Ultraviolet light absorber with low surface energy: Synthesis and characterization

Article abstract of DOI:10.1016/j.tet.2014.07.008

Novel fluorine-containing ultraviolet absorbers (FBPs) with low surface energy were successfully synthesized based on 2,4-dihydroxy benzophenone (BP-1), and their structures were characterized by ¹H NMR, ¹³C NMR, FTIR, and HRMS. UV a

Full text of DOI:10.1016/j.tet.2014.07.008

Tetrahedron 70 (2014) 6585e6593
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Ultraviolet light absorber with low surface energy: synthesis and
characterization
,
a
b
a
a
Yuanpeng Liang a, Bin Xiang a , Chao Liu , Xiangdong Zhou , Dan Wang , Shan Song ,
*
Genghua Bai a, Qi An a, Quehong Huang a, Shujun Chen a, Xuefeng Wei c
a College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044, PR China
b Department of Medicinal Chemistry, College of Pharmacy, Third Military Medical University, Chongqing 400038, PR China
c Chongqing Sanxia Paints Company Limited, Chongqing 402260, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel fluorine-containing ultraviolet absorbers (FBPs) with low surface energy were successfully syn-
thesized based on 2,4-dihydroxy benzophenone (BP-1), and their structures were characterized by 1H
NMR, 13C NMR, FTIR, and HRMS. UV absorption of FBPs was studied in 10ꢀ4 M dichloromethane (CH2Cl2),
Received 10 April 2014
Received in revised form 26 June 2014
Accepted 2 July 2014
which demonstrated the superior UV absorption capability of FBPs (ca.
3
¼1.7ꢁ104 to 2.2ꢁ104 at lmax
)
Available online 7 July 2014
over the matrix (
3
¼1.7ꢁ104 at lmax). Quantum chemistry calculation was performed to investigate the
stable structure and UV electronic absorption bands of FBPs. The surface chemistry information of high-
chlorinated polyethylene (HCPE) coating films embedded with ultraviolet absorbers (UVAs) was given by
X-ray photoelectron spectroscopy (XPS) and contact angle measurement. The results show that the
surface enrichment capability of FBPs is remarkably better than traditional UVAs (including BP-1, BP-3,
BP-12) because of the low surface energy properties of FBPs.
Keywords:
Low surface energy
Ultraviolet light absorber
DFT
TD DFT
Ó 2014 Elsevier Ltd. All rights reserved.
XPS
Contact angle
1. Introduction
most representative in the ultraviolet absorber family.1a,2g,3 Intra-
molecular hydrogen bond (IMHB) chelate ring can form in these
It is widely known that UV light (wavelengths between 280 nm
and 400 nm) is a major contributor to photo-degradation of poly-
mers, skin aging, and eye diseases.1 In order to protect polymer
materials against the damage of UV light and extend their service
life, ultraviolet absorber (UVA) is an extremely effective and con-
venient additive in practice.2 Currently, benzophenones, benzo-
triazoles (Fig. 1), and other o-hydroxy aromatic compounds are
ultraviolet absorbers, which is the structural basis for energy dis-
sipation. During the reversible ketoeenol tautomerism cycle, fast
excited state intramolecular proton transfer (ESIPT)1e,2a,4 (Fig. 2)
effectively converts excitation energy into harmless heat, fluores-
cence, or phosphorescence without chemical damage.5
Fig. 2. ESIPT of o-hydroxy aromatic UVAs.
Fig. 1. Molecular structures of benzophenones, benzotriazoles type UVAs.
Various UVAs have been prepared and studied in many fields to
satisfy practical needs. The ideal UVAs should be highly effective in
the absorption band of UV light (280e400 nm) as well as trans-
parent for visible light.2d,6 UVAs with square wave type absorption
* Corresponding author. Tel./fax: þ86 23 65102531; e-mail address: xiangbin@
cqu.edu.cn (B. Xiang).
http://dx.doi.org/10.1016/j.tet.2014.07.008
0040-4020/Ó 2014 Elsevier Ltd. All rights reserved.

6586
Y. Liang et al. / Tetrahedron 70 (2014) 6585e6593
peak were desired for this purpose, however, there are not any
applications reported yet. Detail experiments have demonstrated
that UVAs in polymer products present a gradient rather than even
distribution, which makes the concentration of UVAs in the exter-
nal surface significantly lower than in the bulk.7 This is one reason
that polymers added with UVAs still degraded rapidly once ex-
posed to the environment. A solution for this problem is that the
enrichment of UVA nearby the surface of polymer would effectively
protect the inner layers in the bulk from the ultraviolet damage,
which extends the service life of polymers.
Herein, we report the successful synthesis of a series of fluorine-
containing benzophenone UV absorbers (FBPs) based on 2,4-dihy-
droxy benzophenone (BP-1). The purpose of this paper is to obtain
UVAs with surface enrichment property and testify their related
performances. We believe this work will offer a direction for future
design and modification of UVA.
2.2. Structural characterization
2.2.1. NMR spectroscopy. The 1H NMR, 13C NMR spectra of typical
12FBP (n¼3) are shown in Fig. 4. The NMR spectra of BrBPs and
other FBPs are given in Fig. SI-1e10 (Supplementary data).
Compared to BrBPs, the most significant change in the 1H NMR
spectra of FBPs is a nonet at ca. 6.2e5.9 ppm and a triplet at ca.
4.0 ppm. The characteristic peaks of the end hydrogen atom of
fluorocarbon chain (eCF2H) might be split into a nonet since 1H is
coupled with 19F on the same geminal carbon and other remote
carbon atoms. Meanwhile, its characteristic peaks ought to appear
at lower field due to the electron-withdrawing effect of fluorine
atom. Accordingly, the nonet at ca. 6.2e5.9 ppm refers to the eCF2H
and the triplet at ca. 4.0 ppm is assigned to the methylene of
fluorocarbon chain (eCH2e(CF2)me). From the 13C NMR spectra of
FBPs, it can be found that the carbon signals of aliphatic methylene
of BrBPs are also present. Different from the BrBPs, the 13C NMR
spectra of FBPs generate a group of very weak signals at ca.
