Photophysical properties of 2,3-dihydroquinazolin-4(1H)-one derivatives

Article abstract of DOI:10.1016/j.jphotochem.2014.07.005

2,3-Dihydroquinazolin-4(1H)-one (DHQ) derivatives were synthesized by treatment of isatoic anhydride with amines and subsequent cyclocondensation with aldehydes or ketones. The derivatives were characterized by ¹H and ¹³C NMR, elemental analysis and HRMS. Absorption and emission spectra of DHQ derivatives were recorded in different solvents (hexadecane, benzene, chloroform, methanol and acetonitrile). Both the absorption and the emission maxima are solvent-dependent and red-shifted. Molar extinction coefficients were determined to be 2364-4820 M^-1 cm^-1. The Stokes shifts of the compounds are large and increase with solvent polarity. This feature and the bathochromic effect shown for the absorption and emission processes indicate that the dipole moment of these fluorescent molecules is higher in the excited state than in the ground state. The fluorescence quantum yield and lifetime were obtained in different solvents for DHQ 4.

Full text of DOI:10.1016/j.jphotochem.2014.07.005

Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 31–37
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Photophysical properties of 2,3-dihydroquinazolin-4(1H)-one
derivatives
Fanny A. Cabrera-Riveraa, Jaime Escalantea,∗, Hugo Morales-Rojasa, David F. Ziglerb,
Robert D. Schmidtb, Lauren E. Jarochab, Malcolm D.E. Forbesb,∗
a Centro de Investigaciones Químicas, UAEM Av. Universidad No. 1001, Col. Chamilpa, C.P. 62209 Cuernavaca, Morelos, Mexico
b Caudill Laboratories, CB #3290, Department of Chemistry, University of North Carolina, Chapel Hill, NC, 27599, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
2,3-Dihydroquinazolin-4(1H)-one (DHQ) derivatives were synthesized by treatment of isatoic anhydride
with amines and subsequent cyclocondensation with aldehydes or ketones. The derivatives were char-
acterized by 1H and 13C NMR, elemental analysis and HRMS. Absorption and emission spectra of DHQ
derivatives were recorded in different solvents (hexadecane, benzene, chloroform, methanol and ace-
tonitrile). Both the absorption and the emission maxima are solvent-dependent and red-shifted. Molar
extinction coefficients were determined to be 2364–4820 M−1 cm−1. The Stokes shifts of the compounds
are large and increase with solvent polarity. This feature and the bathochromic effect shown for the
absorption and emission processes indicate that the dipole moment of these fluorescent molecules is
higher in the excited state than in the ground state. The fluorescence quantum yield and lifetime were
obtained in different solvents for DHQ 4.
Received 1 February 2014
Received in revised form 4 July 2014
Accepted 9 July 2014
Available online 12 August 2014
Keywords:
2,3-Dihydroquinazolin-4(1H)-one
Photophysical properties
Fluorescence
Quantum yield
Lifetime
Molar extinction coefficient
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
quinazolin-4(3H)-ones and 2,3-dihydroquinazolin-4(1H)-ones are
two of the most studied derivatives, where the first compound can
4-Quinazolinones and their derivatives are an important class of
N-heterocycles due to their wide range of interesting biological and
pharmaceutical properties. These include hypnotic, sedative, anal-
gesic, anti-convulsant, anti-tussive, anti-bacterial, anti-diabetic,
anti-inflammatory, anti-tumor activities and others [1]. Among the
easily be converted into the second by oxidation [2] or through free
radical reactions, which can be carried out under UV irradiation [3].
Derivatives of quinazolin-4-one are lesser known dyes and/or
pigments, and their luminescent properties are only minimally
studied. Derivatives that have been reported on include quinazolin-
4(3H)-ones with a styryl a [4] or 2-hydroxyphenyl b [5] moiety at
position 2.
