Synthesis and chemical-optical characterization of novel two-photon fluorescent borinates derived from Schiff bases

Article abstract of DOI:10.1016/j.jorganchem.2013.12.036

Herein is reported the synthesis and characterization of eight borinates (2a-h) prepared from the reaction of the corresponding bidentate imine ligands (1a-h) and diphenylborinic acid. All compounds were characterized by MS, IR and NMR spectroscopies wher

Full text of DOI:10.1016/j.jorganchem.2013.12.036

Journal of Organometallic Chemistry 755 (2014) 33e40
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and chemicaleoptical characterization of novel two-photon
fluorescent borinates derived from Schiff bases
,
a
b
Cristina C. Jiménez a, Norberto Farfán a , Margarita Romero-Avila , Mario Rodríguez ,
Laura Aparicio-Ixta b, Gabriel Ramos-Ortiz b, José Luis Maldonado b, Rosa Santillan c,
Nancy E. Magaña-Vergara c, Ma. Eugenia Ochoa c
*
a Facultad de Química, Depto. de Química Orgánica, Universidad Nacional Autónoma de México, 04510 México D.F., Mexico
b Centro de Investigaciones en Óptica A.P. 1-948, 37000 León, Gto., Mexico
c Depto. de Química, Centro de Investigación y de Estudios Avanzados del IPN, Apdo. Postal. 14-740, 07000 México D.F., Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
Herein is reported the synthesis and characterization of eight borinates (2aeh) prepared from the reaction
of the corresponding bidentate imine ligands (1aeh) and diphenylborinic acid. All compounds were
characterized by MS, IR and NMR spectroscopies whereas the molecular structures of derivatives 2c and 2e
were also studied by X-ray diffraction analysis that corroborated the presence of a tetra-coordinated
boron atom. In addition, the linear and nonlinear optical (NLO) characterization of these molecules
Received 10 January 2013
Received in revised form
11 December 2013
Accepted 21 December 2013
having De
nonlinear optical responses were measured by using the two-photon excited fluorescence and the third-
harmonic generation (
3 determination) techniques. The borinates showed two-photon absorption (2PA)
p peD and Dep peA electronic systems was performed, i.e., the third-order
eC]Nþe eC]Nþe
Keywords:
Borinates
Schiff bases
NLO properties
TPA or 2PA
c
effect in solution under femtosecond excitation: 2g and 2h having Dep peA architecture showed
eC]Nþe
the largest 2PA cross-sections (s2PA) values at 760 nm: 124 and 174 GM (1 GM ¼ 10ꢀ50 cm4 s), respectively,
while the values for 2e and 2f that possess Dep peD structure were 12 and 37 GM. The c
eC]Nþe 3 values,
with nanosecond excitation, were of the order of 10ꢀ12 esu at 1200 nm.
Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
(asymmetric); (ii) quadrupolar (symmetric), Ae
peA, DepeD, Ae
p
eDe eA, De eAe eD; and (iii) octupolar; 3-branched, A3e
p
p
p
In the last two decades there has been an increasing interest in
the study of materials possessing 2PA properties. In particular, great
efforts have been devoted to develop organic chromophores with
large 2PA cross-sections (s2PA) for a wide range of applications,
which include up-converted lasing [1], data storage and micro-
fabrication [2,3], two photon photodynamic therapy [4], labels to
track the migration of non-fluorescent drugs inside the cells and for
the localized release of bio-active species [5]. The research groups
of Marder [6e8], Prasad [9], and Blanchard-Desce [10,11], are
leading pioneers in this field.
(D-core) and D3e(A-core) [9]. For these systems the non-linear
optical response is a non-trivial function of the donor and
acceptor strengths,
p-conjugated bridge length and type, nature
of the conjugated core, torsional disorder, symmetry and topol-
ogy [12]. Additionally, the opto-electronic properties can be
tuned by the introduction into the
p-plane of elements such as
silicon [13], nitrogen [14], sulfur [15], phosphorus [16], and boron
[17].
In the case of boron compounds their accessible structural
design and facile synthesis [18] makes of them interesting mate-
rials for several photonic and opto-electronic devices [19], such as
organic light-emitting diodes (OLEDs) [20,21], organic photovoltaic
cells (OPVs) [22] and charge transport [23]. For these applications,
the three coordinated boron species have received considerable
For the design of 2PA chromophores, three essential compo-
nents are required: a strong
-bridge, and a strong -electron acceptor (A). Appropriate
combinations and numbers of these components have resulted in
p-electron donor (D), a polarizable
p
p
molecular systems of three general classes: (i) dipolar, Ae
p
eD
attention since the vacant p-orbital is a strong p-electron acceptor,
which promotes delocalization with adjacent organic conjugated
systems and also these boron derivatives can function as sigma
donor due to their electronegativity.
As for the four-coordinated systems, studies of the second-order
NLO character have shown that this property is enhanced with
* Corresponding author.
E-mail address: norberto.farfan@gmail.com (N. Farfán).
0022-328X/$ e see front matter Ó 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.12.036

34
C.C. Jiménez et al. / Journal of Organometallic Chemistry 755 (2014) 33e40
respect to the boron-free counterparts [24], as demonstrated in the
case of theoretical [25e27] and experimental [24] studies of stil-
bazoles and pyridines. similarly, zwitterionic borates show much
larger second-order NLO properties and higher transparency than
the uncharged pushepull species [28,29]. Our research group has
previously synthesized and optically characterized different boron
complexes [30e33], studying the second- and the third-order op-
tical nonlinearities in four-coordinated boron systems prepared
from tridentate ligands. In this kind of compounds the appropriate
combination of donoreacceptor groups and the formation of the
N / B coordinative bond optimize the nonlinear optical effects.
Among the advantages of tetra-coordinated compounds are an
intrinsic high electron affinity, a large capacity to perturb the
electronic structure by decreasing the LUMO level as well as the
possibility to obtain very stable compounds with high
transparency.
More recently, boron-containing two-photon absorbing fluo-
rophores based on a pyrazabole [34] core have shown s2PA values of
325 GM around 800 nm; in particular, for the ferrocenyl substituted
pyrazaboles, the two-photon absorption cross-section values were
enhanced by increasing the conjugation giving values as high as
1016 GM [35]. Other boron-containing 2PA fluorophores are based
on a one-dimensional conjugated system containing a terminal p-
carborane unit and various donor groups at the other end. These
systems exhibited 2PA cross-sections of 470 GM at 810 nm for the
diphenylamino-substituted chromophore and 200e300 GM at
700 nm for the chromophores containing oxygen donor groups
[36].
Investigations on the 2PA effect involving Schiff bases are scarce,
in spite of their facile synthesis and design [37e42]. In general it has
been shown that the cross section is highly increased upon
complexation to metals. In particular, for boron derivatives of Schiff
bases the studied systems include cyclodiborazane and pyrazabole
moieties as central cores [43]. Following our research on boron
complexes containing the coordinative N / B bond in electronic
pushepull systems, and on the search for new fluorescent chro-
mophores that could exhibit 2PA properties, we report herein the
facile synthesis and characterization of eight strong fluorescent
diphenylboron complexes (2aeh) with a strong electron donor
group (eNEt2) at the salicylidene derived fragment and different
substituents at the aniline fragment. The aim of this study was to
investigate the effect of the incorporation of different substituents
as well as the influence of the boron atom on the fluorescent and
NLO properties. Results show that while the Schiff bases exhibit
poor fluorescence emission, after boron complexation, an intense
green emission is observed when excited at 370 nm. Moreover,
incorporation of electron withdrawing substituents at the aniline
fragment of boron derived Schiff bases resulted in the enhance-
ment of the third-order nonlinearities, i.e., 2PA effect and third-
harmonic generation.
coupling constants are given in Hertz. Elemental analyses were
obtained on an EA 1108 FISONS Instruments analyzer. MS spectra
were obtained on a Thermo-Electron DFS (Double Focus Sector)
with a double sector mass analyzer of inverse geometry. The high
resolution mass spectra (HRMS) were determined with an Agilent
spectro-photometer.
