Synthesis, characterization, optical properties and theoretical calculations of 6-fluoro coumarin

Article abstract of DOI:10.1016/j.saa.2014.01.123

6-Fluoro coumarin is synthesized and characterized by ¹H NMR and ¹³C NMR. The optical properties of the title compound are investigated by UV-vis absorption and fluorescence emission spectra, the results show the title compound can a

Full text of DOI:10.1016/j.saa.2014.01.123

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 14–20
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization, optical properties and theoretical
calculations of 6-fluoro coumarin
⇑
⇑
Yihui Bai , Jinyan Du, Xuexiang Weng
College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua, Zhejiang 321004, PR China
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
ꢀ
ꢀ
Calculated IR spectra may reproduce
the experimental results.
Description of the largest vibrational
contributed to the normal modes are
given.
ꢀ
ꢀ
ꢀ
Calculated 1H NMR , 13NMR chemical
shifts mainly agree with the
experimental values.
TD-DFT can be used to give precise
simulation of the absorption and
emission spectra.
Theoretical B3LYP/6-311G(d,p)/
B3LYP/Aug-CC-Pvdz calculations are
valid for the structural-similar
compounds.
a r t i c l e i n f o
a b s t r a c t
6-Fluoro coumarin is synthesized and characterized by 1H NMR and 13C NMR. The optical properties of
the title compound are investigated by UV–vis absorption and fluorescence emission spectra, the results
show the title compound can absorb UV–vis light at 319, 269 and 215 nm, moreover it exhibits blue-pur-
ple fluorescence emission at 416 nm. Theoretical studies on molecular structure, infrared spectra (IR),
nuclear magnetic resonance (1H NMR, 13C NMR) chemical shifts, UV–vis absorption and fluorescence
emission of the synthesized compound have been worked out. Most chemical calculations were per-
formed by density functional theory (DFT) method at the B3LYP/6-311G(d,p) level (NMR at B3LYP/
Aug-CC-Pvdz level) using Gaussian 09 program. The compared results reveal that the scaled theoretical
vibrational frequencies are in good accordance with the observed spectra; computational chemical shifts
are consistent with the experimental values in most parts, except for some minor deviations; the UV–vis
absorption calculated matches the experimental one very well, and the fluorescence emission spectrum
is in good agreement with the experimental one when the solute–solvent hydrogen-bonding interaction
is considered. These good coincidences prove that the computational methods selected can be used to
predict these properties of other similar materials where it is difficult to arrive at experimental results.
Ó 2014 Elsevier B.V. All rights reserved.
Article history:
Received 25 August 2013
Received in revised form 17 January 2014
Accepted 26 January 2014
Available online 11 February 2014
Keywords:
6-Fluoro coumarin
DFT calculation
IR
NMR
Absorption
Fluorescence
Introduction
derivatives can be used as intermediates in the manufacture of
agrochemicals and pharmaceuticals with strong anti-bacterium,
Coumarins, known for their pleasant odor, are widely used in
perfumery, foods and beverage manufacture [1,2]. Also coumarin
anti-cancer, anti-HIV activities, etc. [3–8]. Moreover, coumarins
are known to be strongly fluorescent with absorption and emission
phenomena, and can be used as photo luminescent materials
[9,10]. With valuable biological activities, products that contain
fluorinated heteroaromatic moieties get high priority research in
⇑
Corresponding authors. Tel.: +86 57982283702 (Y. Bai).
E-mail addresses: baiyihui@zjnu.cn (Y. Bai), xuexian@zjnu.cn (X. Weng).
http://dx.doi.org/10.1016/j.saa.2014.01.123
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

Y. Bai et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 14–20
15
organofluorine chemistry [11,12]. 6-Fluoro coumarin could be very
Experiments
extensive in application with such a typical structure, which urges
us to explore its chemical and optical behaviors.
