Synthesis, photophysical and photochemical properties of photoacid generators based on N-hydroxyanthracene-1,9-dicarboxyimide and their application toward modification of silicon surfaces

Article abstract of DOI:10.1021/jo301367y

We have introduced a series of nonionic photoacid generators (PAGs) for carboxylic and sulfonic acids based on N-hydroxyanthracene-1,9-dicarboxyimide (HADI). The newly synthesized PAGs exhibited positive solvachromatic emission (λ_max(hexane) 461 nm, λ_max(ethanol) 505 nm) as a function of solvent polarity. Irradiation of PAGs in acetonitrile (ACN) using UV light above 410 nm resulted in the cleavage of weak Na-O bonds, leading to the generation of carboxylic and sulfonic acids in good quantum and chemical yields. Mechanism for the homolytic Na-O bond cleavage for acid generation was supported by time-dependent density functional theory (TD-DFT) calculations. More importantly, using the PAG monomer N-(p-vinylbenzenesulfonyloxy)anthracene- 1,9-dicarboxyimide (VBSADI), we have synthesized N-(p-vinylbenzenesulfonyloxy) anthracene-1,9-dicarboxyimidea-methyl methacrylate (VBSADI-MMA) and N-(p-vinylbenzenesulfonyloxy)anthracene-1,9-dicarboxyimidea-ethyl acrylate (VBSADI-EA) copolymer through atom transfer radical polymerization (ATRP). Finally, we have also developed photoresponsive organosilicon surfaces using the aforementioned polymers.

Full text of DOI:10.1021/jo301367y

Article
pubs.acs.org/joc
Synthesis, Photophysical and Photochemical Properties of Photoacid
Generators Based on N-Hydroxyanthracene-1,9-dicarboxyimide and
Their Application toward Modification of Silicon Surfaces
Mohammed Ikbal, Rakesh Banerjee, Sanghamitra Atta, Dibakar Dhara,* Anakuthil Anoop,*
and N. D. Pradeep Singh*
Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur-721302, India
S
* Supporting Information
ABSTRACT: We have introduced a series of nonionic photoacid
generators (PAGs) for carboxylic and sulfonic acids based on N-
hydroxyanthracene-1,9-dicarboxyimide (HADI). The newly synthesized
PAGs exhibited positive solvachromatic emission (λmax(hexane) 461 nm,
λmax(ethanol) 505 nm) as a function of solvent polarity. Irradiation of PAGs
in acetonitrile (ACN) using UV light above 410 nm resulted in the cleavage
of weak N−O bonds, leading to the generation of carboxylic and sulfonic
acids in good quantum and chemical yields. Mechanism for the homolytic
N−O bond cleavage for acid generation was supported by time-dependent
density functional theory (TD-DFT) calculations. More importantly, using
the PAG monomer N-(p-vinylbenzenesulfonyloxy)anthracene-1,9-dicarbox-
yimide (VBSADI), we have synthesized N-(p-vinylbenzenesulfonyloxy)-
anthracene-1,9-dicarboxyimide−methyl methacrylate (VBSADI-MMA) and
N-(p-vinylbenzenesulfonyloxy)anthracene-1,9-dicarboxyimide−ethyl acrylate (VBSADI-EA) copolymer through atom transfer
radical polymerization (ATRP). Finally, we have also developed photoresponsive organosilicon surfaces using the
aforementioned polymers.
surface wettability in the presence of external light, has emerged
as an exciting topic in surface science and materials chemistry.
Numerous research groups are working on the development of
inorganic/polymer hybrid materials, since inorganic and
organic materials have complementary properties. Especially,
inorganic materials have good mechanical and thermal stability,
while organic compounds can provide flexibility, hydro-
phobicity, and versatility for further functionalization.13 To
date, several techniques14 have been attempted to combine
these two materials to create new kinds of materials which will
possess better thermal, chemical, and mechanical properties. In
particular, the modification of silica surfaces via the formation
of a SiO2/polymer hybrid material usually known as organo-
silica15 has long been studied and utilized in many fields of
chemistry, mainly in chromatography16 and catalysis.17 More
recently, organosilica appears as a key topic in areas such as
polymer nanocompounds18 and the development of hydro-
phobic19 and superhydrophobic materials.20
INTRODUCTION
■
Over the past few decades, photoacid generators (PAGs) have
gained enormous interest, due to their immense applications in
the microlithographic industry.1 PAGs are the key material used
in the field of photoresists for semiconductor fabrication.2
Photoirradiation of a polymer film containing a PAG results in
generation of acid, which catalyzes certain important chemical
transformations within the polymer film such as deprotection of
functional groups, initiation of polymerization, and cross-
linking processes.3,4 These processes either make the polymer
more soluble in the developing solvent, resulting in positive
resists, or less soluble, generating negative resists. Generally,
two types of PAGs are known: ionic5 and nonionic6 types. A
large number of onium salts based on ionic PAGs such as
aryldiazonium, diaryliodonium, triarylsulfonium, and triaryl-
phosphonium are known, and their photochemistry has been
investigated in detail.7 On the other hand, among nonionic
PAGs, iminosulfonates,8 N-hydroxyimide sulfonates,7 tris-
(methylsulfonyloxy)benzene,7 and 1-(sulfonoxy)-2-quinolone9
are known to generate sulfonic acids through homolytic N−O
bond cleavage. Due to the limited solubility of the onium salts
in common organic solvents, nonionic PAGs have gained much
attention over the ionic types.10
In recent years, our research interest in the development of
PAGs9,21 based on N−O bond cleavage chemistry has drawn
our attention toward the well-established PAGs sulfonyloxyph-
thalimide22 (PIT) and sulfonyloxy-1,8-naphthalimide23 (NIT),
as they have a weak N−O bond which can be easily cleaved
Recently, the use of PAG-containing polymers for the
development of smart photoresponsive surfaces11 and
inorganic/polymer hybrid materials,12 which can change their
Received: July 9, 2012
Published: November 11, 2012
© 2012 American Chemical Society
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Scheme 1. Synthesis of HADI-Based PAGs 3a−e and 4a−e
Table 1. Synthetic Yields, UV/Vis, and Fluorescence Data of PAGs 3a−e and 4a−e
photophysical data in EtOH
UV/vis
fluorescence
a
b
c
d
e
f
PAG
acid chloride
synthetic yield (%)
λmax (nm)
log ε
λmax (nm)
Stokes shift (nm)
Φf
3a
3b
3c
3d
3e
4a
4b
4c
4d
4e
C6H5CH2COCl
C6H5COCl
80
82
80
79
75
82
80
75
80
79
438
438
437
437
437
438
439
437
437
438
356
3.92
3.87
3.86
3.85
3.82
4.01
4.05
3.93
3.96
3.97
523
521
522
522
524
524
523
523
524
522
400
86
83
85
85
88
85
83
85
86
84
0.45
0.43
0.41
0.42
0.38
0.60
0.61
0.56
0.59
0.58
0.27
p-CH3C6H4COCl
p-CH3OC6H4COCl
p-NO2C6H4COCl
CH3SO2Cl
C4H9SO2Cl
C6H5SO2Cl
p-CH3C6H4SO2Cl
2, 4 (df) C6H3SO2Cl
anthracene
a
b
c
d
Based on isolated yield. Maximum absorption wavelength. Molar absorption coefficient at the maximum absorption wavelength. Maximum
e
f
emission wavelength. Difference between maximum absorption wavelength and maximum emission wavelength. Fluorescence quantum yield (error
limit within 5%).