2.2. Crystal structure determination
Crystals of compounds 2c and 2e suitable for X-ray diffraction
analysis were obtained by slow evaporation of solutions of chlor-
oform:ethyl acetate at room temperature. Data collection was
performed at 293 K on a Kappa CCD diffractometer with lMo-
ꢀ
¼ 0.71073 A radiation. The molecular structures of the com-
Ka
pounds were solved by direct methods using SIR2004 [45] and
were refined with SHELXL-97 [46], using full matrix least squares.
All non-hydrogen atoms were refined anisotropically, the H atoms
were refined using a riding model.
2.3. General procedure for the synthesis
The Schiff bases 1aeh were obtained by reaction of equimolar
amounts of 4-diethylamino-2-hydroxybenzaldehyde and the
appropriate aniline under reflux of ethanol for 12 h. Solvent excess
was eliminated with a DeaneStark trap, the solid precipitated was
collected by filtration and the products were purified by recrys-
tallization technique from ethanol [47,48].
The series of borinates 2aeh were prepared by reaction of the
corresponding Schiff base and diphenylborinic acid obtained from
the ethanol amine ester complex under reflux of ethyl acetate for
2 h. The borinates 2aeh were obtained in good yields as yellow
solids, which are soluble in common organic solvents.
2.3.1. N,N-Diethyl-2,2,3-triphenyl-2H-benzo[e][1,3,2]oxazaborinin-
7-amine (2a)
The title compound was prepared from 1a (0.50 g, 1.80 mmol)
and 0.46 g (2.00 mmol) of diphenylborinic acid to give 0.44 g of 2a
in 55% yield. M.P: 165e167 ꢁC. IR nmax: 3069, 3040, 2974,1612,1585,
1507, 1352, 1267, 1237, 1205, 1188, 1137, 695 cmꢀ1. 1H NMR (CDCl3,
500 MHz)
d
: 1.17 (6H, t, J ¼ 7.1 Hz, N(CH2CH3)2), 3.36 (4H, q,
J ¼ 7.1 Hz, N(CH2CH3)2), 6.15 (1H, s, H-2), 6.17 (1H, d, J ¼ 2.2, Hz, H-
4), 7.01e7.18 (12H, m, H-5, H-9, H-11, H-10, H-m, H-p), 7.44 (4H, d,
J ¼ 6.8 Hz, H-o), 8.08 (1H, s, H-7) ppm. 13C NMR (CDCl3, 75 MHz)
d:
12.8 (CH3), 44.9 (CH2), 98.7 (C-2), 105.2 (C-4), 109.5 (C-6), 124.5 (C-
11), 126.0 (C-10), 126.9 (Cm), 126.8 (Cp), 128.6 (C-9), 134.0 (Co),
134.3 (C-5), 146.5 (C-8), 148.6 (C-i-B), 156.1 (C-3), 158.6 (C-7), 164.2
(C-1). MS (70 eV) m/z (%): 355 (M ꢀ 77, 100%), 311(30), 253(20),
432(2). HRMS calcd. m/z C29H30BN2O[Mþ þ H]þ: 433.2445 found:
433.2459. 11B NMR (CDCl3, 87 MHz)
d: 5.0 ppm. Anal. Calcd. C 80.56,
H 6.76, N 6.48%. Found: C 80.50, N 6.93, H 6.49%.
2. Experimental
2.3.2. N,N-Diethyl-2,2-diphenyl-3(4-fluoro)-2H-benzo[e][1,3,2]
oxazaborinin-7-amine (2b)
2.1. Starting materials and equipment
N,N-Diethyl-2,2-diphenyl-3(4-fluoro)-2H-benzo[e][1,3,2]oxaza-
borinin-7-amine (2b) was prepared as described in the literature
[18].
Starting materials were commercially available and used
without further purification. 4-Diethylaminobenzoate and 4-
dimethylaminobenzoate were synthesized from 4-aminobenzoic
acid using the method reported by Zheng [44] and compound 2b
was prepared as described in the literature [18]. Melting points
were determined on a Fisher-Johns melting point apparatus and are
uncorrected. Infrared spectra were obtained using a FT-IR (ATR)
spectrophotometer. The 1H, 11B and 13C NMR spectra were recorded
on Jeol ECA 500, Varian Unity 300 and 400 MHz. Chemical shifts
(ppm) are relative to (CH3)4Si for 1H and 13C and BF3.Et2O for 11B,
2.3.3. N,N-Diethyl-2,2-diphenyl-3(4-chlorophenyl)-2H-benzo[e]
[1,3,2]oxazaborinin-7-amine (2c)
The title compound was prepared from 1c (0.56 g, 1.86 mmol)
and 0.50 g, (2.20 mmol) of diphenylborinic acid to give 0.63 g of 2c
in 81% yield. M.P: 168e170 ꢁC. IR nmax: 3068, 3043, 2926, 2971,
1614, 1602, 1577, 1501, 1486, 1437, 1343, 1205, 1135, 1010, 882, 742,
698 cmꢀ1
.
1H NMR (CDCl3, 300 MHz)
d
: 1.18 (6H, t, J ¼ 6.0 Hz,
N(CH2CH3)2), 3.37 (4H, q, J ¼ 6.0 Hz, N(CH2CH3)2), 6.14 (1H, d,

C.C. Jiménez et al. / Journal of Organometallic Chemistry 755 (2014) 33e40
35
J ¼ 3.0 Hz, H-2), 6.18 (1H, dd, J ¼ 3.0, 9.0 Hz, H-4), 7.07e7.23 (11H, m,
H-5, H9, H-10, H-m, H-p), 7.44 (4H, dd, J ¼ 3.0, 9.0 Hz, H-o), 8.04 (1H,
NMR (CDCl3, 75 MHz)
d
: 12.5 (CH3), 12.7 (CH3), 44.3 (CH2), 44.8
(CH2), 98.7 (C-2), 104.5 (C-4), 109.3 (C-6), 110.9 (C-10), 125.1 (C-9),
125.7 (C-p), 126.8 (C-m), 133.5 (C-5), 133.8 (C-o), 135.1 (C-11), 146.5
(C-8), 155.3 (C-3), 156.9 (C-7), 163.4 (C-1) ppm. MS (70 eV) m/z (%):
503(Mþ, 2), 426 (Mþ ꢀ 77, 100), 382 (17), 338 (8), 206 (11). HRMS
s, H-7) ppm. 13C NMR (CDCl3, 75 MHz)
d: 12.7 (CH3 NEt2), 44.9 (CH2
NEt2), 98.6 (C-2), 105.3 (C-4), 109.3 (C-6), 125.5 (C-9), 126.0 (C-10),
126.9 (C-m), 128.5 (C-p), 132.3 (C-11), 133.7 (C-o), 134.2 (C-5), 144.9
(C-8), 148.4 (C-i), 156.3 (C-3), 158.2 (C-7), 164.2 (C-1), MS (70 eV) m/
z (%): [Mþ þ H]þ: 467 (3), 389 (M ꢀ 77, 100), 345 (35), HRMS calcd.
m/z C29H29BN2OCl [Mþ þ H]þ: 467.2055, found: 467.2067. 11B NMR
calcd. m/z C29H29BN2OCl [Mþ þ H]þ: 504.3180, found: 504.3185. 11
B
NMR (CDCl3, 87 MHz) d: 4.8 ppm. Anal. Calcd. C 78.72, H 7.61, N
8.35%. Found: C 78.87, H 7.54, N 8.52%.
