Attachment of different donor groups to a cryptand for modulation of two-photon absorption cross-section

Article abstract of DOI:10.1002/chem.200801396

Two-photon absorption (TPA) properties of a laterally nonsymmetric aza cryptand with attached side arms have been investigated. This series of Schiff base derivatives supports the mechanistic approach for enhancing the TPA process, which is usually dictated by molecular geometry, π-bridging, derealization length, and corresponding charge-transfer possibilities. The results described here suggest that on increasing the branching units, the TPA cross-section, σ⁽²⁾, can be tuned to a larger value. The TPA activity is synthetic strategy for designing novel octupolar molecules with high σ⁽²⁾ values. Theoretical calculations at the B3LYP functional with the 6-31G* basis set under DFT formalism provide supporting evidence that the communication between the side arms through the metal d orbital and more ordered geometry of chromophores leads to a smaller HOMO-LUMO gap, which has a great influence upon the electronic properties of the molecules. switched on when a metal atom enters the cavity and serves as a conduit of electronic derealization. The σ⁽²⁾ value increases as the donor strength increases. The maximum value is obtained on moving from the singlebranched system to the nearly three-fold symmetry. This serves as a useful

Full text of DOI:10.1002/chem.200801396

DOI: 10.1002/chem.200801396
Attachment of Different Donor Groups to a Cryptand for Modulation of
Two-Photon Absorption Cross-Section
Atanu Jana,[a] So Young Jang,[b] Jae-Yoon Shin,[b] Arijit Kumar De,[a]
Debabrata Goswami,[a] Dongho Kim,*[b] and Parimal K. Bharadwaj*[a]
Abstract:
Two-photon
absorption
“switched on” when
a
metal atom
synthetic strategy for designing novel
octupolar molecules with high s(2)
values. Theoretical calculations at the
B3LYP functional with the 6–31G*
basis set under DFT formalism provide
supporting evidence that the communi-
cation between the side arms through
the metal d orbital and more ordered
geometry of chromophores leads to a
smaller HOMO–LUMO gap, which
has a great influence upon the elec-
tronic properties of the molecules.
(TPA) properties of a laterally nonsym-
metric aza cryptand with attached side
arms have been investigated. This
series of Schiff base derivatives sup-
ports the mechanistic approach for en-
hancing the TPA process, which is usu-
ally dictated by molecular geometry, p-
bridging, delocalization length, and cor-
responding charge-transfer possibilities.
The results described here suggest that
on increasing the branching units, the
TPA cross-section, s(2), can be tuned to
a larger value. The TPA activity is
enters the cavity and serves as a con-
duit of electronic delocalization. The
s(2) value increases as the donor
strength increases. The maximum value
is obtained on moving from the single-
branched system to the nearly three-
fold symmetry. This serves as a useful
Keywords:
charge transfer
·
cryptands
· density functional
calculations · one-photon absorp-
tion · two-photon absorption
Introduction
suggest that donor–acceptor strength, conjugation length,
and dimensionality of charge transfer symmetry are the
most important molecular parameters affecting TPA activity.
Thus, the most extensively investigated basic structural
motifs for appreciable TPA cross-sections are D–p–A, D–p–
D, A–p–A, D–p–A–p–D, and A–p–D–p–A (D=donor, A=
acceptor, p=conjugated spacer).[1] Strategies have been
evolved to arrange various D–p–A fragments around suita-
ble skeletons to afford dipoles,[2] octupoles,[3] quadrupoles,[4]
and multi-branched structures.[5] Organic molecules have the
advantage of easy chemical modifications for structural di-
versity and processability for optimized TPA activity. Com-
mensurate with this, recent years have witnessed an upsurge
in the synthesis of organic molecules possessing large s(2)
values. However, metal ions can further influence TPA ac-
tivity by various means that include interaction of the
vacant metal orbitals with the donor/acceptor groups in-
creasing the polarizability. The enhancement in TPA activity
originating from the bathochromic shift of the intraligand
charge transfer (ILCT) transition can also be controlled by
the Lewis acceptor property of the metal ion. Besides, when
metal ions are attached to these conjugated organic ligands,
they attain a high damage threshold and fast response time
properties that are important from the perspectives of appli-
The two-photon absorption process is a third-order nonlin-
ear optical phenomenon, and the efficiency of this process is
determined by measuring two-photon absorption cross-sec-
tion (s(2)) values. The design and synthesis of materials ex-
hibiting large s(2) values have been motivated by their tre-
mendous potential for applications in several areas of bio-
photonics and materials science. At the molecular level,
compounds likely to exhibit large s(2) values must have po-
larizable electrons (i.e., p electrons) spread over a large dis-
tance. Both experimental results and theoretical calculations
[a] A. Jana, A. Kumar De, Dr. D. Goswami, Prof. Dr. P. K. Bharadwaj
Department of Chemistry, Indian Institute of Technology Kanpur
Kanpur 208016 (India)
Fax : (+91)512-259-7436
E-mail: pkb@iitk.ac.in
[b] S. Y. Jang, J.-Y. Shin, Prof. Dr. D. Kim
Department of Chemistry, Yonsei University
Seoul 120749 (Korea)
Fax : (+82)2-2123-2434
E-mail: dongho@yonsei.ac.kr
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200801396.
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Chem. Eur. J. 2008, 14, 10628 – 10638

FULL PAPER
cations. Such an extended p-conjugation leads to the reduc-
tion of the HOMO–LUMO gap in the presence of the metal
ion, altering the energies of electronic transitions to the
larger wavelengths.[6] Hence, these dyes can be used readily
as biochemical sensitizers, as their absorption maxima fall
within the therapeutic window.
charge transfer symmetry as well as the nature of the donor
group in modulating TPA activity in the presence of a metal
ion such as ZnII or CdII.
We chose the ZnII salt in almost all the experiments be-
cause it is spectroscopically silent in the region of measure-
ment of TPA activity, and hence it would not interfere with
the TPA cross-section values. Our interest in zinc stems
from the fact that it is an essential nutrient required in
normal growth and development,[12] and for cellular process-
es such as DNA repair[13] and apoptosis.[14] This metal plays
a key role in the synthesis of insulin and the pathological
state of diabetes.[15] It is thus a biologically very important
element. Therefore, its static concentration in vivo can facili-
tate the understanding of biological processes.
Molecules like calixarenes, macrocycles, and cryptands
form an integral part of supramolecular chemistry and are
important for their wide-ranging applications in chemistry,
biochemistry, and materials research. Except for macrocy-
cles like porphyrins[7] and crown ethers,[8] these molecules
remain mostly unexplored in third-order optical nonlineari-
ty. Macrobicyclic cryptands can serve as skeletons for the at-
tachment of different electroactive groups for multidimen-
sional charge transfer possibilities. Besides, they can accom-
modate one or more metal ions, anions, or neutral molecules
inside the cavity to act as mediator(s) for cooperative inter-
action among the individual arms leading to enhanced non-
linear responses.[9] Apart from tuning the TPA activity, a
cryptand can act as a suitable host for the switching of opti-
cal properties through translocation[10] of the metal ion. To
realize some of these possibilities, we have attached differ-
ent numbers of 4-(dimethylamino)benzene or ferrocene
moieties through a benzene spacer to a laterally nonsym-
metric aza cryptand to have mono-, bis- or tris-D–p–D’ (D’
is the “N” in the cryptand core and D is either 4-(dimethyl-
amino)benzene or ferrocene systems (Scheme 1). Whereas
4-(dimethylamino)benzene is a strong donor, the ferrocene
moiety is a very good electron transfer group.[11] The six
molecules described herein allow us to probe the effect of
We also performed additional experiments with CdII, and
similar TPA results are obtained. This shows that once a
metal inside the cryptand cavity communicates electronical-
ly with the side groups, they exhibit similar TPA activity.
Transition metals also enter the cavity of the cryptand,[16]
but they have ligand field transitions in the wavelength
range where the TPA cross-sections are measured. This
leads to erroneous TPA cross-section values and hence we
have totally ignored them.
