Synthesis, structure, electronic and vibrational spectra of 9-(Diethylamino)-benzo(a)phenoxazin-7-ium-5-N-methacrylamide

Article abstract of DOI:10.1016/S1386-1425(02)00119-1

The electronic and vibrational spectra of 9-(Diethylamino)-benzo(a)phenoxazin-7-ium-5-N-methacrylamide (Nile Blue-5-N-methacrylamide) are measured, and the results are compared with the theoretical values obtained by quantum chemical calculations. The geometry, electronic transitions, charge distribution, and the IR normal modes of this new dye and of its precursor Nile Blue have been computed by using Density Functional Theory (DFT) method with the functional B3LYP and the 6-31G(d) Gaussian basis set. The molecular properties of the two dyes, predicted and observed, are very similar in the electronic ground state. In the excited state, however, the longer lifetime and larger fluorescence quantum yield of the Nile Blue-5-methacrylamide is ascribed to an inhibition of the twisted intramolecular charge transfer (TICT) process, when the NH₂ is substituted by the methacrylamide in the 5-position of the aromatic extended ring of the dye. The change in charge density of the N atom in 5-position, as well as the difference in dipole moment and ionization potential of the two dyes molecules, explain the attenuation of TICT process. The vibration spectra of both dyes are simulated properly by using the DFT method.

Full text of DOI:10.1016/S1386-1425(02)00119-1

Spectrochimica Acta Part A 58 (2002) 3103ꢀ3111
/
www.elsevier.com/locate/saa
Synthesis, structure, electronic and vibrational spectra of 9-
(Diethylamino)-benzo(a)phenoxazin-7-ium-5-N-
methacrylamide
H.P.M. Oliveira, A.J. Camargo, L.G. Macedo, M.H. Gehlen *, A.B.F. da Silva
Instituto de Qu´ımica de Sao Carlos, Universidade de Sao Paulo, CP 780, CEP 13560-970 Sao Carlos, SP, Brazil
˜ ˜
Received 9 January 2002; accepted 19 January 2002
Abstract
The electronic and vibrational spectra of 9-(Diethylamino)-benzo(a)phenoxazin-7-ium-5-N-methacrylamide (Nile
Blue-5-N-methacrylamide) are measured, and the results are compared with the theoretical values obtained by quantum
chemical calculations. The geometry, electronic transitions, charge distribution, and the IR normal modes of this new
dye and of its precursor Nile Blue have been computed by using Density Functional Theory (DFT) method with the
functional B3LYP and the 6-31G(d) Gaussian basis set. The molecular properties of the two dyes, predicted and
observed, are very similar in the electronic ground state. In the excited state, however, the longer lifetime and larger
fluorescence quantum yield of the Nile Blue-5-methacrylamide is ascribed to an inhibition of the twisted intramolecular
charge transfer (TICT) process, when the NH2 is substituted by the methacrylamide in the 5-position of the aromatic
extended ring of the dye. The change in charge density of the N atom in 5-position, as well as the difference in dipole
moment and ionization potential of the two dyes molecules, explain the attenuation of TICT process. The vibration
spectra of both dyes are simulated properly by using the DFT method.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Dye laser; Nile Blue; Photophysical properties; DFT calculations
1. Introduction
nm. On the other hand, these dyes are also
standards for fluorescence measurements, and
Oxazine dyes have been a topic of many kinds of
spectroscopic investigations because their wide
very useful biological stains [1ꢀ3]. Phenoxazines
/
dyes have been recently used as electrode surface
modifiers with applications in biosensors [4,5].
Furthermore, a number of studies have focused
on the photophysical properties of amphiphilic,
random, alternating and block copolymers, having
used as tunable dye laser in the range 600ꢀ900
/
* Corresponding author. Tel.: ꢁ
16-273-9952
E-mail address: marcelog@iqsc.sc.usp.br (M.H. Gehlen).