The FT-IR spectra of the title compounds diluted in the KBr pel-
lets were recorded on a Thermo Electron Nexus 670 spectropho-
Vibrational spectroscopy especially infrared resonance (IR) and
nuclear magnetic resonance (NMR) techniques are the most pow-
erful methods for the identifications of organic structural groups
[13,14]. Experimental and theoretical studies on the vibrational
spectra and NMR chemical shifts have been proven to be essential
tools for interpretations and predictions of the chemical behaviors
[14,15]. Moreover, the density functional theory (DFT) methods,
combining the hybrid exchange–correlation functional Becke-3-
Lee–Yang–Parr (B3LYP) with the standard 6-311G(d,p) basis set,
yield good and consistent results in most organic molecular analy-
ses [16–20], and the DFT B3LYP/Aug-CC-Pvdz method gives high
accuracy in NMR simulation especially [21–24].
In this paper, 6-fluoro coumarin is synthesized and character-
ized by IR, 1H NMR and 13C NMR. The optical properties of the title
compound are investigated by UV–vis absorption and fluorescence
emission spectra. Calculation on nuclear magnetic resonance (1H
NMR, 13C NMR) chemical shifts have been performed by using
Gaussian 09 program [25] with DFT method at the B3LYP/Aug-
CC-Pvdz level. Theoretical studies on molecular structure, IR,
UV–vis absorption and fluorescence emission of the synthesized
compound have been performed by using Gaussian 09 program
with all the calculations performed by DFT at B3LYP/6-311G(d,p)
level. By comparing the agreement between experimental and cal-
culated results, we can check whether the selected methods are
reliable to forecast the characteristics of other structural-similar
compounds.
tometer in the range of 400–4000 cmÀ1
.
The 1H NMR
measurements of 6-fluoro coumarin were carried out using a Bru-
ker AV600 NMR spectrometer with tetramethylsilane (TMS) as an
internal standard in dimethylsulfoxide-d6 (DMSO-d6). The UV–
vis absorption spectra were carried out on a Perkin Elmer Lambda
950 spectrometer using methanol (MeOH) as solvent, in the con-
centration of 10À5 g/mL. Fluorescence spectrum of 6-fluoro couma-
rin in methanol was recorded with
a Perkin Elmer LS 55
fluorescence spectrometer with a concentration of 10–4 g/mL in
MeOH, the range for recording fluorescence emission was from
360 to 800 nm, and the excitation wavelength was set at 357 nm.
All these spectra were recorded at room temperature.
Computational details
Gaussian 09 software was used in the calculations of geometri-
cal parameters, vibrational frequencies, chemical shifts, UV–vis
absorption and fluorescence emission. All the calculations except
NMR were performed by using DFT/B3LYP method with 6-
311G(d,p) basis set in this study. There are no imaginary frequen-
cies in the results of vibrational analyses, indicating that all the
optimized geometry corresponds to the local minima on potential
energy hypersurface. The calculated vibrational wavenumbers
were scaled with the scale factors [27], yielding good agreements
between calculated assignments and experimental data. Detailed
assignments of the signals for each spectrum were made by
employing the animate vibration function of the Gaussview pro-
gram [28].
Synthesis and experimental methods
The calculations of potential energy distribution (PED) were
done by Gaussian 09 software package with the key word: freq.
intmodes. NMR chemical shifts were calculated at the B3LYP/
Aug-CC-Pvdz level with the gauge including atomic orbital (GIAO)
approach [29–31]. Absolute isotropic magnetic shielding constants
were transformed into chemical shifts by referring to one of the
standard compounds, TMS [32,33]. The calculated shielding con-
stants of TMS is 31.78 ppm for 1H NMR spectra and 192.72 for
13C NMR spectra.
The UV/vis spectra absorption are determined using the con-
ventional Time-Dependent Density Functional Theory (TD-DFT)
procedure on the ground state geometries [34–37]. The emission
from the excited to the ground state, corresponding to a fluores-
cence process is computed with the same procedure but with the
optimized excited-state structure. The solvent effect of methanol
(MeOH) is incorporated by using the conductive polarized contin-
uum model (CPCM) [38,39], comparing with the results of the cal-
culated absorption and emission spectra of the hydrogen-bonded
solute–solvent complex [40,41].
The general synthetic route is shown in Fig. 1. All the chemicals
used were of analytical reagent grade obtained commercially and
used as received without further purification, unless otherwise
stated.