Results and Discussion
Single-photon absorption spectra: All single-photon absorp-
tion studies were carried out in 10ꢀ5 m acetonitrile solutions
after purging with argon for 3 min. The unsubstituted crypt-
and Lo shows only negligible
absorption in the region of in-
terest. The metal-free NLO-
phores L7–L9 exhibit[17] two in-
traligand charge transfer peaks;
the weaker higher energy
320 nm band is partially hidden
under the envelope of the
strong long wavelength 375 nm
band. After the addition of
metal ions, for each of these li-
gands the 375 nm band shows
appreciable redshift along with
an increase in its intensity (Fig-
ure 1a). The remarkable red
shift is observed for the dye L7
with Dl=102 nm after com-
plexation, which is 80 and
81 nm for L8 and L9, respective-
ly.
The NLO-phores L10–L12 ex-
hibit a strong band at around
365 nm that is sensitive to the
number of ferrocenyl groups at-
tached to the cryptand (Fig-
ure 1b), and
a broad weak
Scheme 1. Cryptand-based TPA active systems studied in this work.
band at 465 nm. The 365 nm
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P. K. Bharadwaj, D. Kim et al.
plex, respectively, and [M] is the concentration of the vari-
ous metal ions added.
A0=ðAꢀA0Þ ¼ ½a=ðbꢀaÞꢁ½1=Ks½MꢁÞ þ 1ꢁ
ð1Þ
When A /
G
tration [M]ꢀ1, Ks was directly obtained from the intercept/
slope ratio (Figure 2b). The details of the theoretical analy-
Figure 1. a) Single photon absorption spectra of ligands L7 to L9 and their
corresponding ZnII complexes and b) for ligands L10 to L12 and their cor-
responding ZnII complexes in 10ꢀ5 m CH3CN solution.
band is due to ligand-centered p–p* electronic transition[18]
,
and the lower energy broad band is assignable to another lo-
calized excitation produced either by two nearly degenerate
transitions, a FeII d–d transition, or a metal–ligand charge
transfer process following the treatment of Marder and co-
workers.[19] Both these bands are significantly red-shifted
and become more intense in the presence of a metal ion.
This indicates a very strong intraligand charge transfer tran-
sition (ILCT) accelerated by the metal ion due to the en-
hanced acceptor strength. Here the greatest shift is observed
for the dye L12 with Dl=35 nm, and others are comparable.
Enhancement of optical nonlinearity upon addition of a
metal ion originates[20] from the red shift of the intraligand
charge transfer transition modulated by the Lewis acceptor
properties of the metal ion.
Figure 2. a) Absorption spectra of the chromophore L7 as a function of
[ZnII]. The arrows indicate the trend for increasing [ZnII]. [L7] = 1ꢁ
10ꢀ5 m. b) Plot of A0/AꢀA0 against [ZnII]ꢀ1 for binding constant determi-
nation. The absorption data yield log Ks =5.153.
sis of the stoichiometry and corresponding binding constant
determination are available in the literature.[22] Here the cal-
culated values are in consistence with good correlation coef-
ficients (ꢂ0.99).
A typical example of spectral change in the case of chro-
mophore L7 upon addition of metal salt is given in Fig-
ure 2a, which clearly shows one isosbestic point correspond-
ing to only one equilibrium process. Here, for the complexa-
tion of chromophores L7 to L9 with ZnII salts, the log Ks
values were found to be 5.15, 4.13, and 4.06, respectively. In
the case of chromophores L10 to L12 with ZnII salts, these
values were 4.65, 4.42, and 4.62, respectively.
Binding constant determination: The binding constant (Ks)
for the complex between the chromophores and the Zn-
ACHTUNGTRENNUNG(ClO4)2·6H2O salt were determined by using a UV/Vis spec-
troscopic titration method. The concentration of the ligands
was 1ꢁ10ꢀ5 m and that of metal ions was in the range of 1ꢁ
10ꢀ3 to 1ꢁ10ꢀ6 m. The linear fit of the absorption spectral
data at a particular wavelength for 1:1 complexation was ob-
tained by applying Equation (1),[21] in which A0 and A are
the absorbance of the metal-free ligand and the metal com-
Two-photon absorption measurement: We measured the
TPA cross-section s(2) in the wavelength of 800 nm, which is
within the window of minimum cell damage for any in vivo
studies. The s(2) values for L7 to L12 alone and in the pres-
ence of a metal ion are collected in Table 1, along with
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Cryptand Derivatives for Third Order Optical Nonlinearity
FULL PAPER
The open-aperture Z-scan traces for ZnII complexes of L7
to L12, measured in dry CH3CN solution, are shown in
Figure 3, and those for CdII complexes are given as Support-
ing Information. We scanned all the chromophores at the
wavelength of 800 nm, where the contribution of one-
photon absorption is negligible and we obtain moderate
values for all the chromophoric systems.
We also recorded the change in TPA cross-section values
as a function of wavelength for all the ZnII complexes of L7
to L12. In the literature there are many examples in which
the TPA spectra of various chromophores have been studied
extensively.[23] The quantum-mechanical selection rules for
TPA differ from those for one-photon excitation. Its com-
parison with one-photon absorption (OPA) spectra reveals
that in most cases, the TPA is “blue-shifted”.[24] This means
that the molecular eigenstates accessible by OPA and TPA
have different Franck-Condon factors. This difference arises
due to the dependence of TPA on the virtual state coupling
and due to the different parity-dependent selection rules for
TPA and OPA.
Table 1. Photophysical data for the chromophores L7–L12 and their corre-
sponding ZnII and CdII complexes.
Compound
lmax
eꢁ104
s(2) [GM]
at 800 nm
[nm]
[molLꢀ1 cmꢀ1
]
L7
382, 319
484, 371
487, 369
374, 318
454
460
375, 322
456
3.891, 2.281
5.207, 1.005
4.903, 0.996
8.915, 4.815
12.487
11.459
13.587, 7.468
19.783
450
L7 + Zn
L7 + Cd
L8
L8 + Zn
L8 + Cd
L9
L9 + Zn
L9 + Cd
L10
L10 + Zn
L10 + Cd
L11
L11 + Zn
L11 + Cd
L12
L12 + Zn
L12 + CdACHTUNGTRENNUNG
G
1220
1340
940
2860
2750
1640
4640
4990
910
2700
2560
1940
7490
6750
3050
11200
10660
ACHTUNGTRENNUNG
R
N
ACHTUNGTRENNUNG
G
462
17.98
370, 467
401, 533
407, 543
357, 456
384, 537
386, 544
352, 460
387, 540
393, 547
4.109, 0.437
4.877, 1.955
3.851, 1.524
4.819, 1.266
10.334, 3.323
8.345, 2.66
7.136, 0.814
13.951, 5.141
12.751, 4.753
N
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
Unfortunately, our experimental setup did not allow us to
extend the measurements to higher wavelength beyond
900 nm. We scanned the range 740–900 nm and the maxi-
mum TPA cross-section values in the wavelengths are not
exactly double the lmax in the one-photon absorption spec-
tra. Deriving the multi-photon excitation wavelength maxi-
mum is not as simple as doubling the single-photon excita-
tion wavelength maximum, although in some cases this can
be a good place to start. A “rule of thumb” that can help
(but still does not allow optimal TPE conditions to be pre-
dicted) states that one may expect the TPE cross-section to
peak at twice the wavelength with respect to the one-photon
absorption condition, especially in symmetrical molecules.
However, it may shift (TP excitation maximum versus 2ꢁ
OP excitation maximum) up to 200 nm.[25] The highest TPA
cross-section values and their corresponding lmax are shown
other photophysical properties. Interestingly, there is a grad-
ual increasing trend of TPA cross-section values when we go
from the singly branched system to the triply branched one,
both for free chromophores and their metal complexes. As
the number of branches increases in L7–L9 and L10–L12, re-
spectively, TPA cross-section values are also increased. Fur-
thermore, in the presence of metal ions as input, the s(2)
value increases in each case due to the enhanced acceptor
strength. Especially, compared with L7 to L9, the s(2) values
of L10 to L12 are more enhanced. This is commensurate with
the fact that while 4-(dimethylamino)benzene is a strong
donor, ferrocene is a good electron transfer group, and we
get the maximum value for the ZnII complex of L12. There is
a similar trend for both ZnII and CdII and all the results are
given in Table 1.