/
55-16-273-9951; fax: ꢁ55-
/
these dyes as pendant fluorescence molecules [6ꢀ
/
1386-1425/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 1 3 8 6 - 1 4 2 5 ( 0 2 ) 0 0 1 1 9 - 1

3104
H.P.M. Oliveira et al. / Spectrochimica Acta Part A 58 (2002) 3103ꢀ3111
/
12]. Although there are several experimental
studies employing these fluorescent dyes and
derivatives, only a few reports are based on the
combination of modern theoretical and experi-
Fluorescence decays of NB and NB-5-N-metha-
crylamide were measured by time correlated sin-
gle-photon counting technique using a CD-900
Edinburgh spectrometer equipped with Glan-
Thompson polarizers in magic angle, and a Peltier
cooled PMT (Hamamatsu R955). The light pulse
was provided by a 100-ps pulsed diode laser at 633
nm (Hamamatsu PLP 01). The fluorescence decays
were analyzed by reconvolution procedure with
the exponential model of the Edinburgh Instru-
ments software.
mental method of investigation [13ꢀ15].
/
In the present work, the photophysical proper-
ties of the new dye (9-(Diethylamino)-ben-
zo(a)phenoxazin-7-ium-5-N-methacrylamide),
here defined as Nile Blue-5-N-methacrylamide, are
described. The experimental results in electronic
absorption, emission, and infrared (IR) spectro-
scopies of the Nile Blue (NB) and its new
derivative are compared with quantum chemical
calculation predictions using various theoretical
approaches, including the Density Functional
Theory (DFT) method. The molecular geometry
and mapped electrostatic surfaces are also investi-
gated.
2.2. Synthesis
The compound 9-(Diethylamino)-benzo(a)phe-
(NB-5-N-
noxazin-7-ium-5-N-methacrylamide
methacrylamide) was obtained by reacting NB
with MAA in methanol using 1,3-diisopropylcar-
bodiimide under nitrogen atmosphere and in the
presence of N-methylmorpholine, as described in
Scheme 1. The product was recristallized from
acetone, and dried under reduced pressure. The
product was confirmed from 13C NMR, 1H NMR,
and FT-IR data (vide infra). The additional signals
Recent theoretical studies [16ꢀ18] about the
/
harmonic vibrational frequencies for a large num-
ber of molecules were well succeeded with applica-
tion of DFT and other theories. These studies
showed that the DFT combined with the B3LYP
functional was found to be more reliable than the
other methodologies [16].
of 1H NMR at 5.98ꢀ
/
5.49 (2H), 4.84 (1H) and 1.86
(3H), and of 13C NMR at 162.36 ppm (Cꢀ
confirms the presence of the NB-5-N-methacryla-
mide.
/O),
2. Experimental
2.1. Materials and methods
2.3. Computational
NB and diisopropyl-carbodiimide, from Al-
drich, were used without further purification.
Methacrylic acid (MAA, Aldrich) was distilled
prior to reaction. All the other reagents were used
as received. The IR spectra were recorded in the
The chemical and electronic structures, and the
vibrational spectra of NB and NB-5-N-methacry-
lamide were calculated by DFT [11]. DFT calcula-
tions were carried out with the functional B3LYP
(the exchange functional of Becke [19ꢀ21] and Lee
/
400ꢀ
/
4000 cmꢂ1 region with resolution of 4 cmꢂ1
[22]) starting from previous AM1 optimized geo-
metry, and following a subsequent harmonic
frequency calculations. All calculations (DFT
and semi-empirical) were performed with the
molecular package Gaussian 98 (Rev A.6), in a
Silicon Graphics Origin 2000 workstation. The
homogeneous IR frequencies of compounds were
evaluated from the empirical scaling factor of
0.9614 determined by Scott and Radom [16].
The size of the molecule imposes some restric-
tions on the level of the quantum mechanical
method used for an additional description of the
at room temperature with samples in KBr plates,
by using of a Bomem MB-100 FT-IR spectro-
meter.
Absorption measurements were performed on a
Hitachi U-2000 spectrophotometer, and the cor-
rected steady-state fluorescence spectra were re-
corded
spectrofluorimeter. The samples were conditioned
in a 1ꢃ
1 cm2 quartz cuvette, thermostatted by
on
a
CD-900
Edinburgh
/
circulating fluid through a jacketed cuvette-holder,
and in air equilibrated condition.