(CDCl3, 96 MHz) d: 5.5 ppm. Anal. Calcd. C 74.62, H 6.05, N, 6.00%.
Found. C 74.15, H 5.59, N, 6.30%.
2.3.7. N,N-Diethyl-2,2-diphenyl-3(4-methoxycarbonylphenyl)-2H-
benzo[e][1,3,2]oxazaborinin-7-amine (2g)
2.3.4. N,N-Diethyl-2,2-diphenyl-3(4-iodophenyl)-2H-benzo[e]
[1,3,2]oxazaborinin-7-amine (2d)
The title compound was prepared from 1g (0.60 g, 1.86 mmol)
and 0.50 g (2.20 mmol) of diphenylborinic acid to give 0.28 g of 2g
in 58% yield. M.P: 221e222 ꢁC. IR nmax: 3067, 3043, 3002, 2950,
2975, 1720 (C]O), 1619 (C]N), 1580, 1501, 1438, 1347, 1274, 1207,
The title compound was prepared from 1d (0.73 g, 1.86 mmol)
and 0.50 g (2.20 mmol) of diphenylborinic acid to give 0.31 g of 2d
in 44% yield. M.P: 192e193 ꢁC. IR nmax3042, 3007, 2927, 2967, 1596,
1569, 1500, 1481, 1434, 1415, 1375, 1235, 1202, 1188, 1136, 975, 918,
1189, 1141, 1111, 1077, 972, 927, 742, 703 cmꢀ1 1H NMR (CDCl3,
.
400 MHz)
d
: 1.18 (6H, t, J ¼ 8.0 Hz, N(CH2CH3)2), 3.37 (4H, q,
794, 743, 701 cmꢀ1
.
1H NMR (CDCl3, 400 MHz)
d
: 1.16 (6H, t,
J ¼ 8.0 Hz, N(CH2CH3)2), 3.84 (3H, s, OCH3),6.13 (1H, d, J ¼ 4.0 Hz, H-
2), 6.18 (1H, dd, J ¼ 8.0, 2.0 Hz, H-4),7.08e7.19 (9H, m, H-m, H-p, H-
9, H-5),7.42 (4H, dd, J ¼ 8.0, 2.0 Hz, H-o),7.79 (2H, d, J ¼ 9.0 Hz, H-
J ¼ 8.0 Hz, N(CH2CH3)2), 3.35 (4H, q, J ¼ 8.0 Hz, N(CH2CH3)2), 6.12
(1H, d, J ¼ 3.0 Hz, H-2), 6.15 (1H, dd, J ¼ 9.0, 3.0 Hz, H-4), 6.76 (2H, d,
J ¼ 5.0 Hz, H-9), 7.05 (1H, d, J ¼ 9.0 Hz, H-5), 7.10e7.19 (6H, m, H-m
H-p), 7.41e7.42 (6H, m, H-10, H-o), 8.01 (1H, s, H-7), ppm. 13C NMR
10), 8.10 (1H, s, NH) ppm. 13C NMR (CDCl3, 75 MHz)
d: 12.7 (CH3),
45.0 (CH2), 52.1 (OCH3), 98.6 (C-2), 105.6 (C-4), 109.7 (C-6), 124.1 (C-
9), 126.0 (C-p), 126.9 (C-m), 127.9 (C-11), 130.0 (C-10), 133.8 (C-o),
134.4 (C-5), 150.0 (C-8), 156.5 (C-3), 158.2 (C-7), 164.5 (C-1), 166.3
(CO) ppm. MS (70 eV) m/z (%): 490 (5) Mþ, 489 (Mþ ꢀ 1, 10), 414
(26), 413 (M ꢀ 77, 100), 412 (20), 369 (25), 326 (20), 311 (45), 182
(20), 78 (42), 77 (15). HRMS calcd. m/z C31H32BN2O3 [Mþ þ H]þ:
(CDCl3, 75 MHz) d: 12.7 (CH3), 44.9 (CH2), 91.5 (C-11), 98.5 (C-2),
105.4 (C-4), 109.4 (C-6), 126.0 (C-9), 126.1 (C-p), 126.8 (C-m), 133.7
(C-o), 134.2 (C-5), 137.4 (C-10), 146.0 (C-8), 148.0 (C-i), 156.3 (C-3),
158.0 (C-7), 164.0 (C-1), MS (70 eV) m/z (%): 558 (3) Mþ, 482
(Mþ ꢀ 76, 24), 481 (100), 480 (24), 437 (15), 354 (17), 310 (15).
HRMS calcd. m/z
C
29H29BN2OI[Mþ
þ
H]þ: 559.1411, found:
491.2500. Found: 491.2505. 11B NMR (CDCl3, 87 MHz)
d: 5.6 ppm.
559.1405. 11B NMR (CDCl3, 87 MHz)
d: 5.5 ppm Anal. Calcd. C 62.39,
Anal. Calcd. C 75.92, H 6.37, N 5.71%. Found: C 76.56, H 6.42, N
5.79%.
N 5.02, H 5.06%. Found: C 62.16, N 5.22, H5.28%.
2.3.5. N,N-Diethyl-2,2-diphenyl-3(4-methoxyphenyl)-2H-benzo[e]
[1,3,2]oxazaborinin-7-amine (2e)
2.3.8. N,N-Diethyl-2,2-diphenyl-3(4-ethoxycarbonylphenyl)-2H-
benzo[e][1,3,2] oxazaborinin-7-amine (2h)
The title compound was prepared from 1e (0.55 g, 1.86 mmol)
and 0.50 g (2.20 mmol) of diphenylborinic acid to give 0.26 g, 33%
yield of 2e. M.P: 214e215 ꢁC. IR nmax: 3039, 2931, 2976, 1618, 1592,
The title compound was prepared from 1h (0.63 g, 1.86 mmol)
and 0.50 g (2.20 mmol) of diphenylborinic acid to give 0.43 g, 58%
yield of 2h. M.P: 214e215 ꢁC. IR nmax: 3066, 3037, 3004, 2970, 1708
(C]O), 1616, (C]N), 1576, 1498, 1437, 1409, 1376, 1346, 1271, 1206,
1187, 1136, 1103, 1077, 971, 924, 884, 742, 702 cmꢀ1. 1H NMR (CDCl3,
1506, 1440, 1350, 1249, 1187, 1141, 1074, 1031, 835, 707 cmꢀ1 1H
.
