Photocatalytic hydrogen evolution through fully conjugated poly(azomethine) networks

Article abstract of DOI:10.1039/c0cc04057f

Three-dimensional conjugated poly(azomethine) networks were found to be promising candidates for applications in photocatalytic water splitting. Straightforward synthetic protocols lead to fully organic photocatalysts that showed enhanced long-time stability. Furthermore, the catalytic performance of these materials was correlated to the molecular composition and the optoelectronic properties of the samples.

Full text of DOI:10.1039/c0cc04057f

Electronic Supplementary Information
For the manuscript
Photocatalytic Hydrogen Evolution
Through Fully Conjugated Poly(azomethine)
Networks
by
a
a
a
Matthias Georg Schwab, Manuel Hamburger, Jie Shu,
a
b
b
Hans Wolfgang Spiess, Xinchen Wang,* Markus Antonietti,
a
a
Xinliang Feng and Klaus Müllen*
a
Max Planck Institute for Polymer Research
Ackermannweg 10, D-55128 Mainz, Germany
muellen@mpip-mainz.mpg.de
b
Max Planck Institute of Colloids and Interfaces
Research Campus Golm, D-14424 Potsdam, Germany
xinchen.wang@mpikg.mpg.de
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S1

Materials and methods
Unless otherwise noted, all starting materials were purchased from Aldrich, Acros and TCI.
The compounds were used as received without further purification.
1
2
Naphthalene-2,6-dicarbaldehyde and anthracene-9,10-dicarbaldehyde were prepared
according to literature-known procedures in 71 % and 58 % yield, respectively.
Photocatalytic reactions were carried out in a Pyrex top-irradiation reaction vessel connected
to a glass closed gas circulation system. H
of ANW catalyst powder in 100 ml of an aqueous solution containing triethanolamine (10
vol%). For the deposition of platinum, an appropriate amount of H PtCl was dissolved in the
2
production was performed by dispersing 100 mg
2
6
catalyst solution. The solution was evacuated several times to remove air completely prior to
irradiation under a 300 W xenon lamp and a water filter. The wavelength of the incident light
(λ > 300 nm) was controlled by using an appropriate cut-off filter. The temperature of the
reactant solution was maintained at room temperature by a flow of cooling water during the
reaction. The evolved gases were analyzed by gas chromatography. The experimental error
2
in the rate of H evolution was within 15 %.
Fourier transform infrared (FTIR) spectra were collected with a Nicolet 730 spectro-meter,
equipped with an attenuated total reflection (ATR) setup.
13
1
Solid-state C [ H] cross-polarization (CP) NMR spectra were recorded on a Bruker ASX
1
5
1
00 instrument equipped with a 2.5mm MAS double H-X probe at a Lamour frequency of
13
25.8 MHz for C. The samples were packed in 2.5mm rotors and experienced fast magic
15
1
angle spinning (MAS) at the rate of 25 kHz. The N [ H] CP spectra were obtained on a
15
Bruker DSX 300 instrument at 21.7 MHz for N. The samples were packed in 4mm rotors
13
15
and the MAS rate was 10 kHz. The C and N CP measurements were performed using a
contact time of 3 ms and 7 ms, respectively. Two-pulse, phase modulation (TPPM) sequence
1
13
15
was introduced as a H decoupling method at the power of 100 kHz. Both of the C and
N
13
NMR spectra were referenced with respect to tetramethyl silane using adamantane ( C,
15
2
9.456 ppm) and nitromethane ( N, -358.4 ppm) as secondary standards. All the spectra
13
were acquired at room temperature with accumulations of 6000 and 30000 scans for C and
15
N spectra.
DFT calculations were performed with ORCA, B3LYP being the (hybrid) exchange functional,
employing 6-311G** as basis set. A representative linear fragment of the ANW network
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structure was chosen and its geometry optimized (gas phase). It should be noted however
that these fragments may be heavily distorted in the network formed during polymerization.
Experimental section
General considerations
The ANW networks were synthesized at fixed molar ratio of amine to aldehyde groups of
1
.15 / 1.00 to allow for efficient cross-linking.
Synthesis of 1,3,5-tris(4-aminophenyl)benzene
NH2
H N
NH2
2
2
.0 g (6.35 mmol) of 1,3,5-tribromobenzene and (4-aminophenyl)boronic acid were dissolved
in 50 ml of toluene. Then, a few drops of Aliquat 336 and 15.0 ml of an aqueous K CO (2 M)
were added. After degassing by argon bubbling, 0.11 (0.095 mmol) of
tetrakis(triphenylphosphine)palladium(0) were added. The reaction mixture was heated to
00 °C for 24 h. The crude product was purified by column chromatography (hexane/ethyl
2
3
g
1
acetate 7/3) to yield 1.38 g (3.937 mmol) of 1,3,5-tris(4-aminophenyl)benzene in 62 % as an
off-white solid.
1
2 2
H NMR (300 MHz, CD Cl ) δ 7.59 (s, 3H), 7.51 (dd, J = 2.1, 8.7, 6H), 6.77 (dd, J = 2.2, 8.7,
6
H), 3.82 (s, 6H).
13
C NMR (75 MHz, CD
2
Cl
2
) δ 146.79, 142.32, 131.69, 128.39, 122.80, 115.49.
+
-1
MS (FD, 8kV): m/z (%) = 350.8 (100.0 %, M ), (calc. for C24
H N
21 3
= 351.17 g mol ).
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Synthesis of anthracene-2,6-dicarbaldehyde
OHC
CHO
0
.50 g (1.48 mmol) of 2,6-dibromoanthracene was placed in a flame-dried Schlenk tube
