Third-order nonlinear optical properties of a new type of D-π-D unsymmetrical phenoxazinium chloride with resonance structures

Article abstract of DOI:10.1016/j.chemphys.2011.02.013

A new series of unsymmetrical phenoxazinium chlorides, featuring a heterocyclic aromatic π-bridge with dialkylamino donors, were evaluated in acetonitrile solution for third-order nonlinear optical properties at 532 nm using a Z-scan technique. The title

Full text of DOI:10.1016/j.chemphys.2011.02.013

Chemical Physics 382 (2011) 74–79
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Chemical Physics
journal homepage: www.elsevier.com/locate/chemphys
Third-order nonlinear optical properties of a new type of D–
phenoxazinium chloride with resonance structures
p
–D unsymmetrical
b
Jian-Feng Ge a,c, Yue-Ting Lu a, Qing-Feng Xu a, Wu Liu a, Na-Jun Li a, Ru Sun a, , Ying-Lin Song ,
⇑
Jian-Mei Lu a,
⇑
a Key Laboratory of Organic Synthesis of Jiangsu Province, Soochow University, Suzhou 215123, China
b School of Physical Science and Technology, Soochow University, Suzhou 215006, China
c Key Laboratory for Carbon-Based Functional Material and Device of Jiangsu Province, Soochow University, Suzhou 215123, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new series of unsymmetrical phenoxazinium chlorides, featuring a heterocyclic aromatic p-bridge with
Received 30 November 2010
In final form 23 February 2011
Available online 28 February 2011
dialkylamino donors, were evaluated in acetonitrile solution for third-order nonlinear optical properties
at 532 nm using a Z-scan technique. The title compounds exhibit strong reverse saturable absorption and
nonlinear refraction. The third-order nonlinear optical properties were obtained under nanosecond and
picosecond laser beams. The nonlinear mechanism is revealed by the excited-state nonlinearity, as
observed from a picosecond pump-probe response experiment for one of the compounds. They are poten-
tial nonlinear optical materials because they also have good solubility in polar solvents and good thermal
stability.
Keywords:
Phenoxazinium chloride
Third-order NLO
Resonance structure
Z-scan
Ó 2011 Elsevier B.V. All rights reserved.
NLO material
Functional dyes
1. Introduction
capacity due to the positive charges localized on the central ring that
may, in turn, lead to more significant NLO activity [23,24]. An
Nonlinear absorption materials have attracted extensive atten-
tion quite recently due to their different nonlinear absorption pro-
cesses which have a potential impact on their application in
science and technology [1–5]. Organic third-order nonlinear opti-
cal (NLO) materials, which can be designed and obtained as speci-
fied structures, and possess relatively large nonlinearities and fast
response time [6–8], are given special attention. The molecular
structural design is based on the empirical models of the aromatic
oxyallyl-based dye with no central ring, BM4i4i, and has large NLO
activities was recently reported [24–26]. The large coupling between
the two valence bond (VB) resonance structural forms is responsible
for the large second hyperpolarizability values [26–29].
To meet these requirements, benzo[a]phenoxazinium salts with
resonance structures were recently designed. They demonstrated
strong reverse saturable absorption (RSA) and nonlinear refraction
with third-order NLO coefficient v(3) = 0.42–1.20 ꢀ 10ꢁ11 esu and
cyclic compounds or conjugated systems (i.e.,
p-bridges) that may
the second hyperpolarizabilities
c
’ = 2.75–7.29 ꢀ 10ꢁ29 esu under
be attached by the donor (D) and/or acceptor (A) groups [9–16].
