Fluorescence analysis of iodinated acetophenone derivatives

Article abstract of DOI:10.1016/j.saa.2014.12.037

In the present paper the synthesis and optical characterization of iodinated acetophenone, 4-hydroxy-3-iodoacetophenone and 4-hydroxy-3,5-diiodoacetophenone obtained from 4-hydroxyacetophenone, were carried out. The optical features of iodinated molecules

Full text of DOI:10.1016/j.saa.2014.12.037

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 139 (2015) 63–67
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Fluorescence analysis of iodinated acetophenone derivatives
a
a
b
b
c
d
F. Crivelaro , M.R.S. Oliveira , S.M. Lima , L.H.C. Andrade , G.A. Casagrande , C. Raminelli
a,
⇑
A.R.L. Caires
a
Grupo de Óptica Aplicada, Universidade Federal da Grande Dourados, CP 533, 79804-970 Dourados, MS, Brazil
Grupo de Espectroscopia Óptica e Fototérmica, Universidade Estadual do Mato Grosso do Sul, CP 351, 79804-970 Dourados, MS, Brazil
Instituto de Química, Universidade Federal de Mato Grosso do Sul, CP 549, 79074-460 Campo Grande, MS, Brazil
b
c
d
Departamento de Ciências Exatas e da Terra, Universidade Federal de São Paulo, Rua Prof. Artur Riedel, 275, Jd. Eldorado, 09972-270 Diadema, SP, Brazil
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
Two iodinated
hydroxyacetophenones were
synthetized from 4-
hydroxyacetophenone.
ꢀ
ꢀ
The optical behavior of these
iodinated compounds was
determined and analyzed.
The optical properties were strongly
altered by the presence of the iodine
atom.
ꢀ
ꢀ
Iodine atoms induced a red shift of
the absorption bands.
Fluorescence quantum yield was also
altered by the iodine atoms.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 June 2014
Received in revised form 25 November 2014
Accepted 10 December 2014
Available online 23 December 2014
In the present paper the synthesis and optical characterization of iodinated acetophenone, 4-hydroxy-3-
iodoacetophenone and 4-hydroxy-3,5-diiodoacetophenone obtained from 4-hydroxyacetophenone, were
carried out. The optical features of iodinated molecules were determined by performing the UV–Vis
absorption, fluorescence and thermal lens spectroscopies. The results showed that the optical properties
of the 4-hydroxyacetophenone is altered when the iodine atom is inserted, as substituent, in the aromatic
ring. Although it was determined that the optical feature was changed when one iodine atom was
inserted in the aromatic ring (4-hydroxy-3-iodoacetophenone), the results revealed that emission behav-
ior was strongly altered when two iodine atoms (4-hydroxy-3,5-diiodoacetophenone) were acting as sub-
stituents: the fluorescence quantum efficiency increases approximately 60%.
Keywords:
Fluorescence
Fluorescence quantum yield
Acetophenone
Iodine
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
intermediates in organic synthesis, especially by Sonogashira and
Suzuki cross-coupling reactions [3,4]. Additionally, iodinated aro-
Iodinated aromatic compounds have been widely used for over
a century. They have been utilized as valuable compounds for
pharmaceutical and agricultural applications due to their antibac-
terial and antifungal properties [1,2]. They have also been used as
matic compounds are also important building blocks used in the
synthesis of biologically active products [5], for instance, being
usually related to the production of new hormone derivatives in
the thyroid gland [6]. In fact, they are widely applied as drugs
and diagnostic agents in medicine [7,8].
As recently reported by Gallo et al. [9], it is possible to obtain
significant yields of iodinated aromatic compounds derived from
4-hydroxyacetophenone under mild reaction conditions. This is
⇑
Corresponding author.
E-mail address: andersoncaires@ufgd.edu.br (A.R.L. Caires).
http://dx.doi.org/10.1016/j.saa.2014.12.037
386-1425/Ó 2014 Elsevier B.V. All rights reserved.
1

6
4
F. Crivelaro et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 139 (2015) 63–67
done by using molecular iodine as an iodine source, aqueous
hydrogen peroxide as a safe and environmentally accepted oxi-
dizer, and water as a nonflammable and innocuous solvent [10].
