An adduct of Cl-substituted benzotriazole and hydroxy benzophenone as a novel UVA/UVB absorber: Theory-guided design, synthesis, and calculations

Article abstract of DOI:10.1016/j.molstruc.2012.07.050

A novel UVA/UVB absorber UV-D, a combination of Cl-substituted benzotriazole (ClBTZ) and hydroxybenzophenone (HBP) anti-UV functional groups in one molecule, which absorbs UVA and UVB radiation with high efficiency, was synthesized based on the first principle theory-guided design. The synthesized UV absorber was characterized by ¹H NMR, FT-IR and UV spectroscopy in detail. Systematic quantum chemistry calculations were performed to investigate the stable structure and UV electronic absorption bands of UV-D. Structure parameters, atoms in molecule (AIM) and natural bond orbital (NBO) analysis show that the intramolecular hydrogen bond (IMHB) in HBP part is stronger than that in ClBTZ part. This work shows that the combination of the first principle theory-guided design and organic synthesis can be used to develop highly efficiency UV absorbers effectively.

Full text of DOI:10.1016/j.molstruc.2012.07.050

Journal of Molecular Structure 1032 (2013) 100–104
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
An adduct of Cl-substituted benzotriazole and hydroxy benzophenone as a novel
UVA/UVB absorber: Theory-guided design, synthesis, and calculations
⇑
Kemei Pei, Zhihua Cui , Weiguo Chen
Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education of China, Zhejiang Sci-Tech University, Hangzhou 310018, China
Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, China
Engineering Research Center for Eco-Dyeing & Finishing of Textiles, Ministry of Education of China, Zhejiang Sci-Tech University, Hangzhou 310018, China
h i g h l i g h t s
"
"
"
A high efficiency UVA/UVB absorber UV-D was synthesized guided on quantum chemistry calculations.
The excellent absorption of UV-D comes from three electronic transition bands (S0 ? S1, S0 ? S2, S0 ? S6).
Structural parameters, AIM and NBO analysis show IMHB in HBP group is stronger than that in ClBTZ.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 May 2012
Received in revised form 27 July 2012
Accepted 27 July 2012
Available online 7 August 2012
A novel UVA/UVB absorber UV-D, a combination of Cl-substituted benzotriazole (ClBTZ) and hydroxyben-
zophenone (HBP) anti-UV functional groups in one molecule, which absorbs UVA and UVB radiation with
high efficiency, was synthesized based on the first principle theory-guided design. The synthesized UV
absorber was characterized by 1H NMR, FT-IR and UV spectroscopy in detail. Systematic quantum chem-
istry calculations were performed to investigate the stable structure and UV electronic absorption bands
of UV-D. Structure parameters, atoms in molecule (AIM) and natural bond orbital (NBO) analysis show
that the intramolecular hydrogen bond (IMHB) in HBP part is stronger than that in ClBTZ part. This work
shows that the combination of the first principle theory-guided design and organic synthesis can be used
to develop highly efficiency UV absorbers effectively.
Keywords:
Adduct
UV absorber
Theory-guided design
Synthesis
Ó 2012 Elsevier B.V. All rights reserved.
Calculations
1. Introduction
dominant classes of commercially available UV absorbers are ben-
zotriazoles (BZTs) and hydroxybenzophenones (HBPs) [4,5]. Both
Due to ozone depletion, more and more ultraviolet (UV) radia-
tion has been progressively increased on the earth [1]. UV light
(wavelengths between 280 nm and 400 nm) from the sun is known
to degrade exposed organic matter. Materials used in exterior
applications as well as interior applications are susceptible to pho-
tochemical degradation. In order to protect against the damaging
effects of UV light, UV absorbers are used to absorb UV light and
thereby prevent the damage. An ideal UV absorber must have the
key property: highly efficient absorption between 280 and
400 nm coupled with high optical transparency in the visible
range.
utilize an excited state intramolecular proton transfer from a hy-
droxyl group to dissipate light energy. They are transparent to vis-
ible light and supposed to dissipate the absorbed light energy in a
harmless manner, i.e. to convert the absorbed photon energy into
heat without chemical damage [6]. BZTs UV absorbers have rela-
tively strong absorption in 300–385 nm (UV-A) range, while HBPs
have middle strong absorption in 280–340 nm (UV-B) range. If the
benzotriazole and benzophenone anti-UV functional groups are
combined into one molecule which may result in a new type of
UV absorber with anti-UVA and UVB function, as Fig. 1 shows.