upon UV irradiation. Among these, 1,8-naphthalimide-based
photoacid generators bearing different kinds of substituents
exhibited good fluorescence properties.23 Especially, the
fluorescence nature and acid generation ability of NIT
prompted us to design a new fluorescent PAG based on the
NIT skeleton which can be used both for generation of
carboxylic and sulfonic acids by irradiating with light above 410
nm and for the development of photoresposive organosilicon
surfaces.
Hence, herein we report new fluorescent PAGs based on N-
hydroxyanthracene-1,9-dicarboxyimide (HADI) for carboxylic
and sulfonic acids. In the present study, we describe the
synthesis, characterization, and photophysical properties of the
anthracene-1,9-dicarboxyimide-based PAGs. We examine the
acid generation ability of PAGs by irradiating with light above
410 nm. The mechanism of photochemical N−O bond
cleavage is analyzed using time-dependent density functional
theory. The polymers VBSADI-MMA and VBSADI-EA were
synthesized through the ATRP process using a PAG monomer
(VBSADI). Moreover, we also discuss the surface modification
of silica (60−120 mesh) by using VBSADI-MMA polymer and
investigate the photoresponsive behavior of the modified silicon
surface24 in terms of controlled wettability.
RESULTS AND DISCUSSION
1. HADI-Based PAGs for Carboxylic and Sulfonic
■
Acids: Synthesis of PAGs 3a−e and 4a−e. We have
synthesized HADI based PAGs 3a−e and 4a−e as outlined in
Scheme 1. Anthracene-1,9-dicarboxylic anhydride (1) was
prepared by following the literature procedure.25 Condensation
of 1 with hydroxylamine hydrochloride in dry pyridine at 100
°C yielded N-hydroxyanthracene-1,9-dicarboxyimide26 (2).
Treatment of 2 with various carboxylic and sulfonyl chlorides
in the presence of triethylamine in dry DCM at 0 °C resulted in
the formation of PAGs 3a−e and 4a−e in moderate to good
1
yields (Table 1). All the PAGs were characterized by H and
13C NMR, FTIR, and mass spectral analysis.
2. Photophysical Properties of HADI-Based PAGs.
2.1. Absorption and Emission Properties of PAGs 3a−e and
4a−e. The UV/vis absorption spectra of degassed 1.5 × 10−5
M solution of PAGs 3a−e in ethanol (EtOH) have been
recorded, and the results are tabulated in Table 1. All the PAGs
exhibited similar kinds of absorption (Figure 1) and emission
(Figure F1, see supporting information page-S8) behaviour,
indicating that substituents on the aromatic ring of the carboxyl
moiety have no significant effect on the photophysical
properties of HADI. The absorption wavelengths of all the
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Figure 3. Fluorescence spectra of 3a (0.5 × 10−5 M) in solvents of
different polarity and hydrogen-bonding capabilities.
shift along with an increase in fluorescence intensity for 3a was
noticed and the emission maximum was found to shift from
461 to 505 nm. Moreover, the fluorescence quantum yield (Φf)
of 3a was also found to increase from 0.39 to 0.52 as we
changed the solvent from hexane to acetone (Table 2). The
Figure 1. UV/vis absorption spectra of PAGs 3a−e in EtOH (1.5 ×
10−5 M).
Table 2. Photophysical Data of PAG 3a in Different Solvents
PAGs are significantly red-shifted by ∼85 nm in comparison to
the parent anthracene. This is due to the efficient π conjugation
and donor−acceptor interaction between the anthracene
moiety and the dicarboxylic imide group.27 Figure 2 shows
λmax(abs)
a
λmax(em)
b
c
d
solvent
hexane
ε(25 °C)
(nm)
log ε
(nm)
Φf
1.882
2.015
2.379
4.806
20.70
24.30
429
431
437
438
437
438
3.50
3.75
3.66
3.38
3.37
3.92
461
463
484
489
493
505
0.39
0.50
0.51
0.48
0.52
0.45
cyclohexane
toluene
chloroform
acetone
ethanol
a
b
Maximum absorption wavelength. Molar absorption coefficient at
c
the maximum absorption wavelength. Maximum emission wave-
d
length. Fluorescence quantum yield (error limit within 5%),
calculated using quinine sulfate as a standard (Φf = 0.54630) in EtOH.
solvent effect observed above is due to a large increase in the
dipole moment of the PAG on excitation, followed by solvent
relaxation. Further, we also noticed a bathochromic shift as we
moved from chloroform to a hydrogen-bonding polar solvent
(ethanol), indicating an intermolecular hydrogen bond between
unshared electron pairs on the carbonyl oxygen of PAG with
ethanol. The above solvent effect was also noted in the case of
N-substituted benzoperylene monoimides.28,29
3. Photoacid Generation and Quantum Yield Meas-
urement for PAGs 3a−e and 4a−e. To demonstrate the
acid generation ability of newly synthesized PAGs, we irradiated
PAGs 3a−e and 4a−e (2.0 × 10−4 M) individually, in N2-
saturated acetonitrile solution using a 125 W medium-pressure
Hg lamp as the visible light source (≥410 nm) and a 1 M
NaNO2 solution as the UV cutoff filter. We noted that all the
PAGs generated corresponding carboxylic (6a−e) and sulfonic
acids (7a−e) in good chemical yields (75−85%) along with the
major photoproduct anthracene-1,9-dicarboxyimide (5)
(Scheme 2). Quantum yields for the generation of acids by
the corresponding PAGs were calculated and found to be
within the range of 0.26−0.35 (Φp) (Table 3), using potassium
ferrioxalate as an actinometer.31
Figure 2. Normalized UV/vis absorption spectrum (red line) and
emission spectrum (black line) of PAG 3c in EtOH (1.5 × 10−5 M).
the normalized absorption and the emission spectra of PAG 3c
in ethanol. The absorption spectrum of 3c has an intense band
centered at 437 nm, while in the emission spectrum the
emission maximum was red-shifted to about 524 nm. Similar
photophysical properties were also noted for PAGs of sulfonic
acids (4a−e) (see the Supporting Information, Figure F2a,b, p
S14).