111.4e107.2 ppm, two triplet signals at ca. 105.3e104.7 ppm, and ca.
68.3e67.4 ppm. These weak signals at ca. 111.4e107.2 ppm should
belong to the carbon signals of fluorocarbon chain due to carbon
coupled with fluorine. It is difficult to accurately assign a specific
peak for difluoromethylene (eCF2e), but the above analysis show
that the fluorine-containing segment exists in FBPs. In addition,
according to the ‘nþ1’ splitting rules and the influence of electro-
negativity, it may be deduced that the triplet at ca.
105.3e104.7 ppm and the triplet at ca. 68.6e67.4 ppm are attrib-
uted to the end carbon atom and the methylene of fluorocarbon
chain, respectively.
2. Result and discussion
2.1. Syntheses
UVAs containing benzophenone structure have been frequently
employed as polymer additives due to their simple structure and high
efficiency in ultraviolet protection.8 The optimization of alkyl group in
UVA molecules can improve their compatibility and photostability
within the polymer matrix. For this purpose, 2,4-dihydroxy benzo-
phenone (BP-1), 2-hydroxy-4-methoxybenzophenone (BP-3), and 2-
hydroxy-4-n-octoxybenzophenone (BP-12) (Fig. 3) are most widely
applied. Besides, BP-1 is mainly used as chemical intermediate to
synthesize other UVAs due to its low molecular weight and easy ex-
traction and volatilization from the polymer matrix. As a result, BP-1
was used as the parent molecule in our work.
In summary, the NMR spectra of FBPs show that the fluorine-
containing segment has been grafted in BP-1 molecule by in-
termediate linkers and the target products (fluorine-containing
benzophenones, FBPs) are successfully obtained.
2.2.2. FTIR spectroscopy. Fig. 5 shows the FTIR spectra of BP-1 and
typical BrBP (n¼3), 12FBP (n¼3). In the spectrum of BP-1, the broad
smooth strong band at 3185 cmꢀ1 and the peak at 1280 cmꢀ1 are
related to the stretching vibration of phenolic hydroxyl group
(AreOH) while the peak at 1321 cmꢀ1 refers to the deformation
vibration of AreOH. The weak peak at 3064 cmꢀ1 is the stretching
vibration of the methyne (eCHe) of benzene ring and the signals at
1450e1600 cmꢀ1 are the skeletal vibration of benzene ring. Addi-
tionally, the peaks at 781 and 700 cmꢀ1 further demonstrate the
asymmetric tri-substitute and mono-substitute of benzene, re-
spectively. However, on account of conjugation effect from benzene
ring, the characteristic signal of carbonyl (C]O) is shifted to
1629 cmꢀ1 from ordinary values (ca. 1730e1700 cmꢀ1).
Fig. 3. Molecular structures of BP-1, BP-3, and BP-12.
It is known that perfluorocarbon has low surface energy, but its
low polarizability also brings poor miscibility and inferior chemical
reactivity in hydrocarbon solvent,9 which makes it difficult to graft
fluorocarbon into the BP-1 molecule directly. To partially solve this
problem, linear fluorocarbon alcohol was applied as the fluorine
segment.
It is necessary to couple a linker between linear fluorocarbon al-
cohol and benzophenone for the introduction of fluorine-containing
group. Because the chemicalactivity of primary brominated alkyls are
superior over chlorinated alkyls in the coupling reaction,10 the pri-
mary dibromoalkanes (Br(CH2)nBr) were employed as intermediate
linkers in this paper. A series of intermediates (bromo-benzophe-
nones, BrBPs)were prepared through the O-alkylation reaction under
a mild condition followed by reaction with linear fluorinated alcohol
(HOCH2(CF2)mCF2H). Finally the desired products (fluorine-contain-
ing benzophenones, FBPs) were successfully synthesized. The re-
action process is shown in Scheme 1.
Compared with BP-1, it can be found that the broad smooth
strong band of BrBP at 3185 cmꢀ1 moved to a higher wavenumber
3443 cmꢀ1, which might be resulted from the tautomeric in-
terconversion of ketoeenol. This means that the structures of BrBPs
mainly display enol form while BP-1 presents keto form. The dis-
appearance of signals at 1321, 1280 cmꢀ1 suggests the para-hy-
droxyl of BP-1 is substituted by other groups. Another difference
between BrBPs and BP-1 is the appearance of stretching vibration
signals of aliphatic methylene (eCH2e) at ca. 2973, 2935,
2876 cmꢀ1 and the aryl ether (AreOeC) at ca. 1256, 1224 cmꢀ1
indicating that the para-hydroxyl of BP-1 is replaced by alkoxy. The
,
Scheme 1. Synthetic route (n¼2, 3, 4, 5, 6; m¼3, 5).

Y. Liang et al. / Tetrahedron 70 (2014) 6585e6593
6587
Fig. 4. The 1H NMR and 13C NMR spectra of 12FBP (n¼3).
results certify that the intermediates (BrBPs) were successfully
obtained.
content. It shows that the improvement of UV absorption capacity
of FBPs has little relationship with the fluorine-containing segment.
However, the UV absorption capacity of the 12FBP (n¼2) only
slightly improves while the 12FBP (nꢂ3) generates significant ex-
altation in comparison to BP-1, which suggests the length of in-
termediate linker plays an important role in UV absorption.
However, with the increase of intermediate linker (nꢂ3) length, the
change of UV absorption capacity is no longer outstanding. It is well
known that the electron donation effect of alkoxy can increase the
UV absorption while the fluorine-containing segment has electron-
withdrawing effect. The electron donation effect of alkoxy will be
reduced if it is bonded with fluorine-containing segment. However,
when the length of alkoxy goes beyond a certain extent, the effect
of electron-withdrawing of fluorine-containing segment will be
negligible. This explains the nearly constant UV capacity of 12FBP
(nꢂ3).