Figure 3. Open-aperture Z-scan traces for the ZnII complexes of L7 to L12 in CH3CN solution. Solid lines are the best fits to the experimental data.
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P. K. Bharadwaj, D. Kim et al.
in Table 2 separately. All the wavelengths of the highest
TPA cross-section values are blue-shifted as well. In all
cases, however, there is no significant variation of TPA
cross-section beyond 840 nm wavelength. The results are
given graphically in Figure 4.
cantly, indicating formation of 1:1 complex and saturation
thereafter.
Factors and rationale for influencing the TPA cross-section
in branched systems: A detailed literature study on first ver-
tical ionization potentials (IPs) of ferrocene and 4-(dimeth-
AHCTUNGTREGyNNNU lamino)benzene indicates that the former is the stronger
Table 2. Comparison between lmax of OPA and l at highest TPA cross-
section value for the ZnII complexes of chromophores L7–L12.
electron-transfer donor (the first IPs are 6.86 and 7.45 eV,
respectively) than the latter.[11] Substitution of C=N and N=
N for C=C plays an important role in altering the lmax of the
OPA spectra as well as the maximum TPA cross-sections of
metal complexes.[26] Of these, C=N substituted metal com-
plexes have relatively larger TPA cross-section values than
the others. Based on this principle, we made these Schiff
base ligands using different groups with different donor ca-
pability.
Compound
lmax of OPA
spectra [nm]
Max. s(2)
[GM]
l at highest
s(2) [nm]
l shift TPA vs.
2ꢁOPA [nm]
L7 + ZnII
L8 + ZnII
L9 + ZnII
L10 + ZnII
L11 + ZnII
L12 + ZnII
484
454
456
401
384
387
1860
2860
5300
3740
9510
16420
780
800
780
760
760
750
ꢀ188
ꢀ108
ꢀ132
ꢀ42
ꢀ8
ꢀ24
Consequently, there is a regular gradual increase in TPA
cross-section value from 4-(dimethylamino)benzene to all
the ferrocenyl derivatives, and also from mono-, bis-, to tris-
derivatives of the cryptand. Here, L7 and L10 are typical D–
p–D’ systems and give a moderate TPA value, but upon ad-
dition of ZnII, the metal goes into the cavity and directional
electron flow in these systems results in an increase in the
delocalization of electrons, which gives rise to the high TPA
values. Similar behavior is observed for L8 and L11, also D–
p–D’ systems with two side arms, but when ZnII ion goes
into the cavity it converts into a typical D–p–A–p–D
system, and these two side arms are now electronically con-
nected through the encapsulated metal ion by its d-electrons
and we get a larger value than for L7 and L10 in the presence
Figure 4. Plot of TPA cross-section values for the ZnII complex of L7 to
L12 at different wavelengths in 10ꢀ5 m CH3CN solution. The solid lines are
shown as guides for the eye.
of ZnACTHNUGTRNENUG(ClO4)2·6H2O. Metal ions are excellent 3D templates
and can assemble simple organic NLO-phores around them,
with concomitant tuning of the molecular nonlinear optical
properties by virtue of inducing a strong intraligand charge
transfer (ILCT) transition, which thus plays a very signifi-
cant role. Therefore, the largest s(2) value among these
cases, found in the tris-ferrocenyl derivative of the cryptand
Complexometric titration of L12 with ZnACHTNUGRTNE(UGN ClO4)2·6H2O: This
experiment was carried out in 10ꢀ4 m acetonitrile solution at
800 nm. From the titration curve (Figure 5) of ligand L12, it
is clear that upon addition of the metal ion the TPA value
gradually increases to a certain limit, and then further addi-
tion of the metal ion does not change any TPA value signifi-
L
12 with a metal ion, suggests that here the maximum intrali-
gand charge transfer transition takes place in this octupolar-
like molecule, which gives the maximum communication be-
tween the side arms. This comparison demonstrates that the
electronic communication between the side arms, achieved
by introducing a 4-(dimethylamino)benzene group and fer-
rocenyl moiety, which is triggered by the injection of the
ZnII metal ion, is the overriding factor in increasing the s(2)
value.
Computational details: We employed a blend of quantum-
chemical approaches to rationalize both the linear and non-
linear spectra of the chromophores of interest. Geometry
optimization was carried out for the first three simple ligand
systems L7 to L9 and their corresponding ZnII complexes.
We expect that a similar trend will be observed for the re-
maining molecules L10 to L12. All calculations were per-
formed with the Gaussian 03[27] program, using the
B3LYP[28] functional with a 6–31G* basis set. The optimized
geometry of these molecules predicts that the substituted
Figure 5. Titration curve for the ZnII complex of L12 in different metal
ion concentrations at 770 nm in CH3CN solution. The lines are shown as
guides for the eye.
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Cryptand Derivatives for Third Order Optical Nonlinearity
FULL PAPER
side arms in secondary amine
groups that are tilted in the free
state become much more
planar when the metal atom is
incorporated into the cavity. Fi-
nally, in the case of L9 the three
side arms make an almost
planar geometry round the cen-
tral ZnII atom, whereas in the
free state these are situated in
an angular fashion. Therefore,
by introducing
a metal ion
these molecules come to pos-
sess higher symmetry of charge
delocalization. This demon-
strates an interesting point that
the most regular arrangement
of these kinds of macrobicyclic
compounds has a marked influ-
ence upon their electronic
properties.
Experimentally, we found
that when free chromophores
(L7 to L12) coordinate with
metal ions, the magnitude of
the TPA cross-section in-
creased. The TPA cross-section
is directly correlated with the
extent of intramolecular charge
transfer transition through the
p-conjugated bridge. Generally,
the frontier molecular orbitals,
especially HOMOꢀ1, HOMO,
LUMO, and LUMO+1, play
the significant role in electronic
transitions during two-photon
absorption.[8b] For more intui-
tive analysis of the influence of
the metal ion upon the TPA
properties, we should consider
the contours of some correla-
tive occupied and unoccupied
frontier orbitals (Figure 6).
From the contour surface dia-
grams (L7 to L9) it is clear that
in the case of all the free li-
gands both the HOMOs and
LUMOs are nearly completely
localized upon the conjugated
side arm of the cryptand, indi-
cating only a p!p* electronic
transition
(i.e.,
intraligand
charge transfer, ILCT). Con-
versely, in metal incorporated
cryptand
derivatives
the
HOMO is mainly concentrated
on the p-conjugated side arm
Figure 6. Contour surfaces of HOMO and LUMO for L7 to L9 and their corresponding ZnII complexes.
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P. K. Bharadwaj, D. Kim et al.
and the LUMO resides on the ZnII ion, clearly indicating
that a strong intraligand charge transfer transition, acceler-
ated by the metal atom, takes place after complexation.
Here, in every case, it is worth noting that a more obvious
increased intramolecular charge transfer transition triggered
by metal ions is very beneficial to interpret the enhance-
ment of the TPA cross-section from the free chromo-
phores.[29] Especially, the electron density is more delocal-
ized from one side arm to another two side arms in the
LUMO of L9 with ZnII metal atom than in that of L7 and L8
with ZnII, which induces the largest enhancement of the
TPA cross-section value. Also from the energy level dia-
grams of the chromophores it is clear that the energies of
both HOMO and LUMO orbitals decrease significantly
when both form complexes with ZnII metal ion, indicating
that an electronic charge delocalization takes place after
complexation. As, for example, we find from Figure 7, the
of the fact that the experiments were carried out in a polar
solvent where the counter anion plays an important role,
whereas a vacuum environment was assumed when perform-
ing the calculations. The experimentally determined lmax and
the calculated values are given in Table 3, which details the
nature of the electronic transitions, the corresponding oscil-
lator strengths, and the major orbitals participating in the
transitions in the case of ligands L7, L8, L9 and their corre-
sponding ZnII complexes.
Table 3. OPA data for the chromophores L7 to L9 and their correspond-
ing ZnII complexes.
