Synthesis of new 2-(2′-hydroxyaryl)benzotriazoles and evaluation of their photochemical behavior as potential UV-filters

Article abstract of DOI:10.3390/molecules15096205

Two new 2-(2′-hydroxyaryl)benzotriazole derivatives were synthesized and studied by photophysical and photochemical techniques in order to assess their ability to act as UV-filters. The absorption and emission properties of both compounds were determined

Full text of DOI:10.3390/molecules15096205

Molecules 2010, 15, 6205-6216; doi:10.3390/molecules15096205
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis of New 2-(2´-Hydroxyaryl)benzotriazoles and
Evaluation of Their Photochemical Behavior as
Potential UV-Filters
Renata Farkas 1, Virginie Lhiaubet-Vallet 2, Jordi Corbera 3, Mercedesz Törincsi 1,
Olga Gorchs 4, Carles Trullas 4, Oscar Jiménez 4, Miguel A. Miranda 2,* and Lajos Novak 1,*
1
Research Group for Alkaloid Chemistry, Department of Organic Chemistry and Technology,
Budapest University of Technology and Economics, Hungarian Academy of Sciences. Gellért tér 4,
1111 Budapest, Hungary
2
Instituto de Tecnología Química UPV-CSIC, Universidad Politécnica de Valencia, Avda de Los
Naranjos s/n, 46022 Valencia, Spain
3
ESTEVE. Avda. Mare de Déu de Montserrat, 221, 08041 Barcelona, Spain
4
ISDIN. Provençals 33, 08019 Barcelona, Spain
* Authors to whom correspondence should be addressed; E-Mail: lnovak@mail.bme.hu (L.N.);
Tel.: +36 14632207; Fax: +36 14633297; E-Mail: mmiranda@qim.upv.es (M.A.M.);
Tel.: + 34 963877807; Fax: + 34 963877809.
Received: 29 June 2010; in revised form: 23 August 2010 / Accepted: 1 September 2010 /
Published: 3 September 2010
Abstract: Two new 2-(2´-hydroxyaryl)benzotriazole derivatives were synthesized and
studied by photophysical and photochemical techniques in order to assess their ability to
act as UV-filters. The absorption and emission properties of both compounds were
determined in solvents of different polarity. In non polar solvent, a photoinduced excited
state intramolecular proton transfer was established leading to efficient non radiative
dissipation of UV-energy. In addition, the compounds considered were photostable under
irradiation with simulated sunlight.
Keywords: benzotriazoles; benzenediol; UV-filters; UV-stabilizers

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1. Introduction
A number of molecules with intramolecular H-bonds are commercially employed as UV-stabilizers,
due to their strong UV-absorption bands, short excited state lifetimes, and high photostability. An
essential property of UV absorbers is that they possess a mechanism for rapid dissipation of the
absorbed radiation via an appropriate intramolecular rearrangement. Among the best known
chromophores of this type are 2-(2´-hydroxyphenyl)benzotriazole derivatives, and especially 2-(2´-
hydroxy-5´-methylphenyl)benzotriazole (TIN, trade name Tinuvin P) [1], widely used as
UV-stabilizer, or its silylated analog (trade name Mexoryl XL) used as a UV filter [2,3]. The
photostability of these compounds has been attributed to photoinduced excited state intramolecular
proton transfer (ESIPT) leading to an efficient (more than 99%) and rapid non-radiative dissipation of
the harmful UV-energy.
From a mechanistic point of view, the relaxation mechanism involves ESIPT from the S1 state
occurring in the femtosecond timescale [4,5], then radiative decay of the excited keto tautomer
(fluorescence emission with a large Stokes shift) is followed by back proton transfer, causing a return
to the ground state phenol (or enol) form (Scheme 1).
Scheme 1. Non-radiative dissipation of UV-energy by photoinduced excited state
intramolecular proton transfer.
ESIPT
S1
S´1
λ´εm~ 640 nm
hν
S´0
back
S0
ESIPT
In this context, the existence of an intramolecular hydrogen bond is of fundamental importance for
photostability [6]. In the case of TIN, blue fluorescence of the non proton transferred form S1 (λmax ca.
390 nm) and phosphorescence at low temperature have been observed in polar solvents [7-9], where
the intramolecular hydrogen bond is broken in favor of the intermolecular interactions with the solvent,
or when the molecule is distorted or held a non planar conformation [10,11]. In addition, a short-lived
triplet state has been detected for TIN in DMSO by laser flash photolysis experiments performed at
room temperature [12]. By contrast, in non polar solvents blue emission is not observed due to the
strong intramolecular hydrogen bond, which favors formation of the S1´ excited state whose long
wavelength emission is detected at low temperature [7,13]. With this background, the aim of the
present study is to synthesize two derivatives of 2-(2´-hydroxyphenyl)benzotriazole ((Figure 1) and to
study their photophysical and photochemical properties in order to evaluate their ability to act as new
UV-filters.