Similar to BrBPs, the spectra of FBPs also show a broad smooth
strong band at ca. 3456 cmꢀ1. Besides, the signals of eCH2e at ca.
2964, 2935, 2887 cmꢀ1 and the signals of AreOeC at ca. 1261,
1220 cmꢀ1 are still present in FBPs. Different from the BrBPs, there
is an additional strong absorption band at ca. 1140 cmꢀ1 for FBPs,
which might be attributable to the characteristic signal of aliphatic
ether (CeOeC).
2.3. UV absorption
The UV absorption spectra of BP-1, FPBs in 10ꢀ4 M dichloro-
methane (CH2Cl2) were measured and the results are shown in
Fig. 6. Their maximum absorption wavelengths (lmax) are in dif-
ferent regions and the values of the molar absorptivity (
are summarized in Table 1.
3 ) at lmax
From Fig. 6, it can be observed that FBPs possess similar ab-
sorption characteristics with BP-1. Both have three broad bands and
the maximum absorption is around 280e290 nm. Compared to BP-
1, FBPs have higher molar absorptivity (listed in Table 1), thus
a much better UV absorption capacity. Additionally, a significant
red shift appears with the increase of the length of intermediate
2.4. Theoretical calculation
Theoretical calculations were done to obtain the optimized
molecular geometry and electron distribution through density
functional theory (DFT). The optimized structures of BP-1 and
typical 12FBP (n¼3) are shown in Fig. 7. The structure of benzo-
phenone is warped rather than coplanar to obtain the highest
stability, and the side chain substituent of FBPs is coplanar with the
adjacent benzene ring. From the optimized structures of FBPs, it is
observed that the carbon chain of fluorine-containing segment
linker due to the pep transition (ca. 280e290 nm). These results
*
may stem from the electron donation effect of alkoxy.
Compared 8FBP (n¼3) with 12FBP (n¼3), they display almost
identical UV absorption except for the difference of fluorine

6588
Y. Liang et al. / Tetrahedron 70 (2014) 6585e6593
Table 1
Absorption properties of the BP-1 and FBPs
a
b
a
b
a
b
3
UVA
lmax1
3
1
lmax2
3
2
lmax3
3
BP-1
241.4
12,000
15,000
17,000
15,000
14,000
15,000
15,000
284.8
288.8
287.8
288.8
289.6
290.0
290.4
17,000
21,000
17,000
22,000
20,000
22,000
21,000
324.4
325.6
325.6
325.6
326.2
326.6
325.4
10,000
11,000
14,000
14,000
15,000
15,000
15,000
8FBP (n¼3)
12FBP (n¼2)
12FBP (n¼3)
12FBP (n¼4)
12FBP (n¼5)
12FBP (n¼6)
243.4
240.4
243.4
243.4
243.8
243.4
a
Absorption wavelength, nm.
b
Molar absorptivity, L molꢀ1 cmꢀ1
.
Fig. 7. The optimized structures of BP-1 and typical 12FBP (n¼3).
is supposed that the structure of FBPs present a ‘rigid-flexible-rigid’
mode. The electron distribution of the frontier orbitals of the BP-1
and typical 12FBP (n¼3) is shown in Fig. 8. Compared with BP-1,
more efficient conjugation is provided by the alkoxy in FBPs,
which may contribute to the red shift phenomenon in UV spectra.
The frontier orbital energies of BP-1 and FBPs are listed in Table 2.
The results show a decreasing energy gap of 12FBPs with the in-
crease of the length of intermediate linker, which agrees with the
UV absorption analysis.
Fig. 5. The FTIR spectra of BP-1 and typical BrBP (n¼3), 12FBP (n¼3).
Fig. 8. The HOMO and LUMO of BP-1 and 12FBP (n¼3).
Table 2
The frontier orbital energies of BP-1 and FBPs
Energy BP-1
(eV)
8FBP
12FBP
n¼3
n¼2
n¼3
n¼4
n¼5
n¼6
ELUMO ꢀ1.7452 ꢀ1.7401 ꢀ1.7684 ꢀ1.7466 ꢀ1.7164 ꢀ1.7050 ꢀ1.6903
EHOMO ꢀ6.0998 ꢀ6.0556 ꢀ6.0934 ꢀ6.0632 ꢀ6.0262 ꢀ6.0115 ꢀ5.9933
DE
4.3545
4.3155
4.3250
4.3166
4.3098
4.3065
4.3030
Fig. 6. The UV absorption spectra of BP-1, FPBs in CH2Cl2 (10ꢀ4 M).
Time dependent DFT (TD DFT) calculation was performed to
further study the UV absorption spectra2d,4b,6a,11 of BP-1 and FBPs.
The calculation results about electronic absorption bands, the cor-
responding electric transition orbital, transition energies, and the
oscillator strength (f) above 270 nm are listed in Table 3. The
electronic transition pattern of these benzophenone type UVAs is
the singlet state excitation. Among the calculated electronic
displays a spiral structure, while the alkane shows a zig-zag con-
formation. Particularly, due to the electron repulsion and steric
hindrance of fluorine atom, fluorine-containing carbon chain loses
flexibility and turns into rigid segments.9 Based on these results, it

Y. Liang et al. / Tetrahedron 70 (2014) 6585e6593
6589
Table 3
TD DFT calculated transition states, transition orbitals, electronic transition energies,
and oscillator strengths (f) for BP-1, FBPs
Transition Transition Transition energies (eV)
Oscillator
states
orbitals
strengths (f)
Calcd
Expt.
