Synthesis and photophysical characterization of novel ESIPT triazinyl-benzazole derivatives

Article abstract of DOI:10.5935/0103-5053.20150148

In this work, the synthesis, characterization and photophysical study of new derivatives of triazinyl-benzazoles with fluorescence by excited-state intramolecular proton transfer (ESIPT) are presented. It regards the synthesis of cyanuric chloride with di

Full text of DOI:10.5935/0103-5053.20150148

http://dx.doi.org/10.5935/0103-5053.20150148
J. Braz. Chem. Soc., Vol. 26, No. 12, 2496-2506, 2015.
Printed in Brazil - ©2015 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Article
A
Synthesis and Photophysical Characterization of Novel ESIPT Triazinyl-Benzazole Derivatives
Fábio S. Grasel,*,a,b Fabiano Barreto,c Louise Janka,c and Valter Stefani*,a
aInstituto de Química, Universidade Federal do Rio Grande do Sul,
CP 15003, 91501-970 Porto Alegre-RS, Brazil
bPrograma de Pós-graduação em Engenharia e Tecnologia de Materiais, Pontifícia Universidade
Católica do Rio Grande do Sul, CP 1429, 90619-900 Porto Alegre-RS, Brazil
cLaboratório Nacional Agropecuário - LANAGRO/RS, Ministério da Agricultura,
Pecuária e Abastecimento, 91780-580 Porto Alegre-RS, Brazil
In this work, the synthesis, characterization and photophysical study of new derivatives of
triazinyl-benzazoles with fluorescence by excited-state intramolecular proton transfer (ESIPT)
are presented. It regards the synthesis of cyanuric chloride with different 2-(2’-hydroxyphenyl)
benzazoles, two quite attractive groups from the synthetic and technological point of view.
These new compounds have several potential applications such as biological markers and new
photoluminescent materials. The derivatives were characterized by 1H and 13C nuclear magnetic
resonance (NMR), Fourier transform infrared spectroscopy (FTIR), high-resolution mass
spectrometry (HRMS), UV-Vis absorption and fluorescence emission. The dyes are fluorescent
by an excited-state ESIPT in the blue-orange region, with a large Stokes’ shift.
Keywords: benzazole, cyanuric chloride, ESIPT, reactive dye, large Stokes’shift, fluorescence
Introduction
agrochemical industry,16-19 anti-bactericides,20-22 and
antimicrobials.23,24 Another important application for TCT
and its derivatives is in the dye industry. These dyes have
a reactive triazinic group that is able to form a covalent
bond with the fibers of several fabrics, mainly cotton.25-28
The hydroxyl, thiol or amino groups present in cellulose
(cotton),25-29 polyamides, or proteins,25,30 respectively, can
substitute the chlorine atoms of TCT. TCT has also been
employed to obtain optical whiteners.31
2,4,6-Trichloro-1,3,5-triazine, also known as cyanuric
chloride (TCT) has been widely studied due to its
synthetic versatility because it is a very reactive molecule
that presents an easily controlled reaction behavior with
nucleophiles (Scheme 1).1-7
Because of this behavior, TCT presents several
applications,suchas:producingnewpolymericmaterials,8-12
as a chiral stationary phase in high-performance liquid
chromatography (HPLC),13 obtaining fluorescent
oligomers,12,14,15 as a precursor of herbicides for the
Polymers, natural fibers and paper tend to darken or
yellow after some time due to the weak absorption of light
in the zone of 400 nm by certain groups: peptides in wool or
3
R
Second substitution at room temperature
Y
Cl
N
First substitution at 0-5 ºC
N
N
Cl
N
1
2
R
R
N
Y
N
Y
Y = N, O
Cl
Third substitution at > 60 ºC
1
2
3
R , R , R = alkyl,
alkenyl, aryl groups
Scheme 1. Differential reactivity of TCT towards nucleophiles.2-4
*e-mail: fsgrasel@gmail.com, vstefani@iq.ufrgs.br

Vol. 26, No. 12, 2015
Grasel et al.
2497
silk, flavonoids in cellulose, and products of decomposition
in polymers.31,32 One of the solutions used to reduce or even
eliminate this effect is to add optical whiteners. They increase
the whiteness of the material by a process of light absorption
in the ultraviolet region (330-380 nm) and posterior emission
of light in the visible region (400-450 nm). These optical
whiteners are obtained from the reaction of the TCT with
chromophore groups and are used in papers, woven fabric,
detergents, soaps and polymers.12,14,25,26,30
Benzazole dyes are a class of chromophores extensively
studied because of their very interesting photophysical
properties.33-39 This class of molecules presents a large
Stokes’ shift due to the intramolecular proton transfer
(ESIPT) mechanism (Scheme 2).33-39
were used for fluorescence and UV-Vis measurements.All the
chemicals were analytical grade and were used as received.
The reactions were monitored by thin layer chromatography
(TLC) on ALUGRAM® SIL Macherey-Nagel silicagel
plates. Dichloromethane was used as eluent and the plates
were visualized under UV light (254-365 nm). The dyes
were purified by column chromatography using silica gel 60
(70-230 mesh ASTM) and dichloromethane. Infrared (IR)
spectra were recorded on a Shimadzu FTIR8300 in nujol.