The 4-hydroxyacetophenone is commonly used in the plastic,
pharmaceutical, agrochemical and cosmetic industries [11]. In
addition to these applications, the 4-hydroxyacetophenone has
been studied by various spectroscopic techniques for presenting
fluorescence, phosphorescence and nonlinear optical properties.
Results obtained by analyzing Raman spectroscopy, infrared,
X-ray diffraction, SERS and theoretical simulations have demon-
strated that 4-hydroxyacetophenone has great potential to be used
in nonlinear optic applications [12,13]. Fluorescence and phospho-
rescence properties of 4-hydroxyacetophenone were also
determined [14,15]. Kearns and Case observed that the phospho-
rescence transitions are directly related to the inter system cross-
ing process (triplet state population) induced by the presence of
substituent groups such as carbonyl groups [14]. In the case of
fluorescence, Catalán and co-workers observed that 4-hydroxyace-
tophenone presented a maximum emission band at 480 nm when
excited at 320 nm. According to the authors, this single emission
band in the visible range corresponds to the formation of an intra-
molecular hydrogen bond [15].
4
MgSO . After filtration, the solvent was evaporated under reduced
pressure. The residue was purified by column chromatography on
silica gel using dichloromethane as eluent, affording #2 and #3
samples in yields of 65% and 15%, respectively.
UV absorption spectra were collected in the 200–400 nm range
by using an absorption spectrophotometer Cary 50 from Varian.
The spectrophotometer has a pulsed xenon lamp, a 0.25 m
Czerny–Turner monochromator and a Si diode detector. The
ꢂ6
samples were diluted in dichloromethane (CH
2
Cl
2
) at 8.8 ꢁ 10
ꢂ1
mol L . All measurements were performed at room temperature
using a quartz cuvette (sample holder) with a 10 mm optical path
length and two polished faces.
Fluorescence measurements were performed on a spectrofluo-
rimeter Cary Eclipse from Varian. A pulsed xenon lamp (80 Hz),
with half the width of the pulse approximately 2 lm and peak
power equivalent to 75 kW, was used as an excitation source.
Two Czerny–Turner monochromators were used for selecting the
excitation and emission wavelengths. The fluorescence signal
was detected using a photomultiplier tube (R928). Emission spec-
tra were collected in the 375–600 nm range when excited at
355 nm and excitation spectra were obtained between 250 and
410 nm when emission signal was detected at 430 nm. The sam-
ꢂ3
4
-Hydroxyacetophenone presents good optical properties and
ples were diluted in dichloromethane (CH
2
Cl
2
) at 4.4 ꢁ 10
ꢂ1
was already extensively studied [12–15]. Nevertheless, to the best
of our knowledge, there is a lack of information concerning the
optical features of the iodinated aromatic compounds obtained
from 4-hydroxyacetophenone. Therefore, due to the importance
of obtaining iodinated aromatic compounds with relevant optical
properties, the present study aimed to synthetize two iodinated
hydroxyacetophenones (4-hydroxy-3-iodoacetophenone and 4-
hydroxy-3,5-diiodoacetophenone) and characterize its optical
properties. UV–Vis absorption, fluorescence and thermal lens spec-
troscopies were performed in order to analyze the optical behavior
of hydroxyacetophenone and iodinated hydroxyacetophenones.
mol L . All measurements were performed at room temperature
using a quartz cuvette (sample holder) with a 10 mm optical path
length and four polished faces.
Thermal lens (TL) transient signal was obtained in the mode-
mismatched experimental setup by using two lasers: an Ar laser
and a HeNe laser operating at kexc = 361 nm and k = 632.8 nm,
p
respectively. The first laser was used to excite the sample in order
to create the TL effect, while the second laser was used to probe the
TL effect. All measurements were performed at room temperature
using a quartz cuvette with a 1 mm optical path length (L) and two
polished faces. The samples were added in the cuvette and then
placed in the beam waist of the pump laser (Ar laser). After the
pump laser energy was absorbed by the sample, a localized change
could be observed in the refractive index due the variation in the
local temperature, which was detected by the probe laser (HeNe
laser).