A very important example is the phosphate CPPCQ c, which is
used as fluorogenic substrate in the field of Enzyme-Labeled Fluo-
rescence (ELF). The CPPCQ c is soluble in water and upon enzymatic
cleavage of the phosphate group, this weakly blue-fluorescent sub-
strate yields an extremely photostable yellow–green fluorescent
precipitate (ELF alcohol d), with maximal excitation at 360 nm and
maximal emission at 530 nm [6].
∗
Corresponding authors. Tel.: +52 777 3 29 79 97.
E-mail addresses: jaime@ciq.uaem.mx (J. Escalante), mdef@unc.edu
(M.D.E. Forbes).
http://dx.doi.org/10.1016/j.jphotochem.2014.07.005
1010-6030/© 2014 Elsevier B.V. All rights reserved.

32
F.A. Cabrera-Rivera et al. / Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 31–37
Fluorescent organic molecules have a long history of interest
owing to their potential applications in electronics optic, sensors
[5] and as materials for organic light emitting diodes (OLEDs)
[4]. Certain DHQ derivatives may also have interesting features in
their electronic spectra but their photophysical behavior has not
been extensively studied. Here we report the spectroscopic and
photophysical properties of several 2,3-dihydroquinazolin-4(1H)-
one derivatives.
2.1. Synthesis and characterization
2.1.1. General procedure for the synthesis of aminobenzamides
(GP-1)
A suspension of isatoic anhydride and 1.1 equiv of aryl- or
benzyl-amine in EtOAc was stirred at 40 ◦C or irradiated using
microwave heating equipment. After the reaction was completed,
as indicated by TLC (eluent hexane:EtOAc 6:4), the brown solution
was filtered in a Büchner funnel that had been packed with a layer
of celite and activated charcoal; the colorless solution was then
evaporated under reduced pressure.
2. Material and methods
Measurement of the molar extinction coefficients was carried
out in several solvents at different concentrations (in triplicate)
ranging from 1 to 4 × 10−4 M. An HP 8453 UV/VIS spectropho-
tometer was used to measure the absorbance of the samples. The
molar extinction coefficient was calculated by averaging the slope
of the absorption vs concentration lines for six different mea-
surements. Excitation and emission spectra were collected using
a Perkin-Elmer LS-55 fluorimeter and recorded using solutions
with concentrations between 8 × 10−7 M and 8 × 10−6 M in a 1 cm
cuvette.
2.2. General procedure for the synthesis of
2,3-dihydro-4(1H)-quinazolinones (GP-2)
1.2 equiv of appropriate aldehyde was added to a solution of
aminobenzamide in CH2Cl2. To this, 2–5% by weight of p-TsOH was
added and refluxed. The reactions were carried out in the absence
of light due to possible degradation reactions[3]; the reaction was
monitored by TLC (hexane:EtOAc 6:4). A final straw yellow solution
was obtained and the crude reaction mixture was purified by flash
chromatography eluting with hexane:EtOAc, 9:1–6:4.
Quantum yields were determined by an absolute method using
an integrating sphere[7]; the experiments were carried out on a
FLS920 Fluorescence Spectrometer from Edinburgh Instruments.
The quantum yields were also determined by a comparative
method where one uses a standard that has similar fluorescence
properties as the compound. At least six concentrations in trip-
licate were measured in order of increasing concentration to
obtain the quantum yield of the fluorescence; the samples and
standard were measured under the same environmental con-
ditions and instrumental settings (25 ◦C, Slits 5, ꢀexc 345 nm).
To avoid photodegradation, fresh samples were used for each
measurement.
Fluorescence quantum yields of 4 were measured in different
solvents and were determined by the comparative method using
quinine sulfate as a reference [8,9] and by the integrating sphere
technique [7]. For the comparative method, fluorescence quantum
yields were calculated according to the following equation:
2.3. General procedure for the halogenation reaction (GP-3)
2.1 equiv of Et3N and 2.0–2.27 equiv of Br2 or 4.2 equiv of
NCS was added to a solution of 2,3-dihydro-4(1H)-quinazolinone
(0.34 mmol) in CHCl3 (5 mL). The solution was stirred and heated at
50 ◦C. The colored solution was monitored by TLC (hexane:EtOAc
6:4) until the starting material has completely disappeared. The
reaction mixture was evaporated under reduced pressure and
the crude of reaction was suspended in water (5 mL), which was
extracted with EtOAc (3× 5 mL). The organic layer was dried with
anhydrous sodium sulfate and evaporated. The residue was purified
by flash chromatography eluting with Hex:EtOAc, 9:1–6:4.
