Synthesis and two-photon absorption property of novel salen complexes incorporated with two pendant azo dyes

Article abstract of DOI:10.1016/j.tetlet.2008.12.112

New salen compounds have been developed to possess two pendant azo dye chromophores. The two-photon absorption properties have been observed which result from the chromophores. The additive property has been found to exist as a result of no detrimental di

Full text of DOI:10.1016/j.tetlet.2008.12.112

Tetrahedron Letters 50 (2009) 1371–1373
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis and two-photon absorption property of novel salen complexes
incorporated with two pendant azo dyes
Zihong Ye a, Leonardo De Boni b, Ubaldo Martins Neves b, C. R. Mendonça b, Xiu R. Bu a,
*
a Department of Chemistry and NASA Center for High Performance Polymers and Composites, Atlanta, GA 30314, USA
b Departamento de Física e Ciência dos Materiais, Instituto de Física de São Carlos, Caixa Postal 369, 13560-970 São Carlos, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
New salen compounds have been developed to possess two pendant azo dye chromophores. The two-
photon absorption properties have been observed which result from the chromophores. The additive
property has been found to exist as a result of no detrimental dipole–dipole interaction between
chromophores.
Received 13 January 2006
Revised 18 November 2008
Accepted 22 December 2008
Available online 8 January 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Two-photon absorption material
Azo dyes
Schiff base ligands
Metal complexes
Applications of two-photon absorption (2PA) technology have
been manifested in many important areas such as optical power
limiting, up-converted lasing, photodynamic therapy and genera-
tion of singlet oxygen, three-dimensional microfabrication and
data storage, and three-dimensional fluorescence microscopy,1–6
Requiring molecules with desirable two-photon absorption prop-
erties have led to the development of several design strategies.
Molecules with various geometries (linear, branched, and den-
was selectively masked to give 1.16 The hydroxyl at the 3-position
of 1 coupled with azo dye 2 under Mitsnobu condition led to the
formation of 3. The release of hydroxyl group at the 2-position
was achieved by the deprotection of 3 using Pd–C in the presence
of HClO4. Azo dyes-containing salen ligand 4 was obtained by con-
densation of 3 with ethylenediamine. Reactions of 4 with Cu(OAc)2
and VO(acac)2 gave desirable complexes 5 and 6,17 respectively
(Scheme 1).
dritic) coupled with D–
p
–D, D–
p
–A–
p
–D, and A–
p
–D–
p
–A struc-
Ligand 4 and complexes 5–6 are found to be dominated with
tural features have been found to enhance the two-photon
absorptivity.7–12 Recently, the development of metal-containing
two-photon absorbing chromophores has received a great interest
due to the potential applications from multi-functional systems.
Maggini and Meneghetti showed Zn-induced on-off switching of
nonlinear transmittance through coordination to donating
atoms.13 Humphrey and co-workers observed reversible electro-
chemical switching of nonlinear absorption in ruthenium com-
plexes, where metal centers are directly embedded in the
conjugated systems.14 Perry and co-workers have demonstrated
the ultrabright beacon effect with 2PA molecules-coated nanopar-
ticles where 2PA molecules are tethered to nanoparticles via long
alkyl chains.15 We disclose here the synthesis and 2PA properties
of new salen metal complexes incorporated with azo dyes.
one p?
p* absorption band in the visible region (at ca. 500 nm,
NMP solution). The d–d transitions from the metal complexes are
*
p?p band in the same region. It is com-
masked by the strong
pletely transparent beyond 640 nm. The linear absorption was
measured with a concentration in the order of 2.5 Â 106 mole-
cules/cm3 (left side, solid line, Fig. 1).
The 2PA spectrum of the vanadyl complex is shown in Figure 1
(right side, middle, solid dots). A 2PA band was found to be at ca.
1000 nm, which is twice the one-photon absorption wavelength.
The 2PA cross-section was found to be monotonically increasing
below 800 nm, which is due to the resonance enhancement as
one-photon transition is approached. The copper complex showed
the same 2PA properties (Fig. 1, bottom, solid dots). These results
indicate that azo-dye components uniquely dominate the 2PA pro-
cess. This is further manifested by the fact that the ligand 4 also
shows the identical 2PA properties.
The synthetic approach to salen-azo dye 4 started with 2,3-
dihydroxybenzaldehyde. The hydroxyl group at the 2-position
The current ligand and complex systems were also found to
possess additive 2PA properties. This conclusion was made by
comparison with DR1 dye (see the structure in Scheme 1),
the azo chromophore used in the salen ligand 4 and complexes
* Corresponding author. Tel.: +1 404 880 6897; fax: +1 404 880 6890.
E-mail addresses: crmendon@if.sc.usp.br (C.R. Mendonça), xbu@cau.edu (X.R.
Bu).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.12.112

1372
Z. Ye et al. / Tetrahedron Letters 50 (2009) 1371–1373
CHO
CHO
O
OH
O
CHO
CHO
O
N
N
N
N
OH
OH
O
i
ii
iii
58%
51%
OH
83%
1
N
N
NO
2
NO
2
3
H
2
H
H
H
C
C
N
N
C
N
O
N
C
M
OH
HO
O
O
O
O
O
vi
90%
N
N
N
N
v
N
N
N
76% for
63% for
5
6
N
N
N
N
N
NO2
NO2
5: M=VO
6: M=Cu
NO2
NO2
4
Scheme 1. Reagent and conditions: (i) allyl bromide/NaH; (ii) p-[HOCH2CH2N(C2H5)]C6H4N2C6H4-(p-NO2), DR1, DEAD/PPh3; (iii) DMF–H2O/Pd–C; (iv) H2NCH2CH2NH2; (v)
Cu(OAc)2 or VO(acac)2/EtOH.
ligand, 4
800
0.4
5–6. The ligand 4 showed that its 2PA cross-section magnitude
is twice that of DR1,18 when concentrations of 4 and DR1 are
normalized to be the same. Both copper and vanadyl complexes
also showed the same increase. The 2PA properties being the
400
0.2
sum of two discrete azo dye chromophores indicate that there
is no detrimental dipole–dipole interaction between them.19
0
0.0
0.4
The molecular modeling suggests that two azo dye chromoph-
ores units are pointed away from each other, and the coordina-
tion core essentially acts as a scaffold to distance the two
chromophores. Each unit exhibits an inherent 2PA property on
its own so that it is possible for the current salen system with
high chromophore density to exhibit corresponding additive
2PA properties.
In summary, we have developed a new class of salen complexes
that possess two discrete azo dye chromophores with the coordi-
nation core serving as a scaffold to separate the two units. The
2PA cross-section peak is found to be ca. 1000 nm. The additive
2PA properties have been found to be the sum of the two chromo-
phore units.
VO, 5
Cu, 6
800
400
0.2
0
0.0
0.6
800
0.4
0.2
0.0
400
0
Acknowledgments
400
800
1200
1600
Support by NASA (NCC3-552) and NSF (# HRD-0630456) is
gratefully acknowledged. XRB also thanks NASA and NASA Langely
for NASA Langley faculty fellow research program (LFFP). The sup-
Wavelength (nm)
Figure 1. One-photon (left, solid line) and two-photon (right, solid dot) absorption
spectra.

Z. Ye et al. / Tetrahedron Letters 50 (2009) 1371–1373
1373
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Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2008.12.112.
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