Materials and methods
Iodinated hydroxyacetophenones were synthetized as previ-
ously reported by Gallo and co-workers [10]. The 4-hydroxyaceto-
phenone (99.99%) was purchased from Sigma–Aldrich (Brazil) and
used as starting material. The 4-hydroxyacetophenone (#1) was
reacted with 1.5 equivalents of iodine and 3 equivalents of hydro-
gen peroxide in water at room temperature for 24 h. 4-hydroxy-3-
iodoacetophenone (#2) and 4-hydroxy-3,5-diiodoacetophenone
Results and discussion
The UV absorption analysis showed that the sample #1 presents
two maximum bands at around 226 and 265 nm, as shown in
⁄
(
#3) were obtained in a very good yields (Scheme 1).
Fig. 1a, which involves
p
?
p
transitions [12]. In the case of both
To a solution of #1 (2.7586 g, 20 mmol) and iodine (7.68 g,
0 mmol) in distilled water (100 mL) was added to hydrogen per-
oxide (6.4 mL of a 30% (w/v) aqueous solution, 60 mmol). The mix-
ture was stirred at room temperature for 24 h. Afterwards, a 10%
w/v) sodium thiosulfate aqueous solution (100 mL) was added
iodinated hydroxyacetophenones, the results revealed a red shift of
these two absorption bands, as presented in Fig. 1b and c. The red
shift may be explained by electron delocalization introduced by
3
the presence of the iodine (substituent). The electron delocaliza-
⁄
(
tion may induce a less antibonding character of the
p
orbital, low-
to the mixture, which was extracted with dichloromethane or
ethyl acetate (3 ꢁ 100 mL). The organic phase was dried over
ering the energy level of this orbital [16]. In addition, it was also
determined a new absorption band at 242 nm for the sample #3.
I
I
1
.5 I2
OH
OH
OH
3
H O , 30%
2
2
O
H2O, r.t.
4h
O
O
2
#1
#2
#3
I
Scheme 1. Synthesis of iodinated hydroxyacetophenones. The studied samples are named as #1, #2 and #3, as indicated in the scheme.

F. Crivelaro et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 139 (2015) 63–67
65
3
75–600 nm range when excited at 355 nm. The results reveal an
enhancement of the fluorescence signal associated with the pres-
ence of the iodine in the molecular structure. In fact, the molecule
containing two iodine atoms (sample #3) presented a higher
enhancement than the molecule with one iodine atom (sample
#2). Additionally, the Stokes shifts were also determined by ana-
lyzing the excitation and emission spectra. As it can be seen in
Fig. 3, the Stokes shift presented a significant change only for the
sample #3 in which the determined values are presented in
Table 1.
Aiming to understand the fluorescence behavior, a close analy-
sis of the fluorescence quantum yield and absorption changes (at
3
55 nm – excitation wavelength) was conducted as follows. Table 2
presents the absorption enhancement ratio at 355 nm and the fluo-
rescence enhancement ratio when excited at 355 nm. It was
obtained by comparing the 4-hydroxyacetophenone and iodinated
hydroxyacetophenones. It is worth pointing out that the fluores-
cence enhancement was determined by calculating the area under
the emission curve. Furthermore, in this analysis, the determina-
tion of the molecular absorption at 355 nm was carried out with
the same concentration used in the fluorescence measurement
ꢂ3
ꢂ1
(
i.e., 4.4 ꢁ 10 mol L ). The results show a similar increase in
the absorption and fluorescence ratios when one iodine atom
was introduced in the molecular structure, where the absorption
and fluorescence ratios increased about 1.8 times. This result
shows that the fluorescence enhancement was only due to the
increase in the absorption. On the contrary, different increases in
the absorption and fluorescence ratios were found when two
iodine atoms were introduced in the molecular structure. It was
found that the fluorescence ratio increase (about 4.30) was higher
than the absorption ratio increase (about 2.9). In this case, the fluo-
rescence enhancement cannot only be attributed to the increase in
the absorption process. It also revealed that fluorescence quantum
Fig. 1. Absorbance of the: (a) 4-hydroxyacetophenone (sample #1); (b) 4-hydroxy-
-iodoacetophenone (sample #2); and (c) 4-hydroxy-3,5-diiodoacetophenone
3
(
sample #3). The samples were diluted in dichloromethane (CH
2
2
Cl )
at
yield (
-hydroxyacetophenone.