Synthetic steps [26]
0.01 mol of 4-fluorophenol, 0.01 mol of maleic anhydride and
1 mL of concentrated H2SO4 were mixed together. And the mixture
was heated to 150 °C for 1.5 h. After cooling to room temperature,
the reaction solution was diluted with 50 mL of water and ex-
tracted four times with 20 mL of ethyl acetate. The extracted liquid
was dried with anhydrous magnesium sulfate, and then filtered
and concentrated. The obtained crude product was further eluted
and recrystallized from ethyl acetate for several times. Thus, we
got 0.52 g 6-fluoro coumarin and the yield was 32%. 1H NMR
(DMSO, 600 MHz) d: 6.58 (d, J = 9.6 Hz,1H), 7.46(m,1H),
7.50(m,1H), 7.62(m, 1H); 8.04 (d, J = 9.6 Hz, 1H); 13C NMR (DMSO,
600 MHz) d: 114.12, 114.29, 117.88, 118.69, 118.75, 119.56,
119.72, 120.13, 120.20, 143.83, 143.85, 150.34, 150.36,157.69,
Results and discussion
159.28, 160.21; IR (KBr)
t: 584, 887, 916, 1055, 1274, 1261 ,
1441, 1485, 1568, 1591, 1724, 3074 cmÀ1
.
Optimized structures
The optimized structural parameters of 6-fluoro coumarin are
summarized in Table 1, and shown in Fig. 2, using a consistent
atom numbering scheme.
As shown in Table 1, the ranges of CAC bond lengths of 6-fluoro
coumarin are 1.349–1.460 Å. C11AC12 bond length is 1.460 Å,
indicating that it is a single bond. The CAC bond lengths in the aro-
matic ring are 1. 378–1.406 Å, C9AC11 bond length is 1.349 Å,
C4AC9 bond length is 1.441 Å, indicating that C9AC11 bond is a
double bond, while C4AC9 is more like a single bond. The ester
F
O
O
O
H+
O
F
O
OH
Fig. 1. The synthetic route of 6-fluoro coumarin.

16
Y. Bai et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 14–20
Table 1
AC11, which are critical geometry parameters in the ground state,
are À179.973°, 0.006°, and 0.002°, indicating that the benzene and
pyran ring are almost at the same plane.
Optimized parameters of 6-fluoro coumarin.
Geometrical parameters
B3LYP/6-311G(d,p)
Vibrational assignments
Bond length (Å)
Bond length (Å)
R(5,6)
R(5,10)
R(6,15)
R(9,11)
R1
R2
R3
R4
R5
R6
R7
R8
R9
R(1,2)
R(1,6)
R(1,7)
R(2,3)
R(2,8)
R(3,4)
R(3,16)
R(4,5)
R(4,9)
1.388
1.396
1.083
1.394
1.083
1.405
1.365
1.406
1.441
R10
R11
R12
R13
R14
R15
R16
R17
R18
1.378
1.083
1.354
1.349
1.085
1.460
1.081
1.396
1.202
The simulated spectra are shown in Fig. 3. Theoretical (unscaled
and scaled) and experimental vibrational frequencies (cmÀ1), peak
intensities (km molÀ1) and the corresponding assignments for the
vibrational modes are gathered in Table 2.
According to Fig. 3, it is easy to discover that the main absorp-
tion peaks of the calculated spectrum are mainly in accordance
with those of the experimental one, demonstrating that the calcu-
lated results are dependable. Taking into account the satisfactory
agreement between theoretically predicted and experimental
vibrational frequencies, it may be suggested that DFT method with
hybrid B3LYP functional is quite reliable in the prediction of IR
spectra of 6-fluoro coumarin and related compounds.
