Novel substituted porphyrins: synthesis, characterization and photocatalytic activity of their TiO2-based composites

Article abstract of DOI:10.1007/s10847-017-0724-6

Four novel porphyrins and their corresponding zinc complexes were synthesized and characterized spectroscopically. Effects of the spacer length of peripheral substituents of porphyrin are investigated in TiO₂-porphyrins hybrid systems by photod

Full text of DOI:10.1007/s10847-017-0724-6

J Incl Phenom Macrocycl Chem
DOI 10.1007/s10847-017-0724-6
ORIGINAL ARTICLE
Novel substituted porphyrins: synthesis, characterization
and photocatalytic activity of their TiO -based composites
2
Shaorui Chen · Fengjuan Shen1
1
Received: 19 July 2016 / Accepted: 24 May 2017
©
Springer Science+Business Media Dordrecht 2017
Abstract Four novel porphyrins and their corresponding
zinc complexes were synthesized and characterized spec-
troscopically. Effects of the spacer length of peripheral sub-
most active photocatalysts, but TiO has a wide energy
2
band gap of 3.2 eV so that it can be excited only by the
ultra-violet light which is only about 4–6% of the solar
spectrum. All these drawbacks limit its application espe-
cially in the large-scale industry [2, 3].
stituents of porphyrin are investigated in TiO -porphyrins
2
hybrid systems by photodegradation of methyl orange in
aqueous solution under visible light. The photocatalysts
were characterized by means of scanning X-ray diffrac-
tion, UV–Vis spectra, X-ray photoelectron spectroscopy
and FT-IR spectra. The results indicated that zinc porphy-
rins were successfully loaded and interacted with the sur-
Because of their rich electronic, catalytic property,
strong optical absorption and emission, porphyrin and
metalloporphyrins have attracted great research attention
and used in a series of fields including photosynthesis [4],
molecular recognition [5], medical treatment [6–8], photo-
sensitization [9–11], oxidation [12, 13], electron transfer
[14, 15]. Zinc porphyrins are one of the most widely studied
sensitizers for dye-sensitized solar cells (DSSC) because
of their strongly absorbing Soret bands (400–450 nm) and
moderately absorbing Q-bands (550–600 nm). Except for
its use in DSSCs, zinc porphyrins (ZnPp) have also been
studied extensively in catalytic or photocatalytic applica-
tions, which are better photosensitizers for extending the
face of TiO microsphere, which is crucial to enhance the
2
activity of the catalytic composite under visible light. All
the new photocatalysts showed much enhanced photoactiv-
ity than bare TiO . Especially, the photocatalytic activity of
2
5
,10,15-triphenyl-20-[4-(4-naphthoxy)butoxy] phenyl zinc
porphyrin-TiO is higher than others.
2
Keywords Zinc porphyrins · TiO · Photocatalysis ·
2
Degradation
light absorption of wide band gap TiO into the visible light
2
region than many other dye sensitizers, due to their small
singlet–triplet splitting, high quantum yield for intersystem
crossing, the long triplet state lifetimes, and good chemical
stability [16, 17]. Thus, zinc porphyrins have been widely
investigated for their photoactivity in hydrogen evolution
and degradation of organic compounds.
Introduction
Photocatalysis has enormous potential as an economical
and environment-friendly technique for the treatment and
purification of all kinds of contaminants for decades, espe-
cially for the decomposition of toxic organic compounds
Though the detailed mechanism of the photosensitized
catalysis is not fully understood [18], several factors influ-
[
1]. TiO has been extensively investigated as one of the
ence the efficiency of TiO -porphyrins systems, including
2
2
the molecule structure of porphyrin, the center metal, and
the crystal and specific surface area of TiO , etc [19–22].
2
*
Shaorui Chen
So it is significant to explore the influential factors of the
sjz_wgq@126.com
efficiency of TiO -porphyrins systems by designing and
2
synthesizing special structure porphyrins. Xiang-fei Lü
1
College of Science, Hebei University of Science
and Technology, Shijiazhuang 050018,
People’s Republic of China
[
23] reported that copper porphyrins show an enhanced
photocatalytic efficiency in sensitizing TiO for the
2
Vol.:(0
1
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3

J Incl Phenom Macrocycl Chem
photodegradation of organic pollutants, moreover the num-
ber of the substitutions of copper porphyrin influences the
photocatalytic efficiency up to a certain extent. However it
remains unclear as to whether the length of peripheral sub-
Synthesis of porphyrins and metalloporphyrins
General procedure for the synthesis of 3‑naphthoxypropyl
bromide (1a), 4‑naphthoxybutyl bromide (1b),
5‑naphthoxypentyl bromide (1c), 6‑naphthoxyhexyl
bromide (1d)
stituents influence the efficiency of TiO -porphyrins hybrid
2
systems. For these reasons, this work concerns the synthesis
and characterization of four novel porphyrins 5,10,15-tri-
phenyl-20-[4-(3-naphthoxy)-propoxy] phenyl porphyrin
3-Naphthoxypropyl bromide (1a) was synthesized accord-
ing to Ref [24]. (Scheme 1). Under nitrogen atmosphere,
1-naphthol (5.0 g, 34.7 mmol) and 7.2 g (52.2 mmol) of
potassium carbonate in 30 mL dried dimethyl formamide
(DMF) were stirred for 15 min at room temperature and
the solution of 8.3 g (41.6 mmol) 1,3-dibromopropane and
40 mL DMF was added dropwise to the reaction system.