2.2. Solvent-Dependent Fluorescence Properties of PAGs.
The excited-state properties of the PAGs were investigated by
emission spectroscopy. These synthesized PAGs showed
positive solvachromatic emission as a function of solvent
polarity. As a representative example, the emission spectra of 3a
in solvents of increasing polarity are shown in Figure 3, which
indicates a strong solvent-dependent fluorescence. As the
solvent polarity increases (hexane to ethanol), a bathochromic
As a representative example, we have presented the UV/vis
and fluorescence spectral change of PAG 4d at regular intervals
of irradiation time (see the Supporting Information, Figure
F3a,b, p S14).
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of the phenyl group with respect to the anthracenyl moiety,
characterized by the torsion angle N−O−C(O)−C(Ph), either
0 or 180°. The former conformation A, where the phenyl group
is placed above the anthracenyl moiety, is found to be 5.32
kcal/mol higher in energy in comparison to the latter
conformation (B), in which the phenyl group stays away
from the anthracenyl moiety (see the Supporting Information p
S17 for geometries). Hence, conformation B is considered for
detailed analysis at the PBE/def2-SVP level of theory. TD-DFT
calculations revealed that thermal dissociation from the ground
state (S0) is much more endothermic for the heterolytic
dissociation to yield ions (183.23 kcal/mol) in comparison to
homolytic cleavage to form a separate radical pair (66.38 kcal/
mol). The effect of solvent is introduced to account for the
stabilization of ions in the solvent media, using the continuum
solvation model (COSMO with ε′ = 35.688). In the solvent
media, the dissociation energies for heterolytic and homolytic
cleavage were reduced to 82.02 and 60.32 kcal/mol,
respectively. The dissociation energy for homolytic dissociation
from the S1 state is found to be 20.75 kcal/mol. The inclusion
of solvent effects reduced the dissociation energy to −12.58
kcal/mol (exothermic).
Vertical excitation energy for the lowest singlet (π−π*)
excitation was computed using TD-DFT calculations with five
different functionals at the geometry optimized at the PBE/
def2-SVP level. The vertical excitation energies are 514 nm
(PBE/def2-SVP), 458 nm (B3LYP-D/6-31+G*), 407 nm
(CAM-B3LYP/6-31+G*), 444 nm (PBE0/6-31+G*), and
471 nm (TPSSh/6-31+G*). Considering the accuracy of TD-
DFT methods, these values are in reasonable agreement with a
λmax value of 438 nm for 3b. We have further optimized the
excited S1 state using PBE/def2-SVP. The adiabatic excitation
energy is 45.63 kcal/mol (in comparison to the vertical
excitation energy of 55.63 kcal/mol). The computed Stokes
shift is 71 nm, which is in good agreement with the
experimental value of 83 nm.
The potential energy surface (PES) for dissociation through
the S1 state was computed to analyze the dissociation process
and to locate the transition state. The PES was calculated with a
relaxed surface scan, where the N−O bond distance was
restrained along the reaction coordinate and all other degrees of
freedom were optimized. Similarly, the ground state PES was
also computed for comparison. In the ground state the energy
continuously increases, while in the S1 state the energy
increases up to 1.712 Å and decreases on increasing the
distance further (Figure 4).
The geometry with the highest S1 state energy was used as
the starting estimate for transition state optimization. At the TS
geometry, the N−O bond is bent out of the plane containing
anthracene. The N−O distance is 1.717 Å. The activation
energy (ΔE⧧) for the N−O bond dissociation in the S1 state at
Scheme 2. Photogeneration of Carboxylic and Sulfonic Acids
by PAGs 3a−e and 4a−e
Table 3. Photolytic Data of PAGs 3a−e and 4a−e on
Irradiation by Visible Light (≥410 nm) in Acetonitrile
photolytic
data of PAGs
time of
acid
carboxylic (6a−e) and
sulfonic acids (7a−e)
photolysis
generated
quantum
yield (Φp)
a
b
c
PAGs
(min)
(%)
3a
3b
3c
3d
3e
4a
4b
4c
4d
4e
C6H5CH2CO2H
C6H5CO2H
255
252
240
230
265
240
235
225
220
230
80
82
80
85
75
82
85
80
83
80
0.29
0.30
0.31
0.34
0.26
0.32
0.34
0.33
0.35
0.32
p-CH3C6H4CO2H
p-CH3C6H4CO2H
p-NO2C6H4CO2H
CH3SO3H
C4H9SO3H
C6H5SO3H
p-CH3C6H4CO2H
2,4-(df)C6H3SO3H
a
b
Time of photolysis. Percent of carboxylic acid generated as
determined by HPLC and of sulfonic acid as determined by 1H
NMR. Photochemical quantum yield for the generation of carboxylic
c
and sulfonic acids (error limit within 5%).
4. Possible Mechanism for the Photogeneration of
Carboxylic Acids 6a−e and Sulfonic Acids 7a−e. On the
basis of literature studies reported for the photodecomposition
of N-oxyimidosulfonate32 and N-tosyloxyphthalimide,22 we
proposed a possible mechanism for the photogeneration of
carboxylic and sulfonic acids, as shown in Scheme 3. After
initial photoexcitation of the PAG to its singlet excited state, it
undergoes N−O bond cleavage to generate a radical pair. The
radical pair generated above in polar solvent undergoes solvent
cage escape following hydrogen abstraction from the solvent to
produce the corresponding acid (carboxylic acids 6a−e or
sulfonic acids 7a−e) and anthracene-1,9-dicarboxyimide (5).
4.1. Computational Study of N−O Bond Cleavage for PAG
3b. In support of the above mechanistic proposal, we have
carried out time-dependent density functional theory (TD-
DFT) calculations (see Computational Methods below for
details), considering the dissociation of PAG 3b as a
representative example. We have considered two conforma-
tional possibilities of 3b, resulting from the relative orientation
Scheme 3. Possible Mechanism for the Photogeneration of Carboxylic and Sulfonic Acids
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Figure 4. Potential energy surface for the dissociation of theN−O bond in 3b. Calculations were done at the PBE/def2-SVP level of theory. The
geometry of the transition state is shown.
the TD-PBE/def2-SVP level is 21.41 kcal/mol. The corre-
sponding barriers in other functionals are 16.93 (B3LYP), 24.70
(CAM-B3LYP), 22.96 (PBE0), and 17.42 kcal/mol (TPSSh).