R(9,13)
R(11,12)
R(11,14)
R(12,16)
R(12,17)
Selected bond angle (°)
Selected bond angle
A(5,4,9)
A1
A2
A3
A4
A5
A6
A(1,2,3)
A(2,3,4)
A(3,4,5)
A(4,5,6)
A(2,3,16)
A(4,3,16)
119.457
A7
A8
A9
A10
A11
A12
123.654
118.573
119.069
126.183
117.962
122.862
121.171
118.942
118.931
117.452
121.378
A(1,6,15)
A(5,6,15)
A(11,12,17)
A(16,12,17)
A(3,16,12)
Selected dihedral angle (°)
Selected dihedral angle (°)
Phenyl ring vibrations
D1
D2
D3
D4
D5
D6
D(1,2,3,4)
0.0001
D7
D(3,4,9,11)
0.0023
The CAH and CAC related vibrations can help to determine the
existence of aromatic rings in a structure. The CAH stretching
vibrations of aromatic structures often occur in the range of
3030–3100 cmÀ1. The CAH in-plane bending vibrations often ap-
pear in the region 1000–300 cmÀ1. And 650–900 cmÀ1 is the
CAH out-of-plane bending vibrational region. It is reported that
the bands of the phenyl C–C stretching vibrations generally appear
at 1450 cmÀ1, 1500 cmÀ1, 1580 cmÀ1, and 1600 cmÀ1 in IR spectra
with variable intensities [42].
D(2,1,6,15)
D(1,2,3,16)
D(2,3,16,12)
D(4,3,16,12)
D(4,5,6,15)
180.000
D8
D9
D10
D11
D12
D(10,5,6,15)
D(4,9,11,12)
D(9,11,12,16)
D(9,11,12,17)
D(17,12,16,3)
0.001
0.011
À0.021
180.029
179.973
À180.000
À180.008
0.006
À180.000
For 6-fluoro coumarin, the aromatic CAH stretching vibrations
appear at 3074 cmÀ1 in the IR spectrum with medium peaks,
Scaled theoretical CAH stretching modes are found at 3065 cmÀ1
.
In IR spectrum, the frequencies 1261 cm-1 are assigned to the
CAH in-plane bending vibrations, and two intensive bands at
820 cmÀ1 and 887 cmÀ1 are expected to be the CAH out-of-plane
bending vibrations. As shown in Table 2, the IR wave numbers
1441 cmÀ1, 1485 cmÀ1, 1568 cmÀ1 and 1591 cmÀ1 are assigned
as the aromatic CAC semicircle stretching vibrations, they are in
agreement with the calculated data except for 1589 cmÀ1, there
is no such vibration in calculated data, the most probable factor
contribute to such a discrepancy is that this vibration is obscured
by the intense (138.13) vibration at 1550 cmÀ1. As shown in Ta-
ble 2, the predicted vibrations assigned to phenyl ring vibrations
are in good accordance with the experimental assignments.
Fig. 2. The calculated molecular structure and atom numbering of 6-fluoro
coumarin.
bonds C12AO16, C12AO17 are 1.396 Å and 1.202 Å, showing the
latter is a double one. The range of CAH bond lengths are 1.083–
1.085 Å. The C6AF15 bond lengths is 1.354 Å. The calculated values
of the CACAC angles in the aromatic ring are around the typical
hexagonal angle of 120°. The calculated values of the dihedral an-
gles of O17AC12AO16AC3, C4AC3AO16AC12 and C3AC4AC9
C@C vibrations of pyran ring
The C@C stretching vibrations often occur in the range of 1620–
1680 cmÀ1; The CAH stretching vibrations of alkene structures
generally appear above 3000 cmÀ1; The bands at 800–840 cmÀ1
attribute to the CAH in-plane bending vibrations; and
100
A
B 100
80
60
40
20
0
80
60
40
20
0
4000 3500 3000 2500 2000 1500 1000 500
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm-1)
Wavenumber (cm-1)
Fig. 3. Calculated and experimental IR spectra of 6-fluoro coumarin (A) (Exp.); (B) (Cal.).

Y. Bai et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 14–20
17
Table 2
Comparison of theoretical and experimental vibrational parameters.