3. Results and discussion
3.1. Synthesis
ꢂ
ꢃ
ꢀ
ꢁ
m
n2
n2std
2,3-Dihydroquinazolin-4(1H)-one derivatives 4–7 (Scheme 1)
were synthesized following the methodology previously reported
by our group [10]. The reaction of isatoic anhydride with differ-
ent amines in ethyl acetate yields the aminobenzamides 1–3. As
shown in Scheme 1, cyclocondensation of aminobenzamides with
the appropriate aldehyde in dichloromethane and p-TsOH mono-
hydrate gives the corresponding 2,3-dihydroquinazolin-4(1H)-one.
2,3-Dihydroquinazolin-4(1H)-one 9 was obtained by cyclocon-
densation of 1 with triethyl orthoformate in toluene, followed by
reduction of 8 with 2 equiv of NaBH4 in a 1:1 mixture of THF/MeOH
(Scheme 2).
ꢁF = ꢁF(std)
mstd
where ꢁF and ꢁF(std) are the quantum yields of fluorescence of the
compound and the standard; m are the slopes of the graphs plot-
ted between the integrated areas of the emission spectra and the
absorbances of the samples and the standard; n and nstd are refrac-
tive indexes of solvent of the probe and the reference, respectively
[9b].
The fluorescence lifetimes were recorded on a Fluorescence
Spectrometer model FLS920 (Edinburgh Analytical Instruments)
using the time correlated photon counting (TCSPC) method. A
Nd:YAG laser was used as the excitation source.
The halogenated 2,3-dihydroquinazolin-4(1H)-ones (10 and 11)
were obtained by direct halogenation of 4 with NCS and Br2/Et3N,
respectively (Scheme 3) [11].

F.A. Cabrera-Rivera et al. / Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 31–37
33
O
O
O
R1
R1
R2
R1
H2N
N
O
N
H
NH2
R2CHO
CH2Cl2
p-TsOH
AcOEt
N
H
N
H
O
1, R1 = Bn, 90 %
2, R1 = Ph, 96 %
4, R1 = Bn, R2 = t-Bu, 86 %
5, R1 = Bn, R2 = Ph, 83 %
6, R1 = Ph, R2 = t-Bu, 97 %
7, R1 = p-OMePh, R2 = t-Bu, 94 %
3, R1 = p-MeOPh, 92 %
Scheme 1. Synthesis of 2,3-dihydroquinazolin-4(1H)-one derivatives 4–7.
O
O
O
N
H
NH2
N
HC(OEt)3
N
NaBH4
toluene, 3h
THF/MeOH
N
H
N
2 h
1
8, 98 %
9, 88 %
Scheme 2. Synthesis of 2,3-dihydroquinazolin-4(1H)-one 9.
O
O
O
Cl
Br
N
N
N
Br2/Et3N
NCS
CHCl3
3 h
CHCl3
30 min
50 ºC
N
H
N
H
N
H
50 ºC
Cl
Br
10, 90 %
11, 87 %
4
Scheme 3. Synthesis of 2,3-dihydroquinazolin-4(1H)-ones 10 and 11.
3.2. Photophysical properties
in a blue shift of the absorption and emission band maxima. We
also observe that the molar absorptivities are similar, whereas the
Stokes shift is similar for 4 and 5 but smaller for 9.