H.P.M. Oliveira et al. / Spectrochimica Acta Part A 58 (2002) 3103ꢀ
/3111
3105
electronic spectra. In practical terms, the option
used in this work was limited to use a semi-
empirical method approach to perform the CI
calculations. Therefore, the semi-empirical hamil-
tonian Indo-1 implemented in the ZINDO/CER-
IUS2 package was chosen, performing only single
excitations on 20 active orbitals, i.e. those located
excess negative charge. Three-dimensional iso-
potential surfaces of the MEPs at the van der
Walls contact surface represent the potential
superimposed onto a surface of constant electron
density (0.002 e/au3).
at region from HOMO ꢂ
/
9 and LUMO ꢁ9.
/
3. Results and discussion
Molecular electrostatic potentials (MEP) maps of
the new dye were calculated from the DFT
optimized geometry. The MEP iso-potential sur-
3.1. Molecular geometry
face contours were generated from ꢂ0.5 to 0.5 e/
/
Structural parameters of the NB-5-N-methacry-
lamide obtained using DFT method are summar-
ized in Table 1. The calculated chemical structure
with the atom numbering is shown in Fig. 1. The
optimized molecular geometry of the dye was
calculated without symmetry constraints. The
harmonic frequency calculations (only positive
frequencies) showed that the molecular geometry
obtained corresponds to a minimum energy struc-
ture.
a0. The electrostatic potentials were sampled over
the entire accessible surface of the dye (corre-
sponding to a van der Walls contact surface), and
in the space extending beyond the molecular
surface, providing a measurement of the charge
distribution. The regions of positive electrostatic
potential indicate excess positive charge, i.e. repul-
sion for the positively charge test probe, while
regions of negative potential indicate areas of
Scheme 1. Synthetical route of NB-5-methacrylamide.

Table 1
Geometrical parameters of NB-5-methacrylamide
˚
Bond lengths (A)
C(1)ꢀ
C(1)ꢀ
C(1)ꢀ
N(5)ꢀ
N(5)ꢀ
C(9)ꢀ
/
C(2)
H(4)
N(5)
1.503 C(15)ꢀ
1.090 C(19)ꢀ
1.470 C(20)ꢀ
1.470 C(20)ꢀ
1.350 O(24)ꢀ
1.530 C(26)ꢀ
/
C(19)
C(23)
C(14)
O(24)
1.360 C(26)ꢀ
1.420 C(29)ꢀ
1.370 C(30)ꢀ
1.360 C(33)ꢀ
1.350 C(31)ꢀ
1.420 C(33)ꢀ
/
C(29)
H(32)
C(33)
C(31)
C(28)
C(36)
1.380 C(37)ꢀ
1.070 C(34)ꢀ
1.460 C(31)ꢀ
1.420 C(29)ꢀ
1.450 C(23)ꢀ
1.410 C(30)ꢀ
/
C(34)
C(31)
C(28)
C(30)
C(20)
N(35)
1.380 C(39)ꢀ
