes was attempted. When TX-COCl was used, a relatively
high modification efficiency of 64 % can be reached. However, when an alternative route using DMAP
and DCC as catalyst, the modification efficiency was rather low (18.5 %). The reason can be attributed
to the bulky substituent TX group was used, which limited the modification efficiency. Subsequently,
the as-synthesized PHEMA-TX was used as photocatalyst for three substrates. The results showed that
the photocatalyst PHEMA-TX could be easily recovered from the reaction mixture by a simple
precipitation and reused for at least seven times. The excellent photocatalytic property, easy separation,
and recyclability are actually acting solid evidences for the potential of PHEMA-TX developed in this
work.
Acknowledgements
We greatly acknowledge the financial support from Shanghai Science and Technology Committee
(18DZ1201607), International Science & Technology Cooperation Program of China (2014DFE40130),
Fundamental Research Funds for the Central Universities, Pioneering Project of Academy for
Engineering and Technology, Fudan University (gyy2017-002), and State Key Laboratory for
Modification of Chemical Fibers and Polymer Materials, Donghua University (LK1711).
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Highlights
1) A novel synthetic method of thioxanthone-containing macromolecular
photosensitizer was developed.
2) This PHEMA-TX showed very nice photocatalytic activity in photo oxidation of
tris(4-methoxyphenyl)phosphane, methyl(phenyl)sulfane, (4-methoxyphenyl)boronic
acid.
3) This photocatalyst PHEMA-TX could be easily separated, recovered by a simple
precipitation, and reused.