The 1H and 13C nuclear magnetic resonance (NMR) spectra
were performed at room temperature on an INOVAYH300
using tetramethylsilane (TMS) as the internal standard
and DMSO-d6 as the solvent. The chemical shifts (d) are
reported in parts per million (ppm) relative to TMS. The
coupling constants J are reported in Hz. The following
abbreviations are used for the multiplicities: s (singlet), d
(doublet), dd (double of doublets), t (triplet), q (quartet),
m (multiplet) and br s (broad singlet). UV-Vis absorption
spectra were performed on a Shimadzu UV-1601PC
spectrophotometer. Steady state fluorescence spectra were
measured with a Hitachi spectrofluorometer model F-4500.
Spectrum correction was performed to enable measuring a
true spectrum by eliminating instrumental responses such as
wavelength characteristics of the monochromator or detector
using rhodamine B as a standard (quantum counter). For the
photophysical measurements in the solid state, the samples
were measured using a solid sample holder. In this device, the
light beam irradiated the sample at an angle of approximately
30° and the emitted light from the sample was detected at an
angle of approximately 60°.All experiments were performed
at room temperature in a concentration of 10-6 mol L-1. The
high-resolution mass spectrometry (HRMS) spectra analyses
were performed on a Bruker Reflex III spectrometer or an
Agilent 1100 series liquid chromatograph coupled to anAPI
5000 triple quadrupole mass spectrometer equipped with an
electrospray ionization interface (ESI). Melting points (mp)
were measured with a Gehaka PF 1000 apparatus and are
uncorrected.
Stokes' shift
E*
K*
Keto
emission
Enol
emission
Absorption
K
E
H
H
O
O
N
N
Scheme 2. Photophysical pathways from ESIPT-exhibiting dyes: enol
(or normal) emission (left) and ESIPT (or tautomer) emission (right).
The mechanism of ESIPT provides physical and
chemical properties to this class of molecules that make
them highly attractive from the synthetic, technological
and biological point of view.34-44 Several applications
of this type of molecule are described in the literature,
such as stabilization of polymers against UV radiation,45
fluorescent sensors,43 photoactive materials for organic
light emitting diodes,46,47 molecular switches controlled
by light,48 and optical materials.49 This paper presents the
synthesis, characterization, and photophysical study of new
fluorescent triazinyl-benzazole derivatives which present
excited-state ESIPT.
Synthesis of triazinyl-benzazole derivatives
The dyes 2a-d were prepared using a methodology
previously described in the literature.50 The synthesis of
the monosubstituted triazinyl-derivatives (3a-d) was also
performed as described in recent literature.26 The reaction
consisted of the addition of benzazole-precursors (2a-d) in a
TCT solution in acetone (1:1) containing sodium carbonate
(Na2CO3).The reactions were stirred for 1 hour at 0-5°C.The
synthesis of the disubstituted triazinyl-derivatives (4a-d)
comprised adding the benzazole-precursors (2a-d) in a
TCT solution in acetone (2:1), also at 0-5 °C, containing
Experimental
Materials and methods
The 2,4,6-trichloro-1,3,5-triazine was supplied by
ACROS Organics. Spectroscopic grade solvents (Merck)

2498
Synthesis and Photophysical Characterization of Novel ESIPT Triazinyl-Benzazole Derivatives
J. Braz. Chem. Soc.
Na2CO3. The reactions were stirred for 12 hours at room
temperature. The synthesis of the trisubstituted triazinyl-
derivatives (5a-d) comprised adding the benzazole-
precursors (2a-d) in a TCT solution in acetone (3:1),
also at 0-5 °C, containing Na2CO3. The reactions were
refluxed for 24 hours. The Na2CO3 (10%, m/v) was added
stoichiometrically in relation to the hydrochloric acid
(HCl) formed in the reaction. Distilled water was added
to complete precipitation of the product in the end. The
products were filtered, washed with distilled water, dried
and purified on silica gel columns with dichloromethane
as eluent. The final yields were from 70 to 95%. Scheme 3
presents the synthesis of the triazinyl-benzazole derivatives:
mono (3a-d), di (4a-d) and trisubstituted (5a-d).
1581 ν(C=N), 1502 and 1456 νarom(C=C), 1297 ν(Ar-O),
1241 ν(C−N); H NMR (300 MHz, DMSO-d6) d 11.18
1
(s, 1H, OH), 10.76 (s, 1H, NH), 8.23 (d, 1H, J 2.7 Hz,
phenolic-H), 7.89-7.84 (m, 2H, Ar-H), 7.66 (dd, 1H, J 8.7,
2.7 Hz, phenolic-H), 7.50-7.46 (m, 2H,Ar-H), 7.15 (d, 1H,
J 8.7 Hz, phenolic-H); 13C NMR (75.4 MHz, DMSO-d6)
d 169.8 (C2), 163.8 (C4’a), 162.0 (C4’b and C4’c), 154.8
(C2’), 149.0 (C8), 139.8 (C9), 128.8 (C4’), 126.6 (C5 or C6),
125.2 (C5 or C6), 120.8 (C4), 119.4 (C6’ or C3’), 118.0 (C3’
or C6’), 111.1 (C7), 110.2 (C1’); HRMS (MALDI) m/z,
calcd. for C16H9Cl2N5O2 [M + H]+: 373.0113; found:
373.0127.