The ensuing mixture was heated with stirring at 40°C for
6 h, then poured into water. The organic layer was extracted
with dichloromethane, dried over sodium sulfate. Column
chromatography (silica gel/petroleum ether/ethyl acetate)
followed by usual workups gave the product 1a. Yield:
8.4 g (91.6%) as pale yellow liquid.
(
3a), 5,10,15-triphenyl-20-[4-(4-naphthoxy)-butoxy] phe-
nyl porphyrin (3b), 5,10,15-triphenyl-20-[4-(5-naphthoxy)-
pentyloxy] phenyl porphyrin (3c), 5,10,15-triphenyl-20-[4-
(
6-naphthoxy)-hexyloxy] phenyl porphyrin (3d), as well as
their corresponding zinc porphyrins. The ZnPp–TiO pho-
2
tocatalysts were prepared and characterized by X-ray pho-
toelectron spectroscopy (XPS), X-ray diffraction (XRD),
infrared spectroscopy (IR), UV–Vis diffuse reflectance
spectrum (UV–Vis DRS). The photocatalytic activity of
the catalysts was evaluated by measuring the degradation
of methyl orange (MO). It is expected that the prepared
ZnPp–TiO photocatalysts can degraded MO in water
2
under visible irradiation.
The synthesis of 1b–1d was carried out in a similar way.
3
‑Naphthoxypropyl bromide (1a) Yield: 91.6%; pale yel-
1
Experimental
General
low liquid. H NMR (500 MHz, CDCl ) δ, ppm 2.42 (m,
3
2
H, –CH ), 3.89 (t, J=6.3 Hz, 2H, –CH Br), 4.33 (t,
2
2
J=5.9 Hz, 2H, –OCH ), 6.86 (m, 1H, Naph), 7.41(m, 1H,
2
Naph), 7.48 (m, 1H, Naph), 7.53 (m, 2H, Naph), 7.85 (m,
+
Reagents and solvents were purchased from Hebei Chemi-
cal Reagents Company. They were used without further
purification except pyrrole, which was distilled before
1H, Naph), 8.28 (m, 1H, Naph). MS: m/z 215.1 ([M+H] )
amu.
use. TiO (P25) was kindly provided by Suzhou Chemical
4‑Naphthoxybutyl bromide (1b) [25] Yield: 89.4%. Mp:
2
1
materials Company, using in preparation of loaded sam-
42–44°C; H NMR (500 MHz, CDCl ) δ, ppm 2.11 (m,
3
ples applied as photocatalysts in photoreactivity experi-
2H, –CH ), 2.18 (m, 2H, –CH ), 3.56 (t, J=6.5 Hz, 2H,
2
2
1
ments. H NMR spectra were measured with a Bruker
–CH Br), 4.19 (t, J=5.8 Hz, 2H, –OCH ), 6.81 (m, 1H,
2
2
Avance spectrometer at 500 MHz in CDCl as the solvent
Naph), 7.36 (m, 1H, Naph), 7.44 (m, 1H, Naph), 7.48 (m,
2H, Naph), 7.81 (m, 1H, Naph), 8.27 (m, 1H, Naph). MS:
3
with TMS as internal standard. ESI-MS were performed
on LCQ Advantage MAX spectrometer. Elemental analysis
+
m/z 229.4 ([M+H] ) amu.
(
C, H and N) was performed by VarioEL superuser. FT-IR
spectra were obtained with samples in KBr matrix for the
title complexes on A BEQUZNDX-550 series FT-IR spec-
5‑Naphthoxypentyl bromide (1c) [24] Yield: 90.5%; pale
1
yellow liquid; H NMR (500 MHz, CDCl ) δ, ppm 1.78 (m,
3
−
1
trophotometer in the range 4000–400 cm . Model NBeT
photocatalytic reactor (Beijing Electromechanical Plant,
Beijing, China) was employed to evaluate for the degrada-
tion of MO. UV–Vis diffuse reflectance spectra (UV–Vis
DRS) were performed in the range of 200–800 nm with
2H, –CH ), 2.00–2.06 (m, 4H, –CH ), 3.46 (t, 2H, –CH Br),
2
2
2
4.20 (t, 2H, –OCH ), 6.81 (m, 1H, Naph), 7.32 (m, 1H,
2
Naph), 7.44 (m, 1H, Naph), 7.53 (m, 2H, Naph), 7.83 (m,
+
1H, Naph), 8.28 (m, 1H, Naph). MS: m/z 243.2 ([M+H] )
amu.
BaSO as a white standard on a SHIMASZU-2550 scan
4
UV–Vis system equipped with an integrating sphere attach-
ment (Shimadzu Co., Japan). X-ray diffraction (XRD) anal-
ysis was performed on a Rigaku D/MAX 2500 X-ray dif-
fractometer equipped with a Cu Kα radiation source. X-ray
photoelectron spectroscopy (XPS) measurements were
performed with the PHI 5000 C ESCA System with Al Kα
radiation (hν=1486.6 eV).