NMR (CDCl3, 500 MHz)
d
: 1.16 (6H, t, J ¼ 7.0 Hz, N(CH2CH3)2), 3.38
(4H, q, J ¼ 7.0 Hz, N(CH2CH3)2), 3.68 (3H, s, OCH3), 6.17 (1H, dd,
J ¼ 9.0, 2.0 Hz, H-4), 6.19 (1H, d, J ¼ 2.0 Hz, H-2), 6.66 (2H, d,
J ¼ 9.0 Hz, H-10), 6.97 (2H, d, J ¼ 9.0 Hz, H-9), 7.07 (1H, d, J ¼ 9.0 Hz,
H-5), 7.17 (2H, td, J ¼ 7.0, 2.0 Hz, H-p), 7.23 (4H, td, J ¼ 7.0, 2.0 Hz, H-
m), 7.51 (4H, dd, J ¼ 7.0, 2.0 Hz, H-o), 8.03 (1H, s, H-7) ppm. 13C NMR
500 MHz)
d
: 1.18(6H, t, J ¼ 7.1 Hz, N(CH2CH3)2),1.33 (3H, t, J ¼ 7.1 Hz,
OCH2CH3), 3.36 (4H, q, J ¼ 7.1 Hz, N(CH2CH3)2), 4.29 (2H, q,
J ¼ 7.1 Hz, OCH2), 6.13 (1H, d, J ¼ 2.3 Hz, H-2), 6.18 (1H, dd, J ¼ 2.4,
9.0 Hz, H-4), 7.1e7.17 (9H, m, H-9, H-5, H-m, H-p), 7.44 (4H, dd,
J ¼ 2.0, 8.0 Hz, H-o), 7.80 (2H, d, J ¼ 8.0 Hz H-10), 8.1 (1H, s, H-7)
(CDCl3, 75 MHz)
d: 12.9 (CH3), 45.0 (CH2), 55.4 (OCH3), 98.7 (C-2),
ppm. 13C NMR (CDCl375 MHz)
d: 12.7 (NeCH2CH3), 14.3 (OCH2CH3),
105.0 (C-4), 109.3 (C-6), 113.7 (C-10), 125.5 (C-9), 126.0 (C-p), 126.9
(C-m), 133.0 (C-o), 134.1 (C-5), 139.8 (C-8), 148.9 (C-3), 155.9 (C-11),
158.2 (C-7), 163.9 (C-1). MS (70 eV) m/z (%): 462 (4) Mþ, 386 (30),
385 (M ꢀ 77, 100), 434 (30), 341 (42), 297 (25), 283 (18), 185 (42),
171 (22), 77 (18). HRMS calcd. m/z C30H32BN2O2 [Mþ þ H]þ:
45.0 (CH2N), 61.0 (OCH2), 98.5 (C-2), 105.6 (C-4), 109.7 (C-6), 124.0
(C-p), 126.0 (C-9), 126.9 (C-m), 128.3 (C-11), 129.9 (C-10), 133.8 (C-
o), 134.5 (C-5), 148.2 (C-i), 150.0 (C-8), 156.5 (C-3), 158.2 (C-7), 164.5
(C-1),165.8 (CO). MS (70 eV) m/z (%): 504 (2), 427 (M ꢀ 77,100), 399
(15), 355 (17), 325 (14), 206 (7), 78 (12). HRMS calcd. m/z
463.2551, found: 463.2563. 11B NMR (CDCl3, 87 MHz)
d: 4.8 ppm.
C
32H34BN2O3 [Mþ þ H]þ: 505.2657 Found: 505.2661. 11B NMR
Anal. Calcd. C 77.93, H 6.76, N 6.06%. Found. C 78.19, H 6.90, N 6.15%.
(CDCl3, 87 MHz) d: 5.2 ppm. Anal. Calcd. C 76.19, H 6.59, N 5.55%.
Found: C 76.24, H 6.18, N 5.79%.
2.3.6. N,N-Diethyl-2,2-diphenyl-3(4-diethylaminophenyl)-2H-
benzo[e][1,3,2]oxazaborinin-7-amine (2f)
2.4. NLO measurements
The title compound was prepared from 1f (0.63 g, 1.86 mmol)
and 0.50 g (2.20 mmol) of diphenylborinic acid to give 0.31 g, 42%
yield of 2f. M.P: 183e184 ꢁC. IR nmax: 3067, 3045, 3002, 2867, 2973,
1608 (C]N), 1584, 1504, 1431, 1408, 1376, 1349, 1268, 1250, 1189,
1136, 1074, 1013, 971, 919, 898, 884, 744, 702 cmꢀ1. 1H NMR (CDCl3,
2.4.1. Third-harmonic generation (THG) experiments
Third-order NLO properties of borinates 2aeh were first eval-
uated through the generation of visible optical frequencies in thin
solid films when pumped with infrared optical frequencies. Thin
films of each borinate were prepared in a guest:host approach us-
ing polystyrene as a host matrix doped with 30% of the guest. The
films were deposited over glass substrates from chloroform solu-
tions using the spin-coating method obtaining thicknesses in the
range 250e265 nm. For optical setup information see previous
work [31].
300 MHz)
d
: 1.08 (6H, t, J ¼ 7.0 Hz, N(CH2CH3)2), 1.16 (6H, t,
J ¼ 7.0 Hz, N(CH2CH3)2), 3.25 (4H, q, J ¼ 7.0 Hz, N(CH2CH3)2), 3.35
(4H, q, J ¼ 7.0 Hz, N(CH2CH3)2), 6.13 (1H, dd, J ¼ 8.0, 2.0 Hz, H-4),
6.16 ( 1H, d, J ¼ 2.0 Hz, H-2), 6.38 (2H, d, J ¼ 9.0 Hz, H-10), 6.86 (2H,
d, J ¼ 9.0 Hz, H-9), 7.04 (1H, d, J ¼ 8.0 Hz, H-5), 7.09e7.21 (6H, m, H-
m, H-p), 7.47 (4H, dd, J ¼ 8.0, 2.0 Hz, H-o), 8.02 (1H, s, H-7) ppm. 13
C

36
C.C. Jiménez et al. / Journal of Organometallic Chemistry 755 (2014) 33e40
Briefly, the method consists in focusing infrared laser irra-
diation (1200 nm, pulses of 8 ns at a repetition rate of 10 Hz)
into each tested film. The third-harmonic beam that emerges
from films was selected by using a color filter and detected
with a PMT and a lock-in amplifier. The THG measurements
were performed for incident angles in the range from 40
to ꢀ40ꢁ with steps of 0.27ꢁ so that the nonlinear susceptibility
c
3(e3
u, u, u, u) was calculated using the THG Maker-Fringes
formalism [49e53].
2.4.2. Determination of quantum yields
Fluorescence quantum yield (F) for borinates 2aeh were
measured through the integration sphere method using Rhoda-
mine 6G (F(ref) ¼ 0.95) in methanol as a reference [54] and using a
diode-laser (370 nm) as excitation source. The concentration of
samples in THF solutions was 10ꢀ4 M. The Fluorescence quantum
yield was estimated according to Eq. (1).
Scheme 1.
3.1. Spectroscopic characterization of the boron complexes 2aeh
A
I
ðref Þ
A
The formation of borinates 2aeh was evidenced by the shift of
the C]N band (1596e1619 cmꢀ1) in the IR spectrum. In the 1H
NMR solution spectra, H-7 resonates from 8.01 to 8.44 ppm, this
signal is shifted to low frequency with respect to the corresponding
Schiff base. The imine carbon appears from 156.9 to 159.9 ppm in
the 13C NMR spectra, in agreement with previous reports [32,33].
The presence of four-coordinated boron atoms in 2aeh was
confirmed by the 11B NMR signal from 4.8 to 5.6 ppm.