For the steady-state fluorescence,
F
U ) increased when two iodine atoms were inserted in the
ꢂ6
ꢂ1
8
.8 ꢁ 10 mol L
.
4
F
U can be conveniently
The origin of the band at 242 nm may be related to the emergence
of a charge transfer band induced by increasing the charge density
caused by the iodine. It is well known that a new charge transfer
band (electron transfer band) may arise when an electron acceptor
substituent is introduced in the aromatic ring [16].
expressed in terms of emission spectrum [17]:
Z
1
F
k
ðk
F
Þdk
F
¼
U
F
ð1Þ
0
In which F
k
ðk Þ represents the distribution of the probability of
F
Fig. 2 shows the fluorescence spectra of the 4-hydroxyaceto-
phenone and iodinated hydroxyacetophenones in the
the transitions from the first excited electronic level to the ground
electronic level. In practical situations, the fluorescence intensity
Fig. 2. Fluorescence intensity of the: (a) 4-hydroxyacetophenone (sample #1); (b)
Fig. 3. Thermal lens characteristic signal to the 4-hydroxyacetophenone (sample
ꢂ3
ꢂ1
4
-hydroxy-3-iodoacetophenone (sample #2); and (c) 4-hydroxy-3,5-diiodoace-
#1) diluted at CH
2
Cl
2
solution (4.4 ꢁ 10 mol L ). The sample was excited at
tophenone (sample #3). The samples were excited at 355 nm and diluted in
361 nm with 90 mW and the TL signal was probed at 632.8 nm with a HeNe laser.
Similar curves were also obtained for samples #2 and #3.
ꢂ3
ꢂ1
dichloromethane (CH
2
Cl
2
) at 4.4 ꢁ 10 mol L
.

6
6
F. Crivelaro et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 139 (2015) 63–67
Table 1
Table 4
Stokes-shift values for samples #1, #2 and #3.
au, u and U determined by interpreting the TL experimental results.
Sample #
Stoke shift (nm)
Sample ratio
a
u
ratio
u
ratio
F
U ratio
1
2
3
29
29
38
#2/#1
#3/#1
1.8
1.2
1.0
0.4
1.0
1.6
theoretical fit curve. It can be noted that after the pump laser is
turned on, the central portion of the probe beam in the far field sig-
nal is strongly reduced (from 1.00 to ꢄ0.915). This indicates that
the heated sample induces a divergence in the probe laser, as
expected when solutions are measured by TL technique. Once the
pump laser is turned off (at t ꢄ 1.0 s), the probe laser signal comes
back to the initial position, which indicates that the TL effect is
reversible and consequently, it does not degrade the sample during
the experimental procedure.
Table 2
Absorbance ratio at 355 nm and fluorescence ratio at 430 nm when excited at
3
55 nm.
Sample ratio
Absorption ratio
Fluorescence ratio
#
#
2/#1
3/#1
1.8
2.9
1.8
4.3
I
F
ðk
F
Þ measured at a wavelength k
F
is proportional to F
k
ðk
F
Þ and to
c
According to the fit, the TL characteristic creation time, t , and
the phase shift created at the sample, h, due the TL effect, which
is proportional to the TL amplitude signal, could be determined.
the absorption-related intensity I
k
A
ðk
E
Þ at the excitation wavelength
E
. Therefore, the F
ðk ; k ; Þ
kI
ðk
k
ðk
F
Þ can be written as:
As usual, by using the obtained t
none sample diluted at CH Cl
c
value for the 4-hydroxyacetophe-
I
F
E
F
ꢂ3
F
k
ðk
F
Þ ¼
ð2Þ
2
2
(t
c
= 1.4 ꢁ 10 s) in the relation
A
E
Þ
2
t
w
(
c
¼ w =4D, together with the value for the excitation beam radius
oe
oe = 23.5 lm, it was possible to calculate the thermal diffusivity
where k is a constant that depends on several experimental param-
eters (i.e., the bandwidth of the excitation and emission monochro-
mators, voltage of the photomultiplier tube, solid angle of
fluorescence collection, etc.) [17]. Consequently, the
expressed by the relationship:
ꢂ3
2
D) for the sample (ꢄ1.0 ꢁ 10 cm /s). This value is slightly higher
than that found by measuring the CH Cl solution without any 4-
hydroxyacetophenone concentration (0.77 ꢁ 10 cm /s from Ref.