Additionally, light resistance should be enhanced since an adduct
of the two anti-UV group can increase the molecular weight of
UV absorbers.
UV absorbers with an intramolecular hydrogen bridge are
widely employed as additives against UV radiation [2,3]. The two
In this work, a high efficient UVA/UVB absorber (UV-D) with Cl-
substituted benzotriazole ((2-(5-chloro-2H-benzo[d] [1–3]triazol-
2-yl)phenol, ClBTZ) and hydroxybenzophenone (HBP) anti-UV
functional groups was synthesized based on the first principle the-
ory-guided design. Characterization is performed by 1H NMR, IR
⇑
Corresponding author at: Key Laboratory of Advanced Textile Materials and
Manufacturing Technology, Ministry of Education of China, Zhejiang Sci-Tech
University, Hangzhou 310018, China. Tel./fax: +86 571 86843627.
E-mail address: zhhcui@zstu.edu.cn (Z. Cui).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.07.050

K. Pei et al. / Journal of Molecular Structure 1032 (2013) 100–104
101
HO
Cl
N
N
UV-A type
UV-B type
N
OH
HO
ClBTZ
O
N
N
OH
O
N
Cl
UV-D
HBP
Fig. 1. The chemical structures of UV-D and the two monomers ClBTZ and HBP.
analysis to investigate IMHB interaction of UV-D based on the
B3LYP/6-31G(d) optimized structure. 6-31G(d,p) and higher basis
sets were not performed for limited computer resources. All the
DFT and MP2 calculations in this paper were carried out in the
Gaussian09 program [7].
and UV spectroscopy. Quantum chemistry calculations were calcu-
lated to investigate the stable structure and UV electronic absorp-
tion bands. Intramolecular hydrogen bonds (IMHBs) in title UV
absorber have been explored by atoms in molecule (AIM) and nat-
ural bond orbital (NBO) analysis. This work demonstrates that the
first principle theory-design and organic synthesis can cowork
with each other effectively to develop highly efficiency UV
absorbers.
3. Results and discussion
3.1. Theory-guided design
2. Experimental and computational methods
Quantum chemistry method TD DFT has been used to simulate
the UV absorption spectra successfully [8–10]. Fig. 2 shows the two
views and the optimized structure parameters of the novel UV-D
absorber with ClBTZ and HBP anti-UV functional groups. Fig. 3
shows that the adduct compound UV-D and the two monomers
ClBTZ and HBP absorption spectra at B3LYP-TD/6-31G(d) level.
The optimized structural parameters show that there are two
intermolecular hydrogen bonds, OAHꢁ ꢁ ꢁN on the ClBTZ group
(bond length: 2.628 Å, bond angle: 144.6°) and OAHꢁ ꢁ ꢁO on the
HBP group (bond length: 2.565 Å, bond angle: 148.1°) of UV-D,
and the benzene ring of the HBP part deviates from the whole mol-
ecule skeleton plane, as Table 2 and Fig. 3 shows. ClBTZ shows a
relative strong absorption band in UV-A region with a calculated
maximum molar absorption coefficient 17,000 L/(mol cm). HBP
has a middle strong absorption band in UV-B region with a calcu-
lated maximum molar absorption coefficient 12,000 L/(mol cm).
The adduct UV absorber has two strong absorption bands with
the calculated maximum molar absorption coefficients 27,000 L/
(mol cm) in UV-A region and 18,000 L/(mol cm) in UV-B region
respectively. It is clear that the absorption range in UV-D is wider
and the absorption strength is much stronger than the other two
monomers’, as Fig. 2 shows. Therefore, the adduct UV-D should
be a high efficiency UV absorber from quantum chemistry calcula-
tion results.
2.1. Materials
The reagents, UV-366(99%), AlCl3(Chemical pure, 99%), chloro-
benzene (Analytical reagent, 99%), acetone (Analytical reagent,
99.5%), concentrated hydrochloric acid (Chemical pure, 37%) and
ethanol (Chemical pure, 99.5%) were bought from Haochem Chem-
ical Co. Ltd. (Shanghai, PR China).