Exp. IR (cmÀ1
)
Calculated (cmÀ1
)
Assignments, PEDb (>10%)
Freq. (cmÀ1
)
Inte. (km/mol)
Unscaled
Scaleda
584
820
864
588
832
885
568
804
856
20.47
58.16
50.82
100.56
104.39
3.21
29.34
27.49
62.16
rring(90.5)
c
c
t
t
ring(11.7),
ring(24.7),
CAO(13.2)
ring(33.2)
c
c
CAH(88.3)
CAH(74.4)
887
907
877
1055
1097
1138
1151
1261
1091
1130
1171
1187
1274
1055
1093
1132
1147
1231
bCAH(11.6,12.0)
bCAH(12.9,11.6)
bCAH(9.8,11.7)
t
ring(18.7), tCAF(6.3),
bring(26.8), b = CAH(19.5)
bring(18.1), b = CAH(54.0)
1274
1441
1485
1568
1591
1624
1724
3074
1275
1472
1511
1603
1232
1423
1461
1550
102.11
70.84
57.26
t
t
t
CAC(Ph-ring) (16.1)
CAC(Ph-ring) (16.3)
CAC(Ph-ring) (36.8)
138.13
1667
1806
3170
1611
1746
3065
15.53
711.88
6.54
t
t
t
CAC(Ph-ring) (16.3)
CAC(11.9),
tC@O(22.6)
CAH(63.9,11.4)
a
With the scale factor of 0.9668.
b
t
, Stretching; b, in-plane-bending; c, out-of-plane bending; and r, scissoring.
675–730 cmÀ1 is the CAH out-of-plane bending vibrational region
of cis-alkenes.
Table 3
Comparison of theoretical and experimental values of 1H NMR chemical shifts.
For 6-fluoro coumarin, the IR wave number 1624 cmÀ1 is as-
signed to C@C stretching vibration of pyran ring, in accordance
with predicted frequencies at 1611 cmÀ1; The CAH stretching
vibrations of pyran ring are at about 3200 cmÀ1 with very low
intensity; 820, 864 cmÀ1 are assigned to the CAH in-plane bending
vibrations, the calculated values are 804, 856 cmÀ1 respectively.
The experimental values match well with the theoretical data in
Table 2 .
Assignments (ppm)
13-H
8-H
7-H
10-H
14-H
Calc.a
Exp.
8.31
8.04
7.74
7.62
7.73
7.50
7.68
7.46
6.80
6.58
a
Reference: TMS B3LYP/Aug-CC-Pvdz GIAO/reference shielding: 31.78 ppm.
analyses are shown in Table 3, and 13C NMR in Table 4. The ob-
served 1H NMR spectra are presented in Fig. 4, and 13C NMR in
Fig. 5
O@CAO vibrations
The frequencies around 1050–1310 cmÀ1 in IR spectrum are
usually regarded as the CAO stretching band of the ester. For 6-flu-
oro coumarin, 1724 cmÀ1 is attributed to the C@O stretching band;
1274 cmÀ1 is assigned to CAO asymmetric stretching vibrations;
CAO in-plane bending vibration is observed at 861 cmÀ1. The the-
oretical values are 1746, 1232, 877 cmÀ1 accordingly, which match
well with the experimental data in Table 2 .
1H NMR chemical shifts
The peaks with dH of 2.51, 3.41 ppm in Fig. 4 is supposed to be
related with the protons of the solvent DMSO-d6 and H2O in it. The
presence of other peaks suggests that there are five distinct types
of protons in the compound. The peaks with dH of 6.58 ppm in
Fig. 4 are assigned to the proton of alkenyl at the 14-position of
the coumarin, dH of 8.04 ppm is assigned to the proton of alkenyl
at the 13-position, they have the same coupling constant of
9.6 Hz. Normally, the protons on phenyl ring are expected to yield
NMR signals in the dH region of 6–8 ppm [43]. The substitution of
fluorine atom in phenyl ring changes the chemical environment of
the remaining aryl protons and generates coupling interaction to
them. The peaks with dH of 7.46 ppm, 7.50 ppm, 7.62 ppm in
Fig. 4 are expected to be assigned to the protons of phenyl ring
at the 10-, 7-, 8-position respectively.
CAF vibration
The CAF stretching vibrations of phenyl fluoride often happen
in the range of 1100–1250 cmÀ1 [43].