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Figure 1. Compounds prepared and investigated.
OH
OS
i
N
N
Si
N
OSi
1
HO
HO
N
N
O(CH2)3Si(OEt)3
N
2
2. Results and Discussion
2.1. Synthetic study
Compound 1 was synthesized by a stepwise synthetic protocol shown in Scheme 2. Namely,
compound 3 [14] was heated with methallyl chloride in the presence of K2CO3 and KI to afford ether
4. Thermal rearrangement of the latter in N,N-diethylaniline afforded intermediate 5, which was then
silylated using heptamethyltrisiloxane and Karlstedt catalyst [15,16] to give the wanted product 1 in
good yield.
Scheme 2. Synthesis of 1.
O
OH
N
N
N
N
N
N
a
b
4
3
OH
N
N
N
c
1
5
.
Reagents and Conditions: (a) K2CO3, methallyl chloride; (b) 160 ºC, 6 h; (c) HSiCH3[OSi(CH3)3]2,
Karstedt catalyst.

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Compound 2 was prepared according to Scheme 3. Commercially available o-nitroaniline was
treated with a mixture of NaNO2 and HCl, and the formed diazo compound 7 was coupled with
dibenzyloxyphenol (8) [17]. This reaction gave a 3:1 mixture of isomers 9 and 10. Without separation
the mixture was treated with formamidinesulfinic acid and the formed benzotriazoles 11 and 12 were
separated by fractional crystallization and column chromatography. Compound 11 was subsequently
reacted with NaH and chloropropyl-triethoxy-silane to yield compound 13, from which the benzyl
protective groups were removed by heating with Pd/C and cyclohexene. Product 2 was purified by
column chromatography.
Scheme 3. Synthesis of 2.
OBn
Cl
NH2
NO2
N
N
a
8
OBn
OH
NO2
7
6
9
OBn
OH
N
N
N
N
+
NO2
OBn
NO2
OH
OBn
OBn
10
b
HO
OBn
N
N
N
N
OBn
+
OH
N
N
OBn
OBn
11
12
c
OBn
N
N
d
2
N
O(CH2)3Si(OEt)3
OBn
13
Reagents: (a) NaNO2, HCl; (b) formamidinesulfinic acid; (c) NaH, chloropropyl-triethoxy-silane;
(d) Pd/C, cyclohexene.
2.2. Absorption spectra
The absorption spectra of compound 2 in ethanol showed two maxima, λ1 at ca. 285 nm and λ2 at
ca. 350 nm. As shown in Figure 1, their relative intensity was dependent on the solvent. For example,
in hexane, diethyl ether or acetonitrile, only the UVA absorption band was observed, while in DMSO
or DMF the band at 285 nm was predominating. These results are consistent with the data reported for
the chelated and non chelated forms of TIN and other 2´-hydroxybenzotriazole derivatives [7,9].
Indeed, in solvents with low hydrogen bonding capability, the intramolecular hydrogen bond is intact
and only absorption of the chelated form is observed; by contrast, in solvents where the intramolecular
hydrogen bond is partially disrupted, absorption of the two forms is clearly visible.

Molecules 2010, 15
Figure 2. Absorption spectra of 2 in different solvents (concentration ca. 10-5 M).
6209
0.4
0.2
0.0
DMF
Et2O
Et3N
EtOH
Hexane
MeCN
Pyridine
DMSO
300
350
400
λ, nm
450
500
In the case of compound 1, two absorption maxima, λ1 at ca. 300 nm and λ2 at ca. 350 nm were
also observed; however, by contrast with compound 2 the solvent-dependent spectral changes were not
clearcut (Figure 3). This is probably attributable to overlapping of the absorption bands of the non
chelated form and the hydroxybiphenyl chromophore.
Figure 3. Absorption spectra of 1 in different solvents (concentration ca. 3 × 10-5 M).
0.8
DMF
DMSO
Et2O
0.6
Et3N
EtOH
Hexane
MeCN
Pyridine
0.4
0.2
0.0
300
350
400
λ, nm
450
500
2.3. Fluorescence emission
For compound 2, no emission was observed at room temperature in hexane (data not shown) after
excitation at 350 nm. This is in agreement with previous results reporting only a weak red fluorescence
at low temperature for TIN and other 2´-hydroxybenzotriazole derivatives [7]. Conversely, in polar
solvents after excitation at 280 nm, a blue fluorescence appeared at 410 nm (Figures 4a and 4b). The
corresponding excitation spectra nearly matched the short wavelength absorption band. Thus, taking
into account the literature data and the Stokes shift (9,800 and 10,400 cm-1 in ethanol and DMSO,
respectively), this emission was attributed to the non chelated form of compound 2.