1.410 N(35)ꢀ
1.450 C(39)ꢀ
1.390 C(44)ꢀ
1.430 C(44)ꢀ
1.370 C(41)ꢀ
/
O(45)
1.219 C(10)ꢀ
C(14)
1.000 N(27)ꢀ
C(23)
1.500 N(35)ꢀ
/
1.420
1.330
1.410
1.380
1.340
1.440
/
/
/
/
/
H(40)
C(44)
C(48)
C(47)
C(37)
/
/
/
/
/
/
/
C(39)
/
C(9)
/
/
/
/
1.340 C(36)ꢀ
/
C(41)
/
C(10)
/
C(26)
/
/
/
1.510 C(28)ꢀ
/
N(27)
/
C(11)
/
C(28)
/
/
/
1.400 C(10)ꢀ
/
C(15)
Bond angles (8)
C(9)ꢀ
C(10)
N(27)ꢀ
C(20)
C(10) 122.740 C(23)ꢀ
C(28)
/
N(5)ꢀ
C(23)ꢀ
N(27)ꢀ
C(20)ꢀ
/
122.000 C(34)ꢀ
/
C(37)ꢀ
/
119.950 C(31)ꢀ
/
C(34)ꢀ
/
120.520 N(27)ꢀ
/
C(28)ꢀ
/
121.400
H(43)
N(37)
120.420 N(35)ꢀ
O(45)
C(26)
/
/
122.040 C(26)ꢀ
/
O(24)ꢀ
/
/
C(39)ꢀ
/
121.970 C(48)ꢀ/C(44)ꢀ
/
122.670
117.880
120.730
116.250
123.680
110.290
112.240
112.230
117.610
120.110
118.390
C(20)
C(47)
C(1)ꢀ
/
N(5)ꢀ
/
/
/
118.640 O(24)ꢀ
/
C(26)ꢀ
/
117.340 H(43)ꢀ
/
C(37)ꢀ
/
120.040 H(53)ꢀ
/
C(48)ꢀ
/
C(29)
C(41)
H(52)
N(5)ꢀ
C(15)
C(10)ꢀ
H(22)
/
C(10)ꢀ
/
120.850 C(23)ꢀ
/
/
118.000 C(26)ꢀ
/
C(29)ꢀ
/
120.070 C(37)ꢀ
/
C(41)ꢀ
/
120.260 C(44)ꢀ/C(48)ꢀ
/
O(24)
H(32)
C(36)
119.600 H(46)ꢀ
H(53)
/
C(15)ꢀ
/
119.640 O(24)ꢀ
/
C(20)ꢀ
/
118.770 C(26)ꢀ
/
C(29)ꢀ
/
/
C(41)ꢀ
/
119.670 C(39)ꢀ/C(44)ꢀ
/
C(14)
C(30)
C(36)
N(48)
H(22)ꢀ
/
C(15)ꢀ
/
118.590 C(20)ꢀ
H(21)
121.210 H(21)ꢀ
/
C(14)ꢀ
/
118.100 C(29)ꢀ
/
C(30)ꢀ
/
121.280 C(41)ꢀ
/
C(36)ꢀ
/
121.300 O(45)ꢀ
/
C(39)ꢀ
/
C(19)
N(35)
122.260 N(35)ꢀ
C(33)
118.900 H(42)ꢀ
C(33)
C(44)
C(15)ꢀ
/
C(19)ꢀ
/
/
C(14)ꢀ
/
/
C(30)ꢀ
/
/
C(36)ꢀ
/
121.490 C(44)ꢀ/C(47)ꢀ
/
H(25)
H(25)ꢀ
C(23)
C(10)
C(33)
H(49)
/
C(19)ꢀ
/
117.520 C(14)ꢀ
/
C(10)ꢀ
/
117.720 C(30)ꢀ
/
C(33)ꢀ
/
118.870 C(30)ꢀ
/
N(35)ꢀ
/
121.970 C(44)ꢀ/C(47)ꢀ
/
C(15)
N(31)
C(39)
119.930 H(40)ꢀ
C(39)
H(50)
C(19)ꢀ
N(27)
C(1)ꢀ
/
C(23)ꢀ
/
121.440 C(28)ꢀ
/
C(26)ꢀ
/
119.330 C(33)ꢀ
/
C(31)ꢀ
/
/
N(35)ꢀ
/
114.960 C(44)ꢀ/C(47)ꢀ
/
O(24)
C(34)
H(51)
/
C(2)ꢀ
C(2)ꢀ
C(2)ꢀ
/
H(6)
H(7)
H(8)
111.610 C(9)ꢀ
/
C(11)ꢀ
/
111.130 N(5)ꢀ
109.700 N(5)ꢀ
111.700 N(5)ꢀ
/
C(9)ꢀ
C(9)ꢀ
C(9)ꢀ
/
C(11) 113.370 N(5)ꢀ
H(13) 106.620 N(5)ꢀ
H(12) 108.990 N(5)ꢀ
/
C(1)ꢀ
C(1)ꢀ
C(1)ꢀ
/C(2) 113.326 C(31)ꢀ
/C(28)ꢀ
/
H(16)
C(26)
C(1)ꢀ
/
/
109.740 C(9)ꢀ
/
C(11)ꢀ
/
/
/
/
/H(3) 109.270 C(28)ꢀ
/C(31)ꢀ
/
H(17)
C(34)
C(1)ꢀ
/
/
111.160 C(9)ꢀ
/
C(11)ꢀ
/
/
/
/
/H(4) 106.460 C(31)ꢀ
/C(34)ꢀ
/
H(18)
H(38)
Dihedral angles (8)
N(5)ꢀ
C(11)ꢀ
60.990 N(5)ꢀC(9)ꢀ
C(11)ꢀH(16)
5.160 N(5)ꢀC(9)ꢀ
C(11)ꢀH(18)
/
C(9)ꢀ
H(17)
/
178.090 C(15)ꢀ
N(5)ꢀC(9)
58.810 C(39)ꢀC(44)ꢀ