Large conjugation, donor and/or acceptor substitutions, and
recently suggested diradical character are normally the major
inducers for significant NLO activity [17]. The large third-order NLO
properties of the widely studied centrosymmetric squaraine mole-
cules have been attributed to their D–A–D structure, with their cen-
tral rings acting as acceptors due to the positive charges localized on
several positions around them [18–22]. The corresponding croconate
dyes have been proposed to be derivatives of the oxyallyl substruc-
ture, such as the squaraine, which would have a larger acceptance
a nanosecond laser beam at 532 nm [30]. However, they partially
dissociate to the free base and the corresponding acids in highly
diluted neutral solvents, which may affect future research. Phenox-
azinium chlorides, used for anti-protozoal bioassays [31,32], were
selected to eliminate the aforementioned disadvantages. In this
paper, six unsymmetrical phenoxazinium chlorides (Fig. 1) were
selected and evaluated for their third-order NLO properties. The
delocalized D–p–D structure of the phenoxazinium chlorides
(1a–f) is constructed by a positively charged heterocyclic aromatic
bridge and two amino groups as donors, and may be expressed by
three stable resonance structures (i–iii). The amino groups partic-
ipated well in the resonance. The presence of the large polarizable
conjugated p-electrons in the aromatic heterocycle, as well as the
potential electron fluctuant ability, complied with the need for
⇑
Corresponding authors. Address: College of Chemistry, Chemical Engineering
and Materials Science, Soochow University, 199 Ren’ai Road, Suzhou Industry Park,
Suzhou 215123, China. Tel.: +86 512 65880368; fax: +86 512 65880367 (J.-M. Lu).
E-mail addresses: sunru924@suda.edu.cn (R. Sun), lujm@suda.edu.cn (J.-M. Lu).
promising third-order NLO materials.
0301-0104/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.chemphys.2011.02.013

J.-F. Ge et al. / Chemical Physics 382 (2011) 74–79
75
Fig. 1. Synthesis and resonance structures of unsymmetrical phenoxazinium chlorides.
2. Experimental
3. Results and discussion
2.1. Materials
3.1. Structure study with quantum-chemical calculation
3-(Diethylamino)-7-(piperidin-1-yl)phenoxazin-5-ium chloride
(1a), 3-(dipropylamino)-7- (piperidin-1-yl)phenoxazin-5-ium
chloride (1b), 3-(dibutylamino)-7-(piperidin-1-yl)phenoxazin-5-
ium chloride (1c), 3-(diethylamino)-7-thiomorpholinophenoxa-
zin-5-ium chloride (1d), 3-(diethylamino)-7-morpholinophenoxa-
zin-5-ium chloride (1e), and 3-(diethylamino)-7- (pyrrolidin-1-yl)
phenoxazin-5-ium chloride (1f) were synthesized by the reported
method (Fig. 1) [31,32]. Their structures are consistent with the
reported values by 1HNMR analysis.
To demonstrate an inside view of the unsymmetrical phenoxaz-
inium cation, the structures were fully optimized by using the DFT
method for the ground states and the CIS method for the excited
states [35]. The basis set used was 6–31G⁄. Based on the optimized
structures, and with the same basis set, vibrational frequencies
were calculated. All predicted vibrational spectra have no imagi-
nary frequency, which implies that the optimized geometries were
located at the local lowest point on the potential energy surface
[36]. All the calculations were performed using the Gaussian 98
program package [37].
The typical molecular orbitals and electric charge distributions
of phenoxazinium cation (1a+), are given in Fig. 2. The graphics
of bonding orbitals clearly demonstrated that the bonding elec-
trons are mainly located in the aromatic phenoxazinium skeleton
and the wings of these structures. The conjugations between the
two nitrogen atoms and phenoxazinium skeleton are contributed
by the orbitals of HOMO-2 and HOMO-5. Comparably, the anti-
bonding orbitals are mostly located in the central part of the
molecular. From the mapping of Total Charge Density (TCD) with
potential, the positive charge is evidently located around the phe-
noxazinium cation. The unsymmetrical structure with two differ-
ent amino groups only makes the slight difference for each
molecular orbital. The calculated HOMO (eV) and LUMO (eV) ener-
gies of phenoxazinium cations (1a+–f+) are listed in Table 1.
2.2. Instruments
Thermogravimetric analyses (TGA) curves were obtained using
a
Thermo-Gravimetric/Differential Thermal Analyzer (TG/DTA
6300, SII NanoTechnology Inc.). UV–Vis spectra were recorded on
a Perkin-Elmer k-17 spectrometer using a 1 cm square quartz cell.
The third-order NLO properties were measured by the Z-scan
technique [33]. An Nd:YAG 532 nm laser (EKSPLA) with a pulse
width of 4 ns (fwhm) and a repetition rate of 10 Hz was used for
nanosecond Z-scan measurements. A Q-switched Nd:YAG 532 nm
laser (EKSPLA) with a pulse width of 21 ps (fwhm) and repetition
rate of 2 Hz was used for picosecond Z-scan measurements. The
nanosecond Z-scan test of the title compounds (1a–f) was mea-
sured using a 2 mm cell with an incident laser beam energy of
6.2
l
J, while the picosecond Z-scan test was measured using a
3.2. Solubility and thermal stability
2 mm cell with an incident laser beam of 0.4
lJ. Two Rj-7620 en-
ergy ratiometers were employed as detectors. The solution was
placed in a high-precision mobile platform moving along the direc-
tion of the incident light (Z). The Z-scan curve, which is the trans-
mittance as a function of the sample position, may thus be
obtained.