Molecules 2010, 15
Figure 4. Fluorescence emission (λexc = 280 nm) spectra of 2 in DMSO (a) and in ethanol
6210
(b). Inset: corresponding excitation spectra.
2.0
1.5
1.0
0.5
0.0
(a)
(b)
2.0
2.0
2.0
1.5
1.0
0.5
0.0
1.5
1.0
0.5
0.0
1.5
1.0
0.5
0.0
260
280
300
320
λ, nm
260
280
λ, nm
300
320
400
450
500
550
400
450
500
λ, nm
λ, nm
Figure 5. Fluorescence emission spectra of 1 in hexane at λexc = 300 nm (a) and in DMSO
λ
exc = 280 nm (b) and 340 nm (c). Inset: corresponding excitation spectra.
1.0
0.8
0.6
0.4
0.2
0.0
(a)
(b)
0.8
1.0
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
0.6
260
280
300
λ, nm
320
340
280
300
320
340
0.4
0.2
0.0
λ, nm
350
400
450
400
450
500
550
λ, nm
λ, nm
0.5
(c)
0.4
0.3
0.2
0.1
0.0
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
300
320
340
λ, nm
360
380
400
450
500
550
600
650
λ, nm
In the case of the biphenyl derivative 1, an emission band centred at 390 nm was detected in hexane
after excitation at 300 nm; accordingly, the corresponding excitation spectrum exhibited a maximum at
ca. 300 nm (Figure 5a). By contrast, no signal was observed after excitation at 350 nm. In ethanol, no
significant fluorescence was detected after excitation at either of the two wavelengths. In the case of
DMSO, a band centred at 410 nm was observed after excitation at 280 nm (Figure 5b), after excitation

Molecules 2010, 15
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at 340 nm this emission was still observed and, remarkably, a new emission band at 590 nm appeared
(Figure 5c). The excitation spectrum of the latter agreed well with the red shifted fluorescence of the
chelated form previously described in the literature [7].
2.4. Photostability
In order to assess the photostability of compounds 1 and 2, irradiations of 2.7 × 10-5 M solutions
were performed in different solvents and their degradation was followed by UV-Vis spectroscopy.
After 2 hours of irradiation, the UVA-band was decreased by less than 5% (Figure 6). Thus, these
results are similar to those previously reported for TIN and reflect the conservation of the UVA
absorption capability of both compounds, an important property of UV-filters.
Figure 6. UVA-absorption changes after simulated solar irradiation (up to 2 h) of
compound 2 in hexane (a) and ethanol (b). Same experiments with compound 1 in hexane
(c) and ethanol (d).
0.8
(b)
(a)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2 h
0
0.6
0.4
0.2
0.0
320
340
360
380
400
420
320
340
360
380
400
420
λ, nm
λ, nm
0.4
0.2
0.0
(d)
(c)
0.4
0.2
0.0
320
340
360
380
400
420
320
340
360
380
400
420
λ, nm
λ, nm
3. Experimental
3.1. General
Solvents for synthesis were used as received from commercial suppliers, and no further attempts
were made to purify or dry them. Melting points were determined on a Büchi apparatus and are
1
uncorrected. IR spectra were recorded on Bruker Alpha FT Spectrophotometer. H-NMR and 13C-
NMR spectra were obtained on a Bruker DRX-500 spectrometer operating at 500 MHz and 125 MHz,
respectively. All NMR spectra are reported in ppm relative to TMS. MS spectra were conducted on