F
F
¼
(1)
ðref Þ
I
ðref Þ
where A and A(ref) are the absorption of sample and reference at the
excitation wavelength, respectively, while I and I(ref) are the corre-
sponding emission intensities.
2.4.3. Determination of 2PA cross-sections (s2PA
)
Two-photon excitation spectra for borinates 2aeh in THF solu-
tion (1 ꢂ 10ꢀ4 M) were measured using the Two-Photon Excited
Fluorescence technique (TPEF) [55,56] with a Ti:Sapphire laser
(Spectra-Physics) as excitation source. The laser provided pulses of
100 fs with a repetition frequency of 80 MHz and was tunable in the
wavelength range 740e830 nm. The laser radiation was focused
inside a quartz cell (1 cm) by a focal lens (5 cm); to avoid absorption
effects, the beam was focused close to the lateral cell wall. Then the
fluorescent emission of the borinate solution was focused and
recorded on a USB 4000, Ocean Optics spectrophotometer. The
measurements were performed in an intensity regime where the
fluorescence signal showed a quadratic dependence on the in-
tensity of the excitation beam. A methanol solution of Rhodamine
6G (1 ꢂ10ꢀ4 M), whose cross-sections values have been completely
characterized in the literature [57,58], was employed as 2PA
reference.
3.2. Crystal structure of borinates
Suitable crystals for compounds 2c and 2e were obtained from
saturated solutions by slow evaporation of the solvent at room
temperature. The most relevant crystallographic parameters are
given in Table 1. Compound 2c crystallized into the monoclinic
system with space group P21/c containing two borinate molecules
and a molecule of ethyl acetate (solvent) per asymmetric unit and
four molecules per unit cell Fig. 1. While compound 2e crystallized
in the triclinic system with space group Pꢀ1 containing two bori-
nate molecules per unit cell Fig. 2.
The X-ray diffraction data from compounds 2c and 2e corrob-
orate the presence of a tetra-coordinated boron atom, the angles
around this atom (from 105.3(3) to 109.3(3)ꢁ for 2c and from
The 2PA cross-section of borinates was calculated at each
wavelength according to Eq. (2), where C and n are the concen-
tration and refraction index of the borinates and Rhodamine 6G
solutions, while F is the integral of the TPEF spectrum.
Table 1
Selected crystal and refinement data for compounds 2c and 2e.
2c
2e
Formula
2(C29H28BClN2O)$C4H8O2
1021.69
Monoclinic
P21/c
11.5250 (1)
41.8790 (5)
12.1040 (2)
90.0
105.340 (1)
90.0
5633.93 (12)
4
1.20
22,957
11,357(0.046)
4665
0.062
C30H31BN2O2
462.38
Triclinic
P-1
10.5920 (2)
11.2214 (2)
12.7019 (3)
70.0883 (8)
87.8000 (8)
63.2112 (9)
1255.14 (5)
2
1.22
17,993
5663(0.034)
4168
0.051
MW/g molꢀ1
Crystal system
Space group
F
C
n
F
ðref Þ ðref Þ ðref Þ
s2PA
¼
s2PAðref Þ
(2)
F
C
n F
ðref Þ
ꢀ
a/A
In this equation the subindex ref stands for the solution
Rhodamine 6G used as reference.
ꢀ
b/A
ꢀ
c/A
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
3
3. Results and discussion
ꢀ
V/A
Z
rc/g cmꢀ3
Collected Refl.
Ind. Ref. (Rint)
Observed Ref
The borinates 2aeh were prepared from bidentate type Schiff
bases. These borinates contain an electronic p-bridge that connects
a strong donor group (eNEt2) in one terminal of the molecular
structure with a variety of substituents R1 located at the other end
(see Scheme 1). The R1 substituents were selected to have different
R[F2 > 2
Rw (all data)
Drmax/e A
Drmin/e A
s
(F2)]
0.235
0.46
ꢀ0.48
0.174
0.273
ꢀ0.325
3
ꢀ
donating or accepting capabilities in order to form De
p
eC]Nþe
3
ꢀ
p
eD and De eA systems.
p
eC]Nþe
p

C.C. Jiménez et al. / Journal of Organometallic Chemistry 755 (2014) 33e40
37
Table 3
Selected angles [ꢁ] around the boron atom.
2c
2e
O1eB1eCph
O1eB1eCph
C15eB1eC21
O1eB1eN1
109.1 (3)
107.3 (3)
117.2 (3)
105.3 (3)
109.3 (3)
107.9 (3)
ꢀ48.0 (4)
107.4 (3)
110.6 (3)
115.1 (3)
104.4 (3)
109.5 (3)
109.2 (3)
ꢀ60.1 (5)
110.45 (13)
103.60 (12)
114.37 (12)
106.88 (11)
107.93 (12)
113.32 (12)
39.93 (19)
C
C
pheB1eN1
pheB1eN1
C9eC8eN1eC7
O1AeB1AeC15A
O1AeB1AeC21A
C15AeB1AeC21A
O1AeB1AeN1A
C15AeB1AeN1A
C21AeB1AeN1A
C9AeC8AeN1AeC7A
Table 4
Fig. 1. Molecular structure of compound 2c with displacement ellipsoids drawn at the
Photophysical properties of borinates 2aeh.
35% probability level.
Molecule labs (nm) ε ꢂ 103 (L cmꢀ1 molꢀ1
)
lem (nm) Fa
s2PA (GM)
b
2a
2b
2c
2d
2e
2f
402
402
409
417
403
425
418
425
42
39
48
38
37
38
55
46
502
494
500
503
513
547
503
504
0.11
0.11
0.16
0.17 100
0.03
0.04
53
49
85
37
12
2g
2h
0.10 124
0.26 174
a
Using Rhodamine 6G as reference,
Using excitation at 760 nm.
F
¼ 0.95 in methanol, lex ¼ 370 nm.
b
resulting in ꢀ48.0(4)ꢁ for 2c and 39.93(19)ꢁ for 2e, which are
similar to those previously reported [18,31].
A detailed examination of the supramolecular structure for
compounds 2c and 2e shows that the crystalline arrangement is
governed by CHep interactions due to the absence of co-planarity
between the phenyl rings, where the CH groups act as donors. For
compound 2c, this interaction is described by the C2eH2/ceꢁntroid
ꢀ
1 (C15eC20) with a distance of 3.675 A and the angle is 151 with
Fig. 2. Molecular structure of compounds 2e with displacement ellipsoids drawn at
the 35% probability level.
symmetry code [2575] ¼ ꢀx, 2 ꢀ y, ꢀz. The crystal structure has an
intramolecular hydrogen bond formed by the interactions of
ꢀ
C(20)eH(20)/O(1) [dO1/C20 ¼ 2.878(3) A]. See Supplementary
material.
103.60(12) to 114.37(12)ꢁ in 2e) are closed to tetrahedral angle
values. The N / B bond lengths for compounds 2c and 2e are: 1.630
The supramolecular structure of compound 2e shows several
CHe
p interactions (see Supplementary material), one of these in-
ꢀ
ꢀ
(5) A and 1.631 (2) A, respectively, these data are in agreement with
values previously reported for analogous compounds where these
volves the C12eH12/centrꢁoid 7 (C15AeC20A) with a distance of
ꢀ
3.720(4) A, an angle of 140 and symmetry code [1555] ¼ x, y, z.