The phenoxazinium chlorides (1a–f) have good solubility in
most polar solvents, such as water, acetone, chloroform and meth-
anol. Fig. 3 shows their TGA curves in a nitrogen environment at a
scan rate of 10 °C ꢂ minꢁ1. Their thermal stabilities are comparable,
up to approximately 250 °C due to their structural similarity. As
seen from the TGA curves, the length of substituted alkyl groups
attached to the nitrogen atom has no significant effect on the sta-
bility of the phenoxazinium chlorides. It shows that the phenoxaz-
inium chloride is stable enough for organic materials as a low
molecular weight organic compound. Both solubility and thermal
stability show that the title compounds are promising candidates
for optical device process.
In the picosecond pump-probe experiments, a Q-switched
Nd:YAG laser (EKSPLA) that delivers 21 ps (fwhm) single pulse at
532 nm with 10 Hz repetition rate was used. The pump–probe
experimental setup was a standard arrangement, and the probe
peak irradiance was approximately 8% of the pump irradiance
[34]. A variable delay was introduced into the probe path, and
the two pulses were recombined at the sample cell (2 mm thick-
ness) at a small angle. The probe waist was three times smaller
than that of the pump. The small angle between the beams, consid-
ering that the probe spot size was noticeably smaller than the
pump, ensured that the probe could test a uniformly excited region
of material in the 2 mm cell. The polarization of the pump beam
was set perpendicular to that of the pump beam to avoid interfer-
ence. The change in the probe beam intensity as a function of time
delay was recorded after the pump beam.
3.3. Linear optical properties
The title compounds exhibit absorption maxima in the range of
644–653 nm (Fig. 4). There is only small variation in the absorption
maxima with different amino groups. The rigid five member ring
(1f) has influence the p–p conjugation, the blue shift of this

76
J.-F. Ge et al. / Chemical Physics 382 (2011) 74–79
Fig. 2. Molecular orbitals and electric charge distributions of phenoxazinium cation (1a+) (TCD: Total Charge Density; NBO: Natural Bond Orbital; S0: Ground state; S1:
Excited state.)
compound is shown. The absorption maxima are gradually in-
creased (1e < 1d < 1a < 1b < 1c), which is influenced by the electric
properties of the donor’s abilities of the alkyl groups attached with
the nitrogen atoms (–C4H9 > –C3H7 > –C2H5 > –C2H4S > –C2H4O).
All the compounds have almost no absorbance at 532 nm, which
ensures low intensity and small temperature change for the
third-order NLO test [38].
3.4. Nonlinear optical properties
To obtain the second hyperpolarizabilities, the concentration of
the title compounds were maintained at 1.79 ꢀ 10ꢁ4 mol ꢂ Lꢁ1 in
acetonitrile solution. The nonlinearity of a pure acetonitrile solvent
was also measured under the same conditions and no signal could
be obtained. Thus, the nonlinearity of the solvent was ignored both
Fig. 3. The thermal stability of the compounds 1a–f.
Table 1
Calculated HOMO (eV) and LUMO (eV) energies of phenoxazinium cations.
under the nanosecond and picosecond laser beams [39,40]. Typical
Entry Cation ꢁR1, ꢁR1
ꢁR2, ꢁR2
HOMO
(eV)
LUMO
(eV)
D
(eV)
EHL
valleys of the normalized transmittance of 1a, as shown in Fig. 5,
indicate that the laser pulses experience strong RSA.
The nonlinear absorption component was evaluated under an
open aperture (OA). Since light transmittance (T) is a function of
the sample’s Z-position (with respect to the focal point at Z = 0),
1
2
1a+
1b+
(CH2)5
(CH2)5
C2H5, C2H5
n–C3H7, n–
C3H7
n–C4H9, n–
C4H9
ꢁ5.955 ꢁ8.408 2.453
ꢁ5.912 ꢁ8.353 2.441
3
1c+
(CH2)5
ꢁ5.892 ꢁ8.326 2.434
the nonlinear absorption [
be well described by the classical Eq. (1), where
and effective third-order NLO absorptive coefficients, respectively.