2-[4’-(N-4,6-Dichloro-1,3,5-triazin-2-yl)-2’-hydroxyphenyl]
benzothiazole (3c)
2-[4’-(N-4,6-Dichloro-1,3,5-triazin-2-yl)-2’-hydroxyphenyl]
benzoxazole (3a)
Yield 80%; light green solid; mp: decomposed before
melting; IR (nujol) νmax / cm-1: 3451 ν(OH), 3328 ν(NH),
1610 ν(C=N), 1548 and 1461 νarom(C=C), 1235 ν(Ar-O),
Yield 70%; white solid; mp: decomposed before melting;
IR (nujol) νmax / cm-1: 3433 ν(OH), 3298 ν(NH), 1612
ν(C=N), 1533, 1492 and 1452 νarom(C=C), 1232 ν(Ar-O),
1
1180 ν(C−N); H NMR (300 MHz, DMSO-d6) d 11.19
(s, 1H, OH), 10.85 (s, 1H, NH), 8.24 (d, 1H, J 2.7 Hz,
phenolic-H), 7.89-7.85 (m, 2H, Ar-H), 7.72 (dd, 1H,
J 9.0 Hz, phenolic-H), 7.51-7.47 (m, 2H, Ar-H), 7.19 (d,
1H, J 9.0 Hz, phenolic-H); 13C NMR (75.4 MHz, DMSO-d6)
d 169.9 (C2), 164.0 (C4’a), 162.0 (C4’b and C4’c), 155.0 (C2’),
148.8 (C9), 139.8 (C4’), 129.0 (C8), 128.1 (C4), 126.0 (C5 or
C6), 125.3 (C5 or C6), 120.7 (C6’), 119.4 (C7 or C3’), 118.0
(C3’ or C7), 111.4 (C5’), 110.2 (C1’); HRMS (MALDI)
m/z, calcd. for C16H9Cl2N5O2 [M + H]+: 388.9903; found:
388.9905.
1
1184 ν(C−N); H NMR (300 MHz, DMSO-d6), d 11.21
(s, 1H, OH), 10.96 (s, 1H, NH), 7.98 (d, 1H, J 8.7 Hz,
phenolic-H), 7.78-7.88 (m, 2H,Ar-H), 7.66 (d, 1H, J 2.1 Hz,
phenolic-H), 7.42-7.48 (m, 2H, Ar-H), 7.21 (dd, 1H, J 8.7,
2.1 Hz, phenolic-H); 13C NMR (75.4 MHz, DMSO-d6)
d 162.2 (C2), 158.4 (C4’a), 153.9 (C4’b and C4’c), 152.8 (C2’),
148.8 (C8), 142.2 (C4’), 138.8 (C9), 128.2 (C5), 125.8 (C6 or
C6’), 125.3 (C6’ or C6), 119.0 (C4), 112.0 (C3’ or C7), 111.0 (C7
or C3’), 107.8 (C5’), 105.8 (C1’); HRMS (MALDI) m/z, calcd.
for C16H9Cl2N5O2 [M + H]+: 373.0113; found: 373.0125.
2-[5’-(N-4,6-Dichloro-1,3,5-triazin-2-yl)-2’-hydroxyphenyl]
benzothiazole (3d)
Yield 80%; yellow solid; mp: decomposed before
melting; IR (nujol) νmax / cm-1: 3454 ν(OH), 3293
ν(NH), 1595 ν(C=N), 1549, 1502 and 1456 νarom(C=C),
2-[5’-(N-4,6-Dichloro-1,3,5-triazin-2-yl)-2’-hydroxyphenyl]
benzoxazole (3b)
Yield 85%; white solid; mp: decomposed before
melting; IR (nujol) νmax / cm-1: 3453 ν(OH), 3296 ν(NH),
HO
N
(2a) X = O, R = NH , R = H
1 2 2
(2b) X = O, R = H, R = NH
1 2
Β
=
z
2
R
1
2c
) X = S, R = NH , R = H
1
(
2
2
X
2d
) X = S, R = H, R = NH
1
(
2
2
R
2
Cl
Bz
Bz
Bz
(2a-d)
(2a-d)
(2a-d)
N
N
N
N
N
N
N
N
Acetone
Acetone
Acetone
1 h / 0 ºC
12 h / r. t.
24 h / ∆
Cl
N
Cl
Cl
N
Cl
Cl
N
Bz
Bz
N
Bz
(5a) X = O, R = NH, R = H
1 2
3a
(
) X = O, R = NH, R = H
1 2
(4a) X = O, R = NH, R = H
1 2
(1)
(5b) X = O, R = H, R = NH
1 2
(3b) X = O, R = H, R = NH
1 2
4b
(
) X = O, R = H, R = NH
1 2
5c
(
) X = S, R = NH, R = H
1 2
(3c) X = S, R = NH, R = H
1 2
(4c) X = S, R = NH, R = H
1 2
5d
3d
(
(
) X = S, R = H, R = NH
1 2
) X = S, R = H, R = NH
1 2
(4d) X = S, R = H, R = NH
1 2
Scheme 3. Synthesis of mono (3a-d), di (4a-d) and trisubstituted (5a-d) triazinyl-benzazole derivatives.