19]), and it was similar to all studied samples. This important fact
2
2
ꢂ3
2
U
F
can be
[
guarantees that the thermo-optical properties of the studied sam-
ples, such as thermal conductivity (K) and temperature depen-
dence of the refractive index (dn/dT) are not affected by the
introduction of one or two iodines at 4-hydroxyacetophenone
sample. Therefore, by determining the value of h for the studied
samples it was possible to calculate the product between the
Z
1
1
U
F
¼ kI
I
F
ðk
E
; k
F
; Þdk
F
ð3Þ
A
ðk Þ
E
0
R
1
where
I
F
ðk
E
; k
F
; Þdk
F
is obtained by calculating the area under the
0
emission curve, hereafter represented by A
F
. Therefore, determining
R
6
00
the absorption intensity I
relations between the 4-hydroxyacetophenone and iodinated
-hydroxyacetophenones, as previous presented in Table 2, the
fluorescence quantum yield ratio can be determined by Eq. (4):
A
ðk
E
Þ at 355 nm and A
F
¼
I
F
ðk
E
; k
F
; Þdk
F
375
absorption coefficient,
converted into heat by the sample,
dn/dT) and P is the excitation power.
Table 4 shows the obtained results to the product
ratio between sample #2 and sample #1 and also for sample #3
normalized by sample #1. By normalizing the product by the
a
, and the fraction of the absorbed energy
u
, so h = ( )B with B = (PL/k K)
u
a
p
4
(
au for the
U
Fi
A
A
Fi ꢃ IAn
Fn ꢃ IAi
¼
ð4Þ
U
Fn
au
absorbance ratio values exhibit in Table 2, a ratio between / for
the samples could be calculate and they are also shown in Table 4.
where the i(n) index represents the iodinated (non-iodinated) mol-
ecules. It is important to point out that the k constant possesses the
same value for the iodinated and non-iodinated molecules as the
same experimental setup was used for obtaining both spectra. The
results revealed that
was introduced into the molecular structure, as presented in Table 3.
However, the of the iodinated molecule containing two iodine
atoms was 1.5 higher than the non-iodinated molecule.
In order to check the relationship to the , the TL characteristic
transient signal for the studied samples were determined and fit-
ted by theoretical model proposed by Shen et al. [18]. This model
is based in the fact that the probe signal amplitude is proportional
to the fraction of the absorbed energy converted into heat (
the sample, and it is related to the by the expression
= 1 ꢂ (kexc/<kem>), in which <kem> is the average emission
wavelength. Fig. 3 shows a typical transient signal obtained to
For sample #2/sample #1,
u = 1 indicates that the fraction of
absorbed energy converted into heat for both samples are identi-
cal, suggesting that no difference could be observed in the fluores-
cence quantum efficiencies for these samples. In opposite way, for
F
U did not change when one iodine atom
the sample #3/sample #1 ratio, it was obtained
u = 0.4. This result
U
F
indicates that there is a strong reduction (60%) in the fraction of
absorbed energy converted into heat at the sample #3 when com-
U
F
pared to the sample #1. It can be assumed that this reduction in
u
is an indication that the fluorescence quantum efficiency increases
in the same proportion when the two samples are compared. In
other words, the thermal lens results are indicating that
Fn, which is in good agreement to the values determined above
Table 3) by using the ratio between the fluorescence and absorp-
UFi = 1.6
u) by
U
(
U
F
u
U
F
tion data.