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Agilent 6140 quadrupole LC/MS instrument. Merck precoated silica gel 60 F254 plates were used for
TLC and Kieselgel 60 for column chromatography.
3.2. Synthesis
2-{4-[(-2-Methyl-2-propen-1-yl)oxy]-3-biphenylyl}-2H-1,2,3-benzotriazole (4). Under an argon
atmosphere, a stirred mixture of 3 (5.0 g, 17 mmol), methallyl chloride (2.7 g, 30 mmol), KI (5.8 g,
35 mmol), and K2CO3 (2.4 g, 17 mmol) in butan-2-one (100 mL) was refluxed for 12 h. After cooling
the precipitate was removed by filtration, the filtrate was concentrated in vacuo, and the resulting solid
was subjected to column chromatography to give a white-yellow solid. Yield: 65% (3.77 g). m.p.
94-96 ºC. Rf = 0.6 (hexane-acetone 5:2). IR (KBr): 1620, 1540, 1500, 1360, 1300, 1280, 1260 cm-1.
1H-NMR (CDCl3): 1.71 (s, 3H, CH3), 4.55 (s, 2H, C1”-H), 4.90 (s, 1H, C3”-H), 5.00 (s, 1H, C3”-H),
7.19 (d, J = 8.7 Hz, 1H, C5’-H), 7.33 (t, J = 8.5 Hz, 1H, C10’-H), 7.43 (m, 2H, C9’-H and C11’-H), 7.45
(m, 2H, C5-H and C6-H), 7.60 (d, J = 8.5 Hz, 2H, C8’-H and C12’-H), 7.70 (dd, J = 8.7 and 2.3 Hz, 1H,
C6’-H), 7.94 (d, J = 2.3 Hz, 1H, C2’-H), 7.98 (m, 2H, C4-H and C7-H). 13C-NMR (CDCl3): 19.17
(CH3), 72.78 (C-1”), 112.90 (C-3”), 114.72 (C-5’), 118.44 (C-4 and C-7), 126.12 (C-2’), 126.82 (C-5,
C-6, C-8’, and C-12’), 127.37 (C-10’), 128.87 (C-9’ and C-11’), 129.28 (C-6’), 130.91 (C-3’), 134.31
(C-1’), 139.33 (C-7’), 139.87 (C-2”), 144.85 (C-3a and C-7a), 152.00 (C-4’). Anal. Calcd for
C22H19N3O: C, 77.40; H, 5.61; N, 12.31. Found: C, 77.14; H, 5.72; N, 12.07.
3-(2H-1,2,3-Benzotriazol-2-yl)-5-(2-methyl-2-propen-1-yl)-4-biphenylol (5). A solution of ether 4
(10.2 g, 30 mmol) in N,N-diethylaniline (50 mL) was heated at reflux for 4 h. After cooling, HCl
(15%, 50 mL) was added and the resulting solution was extracted with CH2Cl2 (3 × 50 mL). The
combined organic extracts were washed with water, evaporated in vacuo, and the residue was
recrystallized from hexane. Yield: 87% (8.9 g, light yellow crystals). m.p. 115-117 ºC. Rf = 0.8
1
(hexane-acetone 5:2). IR (KBr): 3400, 3100, 1620, 1500, 1480, 1450, 1360, 1280 cm-1. H-NMR
(CDCl3): 1.84 (s, 3H, CH3), 3.58 (s, 2H, C1”-H), 4.80 (s, 1H, C3”-H), 4.89 (s, 1H, C3”-H), 7.35
(t, J = 7.5 Hz, C10-H), 7.46 (m, 3H, C6-H, C9-H, and C11-H), 7.49 (m, 2H, C5’-H and C6’-H), 7.67 (d,
J = 8.5 Hz, 2H, C8-H and C12-H), 7.94 (m, 2H, C4’-H and C7’-H), 8.56 (d, J = 2.3 Hz, 1H, C2-H), 11.67
13
(s, 1H, OH). C-NMR (CDCl3): 22.57 (CH3), 38.07 (C-2”), 111.92 (C-3”), 117.67 (C-4’ and C-7’),
117.75 (C-2), 125.39 (C-3), 126.83 (C-8 and C-12), 127.14 (C-10), 127.74 (C-5’ and C-6’), 128.81 (C-
9 and C-11), 129.91 (C-6), 130.10 (C-5), 132.67 (C-1), 139.96 (C-7), 142.82 (C-3a’ and C-7a’),
144.25 (C-2”), 147.52 (C-4). Anal. Calcd for C22H19N3O: C, 77.40; H, 5.61; N, 12.31. Found: C,
77.17; H, 5.82; N, 12.17.
3-(2H-1,2,3-Benzotriazol-2-yl)-5-(2-methyl-3-{1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl}-
propyl)-4-biphenylol (1). To a stirred solution of 5 (2.0 g, 6 mmol) in dry xylene (40 mL) was added
1,1,1,3,5,5,5-heptamethyltrisiloxane (2.5 mL, 2.2 g, 9 mmol) and Karlstedt catalyst (15 drops) and the
resulting mixture was heated at 100 ºC for 5 h. After cooling, the solvent was evaporated in vacuo and
the residue was purified by column chromatography to give compound 1. Yield: 72% (2.4 g), yellow
1
oil. Rf = 0.63 (hexane-acetone 5:02). IR (KBr): 3250 (OH), 1625, 1500, 1250, 1090, 1060 cm-1. H-
NMR (CDCl3): 0.10 (s, 3H, CH3), 0.11 (s, 9H, 3CH3), 0.12 (s, 9H, CH3), 0.56 (dd, J = 14.8 and 9.2 Hz,
1H, C3”-H), 0.78 (dd, J = 14.8 and 4.7 Hz, 1H, C3”-H), 1.05 (d, J = 6.6 Hz, 3H, CH3),