The energies were computed at the geometries obtained from
PBE/def2-SVP optimizations. In conclusion, TD-DFT calcu-
lations support the proposed mechanism of homolytic N−O
bond cleavage in the lowest singlet excited state.
5. HADI-Based Polymer for Modification of Silicon
Surfaces. After successfully demonstrating sulfonyloxy anthra-
cene-1,9-dicarboxyimides as PAGs for sulfonic acids, our
attention turned toward the synthesis of polymers bearing
sulfonates which on photoirradiation generate sulfonic acids.
Further, we wanted to use the aforementioned polymers to
prepare SiO2/polymer hybrid materials for the development of
photoresponsive organosilicon surfaces.
anthracene-1,9-dicarboxyimide−Ethyl Acrylate (VBSADI-EA)
copolymers. The polymers VBSADI-MMA and VBSADI-EA
were synthesized using the ATRP34 process. The monomer
VBSADI (9), cuprous bromide (CuBr), and ethyl 2-
bromoisobutyrate (EBiB) as an initiator were mixed with dry
DMF in a Schlenk flask. The solution was degassed by three
freeze−pump−thaw cycles. Further, the ligand N,N,N′,N′,N″-
pentamethyldiethylenetriamine (PMDETA) in dry DMF was
injected into the reaction mixture and then heated at 40 °C for
6 h. The reaction vessel was maintained in liquid nitrogen, and
DMF was removed by rotary evaporation. Finally the polymer
was dissolved in THF and passed through a neutral Al2O3
column to remove the copper catalyst. The volume of THF was
removed, and the polymer was precipitated from a hexane/
methanol (1/1) mixture at 0 °C. This process was repeated
three times for a complete removal of unreacted monomer. A
yellow solid polymer was recovered, and its molecular weight
was determined by GPC methods.
5.1. Synthesis of the Monomer N-(p-Vinylbenzenesulfonyl-
oxy)anthracene-1,9-dicarboxyimide (VBSADI). The schematic
synthesis of the monomer VBSADI (9) is described in Scheme
4. Under an N2 atmosphere p-vinylbenzene sulfonyl chloride33
Using the same procedure as described for the synthesis of
the homomer, copolymers were synthesized in dry DMF using
the monomer VBSADI with ethyl acrylate (EA) and methyl
methacrylate (MMA) individually, as shown in Scheme 5.
5.3. Characterization of the Polymers VBSADI-MMA (12)
and VBSADI-EA (13). Molecular weights and polydispersities of
the polymers VBSADI-MMA (12) and VBSADI-EA (13) were
recorded by gel permeation chromatography (GPC) and are
tabulated in Table 4. GPC (Figure 5) was carried out at
ambient temperature using a Viscotek-GPC system equipped
with two GMH HR-H nonpolar organic columns in series.
DMF was used as an eluent, at a flow rate of 1 mL/min.
Polystyrene standard in the Mn range of 2000−395000 was
used for calibrations. Further, the polymers synthesized above
were also characterized by UV/vis and fluorescence spectros-
copy (see the Supporting Information, Figure F4a,b, p S16) and
Scheme 4. Synthesis of the Monomer VBSADI (9)
was added to HADI in dry DCM, and then Et3N was added
slowly into the reaction mixture. The reaction mixture was
stirred overnight at room temperature to obtain the orange
monomer VBSADI.
5.2. Synthesis of N-(p-Vinylbenzenesulfonyloxy)-
anthracene-1,9-dicarboxyimide−Methyl Methacrylate
(VBSADI-MMA) and N-(p-Vinylbenzenesulfonyloxy)-
1
IR and H NMR spectroscopy.
5.4. Photoinduced Generation of Sulfonic Acid from
Polymer Film. To investigate the polymers as PAGs, the
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Scheme 5. Synthesis of the Copolymers VBSADI-MMA (12) and VBSADI-EA (13)
Table 4. Polymerization Conditions and Characterization of Polymers
a
polymer
sample
VBSADI
0.07 g,
0.158 mmol
0.07 g,
0.158 mmol
0.07 g,
0.158 mmol
MMA
0.0158 g,
0.158 mmol
EA
CuBr
PMDETA
EBiB
Mn
12
VBSADI-MMA
copolymer
0.452 mg,
0.00316 mmol
0.819 mg,
0.00474 mmol
0.622 mg,
0.00316 mmol
2980
13
14
VBSADI-EA
copolymer
0.016 g,
0.16 mmol
0.452 mg,
0.00316 mmol
0.819 mg,
0.00474 mmol
0.622 mg,
0.00316 mmol
3140
2190
homopolymer
0.226 mg,
0.00158 mmol
0.273 mg,
0.00158 mmol
0.311 mg,
0.00158 mmol
a
Measured against polystyrene standards.
Figure 5. GPC of (a) homomer 14 and (b) copolymers VBSADI-MMA (12) and VBSADI-EA (13).
Scheme 6. Photogeneration of Sulfonic Acid from Polymer Film
VBSADI-MMA (12) polymer was spin-coated onto a thin glass
slide using a Headway Research spinner (Spin Coating Unit
SCU 2005). The polymer films were then baked at 90 °C for 5
min in an oven. The film thicknesses were measured with a
Dektak-150 film thickness measurement gauge. Irradiation of
polymer thin films using UV light above 410 nm resulted in
photodecomposition of the polymer, leading to the generation
of sulfonic acid (Scheme 6).
The FT-IR spectrum (see the Supporting Information,
Figure F5a, p S17) indicated photolysis of polymer films
(VBSADI-MMA). Peaks at 1385, 1193, and 1180 cm−1
(ν(SO2)) due to aminosulfonate units decreased, indicating
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the photodecomposition of the polymer. On the other hand,
the generation of sulfonic acid by the polymer films was
confirmed by using acid-catalyzed polysiloxane formation
techniques.35 FT-IR spectra (see the Supporting Information,
p S17, Figure F5b) showed changes in the irradiated film before
and after treatment with methyltriethoxysilane (MTEOS). The
appearance of new peaks at 780 (Si−CH3), 900 (Si−OH),
1000−1200 (Si−O−Si), and 3200−3500 cm−1 (Si−OH)
supported the formation of silanol, which was obtained on
hydrolysation of MTEOS under humid conditions by the
photogenerated sulfonic acid.
6. Modification of Silicon Surfaces using VBSADI-
MMA. The organosilica surface was prepared by the addition of
SiO2 to the DCM-containing polymer VBSADI-MMA, and the
mixture was stirred for 1 day at room temperature. Then the
mixture was collected by centrifugation (8000 rpm, 10 min).