(nm)
BP-1
S0/S1
S0/S2
S0/S3
S0/S4
S0/S5
S0/S6
54/57
52/57
54/58
52/59
52/58
52/60
3.8183 (324.71 nm) 324.4 0.1629
3.9205 (316.25 nm) 0.0032
4.3505 (284.99 nm) 284.8 0.2274
4.4017 (281.67 nm)
4.5453 (272.78 nm)
4.5859 (270.36 nm)
0.0063
0.0718
0.0473
8FBP (n¼3) S0/S1
122/125 3.7844 (327.62 nm) 325.6 0.2217
120/125 3.9165 (316.57 nm) 0.0024
122/128 4.3142 (287.39 nm) 288.8 0.2695
S0/S2
S0/S3
S0/S4
S0/S5
S0/S6
120/125 4.4143 (280.87 nm)
120/126 4.5505 (272.46 nm)
120/128 4.5825 (270.56 nm)
0.0061
0.0862
0.0570
12FBP (n¼2) S0/S1
142/145 3.7878 (327.33 nm) 325.6 0.2159
140/145 3.9094 (317.15 nm) 0.0027
142/149 4.3295 (286.37 nm) 287.8 0.2753
S0/S2
S0/S3
S0/S4
S0/S5
S0/S6
140/145 4.4116 (281.04 nm)
140/146 4.5446 (272.81 nm)
140/149 4.6040 (269.30 nm)
0.0061
0.0810
0.0589
12FBP (n¼3) S0/S1
146/149 3.7852 (327.55 nm) 325.6 0.2232
144/149 3.9163 (316.59 nm) 0.0025
146/153 4.3160 (287.26 nm) 288.8 0.2730
S0/S2
S0/S3
S0/S4
S0/S5
S0/S6
144/149 4.3958 (282.05 nm)
144/150 4.5482 (272.60 nm)
144/153 4.5843 (270.46 nm)
0.0060
0.0849
0.0582
12FBP (n¼4) S0/S1
150/153 3.7791 (328.08 nm) 326.2 0.2226
148/153 3.9153 (316.66 nm) 0.0021
150/157 4.3007 (288.29 nm) 289.6 0.2707
S0/S2
S0/S3
S0/S4
S0/S5
S0/S6
148/153 4.3992 (281.84 nm)
148/155 4.5618 (271.79 nm)
148/157 4.5702 (271.29 nm)
0.0060
0.0932
0.0528
12FBP (n¼5) S0/S1
154/157 3.7783 (328.15 nm) 326.6 0.2251
152/157 3.9190 (316.37 nm) 0.0022
154/161 4.2936 (288.76 nm) 290.0 0.2718
S0/S2
S0/S3
S0/S4
S0/S5
S0/S6
152/158 4.4002 (281.77 nm)
152/159 4.5634 (271.69 nm)
152/161 4.5669 (271.49 nm)
0.0061
0.0939
0.0522
Fig. 9. The wide XPS scan of the HCPE coating films embedded UVAs (sample 1: added
12FBP (n¼3); sample 2: added 8FBP (n¼3); sample 3: added BP-12; sample 4: added
BP-3; sample 5: added BP-1).
12FBP (n¼6) S0/S1
158/161 3.7753 (328.41 nm) 325.4 0.2250
156/161 3.9179 (316.46 nm) 0.0020
158/166 4.2869 (289.22 nm) 290.4 0.2701
S0/S2
S0/S3
S0/S4
S0/S5
S0/S6
156/162 4.4020 (281.66 nm)
156/163 4.5616 (271.80 nm)
156/166 4.5701 (271.30 nm)
0.0061
0.0977
0.0496
scan. Table 4 lists the relative atomic concentration of elements on
the surface of coating film.
Table 4
transitions above 270 nm in optical region, both BP-1 and FBPs
display two strong absorption bands (S0/S1, S0/S3), however, the
band of FBPs redshifts to longer wavelength, which are consistent
with experimental results. The oscillator strength (f) of FBPs is also
significantly larger than BP-1, which demonstrates that the elec-
tronic transition probability of FBPs is enhanced due to grafted
alkoxy side chains. The theoretical calculation further confirms the
previous experimental results that the UV absorption capacity of
FBPs exceeds BP-1.
Relative atomic concentrations of elements present at the surface of coating by XPS
Sample UVAa
Name
C
O
Cl
F
Formula
M (g molꢀ1
)
1
2
3
4
5
12FBP (n¼3) C23H18O4F12 586
56.01 2.34 30.1 11.55
57.23 2.97 39.1 0.7
61.49 1.11 37.4
60.96 1.05 38
57.98 1.85 40.17
8FBP (n¼3)
BP-12
BP-3
C
C
C
C
21H18O4F8 486
21H26O3
14H12O3
13H10O3
326
228
214
d
d
d
BP-1
a
The added content is 8.532ꢁ10ꢀ5 mol gꢀ1
.
2.5. Low surface energy properties
As expected, carbon, oxygen, chlorine, and fluorine are detected
When the polymer blend system contacts with air, in order to
obtain the most stable state, low surface energy components usu-
ally migrate to polymereair interface12 and enrich nearby the
surface. XPS and contact angle measurement were applied to ob-
tain the evidence of low surface energy properties of FBPs.
from the sample 1 (added 12FBP (n¼3)) and sample 2 (added 8FBP
(n¼3)), however, fluorine is not detected from the other samples. It
can be observed from Fig. 9 and Table 4 that the peak intensity of
fluorine in sample 2 is far weaker than sample 1. Ideally, the ratio of
fluorine peak intensity should be 2e3 for sample 2 to sample 1.
Thus the concentration of 12FBP (n¼3) might be higher than 8FBP
(n¼3) on the film surface or much more fluorine-containing units
concentrated on the film surface for 12FBP (n¼3). It could be
inferred that the surface enrichment ability of FBPs is directly re-
lated to the fluorine content, which diminishes the surface energy
of FBPs as the content of fluorine increases.
