1. Carbazole-Based Porous Organic Frameworks for Visible Light Photocatalysis
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588
Patrick Brady, Jingzhi Lu and Jian Zhang*
Introduction
Synthesis Scheme of Monomers
Oxidative Polymerization
Characterization
Catalytic Reactions
Conclusion and Future Work
References
• Traditional organic photochemical processes use ultraviolet (UV) light as
the energy source to drive chemical reactions. However, solar irradiation
on earth only contains 3% UV light. Therefore, it is important to design
new catalysts systems that efficiently utilize ubiquitous visible light to
promote chemical reactions.
• This research will design and synthesize heterogeneous, porous
materials as new photocatalysts that use visible light to assist the
transformation of organic compounds. We will also control the porosity
and light absorbance of the catalysts to promote organic reactions.
• Carbazole-based porous organic frameworks (Cz-POFs) represent a new
generation of green, sustainable photocatalysts because of the following
features:
1) Do not contain noble metals (metal free)
2) Tunable porosity which allows for access of different sized substrates
3) Heterogeneous in solution (reusable)
4) Can be easily modified with different substituents, which modifies the
HOMO-LUMO energy levels, photoredox potential, and light absorbance.
1) Nowakowska, M.; White, B.; Vogt, S. and Guillet, J. E. Studies of the antenna effect in polymer molecules. XVII. Synthesis
and photocatalytic activity of poly(sodium styrenesulfonate-co-N-vinylcarbazole) and poly[sodium styrenesulfonate-co-N-
(acryloyloxyhexyl)carbazole]. J. Polym. Sci. A Polym. Chem., 1992, 30, 271–277.
2) Lee, Y.T.; Chang, Y.T.; Lee, M.T.; Chiang, P.H.; Chen, C.Ti and Chen, C.Ts. Solution-processed bipolar small molecular host
materials for sing-layer blue phosphorescent organic light-emitting diodes. J. Mater. Chem. C. 2014, 2, 382.
3) Chen, Q.; Luo, M.; Hammershøj, P.; Zhou, D.; Han, Y.; Laursen, B.W.; Yan, C.G.; Han, B.H. Microporous polycarbazole with
hight specific surface area for gas storage and separation. J. Am. Chem. Soc. 2012, 134 (14), 6084-6087.
Catalytic Ability
We have designed and synthesized four carbazole based monomers with different
substituents, which are confirmed using NMR analysis. The four monomer species were
then polymerized and characterized by IR, UV-Vis spectroscopy, and gas adsorption
analysis. Both carbazole monomers and polymers were tested in three different catalytic
reactions. For all reactions, the polymer species exhibits a higher catalytic efficiency.
Specifically, the polymer catalyst was at least two times more effective than the monomer
for the debromination reaction. CN-Cz-POF showed a higher conversion (69%) compared
to monomer (3%) for the amine oxidative coupling. For [2+2] cycloaddition, the polymer
showed an increased selectivity also. In the future, we plan to analyze the
electrochemical properties of the polymers to determine HOMO-LUMO energy levels and
to propose the catalytic reaction mechanisms for their use in other catalytic reactions.
Acknowledgement
This material is based upon work supported by the National
Science Foundation under CHE–1156560. A special thanks to
the Zhang Group and the Department of Chemistry at The
University of Nebraska-Lincoln for their assistance.
Figure 10. TLC plate of catalytic product from four
monomers compared with one polymer (Trial 1)
Flash Column
Chromatography
Figure 1. Silica gel column used for
purification (eluent: 6:1 HEX:DCM)
Byproduct
Disubstituted
Product
Single Substitute
Product
Figure 8. Catalysis reaction under blue
LED
0.0 0.2 0.4 0.6 0.8 1.0
0
50
100
150
0
50
100
150
0
50
100
150
0
50
100
150
200
250
P/P0
Me-Cz-POF
N2
Uptake(cm
3
/g)
Br-Cz-POF
NO2
-Cz-POF
SABET
= 482 m
2
/g
SABET
= 475 m
2
/g
SABET
= 447 m
2
/g
CN-Cz-POF
SABET
= 500 m
2
/g
1 10
0.0
0.5
1.0
0.0
0.5
1.0
0.0
0.5
1.0
0.0
0.5
1.0
Pore Width (nm)
Me-Cz-POF
NormalizedIntensity(a.u.)
Br-Cz-POF
NO2-Cz-POF
CN-Cz-POF
4000 3000 2000 1000
Wavenumber (cm
-1
)
Me-Cz-POF
Br-Cz-POF
NO2
-Cz-POF
CN-Cz-POF
Polymers
Monomers
Photoluminescence
Figure 2. Digital photographs of suspensions of Cz monomers
and polymers in DMF:Water (1:1, v:v) irradiated with UV lamp
Me Br CN NO2
Infrared Spectra
Figure 4. Infrared Spectra of Cz-POFs
with different substituent groups
N2 Uptake
Figure 5. N2 uptake at 77 K and BET surface area
for Cz-POFs with different substituents
Pore Width
Figure 6. Pore size distribution for Cz-POFs
with different substituents
• Debromination
• Amine Oxidative Coupling
0
10
20
30
40
50
60
70
CN NO2 Br Me
YieldofProduct(%)
Substituent Attached
Debromination
0
10
20
30
40
50
60
70
80
CN NO2 Br Me
YieldofProduct(%)
Substituent Attached
Amine Oxidative Coupling
8.8 8.6 8.4 8.2 8.0 7.8 7.6 7.4 7.2 7.0
Chemical shift (ppm)
Me-Cz-Mon
Br-Cz-Mon
NO2
-Cz-Mon
CN-Cz-Mon
NMR Spectra
Figure 3. Nuclear Magnetic Resonance
(NMR) spectra for monomers
Figure 11. TLC plate of catalytic product from four
monomers compared with two polymers (Trial 2)
[2+2] Cycloaddition
• [2+2] Cycloaddition
Monomer Polymer
Monomer Polymer
Figure 9. Catalysis reaction under white
fluorescent light bulb
Figure 7. Ultraviolet-Visible light absorbance for Cz-POFs with different substituents
Me Methyl Monomer
Br Bromo Monomer
NO2 Nitro Monomer
CN Cyano Monomer
MP Methyl Polymer
BP Bromo Polymer
UV-Vis Spectra
300 400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
NormalizedAbsorbance(a.u.)
Wavelength (nm)
Me-Cz-POF
300 400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
NormalizedAbsorbance(a.u.)
Wavelength (nm)
Br-Cz-POF
300 400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
NormalizedAbsorbance(a.u.)
Wavelength (nm)
NO2
-Cz-POF
300 400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
NormalizedAbsorbance(a.u.)
Wavelength (nm)
CN-Cz-POF
CN Starting
materialStarting
material
NO2 Br Me