The strong vibration observed at 1261 cmÀ1 in IR spectrum is
assigned as CAF stretching vibration. The theoretically computed
value at 1231 cmÀ1 has fine consistency with the experimental
result.
NMR chemical shifts
Table 3 gives the comparison of theoretical and experimental
values of 1H NMR chemical shifts for the title compound. The
results indicate that the calculated chemical shifts are in good
agreement with the experimental data. However, there is an
The experimental and calculated values together with the peak
assignments of 6-fluoro coumarin for 1H NMR chemical shifts
Table 4
Comparison of theoretical and experimental values of 13C NMR chemical shifts.
Assignments (ppm)
12-C
6-C
3-C
9-C
4-C
1-C
2-C
11-C
5-C
aCalc.
Exp.
162.53
160.21
159.16
159.28,
157.69
153.49
150.36
150.34
144.54
143.85,
143.83
122.88
120.20,
120.13
118.23
119.72,
119.56
116.51
118.75,
118.69
115.86
117.88
113.65
114.12,
114.29
a
Reference: TMS B3LYP/Aug-CC-Pvdz GIAO/reference shielding: 192.72 ppm.

18
Y. Bai et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 14–20
is assigned to the 9-carbon of alkenyl with a small coupling con-
stant with fluorine atom. dC of 160.20 ppm is attributed to the car-
bon of acyl at the 12-position.
Table 4 gives the comparison of theoretical and experimental
values of 13C NMR chemical shifts for the title compound. The
results indicate that the calculated chemical shifts are in good
agreement with the experimental data in most parts. However,
there are some differences between the experimental and theo-
retical chemical shift values, the biggest one is that computing
cannot give the coupling constants, it is because that the theo-
retical model applied in the calculations cannot simulate the
coupling interaction.
UV–vis absorption and fluorescence spectra
Coumarins are known to be suitable photoluminescence mate-
rials for their strong fluorescence. Photo absorption and emission
phenomena are vital for a photoluminescence material. TD-DFT
method is often found efficient for evaluating the excited spectra
of conjugated molecules [45–47].
Fig. 4. Observed 1H NMR spectrum of 6-fluoro coumarin.
Hydrogen-bonding interaction
In case of the solute molecules in the ground state can form
hydrogen-bonded complexes with the solvent molecules, the
hydrogen-bonding interactions can induce spectral shifts of some
characteristic vibrational modes involved in the formation of
hydrogen bonds [40,41]. In present work, the absorption and emis-
sion spectra are investigated in the hydrogen-donating solvent of
methanol, we employ TD-DFT method for the calculations of the
UV–vis absorption and fluorescence spectra of the isolated 6-fluoro
coumarin with CPCM and the hydrogen-bonded (6-fluoro couma-
rin)-(methanol) complex to simulate the solvent effect. Since the
C@O group is the most important site that is responsible for the
hydrogen bond formation between 6-fluoro coumarin and metha-
nol [41,48], and the CAF bond is capable of significant interactions
with proton donors, although these are generally weak [49], the
calculated geometric structure of the hydrogen-bonded complex
in ground state shown in Fig 6 can be a good model for studying
the hydrogen-bonding interactions between 6-fluoro coumarin
and methanol. In Fig. 6, the length of the hydrogen bond
C@OÁ Á ÁHAO between H and O atom is 1.946 Å, the other hydrogen
bond CAFÁ Á ÁOAH has a hydrogen bond length of 2.252 Å. we can
find that the lengths of the C@O, CAF and HAO bonds are all in-
creased because of the formation of the hydrogen bonds. Com-
pared to the structure in Fig. 2, the C@O bond length in Fig. 6 is
increased to 1.211 Å from 1.202 Å, and the C-F bond length is in-
creased to 1.364 Å from 1.354 Å. And the HAO bonds in
C@OÁ Á ÁHAO and CAFÁ Á ÁOAH are increased to 0.970 Å and 0.963 Å
from 0.961 Å (calculated in the same level), respectively. These
suggest that the C@O and CAF bonds of 6-fluoro coumarin molec-
ular can form hydrogen bonds with methanol moleculars, and the
C@O group is more responsible for the hydrogen-bond formation.