Compound Exptl
lmax
Theor.
lmax [nm]
Transition fos
Major
contributions[a]
[nm]
L7
382
355
319
S0!S1
S0!S2
0.880 H!L (62%)
Hꢀ2!L (15%)
319
0.299 H!L (12%)
Hꢀ1!L (64%)
L7 + ZnII 484
490
446
421
S0!S2
S0!S3
S0!S4
0.106 H!L+1 (70%)
0.075 H!L+2
0.126 H!L+3
H!L+4
ACHTUNGTRENNUNG(69%)
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
L8
374
318
387
S0!S1
1.257 H!L+1 (62%)
Hꢀ1!L (20%)
376
313
S0!S3
S0!S5
0.886 Hꢀ1!L (61%)
0.055 H!L+2 (63%)
H!L+5 (31%)
308
S0!S7
0.044 H!L+6 (64%)
H!L+5 (17%)
L8 + ZnII 454
448
413
S0!S1
S0!S5
0.117 H!L+1
ACHTUNGTRENNUNG(70%)
0.233 H!L+2 (67%)
H!L+6 (10%)
1.148 Hꢀ1!L +2
(62%)
407
S0!S2
Figure 7. B3LYP/6–31G* predicted molecular orbital energy levels for di-
polar ligands and their corresponding ZnII complexes.
L9
375
388
386
S0!S1
S0!S2
1.107 H!L +2 (60%)
0.079 H!L +1 (68%)
H!L +2 (13%)
0.556 Hꢀ1!L +1
(50%)
HOMO and LUMO energies of the ZnII-incorporated crypt-
and L7 (ꢀ8.31 and ꢀ5.99 eV) are more stable than those of
the free chromophore (L7) (ꢀ4.95 and ꢀ1.05 eV, respective-
ly). Furthermore, this is also accompanied by the decrease
of the HOMO–LUMO gap after complexation as expected:
3.89 eV for the ligand (L7) itself and 2.31 eV for the ZnII
complex. A similar trend is followed by the other ligand sys-
tems L8, L9 and their complexes with the ZnII ion. Figure 7
consists of calculated frontier orbital energy data for 10 oc-
cupied molecular orbitals and 10 unoccupied molecular orbi-
tals (obtained using B3LYP/6–31G*) plotted serially for
comparison with the free chromophores. The most signifi-
cant reduction of the HOMO–LUMO gap is observed in the
case of L7 and its metal complex rather than the other chro-
mophores; this is also backed up by the large redshift of the
UV spectra.
We also perform some theoretical calculations to explain
the origin of the peaks that appear in the UV/Vis spectra
for the first three simple metal-free chromophores L7–L9
and their ZnII complexes, using the time-dependent DFT
(TDDFT) method on the basis of optimized geometry. Our
theoretically calculated OPA parameters are quite similar to
the experimental results. The small deviations arise because
385
S0!S4
L9 + ZnII 456
467
451
S0!S1
S0!S2
0.056 H!L (70%)
0.092 Hꢀ1!L (61%)
Hꢀ2!L (33%)
0.126 Hꢀ2!L (58%)
Hꢀ2!L +1
449
445
S0!S3
(14%)
S0!S5
0.726 Hꢀ1!L +1
(58%)
Hꢀ2!L +1
(31%)
[a] H=HOMO and L=LUMO.
Conclusion
Herein, the TPA properties of nonsymmetric azacryptand-
based dipolar and octupolar systems have been investigated
using a femtosecond laser. The linear and nonlinear proper-
ties were also studied in detail, and it was found that the
TPA property of the dyes not only changed upon addition
of a metal ion but also by the variation of branching units
from mono-, bis- to tris-derivatives. There is a regular in-
crease of TPA cross-section with increasing branching units
10634
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 10628 – 10638

Cryptand Derivatives for Third Order Optical Nonlinearity
FULL PAPER
for free chromophores as well as their metal (ZnII and CdII)
complexes. Complexometric titration using a femtosecond
laser was also carried out successfully. Particularly, DFT cal-
culations have allowed a detailed understanding of the elec-
tronic structure, absorption spectra, and TPA properties of
the studied chromophores. The different coplanarities, elec-
tron conjugation, and DFT-calculated energy levels, and
electronic transition details are in excellent agreement with
the experimental findings. Overall, the electronic communi-
cation between the side arms and the three-dimensional ar-
rangement of the molecule were investigated with respect to
their effect on the TPA cross-section. Perhaps one of the
most crucial conclusions of the present paper is that the con-
jugated octupolar molecules based on C3 symmetrical mo-
lecular geometry could serve as a promising alternative TPA
dye for a variety of applications.
After obtaining the nonlinear absorption coefficient b, the TPA cross-sec-
tion s(2) of one solute molecule (in units of 1 GM=10ꢀ50 cm4 s/photo-
n·molecule) can be determined by using Equation (3), in which NA is the
Avogadro constant, d is the concentration of the TPA compound in solu-
tion, h is Planckꢂs constant, and n is the frequency of the incident laser
beam.
s
ð2ÞNAd ꢃ 10ꢀ3
hn
ð3Þ
b ¼
So as to satisfy the condition a0l<<1, which allows the pure TPA s(2)
values to be determined using a simulation procedure, the TPA cross-sec-
tion value of AF-50 was measured as a reference compound; this control
was found to exhibit a TPA value of 50 GM at 800 nm.
Synthesis: The aza cryptand was synthesized following our earlier[31]
method. The synthetic strategy for the NLO-phores was based on the dif-
ꢀ
ference in reactivity of the three NH groups present in the three bridges
of the cryptand. Mono-, bis-, and tris-derivatives of the cryptand with p-
nitrobenzene can be obtained by an aromatic nucleophilic substitution
(ArSN) reaction in which 3.2 equivalents of the reagent is allowed to
react with the cryptand.[32] The three products can be separated easily
using column chromatography. On reduction, the corresponding amines
are formed, which readily undergo Schiff base condensation with differ-
ent aldehydes, leading to the target compounds (Scheme 2).
Experimental Section
Materials: Reagent grade 1-fluoro-4-nitrobenzene, 4-(dimethylamino)-
benzaldehyde, ferrocene carboxaldehyde, and 10% Pd in activated char-
coal were purchased from Aldrich Chemical Company (USA) and used
as received. All the solvents were acquired from S. D. Fine Chemical
(India) and dried properly before use following literature methods. All
the reactions were carried out under dinitrogen atmosphere. Chromato-
graphic separations were performed using column chromatography, with
100–200 mesh silica gel obtained from S. D. Fine Chemicals (India).
Analysis and measurements: 1H NMR spectra (400 MHz) and 13C NMR
spectra (100 MHz) were recorded on a JEOL JNM-LA400 FT spectrom-
eter in CDCl3 with tetramethylsilane as internal standard. Melting points
were measured with an electrical melting point apparatus by PERFIT,
India, and were uncorrected. Elemental analyses were recorded in an El-
ementar Vario EL III Carlo Erba 1108 Elemental Analyser. Mass spectra
(FAB) were recorded by JEOL SX-102/DA-6000 mass spectrometer
using argon as the FAB gas at 6 kV and 10 mA with an accelerating volt-
age of 10 kV at 298 K at CDRI, Lucknow. The electrospray ionization
mass spectra (ESI-MS) were recorded in a MICROMASS QUATRO in-
troduced into the ESI source through a syringe pump at the rate of
5 mLminꢀ1; the capillary was set at 3.5 kV with a cone voltage of 40 V.
UV/Vis spectra were recorded on a JASCO V570 UV-vis-NIR spectro-
photometer in dry acetonitrile at 298 K.