2.2. Equipments
The UV absorption spectrum of UV-D was measured by a UV-
2501 PC ultraviolet/visible spectrometer. Fourier transform infra-
red (FT-IR) spectrum of UV-D was obtained using a Perkin–Elmer
1 FT-IR spectrometer (Spectral range: 400–4000 cmꢀ1, Resolution:
4 cmꢀ1). 1H NMR spectrum was recorded on a Varian INOVA 400
NMR Spectrometer with tetramethylsilane (TMS) as internal stan-
dard in CDCl3.
2.3. Calculations
Density functional theory (DFT) and time dependent (TD) were
done to determine the optimized geometry and UV absorption
spectra. DFT method is efficiency in geometry optimizations, but
weak in weak interaction energy calculations. Therefore, in this
work, by allowing the relaxation of all the parameters, calculation
has been found to converge to a optimized geometry at B3LYP/6-
31G(d) level, as revealed by the absence of imaginary values in
the calculated wavenumbers of all the vibrational modes, while
the electronic transition energies and electronic transition orbital
were calculated by B3LYP-TD/6-31G(d) method. For the weak
interaction energy analysis, second order Moller–Plesset theory
(MP2) is more reliable than density functional theory. Herein, in
this work, MP2/6-31G(d) was used to perform AIM and NBO
3.2. Synthesis
Fig. 4 shows the synthesis principle of UV-D. To a solution of
AlCl3 (1.47 g, 11 mmol) in 100 mL of chlorobenzene, 3.65 g of
UV-366 (10 mmol) were added at room temperature. The resulting
mixture was heated slowly to 120 °C and stirred at this tempera-
ture for 12 h. After cooling the resulting solution was poured in
150 g of ice and the mixture was acidified to pH 2 with 10% hydro-
chloric acid. Then chlorobenzene was removed from the solution
by reduced pressure distillation. The precipitate was filtered off

102
K. Pei et al. / Journal of Molecular Structure 1032 (2013) 100–104
Fig. 2. Two views of the S0 optimized structure of UV-D at B3LYP/6-31G(d) level. (Bond length in Angstrom, red: O atom, blue: N atom, green: Cl atom, white: H atom, gray: C
atom.) (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
(MAH + 2, 34); Element analysis: Found (%): C, 62.42, H, 3.30, N,
11.46; Calcd (%): C, 62.39, H, 3.31, N, 11.49.
3.3. UV–Vis absorption spectrum
Table
1 lists the B3LYP-TD/6-31G(d) computed electronic
absorption bands, the corresponding electric transition orbital,
and the oscillator strength (f) of UV-D. Fig. 5 presents the absorp-
tion spectrum of UV-D in N,N-dimethyllformamide (DMF) solution
(2 ꢂ 10ꢀ5 mol/L) with the maximum absorption wavelengths indi-
cated above the spectrum, while the theoretical results at B3LYP-
TD/6-31G(d) level are also shown with the bar type. Table 1 shows
that among the calculated electronic transitions above 280 nm
optical region there are three transition-allowed absorption bands
(S0 ? S1, S0 ? S2, S0 ? S6) with the oscillator strength (f) 0.4872,
0.2502, 0.2794 respectively. Table 1 and Fig. 5 show that there
are two strong absorption bands in experimental UV spectrum
which induced by three transition-allowed absorption bands
(S0 ? S1, S0 ? S2, S0 ? S6). The maximum experimental molar
absorption coefficients are about 25,000 L/(mol cm) at 355 nm
and 16,000 L/(mol cm) at 285 nm individually, which agree with
the computation results 27,000 L/(mol cm) at 360 nm and
18,000 L/(mol cm) at 287 nm well. Fig. 6 displays the four orbital
(93, 94, 95 and 96) associated with the S0 ? S1, S0 ? S2, S0 ? S6
electronic transitions. It shows that orbital 93(HOMO-1),
Fig. 3. Absorption spectra of UV-D and the two monomers ClBTZ and HBP at B3LYP-
TD/6-31G(d) level.