Finally a rough surface of organosilica (for corresponding FT-
IR spectra of SiO2/polymer hybrid material, see the Supporting
Information, Figure F6, p S17) was obtained on the glass plate.
The plate was kept in a hot oven for 2 h to remove the lagging
solvent completely.
The hydrophobicity of the surface was tested by measuring
the water contact angle (CA). Initially, the prepared organo-
silica surface exhibited a large contact angle (i.e., hydrophobic
in nature in comparison to a common silica surface, which is
hydrophilic). The rough structure on the coating surface and
low surface energy14,36 are believed to contribute to the
hydrophobic properties of organosilica (the water droplet rolls
off spontaneously for a longer time on the surface). However,
the surface of organosilica loses its hydrophobicity and becomes
superhydrophilic on gradual photoirradiation (≥410 nm), as
shown in Figure 6. On photolysis, the polymer decomposes and
generates a polar −SO3H unit, which leads to a decrease in the
contact angle (CA).
demonstrated the application of our fluorescent PAGs in the
development of a smart photoresponsive organosilica surface
which changes surface wettability in the presence of external
light.
EXPERIMENTAL SECTION
■
1
General Considerations. The H and 13C spectra were recorded
in CDCl3/DMSO-d6 solvents on a 200/400 MHz spectrometer using
TMS as the internal standard. HRMS was measured using a TOF
analyzer.
Computational Methods. We have used density functional
theory (DFT) calculations using PBE37 functional in conjunction with
def2-SVP38 basis set. In addition, empirical dispersion correction
(DFT-D)39 and resolution of the identity (RI) approximations were
used. Turbomole v6.240 was used for all calculations. For excited-state
calculations time-dependent density functional theory (TDDFT) was
employed. The unrestricted formalism was used. We have included the
four lowest roots for each calculation. Dl-find,41 implemented in
ChemShell,42 was used for optimizations. In order to compute
transition states at the excited state potential energy surface (PES), the
dimer method43 was used. Vibrational analysis was done using a finite-
difference Hessian in ChemShell for the excited-state calculations, and
analytic gradients from Turbomole were used for ground-state
calculations. Single-point energy evaluations were done with the
Gaussian 09 package44 using B3LYP,45 CAM-B3LYP,46 PBE0,47 and
TPSSh.48
Synthesis of N-Hydroxyanthracene-1,9-dicarboximide
(2). To a mixture of anthracene-1,9-dicarboxylic anhydride (1 g,
4.03 mmol) in pyridine (10 mL) was added hydroxylamine
hydrochloride (272 mg, 3.91 mmol), and this mixture was
heated at 100 °C for 15 h. The reaction mixture was poured
into 50 mL of 1 N HCl. The precipitate was filtered and
washed with water. The crude product was dried and purified
by column chromatography.
N-Hydroxyanthracene-1,9-dicarboximide (2). The crude
product was purified by column chromatography (20% ethyl
acetate/hexane) to give the title compound 2 (890 mg, 84%) as
a deep yellow solid: Rf (50% ethyl acetate/hexane) 0.35; mp
1
255−257 °C; FTIR (neat) νmax (cm−1) 3466, 1664; H NMR
(CDCl3, 200 MHz) δ 7.69−7.95 (m, 3H), 8.18 (d, 1H, J = 8.2
Hz), 8.46 (d, 1H, J = 7.8 Hz), 8.88 (d, 1H, J = 7.2 Hz), 8.94 (s,
1H), 9.98 (d, 1H, J = 9.0 Hz); 13C NMR (CDCl3, 100 MHz) δ
114.1, 125.6, 126.1, 126.9, 129.8, 132.2, 133.6, 134.6, 136.3,
138.0, 157.7, 160.8: HRMS (ES+) calcd for C16H10NO3 [M +
H+] 264.0655, found 264.0651.
General Procedure for the Synthesis of PAGs 3a−e.
To a DCM solution of N-hydroxyanthracene-1,9-dicarboxyi-
mide (300 mg, 1.14 mmol) was added slowly Et3N (2.27
mmol) while the temperature of the reaction solution was
maintained at 0 °C; acid chloride which was dissolved in dry
DCM was slowly added to the reaction mixture, and this
mixture was stirred for a further 12 h at room temperature.
After completion of the reaction cold distilled water was poured
into the reaction mixture and diluted with DCM. The organic
layer was separated and dried over Na2SO4, and the solvent was
removed under vacuum to yield the orange crude carboxylate
ester.
Figure 6. (a) Water drop on a common silica (60−120) surface,
showing superhydrophilicity. (b) Water drop on the organosilica
surface, showing large hydrophobicity. (c) Water drop on the
organosilica surface after photoirradiation, behaving as a super-
hydrophilic surface.
The irreversible change of the modified organosilica surface
from hydrophobic to hydrophilic in term of contact angle (CA)
at regular time intervals of photoirradiation is shown in Figure
7.
OUTLOOK
■
In comparison to the well-known PAGs, our newly developed
PAGs based on HADI provided certain advantages such as the
following: (i) they exhibit strong fluorescence and relatively
higher fluorescence quantum yield; (ii) the fluorescence
properties were found to be highly sensitive to the solvent
environment, thus making them an environment-ally sensitive
PAGs; (iii) they generated both carboxylic and sulfonic acids in
high chemical (75−85%) and quantum yields (0.29−0.35) in
the visible wavelength region (≥410 nm); (iv) they are soluble
in a wide range of organic solvents. Further, we also
N-(Phenylacetyloxy)anthracene-1,9-dicarboximide (3a).
The yellow solid compound 3a (335 mg, 80%) was obtained
by purification of the crude product using column chromatog-
raphy (20% ethyl acetate/hexane): Rf (25% ethyl acetate/
hexane) 0.35; mp 184−186 °C; FTIR (KBr) νmax (cm−1) 1683,
1
1708, 1799; H NMR (CDCl3, 200 MHz) δ 4.19 (s, 2H),
7.35−7.56 (m, 5H), 7.67−7.95 (m, 3H), 8.19 (d, 1H, J = 7.8
Hz), 8.49 (d, 1H, J = 8.2 Hz), 8.85 (d, 1H, J = 7.0 Hz), 8.97 (s,
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Figure 7. Variation in the contact angle of the organosilica surface with irradiation time.