We have measured the photophysical properties of 2,3-
dihydroquinazolin-4(1H)-one derivatives 4–7 and 9–11 in chloro-
form. The results are listed in Table 1. All compounds display similar
absorption and emission profiles (Figs. 1 and 2); we notice a small
difference in the absorption band for 6 and emission band for 11:
they are a bit broader than the corresponding bands of other deriva-
tives. The excitation spectra of the 4–7 and 9–11 derivatives are
mirror images of their emission spectra. From their crossing points,
the corresponding energies of the excited singlet states (E0–0) were
On the other hand, substitution of benzyl at position 3 (4) by
phenyl 6 or p-methoxyphenyl 7 results in a small red-shift of the
absorption and emission band maxima, and a small increase of
the Stokes shift, while molar absorptivity increases in the order:
4 < 6 < 7. Compounds 6 and 7 have almost the same absorption and
emission maxima, so they have almost the same Stokes shift. The
presence of an OMe group on the phenyl ring does not alter the
absorption or emission maximum, but it does cause an increase
in the molar absorption coefficient. The absorption and emission
maxima of 10 and 11 are red-shifted in relation to compound 4 as
a result of the presence of halogens at the 6 and 8 positions. The
molar extinction coefficient is also affected by the presence of the
determined to lie between 25,800 and 27,500 cm−1
Comparing compounds 4, 5 and 9 which have different sub-
stituents at position 2, we can see that the substitution of t-Bu at
position 2 of quinazolinone 4 by phenyl 5 or hydrogen 9 results
.
1.1
1.0
1000
DHQ 4
DHQ 5
DHQ 6
DHQ 7
DHQ 9
DHQ 10
DHQ 11
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
DHQ 4
DHQ 5
DHQ 6
DHQ 7
DHQ 9
500
DHQ 10
DHQ 11
0
400
500
300
350
400
Wavelength (nm)
Wavelength (nm)
Fig. 1. Normalized absorption spectra of 4–7, 9–11 in CHCl3.
Fig. 2. Emission spectra for 4–7, 9–11 in CHCl3.

34
F.A. Cabrera-Rivera et al. / Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 31–37
Table 1
Electronic absorption and photoluminescence spectral properties of compounds 4–7, 9–11 in chloroform.
b
Compound
ꢀabs (nm) (FWHM)a
ε (M−1 cm−1
)
ꢀem (nm) (FWHM)a
ꢂꢃstokes (cm−1
)
E0–0 (cm−1
)
ꢁF
( 10%)
4
341 (211,300)
3000
404 (174,840)
4573
27,000
0.055
0.405
5
6
336 (213,900)
344 (175,900)
2900
4130
398 (190,840)
409 (26,600)
4636
4620
27,100
26,800
0.135
0.006
7
344 (196,950)
4820
410 (165,300)
4680
26,700
9
329 (213,750)
357 (203,600)
3070
3720
398 (182,600)
415 (169,820)
5269
3915
27,500
25,900
0.089
0.100
10
11
359 (210,370)
3920
415 (116,880)
3759
25,800
0.002
a
Full-width at half-maximum as measured in wavenumbers.
b
ꢁF Comparative method; SQ ꢁF 0.55 [H2SO4 0.5 M], [12] ꢀexc = 345 nm, 25 ◦C, with a single point.
halogens; it increases in the order 4 < 10 < 11 while the Stokes shift
decreases for DHQ 4 > 10 > 11.
has an appropriate substituent to form a stable free radical, they
can only release the absorbed energy through the photophysical
processes. The ꢁF value is higher for these derivatives. In addi-
tion, derivative 5 has an aromatic ring at position 2, and this also
increases ꢁF.
Fig. 2 shows the fluorescence emission for 4–7, 9–11; the
absorption maxima were used as excitation wavelength to carry
out the emission measurements. As seen in Fig. 2, the strongest
photoluminescence is observed for derivative 5, due to the pres-
ence of the phenyl group at the position 2. Moreover, derivatives 5,
6, 9 and 10 have stronger luminescence than 4, while 7 and 11 have
weaker fluorescence than 4. Due to an internal heavy atom effect,
the weakest luminescence was observed for compound 11.