C(47)ꢀH(50)
61.880 N(5)ꢀC(1)ꢀC(2)ꢀ
H(7)
/
C(10)ꢀ
/
174.910 N(5)ꢀ
C(2)ꢀH(6)
61.020 C(10)ꢀN(5)ꢀ
C(9)ꢀC(11)
177.680 N(5)ꢀ
C(2)ꢀ
/
C(1)ꢀ
/
58.346 C(10)ꢀ
C(1)ꢀC(2)
88.400 C(10)ꢀN(5)ꢀ
C(9)ꢀH(13)
62.280 C(10)ꢀN(5)ꢀ
C(9)ꢀH(12)
/
N(5)ꢀ
/
88.580
/
/
/
/
C(39)ꢀ
C(47)ꢀ
C(15)ꢀ
N(5)ꢀC(1)
/
C(44)ꢀ
H(51)
C(10)ꢀ
/
/
/
/
/
ꢂ/
/
/
/
/
ꢂ/
150.300
/
/
/
/
/
/
/
ꢂ/
/
/
ꢂ/
/
/
/
/
C(1)ꢀ
/
ꢂ/
/
/
ꢂ36.180
/
/
/
/H(8)
/

H.P.M. Oliveira et al. / Spectrochimica Acta Part A 58 (2002) 3103ꢀ
/3111
3107
Fig. 1. The calculated chemical structure and corresponding atom numbering of the NB-5-methacrylamide.
The DFT method using B3LYP/6-31G(d) pre-
dicts an almost planar structure with negligible
deviations of the structural common parameters in
both dyes. The diethylamino group has chains
Table 2
Important calculated and measured electronic transitions
Properties
NB
NB-5-methacrylamide
labs (nm)
lemi (nm)
fF
635
665
0.01
0.76
632
667
0.10
1.11
with dihedral angles of 174.910 (C(15)ꢀ
/
C(10)ꢀ
/
N(5)ꢀC(9)) and 5.160 (C(15)ꢀC(10)ꢀ
/
ꢂ
/
/
/
N(5)ꢀ
/
C(1)) degrees. It is interesting to note that no
significant changes on structure (bond distances,
bond angles or dihedral) were verified when MAA
and NB are compared separately to the product
(Table 1).
t (ns)
labs (nm) theoretical
L)
p0
/
p* (H0
/
503a, 504b 501a, 496b
1.2483a 1.2511a
f
f, oscillator strength.
a
From INDO/ZINDO semi-empirical method.
From DFT method.
3.2. Frontier orbitals, electronic energy levels, and
MEPS
b
The frontier orbitals energies calculated by DFT
B3LYP/6-31G* for reactant and product are listed
on Table 2. The difference between HOMO and
LUMO energy for NB and for product are 0.09039
and 0.09186 Hartrees, respectively. Therefore, the
most important transition, the HOMO0
/LUMO,
is located in about the same wavelength for both
dyes (504.07 and 496.01 nm for NB and NB-5-N-
methacrylamide, respectively) showing that the
addition of the MAA group does not promote a
significant change of electronic energy levels of the
dye. The overall permanent dipole moments of NB
and NB-5-N-methacrylamide were computed by
DFT level, and the values found were 3.4235 D (ꢂ
0.8724x, 3.2938y, 0.3322z) and 2.9911
(2.8312x, 0.9630y, ꢂ0.0527z), respectively. The
/
D
Fig. 2. Three-dimensional MEP isosurface of NB-5-methacry-
lamide (units in e/a0).