1H), 9.95 (d, 1H, J = 8.8 Hz); 13C NMR (CDCl3, 50 MHz) δ
38.1, 114.1, 121.5, 125.2, 125.9, 126.6, 127.6, 128.5, 128.8 (3C),
129.6 (3C), 131.7, 131.9, 132.2, 133.5, 134.1, 136.2, 137.5,
158.9, 160.0, 168.0; HRMS (ES+) calcd for C26H18N2O4 [M +
CH3CN] 422.1266, found 422.1262.
column chromatography (30% ethyl acetate/hexane) gives the
title compound 3d (357 mg, 79%) as an orange solid: Rf (50%
ethyl acetate/hexane) 0.70; mp 225−227 °C; FTIR (KBr) νmax
(cm−1) 1676, 1702, 1762; 1H NMR (CDCl3, 400 MHz) δ 3.96
(brs, 3H), 7.06 (d, 2H, J = 8.8 Hz), 7.64−7.85 (m, 3H), 8.15
(d, 1H, J = 8.8 Hz), 8.31 (d, 2H, 8.8 Hz), 8.45 (d, 1H, J = 8.0
Hz), 8.81 (d, 1H, J = 8 Hz), 8.92 (s, 1H), 9.91 (d, 1H, J = 9.2
Hz); 13C NMR (CDCl3, 100 MHz) δ 55.5, 114.01, 114.08,
114.5, 118.3, 121.9, 125.5, 126.6, 127.0, 127.7, 128.7, 129.4,
129.7, 130.0, 131.7, 132.1, 132.2, 133.8, 134.2, 136.2, 137.5,
159.3, 160.5, 162.7, 164.5; HRMS (ES+) calcd for C26H18N2O5
[M + CH3CN] 438.1216, found 438.1211.
N-(Benzoyloxy)anthracene-1,9-dicarboximide (3b). Purifi-
cation of the crude carboxylate by column chromatography
(25% ethyl acetate/hexane) gives title compound 3b (343 mg,
82%) as a yellow solid: Rf (40% ethyl acetate/hexane) 0.45; mp
1
208−210 °C; FTIR (KBr) νmax (cm−1) 1684, 1703, 1772; H
NMR (CDCl3, 200 MHz) δ 7.46−7.61 (m, 2H), 7.67−7.88 (m,
4H), 8.16 (d, 1H, J = 8.6 Hz), 8.33 (d, 2H, J = 7.2 Hz), 8.46 (d,
1H, J = 8.2 Hz), 8.80 (d, 1H, J = 7.4 Hz), 8.94 (s, 1H), 9.94 (d,
1H, J = 9 Hz); 13C NMR (CDCl3, 50 MHz): 114.6, 122.0,
125.4, 126.2, 126.7, 127.2, 128.2, 128.7, 128.8, 128.9, 129.7,
130.5, 130.8, 131.9, 132.2, 133.9, 134.4, 134.7, 136.3, 137.6,
159.2, 160.4, 163.1; HRMS (ES+) calcd for C24H15NO6 [M +
HCO2H] 413.0899, found 413.0895.
N-(p-Nitrobenzoyloxy)anthracene-1,9-dicarboximide (3e).
Purification of the crude carboxylate by column chromatog-
raphy (25% ethyl acetate/hexane) gives the title compound 3e
(352 mg, 75%) as a yellow solid: Rf (40% ethyl acetate/hexane)
0.45; mp 260−264 °C; FTIR (KBr) νmax (cm−1) 1684, 1699,
1
1774; H NMR (CDCl3, 400 MHz) δ 7.68−7.71 (m, 1H),
N-(p-Methylbenzoyloxy)anthracene-1,9-dicarboximide
(3c). The compound 3c (347 mg, 80%) was obtained as a
yellow solid on purification of the crude product through
column chromatography (20% ethyl acetate/hexane): Rf (50%
ethyl acetate/hexane) 0.60; mp 193−195 °C; FTIR (KBr) νmax
(cm−1) 1678, 1701, 1773; 1H NMR (CDCl3, 200 MHz) δ 2.48
(s, 3H), 7.36 (d, 1H, J = 8.0 Hz), 7.64−7.89 (m, 3H), 8.15−
8.23 (m, 3H), 8.47 (d, 1H, J = 8.6 Hz), 8.86 (d, 1H, J = 9.0
Hz), 8.95 (m, 1H), 9.94 (d, 1H, J = 8.6 Hz); 13C NMR
(CDCl3, 50 MHz) δ 22.1, 114.5, 122.0, 123.6, 125.4, 126.2,
126.8, 127.1, 127.7, 128.8, 129.7, 129.9, 130.2, 130.8, 131.9,
132.2, 133.9, 134.3, 136.4, 137.7, 145.6, 159.4, 160.5, 163.4;
HRMS (ES+) calcd for C24H16NO4 [M + H+] 382.1074, found
382.1078.
7.79−7.85 (m, 1H), 7.87−7.89 (m, 1H), 8.18 (d, 1H, J = 8.8
Hz), 8.44−8.50 (m, 3H), 8.53−8.88 (m, 2H), 8.84 (d, 1H, 8.84
Hz), 8.96 (s, 1H), 9.87 (d, 1H, J = 8.8 Hz); 13C NMR (CDCl3,
50 MHz) δ 121.5, 123.9 (2C), 125.9, 126.2, 127.0, 127.3, 128.1,
129.0, 129.9, 131.8 (2C), 132.2, 132.4, 134.2, 134.8, 136.7,
138.0, 139.3, 151.4, 159.1, 160.2, 161.6; HRMS (ES+) calcd for
C23H13N2O6 [M + H+] 413.0768, found 413.0761.
General Procedure for the Synthesis of PAGs 4a−e.
To a mixture of sulfonyl chloride (1.5 mmol) and N-
hydroxyanthracene-1,9-dicarboximide (250 mg, 0.95 mmol) in
dry DCM was added Et3N (0.52 mL, 1.90 mmol) dropwise at 0
°C. The reaction mixture was then stirred overnight at room
temperature. After the completion of the reaction, it was
quenched by ice-cold water, diluted with DCM. The organic
layer was separated and dried over Na2SO4, and the solvent was
removed under vacuum to yield the orange crude sulfonate.
N-(p-Methoxybenzoyloxy)anthracene-1,9-dicarboximide
(3d). The dark yellow crude solid carboxylate on purification by
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N-(Methylsulfonyloxy)anthracene-1,9-dicarboximide (4a).
The crude product was purified by column chromatography
(20% ethyl acetate/hexane) to give the title compound 4a (265
mg, 82%) as an orange solid: Rf (40% ethyl acetate/hexane)
0.45; mp 218−220 °C; FTIR (KBr) νmax (cm−1) 1387, 1689,
1717; 1H NMR (DMSO-d6, 200 MHz) δ 3.74 (s, 3H), 7.66 (t,
1H, J = 7.2 Hz), 7.79−7.90 (m, 2H), 8.19 (d, 1H, J = 8.2 Hz),
137.9, 159.3, 160.3; HRMS (ES+) calcd for C22H12F2NO5S [M
+ H+] 440.0399, found 440.0390.