6‑Naphthoxyhexyl bromide (1d) Yield: 87.8%. Mp:
1
76–78°C; H NMR(500 MHz, CDCl ) δ, ppm 1.56 (m, 2H,
3
–CH ), 1.78–1.91 (m, 6H, –CH ), 3.42 (t, 2H, –CH Br),
2
2
2
4.11 (t, 2H, –OCH ), 6.85 (m, 1H, Naph), 7.34 (m, 1H,
2
Naph), 7.45 (m, 1H, Naph), 7.56 (m, 2H, Naph), 7.85 (m,
+
1H, Naph), 8.27 (m, 1H, Naph). MS: m/z 257.3 ([M+H] )
amu.
1
3

J Incl Phenom Macrocycl Chem
a: n=3, b: n=4, c: n=5, d: n=6
Scheme 1 Synthesis of porphyrins and metalloporphyrins
+
General procedure for the synthesis of 4‑(3‑naphthoxy)
propoxy benzaldehyde (2a), 4‑(4‑naphthoxy)butoxy
benzaldehyde (2b), 4‑(5‑naphthoxy)pentyloxy benzaldehyde
Naph), 9.88 (s, 1H, –CHO). MS: m/z 257.3 ([M + H] )
amu.
(2c), 4‑(6‑naphthoxy)hexyloxy benzaldehyde (2d) [26]
4‑(4‑Naphthoxy)butoxy benzaldehyde (2b) Yield: 67.1%.
1
Mp: 72–74°C; H NMR (500 MHz, CDCl ) δ, ppm 2.14
3
A mixture of 3-phenoxypropyl bromide (1a) (5 g,
8.9 mmol), 4-hydroxybenzaldehyde (2.5 g, 20.8 mmol)
(m, 4H, –CH ), 4.18 (m, J=6.0 Hz, 2H, –CH O), 4.23 (m,
2
2
1
J=6.0 Hz, 2H, –OCH ), 6.81 (m, 1H, Naph), 7.00 (m, 2H,
2
and potassium carbonate (5.2 g, 37.8 mmol) in 50 mL
acetone were heated to reflux for 24 h, poured into water,
extracted with dichloromethane. The organic layer was
dried over sodium sulfate. Column chromatography (sil-
ica gel/petroleum ether/ethyl acetate) followed by usual
workups gave the product 2a with the yield 62.3% (3.6 g)
as white solid.
Ph), 7.25 (m, 1H, Naph), 7.45 (m, 2H, Naph), 7.48 (m, 1H,
Naph), 7.81 (m, 3H, Naph+Ph), 8.24 (m, 1H, Naph), 9.88
+
(s, 1H, –CHO). MS: m/z 271.3 ([M+H] ) amu.
4‑(5‑Naphthoxy)pentyloxy benzaldehyde (2c) Yield:
1
60.1%. Mp: 56–58°C; H NMR (500 MHz, CDCl ) δ, ppm
3
1.78 (m, 2H, –CH ), 1.92 (m, 2H, –CH ), 2.01 (m, 2H, –
2
2
The synthesis of 2b–2d was carried out in a similar
way starting with 1b–1d.
CH ), 4.08 (t, J=6.0 Hz, 2H, –OCH ), 4.17 (t, J=6.0 Hz,
2
2
2H, –OCH ), 6.79 (m, 1H, Naph), 6.99 (m, 2H, Ph), 7.35 (m,
2
1
H, Naph), 7.43–7.49 (m, 3H, Naph), 7.78 (m, 1H, Naph),
4
6
2
4
7
7
‑(3‑Naphthoxy)propoxy benzaldehyde (2a) Yield:
7.80 (m, 2H, Ph), 8.26 (m, 1H, Naph), 9.87 (s, 1H, –CHO).
1
+
2.3%. Mp: 46–48 °C H NMR (500 MHz, CDCl ) δ, ppm
MS: m/z 285.1 ([M+H] ) amu.
3
.26 (m, 2H, –CH ), 4.18 (m, J = 6.0 Hz, 2H, –CH O),
2
2
.26 (m, J = 6.0 Hz, 2H, –OCH ), 6.81 (m, 1H, Naph),
4‑(6‑Naphthoxy)hexyloxy
benzaldehyde
(2d) Yield:
2
1
.00 (m, 2H, Ph), 7.35 (m, 1H, Naph), 7.45 (m, 2H, Ph),
61.1%. Mp: 86–88°C; H NMR (500 MHz, CDCl ) δ, ppm
3
.47 (m, 1H, Naph), 7.81 (m, 1H, Naph), 8.24 (m, 1H,
1.57–1.70 (m, 4H, –CH ), 1.92 (m, 2H, –CH ), 1.98 (m, 2H,
2
2
1
3

J Incl Phenom Macrocycl Chem
+
–
–
1
7
CH ), 4.05 (t, J=6 Hz, 2H, –OCH ), 4.16 (t, J=6 Hz, 2H,
Naph), 8.88 (m, 8H, pyrrole). MS: m/z 843.5 ([M+H] )
2
2
OCH ), 6.78 (m, 1H, Naph), 6.98 (m, 2H, Ph), 7.36 (m,
amu. UV–Vis (CH Cl ): λmax, nm, 418 (Soret band), 516,
2
2
2
H, Naph), 7.37–7.48 (m, 3H, Naph), 7.78 (m, 1H, Naph),
551, 591, 646 (Q bands).