Here, is the time and L is the optical path [41–43].
a
= b(Ii)] and linear absorption (
a0) can
4
5
6
1d+
1e+
1f+
(CH2)2S(CH2)2
(CH2)2O(CH2)2 C2H5, C2H5
(CH2)4 C2H5, C2H5
C2H5, C2H5
ꢁ6.097 ꢁ8.454 2.357
ꢁ6.077 ꢁ8.521 2.444
ꢁ5.955 ꢁ8.434 2.479
a
0 and are linear
a
s

J.-F. Ge et al. / Chemical Physics 382 (2011) 74–79
77
Fig. 4. Linear absorption spectra of 1a–f in CH3CN (c = 1 ꢀ 10ꢁ5 mol ꢂ Lꢁ1).
Fig. 6. Z-scan data of refractive parts for 1a (Data are the ratio of CA/OA
transmittance; nnanosecond, ppicosecond).
values at valley and peak positions (DTV–P) are found to correspond
to a set of equations,
DZV–P = 1.72p /
x02/k, and n2eff = ka0DTV–P
a
[0.812
p
I(1ꢁeꢁ L)], which were derived for a third-order NLO pro-
cess [41,44]. An effective third-order nonlinear refractive index n2
may be derived from
DTV–P, where a0 is the linear coefficient, L is
the sample thickness, I is the peak irradiation intensity at the focus,
and k is the wavelength of the laser.
From the b and n2 values, the effective third-order NLO suscep-
tibilities (
to the following equations:
vI(3) = 9 ꢀ 108 0n02c2b/(4
[(vI(3))2 + (vR(3))2]1/2, respectively [41,45].
The second hyperpolarizabilities (c0) of the compounds were
v
(3)) of the title compounds may be calculated according
e
xp p =
), vR(3) = cn02n2/(80 ), and v(3)
obtained by c
’ = v(3)/[N((n02 + 2)/3)4] [40,41], where N is the den-
sity of the molecules in the unit of number of molecules per cm3,
and n0 is the linear refractive index of the acetonitrile
(n0 = 1.344). The third-order NLO properties obtained using nano-
second and picosecond laser beams are listed in Table 2.
Fig. 5. Z-scan data of OA transmittance for 1a (nnanosecond, ppicosecond).
ꢀ
ꢁ
Z
1
a0L
a0
1 ꢁ eꢁ
The effective v(3 )and
c
’ are up to 5.35–8.78 ꢀ 10ꢁ11 and 1.14–
s2
pffiffiffi
TðZÞ ¼
ln 1 þ bIiðZÞ
eꢁ
ds:
a0L
8.78 ꢀ 10ꢁ28 esu by the nanosecond Z-scan results, while
3.38–4.20 ꢀ 10ꢁ12 and 7.17–8.91 ꢀ 10ꢁ30 esu by the picosecond
Z-scan results. The data obtained from the former are one order
of magnitude or nearly 15 times larger than those from the pico-
second Z-scan test. At this point, due to the complexities of the
third-order NLO mechanisms, it is difficult to provide a precise
explanation for the obtained values. However, it is evident that
the energy and frequency of the laser beam and the other condi-
a0
p
bIiðZÞð1 ꢁ eꢁ
Þ
ꢁ1
ð1Þ
From Fig. 6, for the typical refractive parts of 1a, the compounds
also exhibit strong nonlinear refraction at 532 nm. The nonlinear
refractive data were obtained from the ratio of the closed aperture
(CA) transmittance divided by the OA transmittance. A positive
refractive nonlinearity is observed in Fig. 6, indicating a self-
focusing behavior. The valley and peak positions occur at equal
distances from the focus. Moreover, the valley–peak separation
tions affect the effective v(3) and
c’ values.
The energies of cation’s HOMO are somewhat related to the
(D
ZV–P) and the difference between the normalized transmittance
third-order NLO properties in nanosecond test. 1d and 1f show

78
J.-F. Ge et al. / Chemical Physics 382 (2011) 74–79
Table 2
NLO properties of 1a–f in CH3CN solution.
c
Entry
Compds.