which was subsequently evacuated and refilled with argon for three times. 15.0 ml of dry
tetrahydrofuran were added and the mixture was cooled to -78 °C. Then, 21.4 mmol ml of n-
butyllithium (1.6 M in hexane) was added and the reaction was allowed to proceed for 1 h at
this temperature. 10.0 ml of anhydrous dimethyl formamide were added and the mixture was
stirred for 1 h. The mixture was slowly brought to room temperature and quenched by the
addition of methanol/water. The crude product was purified by column chromatography
(
(
hexane, hexane/ethyl acetate 7/3) and recrystallized from toluene/ethanol to yield 0.22 g
0.94 mmol) of anthracene-2,6-dicarbaldehyde in 61 % as a yellow crystalline solid.
1
2 2
H NMR (300 MHz, CD Cl ) δ 10.21 (s, 2H), 8.72 (s, 2H), 8.58 (s, 2H), 8.18 (d, J = 9.1, 2H),
7
.97 (d, J = 8.8, 2H).
13
2 2
C NMR (176 MHz, CD Cl ) δ 192.16, 136.78, 135.43, 134.23, 132.76, 130.15, 129.70,
1
22.15.
+
-1
MS (FD, 8kV): m/z (%) = 233.2 (100.0 %, M ), (calc. for C H O = 351.17 g mol ).
16
10
2
Synthesis of ANW 1
2
50 mg (0.71 mmol) of 1,3,5-tris(4-aminophenyl)benzene and 125 mg (0.93 mmol) of
terephthalaldehyd were placed in a Schlenk tube. Then, 10.0 ml of dioxane and 2.2 ml of
acetic acid (3 M) were added and the mixture was degassed by argon bubbling. The reaction
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mixture was heated to reflux for 3 d. The yellow precipitate was collected by filtration and
subjected to Soxhlet extraction in tetrahydrofuran for 24 h to yield 276 mg (82 %) of ANW 1.
42 6
Elemental analysis: for C72H N , calculated: C, 87.25; H, 4.27; N, 8.48 %. Found: C, 82.06 ;
H, 3.55; N, 7.70 %.
Synthesis of ANW 2
2
50 mg (0.71 mmol) of 1,3,5-tris(4-aminophenyl)benzene and 171 mg (0.93 mmol) of
naphhtalene-2,6-dicarbaldehyde were placed in a Schlenk tube. Then, 10.0 ml of dioxane
and 2.2 ml of acetic acid (3 M) were added and the mixture was degassed by argon
bubbling. The reaction mixture was heated to reflux for 3 d. The orange-yellow precipitate
was collected by filtration and subjected to Soxhlet extraction in tetrahydrofuran for 24 h to
yield 291 mg (76 %) of ANW 2.
48 6
Elemental analysis: for C84H N , calculated: C, 88.40; H, 4.24; N, 7.36 %. Found: C, 84.63 ;
H, 4.28; N, 6.98 %.
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Synthesis of ANW 3
N
N
N
N
N
N
1
50 mg (0.43 mmol) of 1,3,5-tris(4-aminophenyl)benzene and 131 mg (0.56 mmol) of
anthracene-2,6-dicarbaldehyde were placed in a Schlenk tube. Then, 10.0 ml of dioxane and
.1 ml of acetic acid (3 M) were added and the mixture was degassed by argon bubbling.
2
The reaction mixture was heated to reflux for 3 d. The orange-yellow precipitate was
collected by filtration and subjected to Soxhlet extraction in tetrahydrofuran for 24 h to yield
1
80 mg (70 %) of ANW 3.
54 6
Elemental analysis: for C96H N , calculated: C, 89.28; H, 4.21; N, 6.51 %. Found: C, 81.55;
H, 5.23; N, 6.21 %.
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Synthesis of ANW 4
1
50 mg (0.43 mmol) of 1,3,5-tris(4-aminophenyl)benzene and 131 mg (0.56 mmol) of
anthracene-9,10-dicarbaldehyde were placed in a Schlenk tube. Then, 6.0 ml of dioxane and
.3 ml of acetic acid (3 M) were added and the mixture was degassed by argon bubbling.
1
The reaction mixture was heated to reflux for 3 d. The red-orange precipitate was collected
by filtration and subjected to Soxhlet extraction in tetrahydrofuran for 24 h to yield 185 mg
(
72 %) of ANW 4.
54 6
Elemental analysis: for C96H N , calculated: C, 89.28; H, 4.21; N, 6.51 %. Found: C, 85.10;
H, 3.66; N, 5.52 %.
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Fourier transform infrared (FTIR) spectroscopy
ANW-1
96
94
92
90
88
86
84
82
80
78
76
74
72
70
68
66
64
62
4000
3500
3000
2500
2000
Well enzahlen (cm-1)
1500
1000
500
Figure S1. Fourier transform infrared (FTIR) spectra of ANW 1.
96
ANW-2
94
92
90
88
86
84
82
80
78
76
74
72
70
68
66
64
62
60
58
3500
3000
2500
Well enzahlen (cm-1)
2000
1500
1000
Figure S2. Fourier transform infrared (FTIR) spectra of ANW 2.
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82
ANW-3
80
78
76
74
72
70
68
66
64
62
60
58
56
54
52
4000
3500
3000
2500
2000
Well enzahlen (cm-1)
1500
1000
500
Figure S3. Fourier transform infrared (FTIR) spectra of ANW 3.
ANW-4
100
99
98
97
96
95
94
93
92
91
90
89
88
87
86
85
3500
3000
2500
Well enzahlen (cm-1)
2000
1500
1000
Figure S4. Fourier transform infrared (FTIR) spectra of ANW 4.
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Solid-state NMR spectroscopy
1
3
Figure S5. Cross-polarization (CP) C MAS natural abundance NMR spectrum of ANW 1.
1
3
Figure S6. Cross-polarization (CP) C MAS natural abundance NMR spectrum of ANW 2
before catalysis).
(
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1
3
Figure S7. Cross-polarization (CP) C MAS natural abundance NMR spectrum of ANW 2
after catalysis).
(
1
5
Figure S8. Cross-polarization (CP) N MAS natural abundance NMR spectrum of ANW 2.
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1
3
Figure S9. Cross-polarization (CP) C MAS natural abundance NMR spectrum of ANW 3.
1
3
Figure S10. Cross-polarization (CP) C MAS natural abundance NMR spectrum of ANW 4.
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S12