.81 (m, 2H, Ph), 8.26 (m, 1H, Naph), 9.87 (s, 1H, –CHO).
+
MS: m/z 299.4 ([M+H] ) amu.
5,10,15‑Triphenyl‑20‑[4‑(6‑naphthoxy)‑hexyloxy] phenyl
porphyrin (3d) Yield: 7.0%. Mp: >300°C. Anal. Calcd.
for C H N O , %: C, 84.08; H, 5.65; N, 6.54. Found C,
General procedure for the synthesis of free‑base
porphyrins H Pp (3a), H Pp (3b), H Pp (3c), H Pp (3d)
6
0
48
4
2
1
84.25; H, 5.89; N, 6.66. H NMR (500 MHz, CDCl ) δ, ppm
2
2
2
2
3
−
2.74 (s, 2H, –NH), 1.69 (m, 4H, –CH ), 1.97 (m, 4H, –
2
The synthesis of compound 3 was according to Lindsey
methods [27]. 1.53 g (5 mmol) 4-(3-naphthoxy)-propoxy-
benzaldehyde (2a), 1.53 mL (15 mmol) benzaldehyde
and 1.4 mL (20 mmol) pyrrole in 600 mL of chloroform
were stirred at room temperature for 15 min under a nitro-
gen atmosphere. 0.03 mL (0.25 mmol) BF ·Et O in 10mL
CH ), 4.15 (m, 4H, –CH O), 7.19 (m, 2H, Ph), 7.37 (m, 2H,
2 2
Ph), 7.45 (m, 2H, Ph), 7.73 (m, 11H, Ph), 8.20 (m, 2H, Ph),
8.33 (m, 7H, Naph), 8.89 (m, 8H, pyrrole). MS: m/z 857.1
+
([M+H] ) amu. UV–Vis (CH Cl ): λmax, nm, 418 (Soret
2
2
band), 516, 551, 591, 646 (Q bands).
3
2
CHCl were added and the reaction mixture was stirred
General procedure for the synthesis of zinc porphyrins
(ZnPp:4a–4d)
3
at room temperature for 48 h and thereafter, for a further
3
0 h following the addition of 0.85 g (3.75 mmol) DDQ
in CHCl . The solvent was removed under vacuum and
52.5 mg (0.24 mmol) of Zn(OAc) ·2H O was added to
3
2
2
the crude product was purified by chromatography on a
silica gel column with dichloromethane/petroleum ether as
eluant.
100.0 mg (0.12 mmol) of compound 3a dissolved in 50 mL
CH Cl . The mixture was stirred for 1 h at room tempera-
2
2
ture. The unreacted solid salt was filtered and the solvent
removed under vacuum. The crude product was purified by
chromatography on a silica gel column with dichlorometh-
ane/petroleum ether to offord compound 4 [28].
The synthesis of 4b–4d was carried out in a similar way
starting with 3b–3d.
The synthesis of 3b–3d was carried out in a similar way
starting with 2b–2d.
5
,10,15‑Triphenyl‑20‑[4‑(3‑naphthoxy)‑propoxy]
phenyl
porphyrin (3a) Yield: 7.6%. Mp: >300°C. Anal. Calcd.
for C H N O , %: C, 84.00; H, 5.19; N, 6.87. Found C,
5
7
42
4
2
1
8
3.82; H, 5.27; N, 6.96. H NMR (500 MHz, CDCl ) δ,
ZnPp (4a) Yield: 93.4%. Mp: >300°C. Anal. Calcd. for
3
ppm −2.76 (s, 2H, –NH), 2.43 (m, 2H, –CH ), 4.32 (m,
C H N O Zn, %: C, 77.94; H, 4.59; N, 6.38. Found C,
2
57 40
4
2
1
2
H, –CH O), 4.40 (m, 2H, –CH O), 7.27 (m, 2H, Ph), 7.53
78.12; H, 4.69; N, 6.66. H NMR (500 MHz, CDCl ) δ, ppm
2
2
3
(
(
(
m, 2H, Ph), 7.73 (m, 12H, Ph), 8.11 (m, 2H, Ph), 8.22
2.41 (m, 2H, –CH ), 4.31–4.39 (m, 4H, –CH O), 7.22 (m,
2
2
m, 7H, Naph), 8.87 (m, 9H, pyrrole+Ph). MS: m/z 815.4
2H, Ph), 7.55 (m, 2H, Ph), 7.73–7.80 (m, 12H, Ph), 8.13 (m,
+
[M+H] ) amu. UV–Vis (CH Cl ): λmax, nm, 418 (Soret
2H, Ph), 8.20 (m, 7H, Naph), 8.89 (m, 9H, pyrrole+Ph).