T0
Laser
n2 (10ꢁ17m2 ꢂ Wꢁ1
)
beff (10ꢁ10m ꢂ Wꢁ1
)
v(3) (10ꢁ11 esu)
v(3) (10ꢁ11 esu)
v(3) (10ꢁ11 esu)
c
’ (10ꢁ29 esu)
R
I
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1a
1b
1c
1d
1e
1f
68%
69%
68%
62%
61%
67%
61%
65%
60%
58%
53%
57%
nsn
nsn
nsn
nsn
nsn
nsn
psp
psp
psp
psp
psp
psp
7.33
5.73
5.46
9.33
6.96
9.37
0.403
0.391
0.341
0.402
0.445
0.369
6.21
5.68
5.93
6.47
5.56
7.26
0.428
0.418
0.397
0.451
0.374
0.413
6.52
5.09
4.86
8.30
6.19
8.34
0.359
0.347
0.303
0.358
0.395
0.328
2.34
2.14
2.23
2.44
2.09
2.74
0.161
0.157
0.150
0.170
0.141
0.156
6.93
5.53
5.35
8.65
6.53
8.78
0.393
0.381
0.338
0.396
0.420
0.363
14.7
11.7
11.4
18.4
13.9
18.6
0.833
0.808
0.717
0.840
0.891
0.770
9
10
11
12
c
n
p
Concentration: 1.79 ꢀ 10ꢁ4 mol Lꢁ1
.
With nanosecond laser beam at 6.2
l
J, 4 ns.
With picosecond laser beam at 0.4
lJ, 21 ps.
higher
c
’ in nanosecond test (Table 2, Entry 4, 6), their energies of
the pump pulse. The instant drop of the probe is dominant due
to the excited singlet absorption, which has a larger cross section
than that of the ground state. Once the pump pulse has passed
through the sample, the initial response is followed by recovery
and the appearance of a long low transmission tail. This behavior
is consistent with induced absorption in the first excited singlet
state that increases as the excited state is populated, and subse-
quently diminishes as the population in that state relaxes to the
ground state. Hence, the nonlinear mechanism of the compound
is typical excited-state nonlinearity [38]. The NBO charge distribu-
tions of ground state and excited state for 1a+ are shown in the
Fig. 2. There are only slight changes for the charge distributions of
each atoms, that might be a reason for the comparatively stability
of the excited state.
HOMO (1d+, 1f+) are quite low (Table 1, Entry 4, 6). Antiphonally,
higher HOMO energies of 1b+, 1c+ (Table 1, Entry 2, 3) lead to the
decrease of
has low HOMO energy (Table 1, Entry 5) and relatively low
probably the result of this compound is influenced by other factors,
c
’ values (Table 2, Entry 2, 3). 1e+ (Table 2, Entry 5)
c
’ value,
for example, response time.
Both low HOMO energies and the small energy gaps (
benefit for the third-order NLO properties in picosecond test. Cat-
ions (1a+–b+, 1d+–e+) with lower HOMO energies and small
EHL
values (Table 1, Entry 1, 2, 4, 5) show better ’ values of compounds
(Table 2, Entry 7, 8, 10, 11), and cations (1c+, 1f+) with higher
HOMO energy (Table 1, Entry 3) or big EHL value (Table 1, Entry
3) show slight decline of ’ values (Table 2, Entry 9, 12).
Moreover, the longer alkyl chain attached to nitrogen atom
might slightly decrease theirs ’ values (Table 2, Entry 1–3, 7–9)
DEHL) are
D
c
D
c
c
4. Conclusion
from the results of 1a–c under nanosecond and picosecond laser
beams’ data. All the results under nanosecond laser beams are bet-
ter than the previous reported benzo[a]phenoxazinium salts [30].
The third-order NLO properties of the phenoxazinium chloride re-
veal that the D–p–D unsymmetrical phenoxazinium chloride with
resonance structures is a potential candidate for NLO material.
In summary, six unsymmetrical phenoxazinium chlorides are
selected for the evaluation of third-order nonlinear optical proper-
ties. These compounds have potential electron fluctuant abilities
with resonance heterocyclic aromatic bridge-donor structural
characteristics. The title compounds exhibit strong reverse satura-
ble absorption and nonlinear refraction. The effective third-order
NLO susceptibilities (v c’)
(3)) and second hyperpolarizabilities (
3.5. Pump-probe measurement
are up to 5.35–8.78 ꢀ 10ꢁ11 and 1.14–8.78 ꢀ 10ꢁ28 esu by nanosec-
ond Z-scan results, while 3.38–4.20 ꢀ 10ꢁ12 and 7.17–
8.91 ꢀ 10ꢁ30 esu by picosecond Z-scan results. The picosecond
pump–probe response of compound 1a implies that the nonlinear
mechanism is of excited-state nonlinearity. The characteristics of
solubility and thermal stability indicate they are potential candi-
dates for third-order NLO materials.