Measurement of two-photon absorption cross-section (s(2)): The two-
photon absorption coefficients were measured by using an open aperture
Z-scan method[30] with about 130 fs pulses at 5 kHz repetition rate gener-
ated from a Ti:sapphire regenerative amplifier system (Spectra-Physics,
Hurricane). The laser beam was divided into two parts. One was moni-
tored by a Ge/PN photodiode as intensity reference and the other was
used for transmittance measurements. After passing through a lens (f=
10 cm), the laser beam was focused and passed through a quartz cell. The
position of the sample cell could be varied along the laser-beam direction
(z axis), so the local power density within the sample cell could be
changed under a constant laser power level. The thickness of the cell was
1 mm. The transmitted laser beam from the sample cell was then detect-
ed by the same photodiode as used for reference monitoring. The on-axis
peak intensity of the incident pulses at the focal point, I0, ranged from 40
to 80 GWcmꢀ2. Assuming a Gaussian beam profile, the nonlinear absorp-
tion coefficient b can be obtained by curve fitting to the observed open-
aperture traces using Equation (2), in which a0 is the linear absorption
coefficient, l the sample length, and z0 the diffraction length of the inci-
dent beam.
Scheme 2. Synthetic scheme for the preparation of chromophores L7 to
L12 studied in this work.
Synthesis of the p-nitrobenzene derivatives: Anhydrous K2CO3 (0.44 g,
3.2 mmol) was added to a solution of the cryptand, L0 (0.56 g, 1 mmol) in
dry DMSO (15 mL). Subsequently 1-fluoro-4-nitrobenzene (0.45 g,
3.2 mmol) in dry DMSO (15 mL) was added dropwise over 30 min and
the reaction mixture was stirred at 708C for 48 h. It was then poured into
ice water (250 mL). The yellow solid that separated was collected by fil-
tration and washed thoroughly with water (5ꢁ100 mL). This yellow solid
contained a mixture of mono-, bis-, and tris-derivatives and was separat-
ed by column chromatography (SiO2 100–200 mesh). The tris-derivative
(L3) was eluted first using CHCl3/MeOH (99.75:0.25 v/v) as the eluent.
bI0ð1ꢀeꢀa0l
Þ
2
ð2Þ
TðzÞ ¼ 1ꢀ
2a0ð1 þ ðz=z0Þ Þ
Chem. Eur. J. 2008, 14, 10628 – 10638
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
10635

P. K. Bharadwaj, D. Kim et al.
After evaporating the solvent, the yellow solid was recrystallized from
MeCN to obtain a bright yellow crystalline solid. Yield ꢄ60%; m.p.
2308C. The bis-derivative (L2) was eluted out next using CHCl3/MeOH
(99:1 v/v). Upon slow evaporation, the desired product was isolated as a
bright yellow crystalline solid. Yield 30%; m.p. 1388C. The mono-deriva-
tive (L1) was eluted out last using CHCl3/MeOH (96:4 v/v) as the eluent.
The product was obtained as a yellow crystalline solid on slow evapora-
tion. Yield 27%; m.p. 1758C.
[M++H], 805 (60) [M++Na]; elemental analysis calcd (%) for
C48H59N7O3: C 73.72, H 7.60, N 12.54; found: C 73.67, H 7.39, N 11.99.
L8: Yield ꢄ78%; m.p. 1878C; 1H NMR spectra (400 MHz, CDCl3, 258C,
TMS): d=2.05 (br, 1H), 2.13 (t, J=8.1 Hz, 6H), 2.39 (t, J=5.4 Hz, 2H),
2.58 (t, J=5.4 Hz, 2H), 2.95 (t, J=3.9 Hz, 4H), 2.98 (s, 12H), 3.15 (t, J=
5.6 Hz, 4H), 3.22 (t, J=5.4 Hz, 4H), 3.65 (s, 2H), 4.04 (t, J=5.8 Hz, 2H),
4.12 (t, J=5.4 Hz, 4H), 6.60–6.72 (m, 4H), 6.74–6.90 (m, 6H), 6.97–7.25
(m, 14H), 7.60–7.75 (m, 4H), 8.25 ppm (d, J=6.3 Hz, 2H); 13C NMR
spectra (100 MHz, CDCl3, 258C, TMS): d=29.6, 31.5, 40.1, 42.1, 50.6,
53.9, 54.5, 55.3, 66.9, 110.6, 111.6, 113.5, 120.2, 122.2, 126.7, 129.9, 130.6,
132.3, 143.2, 146.4, 151.9, 156.8 ppm; FAB-MS: m/z (%): 1005 (45) [M+
+H]; elemental analysis calcd (%) for C63H73N9O3: C 75.34, H 7.33, N
12.55; found: C 75.42, H 7.23, N 12.29.
L9: Yield ꢄ60%; m.p. 1808C; 1H NMR spectra (400 MHz, CDCl3, 258C,
TMS): d=2.48 (t, J=5.5 Hz, 6H), 2.68 (t, J=5.5 Hz, 6H), 3.03 (s, 18H),
3.35 (t, J=5.4 Hz, 6H), 3.75 (s, 6H), 4.22 (t, J=5.3 Hz, 6H), 6.53 (d, J=
8.5 Hz, 6H), 6.69 (d, J=8.6 Hz, 6H), 6.85–7.05 (m, 12H), 7.14 (d, J=
8.6 Hz, 3H), 7.23 (d, J=7.3 Hz, 3H), 7.42 (d, J=8.8 Hz, 6H), 8.29 ppm
(d, J=7.8 Hz, 3H); 13C NMR spectra (100 MHz, CDCl3, 258C, TMS): d=
40.2, 41.9, 53.0, 54.7, 68.2, 110.7, 112.0, 113.4, 121.8, 122.4, 124.1, 124.5,
128.8, 129.0, 130.5, 142.0, 142.8, 146.7, 150.9, 156.8 ppm; FAB-MS: m/z
(%): 1228 (80) [M++H]; elemental analysis calcd (%) for C78H87N11O3:
Reduction of nitro to amine (L4 to L6): The reduction of the nitro group
to the corresponding amine was achieved using hydrazine hydrate and
Pd-C in ethanol, heated under reflux.[33] Typically, the mono nitro-deriva-
tive, L1 (1.362 gm, 2 mmol), was taken in a two-necked round bottom
flask with 50 mL absolute ethanol, purged with N2 for a few minutes, and
10% Pd in activated charcoal (5 mol% per nitro group) was added, fol-
lowed by dropwise addition of hydrazine hydrate (3 mL) over a period of
30 min. The mixture was refluxed for 3 h, filtered hot, and the filtrate
evaporated under reduced pressure almost to dryness. After shaking the
remaining mass with water (100 mL) to remove excess hydrazine hydrate,
the desired amine was extracted with chloroform, dried over anhydrous
Na2SO4, and finally evaporated to obtain a colorless semi-solid in each
case.
L4: Yield ꢄ70%; 1H NMR spectra (400 MHz, CDCl3, 258C, TMS): d=
2.30–2.58 (m, 6H), 2.84–3.10 (m, 6H), 3.23–3.38 (m, 2H), 3.53 (d, J=
13.4 Hz, 4H), 3.92–4.13 (m, 6H), 4.23 (s, 2H), 4.35–4.39 (m, 4H), 6.28 (d,
J=8.56 Hz, 2H), 6.36–6.48 (m, 6H), 6.62 (d, J=8.28 Hz, 2H), 6.72–6.86
(m, 3H), 6.99–7.19 ppm (m, 3H); 13C NMR spectra (100 MHz, CDCl3,
258C, TMS): d=49.8, 51.1, 53.3, 54.7, 55.2, 66.6, 67.2, 111.6, 113.8, 116.9,
120.2, 120.8, 126.7, 127.5, 128.9, 132.3, 153.6 ppm; ESI-MS: m/z (%): 651
(100) [M+]; elemental analysis calcd (%) for C39H50N6O3: C 71.97, H
7.74, N 12.91; found: C 71.87, H 7.52, N 12.78.