2
2
+
band), 515, 550, 591, 646 (Q bands).
MS: m/z 877.1 ([M+H] ) amu. UV–Vis (CH Cl ): λmax,
2
2
nm, 419, (Soret band), 548, 586 (Q bands).
5
,10,15‑Triphenyl‑20‑[4‑(4‑naphthoxy)butoxy] phenyl por‑
phyrin (3b) Yield: 6.9%. Mp: >300°C. Anal. Calcd. for
ZnPp (4b) Yield: 90.2%. Mp: >300°C. Anal. Calcd.
C H N O , %: C, 84.03; H, 5.35; N, 6.76. Found C, 84.23;
for C H N O Zn, %: C,78.06; H, 4.74; N, 6.28. Found
5
8
44
4
2
58 42
4
2
1
1
H, 5.39; N, 6.87. H NMR (500 MHz, CDCl ) δ, ppm −2.76
C, 78.25; H, 4.89; N, 6.56. H NMR (500 MHz, CDCl )
3
3
(
s, 2H, –NH), 2.28 (m, 4H, –CH ), 4.35 (m, 4H, –CH O),
δ, ppm 2.28–2.29 (m, 4H, –CH ), 4.34 (m, 2H, –CH O),
2
2
2
2
6
.88 (m, 2H, Ph), 7.23–7.81 (m, 15H, Ph), 8.36 (m, 2H,
4.38 (m, 2H, –OCH ), 6.87 (m, 1H, Naph), 7.25 (m, 2H,
2
Ph), 8.38 (m, 7H, Naph), 8.89 (m, 8H, pyrrole). MS: m/z
Ph), 7.37 (m, 2H, Ph), 7.45 (m, 2H, Naph), 7.73–7.78 (m,
+
8
29.3([M+H] ) amu. UV–Vis (CH Cl ): λmax, nm, 418
10H, Ph+Naph), 8.12 (m, 2H, Ph), 8.21 (m, 6H, Ph), 8.21
2
2
(
Soret band), 515, 551, 591,645 (Q bands).
(m, 1H, Naph), 8.93–8.99 (m, 8H, pyrrole). MS: m/z 891.2
+
(
[M+H] ) amu. UV–Vis (CH Cl ): λmax, nm, 419, (Soret
2
2
5
,10,15‑Triphenyl‑20‑[4‑(5‑naphthoxy)‑pentyloxy] phenyl
band), 548, 586 (Q bands).
porphyrin (3c) Yield: 6.7%. Mp: >300°C. Anal. Calcd.
for C H N O , %: C, 84.06; H, 5.50; N, 6.65. Found C,
ZnPp (4c) Yield: 91.3%. Mp: >300°C. Anal. Calcd. for
5
9
46
4
2
1
8
4.32; H, 5.67; N, 6.78. H NMR (500 MHz, CDCl ) δ,
C H N O Zn, %: C, 78.18; H, 4.89; N, 6.18. Found C,
3
59 44
4
2
1
ppm −2.74 (s, 2H, –NH), 1.84 (m, 2H, –CH ), 2.02 (m, 4H,
78.39; H, 4.99; N, 6.36. H NMR (500 MHz, CDCl ) δ,
2
3
–
2
CH ), 4.17 (m, 4H, –CH O), 7.20 (m, 2H, Ph), 7.40 (m,
ppm 1.99 (m, 2H, –CH ), 2.18 (m, 4H, –CH ), 4.31 (m, 2H,
2
2
2
2
H, Ph), 7.76 (m, 13H, Ph), 8.07 (m, 2H, Ph), 8.21 (m, 7H,
–CH O), 4.36 (m, 2H, –OCH ), 6.89 (m, 1H, Naph), 7.30
2
2
1
3

J Incl Phenom Macrocycl Chem
(
m, 2H, Ph), 7.34 (m, 2H, Ph), 7.45 (m, 2H, Naph), 7.81(m,
were withdrawn from the suspension every 30 min during
the irradiation. The photocatalysts were separated from
the solution by centrifugation and the quantitative deter-
mination of MO was performed by measuring its absorp-
tion at 464 nm with a Shimadzu UV2550 UV–Vis-NIR
spectrophotometer. The decoloration rate is reported as C/
1
0H, Ph+Naph), 8.16 (m, 2H, Ph), 8.27 (m, 6H, Ph), 8.39
(
m, 1H, Naph), 8.99–8.04 (m, 8H, pyrrole). MS: m/z 905.3
+
(
[M+H] ) amu. UV–Vis (CH Cl ): λmax, nm, 419, (Soret
2
2
band), 548, 586 (Q bands).
ZnPp (4d) Yield: 92.5%. Mp: >300°C. Anal. Calcd. for
C , where C is the pollutant’s concentration after adsorp-
0
C H N O Zn, %: C, 78.29; H, 5.04; N, 6.09. Found C,
tion or photocatalysis, and C is the pollutant’s initial
6
0
46
4
2
0
1
7
8.39; H, 5.19; N, 6.36. H NMR (500 MHz, CDCl ) δ,
concentration.