and washed with water. The crude product was dissolved in a hot
mixture solvent of water (50 mL) and ethanol (50 mL), and the
undissolved residue was filtered off. The filtrate then was recrys-
tallisation from acetone and afforded 1.63 g (44.7%) of UV-D as a
light yellow solid. FTIR (KBr)/cmꢀ1: 3096 (OH), 1638 (C@O), 703
(CACl); 1H NMR (CDCl3)/ppm: d 11.58 (s, 1H, OHꢁꢁꢁN), 11.45 (s,
1H, OHꢁꢁꢁO), 8.17 (s, 1H, ArAH), 8.06 (d, 1H, ArAH), 7.77 (s, 1H,
ArAH), 7.72 (d, 2H, ArAH), 7.63 (t, 1H, ArAH), 7.49–7.55 (m, 3H,
ArAH), 6.72 (s, 1H, ArAH); MS (m/z, %): 364.1 (MAH, 100), 366.1
94(HOMO), 95(LUMO) and 96(LUMO + 1) are
p orbital. It is clear
from Table 1 and Fig. 6 that the electron density of orbital 93 is
mainly localized on the share part of ClBTZ group and HBP group,
electronic clouds of orbital 94(HOMO,
mainly delocalized on the ClBTZ group, while orbital 96(LUMO + 1,
p
) and 95 (LUMO, p⁄) are

K. Pei et al. / Journal of Molecular Structure 1032 (2013) 100–104
103
HO
Cl
HO
N
N
Cl
Fries Rearrangement
N
N
N
OH
O
N
O
O
UV-D
UV-366
Fig. 4. Synthesis principle of UV-D.
Table 1
B3LYP-TD/6-31G(d) calculated transition states, character, transition orbitals, elec-
tronic transition energies, and oscillator strengths (f) for UV-D.
Transition Character Transition
states orbitals
Transition
energy (eV)
Oscillator
strength (f)
Calc.
Expt. (nm)
p⁄
p⁄
p⁄
p⁄
p⁄
p⁄
p⁄
p⁄
)
)
)
)
)
)
)
)
94 ? 95(0.62) 3.44 (360 nm) 357
94 ? 96(0.61) 3.77 (328 nm)
93 ? 95(0.38) 3.87 (320 nm)
93 ? 95(0.57) 3.90 (318 nm)
92 ? 95(0.62) 4.17 (297 nm)
93 ? 96(0.52) 4.32 (287 nm) 285
91 ? 95(0.53) 4.39 (282 nm)
90 ? 95(0.57) 4.43 (280 nm)
0.4872
0.2502
0.0071
0.0091
0.0087
0.2794
0.0486
0.0115
1
1
1
1
1
1
1
1
S0 ? S1
S0 ? S2
S0 ? S3
S0 ? S4
S0 ? S5
S0 ? S6
S0 ? S7
S0 ? S8
(p
(p
(p
(p
(p
(p
(p
(p
,
,
,
,
,
,
,
,
Fig. 5. UV-D absorption spectrum in DMF (2 ꢂ 10ꢀ5 mol/L) (line) and comparison
Table 2
with the B3LYP-TD/6-31G(d) calculation results (bar).
Structural parameters, NBO and AIM analysis for IMHB in UV-D at MP2//B3LYP/6-
31G(d) level.a
IMHB
r(OAH)b r(OAHꢁ ꢁ ꢁX)b \(OAHꢁ ꢁ ꢁX)c NBOd
AIMe
2q
ð2Þ
/
/
q
i
j
r
DE
to give further insight about IMHB in UV-D, as Table 2 shows.
Hydrogen bond structural parameters are also list in Table 2.
The AIM analysis was performed in this work, because it is well
ij
OAHꢁ ꢁ ꢁN 0.990
OAHꢁ ꢁ ꢁO 0.997
2.628
2.565
144.6
148.1
nN rꢃOAH 31.11 0.0153 1.025
nO rꢃOAH 36.52 0.0180 1.248
known that the electronic density
q
(r) and its Laplacian52 q(r) at
a
NBO and AIM analysis are performed by MP2/6-31G(d) method based on the
the bond critical point (BCP) or ring critical point (RCP) or cage
critical point (CCP), are very useful parameters for estimation of
the relative strength of hydrogen bonding interaction [11–13]. Lar-
B3LYP/6-31G(d) optimized structure.
b
Interatomic distances is in Angstrom unit. r(OAH) is the length of the H-bond.
r(OAHꢁ ꢁ ꢁX) is the distance from X(O or N) to OAH in the OAHꢁ ꢁ ꢁO and OAHꢁ ꢁ ꢁN
hydrogen bonds.
ger
that to UV-D there are two ring critical points OAHꢁ ꢁ ꢁN in ClBTZ
group and Oꢁ ꢁ ꢁOAH in HBP group. In this case, (r) of the two IMHB
are 0.0153 (OAHꢁ ꢁ ꢁN) and 0.0180 (Oꢁ ꢁ ꢁOAH) respectively, which
are in (r) at critical points range [0.002,0.035]. According to the
q(r) value represents stronger bond interaction. AIM indicates
c
\Oꢁ ꢁ ꢁHAO or \Oꢁ ꢁ ꢁHAC angle is in degree.
d
NBO donor orbitals /i; aðc2cÞeptor orbitals /j and their corresponding second-
q
order interaction energies
DEij in kcal/mol.