ꢂ3
ꢂ1
the sample #1 diluted at CH
ilar curves were also obtained to the samples #2 and #3. The open
balls are the experimental data and the solid line represents the
2
Cl
2
solution (4.4 ꢁ 10 mol L ). Sim-
Conclusions
The molecular absorption studies shown that iodine atoms, as
substituent in the aromatic ring, induced a red shift of the absorp-
tion bands as well as the emergence of a new band at 242 nm for
the 4-hydroxy-3,5-diiodoacetophenone. The results suggest that
the red shift was caused by the electron delocalization while the
new absorption band at 242 nm was originated by the emergence
of a charge transfer band. In addition to the absorption changes, an
Table 3
Fluorescence quantum yield obtained by calculating the
absorption and fluorescence intensities.
Sample ratio
F
U ratio
#
#
2/#1
3/#1
1.00
1.50

F. Crivelaro et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 139 (2015) 63–67
[3] R. Chinchilla, C. Nájera, Chem. Rev. 107 (2007) 784–922.
67
increase in the fluorescence intensity was also observed for both
[
[
4] N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995) 2457–2483.
5] C. Frota, G.A. Casagrande, L. Pizzuti, C. Raminelli, Curr. Org., Synthesis 10
2013) 265–287.
[6] P. Goswami, S. Ali, M. Khan, A.T. Khan, ARKIVOC xv (2007) 82–89.
7] A. Vibhute, S. Mokle, K. Karamunge, V. Gurav, Y. Vibhute, Chin. Chem. Lett. 21
2010) 914–918.
8] P. Jasminka, K. Laal, M. Zupan, S. Stavber, Aust. J. Chim. 61 (2008) 946–955.
[9] K.S. Gebara, G.A. Casagrande, C. Raminelli, Tetrahedron Lett. 52 (2009) 2849–
852.
10] R.D.C. Gallo, K.S. Gebara, R.M. Muzzi, C. Raminelli, J. Braz. Chem. Soc. 21 (2012)
70–774.
11] C.E.S. Bernardes, M.F.M. Piedade, M.E.M. Piedade, Cryst. Growth Des. 8 (2008)
419–2430.
iodinated acetophenones, the 4-hydroxy-3-iodoacetophenone and
the 4-hydroxy-3,5-diiodoacetophenone. However, our results
(
revealed that the
not change when compared with the 4-hydroxyacetophenone
while for the 4-hydroxy-3-iodoacetophenone the
higher than the non-iodinated molecule. This conclusion was sup-
ported by a close analysis of absorption, fluorescence and thermal
lens data.
F
U of the 4-hydroxy-3-iodoacetophenone did
[
(
U
F
was ꢄ1.55
[
2
[
[
[
7
2
Acknowledgments
12] N. Vijayan, R.R. Babu, M. Gunasekaran, R. Gopolakrishnan, R. Kumaresan, P.
Ramasamy, C.W. Lan, J. Cryst. Growth 249 (2003) 309–315.
We are grateful for financial support from CNPq, CAPES, and
FUNDECT. The authors also acknowledge the support provided by
the National Institute of Science and Technology of Optics and
Photonics (INOF).
[13] D. Sajan, I.H. Joe, V.S. Jayakumar, J. Raman Spectrosc. 37 (2006) 508–529.
[
[
[
14] D.R. Kearns, W.A. Case, J. Am. Chem. Soc. 88 (1966) 5087–5097.
15] J. Catalán, F. Torlblo, A.U. Acuña, J. Phys. Chem. 86 (1982) 303–306.
16] D.L. Pavia, G.M. Lampman, G.S. Kriz, J.R. Vyvyan, Introduction to Spectroscopy,
third ed., Brooks/Cole, Belmont, 2001.
[
17] B. Valeur, Molecular Fluorescence: Principles and Applications, Wiley-VCH,
New York, 2001.
References
[
[
18] J. Shen, R.D. Lowe, R.D. Snook, Chem. Phys. 165 (1992) 385–396.
19] S.E. Bialkowski, Photothermal Spectroscopy Methods for Chemical Analysis,
first Ed., John Wiley-Interscience, New York, 1996.
[
[
1] P. Carniti, S. Colonna, A. Gervasini, Catal. Lett. 137 (2010) 55–62.
2] S. Matsumoto, K. Takase, K. Ogura, J. Org. Chem. 31 (2007) 1726–1731.