3
ppm 1.66(m, 4H, –CH ), 1.99 (m, 4H, –CH ), 4.11 (m, 4H,
2
2
–
CH O), 7.12 (m, 2H, Ph), 7.37 (m, 2H, Ph), 7.48 (m, 2H,
2
Ph), 7.73–7.77 (m, 11H, Ph+Naph), 8.22 (m, 2H, Ph), 8.28
Results and discussion
(
m, 7H, Naph), 8.91–8.99 (m, 8H, pyrrole). MS: m/z 919.5
+
(
[M+H] ) amu. UV–Vis (CH Cl ): λmax, nm, 419, (Soret
Synthesis and characterization of H Pp and ZnPp
2
2
2
band), 548, 586 (Q bands).
The synthetic route has been illustrated in Scheme 1.
Started from 1-naphthol, the precursors 3-phenoxypropyl
bromide (1) was obtained in the presence of dried DMF
and nitrogen atmosphere, which could effectively inhibit
the hydrolysis of bromo-compounds. Compound 1 could
react with 4-hydroxybenzaldehyde in acetone solution
under refluxed condition for 24 h to produce the key inter-
mediate 2 in the yield of 60–67%. The four novel porphy-
rins (3a, 3b, 3c, 3d) were synthesized by using a procedure
Lindsey methods. Corresponding zinc porphyrins 4a–4d
were prepared in nearly quantitative yields by 3 reacting
Preparation of the ZnPp–TiO photocatalysts
2
An amount (6.0 μmol) of the sensitizer (ZnPp) was dis-
solved in 25 mL CH Cl and 0.2 g TiO (P25) was added to
2
2
2
the solution. The suspension was stirred for 8 h at the room
temperature. Then the solvent was removed under vacuum
and the catalyst was collected and dried to obtain photo-
catalysts of 4a-TiO , 4b-TiO , 4c-TiO , 4d-TiO [21, 23] .
2
2
2
2
Photoreactivity experiments
with Zn(Ac) .
2
The photodegradation setup consisted of a 200 mL beaker
irradiated by a 300 W, 24 V Xenon lamp-house system
As shown in Table 1, the UV–Vis absorption band
maxima (molar extinction coefficients) of H Pp (3a–3d)
2
(
instrument: NBeT. Beijing Trusttech Co. Ltd. China)
and their metalloporphyrins (4a–4d) in CH Cl were
2
2
placed in a black box. The distance between the lamp and
the solution was 16.5 cm, and the irradiance measured at
presented. The UV–Vis spectra of 3a, 3b, 3c, 3d show
almost the same Soret and Q bands which is a band cen-
tered at λ = 418 (Soret band) and Q bands absorption
respectively at 515, 551, 591, 646 nm. The Q bands of
zinc porphyrins 4a, 4b, 4c, 4d decrease because of the
symmetry of zinc porphyrin, and display Q bands at
554–556, 597–598 nm. The mass spectra of the porphy-
rins 3a, 3b, 3c, 3d and the zinc porphyrins 4a, 4b, 4c, 4d
2
the distance of 16.5 cm was 37.0 mW/cm .
The reaction was carried out according to methods
described in the literature [29].The reacting suspension
consisted of 100 mL 10 mg/mL of MO and 0.1 g catalyst
and it was stirred with a magnetic bar prior to the photo-
catalytic reaction, the suspension was stirred in darkness
for 30 min to reach adsorption/desorption equilibrium. The
photoreactivity runs lasted 150 min and samples of 3 mL
+
1
showed the positively charged [M + H] m/z adducts. H
NMR spectra were also consistent with the structure of
Table 1 UV–Vis data of the
Compounds
λmax/nm(ε)
ZnPp
H Pp(3) and diffuse reflectance
2
spectral data of photocatalysts
ZnPp–TiO2
Soret band
Q bands
Soret band
Q bands
5
a
H Pp(3a–3d)
418(2.43×10 )
515, 551, 591, 646
–
–
2
5
4
3
ZnPp(4a)
ZnPp(4b)
ZnPp(4c)
ZnPp(4d)
419(4.01×10 )
548(2.41×10 ), 586(3.72×10 )
432
431
430
432
556, 597
554, 598
556, 598
556, 597
5
4
3
419(4.34×10 )
548(2.78×10 ), 586(3.98×10 )
5
4
3
419(5.67×10 )
548(3.02×10 ), 586(4.78×10 )
5
4
3
419(4.87×10 )
548(3.12×10 ), 586(4.72×10 )
aMolar extinction coefficients of compound 3b
1
3

J Incl Phenom Macrocycl Chem
the synthesized compounds. These spectroscopy data are
well consistent with the structure of the synthesized por-
phyrins and zinc porphyrins.