Vol. 26, No. 12, 2015
Grasel et al.
2499
1
1241 ν(Ar-O), 1194 ν(C−N); H NMR (300 MHz,
DMSO-d6) d 11.09 (s, 1H, OH), 10.90 (s, 1H, NH), 8.41
(d, 1H, J 2.7 Hz, phenolic-H), 7.62-7.58 (m, 2H, Ar-H),
7.60 (dd, 1H, J 9.0, 2.7 Hz, phenolic-H), 7.57-7.52 (m,
2H, Ar-H), 7.13 (d, 1H, J 9.0 Hz, phenolic-H); 13C NMR
(75.4 MHz, DMSO-d6) d 169.9 (C2), 168.9 (C5’a), 163.9
(C5’b or C5’c), 153.8 (C2’), 151.3 (C9), 134.8 (C5’), 129.0 (C8),
127.4 (C5 or C6), 126.7 (C5 or C6), 124.8 (C4), 122.2 (C7 or
C4’), 122.0 (C4’ or C7), 119.8 (C6’), 118.2 (C1’), 117.3 (C3’);
HRMS (MALDI) m/z, calcd. for C16H9Cl2N5O2 [M + H]+:
388.9903; found: 388.9897.
596.0755; HRMS (ESI) m/z, calcd. for C29H18ClN7O2S2
[M – H]-: 594.0573; found: 594.0546.
2,4-Di[2-(5’-aminyl-2’-hydroxphenyl)benzothiazole]-6-
chloro-1,3,5-triazine (4d)
Yield 70%; beige solid; mp: decomposed before
melting; IR (nujol) νmax / cm-1: 3442 ν(OH), 3334 ν(NH),
1605 v(C=N), 1577 and 1502 νarom(C=C), 1260 ν(Ar-O),
1185 ν(C−N); 1H NMR (300 MHz, DMSO-d6) d 8.16 (d,
2H, J 1.8 Hz, 2phenolic-H); 8.01-7.85 (m, 4H, 2Ar-H);
7.58 (br, 2H, 2phenolic-H); 7.43-7.26 (m, 4H, 2Ar-H);
6.68 (br, 2H, 2phenolic-H); HRMS (ESI) m/z, calcd. for
C29H18ClN7O2S2 [M + H]+: 596.0730; found: 596.0732;
HRMS (ESI) m/z, calcd. for C29H18ClN7O2S2 [M – H]-:
594.0573; found: 594.0572.
2,4-Di[2-(4’-aminyl-2’-hydroxphenyl)benzoxazole]-6-chloro-
1,3,5-triazine (4a)
Yield 80%; white solid; mp: decomposed before
melting; IR (nujol) νmax / cm-1: 3454 ν(OH), 3295
ν(NH), 1619 ν(C=N), 1535, 1498 and 1451 νarom(C=C),
2,4,6-Tri[2-(4’-aminyl-2’-hydroxphenyl)benzoxazole]-1,3,5-
triazine (5a)
1
1236 ν(Ar-O), 1180 ν(C−N); H NMR (300 MHz,
DMSO-d6) d 11.46 (s, 2H, 2OH), 10.94 (s, 2H, 2NH),
8.08 (d, 2H, J 8.4 Hz, 2phenolic-H), 7.75 (d, 2H, J 1.8 Hz,
2phenolic-H), 7.72-7.60 (m, 4H, 2Ar-H), 7.44-7.37 (m, 4H,
2Ar-H), 7.14 (dd, 2H, J 8.4, 1.8 Hz, 2phenolic-H); HRMS
(ESI) m/z, calcd. for C29H18ClN7O4 [M + H]+: 564.1187;
found: 564.1191; HRMS (ESI) m/z, calcd. for C29H18ClN7O4
[M – H]-: 562.1030; found: 562.1020.
Yield 75%; white solid; mp: decomposed before
melting; IR (nujol) νmax / cm-1: 3494 ν(OH), 3379 ν(NH),
1641 ν(C=N), 1467 and 1388 νarom(C=C), 1246 ν(Ar-O),
1188 ν(C−N); 1H NMR (300 MHz, DMSO-d6) d 11.63 (s,
3H, 3OH), 7.68 (m, 6H, 3Ar-H and 3H, 3phenolic-H), 7.34
(m, 6H, 3Ar-H), 6.28 (dd, 3H, J 8.8, 2.3 Hz, 3phenolic-H),
6.18 (d, 3H, J 2.3, 3phenolic-H), 6.10 (s, 3H, 3NH); HRMS
(ESI) m/z, calcd. for C16H9Cl2N5O2 [M + H]+: 754.2163;
found: 754.2197; HRMS (ESI) m/z, calcd. for C16H9Cl2N5O2
[M – H]-: 752.2006; found: 752.2026.