Finally, fluorescence quantum yields (ꢁF) of DHQ derivatives
vary dramatically throughout these chemical modifications, from
0.43 (the highest value corresponds to 5) to 0.002 for 11 (the low-
est value). Comparing the ꢁF values for 4, 5 and 9, we hypothesize
that the smaller ꢁF value for 4 is due to the elimination photo-
chemical reaction. This seems to imply that photophysical and
photochemical process are competing. Since neither DHQ 5 or 9
Similar to DHQ 4, compounds 6 and 7 are sensitive to light and
therefore have a low fluorescence quantum yield.
For compound 10 we found that the presence of Cl does
not diminish the fluorescence process but rather, we found
that the ꢁF value is higher compared to DHQ 4, probably
due to the fact that DHQ 10 is not as sensitive to light as
compound 4.
On the other hand, the presence of bromine in DHQ 11 prac-
tically inhibits the fluorescence process; the fact that DHQ is less
sensitive to light suggests that state leading to homolytic rupture
between the tert-butyl carbon and the carbon 2 is the excited singlet
state.

F.A. Cabrera-Rivera et al. / Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 31–37
35
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1.1
Hexadecane
1.0
Benzene
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Chloroform
Methanol
Acetonitrile
Hexadecane
Benzene
Chloroform
Methanol
Acetonitrile
300
350
400
Wavelength (nm)
350
400
450
500
550
600
650
Wavelength (nm)
Fig. 3. UV absorption spectra of 4 in different solvents.
Fig. 4. Fluorescence spectra of DHQ 4 in different solvents, 25 ◦C, ꢀexc = 345 nm.
3.3. Solvent dependence
1.0
0.9
To probe the excited state of DHQs further, we examined the
effect of solvent on the absorption and photoluminescent proper-
ties of 3-benzyl-2-tert-butyl-2,3-dihydro-4(1H)-quinazolinone 4.
These results are shown in Table 2. Hexadecane, benzene, chlo-
roform, methanol, and acetonitrile were used to cover a range of
solvent polarity–polarizability (SPP), acidity (SA), and basicity (SB).
The various solvent parameters are listed in Table 2.
Normalized UV spectra of 4 in different solvents are shown in
Fig. 3; where absorption band maxima (ꢀabs) are located between
333 and 344 nm. Here, the absorption band maxima shift to higher
wavelengths (lower energies) as the dielectric constant and H-
bonding ability of the solvent increases. The absorption band of 4 in
methanol is wider than in the other solvents, while the absorption
band in hexadecane is the narrowest.
0.8
Excitation
Emission
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
300
350
400
450
500
550
Wavelength (nm)
The values of the molar extinction coefficient did not change sig-
nificantly between 2900 and 3000 M−1 cm−1 in different solvents.
The bathochromic effect, due to the polarity of the solvent and the
molar extinction coefficient, suggest that the signal corresponds to
a ␲–␲* electron transition. [13]
Fig. 4 shows fluorescence spectra of 4 in different solvents, the
spectral maxima appeared between 381 and 439 nm. In the case of
chloroform and acetonitrile, the emission spectra are almost identi-
cal. Comparing the emission spectra of 4 in different solvents we can
see that they display a significant red shift upon increasing solvent
polarity. This trend indicates an increase in molecular dipole on
going from the ground state (S0) to the lowest singlet excited state
(S1). This is a common photophysical feature of organic compounds
with an electron donor such alkylamino group and an acceptor
moiety such as C O attached to an aromatic ring [14].
Fig. 5. Normalized excitation and emission spectra of
ꢀexc = 335 nm, ꢀem = 404 nm.
4
in chloroform, 25 ◦C,
the Franck–Condon principle and Kasha’s rule for both absorp-
tion and emission (for example, 4 in chloroform). Compound 4
shows large Stokes shifts in the range of 3783–5549 cm−1 (Table 2).
Which increases with emprical solvent polarity and solvent basicity
(Fig. 5). The greater stabilization of the excited state relative to the
ground state with increasing solvent basicity supports the assign-
ment of the excited state as a charge transfer state with an amine
donor.