To gain insight into the nonlinear origin of these compounds,
picosecond time-resolved pump-probe experiments were con-
ducted at 532 nm on 1a. The experimental curve is shown in
Fig. 7. Initially, the absorption of the solution increases as a func-
tion of time, which is consistent with the temporal integration of
Acknowledgments
We thank Professor Masataka Ihara (Hoshi University, Japan)
for the encouragements and helpful discussion about the synthesis
of title compounds. We are also grateful for financial support from
the Natural Science Fund of China (20876101), the Natural Science
Fund (BK2009113) and the Natural Science Fund for Colleges and
Universities (08KJB430013) in Jiangsu Province.
References
[1] J.E. Ehrlich, X.L. Wu, Y.L. Lee, Z.Y. Hu, H. Rockel, S.R. Marder, J.W. Perry, Opt.
Lett. 22 (1997) 1843.
[2] G.S. He, L.S. Tan, Q. Zheng, P.N. Prasad, Chem. Rev. 108 (2008) 1245.
[3] M. Pawlicki, H.A. Collins, R.G. Denning, H.L. Anderson, Angew. Chem., Int. Ed.
48 (2009) 3244.
Fig. 7. Pump–probe results for the compound 1a.
[4] D.A. Parthenopoulos, P.M. Rentzepis, Science 245 (1989) 843.

J.-F. Ge et al. / Chemical Physics 382 (2011) 74–79
79
[5] S. Kawata, H.B. Sun, T. Tanaka, K. Tanaka, Nature 412 (2001) 697.
[6] T. Kaino, S. Tomaru, Adv. Mater. 5 (1993) 172.
[32] J.F. Ge, C. Arai, M. Kaiser, S. Wittlin, R. Brun, M. Ihara, J. Med. Chem. 51 (2008)
3654.
[7] H.S. Nalwa, Adv. Mater. 5 (1993) 341.
[8] J.L. Bredas, C. Adant, P. Tackx, A. Persoons, B.M. Pierce, Chem. Rev. 94 (1994)
243.
[9] G.l. Torre, P. Vazquez, F. Agullo-Lopez, T. Torres, Chem. Rev. 104 (2004) 3723.
[10] H. Rath, J. Sankar, V. PrabhuRaja, T.K. Chandrashekar, A. Nag, D. Goswami, J.
Am. Chem. Soc. 127 (2005) 11608.
[11] C. Bucher, C.H. Devillers, J.C. Moutet, G. Royal, E. Saint-Aman, Coordin. Chem.
Rev. 253 (2009) 21.
[12] J.A. Delaire, K. Nakatani, Chem. Rev. 100 (2000) 1817.
[13] R.L. Roberts, T. Schwich, T.C. Corkery, M.P. Cifuentes, K.A. Green, J.D. Farmer,
P.J. Low, T.B. Marder, M. Samoc, M.G. Humphrey, Adv. Mater. 21 (2009) 1.
[14] M.P. Cifuentes, M.G. Humphrey, J.P. Morrall, M. Samoc, F. Paul, C. Lapinte, T.
Roisnel, Organometallics 24 (2005) 4280.
[15] J. Mattu, T. Johansson, G.W. Leach, J. Phys. Chem. C 111 (2007) 6868.
[16] A. Faccinetto, S. Mazzucato, D. Pedron, R. Bozio, S. Destri, W. Porzio, Chem.
Phys. Chem. 9 (2008) 2028.
[33] C. Zhang, Y.L. Song, X. Wang, F.E. Kühn, Y.X. Wang, Y. Xu, X.Q. Xin, J. Chem.
Mater. 13 (2003) 571.
[34] T. Xia, A. Dogariu, K. Mansour, D.J. Hagan, A.A. Said, E.W. Van Stryland, S. Shi, J.
Opt. Soc. Am. B 15 (1998) 1497.
[35] C. Lee, W.T. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[36] W. Li, Q.F. Wu, Y. Ye, M.D. Luo, L. Hu, Y.H. Gu, F. Niu, J.M. Hu, Spectrochim. Acta.