Fig. 5. Observed 13C NMR spectrum of 6-fluoro coumarin.
obvious difference between the experimental and theoretical
chemical shift values, that is none of the coupling constants can
be given by computing. That is the limitation of theoretical model
applied in the calculations.
13C NMR chemical shifts
The peaks with dC of 40.11 ppm are supposed to be related with
the carbons of the solvent DMSO-d6. Normally, the carbons on
alkenyl are expected to yield NMR signals in the dC region of
100–150 ppm [43].
The carbons on phenyl ring are supposed to give NMR signals in
the region of 110–175 ppm. The substitution of fluorine atom in
phenyl ring changes the chemical environment of the remaining
aryl carbons and generates coupling interaction to them. 13C
NMR signals of carbons in the ortho- or para- position to a fluoro
substituent are significantly shifted to lower frequencies, whereas
ipso C-atoms are characterized by a marked downfield shift
[43,44].
Based on these, the peaks observed in Fig. 5 with dC of 114.12/
114.29 ppm, 118.69/118.75 ppm, 119.56/119.72 ppm, 120.13/
120.20 ppm, 150.36/150.34 ppm and 157.69/159.28 ppm are ex-
pected to be assigned to the carbons of phenyl ring at 5-, 2-, 1-,
4-, 3-, 6-position respectively, each of them has coupling interac-
tion with fluorine atom in some different degrees according to
the distance to fluorine atom. dC of 117.88 ppm is assigned to
the carbon of alkenyl at the 11-position, and 143.83/143.85 ppm
Fig. 6. The calculated molecular structure of hydrogen-bonded (6-fluoro couma-
rin)-(methanol) complex.

Y. Bai et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 14–20
19
2.5
hydrogen-bonded complex
isolated compound
10000
8000
6000
4000
2000
0
A
B
2.0
1.5
1.0
0.5
0.0
175 200 225 250 275 300 325 350 375 400
175 200 225 250 275 300 325 350 375 400
Wavelength (nm)
Wavelength (nm)
Fig. 7. UV–vis absorption spectra of 6-fluoro coumarin in methanol ((A) observed, (B) calculated).
Table 5
Absorption spectra
Comparison of theoretical values of UV–vis absorption spectra of isolated 6-fluoro
coumarin in CPCM and the hydrogen-bonded complex with experimental data.a
The UV/vis spectra absorption are determined using the
conventional TD-DFT procedure on the ground state geometries.
Experimental absorption spectrum of 6-fluoro coumarin in
methanol, and the calculated absorption spectra of isolated
6-fluoro coumarin in CPCM and hydrogen-bonded (6-fluoro cou-
marin)-(methanol) complex are shown in Fig. 7. Theoretical and
experimental values are listed in Table 5.
State
kCalc. (nm)
E (eV)
f
kexp. (nm)
Isolated compound in CPCM
S1
S3
S5
313
266
213
3.96
4.66
5.81
0.108
0.177
0.136
319
269
215
Hydrogen-bonded complex
Results in Fig. 7 and Table 5 show that 6-fluoro coumarin has
strong absorption at 319, 269, 215 nm in UV–vis region experi-
mentally. For isolated 6-fluoro coumarin in CPCM, the calculated
excitation energy (3.96 eV, 313 nm) with strong intensity (0.108)
for the singlet state S1 is close to the experimental absorption of
319 nm, the other higher energy absorption peaks calculated at
266 nm (4.66 eV) and 213 nm (5.81 eV) with large oscillator
strength for S3 and S5 can be associated with the experimentally
observed absorption of 269 and 215 nm. The simulated spectra
exhibit only slightly blue-shifted compared with experimental
ones. And as to the hydrogen-bonded complex, the absorption
peaks calculated are at 308 nm (4.02 eV) for S1, 269 nm
(4.62 eV) for S3, 214 nm (5.79 eV) for S5, which are very close
to the data of the isolated model. From that we can see that
the theoretical absorption data of isolated 6-fluoro coumarin in
CPCM are in good agreement with the experimental values, the
influence of the hydrogen-bonding interaction between 6-fluoro
coumarin and methanol is negligible in calculating the absorp-
tion spectrum of 6-fluoro coumarin.