ꢀ
ꢀ
bond distances are between 1.602(3) A and 1.646(3) A [32e34]. A
summary of bond length distances and angles around de boron
atom are shown in Table 2 and Table 3. A non-planar conformation
Another intramolecular interaction is that of C17Ae
ꢀ
H17A/centroid 3 (C15eC20) with a distance of 3.805(5) A, an angle
of 152ꢁ and with symmetry code [1555] ¼ x, y, z. Additionally, the
crystal structure of compound 2c shows an intermolecular
hydrogen bond between the C7eH7/O3 interaction)
on the main
p-backbone of the borinates is observed from the
torsion angles values for the fragment C(7)eN(1)eC(8)eC(9),
ꢀ
[dO3/C7 ¼ 3.423(6) A] with symmetry code [3556] ¼ ꢀx, ꢀy, 1 ꢀ z.
Other important intramolecular hydrogen bonds are formed by the
ꢀ
Table 2
Selected bond lengths [A].
interaction of C(16)eH(16)/N1 [dO1/C20 ¼ 2.878(3) A], C(16A)e
ꢀ
ꢀ
H(16A)/O(1A) [dO1A/C16A ¼ 2.865(4) A], and C(16A)eH(16A)/
ꢀ
O(1A) [dO1A/C16A ¼ 2.865(4) A.
2c
2e
1.622 (2)
1.622 (2)
1.5061 (19)
1.631 (2)
C21eB1
C15eB1
B1eO1
B1eN1
C7eN1
C21AeB1A
C15AeB1A
B1AeO1A
B1AeN1A
1.605 (5)
1.608 (6)
1.516 (4)
1.630 (5)
1.310 (4)
1.615 (5)
1.616 (5)
1.517 (4)
1.613 (5)
3.3. Optical characterization
3.3.1. Lineal absorption and light emission
1.3115 (18)
The photophysical properties of borinates 2aeh are summa-
rized in Table 4. The linear absorption and emission spectra for the
boron complexes in THF solution are shown in Fig. 3. These boron
complexes have an intense absorption band from 402 to 425 nm,

38
C.C. Jiménez et al. / Journal of Organometallic Chemistry 755 (2014) 33e40
which is assigned to typical n /
p* electronic transition. In
particular, compounds 2g and 2h possessing both the strong donor
(eNEt2) but different acceptor groups (eCOOEt and eCOOMe),
showed a red shift Dl of 16 and 23 nm, respectively, compared with
the absorption band of the borinate 2a (having a eH end group).
Similarly, a shift of 23 nm was observed in the case of compound 2f
containing the eNEt2 donor group in a quadrupolar architecture
Dep peD. In the case of borinate 2e, possessing a quad-
eC]Nþe
rupolar architecture with an eOMe group, the absorption band is
similar to 2a. It is also observed an increment of molar absorption
(ε) in compounds with architecture DeC]NþeA and surprisingly a
reduction in compounds with DeC]NþeD design.
It is important to note that, after boron complexation, com-
pounds 2aeh give intense green emission (band around 500 nm)
when excited at 370 nm. Compound 2f, possessing a Dep
eC]Nþe
Fig. 4. 2PA cross section spectra of borinates 2aeh in THF solution.
p
eD architecture (with eNEt2 as donor groups) showed the largest
Stoke shift (81,967 cmꢀ1) of this series of borinates, while com-
pound 2e containing the combination of eNEt2 and eOMe groups
respectively. These values are slightly larger than those recorded for
connected to the main
shift (90,909 cmꢀ1). However, compounds 2h and 2g with De
C]Nþe
eA architectures with eCOOEt and eCOOMe acceptor
groups showed larger Stoke shifts of 117,647 cmꢀ1 and
126,582 cmꢀ1, respectively. Quantum yields
for all borinates were
pebackbone, has also a considerable Stoke
borinates (1.1e1.5 ꢂ 10ꢀ12 esu) containing De
peA architecture,
p
e
with strong acceptor eNO2 groups reported previously [31].
p
Note that these values of c
3 were obtained at 1200 nm, which is
exactly 3 times the wavelength where the maximum linear ab-
sorption of the boron compounds is located. Despite the possible
presence of resonant effects, the THG technique was employed
since it is a quick screening method to evaluate the nonlinearities,
and in our case permitted to determine easily that 2h (with the
F
measured in THF solutions, giving values from 0.03 to 0.26 (see
Table 4), which are in agreement with those values obtained from
similar boron compounds (0.01e0.6) reported by other authors
[18]. But lower that those reported in the range 0.31e0.65 for boron
compounds derivates from benzoxazole [59]. A possible explana-
architecture Dep peA) exhibited the most efficient
eC]Nþe
nonlinear response in the molecular series studied herein. This was
also proved through a different nonlinear optical effect, i.e., 2PA
performed in another region of wavelengths (see discussion
below).
tion of the low
the -backbone of 2c and 2e (see X-ray diffraction analysis section)
in comparison to the -system of benzoxazole derivatives that have
flat conformation. In general, the experimental values obtained
F values is the non-planar conformation observed in
p
p
F
from 2aeh showed a dramatic decrement for compounds with De
C]NþeD architecture, in which there is an increase of electronic
density in the p-skeleton.
3.3.3. Two-photon absorption properties of borinates 2aeh
To obtain information of the efficiency of the 2PA process in this
series of compounds, the cross section (s2PA) of borinates 2aeh
were calculated from data of TPEF experiments. This technique is
based on a comparison of the two-photon excited fluorescence
spectra from the sample (borinate) with a standard (Rhodamine
6G). Fig. 4 displays the values measured for sTPA at the wavelength
range 740e830 nm. From this figure we observe that at such
wavelength range the molecules exhibit only small variations in
their s2PA values. For shorter wavelengths (corresponding to en-
ergies higher than the one-photon transitions that define the peaks
shown in Fig. 3a), it is expected that some 2PA resonances might
occur. In our case, however, the two-photon absorption spectra
were not extended to shorter wavelengths due to the limited
tunability of our laser system. Nevertheless, the sTPA values shown
3.3.2. Non-linear optical characterization
The third-order nonlinear susceptibility (c
3) for the series 1aeh
and 2aeh was first evaluated at the telecommunication wavelength
of 1200 nm by THG Maker-fringes technique. THG signal (400 nm)
was measured for the polymeric film doped with ligands 1aeh or
borinates 2aeh. The level of THG signal from ligands 1aeh and
borinates 2b and 2deg was very weak and below the sensibility of
our experimental setup. However, polymeric films doped with
borinates 2a, 2c and 2h generated significant THG signals. The plots
of THG as a function of the angle of incidence for the fundamental
beam were used to apply THG-Marker formalism. The so obtained
values of
c
3 were 1.82, 1.48 and 2.28 ꢂ 10ꢀ12 esu for 2a, 2c and 2h,
Fig. 3. Linear absorption a) and emission b) spectra for borinates 2aeh in THF.

C.C. Jiménez et al. / Journal of Organometallic Chemistry 755 (2014) 33e40
39
in Fig. 4 allowed comparison of the effect of the molecular structure
Appendix A. Supplementary material
on the nonlinear optical properties.
The studied borinates can be grouped in two categories, those
CCDC Nos. 914469 and 914470 contain the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
comprising a De
donor groups at the end of the molecule, i.e., 2e (eOCH3) and 2f (e
NEt2), and compounds containing a De eA architecture,
eC]Nþe
2b (eF), 2c (eCl), 2d (eI), 2g (eCOOCH3) and 2h (eCOOCH2CH3).