A 60 (2004) 2343.
[37] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
J.A. Montgomery, T.J. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J.
Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson,
H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian,
J.B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J.
Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A.
Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels,
M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman,
J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A.
Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-
Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W.
Chen, M.W. Wong, C. Gonzalez, J.A. Pople, Gaussian 98, Revision A. 5, Gaussian,
Inc, Pittsburgh PA, 2003.
[17] S. Alolse, J. Rehault, B. Moine, O. Poizat, G. Buntinx, V. Lokshin, M. Vales, A.
Samat, J. Phys. Chem. A 111 (2007) 1737.
[18] Z. Fushi, Z.K. Kazuo, Chem. Phys. Lett. 441 (2007) 123.
[19] Z.Y. LI, Z.H. Jin, K. Kasatani, H. Okamoto, Chin. Phys. Lett. 22 (2005) 2282.
[20] C.W. Dirk, W.C. Herndon, F. Cervantes-Lee, H. Selnau, S. Martinez, P.
Kalamegham, A. Tan, G. Campos, M. Velez, J. Zyss, I. Ledoux, L.T. Cheng, J.
Am. Chem. Soc. 117 (1995) 2214.
[38] J.Y. Yang, J.H. Gu, Y.L. Song, S. Guang, Y.X. Wang, W.H. Zhang, J.P. Lang, J. Phys.
Chem. B 111 (2007) 987.
[21] K. Tran, G.W. Scott, D.J. Funk, D.S.J. Moore, Chem. Phys. 100 (1996) 11863.
[22] J.H. Andrews, J.D.V. Khaydarov, K.D. Singer, Opt. Lett. 19 (1994) 984.
[23] Z. Li, Z.H. Jin, K. Kasatani, H.B. Okamoto, Physica B 382 (2006) 229.
[24] Z. Li, Z.H. Jin, K. Kasatani, H. Okamoto, S. Takenaka, J. Jpn. Appl. Phys. 44 (2005)
4956.
[25] H. Langhals, Angew. Chem., Int. Ed. 42 (2003) 4286.
[26] S. Tatsuura, M. Tian, M. Furuki, Y. Sato, I. Iwasa, H. Mitsu, App. Phy. Lett. 84
(2004).
[39] R. Signorini, C. Ferrante, D. Pedron, M. Zerbetto, E. Cecchetto, M. Slaviero, I.
Fortunati, E. Collini, R. Bozio, A. Abbotto, L. Beverina, G.A. Pagani, J. Phys. Chem.
A 112 (2008) 4224.
[40] M.T. Zhao, B.P. Singh, P.N. Prasad, J. Chem. Phys. 89 (1988) 5535.
[41] M. Sherk-Bahae, A.A. Said, T.H. Wei, D.J. Hagan, E.W. van Stryland, IEEE J.
Quant. Electron. 26 (1990) 760.
[42] C. Zhang, Y.L. Song, Y. Xu, H.K. Fun, G.Y. Fang, Y.X. Wang, X.Q. Xin, Dalton Trans.
28 (2000) 23.
[27] Y. Orimoto, Y. Aoki, J. Phys. Chem. A 111 (2007) 8241.
[28] H. Fukui, R. Kishi, T. Minami, H. Nagai, H. Takahashi, T. Kubo, K. Kamada, K.
Ohta, B. Champagne, E. Botek, M. Nakano, J. Phys. Chem. A 112 (2008) 8423.
[29] K. Yesudas, K. Bhanuprakash, J. Phys. Chem. A 111 (2007) 1943.
[30] B.Q. Liu, R. Sun, J.F. Ge, N.J. Li, X.L. Shi, L.H. Qiu, J.M. Lu, Dyes. Pig. 88 (2011) 50.
[31] J.F. Ge, C. Arai, M. Ihara, Dyes. Pig. 79 (2008) 33.
[43] Y.Y. Niu, Y.L. Song, H.W. Hou, Y. Zhu, Inorg. Chem. 44 (2005) 2553.
[44] H.W. Hou, Y.L. Wei, Y.L. Song, Y. Zhu, L.K. Li, Y.T. Fan, J. Mater. Chem. 12 (2002)
838.
[45] C. Zhang, Y.L. Song, X. Wang, F.E. Kühn, Y.X. Wang, Y. Xu, X.Q. Xin, J. Mater.
Chem. 13 (2003) 571.