2,4-Di[2-(5’-aminyl-2’-hydroxphenyl)benzoxazole]-6-chloro-
1,3,5-triazine (4b)
Yield 80%; white solid; mp: decomposed before
melting; IR (nujol) νmax / cm-1: 3418 ν(OH), 3330
ν(NH), 1616 ν(C=N), 1568, 1524 and 1498 νarom(C=C),
2,4,6-Tri[2-(5’-aminyl-2’-hydroxphenyl)benzoxazole]-1,3,5-
triazine (5b)
1
1235 ν(Ar-O), 1173 ν(C−N); H NMR (300 MHz,
Yield 80%; white solid; mp: decomposed before
melting; IR (nujol) νmax / cm-1: 3457 ν(OH), 3291
ν(NH), 1616 ν(C=N), 1568, 1533 and 1498 νarom(C=C),
DMSO-d6) d 10.59 (s, 2H, 2OH), 10.40 (s, 2H, 2NH), 8.62
(s, 2H, 2phenolic-H), 7.54-7.47 (m, 4H, 2Ar-H), 7.36 (d,
2H, J 8.1 Hz, 2phenolic-H), 7.16-7.28 (m, 4H, 2Ar-H), 7.04
(d, 2H, J 8.1 Hz, 2phenolic-H); HRMS (ESI) m/z, calcd.
for C29H18ClN7O4 [M + H]+: 564.1187; found: 564.1207;
HRMS (ESI) m/z, calcd. for C29H18ClN7O4 [M – H]-:
562.1030; found: 562.1041.
1
1226 ν(Ar-O), 1173 ν(C−N); H NMR (300 MHz,
DMSO-d6) d 11.18 (s, 3H, 3OH), 10.43 (s, 3H, 3NH),
8.62 (d, 3H, J 2.1 Hz, 3phenolic-H), 7.55 (dd, 3H, J 8.7,
2.1 Hz, 3phenolic-H), 7.48 (m, 6H, 3Ar-H), 7.37-7.23 (m,
6H, 3Ar-H), 7.05 (d, 3H, J 8.7 Hz, 3phenolic-H); HRMS
(ESI) m/z, calcd. for C42H27N9O6 [M + H]+: 754.2163;
found: 754.2174; HRMS (ESI) m/z, calcd. for C42H27N9O6
[M – H]-: 752.2006; found: 752.2028.
2,4-Di[2-(4’-aminyl-2’-hydroxphenyl)benzothiazole]-6-
chloro-1,3,5-triazine (4c)
Yield 75%; light green solid; mp: decomposed before
melting; IR (nujol) νmax / cm-1: 3454 ν(OH), 3333 ν(NH),
1609 ν(C=N), 1544 and 1460 νarom(C=C), 1236 ν(Ar-O),
2,4,6-Tri[2-(4’-aminyl-2’-hydroxphenyl)benzothiazole]-1,3,5-
triazine (5c)
1
1180 ν(C−N); H NMR (300 MHz, DMSO-d6) d 11.05
Yield 80%; beige solid; mp: decomposed before
melting; IR (nujol) νmax / cm-1: 3464 v(OH), 3370 ν(NH),
1619 ν(C=N), 1465 and 1371 νarom(C=C), 1193 ν(Ar-O),
1141 ν(C−N); 1H NMR (300 MHz, DMSO-d6) d 11.19 (s,
3H, 3OH), 8.03-7.86 (m, 6H, 3Ar-H), 7.62 (d, 3H, J 8.8 Hz,
3phenolic-H), 7.48-7.30 (m, 6H, 3Ar-H), 6.25-6.22 (dd,
(s, 2H, 2OH), 10.73 (s, 2H, 2NH), 8.26 (d, 2H, J 8.4,
2phenolic-H), 8.19-7.97 (m, 4H, 2Ar-H), 7.72 (d, 2H,
J 1.8 Hz, 2phenolic-H), 7.57-6.93 (m, 4H, 2Ar-H), 7.09
(dd, 2H, J 8.4, 1.8 Hz, 2phenolic-H); HRMS (ESI) m/z,
calcd. for C29H18ClN7O2S2 [M + H]+: 596.0730; found:

2500
Synthesis and Photophysical Characterization of Novel ESIPT Triazinyl-Benzazole Derivatives
J. Braz. Chem. Soc.
1H, J 8.8, 2.3 Hz, 3phenolic-H), 6.15 (d, 3H, J 2.3 Hz,
3phenolic-H), 5.95 (s, 3H, 3NH); HRMS (ESI) m/z, calcd.
for C42H27N9O3S3 [M+H]+: 802.1477; found: 802.1527;
HRMS (ESI) m/z, calcd. for C42H27N9O3S3 [M – H]-:
800.1321; found: 800.1339.
Results and Discussion
Photophysical characterization
Figures 1 to 4 present the normalized UV-Vis absorption
spectra and fluorescence emission of the derivatives 3a-d
in solution. The spectra in the solid state are also presented
for comparison. The relevant spectroscopic data from these
dyes are summarized in Table 1.
The derivatives 3a-d presented an absorption
maximum (λ) in solution in the range of 337 to 355 nm,
while in the solid state the range was from 350 to 398 nm.
The location of the absorption showed a slight dependence
(2-4 nm) on the solvent. This behavior is usually related to
the conformational equilibrium in solution in the ground
state.51-55 The molar absorptivity (ε) according to transitions
of type p→p* and fluorescence quantum yields (φ) showed
results in the range from 1.00 to 5.06 104 L mol-1 cm-1 and
0.003 to 0.061, respectively (Table 1).