General Procedure for the Synthesis of the Monomer
N-(p-Vinylbenzenesulfonyloxy)anthracene-1,9-dicar-
boximide (9). To a mixture of N-hydroxyanthracene-1,9-
carboxyimide (500 mg, 1.90 mmol) and 4-styrenesulfonyl
chloride (2.84 mmol) in dry DCM was added Et3N (0.52 mL,
3.80 mmol) dropwise at 0 °C. The reaction mixture was then
stirred overnight at room temperature. After the completion of
the reaction, it was quenched by ice-cold water, diluted with
DCM. The organic layer was separated and dried over Na2SO4,
and the solvent was removed under vacuum to yield the orange
crude monomer.
N-(p-Vinylbenzenesulfonyloxy)anthracene-1,9-dicarboxi-
mide (9). The crude product was purified by column
chromatography (30% ethyl acetate/hexane) to give the title
compound 9 (676 mg, 83%) as a deep orange solid: mp 195−
198 °C; Rf (30% ethyl acetate/hexane) 0.40; FTIR (KBr) νmax
(cm−1) 1386, 1717, 1734; 1H NMR (CDCl3, 200 MHz) δ 5.53
(d, 1H, J = 10.8 Hz), 5.98 (d, 1H, J = 17.6 Hz), 6.82 (dd, 1H, J1
= 11.2 Hz, J2 = 17.8 Hz), 7.62−7.71 (m, 3H), 7.73−7.89 (m,
2H), 8.13−8.17 (m, 3H), 8.45 (d, 1H, J = 8.4 Hz), 8.79 (d, 1H,
J = 7.0 Hz), 8.92 (s, 1H), 9.81 (d, 1H, J = 9.0 Hz); 13C NMR
(CDCl3, 100 MHz) δ 114.4, 118.5, 121.7, 125.3, 126.1, 126.6,
126.8, 127.6 (2C), 128.7, 129.6, 129.8 (2C), 131.9, 132.1,
133.8, 133.9, 134.6, 135.2, 136.3, 137.6, 144.0, 159.3, 160.4;
HRMS (ES+) calcd for C24H16NO5S [M + H+] 430.0743,
found 430.0740.
8.55−8.67 (m, 2H), 9.14 (s, 1H), 9.59 (d, 1H, J = 9.0 Hz); 13
C
NMR (DMSO-d6, 50 MHz) δ 39.0, 114.2, 121.8, 125.6, 126.5,
127.4, 127.7, 129.1, 130.9, 132.3, 132.9, 133.5, 135.5, 137.7,
139.3, 159.9, 161.1; HRMS (ES+) calcd for C17H12NO5S [M +
H+] 342.0431, found 342.0427.
N-(1-Butanesulfonyloxy)anthracene-1,9-dicarboximide
(4b). Purification of the crude product by column chromatog-
raphy (25% ethyl acetate/hexane) gives the title compound 4b
(291 mg, 80%) as a yellow solid: Rf (30% ethyl acetate/hexane)
0.50; mp 210−213 °C; FTIR (KBr) νmax (cm−1) 1387, 1686,
1711; 1H NMR (CDCl3, 200 MHz) δ 1.07 (t, 3H, J = 7.4 Hz),
1.51−1.62 (m, 2H), 2.18 (m, 2H), 3.79−3.87 (m, 2H), 7.66−
7.93 (m, 3H), 8.17 (d, 1H, J = 8.4 Hz), 8.47 (d, 1H, J = 8.0
Hz), 8.83 (d, 1H, J = 6.2), 8.94 (s, 1H), 9.94 (d, 1H, J = 9.0
Hz); 13C NMR (CDCl3, 50 MHz) δ 13.7, 21.7, 25.8, 54.4,
114.2, 121.6, 125.6, 126.2, 127.0, 127.6, 128.7, 129.9, 132.2,
133.9, 134.8, 136.8, 138.1, 159.8, 160.8; HRMS (ES+) calcd for
C20H18NO5S [M + H+] 384.0900, found 384.0905.
N-(Phenylsulfonyloxy)anthracene-1,9-dicarboximide (4c).
The crude product on purification by column chromatography
(20% ethyl acetate/hexane) yielded the title compound 4c (287
mg, 75%) as an orange solid: Rf (50% ethyl acetate/hexane)
0.55; mp 225−227 °C; FTIR (KBr) νmax (cm−1) 1378, 1689;
1H NMR (CDCl3, 400 MHz) δ 7.66−7.78 (m, 3H), 7.79−7.89
(m, 2H), 7.90−7.92 (m, 1H), 8.19 (d, 1H, J = 8.4 Hz), 8.23−
8.25 (m, 1H), 8.48 (d, 1H, J = 8.4 Hz), 8.81−8.83 (m, 1H),
8.96 (s, 1H), 9.86 (d, 1H, J = 8.8 Hz); 13C NMR (CDCl3, 50
MHz) δ 114.3, 121.6, 125.4, 126.1, 126.3, 126.8, 126.9, 128.7,
129.2 (2C), 129.5 (2C), 129.7, 132.0, 133.7, 134.7, 135.0,
135.4, 136.5, 137.8, 159.4, 160.4; HRMS (ES+) calcd for
C22H14NO5S [M + H+] 404.0587, found 404.0581.
Photophysical Poperties of PAGs 3a−e and 4a−e. The
UV/vis absorption spectra of degassed 1.5 × 10−5 M solutions
of the PAGs 3a−e and 4a−e in absolute ethanol were recorded
on a Shimadzu UV-2450 UV/vis spectrophotometer, and the
fluorescence emission spectra were recorded on a Hitachi F-
7000 fluorescence spectrophotometer. The fluorescence
quantum yields of the PAGs were calculated using eq 1,49
η2
(GradPAG
(GradST)
)
PAG
ηS2T
(Φ )PAG = (Φ )ST
f
f
(1)
N-(Tolylsulfonyloxy)anthracene-1,9-dicarboximide (4d).