Molecules 2010, 15
6213
2.23 (m, 1H, C2”-H), 2.73 (dd, J = 13.2 and 8.2 Hz, 1H, C1”-H), 2.89 (dd, J = 13.2 and 6.2 Hz, 1H, C1”-
H), 7.38 (t, J = 7.4 Hz, 1H, C10-H), 7.49 (m, 3H, C6-H, C9-H, and C11-H), 7.52 (m, 2H, C5’-H and C6’-
H), 7.71 (d, J = 7.5 Hz, 2H, C8-H and C12-H), 7.98 (m, 2H, C4’-H and C7’-H), 8.57 (d, J = 3.3 Hz, 1H,
13
C2-H), 11.60 (s, 1H, OH). C-NMR (CDCl3): 0.85 (CH3), 1.87 (6CH3), 22.48 (CH3), 26.18 (C-3”),
29.31 (C-2”), 41.27 (C-1”), 117.39 (C-2), 117.66 (C-4’ and C-7’), 125.34 (C-3), 126.83 (C-8 and C-
12), 127.03 (C-10), 127.64 (C-5’ and C-6’), 128.77 (C-9 and C-11), 130.56 (C-6), 132.14 (C-5),
132.34 (C-1), 140.14 (C-7), 142.81 (C-3a’ and C-7a’), 147.66 (C-4). MS (m/z): 563 (M+, 5%), 474
[M+- (CH3)3SiO, 46], 101 (100). Anal. Calcd for C29H41N3O3Si3: C, 61.77; H, 7.33; N, 7.45. Found: C,
61.70; H, 7.52; N, 7.67.
4-(2H-1,2,3-Benzotriazol-2-yl)-3,5-bis(benzyloxy)phenol (11). To a cold (0–5 ºC) suspension of 2-
nitrobenzeneamine (6, 27.62 g, 0.2 mol) in concentrated HCl 100 mL), crashed ice (100g) and water
(100 mL), was added dropwise 5N solution of NaNO2 (41 mL). The resulting mixture was stirred at
5 ºC for 1 h and then filtered. This solution of 7 was then added dropwise to a stirred solution of 3,5-
bis(benzyloxy)phenol (8, 61.3 g, 0.2 mol) in methanol (600 mL). Stirring was continued at room
temperature for 2 h and the precipitated red crystalline compound was collected by filtration to give a
2:1 mixture of isomeric azo compounds 9 and 10. Yield: 88% (80.77 g). m.p. 171-180 ºC. Rf = 0.52
and 0.88 (toluene-MeOH 9:1). To a boiling suspension of the above mixture of azo-compounds
(45.5 g, 0.1 mol) in a mixture of EtOH (250 mL) and 4N NaOH (250 mL) was added
formamidinesulfinic acid (23.65 g, 0.22 mol) during 0.5 h. The resultant mixture was heated with
stirring for 1 h, cooled to room temperature, and then poured into a mixture of ice and water (700 g).
The resulting mixture was acidified with concentrated HCl (80 mL) and extracted with EtOAc. The
organic layer was successively washed with water and brine, and then dried (MgSO4). Evaporation of
the solvent in vacuo afforded a red oil (42 g), which was then treated with a mixture of hexane and
EtOAc (60 mL, each). The precipitated crystalline compounds were collected by filtration and washed
with hexane-acetone (1:1) to give compound 11. Yield: 28% (12.64 g). m.p. 147-152 ºC. Rf = 0.38
1
(toluene-MeOH 9:1) and 0.26 (hexane-EtOAc 2:1). H-NMR (CDCl3): 4.73 (s, 4H, 2OCH2), 6.11 (s,
2H, C2-H and C6-H), 6.98 (m, 4H, 2C2”-H and 2C6”-H), 7.07 (m, 2H, 2C4”-H), 7.10 (m, 4H, 2C3”-H and
2C5”-H), 7.43 (dd, J = 6.7 and 3 Hz, 2H, C5’-H and C6’-H), 7.95 (dd, J = 6.7 and 3 Hz, 1H, C4’-H and
C7’-H), 8.62 (s, 1H, OH). 13C- NMR (CDCl3): 70.31 (OCH2), 94.55 (C-2), 113.03 (C-4), 118.23 (C-4’
and C-7’), 126.61 (C-2” and C-6”), 126.88 (C-5’ and C-6’), 127.65 (C-4”), 128.27 (C-3” and C-5”),
136.01 (C-1”), 144.37 (C-3a’ and C-7a’), 156.00 (C-3 and C-5), 159.99 (C-1). Anal. Calcd for
C26H21N3O3: C, 73.74; H, 5.00; N, 9.92. Found: C, 73.47; H, 5.22; N, 9.67.
The isomer – 2-(2H-1,2,3-benzotriazol-2-yl)-3,5-bis(benzyloxy)phenol (12) – was ISOLATED by
column chromatography From the mother liquor. Yield: 12% (5.4 g). m.p. 71-78 ºC. Rf = 0.73
1
(toluene-MeOH 9:1) and 0.48 (hexane-EtOAc 2:1). H-NMR (CDCl3): 5.04 (s, 2H, OCH2), 5.16 (s,
2H, OCH2), 6.38 (d, J= 2.4 Hz, 1H, C4-H), 6.41 (d, J = 2.4 Hz, 1H, C6-H), 7.25 (t, J = 7 Hz, 1H, C4”-
H), 7.30 (t, J = 7.5 Hz, 2H, C3”-H and C5”-H), 7.35 (t, J = 7.2 Hz, 1H, C4”’-H), 7.39 (m, 4H, C2”-H ,C6”-
H, C3”’-H and C5”’-H), 7.41 (m, 2H, C2”’-H and C6”’-H), 7.45 (dd, J = 6.5 Hz, 2H, C5’-H and C6’-H),
13
7.94 (dd, J = 6.5 Hz, 2H, C4’-H and C7’-H), 9.36 (br. s, 1H, OH). C-NMR (CDCl3): 70.33 (OCH2),
71.28 (OCH2), 95.21 (C-4), 95.81 (C-6), 112.50 (C-2), 117.87 (C-4’ and C-7’), 126.86 (C-2” and C-

