Light Induced Dehalogenation of Halobenzene using Carbon Dots

Light Induced Dehalogenation of Halobenzene using Carbon Dots

Light Induced Dehalogenation of Halobenzene using Carbon Dots
Anthony J. Lemieux, Christine A. Caputo
Department of Chemistry, University of New Hampshire, Durham, NH 03824

Introduction
Carbon Dots (CDs) are fluorescent nanoparticles that consist of a
graphitic carbon core with a passivated surface and are typically
2-10 nm in diameter.1,2 CDs are non-toxic and can be made from
inexpensive materials such as citric acid. CDs possess unique
electronic, redox, and optical properties which can be exploited for
use in photocatalytic systems for energy conversion.2 As such, CDs
are most often used in biochemical sensing, drug delivery, bioimaging, and catalysis.1
Interestingly, CDs show great potential to replace other expensive
photosensitizers, including organic and transition metal dyes,
which are short-lived due to photodecomposition and are toxic.1,2
It is also possible to dope CDs with group 13 and 15 elements such
as boron and nitrogen to improve or further tune the
photoluminescent properties.1
To this end, un-doped CDs and boron-doped CDs (B-CDs) have
been synthesized and characterized using various spectroscopic
methods. As CDs have been shown to mediate highly selective
oxidation reactions using NIR light, likely via a radical mechanism,
it is possible that CDs may also mediate photo-dehalogenation
reactions.3

Figure 1. Fluorescence of various types of CDs under a
handheld UV lamp. From left to right: un-doped CDs, borondoped CDs, zinc-doped CDs, sour patch kids/potential
phosphorous-doped CDs.

Figure 4. SEM images of un-doped CDs
deposited via drop casting and allowing the
solvent to evaporate.

Results and Discussion
O

O
HO

OH

O
OH

OH

OH

HO
O O
O O

O

H2O, CO2, H2

OH
O

HO

OH HO

O

Fluorescent doped and un-doped CDs have been synthesized
and characterized. Un-doped CDs have been applied to various
dehalogenation reactions with mixed results. Results suggest
that CDs do not have enough driving force to dehalogenate
unsubstituted aryl rings. This can be attributed to the low
reduction potential of CDs to act as both the photosensitizer and
electron transport mechanism.
In order to dehalogenate an aryl ring using CDs as the
photosensitizer, it may be necessary to activate the aryl ring
with various electron donating groups to reduce the potential
needed to carry out the reaction.
Additionally, it may also be possible to dope and otherwise
functionalize the CDs to increase their reduction potential. At
the present moment, CDs have the inability to proceed with
radical mediated dehalogenation of aryl rings, but can
photocatalyze the dehalogenation of an -bromide via a hydride -bromide via a hydride
donation mechanism.

Future Work
Further dehalogenation reactions, via different mechanisms,
will need to be performed to probe the ability and efficacy of
CDs as replacements to traditional photosensitizers. Additional
doping and surface functionalization will be conducted to study
the effects this has on the electronics and reduction potential of
CDs.

OH O

O

1)180C, ~48 h
2)H2O

Conclusions

Figures and Data

Scheme 1. Synthesis of Undoped CDs

O

O

HO

OH

O

+

OH

OH

1)H2O, 180C, ~4 h
2)H2O

OH
HO

B

OH

HO

O

O B

B
HO

H2O, CO2, H2

Acknowledgements

OH O

B O

HO

OH
OH
B OH
O

OH
HO

O

Figure 2. The fluorescence emission spectra of CDs showing
the excitation wavelength-dependent emissions of un-doped
CDs.

Scheme 2. Synthesis of B-CDs

EtO2C

CO2Et

1.1 eq.

Figure 5. TEM images of un-doped CDs
showing the approximate size regime of a
batch of acidic un-doped CDs.

Special thanks to the Department of Chemistry, UNH for
funding. Dr. Caputo for taking me on and allowing me to pursue
this project. Dr. Planalp and Dr. Pazicni for their input on Raman
Spectroscopy. Dr. Berda and Dr. Boudreau for use of their
instruments. As well as Ashley Hanlon, Sharon Song, and Lea
Nyiranshuti for their assistance with instrumentation.

COO
Br

Br

References

N
H
O

2.5 mol% CD
Br

O

or

O
Br

O

O
Br

2 eq. DIPEA, DMF, RT,
h, 18 h

H

Scheme 3. Photocatalytic -dehalogenation of -bromoacetophenone

OH O

O
O
H2N

O

+
NH2

HO

O

OH

Zn

Zn

OH
O

+
OH

Toluene
Cl Zn Cl

165C, 22hrs

O

Zn O
O Zn

Scheme 4. Synthesis of zinc doped CDs

OH
O

HO
O

OH Zn

Cayuela, A; Soriano, M. L.; Carrillo-Carrin, C.; Valcrcel, M. Chem. Commun.
2016, 52, 1311-1326.
2
Martindale, B. C. M.; Hutton, G. A. M.; Caputo, C. A.; Reisner, E. J. Am. Chem.
Soc. 2015, 137, 6018-6025.
3
Li, H.; Liu, R.; Lian, S.; Liu,Y.; Huang, H.; Kang, Z. Nanoscale. 2013, 5, 32893297.
4
Shiral Fernando, K. A.; Sahu, S.; Liu Y.; Lewis, W. K.; Guliants, E. A.; Jafariyan,
A.; Wang, P.; Bunker, C. E.; Sun, Y. P. ACS Appl. Mater. Interfaces 2015, 7,
8363-8376.
5
Neumann, M.; Fldner, S.; Knig, B.; Zeitler, K. Angew. Chem. Int. Ed. 2011,
50, 951-954.
6
Discekici, E.H.; Treat, N.J.; Poelma, S.O.; Mattson, K.M.; Hudson, Z.M.; Luo, Y.;
Hawker, C.J.; Read de Alaniz, J. Chem. Commun. 2015, 51, 11705-11708.
1

Figure 3. The fluorescence emission spectra of B-CDs
showing the shift from excitation dependent emissions of
doped CDs.

Figure 6. Gas chromatogram of the
dehalogenation of bromoacetophenone using
CDs as photosensitizers after simulated solar
irradiation.

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