2,4,6-Tri[2-(5’-aminyl-2’-hydroxphenyl)benzothiazole]-1,3,5-
triazine (5d)
Yield 75%; beige solid; mp: decomposed before
melting; IR (nujol) νmax / cm-1: 3431 ν(OH), 3300 v(NH),
1603 ν(C=N), 1461 and 1382 νarom(C=C), 1241 ν(Ar-O),
1189 ν(C−N); 1H NMR (300 MHz, DMSO-d6) d 11.74 (s,
3H, 3OH), 10.06 (s, 3H, 3NH), 8.28 (s, 3H, 3phenolic-H),
8.05-7.98 (m, 6H, 3Ar-H), 7.67 (s, 3H, 3phenolic-H),
7.54-7.40 (m, 6H, 3Ar-H), 6.93 (d, 3H, J 8.1 Hz,
3phenolic-H); HRMS (ESI) m/z, calcd. for C42H27N9O3S3
[M+H]+: 802.1477; found: 802.1510; HRMS (ESI) m/z,
calcd. for C42H27N9O3S3 [M – H]-: 800.1321; found:
800.1333.
Figure 1. Normalized UV-Vis absorbance and fluorescence emission
espectra of 3a.
Figure 3. Normalized UV-Vis absorbance and fluorescence emission
espectra of 3c.
Figure 2. Normalized UV-Vis absorbance and fluorescence emission
espectra of 3b.
Figure 4. Normalized UV-Vis absorbance and fluorescence emission
espectra of 3d.

Vol. 26, No. 12, 2015
Grasel et al.
2501
Table 1. Data from UV-Vis absorption and fluorescence emission for derivatives 3a-d
b
ε × 10-4 /
a
c
Dye
Solvent
λ / nm
λ
enol / nm
λ
keto / nm
DλSTenol / nm
DλSTketo / nm
φ
(L mol-1 cm-1)
−
solid state
chloroform
ethyl acetate
acetonitrile
methanol
373
357
357
353
353
350
337
339
337
339
398
354
352
352
352
373
354
355
351
352
−
459
467
470
468
463
492
507
512
508
512
509
500
505
503
498
536
540
549
547
543
−
−
−
−
4.02
3.29
3.11
3.49
−
−
110
113
115
110
−
0.061
0.021
0.010
0.016
−
3a
382
380
379
−
25
27
26
−
solid state
chloroform
ethyl acetate
acetonitrile
methanol
1.22
1.02
1.09
1.00
−
−
−
170
173
171
173
−
0.009
0.010
0.005
0.006
−
3b
375
373
396
−
36
36
57
−
solid state
chloroform
ethyl acetate
acetonitrile
methanol
4.69
4.94
4.80
5.06
−
−
−
146
153
151
146
−
0.043
0.009
0.004
0.011
−
3c
440
393
397
−
88
41
45
−
solid state
chloroform
ethyl acetate
acetonitrile
1.69
1.52
1.54
1.44
−
−
186
194
196
191
0.008
0.005
0.003
0.006
3d
393
402
420
38
51
68
methanol
b
c
aAbsorption maximum; molar absorptivity; fluorescence quantum yields; λenol: emission of the enol tautomer; λketo: emission of the keto tautomer;
DλSTenol: Stokes’ shift for the emission of enol tautomer; DλSTketo: Stokes’ shift for the emission of keto tautomer.
The wavelength of maximum emission in solution for
molecules 3a-d was in the range of 373 to 440 nm for the
enol tautomer and 463 to 549 nm for the keto tautomer. The
first Stokes’ shift in solution was between 25 and 88 nm
(emission of the enol tautomer) and the second one was
between 110 and 196 nm (emission of the keto tautomer).
Depending on the polarity of the solvent, dual fluorescence
emission was observed for all monosubstituted-triazine
derivatives (3a-d). This behavior is related to the
conformational equilibrium in solution in the ground state.
The benzothiazole-derivatives (3c-d) were more sensitive
to the effect of the solvent. The ESIPT mechanism was
hardly observed in methanol, with most of the emission
being due to the enol tautomer (Scheme 1).
Figures 5 to 8 present normalized UV-Vis absorption
spectra and fluorescence emissions of derivatives 4a-d in
solution. The spectra in the solid state are also presented
for comparison. The relevant spectroscopic data from these
dyes are summarized in Table 2.
The derivatives 4a-d presented an absorption maximum
(λ) in solution in the range of 312 to 361 nm, while in
the solid state the range was from 378 to 396 nm. The
location of the absorption showed a slight dependence
(4-10 nm) on the solvent. This behavior is usually related
to the conformational equilibrium in solution in the ground
state.52-56 The molar absorptivity (ε), according to transitions
of the type p→p* and fluorescence quantum yields (φ)
showed results from 0.55 to 2.51 104 L mol-1 cm-1 and 0.006
to 0.226, respectively (Table 2).
The wavelength of maximum emission in solution for
molecules 4a-dwas in the range of 373 to 425 nm for the enol
tautomer and 461 to 571 nm for the keto tautomer. The first
Stokes’shift was between 23 and 73 nm (emission of the enol
tautomer) and the second one was between 110 and 210 nm
(emission of the keto tautomer). Dual fluorescence emission
was observed for disubstituted-triazine derivatives 4a, 4c and
4d depending on the polarity of the solvent. The derivative 4b
did not show any influence of the solvent on the fluorescence
emission. In the analysis of the monosubstituted-triazine
derivatives (3a-d), the benzothiazole-derivatives were more
sensitive to the solvent effect. This effect was not observed
for the disubstituted-derivatives (4a-d). For the disubstituted
group (4a-d), the 4’-derivative (4a and 4c) showed greater
sensitivity to the solvent than the 5’-derivative (4b and 4d).