/

3108
H.P.M. Oliveira et al. / Spectrochimica Acta Part A 58 (2002) 3103ꢀ3111
/
Table 3
The electronic energy levels of the dye molecules
were further calculated by using INDO/ZINDO
semi-empirical method. The difference between
HOMO and LUMO energy for NB and for
product are evaluated as 0.09058 and 0.09095
Hartrees, respectively. These results would corre-
Calculated energies (in Hartrees) of some of the highest
occupied and lowest unoccupied molecular orbitals of reactants
MAA and NB and product NB-5-methacrylamide by DFT
method
NB
NB-5-methacrylamide
spond to HOMO0
/
LUMO electronic transition
LUMO
HOMO
ꢂ
/
0.11532
0.12809
0.15271
0.21901
0.30940
0.35020
0.36426
0.37110
ꢂ
/
0.12343
0.12739
0.15783
0.22359
0.31545
0.35071
0.35698
0.35868
with p0p* character located in about the same
/
ꢂ
/
ꢂ
/
wavelength for both dyes (503.02 and 500.97 nm
for NB and NB-5-N-methacrylamide, respec-
tively). Note that the results obtained with the
semi-empirical method do not differ appreciable
from the previous results from DFT calculations.
The INDO/ZINDO calculation also predicts simi-
lar oscillator strength for the two dyes (1.2483 and
1.2511 for NB and NB-5-N-methacrylamide, re-
spectively).
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ/
ꢂ/
Note: Overall predicted dipole moment is 2.9911 Debye for
product.
3.3. Electronic spectra and other experimental
photophysical properties
The photophysical properties of the dyes NB
and NB-5-N-methacrylamide are reported in Ta-
ble 3. The introduction of a polar group metha-
crylamide does not change appreciable the
electronic absorption spectrum of the NB, but
only a small shift in about 3 nm is observed for the
low energy p0p* electronic transition. The max-
/
Fig. 3. Emission and absorption electronic spectra for NB-5-
methacrylamide in water, [NB-5-methacrylamide]ꢄ
10ꢂ5 M,
Tꢄ298 K.
/
/
HOMO energy of the dyes is ꢂ
0.31545 Hartrees) for the product, and ꢂ
eV (ꢂ0.3094 Hartrees) for NB. Therefore the
/
8.576 eV (ꢂ
/
/8.4193
/
expected IP of the product (NB-5-N-methacryla-
mide) is slightly higher than the IP of the original
NB dye, which in part reflect the inductive effect of
the amide group in the 5-position of the aromatic
extended ring of the dye. The three-dimensional
MEP map (Fig. 2) shows that the lowest electro-
static potential are found near from O(45), O(24)
and N(27) atoms. The rest of the molecule presents
a low positive potential, being stronger near
hydrogen positions.
Fig. 4. Fluorescence decay of NB-5-methacrylamide in water,
[NB-5-methacrylamide]ꢄ 298 K. Time in-
10ꢂ5 M, Tꢄ
crementꢄ25 ps/channel. Instrument response functionꢄ700
ps. Exponential fit yields tꢄ 1.091.
1.11 ns and x2ꢄ
/
/
/
/
/
/

H.P.M. Oliveira et al. / Spectrochimica Acta Part A 58 (2002) 3103ꢀ
/3111
3109
Table 4
Observed and calculated IR wavenumbers and intensities for MAA compound using the method B3LYP/6-31G(d)
Mode
Freq. scaled
IR intens.
Measured peak
Assignmenta
n11(aƒ)
n13(aƒ)
n14(a?)
n17(a?)
n18(a?)
n19(a?)
n21(aƒ)
n22(a?)
n23(a?)
n24(a?)
n27(a?)
