of trans-stilbene or DPB by locating the substrate and sensitizer
molecules in the same or different sets of dendrimers, and the
1O2 can transfer from one dendrimer to another. The higher
generation dendrimers show a better control effect. After the
photoreaction, products could be more easily extracted from a
dendrimer than from a micelle or a vesicle, and the dendrimer
can be simply recovered by neutralization of the solution and
reused, which accords with the concept of ‘‘green chemistry’’.17
Dendrimers have a relatively small inner cavity and less
confined medium than vesicles, which gives dendrimer a
special selectivity in photooxidation products.
Photooxidation and product analysis in dendrimer aqueous
solutions
The samples were purged with oxygen for 30 min prior to use,
and oxygen was bubbled through the solution during the
photolysis. A 500 W medium-high pressure Hg lamp was
employed as the light source, and a glass filter was used to
cut off the light with the wavelength below 400 nm. The
irradiation time is 8 h for procedure I or II. After irradiation,
the basic aqueous solution was acidified with 10% dilute HCl
to neutral. Reactant and products were extracted from the
aqueous solution by using CH2Cl2 and the organic layer was
dried over anhydrous MgSO4, concentrated, analyzed by gas
chromatography. All the photooxidation products derived from
trans-stilbene and DPB were analyzed by GC-MS and identified
by comparing with the commercially available samples.
Experimental section
Materials and instruments
The carboxylic acid terminated poly(aryl ether) dendrimers
were synthesized up to the fourth generation following
Photooxidation and product analysis in acetonitrile solutions
Alkene (1 mg, 1 Â 10À3 M) and 5 mL solution of DCA in
acetonitrile (1 Â 10À4 M) were mixed in a glass reactor. The
mixture solution was purged with oxygen for 30 min prior to
use, and oxygen was bubbled through the solution during the
photolysis. A 500 W medium-high pressure Hg lamp was
employed as the light source, and a glass filter was used to
cut off light with a wavelength below 400 nm, which ensured the
absence of direct excitation of the alkene substrates. After 2 h
irradiation, the solution was concentrated and analyzed by GC.
Frechet’s method. (as shown in ESIw Fig. S1) All reagents
´
were purchased from Acros, Alfa Aesar, or Aldrich and used
without further purification, unless otherwise noted. Milli-Q
water was used in aqueous experiments. Dichloromethane
(CH2Cl2) was distilled from CaH2. Gas chromatography
(GC) experiments were carried out on a BeiFen 3420 gas
chromatography fitted with 3% OV-17 column and FID
detector. GC-MS experiments were run on a Waters GCT
Premier GC mass spectrometer with a J&W DB-5MS column.
Dynamic Light Scattering measurements were performed on a
Malvern Zetasizer 3000HS.
Acknowledgements
Inclusion of reactants within dendrimers
We thank the National Natural Science Foundation of
China (Grant Numbers 20772134, 20733007, and 20853002),
the National Basic Research Program (Grant Number
2007CB808004) and Chinese Academy of Sciences.
The procedures adopted for the inclusion of reactants within
dendrimers using two different methods are described as
follows.
Procedure I. A certain amount of DCA (1 Â 10À4 M) and
alkene (1 Â 10À4 M) were added to a glass reactor and a
known amount of dendrimers in 5 mL aqueous KOH solutions
(8 Â 10À3, 4 Â 10À3, 2 Â 10À3 and 1 Â 10À3 M for G1 to G4,
respectively) were added to the reactor. After sonicating for
4 h, the solution was filtered to remove any floating particles
and stirred for 24 h in the dark. At the same time dialysis was
performed to remove the sensitizer and substrate molecules
located outside of the dendrimers in solution.
Notes and references
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2 C. S. Foote, Photochem. Photobiol., 1991, 54, 659.
3 (a) R. J. Robbins and V. Ramamurthy, Chem. Commun., 1997,
1071; (b) C. H. Tung, H. W. Wang and Y. M. Ying, J. Am. Chem.
Soc., 1998, 120, 5179; (c) A. Moscatelli, Z. Liu, X. Lei, J. Dyer,
L. Abrams, M. F. Ottaviani and N. J. Turro, J. Am. Chem. Soc.,
2008, 130, 11344.
4 (a) H. R. Li, L. Z. Wu and C. H. Tung, Tetrahedron, 2000, 56,
7437; (b) H. R. Li, L. Z. Wu and C. H. Tung, Chem. Commun.,
2000, 1085; (c) H. R. Li, L. Z. Wu and C. H. Tung, J. Am. Chem.
Soc., 2000, 122, 2446.
5 (a) A. Nakamura and Y. Inoue, J. Am. Chem. Soc., 2003, 125, 966;
(b) T. Mori, R. G. Weiss and Y. Inoue, J. Am. Chem. Soc., 2004,
126, 8961; (c) G. Fukuhara, T. Mori, T. Wada and Y. Inoue,
J. Org. Chem., 2006, 71, 8233; (d) C. Yang, T. Mori, T. Wada and
Y. Inoue, New J. Chem., 2007, 31, 697; (e) G. Fukuhara, T. Mori
and Y. Inoue, J. Org. Chem., 2009, 74, 6714; (f) M. Pattabiraman,
A. Natarajan, L. S. Kaanumalle and V. Ramamurthy, Org. Lett.,
2005, 7, 529.
6 (a) M. Pattabiraman, A. Natarajan, R. Kaliappan, J. T. Mague
and V. Ramamurthy, Chem. Commun., 2005, 4542;
(b) L. S. Kaanumalle and V. Ramamurthy, Chem. Commun.,
2007, 1062; (c) A. Natarajan, L. S. Kaanumalle, S. Jockusch,
C. L. D. Gibb, B. C. Gibb, N. J. Turro and V. Ramamurthy,
J. Am. Chem. Soc., 2007, 129, 4132; (d) C. L. D. Gibb,
A. K. Sundaresan, V. Ramamurthy and B. C. Gibb, J. Am. Chem.
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M. Yoshizawa and M. Fujita, J. Am. Chem. Soc., 2007, 129, 7000;
Procedure II. A certain amount of DCA (1 Â 10À4 M) and
alkene/DPA (1 Â 10À4 M) were added to two reactors,
respectively. Two 2.5 mL aqueous KOH solutions with a
known amount of dendrimers (8 Â 10À3, 4 Â 10À3, 2 Â 10À3
and 1 Â 10À3 M for G1 to G4, respectively) were added to
these two reactors, respectively. After sonicating for 4 h, the
solutions were filtered to remove any floating particles and
mixed together. Then the final mixture was stirred with dialysis
for 24 h in the dark to remove the sensitizer and substrate
molecules unencapsulated into dendrimers.
After dialysis, the concentrations of olefins and sensitizers
in dendrimer aqueous solutions were examined by UV-Vis
absorption spectroscopy. The concentrations of substrates
were ca. 20 mM, corresponding to 0.0025, 0.005, 0.01 and
0.02 molecule per dendrimer for G1 to G4, respectively.
ꢁc
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