Molecules 2010, 15
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6”), 127.23 (C-5’ and C-6’), 127.62 (C-2”’ and C-6”’), 127.77 (C-4”), 128.24 (C-4”’), 128.41 (C-3”
and C-5”), 128.68 (C-3”’ and C-5”’), 136.18 (C-1”’), 136.30 (C-1”), 143.64 (C-3a’ and C-7a’), 152.80
(C-1), 153.67 (C-3), 160.62 (C-5). Anal. Calcd for C26H21N3O3: C, 73.74; H, 5.00; N, 9.92. Found: C,
73.49; H, 5.27; N, 9.72.
2-{2,6-bis(Benzyloxy)-4-[3-(triethoxysilyl)propoxy]phenyl}-2H-1,2,3-benzotriazole (13). To a stirred
suspension of NaH (1.8 g, 60% in mineral oil, 44 mmol) in dry DMF (80 mL) was added dropwise a
solution of compound 11 (16.9 g, 40 mmol) in dry DMF (140 mL). After stirring for 45 min at room
temperature chloropropyl-triethoxy-silane (9.87 g, 40 mmol) and KI (6.43 g, 40 mmol) were added,
and the resultant mixture was heated at 80 ºC for 8 h. After cooling, the reaction mixture was poured
into water (200 mL), extracted with ether (3 × 150 mL), the organic layer was washed with brine, and
then dried (MgSO4). Evaporation of the solvent in vacuo afforded a reddish oil, which was purified by
column chromatography (hexane-EtOAc 5:1 as eluent). Yield: 37% (9.13 g), semi solid. Rf = 0.7
1
(hexane-EtOAc 2:1). H-NMR (CDCl3): 0.79 (m, 2H, CH2-Si), 1.27 (t, J =7 Hz, 9H, 3CH3), 1.93 (m,
2H, CH2), 3.88 (q, J = 7 Hz, 6H, 3 OCH2), 3.92 (t, J = 6.6 Hz, 2H, OCH2), 5.07 (s, 4H, 2OCH2), 6.28
(s, 2H, C3’-H and C5’-H), 7.17 (d, J = 7.5 Hz, 4H, C2”-H and C6”-H), 7.23 (m, 6H, C3”-H, C4”-H, and
C5”-H), 7.44 (dd, J = 6.6 and 3 Hz, 2H, C5-H and C6-H), 8.1 (dd, J = 6.6 and 3 Hz, 2H, C4-H and C7-
H). 13C-NMR (CDCl3): 6.47 (C-Si), 18.30 (CH3), 22.62 (C-C-Si), 58.43 (C-O),70.16 (C-O), 70.57 (C-
O), 93.38 (C-3’ and C-5’), 114.53 (C-1’), 118.47 (C-4 and C-7), 126.29 (C-5 and C-6), 126.52 (C-2”
and C-6”), 127.62 (C-4”), 128.32 (C-3” and C-5”), 136.19 (C-1”), 144.74 (C-3a and C-7a), 156.06 (C-
2’ and C-6’), 161.65 (C-4’). Anal. Calcd for C35H41N3O6Si: C, 66.96; H, 6.58; N, 6.69. Found: C,
67.09; H, 6.29; N, 6.47.
2-(2H-1,2,3-Benzotriazol-2-yl)-5-[3-(triethoxysilyl)propoxy]-1,3-benzenediol (2). A stirred mixture of
compound 13 (2 g, 3.2 mmol), palladium catalyst (1 g, 10% Pd on charcoal), and cyclohexene (64 mL,
52 g, 0.6 mol) in EtOH (80 mL) was heated at reflux for 1.5 h. After filtration, the solvent was
evaporated in vacuo and the residue was purified by column chromatography. Yield: 76% (1.08 g,
1
light yellow crystals). m.p. 69-74 ºC. Rf = 0.27 (CH2Cl2). H-NMR (CDCl3): 0.80 (m, 2H, CH2-Si),
1.27 (t, J = 7 Hz, 9H, 3 CH3), 1.95 (m, 2H, CH2), 3.88 (q, J = 7 Hz, 6H, 3 O-CH2), 4.00 (t, J = 6.6 Hz,
13
2H, CH2), 6.29 (s, 2H, C5-H and C6-H), 7.93 (m, 2H, C4-H and C7-H), 11.56 (s, 2H, OH). C-NMR
(CDCl3): 6.45 (C-Si), 18.29 (CH3), 22.64 (C-2’’), 58.43 (C-O), 70.10 (C-1’’), 95.73 (C-6), 108.17 (C-
2), 116.62 (C-4’ and C-7’), 127.87 (C-5’ and C-6’), 140.18 (C-3a and C-7a), 152.07 (C-1 and C-3),
160.93 (C-5). MS (m/z): 447 (M+, 8 %), 283 [M+-HSi(OEt)3, 12], 256 (17), 124 (100). Anal. Calcd for
C21H29N3O6Si: C, 56.36; H, 6.53; N, 9.39. Found: C, 56.59; H, 6.28; N, 9.49.
3.3. Spectroscopic studies
General
The solvents used were of spectroscopic grade and provided by Sigma and Merck. Absorption
spectra were recorded on a double beam Varian UV-VIS Cary 300 Scan spectrometer, using 10 mm
pathway quartz cuvettes. The steady-state fluorescence experiments were carried out on a Photon
Technology International (PTI) LPS-220B spectrofluorometer. Emission and excitation spectra were