801.1
948.7
999.2
21.39
31.84
21.79
18.07
56.94
7.51
810.53
946.64
rt(CH2)
rv(CH2)
d(CH3)
1008.18
1219.87
1299.18
1376.06
1431.06
1453.79
1633.91
1695.52
2993.82
1224.3
1338.3
1381.3
1448.9
1462.9
1650.7
1755.3
3015.0
rr(CH2)ꢁ
d(COH)
/
d(COH)
s(CH2)ꢁ
da(CH3)
ds(CH3)
/
d(CH3)
6.66
22.60
33.58
205.58
58.81
n(Cꢀ
/
C)
O)1
n(Cꢀ
/
n(OH)2
Calculated vibrational frequencies scaled by 0.9614.
a
The number in upper case of the assignment and the respective normal mode is indicated in the vibrational spectra show in Fig. 5.
Table 5
Observed and calculated IR wavenumbers and intensities for NB compound using the method B3LYP/6-31G(d)
Mode
Freq. scaled
IR intens.
Measured peak
Assignmenta
n80(a)
n86(a)
n90(a)
n96(a)
n103(a)
n105(a)
n106(a)
n114(a)
n125(a)
n126(a)
1326.3
1388.2
1452.7
1477.6
1576.1
1628.1
1640.1
3018.1
3473.2
3581.3
638.09
17.27
1333.66
1375.22
1436.41
1479.65
1547.70
1584.43
1640.21
2977.79
3221.58
3343.35
na(Cꢀ
ds(CH3)
d(CH)ꢁ
ds(CH3)ꢁ
na(CꢀC)ꢁ
C)ꢁ
/
C)ꢁ
/
d(CH)ꢁrt(CH2)
/
145.92
74.49
/
s(CH2)
s(CH2)
/
1105.56
456.98
297.22
30.33
/
/s(NH2)
na(Cꢀ
/
/s(NH2)
s(NH2)3
na(CH3)
ns(NH2)4
na(NH2)5
334.54
64.00
Calculated vibrational frequencies scaled by 0.9614.
a
The number in upper case of the assignment and the respective normal mode is indicated in the vibrational spectra show in Fig. 5.
imum values of the absorption spectrum in 635
and 632 nm for NB and NB-5-N-methacrylamide
correspond to energies of 0.06973 and 0.0709
Hartrees, which are lower than the predicted
electronic transition, probably due to the solvent
stabilization effect. Nevertheless, the ordering and
the small difference in energy between the two dyes
are in accordance to the previous quantum chemi-
cal calculations.
(fF). For NB fF is 0.01 while for NB-5-N-
methacrylamide, fF is 0.1. The fluorescence de-
cays of the dyes in water are practically mono-
exponential with lifetimes of 0.76 ns and 1.11 ns,
for NB and NB-5-N-methacrylamide, respectively.
The electronic absorption and emission spectra
and the fluorescence decay profile of NB-5-N-
methacrylamide in water are shown in Fig. 3 and
Fig. 4, respectively.
The fluorescence emission spectra of the dyes
are similar in energy with emission maximum at
665 nm and 667 nm for NB and NB-5-N-
methacrylamide, respectively. However the dyes
have very different fluorescence quantum yields
The difference in fluorescence quantum yield
does not reflects into a difference in lifetimes which
indicates that the two dyes may have slightly
different deactivation pathways of the electronic
excited state. It is well known that some dyes with

3110
H.P.M. Oliveira et al. / Spectrochimica Acta Part A 58 (2002) 3103ꢀ3111
/
Table 6
Observed and calculated IR wavenumbers and intensities for NB-5-methacrylamide compound using the method B3LYP/6-31G(d)
Mode
Freq. scaled
IR intens.