L5: Yield ꢄ55%; 1H NMR spectra (400 MHz, CDCl3, 258C, TMS): d=
2.52–2.56 (m, 4H), 2.61–2.68 (m, 6H), 3.08–3.20 (m, 6H), 3.32–3.36 (m,
2H), 3.83 (s, 2H), 4.05–4.07 (m, 2H), 4.17–4.29 (m, 4H), 4.51 (s, 4H),
6.30(d, J=7.8 Hz, 3H), 6.72 (d, J=7.3 Hz, 3H), 6.78 (d, J=7.3 Hz, 3H),
6.89 (d, J=8.0 Hz, 3H), 7.01–7.09 (m, 4H), 7.18–7.22 ppm (m, 4H);
13C NMR spectra (100 MHz, CDCl3, 258C, TMS): d=41.0, 51.6, 53.9,
54.3, 60.9, 66.6, 67.3, 110.5, 110.6, 111.3, 112.6, 120.8, 124.6, 126.1, 127.1,
128.5, 136.9, 150.3, 153.9, 155.0 ppm; ESI-MS m/z (%): 743 (90) [M+
+H]; elemental analysis calcd (%) for C45H55N7O3: C 72.84, H 7.47, N
13.21; found: C 72.77, H 7.39, N 13.48.
L6: Yield ꢄ60%; 1H NMR spectra (400 MHz, CDCl3, 258C, TMS): d=
2.40–2.53 (m, 6H), 2.65–2.74 (m, 6H), 2.94–3.26 (m, 6H), 3.33–3.44 (m,
6H), 3.94 (s, 6H), 4.97 (b, 6H), 6.58–6.70 (m, 9H), 6.78 (d, J=7.3 Hz,
3H), 6.85 (d, J=6.7 Hz, 3H), 6.90–7.13 ppm (m, 9H); 13C NMR spectra
(100 MHz, CDCl3, 258C, TMS): d=49.1, 49.9, 50.9, 54.8, 63.8, 105.1,
111.5, 121.2, 124.3, 125.5, 128.4, 131.9, 134.7, 145.9, 152.5, 157.9 ppm;
ESI-MS m/z (%): 834 (75) [M++H]; elemental analysis calcd (%) for
C51H60N8O3: C 73.53, H 7.26, N 13.45; found: C 73.76, H 7.12, N 13.24.
C 76.38, H 7.15, N 12.56; found: C 76.67, H 7.23, N 12.54.
1
L
10: Yield ꢄ70%; m.p. 1768C; H NMR spectra (400 MHz, CDCl3, 258C,
TMS): d=1.61 (br, 2NH), 2.25–2.60 (m, 6H), 2.80–3.00 (m, 4H), 3.00–
3.20 (m, 4H), 3.20–3.38 (br, 1H), 3.40–3.70 (m, 4H), 3.99–4.15 (m, 7H),
4.19 (s, 5H), 4.38 (d, J=19.8 Hz, 4H), 4.74 (s, 2H), 5.15 (d, J=13.2 Hz,
2H), 6.43 (d, J=8.1 Hz, 2H), 6.67 (d, J=8.1 Hz, 2H), 6.75–6.95 (m, 3H),
7.03(d, J=8.8 Hz), 7.12–7.22 (m, 7H), 8.30 ppm (s, 1H); 13C NMR spectra
(100 MHz, CDCl3, 258C, TMS): d=30.9, 42.1, 45.6, 53.0, 54.5, 61.8, 67.0,
68.7, 69.1, 69.1, 69.6, 69.6, 69.7, 70.8, 73.2, 110.7, 113.5, 120.3, 121.9, 121.9,
126.5, 126.6, 126.8, 130.7, 144.7, 146.3, 146.8, 156.8 ppm; FAB-MS: m/z
(%): 870 (95) [M++Na]; elemental analysis calcd (%) for C50H58N6O3Fe:
C 70.91, H 6.90, N 9.92; found: C 70.90, H 6.67, N 9.83.
1
L11: Yield ꢄ65%; m.p. 2308C; H NMR spectra (400 MHz, CDCl3, 258C,
TMS): d=1.82 (b, 1H), 2.17 (t, J=5.4 Hz, 4H), 2.50 (t, J=5.9 Hz, 2H),
2.70 (t, J=5.4 Hz, 2H), 3.20 (t, J=5.4 Hz, 2H), 3.28 (t, J=5.4 Hz, 2H),
3.70 (s, 2H), 4.06–4.10 (m, 4H), 4.16–4.25 (m, 8H), 4.26 (s, 10H), 4.41 (s,
4H), 4.59 (s, 2H), 4.70–4.80 (m, 6H), 6.45–6.65 (m, 4H), 6.70–6.95 (m,
6H), 7.00–7.30 (m, 10H), 8.29 ppm (d, J=8.0 Hz, 2H) 13C NMR spectra
(100 MHz, CDCl3, 258C, TMS): d=49.3, 52.8, 54.6, 56.3, 61.7, 68.7, 68.8,
68.9, 69.2, 69.3, 69.6, 70.9, 71.0, 71.3, 73.2, 110.7, 113.3, 115.6, 116.7, 120.3,
121.4, 121.5, 121.7, 121.9, 127.1, 130.6, 148.1, 155.8, 158.5 ppm; FAB-MS:
m/z (%): 1135 (20) [M++H]; elemental analysis calcd (%) for
C67H71N7O3Fe2: C 70.96, H 6.31, N 8.64; found: C 70.93, H 6.26, N 8.53.
1
L
12: Yield ꢄ55%; m.p. 2688C; H NMR spectra (400 MHz, CDCl3, 258C,
TMS): d=2.38 (t, J=5.5 Hz, 6H), 2.58 (t, J=5.6 Hz, 6H), 3.25 (t, J=
5.6 Hz, 6H), 4.12 (t, J=5.4 Hz, 6H), 4.19 (s, 15H), 4.41 (d, J=12.8 Hz,
6H), 4.73 (d, J=12.7 Hz, 6H), 6.72–6.89 (m, 12H), 7.04–7.25 (m, 12H),
8.29 ppm (d, J=15.1 Hz); 13C NMR spectra (100 MHz, CDCl3, 258C,
TMS): d=51.0, 53.6, 54.7, 55.4, 66.6, 67.2, 68.6, 69.1, 70.7, 111.7, 112.0,
120.3, 120.9, 121.8, 126.7, 127.3, 128.9, 132.4, 147.0, 157.6 ppm; FAB-MS:
m/z (%): 1422 (25) [M++H]; elemental analysis calcd (%) for
C84H84N8O3Fe3: C 70.99, H 5.96, N 7.88; found: C 70.89, H 5.94, N 7.75.
Synthesis of the NLO-phores: The NLO-phores were synthesized from
the amines obtained as above through Schiff base condensation with an
equivalent amount of either 4-(dimethylamino) benzaldehyde or ferro-
cene carboxaldehyde in dry ethanol. The desired products precipitated
out after stirring the solution at room temperature for 24 h. The product
was collected by filtration, washed twice with dry ethanol followed by di-
ethyl ether, and finally dried in vacuo. These compounds were directly
used for analysis and further studies. All the compounds were light- and
moisture-sensitive and turn into a brown sticky solid when exposed to air
for about an hour.
L7: Yield ꢄ65%; m.p. 1608C; 1H NMR spectra (400 MHz, CDCl3, 258C,
TMS): d=1.59 (br, 2NH), 2.36 (t, J=16.6 Hz, 2H), 2.44 (t, J=6.1 Hz,
4H), 2.85 (t, J=4.6 Hz, 4H), 2.90 (t, J=9.3 Hz, 2H), 2.96 (s, 6H), 3.01 (t,
J=5.1 Hz, 4H), 3.08 (t, J=6.4 Hz, 2H), 3.54 (d, J=13.7 Hz, 2H), 3.93 (t,
J=4.9 Hz, 2H), 4.06 (t, J=4.4 Hz, 4H), 4.30 (s, 2H), 5.08 (d, J=13.4 Hz,
2H), 6.38 (d, J=8.8 Hz, 2H), 6.6–6.7 (m, 4H), 6.70–6.87 (m, 4H), 6.95–
7.24 (m, 8H), 7.67 (d, J=8.5 Hz, 2H), 8.29 ppm (s, 1H); 13C NMR spec-
tra (100 MHz, CDCl3, 258C, TMS): d=40.2, 47.3, 49.2, 50.2, 51.0, 53.5,
54.8, 55.4, 66.6, 67.2, 111.6, 111.9, 120.3, 122.0, 126.6, 127.7, 128.9, 129.8,
130.4, 138.5, 132.3, 141.9, 155.9, 157.5 ppm; FAB-MS: m/z (%): 783 (15)
Preparation of the ZnII complexes of chromophores: Complexation with
ZnII metal was achieved by stirring the prepared cryptand derivative with
ZnACTHUNGRTNEUNG(ClO4)2·6H2O in 1:1 molar ratio in dry acetonitrile at room tempera-
ture. A dark red (purple) solution results in each case, which on evapora-
tion affords the product as a dark red solid in over 90% yield. The CdII
complexes of all the chromophores were made in a similar way using Cd-
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
ture stirred for 1 h at room temperature. The deep blood-red-colored so-
lution was then evaporated near to dryness under vacuum. The dark red-
colored mass was collected without further purification. [Zn(L7)]
ACHTUNGTRENNUNG(ClO4)2:
ESI-MS: m/z (%): 423 (100) [L7 +Zn]2+; elemental analysis calcd (%)
10636
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 10628 – 10638

Cryptand Derivatives for Third Order Optical Nonlinearity
FULL PAPER
for C48H59N7O11Cl2Zn: C 55.10, H 5.68, N 9.37; found: C 55.12, H 5.54, N
9.25.