Surprisingly, the architecture De eD produced the
eC]Nþe
lowest values of s2PA and the smallest fluorescence quantum yields.
Larger values of s2PA were obtained for the De eA ar-
eC]Nþe
p peD architecture with strong electron
eC]Nþe
p
p
p
p
Appendix B. Supplementary data
p
p
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.12.036.
chitecture, and for the particular case of 2b, 2c, and 2d the cross
section values are inversely related to the electronegativity. For the
same architecture, the highest cross section was found for the ester
groups 2g and 2h where the acceptor provides stabilization. Notice
that there is an agreement between the 2PA and THG experiments, in
both cases the most significant optical nonlinearities were observed
for 2h. This molecular system also exhibited the largest fluorescence
quantum yield among all set of studied molecules.
References
[1] T.-C. Lin, S.-J. Chung, K.-S. Kim, X. Wang, G.-S. He, J. Swiatkiewicz,
H.E. Pudavar, P.N. Prasad, Adv. Polym. Sci. 161 (2003) 157e193.
[2] C.N. LaFratta, J.T. Fourkas, T. Baldacchini, R.A. Farrer, Angew. Chem. Int. Ed. 46
(2007) 6238e6258.
[3] B.H. Cumpston, S.P. Ananthavel, S. Barlow, D.L. Dyer, J.E. Ehrlich, L.L. Erskine,
A.A. Heikal, S.M. Kuebler, I.-Y.S. Lee, D. McCord-Maughon, J.Q. Qin, H. Röckel,
M. Rumi, X.-L. Wu, S.R. Marder, J.W. Perry, Nature 398 (1999) 51e54.
[4] N. Adarsh, R.R. Avirah, D. Ramaiah, Org. Lett. 12 (2010) 5720e5723.
[5] L. Hunyady, A.J. Baukal, Z. Gáborik, J.A. Olivares-Reyes, M. Bor, M. Szaszák,
R. Lodge, K.J. Catt, T. Balla, J. Cell. Biol. 157 (2002) 1211e1222.
[6] L. Beverina, J. Fu, A. Leclercq, E. Zojer, P. Pacher, S. Barlow, E.W. Van Stryland,
D.J. Hagan, J.L. Brédas, S.R. Marder, J. Am. Chem. Soc. 127 (2005) 7282e7283.
[7] S.J.K. Pond, M. Rumi, M.D. Levin, T.C. Parker, D. Beljonne, M.W. Day, J.-
L. Brédas, S.R. Marder, J.W. Perry, J. Phys. Chem. A 106 (2002) 11470e11480.
[8] S.-J. Chung, S. Zheng, T. Odani, L. Beverina, J. Fu, L.A. Padilha, A. Biesso,
J.M. Hales, X. Zhan, K. Schmidt, A. Ye, E. Zojer, S. Barlow, D.J. Hagan, E.W. Van
Stryland, Y. Ying, Z. Shuai, G.A. Pagani, J.-L. Brédas, J.W. Perry, S.R. Marder,
J. Am. Chem. Soc. 128 (2006) 14444e14445.
[9] G.S. He, L.-S. Tan, Q. Zheng, P.N. Prasad, Chem. Rev. 108 (2008) 1245e1330.
[10] C. Katan, S. Tretiak, M.H.V. Werts, A.J. Bain, R.J. Marsh, N. Leonczek,
N. Nicolaou, E. Badaeva, O. Mongin, M. Blanchard-Desce, J. Phys. Chem. B 111
(2007) 9468e9483.
[11] F. Terenziani, C. Katan, E. Badaeva, S. Tretiak, M. Blanchard-Desce, Adv. Mater.
20 (2008) 4641e4678.
The values of
F and s2PA observed around 800 nm for 2h are very
similar to those observed in pyrazabole based fluorescent bioprobes
[34], although somewhat smaller (about half the value) compared
with boron-containing two-photon-absorbing fluorophores based
on the p-carborane entity [36], however, it must be recognized that
in the latter case a more complex synthetic procedure is required.
Indeed, our borinates derived from Schiff bases comprise a simple
synthesis process. The system 2h with architecture De
eA has larger two-photon activity (light emission induced by 2PA)
than ferrocenyl substituted pyrazaboles with architecture De eAe
eD [35]. The substituted pyrazaboles exhibit s2PA values of the
p
eC]Nþe
p
p
p
order of 103 GM, but it was not reported if they can emit light
induced by 2PA. Furthermore, their relatively large s2PA was
measured by Z-scan technique with nanosecond pulses at 532 nm,
but such long temporal pulses induce multi-step nonlinear absorp-
tion, while in the case of our borinates the s2PA values is due
exclusively to simultaneous absorption of two photons.
[12] M. Charlot, N. Izard, O. Monguin, D. Riehl, M. Blanchard-Desce, Chem. Phys.
Lett. 417 (2006) 297e302.
[13] T. Wang, A.J. Pearson, D.G. Lidzey, J. Mater. Chem. C 1 (2013) 7266e7293.
[14] D.-J. Liawa, K.-L. Wang, Y.-C. Huanga, K.-R. Lee, J.-Y. Lai, C.-S. Ha, Prog. Polym.
Sci. 37 (2012) 907e974.
4. Conclusions
[15] C.-H. Tsai, D.N. Chirdon, A.B. Maurer, S. Bernhard, K.J.T. Noonan, Org. Lett. 15
(2013) 5230e5233.
Novel borinates were conveniently synthesized from the reac-
tion of diphenylborinic acid and bidentate ligands. After complex-
ation of these ligands, all of the borinates exhibit fluorescence
induced by absorption of one- or two-photons at the wavelengths
about 400 and 800 nm, respectively. Likewise, the third-order
nonlinearities of such borinates were notoriously enhanced in
comparison with their corresponding ligands. The highest two-
photon absorption cross-section (sTPA ¼ 174 GM) of the series of
[16] T. Baumgartner, R. Réau, Chem. Rev. 106 (2006) 4681e4727.
[17] X. He, T. Baumgartner, RSC Adv. 3 (2013) 11334e11350.
[18] D. Frath, S. Azizi, G. Ulrich, P. Retailleau, R. Ziessel, Org. Lett. 13 (2011) 3414e
3417.
[19] D. Li, Z. Zhang, S. Zhao, Y. Wang, H. Zhang, Dalton Trans. 40 (2011) 1279e
1285.
[20] L. Xiao, Z. Chen, B. Qu, J. Luo, S. Kong, Q. Gong, J. Kido, Adv. Mater. 23 (2011)
926e952.
[21] F. Jäkle, Chem. Rev. 110 (2010) 3985e4022.
[22] A. Mishra, P. Bäuerle, Angew. Chem. Int. Ed. 51 (2012) 2020e2067.
[23] A. Wakamiya, T. Taniguchi, S. Yamaguchi, Angew. Chem. Int. Ed. 45 (2006)
3170e3173.
[24] M.J.G. Lesley, A. Woodward, N.J. Taylor, T.B. Marder, I. Cazenobe, I. Ledoux,
J. Zyss, A. Thornton, D.W. Bruce, A.K. Kakkar, Chem. Mater. 10 (1998) 1355e
1365.
[25] Rajneesh Misra, Thaksen Jadhav, Shaikh M. Mobin, Dalton Trans. 43 (2014)
2013e2022.