S1
S4
S9
308
269
214
4.02
4.62
5.79
0.101
0.214
0.097
319
269
215
a
k, Wavelength; E, electronic excitation energies; f, oscillator strengths; and Sn,
low-lying singlets.
Table 6
Comparison of theoretical values of fluorescence emission spectra of isolated 6-fluoro
coumarin in CPCM and the hydrogen-bonded complex with experimental data.
State
Isolated compound in CPCM
S1 397
Hydrogen-bonded complex
S2 405
kcalc. (nm)
E (eV)
3.121
3.061
f
kexp. (nm)
416
0.0694
0.0831
tra in Fig 8B show that the calculated value for isolated 6-fluoro
coumarin in CPCM is 397 nm (3.12 eV), which is basically consis-
tent with the experimental data (416 nm). The calculated emission
peak at 405 nm (3.05 eV) of hydrogen-bonded complex is closer to
the experimental value compared with that of the isolated model.
It is apparent that the hydrogen-bonding interaction between
6-fluoro coumarin and methanol affects the shift of simulated
emission peak and should be considered in the simulation of fluo-
rescence spectrum for 6-fluoro coumarin with methanol as solvent.
Fluorescence spectra
Experimental fluorescence spectrum of 6-fluoro coumarin in
methanol, and the simulated fluorescence spectra of isolated 6-flu-
oro coumarin with CPM and hydrogen-bonded (6-fluoro couma-
rin)-(methanol) complex are shown in Fig. 8. Theoretical and
experimental values are listed in Table 6.
As shown in Fig. 8A, 6-fluoro coumarin has strong purple light
emission at 416 nm in vis region, and the computed emission spec-
A
B
5000
4000
3000
2000
1000
0
800
hydrogen-bonded complex
isolated compound
600
400
200
0
350 400 450 500 550 600 650 700 750 800
Wavelength (nm)
350 400 450 500 550 600 650 700 750 800
Wavelength (nm)
Fig. 8. Fluorescence spectra of 6-fluoro coumarin ((A) observed, (B) calculated).

20
Y. Bai et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 14–20
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In this study, we have synthesized 6-fluoro coumarin and char-
acterized it by FT-IR and NMR. The geometric parameters have
been optimized, vibrational frequencies and 1H, 13C NMR chemical
shifts of the title compound have been calculated using DFT/B3LYP
method with the 6-311G(d,p) basis sets (NMR chemical shifts were
calculated at the B3LYP/Aug-CC-Pvdz level). The theoretical vibra-
tional frequencies and chemical shift values are in good agreement
with the experimental findings. The major discrepancies between
the experimental and theoretical chemical shift values are mainly
due to the negligence the coupling interaction of the fluorine atom
with carbon atom within the applied theoretical model. The optical
properties of absorption and emission are also addressed theoret-
ically and experimentally. TD-DFT method is used to calculate
the absorption and emission spectra, the solvent effect of methanol
is simulated by using the isolated 6-fluoro coumarin in CPCM and
the hydrogen-bonded (6-fluoro coumarin)-(methanol) complex as
models. Results show that the title compound has good absorption
of UV light and can give purple light emission, which makes it a
good candidate as a photo luminescent material. And the influence
of the hydrogen-bonding interaction between 6-fluoro coumarin
and methanol can be neglected on the calculated absorption val-
ues, but should be considered on the theoretical emission data.
The theoretical absorption data of isolated 6-fluoro coumarin in
CPCM together with the calculated emission values of hydrogen-
bonded (6-fluoro coumarin)-(methanol) complex are in good
agreements with the experimental results. All these conclusions
prove that the selected methods are feasible to predict the param-
eters and characteristics of structural-similar compounds. And we
would like to mention in particular that although it is known that
TD-DFT method overestimates energies of electronic transitions
[50,51], but in this work, the method can give precise simulation
of the fluorescence spectra of 6-fluoro coumarin, which is very use-
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