2.5.1. X-ray photoelectron spectroscopy(XPS) measurement. Elemental
quantitative analysis by XPS has been frequently used to determine
materials composition on polymer surface.13 The type and percentage
of the elements presented on the surface of high-chlorinated poly-
ethylene (HCPE) coating (Fig. 9) were determined with a wide XPS

6590
Y. Liang et al. / Tetrahedron 70 (2014) 6585e6593
Carbon and chlorine are the common elements in all samples
due to the same matrix resin used. Oxygen only comes from UVAs
and can represent amount of UVA. Chlorine only exists in the ma-
trix resin while fluorine only exists in FBPs. Consequently, the
amount of matrix resin and UVAs can be calculated from the con-
tent of chlorine and oxygen, respectively. Therefore, the surface
relative concentration (q) of the UVAs was obtained according to
the following equation:
Oat %
Clat %
ꢁ
g
q
¼
(1)
where:
q
is the surface relative concentration of UVAs on the
coating film surface; is the normalization factor; Oat % is the
g
ꢁ
g
relative amount of ultraviolet absorber (UVA) on the surface; Clat %
is relative amount of the matrix resin on the surface.
Table 5 lists the calculation results. It can be seen that the
q of
FBPs is significantly higher than BP-12, BP-3 and BP-1, suggesting
FBPs have excellent surface enrichment capability for the organic
resin coating. The
q
value of sample 1 (
q
¼0.01944) and sample 2
(q¼0.01899) indicates that the fluorine content of FBPs affects the
Fig. 10. The water contact angles of HCPE coating film surface (sample 1: added 12FBP
(n¼3); sample 2: added 8FBP (n¼3); sample 3: added BP-12; sample 4: added BP-3;
sample 5: added BP-1).
surface enrichment capability, which is consistent with previous
qualitative analysis. However, an interesting phenomenon is found
that the
sample 3 (added BP-12,
q
of sample 5 (added BP-1,
q
¼0.01535) is higher than
q¼0.00989) and sample 4 (added BP-3,
traditional UVAs (BP-1, BP-3, BP-12), and the surface enrichment
capability of FBPs is related to the fluorine content.
q
¼0.00921), namely, the surface migration ability of BP-1 is supe-
rior over BP-12 and BP-3. There is less resistance for BP-1 during
migration to the coating film surface because of its smaller mo-
lecular size, which explains the fact Sample 5 has the highest q. In
3. Conclusion
practice, BP-1 is easily extracted by solvent and has bad protection
ability to coating surface, so it is hardly used directly.
A series of FBPs were successfully synthesized. The ultraviolet
absorption capability of FBPs was found better than BP-1. DFT cal-
culation shows that the energy gap of frontier orbitals of FBPs de-
creases with the increase of the linker length. TD DFT calculation
also confirmed the better UV absorption capacity of FBPs than the
parent molecule (BP-1). XPS and contact angle measurement of the
HCPE coating films embedded with UVAs revealed the low surface
energy properties of FBPs.
Table 5
The calculated results of surface relative concentration (q)
Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Oat %
Clat %
g
2.34
30.1
1/4
2.97
39.1
1/4
1.11
37.4
1/3
1.05
38
1/3
1.85
40.17
1/3
q
0.01944
0.01899
0.00989
0.00921
0.01535
4. Experiment
4.1. General information
2.5.2. Contact angle testing. It is well known that the fluorine-
containing units, which concentrate on the polymer film surface
can increase the contact angle of solvent to film. As a result, water
contact angle test was carried out to reveal the surface information
and hydrophobic properties.
All reagents, starting materials, and solvents were purchased
from commercial sources. Solvents were dried by standard pro-
cedures. TLC analysis was performed on silica gel backed plates. The
products were purified by silica gel (300e400 mesh) column
chromatography. 1H and 13C NMR spectra were recorded with
a Varian Mercury Plus 400 NMR spectrometer (US). IR spectra were
measured on a Magna IR 550II spectrometer (US). HRMS were
obtained on Bruker SolariX FT-ICR-MS instrument (BRD). Melting
points were determined on an SGW-X4 micro melting point ap-
paratus (China) and were uncorrected.
The water contact angle testing results are shown in Fig. 10.
Theoretically, water contact angle of the FBP-added film surface
would be significantly increased because of the enrichment of the
fluorine-containing segment on the film surface. As expected, wa-
ter contact angles of sample 1 (added 12FBP (n¼3)) and sample 2
(added 8FBP (n¼3)) are greater than other samples, which show the
improved hydrophobicity of sample 1 and sample 2. This could be
explained by the fact that FBPs have been effectively enriched on
the film surface, giving a higher surface concentration than BP-1,
BP-3, BP-12. In accordance with the XPS analysis, the water con-
tact angle of sample 1 is also larger than sample 2, which may
confirm above inferences that the surface energy of FBPs is in-
versely related to the fluorine content. Sample 3 (added BP-12) and
sample 4 (added BP-3) almost do not increase compared with
sample 6 (the blank), which shows the poor ability of surface en-
richment for BP-3 and BP-12. Interestingly, sample 5 (added BP-1)
displays a relatively greater value of water contact angle than
sample 3 and sample 4, which is similar to the XPS analysis.
The results of XPS and contact angle measurement prove that
FBPs have more excellent surface enrichment capability than the
4.2. Synthesis of the intermediate products (BrBPs)
2,4-Dihydroxy benzophenone (BP-1) (1 equiv) and solid KOH
powder (2 equiv) were dissolved in acetone and stirred at room
temperature for 30 min. Then, dibromoalkane (3 equiv) was slowly
added to this solution within 1 h. The reaction mixture was stirred
at 60e70 ꢃC until the thin-layer chromatography analysis showed
raw spots disappeared. The reaction mixture was directly purified
via column chromatography on silica gel using a mixture of ethyl
acetate and petroleum ether (1:150) as eluent.