DFT Calculations
HOMO
LUMO
[eV]
HOMO- Dipole
LUMO moment
gap [eV] [D]
Torsional
angles [°]
[
eV]
ANW-1
ANW-2
ANW-3
ANW-4
-5.84
-5.77
-5.55
-5.53
-2.48
-2.51
-2.68
-2.80
3.36
3.26
2.87
2.73
0.11
0.5/0.6
1.2/2.1
0.9/1.7
29.5/34.9
0.16
0.14
0.16
Table S1. DFT calculation summary for ANW 1-4.
Figure S11. DFT calculation and torsion angels of the model segment of ANW 1.
Figure S12. DFT calculation and torsion angels of the model segment of ANW 1.
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Figure S13. DFT calculation and torsion angels of the model segment of ANW 2.
Figure S14. DFT calculation and torsion angels of the model segment of ANW 2.
Figure S15. DFT calculation and torsion angels of the model segment of ANW 3.
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Figure S16. DFT calculation and torsion angels of the model segment of ANW 3.
Figure S17. DFT calculation and torsion angels of the model segment of ANW 4.
Figure S18. DFT calculation and torsion angels of the model segment of ANW 4.
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S15

Solid State UV-Vis Spectroscopy
1
0
0
0
0
0
.0
.8
.6
.4
.2
.0
ANW-1
ANW-3
ANW-2
ANW-4
4
00
500
600
700
800
wavelength / nm
Figure S19. Solid state UV-Vis absorption spectra of the ANW networks.
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Thermogravimetric Analysis
Figure S20. Thermogravimetric analysis of the ANW networks under N atmosphere.
2
References
1
2
.
.
K. Hagiya, S. Mitsui and H. Taguchi, Synthesis, 2003, 823-828.
H. S. Kim, K. S. Moon and D. O. Jang, Supramol. Chem., 2006, 18, 97-101.
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