It is known that having the amino group located in
the meta-position relative to the phenolic hydroxyl group

2502
Synthesis and Photophysical Characterization of Novel ESIPT Triazinyl-Benzazole Derivatives
J. Braz. Chem. Soc.
Figure 5. Normalized UV-Vis absorbance and fluorescence emission
espectra of 4a.
Figure 7. Normalized UV-Vis absorbance and fluorescence emission
espectra of 4c.
Figure 6. Normalized UV-Vis absorbance and fluorescence emission
espectra of 4b.
Figure 8. Normalized UV-Vis absorbance and fluorescence emission
espectra of 4d.
(4’-position) weakens the intramolecular hydrogen bond
when compared to substituted analogs with the same
group in the para-position (5’-position). This behavior is
observed for disubstituted-derivatives (4a-d).56 However,
this behavior was not observed in the monosubstituted-
derivatives (3a-d) because TCT (1), which possesses two
chlorine atoms (electron-withdrawing group by inductive
effect), is bonded in this amino group. The electron density
of the amino group is shifted more to the triazinic ring than
to the phenolic ring due to the electron deficiency of the
cyanuric chloride.
Figures 9 to 12 present the normalized UV-Vis
absorption spectra and fluorescence emission of derivatives
5a-d in solution. The spectra in the solid state are also
presented for comparison. The relevant spectroscopic data
from these dyes are summarized in Table 3.
location of the absorption showed a slight dependence
(4-11 nm) on the solvent. This behavior is usually related
to the conformational equilibrium in solution in the ground
state.51-55 The molar absorptivity (ε), according to transitions
of the type p→p*, and fluorescence quantum yields (φ)
showed results from 1.84 to 13.40 104 L mol-1 cm-1 and
0.003 to 0.048, respectively (Table 3).
The trisubstituted-derivatives (5a-d) showed higher
molar absorptivity (ε) than their mono (3a-d), and
disubstituted (4a-d) analogs. The difference in ε was more
pronounced in the derivatives substituted in the 4’-position
(5a and 5c) than in those substituted in the 5’-position (5b
and 5d). The wavelength of maximum emission in solution
for molecules 5a-d was in the range of 372 to 423 nm for
the enol tautomer and 460 to 558 nm for the keto tautomer.
The first Stokes’shift was between 27 and 65 nm (emission
of the enol tautomer) and the second was between 115 and
201 nm (emission of the keto tautomer), both in solutions.
The behavior presented by the trisubstituted-derivatives
The derivatives 5a-d presented an absorption maximum
(λ) in solution in the range of 334 to 361 nm, while in
the solid state the range was from 374 to 409 nm. The

Vol. 26, No. 12, 2015
Grasel et al.
2503
Table 2. Data from UV-Vis absorption and fluorescence emission for derivatives 4a-d
b
ε ×10-4 /
a
c
Dye
Solvent
λ / nm
λ
enol / nm
λ
keto / nm
DλSTenol / nm
DλSTketo / nm
φ
(L mol-1 cm-1)
−
solid state
chloroform
ethyl acetate
acetonitrile
methanol
378
312
329
336
352
382
346
351
347
349
396
314
333
332
335
388
358
361
357
358
−
461
464
−
−
−
−
1.21
0.56
0.80
0.55
−
375
373
374
379
−
63
44
38
27
−
152
−
0.030
0.226
0.025
0.025
−
4a
446
−
110
−
solid state
chloroform
ethyl acetate
acetonitrile
methanol
523
517
518
515
513
510
500
506
444
−
−
2.15
1.92
1.93
1.60
−
−
−
171
167
168
164
−
0.022
0.016
0.011
0.009
−
4b
391
384
388
−
40
37
39
−
solid state
chloroform
ethyl acetate
acetonitrile
methanol
1.92
1.44
2.51
1.62
−
387
391
389
394
−
73
58
57
59
−
186
173
112
−
0.036
0.036
0.019
0.033
−
4c
solid state
chloroform
ethyl acetate
acetonitrile
557
547
571
560
564
−
1.48
1.39
1.40
1.03
−
−
189
210
203
206
0.009
0.009
0.006
0.006
4d
425
419
425
64
62
67
methanol
b
c
aAbsorption maximum; molar absorptivity; fluorescence quantum yields; λenol: emission of the enol tautomer; λketo: emission of the keto tautomer;
DλSTenol: Stokes’ shift for the emission of enol tautomer; DλSTketo: Stokes’ shift for the emission of keto tautomer.
Figure 9. Normalized UV-Vis absorbance and fluorescence emission
espectra of 5a.
Figure 10. Normalized UV-Vis absorbance and fluorescence emission
espectra of 5b.