4.2.1. (4-(2-Bromoethoxy)-2-hydroxy)-benzophenone
(BrBP
(n¼2)). 2,4-Dihydroxy benzophenone(1.5 g), solid KOH powder

Y. Liang et al. / Tetrahedron 70 (2014) 6585e6593
6591
(0.7850 g), 1,2-dibromoethane(1.8 mL). The product was a white
crystal (1.0506 g, 46.67%). Rf¼0.4342 (developing solvent: PE/
EA¼8:1). Mp 95e98 ꢃC. IR (KBr) 3462, 3064, 3029, 2919, 2843,1628,
30 min. Intermediate products (BrBPs) dissolved in acetone were
added dropwise to the above mixture within 1 h. The reaction
mixture was stirred at 60e70 ꢃC and the progress was monitored by
TLC. Upon the reaction completion, the mixture was cooled to room
temperature, the solid was removed by filtration and the solvent
was distilled off with a rotary evaporator under vacuum. The re-
action mixture was purified via column chromatography on silica
gel using a mixture of ethyl acetate and petroleum ether (1:100) as
eluent.
1600, 1575, 1504, 1447, 1445, 1254, 1222, 784, 580 cmꢀ1 1H NMR
.
(400 MHz, CDCl3)
d 12.67 (s, 1H), 7.78e7.35 (m, 6H), 6.57e6.34 (m,
2H), 4.34 (t, J¼6.1 Hz, 2H), 3.66 (t, J¼6.1 Hz, 2H). 13C NMR (101 MHz,
CDCl3)
d 200.03, 166.11, 164.41, 138.03, 135.39, 131.55, 128.82,
128.29, 113.49, 107.49, 101.68, 67.81, 28.38. HRMS calcd for
C
15H13O3Br [Mꢀ3H]þ 318.99753, found 318.99744.
4.2.2. (4-(3-Bromopropoxy)-2-hydroxy)-benzophenone
(BrBP
4.3.1. (4-(2-(2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluorooctyloxy)ethoxy)-2-
hydroxy)-benzophenone (12FBP (n¼2)). 1H,1H,7H-Dodecafluoro-1-
heptanol (1 mL), NaH (60%) (0.2120 g), 2-hydroxy-4-
bromoethoxybenzophenone (BrBP (n¼2)) (0.6 g). The product
was a pale yellow liquid (0.6232 g, 58.29%). Rf¼0.2923 (developing
solvent: PE/EA¼8:1). IR (KBr) 3058, 3026, 2936, 2882, 1622, 1575,
(n¼3)). 2,4-Dihydroxy benzophenone (1.5 g), solid KOH powder
(0.7850 g), 1,3-dibromopropane (2.1 mL). The product was a white
acicular crystal (1.1069 g, 47.11%). Rf¼0.5000 (developing solvent: PE/
EA¼8:1). Mp 78e80 ꢃC. IR (KBr) 3442, 3063, 3029, 2933, 2850, 1608,
1576, 1506, 1465, 1442, 1621, 1260, 1251, 1224, 781, 740, 571 cmꢀ1. 1H
NMR (400 MHz, CDCl3)
d
12.70e12.59 (m, 1H), 7.67e7.45 (m, 6H),
1503, 1444, 1343, 1259, 1138, 1114, 752 cmꢀ1 1H NMR (400 MHz,
.
6.53 (d, J¼2.4 Hz, 1H), 6.41 (dd, J¼8.9, 2.5 Hz, 1H), 4.18 (t, J¼5.8 Hz,
CDCl3)
6.21e5.89 (m,1H), 4.21e4.16 (m, 2H), 4.09 (t, J¼13.9, 2H), 4.03e3.97
(m, 2H). 13C NMR (101 MHz, CDCl3)
200.32, 166.14, 165.10, 138.03,
d
¼12.70 (s, 1H), 7.69e7.39 (m, 6H), 6.54e6.39 (m, 2H),
2H), 3.60 (t, J¼6.3 Hz, 2H), 2.35 (p, J¼6.1 Hz, 2H). 13C NMR (101 MHz,
CDCl3)
d
199.98, 166.17, 165.15, 138.13, 135.28, 131.47, 128.80, 128.26,
d
113.20, 107.46, 101.63, 65.60, 31.88, 29.57. HRMS calcd for C16H15O3Br
135.44, 131.58, 128.77, 128.29, 113.31, 107.60, 105.35, 105.04, 104.72,
101.62, 70.95, 68.57, 68.32, 68.07, 67.52, 29.67. HRMS calcd for
C
[Mꢀ2H]þ 333.01318, found 333.01307.
22H16O4F12 [MꢀH]þ 571.07842, found 571.07870.
4.2.3. (4-(4-Bromobutoxy)-2-hydroxy)-benzophenone
(BrBP
(n¼4)). 2,4-Dihydroxy benzophenone(1.5 g), solid KOH powder
(0.7850 g), 1,4-dibromobutane (2.5 mL). The product was a buff
acicular crystal (0.8261 g, 33.76%). Rf¼0.5000 (developing solvent:
PE/EA¼8:1). Mp 76e78 ꢃC. IR (KBr) 3448, 3077, 3048, 2940, 2871,
4.3.2. (4-(3-(2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluorooctyloxy)propoxy)-
2-hydroxy)-benzophenone (12FBP (n¼3)). 1H,1H,7H-Dodecafluoro-
1-heptanol (1.7 mL), NaH (60%) (0.3604 g), 2-hydroxy-4-
bromopropoxy benzophenone (BrBP (n¼3)) (1.0 g). The product
was a white crystal (1.074 g, 61.40%). Rf¼0.3692 (developing sol-
vent: PE/EA¼8:1). Mp 50e53 ꢃC. IR (KBr) 3448, 2933, 1626, 1345,
1599, 1575, 1500, 1477, 1444, 1629, 1629, 1259, 1231, 746, 648 cmꢀ1
.