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recorded using 10 × 10 mm2 quartz cells with 4 mL capacity, using air-equilibrated solutions. The
absorbance was adjusted at the excitation wavelength and kept in the range 0.10–0.15. All the
experiments were carried out at room temperature.
3.4. Steady state photolysis
Photolysis of 2.7 × 10-4 M of compounds 1 and 2 were performed to evaluate their photostability in
DMSO, EtOH and hexane. Broadband irradiations of the solutions were carried out using an ABET
Technology solar simulator with a 200 W Xe arc. Its output was adequately filtered to produce a
spectrum approximating natural sunlight (1.5 G air mass filter). The spectral output was measured as
ca 1000 W/m2. The photostability was evaluated by UV-Vis spectroscopy, recording the changes of
the UVA-band.
4. Conclusions
In this work, two new 2-(2´-hydroxyaryl)benzotriazoles were considered as potential UV-filters.
The typical spectroscopic properties of 2´-hydroxybenzotriazole derivatives were obtained for
compound 1, which undergoes a photoinduced excited state intramolecular proton transfer in hexane;
conversely the use of more polar solvents like ethanol or DMSO results in the disruption of the
intramolecular bond. By contrast, no solvent effect was observed for compound 2. Moreover, steady
state photolysis showed that both compounds exhibit a potential applicability as UV filters due to their
UVA-absorption capability and to their photostability.
Acknowledgements
We are grateful to Pal Kolonits and Endre Palosi for the analysis. The financial support for this
investigation provided by ISDIN (Barcelona, Spain) is greatly appreciated. Spanish government was
acknowledged (Ramon y Cajal contract).
References and Notes
1. Crawford, J.C. 2(2-Hydroxy-phenyl)2H-benzotriazole ultraviolet stabilizers. Prog. Polym. Sci.
1999, 24, 7-43.
2. Rastogi, S.C. UV filters in sunscreen products – a survey. Contact Dermatitis 2002, 46, 348-351.
3. Antoniou, C.; Kosmadaki, M.G.; Stratigos, A.J.; Katsambas, A.D. Sunscreens – what’s important
to know. J. Eur. Acad. Dermatol. Venereol. 2008, 22, 1110-1118.
4. Chudoba, C.; Riedle, E.; Pfeiffer, M.; Elsaesser, T. Vibrational coherence in ultrafast excited state
proton transfer. Chem. Phys. Lett. 1996, 263, 622-628.
5. Fournier, T.; Pommeret, S.; Mialocq, J.-C.; Deflandre, A.; Rozot, R. Fentosecond laser studies of
excited state intramolecular proton transfer in an ultraviolet-filter molecule. Chem. Phys. Lett.
2000, 325, 171-175.
6. Otterstedt, J.-E.A. Photostability and molecular structure. J. Chem. Phys. 1973, 58, 5716-5725.