Solid diffuse reflection UV–Vis spectra
As shown in Fig. 2, the diffuse reflectance spectra of the
bare TiO , 4a-TiO , 4b-TiO , 4c-TiO and 4d-TiO photo-
2
2
2
2
2
catalysts were recorded in the range of 300–800 nm. Obvi-
X-ray photoelectron spectroscopy
ously, there was no absorption above 400 nm for bare TiO ,
2
whereas the (4a, 4b, 4c, 4d)-TiO photocatalysts exhibit the
2
Surface elemental compositions of the samples were ana-
lyzed by X-ray photoelectron spectroscopy (XPS). Fig-
ure 1 shows the XPS survey spectra of TiO and TiO /4b
feature peaks of 4a, 4b, 4c, 4d observed in CH Cl solution
2
2
(Table 1), which indicated that 4a, 4b, 4c, 4d successfully
loaded onto the TiO surface with integrated porphyrin
2
2
2
(
37.5:1). It can be found that pure TiO only contains the
framework. Simultaneously, the Soret band of ZnPp (4a,
2
elements of Ti, O and C, and the mass ratios of Ti, O and
C are 50.78, 40.68 and 8.55%, respectively. The binding
energies of Ti 2p, O 1s and C 1s are 455.7, 526.9 and
4b, 4c, 4d)-TiO have a significant red-shifts from 419 nm
2
to 432, 431,430, 432 nm compared with the spectra of 4a,
4b, 4c, 4d and the Q band of 4a, 4b, 4c, 4d-TiO is also
2
2
82.85 eV, respectively. Elements of C, O, Ti, N and Zn
red-shifted and broadened, implying that there exists an
are confirmed to exist in the photocatalysts (4b-TiO ) by
weak interaction between TiO and zinc porphyrin mole-
2
2
the five peaks at binding energies of 281.9, 527.0, 455.8,
cules which dependent on an electrostatic force of attrac-
3
2
97.8 and 1019.3 eV, which are related to C 1 s, O 1 s, Ti
p, N 1 s and Zn 2p respectively [30]. The mass contents
tion and physical absorption [31–33].
of C, O, Ti, N and Zn are 13.99, 40.61, 44.07, 0.97 and
FT-IR spectra of photocatalysts
0
.36% respectively, suggesting that compound 4b exists
on the surface of photocatalysts.
The FT-IR spectra of pure TiO and 4a, 4b, 4c, 4d-TiO
2
2
photocatalysts are displayed in Fig. 3. The absorption peak
−
1
at 3448 cm is associated with the stretching vibrations
of surface hydroxyl groups TiO , whereas the band around
2
−
1
1
643 cm is attributed to the bending vibration of H–OH
groups and Ti–OH bond for bare TiO and ZnPp–TiO
2
2
respectively. The strong and broad peaks around 600 nm
are attributed to the characteristic peaks of anatase TiO .
2
The stretching vibrations of C–C, C–H bonds can be
observed in ZnPp–TiO composites, indicating that there
2
Fig. 2 UV–Vis diffuse reflectance spectra of the spectra of the bare
TiO , 4a-TiO , 4b-TiO , 4c-TiO , 4d-TiO photocatalysts
Fig. 1 XPS spectrum of TiO and TiO /4b (37.5:1)
2
2
2
2
2
2
2
1
3

J Incl Phenom Macrocycl Chem
Fig. 3 FT-IR spectra of bare TiO and 4a–4d-TiO catalysts
Fig. 4 XRD pattern of the bare TiO2 and 4a, 4b, 4c, 4d-TiO2 photo-
2
2
catalysts
contains zinc porphyrins on the surface of TiO . Simulta-
4d-TiO showed much enhanced photoactivity than
2
2
neously, the same amount of the samples was always used
to collect spectra under the same condition and this allows
a quantitative comparison between different photocatalysts.
bare TiO , and in particular 4b-TiO exhibited the high-
2
2
est efficiency of all samples, as the following order:
4b-TiO >4a-TiO >4c-TiO >4d-TiO >bareTiO .
2
2
2
2
2
−
1
Further observation shows that the peaks at 3450 cm are
Figure 5 shows that the photocatalytic activity of 4b-
broader and weaker in the ZnPp–TiO photocatalysts than
TiO is higher than 4a, 4c, 4d-TiO photocatalysts, which
2
2
2
that of pure TiO , because instead of surface hydroxyl
can be considered that the excited potential of 4b displayed
2
groups, the ZnPp were loaded on the surface of TiO . From
best match with conduction band (CB) of TiO potential.
2
2
these observations it is inferred that there is weak inter-
Furthermore, spacer length of the substituent can influence
action between zinc porphyrin and the surface of TiO
the interaction between ZnPp and TiO , and accordingly
2
2
microsphere.
influence the photocatalytic activity, which is beneficial to
the process of initial electron injection from the porphyrins
XRD characterization of ZnPp–TiO photocatalysts
excited singlet state to the CB of the TiO , leading to an
2
2
effective photoactivity.
X-ray diffraction (XRD) was employed to investigate the
crystal identity of TiO samples and the effect of metal-
2
loporphyrins (4a–4d) on the crystal structure of TiO .
2
Figure 4 shows the XRD pattern for the bare TiO and
2
4
a-TiO , 4b-TiO , 4c-TiO , 4d-TiO photocatalysts. No
2
2
2
2
differences were found in these samples, and the promi-
nent diffraction peaks at 25.4°, 37.9°, 48.1°, 54.1°, 62.8°
and 68.4° were observed which were attributed to anatase
TiO . These results indicated that the 4a, 4b, 4c, 4d loaded
2
onto the surface of TiO [34]. Furthermore, this conclusion
2
is well consistent with the previous results of XPS, FT-IR
spectra: 4a, 4b, 4c, 4d were loaded on the surface of TiO
2
photocatalysts, not doped into TiO crystal lattice.