1H NMR (400 MHz, CDCl3)
d 12.71 (s, 1H), 7.70e7.40 (m, 6H),
6.60e6.28 (m, 2H), 4.24e3.89 (m, 2H), 3.49 (t, J¼6.4, 2H), 2.12e2.03
1197, 1262, 1140, 750, 580 cmꢀ1. 1H NMR (400 MHz, CDCl3)
d 12.66
(m, 2H), 1.97 (dt, J¼12.3, 6.1, 2H). 13C NMR (101 MHz, CDCl3)
(d, J¼20.5, 1H), 7.67e7.40 (m, 6H), 6.60e6.30 (m, 2H), 6.24e5.87
d
199.93, 166.20, 165.37, 138.13, 135.23, 131.43, 128.79, 128.25,
(m, 1H), 4.17e4.08 (m, 2H), 3.96 (t, J¼13.8, 2H), 3.80 (t, J¼5.9, 2H),
113.03, 107.57, 101.45, 67.23, 33.22, 29.22, 27.55. HRMS calcd for
2.11 (p, J¼6.0, 2H). 13C NMR (101 MHz, CDCl3)
d 200.00, 166.23,
C
17H17O3Br [Mꢀ2H]þ 347.02883, found 347.02877.
165.42, 138.23, 135.28, 131.44, 128.81, 128.27, 113.14, 107.43, 105.30,
104.98, 104.67, 101.65, 69.21, 68.25, 68.00, 67.74, 64.51, 29.69, 29.23.
HRMS calcd for C23H18O4F12 [MꢀH]þ 585.09407, found 585.09311.
4.2.4. (4-(5-Bromopentyloxy)-2-hydroxy)-benzophenone
(BrBP
(n¼5)). 2,4-Dihydroxy benzophenone(1.5 g), solid KOH powder
(0.7850 g), 1,5-dibromopentane (2.9 mL). The product was a light
green crystal (0.9059 g, 35.58%). Rf¼0.5263 (developing solvent: PE/
EA¼8:1). Mp 50e52 ꢃC. IR (KBr) 3448, 3074, 3050, 2925, 2846, 1626,
4.3.3. (4-(4-(2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluorooctyloxy)butoxy)-2-
hydroxy)-benzophenone (12FBP (n¼4)). 1H,1H,7H-Dodecafluoro-1-
heptanol (1 mL), NaH (60%) (0.2120 g), 2-hydroxy-4-
bromobutoxybenzophenone (BrBP (n¼4)) (0.6 g). The product
was a white crystal (0.4365 g, 42.32%). Rf¼0.3846 (developing
solvent: PE/EA¼8:1). Mp 76e78 ꢃC. IR (KBr) 3445, 3075, 2962,
1594, 1575, 1504, 1472, 1445, 1261, 1228, 784, 744 cmꢀ1 1H NMR
.
(400 MHz, CDCl3)
d
12.72 (s, 1H), 7.72e7.35 (m, 6H), 6.50 (d, J¼2.4,1H),
6.43e6.37 (m, 1H), 4.03 (t, J¼6.3, 2H), 3.45 (t, J¼6.7, 2H), 1.99e1.89 (m,
2H), 1.88e1.79 (m, 2H), 1.63 (ddd, J¼19.2, 9.1, 6.2, 2H). 13C NMR
2875,1628,1594,1575,1498, 1444,1348, 1264,1139, 1120, 743 cmꢀ1
.
(101 MHz, CDCl3)
d
199.89, 166.21, 165.52, 138.15, 135.19, 131.39,
1H NMR (400 MHz, CDCl3)
d
12.66 (d, J¼20.5, 1H), 7.70e7.40 (m,
128.77, 128.22, 112.94, 107.62, 101.41, 67.94, 33.48, 32.29, 28.07, 24.65.
6H), 6.58e6.30 (m, 2H), 6.21e5.85 (m, 1H), 4.13 (t, J¼6.1, 2H), 3.96
HRMS calcd for C18H19O3Br [Mꢀ2H]þ 361.04448, found 361.04432.
(t, J¼13.8, 2H), 3.84e3.75 (m, 2H), 1.96e1.85(m, 2H), 1.85e1.76(m,
2H). 13C NMR (101 MHz, CDCl3)
d 199.98, 166.27, 165.58, 138.23,
4.2.5. (4-(6-Bromohexyloxy)-2-hydroxy)-benzophenone
(BrBP
135.25, 131.43, 128.81, 128.27, 113.02, 107.61, 107.51, 105.29, 104.98,
104.67, 101.49, 72.60, 68.09, 67.85, 67.58, 29.69, 26.11, 25.53. HRMS
calcd for C24H20O4F12 [MꢀH]þ 599.10972, found 599.10796.
(n¼6)). 2,4-Dihydroxy benzophenone(1.5 g), solid KOH powder
(0.7850 g), 1,6-dibromohexane (3.2 mL). The product was a light
green crystal (0.8792 g, 33.25%). Rf¼0.5658 (developing solvent:
PE/EA¼8:1). Mp 70e72 ꢃC. IR (KBr) 3448, 2936, 2858, 1629, 1597,
4.3.4. (4-(5-(2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluorooctyloxy)pentyloxy)-
2-hydroxy)-benzophenone (12FBP (n¼5)). 1H,1H,7H-Dodecafluoro-
1-heptanol (0.9 mL), NaH (60%) (0.1908 g), 2-hydroxy-4-
bromopentyloxybenzophenone (BrBP (n¼5)) (0.6 g). The product
was a white crystal (0.8022 g, 79.04%). Rf¼0.4153 (developing sol-
vent: PE/EA¼8:1). Mp 48e50 ꢃC. IR (KBr) 3436, 3080, 3032, 3058,
2943, 2869, 1624, 1597, 1575, 1504, 1469, 1444, 1348, 1264, 1133,
1574, 1508, 1472, 1443, 1262, 1226, 568 cmꢀ1 1H NMR (400 MHz,
.