[26] D. Locatelli, S. Quici, D. Roberto, F. De Angelis, Chem. Commun. (2005) 5405e
5407.
studied compounds corresponds to 2h with a De
(D ¼ NEt2 and A ¼ COOCH2CH3) architecture. The borinate 2f, with
a De
eC]Nþe
p peA
eC]Nþe
p
p
eD architecture (D ¼ NEt2), has the lowest value
(12 GM). In the case of borinates 2b, 2c and 2d, the cross section is
inversely related to the electronegativity of the halogenated com-
pounds, decreasing in the following order 2b (F) < 2c (Cl) < 2d (I).
The low cross-sections values for borinates 2c (85 GM) and 2e
(37 GM) could be attributed to the structural deformation after
[27] Z.M. Su, X.J. Wang, Z.H. Huang, R.S. Wang, J.K. Feng, J.Z. Sun, Synth. Met. 119
(2001) 583e584.
[28] C. Lambert, S. Stadler, G. Bourhill, C. Bräuchle, Angew. Chem. Int. Ed. 35 (1996)
644e646.
[29] C.D. Entwistle, T.B. Marder, Angew. Chem. Int. Ed. 41 (2002) 2927e2931.
[30] H. Reyes, B.M. Muñoz, N. Farfán, R. Santillan, S. Rojas-Lima, P.G. Lacroix,
K. Nakatani, J. Mater. Chem. 12 (2002) 2898e2903.
boron complexation on the main p-backbone, confirmed by the X-
ray diffraction analysis. Compounds 2aeh are derivatives of Schiff
bases that comprise facile design and synthesis at low cost.
[31] M. Rodríguez, J.L. Maldonado, G. Ramos-Ortíz, O. Domínguez, Ma. E. Ochoa,
R. Santillan, M.A. Meneses-Nava, O. Barbosa-García, Polyhedron 43 (2012)
194e200.
[32] M. Rodríguez, J.L. Maldonado, G. Ramos-Ortíz, J.L. Lamère, P.G. Lacroix,
N. Farfán, Ma. E. Ochoa, R. Santillan, M.A. Meneses-Nava, O. Barbosa-García,
K. Nakatani, New J. Chem. 33 (2009) 1693e1702.
[33] M. Rodríguez, R. Castro-Beltrán, G. Ramos-Ortíz, J.L. Maldonado, N. Farfán,
O. Domínguez, J. Rodríguez, R. Santillan, M.A. Meneses-Nava, O. Barbosa-
García, J. Peon, Synth. Met. 159 (2009) 1281e1287.
Acknowledgements
Authors thank CONACyT-CNRS-LIA and PAPIIT (Grant IN-
214513) for financial support. Gabriel Ramos-Ortiz thanks CON-
ACyT (Grant 132946). Cristina C. Jiménez thanks CONACyT for a
Ph.D. Fellowship (167206) and Nancy E. Magaña-Vergara thanks
ICyT.

40
C.C. Jiménez et al. / Journal of Organometallic Chemistry 755 (2014) 33e40
[34] A. Hayek, F. Bolze, C. Bourgogne, P.L. Baldeck, P. Didier, Y. Arntz, Y. Mely, J.-
F. Nicoud, Inorg. Chem. 48 (2009) 9112e9119.
[35] T. Jadhav, R. Maragani, R. Misra, V. Sreeramulu, D. Narayana Rao, S.M. Mobin,
Dalton Trans. 42 (2013) 4340e4342.
[45] M.C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.L. Cascarano, L. De Caro,
C. Giacovazzo, G. Polidori, R. Spagna, J. Appl. Crystallogr. 38 (2005) 381e388.
[46] G.M. Sheldrick, SHELXL-97, Program for Refinement of Crystal Structures,
University of Göttingen, Göttingen, Germany, 1996.
[36] J.F. Nicoud, F. Bolze, X.H. Sun, A. Hayek, P. Baldeck, Inorg. Chem. 50 (2011)
4272e4278.
[47] G.P. Moloney, R.W. Gable, M.N. Iskander, D.J. Craik, M.F. Mackay, Aust. J. Chem.
43 (1990) 99e107.
[37] A. Jana, S.Y. Jang, J.-Y. Shin, A.K. De, D. Goswami, D. Kim, P.K. Bharadwaj,
Chem. Eur. J. 14 (2008) 10628e10638.
[38] J.S. Zugazagoitia, M. Maya, C. Damián-Zea, P. Navarro, H.I. Beltrán, J. Peon,
J. Phys. Chem. A 114 (2010) 704e714.
[39] L. Tian, Z. Hu, P. Shi, H. Zhou, J. Wu, Y. Tian, Y. Zhou, X. Tao, M. Jiang, J. Lumin.
127 (2007) 423e430.
[40] J. Zhanga, C. Zhong, X. Zhub, H.-L. Tam, K.-F. Li, K.-W. Cheah, W.-Y. Wong, W.-
K. Wong, R.A. Jones, Polyhedron 49 (2013) 121e128.
[48] J.P. Raval, K.R. Desai, Chemija 20 (2009) 101e108.
[49] P.D. Maker, R.W. Terhune, M. Nisenoff, C.M. Savage, Phys. Rev. Lett. 8 (1962)
21e22.
[50] J. Jerphagnon, S.K. Kurtz, J. Appl. Phys. 41 (1970) 1667e1681.
[51] G.R. Meredith, Phys. Rev. B 24 (1981) 5522e5532.
[52] F. Kajzar, J. Messier, C. Rosilio, J. Appl. Phys. 60 (1986) 3040e3044.
[53] X.H. Wang, D.P. West, N.B. McKeown, T.A. King, J. Opt. Soc. Am. B 15 (1998)
1895e1903.
[41] Z. Ye, L. De Boni, U.M. Neves, C.R. Mendonça, X.R. Bu, Tetrahedron Lett. 50
(2009) 1371e1373.
[42] M.-L. Zhang, Y.-P. Tian, X.-J. Zhang, J.-Y. Wu, S.-Y. Zhang, D. Wang, M.-H. Jiang,
S. Chantrapromm, H.-K. Fun, Trans. Met. Chem. 29 (2004) 596e602.
[43] F. Bolze, A. Hayek, X.H. Sun, P.L. Baldeck, C. Bourgogne, J.-F. Nicoud, Opt.
Mater. 33 (2011) 1453e1458.
[44] Q.-Z. Zheng, F. Zhang, K. Cheng, Y. Yang, Y. Chen, Y. Qian, H.-J. Zhang, H.-
Q. Li, C.-F. Zhou, S.-Q. An, Q.-C. Jiao, H.-L. Zhu, Bioorg. Med. Chem. 18 (2010)
880e886.
[54] N.S. Makarov, M. Drobizhev, A. Rebane, Opt. Exp. 16 (2008) 4029e4047.
[55] H.M. Kim, B.R. Cho, Chem. Commun. (2009) 153e164.
[56] M. Pawlicki, H.A. Collins, R.G. Denning, H.L. Anderson, Angew. Chem. Int. Ed.
48 (2009) 3244e3266.
[57] C. Xu, W.W. Webb, J. Opt. Soc. Am. B 13 (1996) 481e491.
[58] A. Fischer, C. Cremer, E.H.K. Stelzer, Appl. Opt. 34 (1995) 1989e2003.
[59] D. Li, H. Zhang, C. Wang, S. Huang, J. Guo, Y. Wang, J. Mater. Chem. 22 (2012)
4319e4328.