Also, from the crossing points of the normalized excitation and
emission spectra the corresponding energies of excited singlet were
estimated to lie between 73 and 77 kcal/mol. [15]
Absorption spectra of 4 obtained in different solvents have
the same profile as the excitation spectra, but the absorption
is wider than the excitation band and they show profiles that
are mirror images or their emission spectra, in agrement with
The fluorescence quantum yield using the comparative method
of 4 in CHCl3 and CH3OH were found to be 0.055 and 0.034, respec-
tively. Absolute fluorescence quantum yields in C6H6 and CH3CN
were determined using a calibrated integrating sphere system and
Table 2
Solvent dependent photophysical properties of 4 in different solvents.
Solvent
ꢀabs (nm) (FWHM)a
ε (M−1 cm−1
)
ꢀem (nm) (FWHM)a
ꢂꢃstokes (cm−1
)
E0–0 (cm−1
)
ꢁF
(
10%)
ꢄs (ns)
n-C16H34
C6H6
CHCl3
CH3OH
CH3CN
333 (227,380)
339 (213,790)
341 (221,940)
353 (203,850)
344 (221,640)
–
2971
3012
2919
2906
381 (197,730)
393 (193,900)
404 (169,220)
439 (137,400)
409 (171,470)
3783
4053
4573
5549
4619
27900
25,900
27,000
25,500
26,700
–
4.97
5.11
5.86
5.24
2.43
0.080b
0.055c
0.034c
0.090b
a
Full-width at half-maximum as measured in wavenumbers.
b
c
ꢁF Integrating sphere technique, 25 ◦C.
ꢁF Comparative method; SQ ꢁF 0.55 [H2SO4 0.5 M], [12] ꢀexc = 345 nm, 25 ◦C.

36
F.A. Cabrera-Rivera et al. / Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 31–37
10000
1000
100
Ludox
Hexadecane
Benzene
Methanol
Acetonitrile
Fig. 7. Plot of the absorption and emission maxima as a function of empirical solvent
parameters, where P = 0.53·SPP + 0.09·SA + 0.38SB.
10
20
30
40
Time (ns)
Table 3
Various empirical parameters for solvents used in this study.a
Fig. 6. Fluorescence decay curves and the instrument response function (Ludox).
For excitation, a pulsed laser with a repetition rate of 10 MHz and pulse length of
200 ps (full width half maximum) was used.
Solvent
SPP
SA
SB
b
n-C16H34
C6H6
CHCl3
CH3OH
CH3CN
0.57
0.67
0.79
0.86
0.9
0.09
0.12
0.07
0.55
0.29
0
0
0.05
0.61
0.04
were found to be 0.08 (8%) and 0.09 (9%). The fluorescence life-
time (ꢀs) of 4 was determined using time-correlated single photon
counting (TCSPC), recording at the emission maxima in the cor-
responding solvent. The lifetime of 4 in hexadecane, benzene,
chloroform and methanol was about 5 ns, while in acetonitrile
2.43 ns, the kinetics followed single exponential decay independent
of solvent (Fig. 6).
a
Parameters from Ref. [16b]. SPP is the solvent polarity–polarizability, SA is the
solvent acidity and SB is the solvent basicity.
b
Parameters reported for dodecane.
Closer examination of the solvent effect can provide insight into
the nature of the lowest energy excited state. We can fit the spec-
tral shifts to linear functions of a global solvent parameter, P, using
solvent parameters provided by Catalán et al. [16] (Table 3) and
supplying proportionality constants, (avg. R2 = 0.97). The parame-
ter P, as it applies to 4, is equal to 0.53·SPP + 0.09·SA + 0.38·SB, where
SPP is the solvent polarity-polarizability, SA is the solvent acidity,
and SB is the solvent basicity (Fig. 7). Fits to single solvent param-
eters were generally poor (R2 = 0.6 to 0.8). While the dependence
on solvent polarity supports stabilization of the excited state, the
dependence on solvent basicity suggests a large shift along the atom
coordinate due to elongation of the N H bond in the excited state.