Chem. Soc. 2006, 128, 11840–11849; d) K. S. Kim, S. B. Noh, T. Kat-
suda, S. Ito, A. Osuka, D. Kim, Chem. Commun. 2007, 2479–2481.
[2] a) B. A. Reinhardt, L. L. Brott, S. J. Clarson, A. G. Dillard, J. C.
Bhatt, R. Kannan, L. Yuan, G. S. He, P. N. Prasad, Chem. Mater.
1998, 10, 1863–1874; b) M. Rumi, J. E. Ehrlich, A. A. Heikal, J. W.
Perry, S. Barlow, Z. Hu, D. McCord-Maughon, T. C. Parker, H.
Rçckel, S. Thayumanavan, S. R. Marder, D. Beljonne, J.-L. Brꢃdas,
J. Am. Chem. Soc. 2000, 122, 9500–9510.
[3] a) B. R. Cho, K. H. Son, S. H. Lee, Y.-S. Song, Y.-K. Lee, S.-J. Jeon,
J. H. Choi, H. Lee, M. Cho, J. Am. Chem. Soc. 2001, 123, 10039–
10045; b) W.-H. Lee, H. Lee, J.-A. Kim, J.-H. Choi, M. Cho, S.-J.
Jeon, B. R. Cho, J. Am. Chem. Soc. 2001, 123, 10658–10667; c) L.
Porrꢄs, O. Mongin, C. Katan, M. Charlot, T. Pons, J. Mertz, M. Blan-
chard-Desce, Org. Lett. 2004, 6, 47–50; d) W. J. Yang, D. Y. Kim,
C. H. Kim, M.-Y. Jeong, S. K. Lee, S.-J. Jeon, B. R. Cho, Org. Lett.
2004, 6, 1389–1392; e) M. Parent, O. Mongin, K. Kamada, C. Katan,
M. Blanchard-Desce, Chem. Commun. 2005, 2029–2031.
[4] a) L. Ventelon, S. Charier, L. Moreaux, J. Mertz, M. Blanchard-
Desce, Angew. Chem. 2001, 113, 2156–2159; Angew. Chem. Int. Ed.
2001, 40, 2098–2101; b) O. Mongin, L. Porrꢄs, L. Moreaux, J. Mertz,
M. Blanchard-Desce, Org. Lett. 2002, 4, 719–722; c) Y. Iwase, K.
Kamada, K. Ohta, K. Kondo, J. Mater. Chem. 2003, 13, 1575–1581;
d) M. H. V. Werts, S. Gmouh, O. Mongin, T. Pons, M. Blanchard-
Desce, J. Am. Chem. Soc. 2004, 126, 16294–16295.
[5] a) M. Drobizhev, A. Karotki, Y. Dzenis, A. Rebane, Z. Suo, C. W.
Spangler, J. Phys. Chem. B 2003, 107, 7540–7543; b) O. Mongin, L.
Porrꢄs, C. Katan, T. Pons, J. Mertz, M. Blanchard-Desce, Tetrahedon
Lett. 2003, 44, 8121–8125.
2) [L8ꢅZn
ACHTUNGTRENNUNG(H2O)]ACHTUNGTRENNUNG(ClO4)2: Following the same procedure as above, in a
round bottom flask one equivalent of bis- derivative of ortho-cryptand
(L8) (0.10 gm, 0.1 mmol) in dry acetonitrile (5 mL) was warmed gently,
the same equivalent of ZnACHTUNRGTNEUNG(ClO4)2·6H2O, (0.037 gm, 0.1 mmol) was added
and the mixture stirred for 1 h. The deep blood-red solution was then
evaporated near to dryness under vacuum and the dark mass was isolat-
ed. [Zn(L8)ACHTUNGTRENNUNG(H2O)]ACHTUNGTRENNUNG ;
(ClO4)2: ESI-MS: m/z (%): 544 (50) [L8 +Zn+H2O]2+
elemental analysis calcd (%) for C63H75N9O12Cl2Zn: C 58.81, H 5.87, N
9.79; found: C 58.73, H 5.94, N 9.75.
3) [L9ꢅZn
0.1 mmol) was dissolved in dry acetonitrile (5 mL), the same equivalent
of Zn(ClO4)2·6H2O, (0.037 gm, 0.1 mmol) was added, and the mixture
ACHTUNGTRENNUNG(MeCN)]ACHTUNGTRENNUNG(ClO4)2: One equivalent of ligand L9 (0.123 gm,
ACHTUNGTRENNUNG
was stirred for 1 h until a homogeneous deep blood-red solution ap-
peared. Then this dark solution was evaporated near to dryness under
vacuum to get the dark solid mass. [Zn(L9)ACHTNUGRTENNUG(MeCN)]ACHTUNTGREN(NNGU ClO4)2: ESI-MS:
m/z (%): 666 (45%) [L9 +Zn+MeCN]2+; elemental analysis calcd (%)
for C80H90N12O11Cl2Zn: C 62.72, H 5.92, N 10.97; found: C 62.80, H 5.79,
N 10.95.
4) [L10ꢅZn]
ortho-cryptand (0.085 gm, 0.1 mmol) was dissolved in dry acetonitrile so-
lution (5 mL), the same equivalent of Zn(ClO4)2·6H2O (0.037 gm,
ACHTUNGTRENNUNG(ClO4)2: One equivalent of mono-ferrocenyl derivative of
AHCTUNGTRENNUNG
0.1 mmol) was added, and the mixture stirred for 1 h. The deep blood-
red solution was then evaporated near to dryness under vacuum to
obtain a solid mass. [ZnACTHNUGTRENN(UG L10)]CAHTUNGTRNE(NUGN ClO4)2: ESI-MS: m/z (%): 456 (35%)
[L10 +Zn]2+; elemental analysis calcd (%) for C50H58N6O11Cl2Zn Fe: C
54.05, H 5.26, N 7.56; found: C 54.11, H 5.24, N 7.49.
[6] D. Kim, A. Osuka, Acc. Chem. Res. 2004, 37, 735–745.
[7] a) T. E. O. Screen, J. R. G. Thorne, R. G. Denning, D. G. Bucknall,
H. L. Anderson, J. Am. Chem. Soc. 2002, 124, 9712–9713; b) K.
Ogawa, A. Ohashi, Y. Kobuke, K. Kamada, K. Ohta, J. Am. Chem.
Soc. 2003, 125, 13356–13357; c) H. Rath, J. Sankar, V. PrabhuRaja,
T. K. Chandrashekar, A. Nag, D. Goswami, J. Am. Chem. Soc. 2005,
127, 11608–11609; d) M. Drobizhev, Y. Stepanenko, A. Rebane,
C. J. Wilson, T. E. O. Screen, H. L. Anderson, J. Am. Chem. Soc.
2006, 128, 12432–12433; e) M. Morone, L. Beverina, A. Abbotto, F.
Silvestri, E. Collini, C. Ferrante, R. Bozio, G. A. Pagani, Org. Lett.