Molecules 2010, 15
6216
7. Woessner, G.; Goeller, G.; Rieker, J.; Hoier, H.; Stezowski, J.J.; Daltrozzo, E.; Neureiter M.;
Kramer, H.E.A. Ultraviolet stabilizers of the 2-hydroxyphenylbenzotriazole class – influence of
the solvent on the absorption spectra and photochemical deactivation mechanism. J. Phys. Chem.
1985, 89, 3629-3636.
8. Wiechmann, M.; Port, H.; Frey, W.; Larmer, F.; Elsaesser, T. Excited-state proton transfer in a
benzotriazole photostabilizer investigated by femtosecond spectroscopy. J. Phys. Chem. 1991, 95,
1918-1923.
9. Huston, A.L.; Scott, G.W. Spectroscopic and kinetic investigations of internally hydrogen-bonded
(hydroxyphenyl)benzotriazoles. J. Phys. Chem. 1987, 91, 1408-1413.
10. Rieker, J.; Lemmert-Schmitt, E.; Goeller, G.; Roessler, M.; Stueber, G.J.; Schettler, H.; Kramer,
H.E.A.; Stezowski, J.J.; Hoier, H.; Henkel, S.; Schmidt, A.; Port, H.; Wiechmann, M.; Rody, J.;
Rytz, G.; Slongo, M.; Birbaum, J.-L. Ultraviolet stabilizers of the 2-(hydroxyphenyl)benzotriazole
class: influence of substituents on structure and spectra. J. Phys. Chem. 1992, 96, 10225-10234.
11. Catalan, J.; Perez, P.; Claramunt, R.M.; Santa Maria, D.; Bobosik, V. On the molecular
conformation of bisaromatic systems. The case of 2-phenyl-2H-benzotriazole. Chem. Phys. 2007,
340, 32-42.
12. Mc Garry, P.F.; Jockusch, S.; Fujiwara, Y.; Kaprinidis, N.A.; Turro, N.J. DMSO solvent induced
photochemistry in highly photostable compounds. The role of intermolecular hydrogen bonding.
J. Phys. Chem. A 1997, 101, 764-768.
13. Woessner, G.; Goeller, G.; Kollat, P.; Stezowski, J.J.; Hauser, M.; Klein, U.K.A.; Kramer, H.E.A.
Photophysical and photochemical deactivation processes of ultraviolet stabilizers of the (2-
hydroxyphenyl)benzotriazole class. J. Phys. Chem. 1984, 88, 5544-5550.
14. Gorchs, O.C.; Alonso, O.J.; Trullas, C.; Ramon, R.; Corbera, A.J.;. Panyella, C.D.; Novak, L.,
Silylated, substituted benzotriazolylphenol compounds. PCT Int. Appl. WO 2008131921 A1, 6
November 2008.
15. Karstedt, B.D. Pt2(divinyltetramethyldisiloxane)3. U.S. Patent 3,814,720, 4 June 1974.
16. Hitchcock, P.B.; Lappert, M.F.; Warhurst, N.J. Synthesis and structure of a rac-
tris(divinyldisiloxane) diplatinum(o) complex and its reaction with maleic anhydride. Angew.
Chem. Int. Ed. Engl. 1991, 30, 438-440.
17. Dean, N.B.; Whalley, W.B. The pigments of “dragon’s blood” resin. Part VI.
3:5dihydroxydiphenyl ether. J. Chem. Soc. 1954, 4638-4641.
Sample Availability: Samples of the compound 1 are available from the authors.
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distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).