2q (Laplacian of charge
e
q
(Charge density at the ‘‘3, ꢀ1’’ critical point) and
r
q
density at the critical point) in atomic units.
theory, it is clearly shows there are two hydrogen bonds in UV-D
molecule, and IMHB in HBP part is stronger than that in ClBTZ part
[14–16].
p⁄)’s electronic clouds are mainly delocalized on the HBP group.
Hydrogen bonds are, in general, interpreted to be formed due to
charge transfer from the proton acceptor to the proton donor, and
hence the amount of charge transfer plays a significant role in
determining the elongation and contraction of the Hꢁ ꢁ ꢁY bond (X-
According to the classic view, we assign the intense experimental
357 nm and 285 nm absorption band to the
p ?
p⁄ transition.
Obviously, S0 ? S1 (94 ? 95) transition comes from the ClBTZ part,
S0 ? S2 (94 ? 96) transition is induced by electron transfer from
ClBTZ group to HBP group, and S0 ? S6 (93 ? 96) transition comes
from the HBP part. UV-D has two important UV absorbing chro-
mophores (BZT unit and HBP unit) in one molecule and it maybe
combine the UV absorbance of both chromophores. In fact, as
shown in Fig. 5 and Figs. S1 and S2 (Supporting information),
UV-D has two absorption maxima (kmax) at 285 and 357 nm with
Hꢁ ꢁ ꢁY). Analysis of the NBO second-order interaction energies
ð2Þ
D
E
of these hydðr2oÞ gen-bonding interactions points to a different
ij
interpretation.
_
D
Eij is calculated as
2
jh/ij F j/jij
ð2Þ
D
E
¼
ij
ð
ei
ꢀ Þ
ej
molar extinction coefficients
(
emax
)
of 1.63 ꢂ 104 and
where _F is the Fock operator, and ej correspond to the energy eigen-
2.52 ꢂ 104 L/(mol cm) and shows much stronger and broader
absorbance than some commercial UV absorbers such as UV-320
and UV-531.
values of the donor molecular orbital /i and the acceptor molecular
ð2Þ
orbital /j;
DE
ensures the strength of the donor–acceptor interac-
ij
tion between orbitals /i and /j and appears to be well suited to
examine hydrogen-bonding interactions [17,18]. NBO analysis indi-
3.4. Intramolecular hydrogen bonding (IMHB) interaction
ð2Þ
cates the sum
D
E
of Oꢁ ꢁ ꢁOAH in HBP part is about 36.52 kcal/mol,
ij
ð2Þ
while in ClBTZ part the
D
E
of OAHꢁ ꢁ ꢁN is about 31.11 kcal/mol.
To the synthesized UV-D absorber, there are two intramolecular
hydrogen bonded structures. AIM and NBO analysis are performed
ij
These results clearly show that IMHB in HBP part is stronger than

104
K. Pei et al. / Journal of Molecular Structure 1032 (2013) 100–104
Fig. 6. Molecular orbitals (93, 94, 95 and 96) for the strong absorption bands of UV-D above 280 nm region at B3LYP-TD/6-31G(d) level.
that in ClBTZ part which agrees with the AIM results well. Structure
parameters, AIM and NBO analysis show that the IMHB in HBP part
is stronger than that in ClBTZ part. Obviously, to UV-D, absorption
in UV-A region comes from for ClBTZ part, while absorption in
UV-B region comes from HBP part, and electron transfer from ClBTZ
group to HBP group enhanced UV-A and UV-B absorption ability.
07.050. These data include MOL files and InChiKeys of the most
important compounds described in this article.
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were used to characterize the product. The excellent absorption
of UV-D comes from three electronic transition bands: S0 ? S1
transition absorption associated with ClBZT part mainly, S0 ? S2
absorption associated with electron transfer from ClBTZ part to
HBP part, and S0 ? S6 transition associated with HBP part. Struc-
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group is stronger than that in ClBTZ, and this result can explain
why UV-D can absorb UV-A/B light effectively. This work appears
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Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molstruc.2012.