Measured peak
Assignmenta
H)
v60(a)
v63(a)
v75(a)
v81(a)
v86(a)
v88(a)
v89(a)
v93(a)
v97(a)
v106(a)
v108(a)
v124(a)
v125(a)
v128(a)
v129(a)
v133(a)
v153(a)
812.3
857.0
48.51
11.44
817.13
857.49
rv(Cꢁ
Ring deformationsꢁ
Ring breathing
d(CH2ꢁCH3)
d(CꢁH)ꢁrr(CH2)
d(CꢁH)
nas(CꢁOꢁ
d(CꢁH)ꢁ
rt(CH2)ꢁRing stretchꢁ
rt(CH2)ꢁd(CꢁH)ꢁn(Nꢁ
d(CꢁH)ꢁRing stretch
s(CH2)ꢁn(NꢁC)ꢁd(Nꢁ
H)ꢁRing stretch 4
/
/
rt(CH2)
1001.8
1079.4
1160.3
1169.6
1183.6
1261.1
1313.1
1401.3
1432.6
1541.6
1572.7
1633.7
1723.3
2957.1
3511.5
112.88
17.30
1011.45
1075.05
1144.55
1169.77
1191.35
1255.47
1334.52
1383.94
1421.22
1549.82
1586.25
1618.75
1654.63
2968.51
3340.59
/
577.36
48.69
/
/
/
36.77
/
/C)ꢁ
/
d(Cꢁ
/
H)
nas(Cꢁ
d(Nꢁ
C)
464.84
1175.41
64.64
/
/
rt(CH2)ꢁ
/
/C)
/
/
/
H)
/
/
/
/
100.20
587.44
595.26
62.41
/
/
/
/
/
/
H)ꢁRing stretch 5
/
d(Nꢁ
/
/
n(Cꢀ
/
C)
O)6
69.31
16.32
104.11
n(Cꢀ
/
nas(CH3)7
n(Nꢁ
H)8
/
Calculated vibrational frequencies scaled by 0.9614.
a
The number in upper case of the assignment and the respective normal mode is indicated in the vibrational spectra show in Fig. 5.
amino groups undergo a twisted intramolecular
charge transfer (TICT) process in electronic ex-
cited state. NB and Nile red are dyes which present
a certain TICT character in the S1 electronic
excited state, and in such a case, the fluorescence
quantum yield are low. Therefore, the longer
lifetime and larger fluorescence quantum yield of
the NB-5-methacrylamide can be ascribed to a
partial inhibition of the TICT process when the
NH2 is replaced by the methacrylamide in the 5-
position of the aromatic extended ring of the dye.
The charge density (Mulliken charge) of the
Table 4, Table 5 and Table 6, and compared with
IR spectra of the compounds at room tempera-
ture. The calculated frequencies for the harmonic
potential and the spectral intensities are computed
in the double harmonic approximation. In addi-
tion, the dipole moment derivatives and polariz-
ability derivatives assumed in the calculation are
those of the isolated molecular systems. Never-
theless, there is a good agreement between experi-
N(35) atom was calculated and the values are ꢂ
/
0.805 (NB) and ꢂ0.773 (NB-5-methacrylamide).
/
Considering this result, the difference in dipole
moment and ionization potential of the two dyes
molecules previously calculated, then the charge
injection process of the nonbonding n electron
density of the N(35) to the p dye ring should be
attenuated, and thus lessening TICT process.
3.4. Vibrational spectra
The calculated IR spectra obtained from the
B3LYP/6-31G(d) level of theory is reported in
Fig. 5. FT-IR spectra of MAA, NB and NB-5-methacrylamide.

H.P.M. Oliveira et al. / Spectrochimica Acta Part A 58 (2002) 3103ꢀ
/3111
3111
mental and simulated IR spectra for the relative
intensities of the different group frequencies. The
Conselho Nacional de Desenvolvimento Cient´ıfico
e Tecnolo´gico (CNPq) for financial support.
main IR bands are in region of 1500ꢀ
and 3000 cmꢂ1 for the MAA; 1500ꢀ
and 3000ꢀ
3400 cmꢂ1 (ring-stretching vibrations,
s(CꢁH), s(NꢁH) and s(CꢀO) vibrations) for the
/
1700 cmꢂ1
1700 cmꢂ1
,
/
/
/
/
/
References
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comparison between the theoretical and experi-
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Acknowledgements
We express thanks to the Fundacao de Amparo
¸˜
a Pesquisa do Estado de Sao Paulo (FAPESP) and
˜