This is consistent with our assignment of lowest excited state as a
CT state.
Table 4
Solvent dependent Photophysical properties of 5–7, 9–11 in different solvents.
Compound
Solvent
ꢀabs (nm)
FWHM (cm−1
)
ε (M−1 cm−1
)
ꢀem (nm)
FWHMa
ꢂꢃstokes (cm−1
)
E0–0 (cm−1
)
5
n-C16H34
C6H6
CHCl3
CH3OH
CH3CN
n-C16H34
C6H6
325
334
336
345
337
337
343
344
356
348
186,943
191,905
213,900
175,580
212,288
178,507
179,439
175,900
179,962
185,308
–
196,094
196,950
172,827
191,124
226,002
221,028
213,750
204,213
217,012
228,657
213,440
203,600
199,563
207,170
226,634
222,083
210,370
205,391
187,692
–
2540
2900
2515
2364
–
3730
4130
3630
3665
–
3600
4820
4014
3300
–
2880
3070
3058
2700
–
2760
3720
3270
2731
–
2985
3920
3810
3070
383
393
398
442
407
388
400
409
449
417
212,230
195,810
190,840
150,927
177,056
189,638
170,736
166,970
156,129
161,840
–
54,620
165,300
149,982
164,637
203,036
189,673
182,600
153,637
143,509
184,673
185,214
169,820
154,832
164,586
186,260
–
4660
4495
4636
6721
5104
3901
4155
4620
5818
4755
–
4240
4680
5646
4405
4713
5079
5269
6839
6082
3695
3599
3915
4927
3968
3427
–
28,063
27,417
27,100
25,490
26,884
27,569
26,912
26,800
25,136
26,189
–
26,413
26,700
25,382
26,251
28,388
27,680
27,500
25,687
25,945
26,600
26,237
25,900
24,857
25,834
26,617
–
6
7
CHCl3
CH3OH
CH3CN
n-C16H34
C6H6
a
a
–
–
342
344
355
348
323
329
329
340
332
350
355
357
367
360
351
356
359
368
360
400
410
444
413
381
395
398
443
416
402
407
415
448
420
399
CHCl3
CH3OH
CH3CN
n-C16H34
C6H6
9
CHCl3
CH3OH
CH3CN
n-C16H34
C6H6
10
11
CHCl3
CH3OH
CH3CN
n-C16H34
C6H6
CHCl3
CH3OH
CH3CN
b
–
415
447
422
116,880
–
160,341
3759
4803
4081
25,800
24,978
25,967
a
The derivative was insoluble and no absorption or emission was observed.
No fluorescence was observed.
b

F.A. Cabrera-Rivera et al. / Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 31–37
37
DHQ derivatives 5–7, 9–11 showed a similar photophysical
behavior in different solvents as the compound 4. The spectral
features are reported in Table 4.
U. S. National Science Foundation for generous support through
grant CHE-1111873. We also thank Dr. Carolina Godoy from CIQ-
UAEM for UV Spectrometer analysis and Dr. M. Kyle Brennaman
from UNC-Chapel Hill for providing fluorescence spectrometer
equipment.
A solvatochromic effect could be observed for these derivatives;
the absorption maximum is between 323 and 368 nm and shifts to
the red as the polarity of the solvent increase. In agreement to the
values obtained from FWHM, the absorption bands of almost all
derivatives are wider in methanol than in other solvents, while the
narrowest absorption bands were found to be in hexadecane.
As seen in Table 4, the molar absorption coefficient ranges
between 2364 and 4820 M−1 cm−1; the highest measured values
for ε were obtained in chloroform.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.jphotochem.2014.07.005.
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and 449; on the other hand, the wider emission bands for almost
all compounds were observed in methanol, the exception being
DHQ 7, in which the very broad emission bands of benzene were
observed and the DHQ 9 in which the widest emission band was
obtained in acetonitrile.
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candidates for deeper investigations.
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We are grateful to CONACYT for financial support (Project
CB2010/151875) and for scholarship to F.A.C.-R. MDEF thanks the