(5a-d) was the same presented by the disubstituted-
derivatives (4a-d). The 4’-derivatives (5a and 5c) were more
sensitive to the solvent effect than the 5’-derivatives (5b
and 5d). The derivatives 3a, 4a, 5a, 3c, 4c and 5c, which
have the amino group in the 4’-position, showed a higher
fluorescence quantum yield than their respective analogues
3b, 4b, 5b, 3d, 4d and 5d, which have the amino group
in the 5’-position. The derivatives with the amino group
in the 5’-position (3b, 4b, 5b, 3d, 4d and 5d) also have a
larger Stokes’ shift than their analogues with the amino
group in the 4’-position (3a, 4a, 5a, 3c, 4c and 5c). The
difference in emissions of the keto tautomers were greater
when the molecules were benzothiazole-derivatives rather
than benzoxazole ones.

2504
Synthesis and Photophysical Characterization of Novel ESIPT Triazinyl-Benzazole Derivatives
J. Braz. Chem. Soc.
Figure 11. Normalized UV-Vis absorbance and fluorescence emission
espectra of 5c.
Figure 12. Normalized UV-Vis absorbance and fluorescence emission
espectra of 5d.
Table 3. Data from UV-Vis absorption and fluorescence emission for derivatives 5a-d
b
ε × 10-4 /
a
c
Dye
Solvent
λ / nm
λ
enol / nm
λ
keto / nm
DλSTenol / nm
DλSTketo / nm
φ
(L mol-1 cm-1)
−
solid state
chloroform
ethyl acetate
acetonitrile
methanol
409
345
335
334
336
374
345
351
345
347
378
349
354
352
354
402
357
361
357
358
−
449
460
469
464
−
−
−
−
9.63
13.40
12.47
12.27
−
372
377
377
381
−
27
42
43
45
−
115
134
130
−
0.048
0.019
0.016
0.019
−
5a
solid state
chloroform
ethyl acetate
acetonitrile
methanol
521
511
517
525
521
470
497
499
−
−
2.37
1.98
2.30
1.84
−
−
−
166
166
180
174
−
0.022
0.017
0.013
0.017
−
5b
380
387
387
−
29
42
40
−
solid state
chloroform
ethyl acetate
acetonitrile
methanol
8.52
10.02
9.56
9.82
−
390
393
393
405
−
41
39
41
51
−
148
145
−
0.010
0.007
0.009
0.025
−
5c
−
−
solid state
chloroform
ethyl acetate
acetonitrile
561
554
558
558
557
−
3.08
2.73
2.73
2.51
400
417
411
423
43
56
54
65
197
197
201
199
0.005
0.004
0.003
0.004
5d
methanol
b
c
aAbsorption maximum; molar absorptivity; fluorescence quantum yields; λenol: emission of the enol tautomer; λketo: emission of the keto tautomer;
DλSTenol: Stokes’ shift for the emission of enol tautomer; DλSTketo: Stokes’ shift for the emission of keto tautomer.
Conclusions
and in the solid state). The properties of derivatives with
the amino group in the 5’-position were less affected
by the solvent than their analogues with the amino
group in the 4’-position. The derivatives with the amino
group in the 4’-position presented higher fluorescence
quantum yields than their analogues with the amino
group in the 5’-position. The trisubstituted-derivatives
Novel fluorescent triazinyl-benzazoles prepared by
the ESIPT mechanism were synthesized, purified and
characterized by IR spectroscopy, nuclear magnetic
resonance (13C and H NMR), HRMS, UV-Vis and
steady-state fluorescence spectroscopies (in solution
1

Vol. 26, No. 12, 2015
Grasel et al.
2505
showed the highest molar absorptivity (ε) among the
derivatives studied. The derivatives with an amino group
in the 5’-position exhibited larger Stokes’ shift than
their analogues with an amino group in the 4’-position
of the phenolic ring. This difference was larger in the
benzothiazoles than in the benzoxazoles.
Monosubstituted benzothiazole-derivatives showed
more intense dual fluorescence than monosubstituted
benzoxazole-derivatives. For di and trisubstituted-
derivatives, dual fluorescence emission was more intense in
the derivatives with the amino group in the 4’-position than
their analogues with the amino group in the 5’-position.
The derivative 2,4-di[2-(5’-aminyl-2’-hydroxphenyl)
benzoxazole]-6-chloro-1,3,5-triazine (4b) was the only
one where the fluorescence emission of the keto tautomer
was not affected by the solvent. The novel ESIPT
triazinyl-benzazole derivatives showed very interesting
photophysical properties and are promising molecules that
could be used to obtain new materials, such as fluorescent
sensors and photoluminescent polymers.
11. Wu, H.; Saikia, D.; Chao, H.; Fang, J.; Tsai, L.; Kao, H.;
Electrochim. Acta 2014, 138, 30.
12. Dodangeh, M.; Yousefi, N.; Mohammadian, M.; Dyes Pigm.
2015, 116, 20.
13. Liebes, L.; Conaway, C. C.; Hochster, H.; Mendoza, S.; Hecht,
S. S.; Crowell, J.; Chung, F. L.; Anal. Biochem. 2001, 291, 279.
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17. Chen, K. Y.; Huang, C. T.; Int. J. Appl. Sci. Eng. 2004, 2, 3.
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Supplementary Information
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Supplementary data are available free of charge at
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Acknowledgments
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The authors thank the Programa de Pós-Graduação em
Química of the Universidade Federal do Rio Grande do Sul,
for the support during the period of this research.
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