The yellow solid compound 4d (316 mg, 80%) was obtained
by purification of the crude product using column chromatog-
raphy (30% ethyl acetate/hexane): Rf (30% ethyl acetate/
hexane) 0.50; mp 208−210 °C; FTIR (KBr) νmax (cm−1) 1386,
1697, 1717; 1H NMR (CDCl3, 200 MHz) δ 2.52 (s, 3H), 7.44
(d, 2H, 8.6 Hz), 7.63−7.89 (m, 3H), 8.09 (d, 2H, J = 8.4 Hz),
8.14 (d, 1H, J = 9.2 Hz), 8.44 (d, 1H, J = 8.4 Hz), 8.78 (d, 1H J
= 7.2 Hz), 8.91 (s, 1H), 9.82 (d, 1H, J = 9.2 Hz); 13C NMR
(CDCl3, 50 MHz) δ 22.0, 114.7, 122.0, 125.6, 126.4, 127.0,
127.8, 129.0, 129.7 (3C), 129.9 (3C), 130.0, 132.1, 132.5,
134.0, 136.6, 137.8, 146.5, 159.6, 160.7; HRMS (ES+) calcd for
C23H16NO5S [M + H+] 418.0743, found 418.0740.
where the subscripts PAG and ST denote the photoacid
generator and standard, respectively. Quinine sulfate in ethanol
was taken as a standard. Φf is the fluorescence quantum yield;
Grad is the gradient from the plot of integrated fluorescence
intensity vs absorbance, and η is the refractive index of the
solvent.
Since the fluorescences for photoacid generators and
standard were recorded in the same solvent, eq 1a was used
for the calculation of fluorescence quantum yield.
GradPAG
GradST
(Φ )PAG = (Φ )ST
f
f
(1a)
N-(2,4-Difluorobenzenesulfonyloxy)anthracene-1,9-dicar-
boximide (4e). The crude sulfonate was purified by column
chromatography (30% ethyl acetate/hexane) to give the title
compound 4e (329 mg, 79%) as an orange solid: Rf (40% ethyl
acetate/hexane) 0.45; mp 223−225 °C; FTIR (KBr) νmax
Preparative Photolysis of PAGs 3a−e and 4a−e.
Nitrogen-purged solutions of PAGs 3a−e and 4a−e (0.05
mmol) in acetonitrile were irradiated individually under visible
light (≥410 nm). The photoreaction was monitored by TLC at
regular intervals. After completion of photolysis, solvent was
removed under vacuum and the photoproducts anthracene-1,9-
dicarboxyimide and the corresponding carboxylic acid or
sulfonic acid were isolated by column chromatography using
EtOAc in hexane as an eluant.
1
(cm−1) 1387, 1689, 1717; H NMR (CDCl3, 400 MHz) δ
7.12−7.16 (m, 2H), 7.69−7.73 (m, 1H), 7.79 (t, 1H, J = 7.6
Hz), 7.87−7.91 (m, 1H), 7.97−8.03 (m, 1H), 8.18 (d, 1H, J =
8.4 Hz), 8.48 (d, 1H, J = 8.4 Hz), 8.78 (d, 1H, J = 7.2 Hz), 8.96
(s, 1H), 9.80 (d, 1H, J = 9.2 Hz); 13C NMR (CDCl3, 100
MHz) δ 106.2, 112.1, 114.0, 121.7, 123.5, 125.4, 126.2, 127.0,
128.9, 129.7, 132.2, 132.3, 132.8, 132.9, 134.1, 134.8, 136.6,
Photoproduct Anthracene-1,9-dicarboxyimide (5):25b or-
ange solid; 1H NMR (CDCl3, 400 MHz) δ 7.67 (t, 1H, J = 7.6
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Hz), 7.77 (t, 1H, J = 7.2 Hz), 7.87 (t, 1H, J = 8.0 Hz), 8.15 (d,
1H, 8.0 Hz), 8.43 (d, 1H, J = 8.4 Hz), 8.62 (s, 1H), 8.77 (d, 1H,
J = 6.8 Hz), 8.91 (s, 1H), 9.99 (d, 1H, J = 9.2 Hz).
Further, the quantum yield for the photolysis of PAGs was
calculated using eq 2
REFERENCES
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(1) (a) Yamato, H.; Asakura, T.; Nishimae, Y.; Matsumoto, A.;
Tanabe, J.; Birbaum, J.-Luc; Murer, P.; Hintermann, T.; Ohwa, T. J.
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(2) (a) Ayothi, R.; Yi, Y.; Cao, H. B.; Yueh, W.; Putna, S.; Ober, C. K.
Chem. Mater. 2007, 19, 1434. (b) Innocenzi, P.; Kidchob, T.; Falcaro,
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(Kp)PAG
(Φ )
=
p PAG
I0(F
)
(2)
PAG
Where, the subscript ‘PAG’ denotes photoacid generator. Φp is
the photolysis quantum yield, kp is the photolysis rate constant
and I0 is the incident photon flux and F is the fraction of light
absorbed. Potassium ferrioxalate was used as an actinometer.
General Procedure for the Synthesis of Copolymers.
The monomer N-(p-vinylbenzenesulfonyloxy)anthracene-1,9-
dicarboxyimide (VBSADI, 9; 0.07 g, 0.158 mmol), MMA or EA
(0.16 mmol), CuBr (0.226 mg, 0.00158 mmol), and the
initiator EBiB (0.311 mg, 0.00158 mmol) were mixed with dry
DMF in a Schlenk flask, and the solutions were degassed by
three freeze−pump−thaw cycles. Finally, the nitrogen-purged
ligand PMDETA (0.273 mg, 0.00158 mmol) in dry DMF was
injected into the reaction mixture and the postreaction mixture
was heated at 40 °C for 6 h. Then the reaction vessel was
immerged in liquid nitrogen, and DMF was removed by rotary
evaporation. Finally the polymer was dissolved in THF and
passed through a neutral Al2O3 column to remove the copper
catalyst. The volume of THF was reduced, and the polymer was
precipitated from a hexane/methanol (1/1) mixture at 0 °C.
This process was repeated three times for complete removal of
unreacted monomer, and finally the yellow solid polymer was
found and the molecular weight of the polymer was determined
by GPC.
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ASSOCIATED CONTENT
* Supporting Information
■
S
Figures and tables giving characterization data (1H and 13C
NMR and TOF-MS data) of N-hydroxyanthracene-1,9-
dicarboxyimide based PAGs 3a−e and 4a−e, monomer 9,
and copolymers 12 and 13 and computational data for N−O
bond cleavage for PAG 3b. This material is available free of
charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: ndpradeep@yahoo.co.in (N.D.P.S.); anoop@chem.
iitkgp.ernet.in (A.A.); dibakar@chem.iitkgp.ernet.in (D.D.).
Tel: (+) 91-3222-282324. Fax: (+) 91-3222-282252.
■
Notes
The authors declare no competing financial interest.
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P.; Takahara, S.; Yamaoka, T. J. Phys. Chem. A 2008, 112, 3879.
ACKNOWLEDGMENTS
■
We thank the DST (SERC Fast Track Scheme) for financial
support and the DST-FIST for the 400 MHz NMR. M.I. is
grateful to the CSIR (India); R.B. and S.A. are grateful to the
UGC (India) for their research fellowships.
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