CDCl3)
4.02 (t, J¼6.4, 2H), 3.43 (t, J¼6.7, 2H), 1.94e1.86 (m, 2H), 1.86e1.78
(m, 2H), 1.56e1.47 (m, 4H). 13C NMR (101 MHz, CDCl3)
199.91,
d
12.72 (t, J¼1.8, 1H), 7.70e7.42 (m, 6H), 6.54e6.33 (m, 2H),
d
166.24, 165.64, 138.19, 135.19, 131.39, 128.78, 128.24, 112.91, 107.68,
101.41, 68.12, 33.75, 32.55, 28.72, 27.79, 25.15. HRMS calcd for
C
19H21O3Br [Mꢀ2H]þ 375.06013, found 375.05995.
1118, 745 cmꢀ1. 1H NMR (400 MHz, CDCl3)
d 12.80e12.55 (m, 1H),
7.72e7.40 (m, 6H), 6.62e6.34 (m, 2H), 6.23e5.86 (m, 1H), 4.02 (t,
J¼6.4, 2H), 3.94 (t, J¼13.9, 2H), 3.64 (t, J¼6.2, 2H),1.89e1.79 (m, 2H),
1.74e1.64 (m, 2H), 1.55 (dt, J¼10.7, 7.7, 2H). 13C NMR (101 MHz,
4.3. Synthesis of the target products (FBPs)
A mixture of 1H,1H,7H-dodecafluoro-1-heptanol (3 equiv) and
CDCl3) d 199.96, 166.28, 165.67, 138.24, 135.22, 131.41, 128.80,
NaH (60%) (3 equiv) in acetone was stirred at room temperature for
128.26, 112.95, 107.68, 105.29, 104.97, 104.67, 101.44, 72.91, 68.11,

6592
Y. Liang et al. / Tetrahedron 70 (2014) 6585e6593
68.05, 67.80, 67.55, 29.68, 29.14, 28.60, 22.35. HRMS calcd for
C
of the contact angle were reported. The values of contact angle
25H22O4F12 [MꢀH]þ 613.12537, found 613.12371.
measurement varied by ꢄ1ꢃ.
4.3.5. (4-(6-(2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluorooctyloxy)hex-
yloxy)-2-hydroxy)-benzophenone (12FBP
4.6.3. X-ray photoelectron spectroscopy (XPS) analysis. All XPS
spectra were acquired on a Vg250 X-ray Photon-electron Spec-
(n¼6)). 1H,1H,7H-
Dodecafluoro-1-heptanol (0.9 mL), NaH (60%) (0.1908 g), 2-
hydroxy-4-bromohexyloxybenzophenone (BrBP (n¼6)) (0.6 g).
The product was a yellow crystal (0.7876 g, 78.80%). Rf¼0.4769
(developing solvent: PE/EA¼8:1). Mp 42e44 ꢃC. IR (KBr) 3445,
3074, 3026, 2933, 2869, 1626, 1596, 1575, 1498, 1471, 1447, 1351,
troscopy (UK), with a monochromatic Al Ka source (1486.6 eV) in
a spot size of 500 m. The wide-scan measurements were per-
m
formed with pass energy of 100.0 eV and an energy step of 1.0 eV,
from which the surface chemical compositions were determined.
1264, 1136, 1120, 745 cmꢀ1 1H NMR (400 MHz, CDCl3)
.
Acknowledgements
d
12.80e12.68 (m, 1H), 7.69e7.37 (m, 6H), 6.55e6.37 (m, 2H),
6.22e5.91 (m, 1H), 4.00 (t, J¼6.4, 2H), 3.92 (t, J¼13.9, 2H), 3.62 (q,
Project No. 21376282 supported by National Natural Science
Foundation of China, Project No. CSTC-2011BB4049 supported by
the Municipal Science Foundation of Chongqing City, and Project
Nos. (CDJZR 12 22 55 02 and CQDXWL-2012-038) supported by the
Fundamental Research Funds for the Central Universities. All au-
thors here express their deep thanks.
J¼6.7, 2H), 1.85e1.76 (m, 2H), 1.64 (dt, J¼13.3, 6.6, 2H), 1.52e1.43
(m, 4H). 13C NMR (101 MHz, CDCl3)
d 199.90, 166.28, 165.73,
138.21, 135.16, 131.36, 128.76, 128.20, 112.87, 107.63, 105.30,
104.99, 104.67, 101.41, 72.97, 68.18, 67.94, 67.69, 67.43, 29.29,
28.78, 26.82, 25.61, 25.48. HRMS calcd for C26H24O4F12 [MꢀH]þ
627.14102, found 627.14055.
Supplementary data
4.3.6. (4-(3-(2,2,3,3,4,4,5,5-Octafluorohexyloxy)propoxy)-2-
hydroxy)-benzophenone (8FBP (n¼3)). 1H,1H,5H-Octafluoro-1-
pentanol (1.1 mL), NaH (60%) (0.2882 g), 2-hydroxy-4-bromopro-
poxybenzophenone (BrBP (n¼3)) (0.8 g). The product was a light
green liquid (0.8418 g, 72.54%). Rf¼0.4739 (developing solvent: PE/
EA¼8:1). IR (KBr) 3061, 3023, 2940, 1627, 1344, 1257, 1224, 1124,
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2014.07.008.
References and notes
1166, 750 cmꢀ1. 1H NMR (400 MHz, CDCl3)
d 12.77e12.53 (m, 1H),
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13C NMR (101 MHz, CDCl3)
d 199.99, 166.25, 165.41, 138.26, 135.27,
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[MꢀH]þ 485.10046, found 485.10105.
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4.4. UV absorption spectrum measurement
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by T-6 UVevis spectrophotometer (China) with the concentration
of 10ꢀ4 M in dichloromethane at room temperature.
4.5. Theoretical calculation methods
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4.6. Surface chemistry analysis of the film surface
4.6.1. Sample preparation. High-chlorinated polyethylene (HCPE)
was solved in xylene as matrix resin. UVAs (BP-1, BP-3, BP-12,12FBP
(n¼3), 8FBP (n¼3)) were added into the matrix resin with amount
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,
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