2
Photoreactivity experiments
The photocatalytic activities for the degradation of
MO in aqueous suspension under the Xenon lamp irra-
diation using prepared photocatalysts were tested. As
expected, all the four new photocatalysts 4a, 4b, 4c,
Fig. 5 Photocatalytic activities of 4a-TiO , 4b-TiO , 4c-TiO and 4d-
2
2
2
TiO samples on the degradation of MO under visible light irradiation
2
1
3

J Incl Phenom Macrocycl Chem
Process features and mechanistic aspects
meso-substituents in porphyrins can effectively increase
the interaction between porphyrin molecules and the sur-
The results that 4a, 4b, 4c, 4d-TiO photocatalysts, show
face of TiO , which is beneficial to the process of initial
2
2
much enhanced photoactivity compared with the bare TiO ,
electron injection from the porphyrins excited singlet
2
and the length of the substitutions influences the photocata-
lytic efficiency up to a certain extent although it is not very
obvious. The appropriate structure of 5,10,15-triphenyl-
state to the TiO CB, leading to an effective photoactiv-
2
ity. Meanwhile, long and flexible spacers of substituents
may prevent these porphyrins from intermolecular π–π
interactions and the consequent decreasement of aggre-
gation. Hence, one may expect 4b to manifest enhanced
ability to trap molecular oxygen and in consequence to
increase the amount of reactive oxidants, necessary for
the degradation of MO in water. It follows that also in
this case the molecular system of 4b is favored over the
other ones.
2
0-[4-(3-naphthoxy)-propoxy]phenyl porphyrin (3a) was
estimated by theoretical calculations Fig. 6, which repre-
sented a planar and extendable molecular structure. Thus,
the planar and extendable molecular structures of 4a, 4b,
4
c and 4d can be expected.
Under the Xenon lamp irradiation, TiO can be excited
2
and create mobile electrons, then the photo-induced elec-
trons inject into the CB of TiO , the reactive electrons
2
in the CB reduce O adsorbed on the surface of TiO
2
2
−
to ·O , which can further transform into ·OH and deg-
Stability of photocatalysts
2
radate MO in water. On the other hand, the holes, cre-
ated in the valence band (VB) of TiO , can immigrate
Stability of photocatalyst is very essential for the prac-
tical application. In order to evaluate stability of
ZnPp–TiO photocatalysts, the recycling of 4a-TiO ,
2
faster to the MO molecules through the metalloporphy-
rins [21, 35], and finally, degrade MO into small mole-
cules or CO , H O. The lone-pair electrons in the oxy-
2
2
4b-TiO , 4c-TiO , 4d-TiO photocatalysis for MO deg-
2
2
2
2
2
gen atoms of substituents in 4a, 4b, 4c, 4d interact with
radation was carried out. Figure 7 shows that 4a-TiO ,
2
the surface of TiO , making porphyrin molecules easily
4b-TiO , 4c-TiO , 4d-TiO catalysts can be recycled six
2
2
2
2
loaded onto the TiO surface, Hence, the presence of the
times without significant loss of activity. At the first cycle
2
for 4a-TiO , 4b-TiO , 4c-TiO and 4d-TiO catalyst, 89.4,
2
2
2
2
9
1.4, 83.5 and 73.3% MO was removed, respectively.
After six cycles, the catalytic efficiency retained 80.1%
(
(
4a-TiO ), 83.1% (4b-TiO ), 75.6% (4c-TiO ) and 62.7%
2
2
2
4d-TiO ). It has been confirmed that these porphyrins
2
supported onto TiO showed good stability under irradia-
2
tion conditions and they continued to maintain good pho-
tocatalytic activity also after several cycles.
Fig. 7 Photocatalytic efficiency of the different 4a, 4b, 4c, 4d-TiO2
catalysts for MO degradation of six cycles (reaction for 150 min, dos-
age 100 mg, 100 mL MO solution)
Fig. 6 Molecular structure of the novel 5,10,15-triphenyl-20-[4-
(
3-naphthoxy)propoxy]phenyl porphyrin (3a)
1
3

J Incl Phenom Macrocycl Chem
combination of porphyrin and alkylating agent. Bioorg. Med.
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Conclusions
9
.
Ge, R.Y., Li, X.Q., Kang, S.Z., Qin, L.X., Li, G.D.: Highly effi-
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In summary, four novel porphyrin derivatives
5
,10,15-triphenyl-20-[4-(3-naphthoxy)-propoxy]
6
7–74 (2016)
phenyl
porphyrin
(3a),
5,10,15-triphenyl-20-[4-
porphyrin (3b),
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(
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phenyl
5
,10,15-triphenyl-20-[4-(5-naphthoxy)-pentyloxy] phenyl
porphyrin (3c), 5,10,15-triphenyl-20-[4-(6-naphthoxy)-
hexyloxy] phenylporphyrin (3d), and their corresponding
zinc porphyrins have been described along with the cor-
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