2006, 8, 2719–2722; f) K. Kurotobi, K. S. Kim, S. B. Noh, D. Kim, A.
Osuka, Angew. Chem. 2006, 118, 4048–4051; Angew. Chem. Int. Ed.
2006, 45, 3944–3947.
[8] a) G. Fabbrini, E. Menna, M. Maggini, A. Canazza, G. Marcolongo,
M. Meneghetti, J. Am. Chem. Soc. 2004. 126, 6238–6239; b) S. J. K.
Pond, O. Tsutsumi, M. Rumi, O. Kwon, E. Zojer, J.-L. Brꢃdas, S. R.
Marder, J. W. Perry, J. Am. Chem. Soc. 2004, 126, 9291–9306;
c) H. M. Kim, M.-Y. Jeong, H. C. Ahn, S.-J. Jeon, B. R. Cho, J. Org.
Chem. 2004, 69, 5749–5751; d) R. Bozio, E. Cecchetto, G. Fabbrini,
C. Ferrante, M. Maggini, E. Menna, D. Pedron, R. Riccꢅ, R. Signo-
rini, M. Zerbetto, J. Phys. Chem. A 2006, 110, 6459–6464.
[9] S.-J. Chung, K.-S. Kim, T.-C. Lin, G. S. He, J. Swiatkiewicz, P. N.
Prasad, J. Phys. Chem. B 1999, 103, 10741–10745.
5) [L11ꢅZn]
ACHTUNGTRENNUNG(ClO4)2: Following the same procedure as earlier, in a 50 mL
round bottom flask, one equivalent of bis- ferrocenyl derivative of ortho-
cryptand (0.113 gm, 0.1 mmol) was dissolved in dry acetonitrile solution
(5 mL), and the same equivalent of ZnACTHUNRGTNEG(UN ClO4)2·6H2O (0.037 gm,
0.1 mmol) was added and the mixture stirred for 1 h. The deep blood-red
solution was then evaporated near to dryness under reduced pressure.
[ZnACHTUNGTRENNUNG(L11)]ACHTUNGTRENNUNG
(ClO4)2: ESI-MS: m/z (%): 599 (65) [L11 +Zn]2+; elemental
analysis calcd (%) for C67H71N7O11Cl2ZnFe2: C 57.55, H 5.12, N 7.01;
found: C 57.71, H 5.23, N 6.96.
6) [L12ꢅZn]
ortho-cryptand (0.142 gm, 0.1 mmol) was dissolved in dry acetonitrile so-
lution (5 mL), the same equivalent of Zn(ClO4)2·6H2O (0.037 gm,
0.1 mmol) was added and the mixture stirred for 1 h. The dark red solu-
tion was then evaporated near to dryness under vacuum resulting in a
ACHTUNGTRENNUNG(ClO4)2: One equivalent of tris-ferrocenyl derivative of
AHCTUNGTRENNUNG
dark solid mass. [ZnACHTUNGTRENNUNG(L12)]AHCTUNGTREN(NGNU ClO4)2: ESI-MS: m/z (%): 743 (50) [L12 +
Zn]2+; elemental analysis calcd (%) for C84H84N8O11Cl2ZnFe3: C 59.86, H
5.02, N 6.65; found: C 59.84, H 4.95, N 6.73.
All these solid masses collected were used directly for NLO measure-
ments without further purification.
[10] B. Bag, P. K. Bharadwaj, Inorg. Chem. 2004, 43, 4626–4630.
[11] S. Barlow, S. R. Marder, Chem. Commun. 2000, 1555–1562.
[12] B. L. Vallee, K. H. Falchuk, Physiol. Rev. 1993, 73, 79–118.
[13] a) E. Ho, B. N. Ames, Proc. Natl. Acad. Sci. USA 2002, 99, 16770–
16775; b) H. Daiyasu, K. Osaka, Y. Ishino, H. Toh, FEBS Lett. 2001,
503, 1–6.
Acknowledgements
Financial support received from CSIR and DRDO, New Delhi, India to
P.K.B. is gratefully acknowledged. A.J. and A.K.D. thank CSIR for their
fellowships. P.K.B and A.J. thank Dr. Kousik Giri, School of Chemistry,
University of Birmingham, for his help with the theoretical calculations.
The work at Yonsei University was supported by BK21 and the Star Fac-
ulty Programs from the Ministry of Education, Science and Technology
of Korea. S.Y.J. and J.Y.S. acknowledge the fellowship from the BK21
program.
[14] A. Q. Troung-Tran, J. Carter, R. E. Ruffin, P. D. Zalewski, Biometals
2001, 14, 315–330.
[15] A. B. Chausmer, J. Am. Coll. Nutr. 1998, 17, 109–115.
[16] a) D. K. Chand, P. K. Bharadwaj, Inorg. Chem. 1996, 35, 3380–3387;
b) D. K. Chand, P. K. Bharadwaj, Inorg. Chem. 1997, 36, 5658–5660;
c) P. Ghosh, S. S. Gupta, P. K. Bharadwaj, J. Chem. Soc. Dalton
Trans. 1997, 935–938.
[17] P. R. Bangal, S. Chakravorti, J. Photochem. Photobiol. A 1998, 116,
191–202.
[18] A. Caballero, A. Tꢆrraga, M. D. Velasco, P. Molina, Dalton Trans.
2006, 1390–1398.
[1] a) Y. Wang, G. S. He, P. N. Prasad, T. Goodson III, J. Am. Chem.
Soc. 2005, 127, 10128–10129; b) S.-J. Chung, M. Rumi, V. Alain, S.
Barlow, J. W. Perry, S. R. Marder, J. Am. Chem. Soc. 2005, 127,
10844–10845; c) A. Bhaskar, G. Ramakrishna, Z. Lu, R. Twieg,
J. M. Hales, D. J. Hagan, E. V. Stryland, T. Goodson III, J. Am.
Chem. Eur. J. 2008, 14, 10628 – 10638
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
10637

P. K. Bharadwaj, D. Kim et al.
[19] S. Barlow, H. E. Bunting, C. Ringham, J. C. Green, G. U. Bublitz,
S. G. Boxer, J. W. Perry, S. R. Marder, J. Am. Chem. Soc. 1999, 121,
3715–3723.
[20] a) D. Roberto, R. Ugo, F. Tessore, E. Lucenti, S. Quici, S. Vezza, P.-
C. Fantucci, S. Bruni, I. Ledoux-Rak, J. Zyss, Organometallics 2002,
21, 161–170; b) Q. Zheng, G. S. He, P. N. Prasad, J. Mater. Chem.
2005, 15, 579–587.
[21] J. Bourson, J. Pouget, B. Valeur, J. Phys. Chem. 1993, 97, 4552–4557.
[22] S. Fery-Forgues, M.-T. Le Bries, J.-P. Guettꢃ, B. Valeur, J. Phys.
Chem. 1988, 92, 6233–6237.
[23] a) W. R. Zipfel, R. M. Williams, R. Christie, A. Y. Nikitin, B. T.
Hyman, W. W. Webb, Proc. Natl. Acad. Sci. USA 2003, 100, 7075–
7080; b) H. M. Kim, M.-Y. Jeong, H. C. Ahn, S.-J. Jeon B. R. Cho, J.
Org. Chem. 2004, 69, 5749–5751; c) Q. Zheng, G. S. He, P. N.
Prasad, Chem. Mater. 2005, 17, 6004–6011; d) M. Williams-Harry, A.
Bhaskar, G. Ramakrishna, T. Goodson III. , M. Imamura, A. Mawa-
tari, K. Nakao, H. Enozawa, T. Nishinaga, M. Iyoda, J. Am. Chem.
Soc. 2008, 130, 3252–3253.
y, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyen-
gar, 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, V. Bakken, 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. Cio-
slowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaro-
mi, 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 and J. A. Pople, Gaussian, Inc.,
Wallingford CT, 2004.
[28] a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652; b) R.-P. ꢇscar,
Y. Luo, H. ꢈgren, J. Chem. Phys. 2006, 124, 094310–1–094310–5.
[29] Q. Zheng, G. S. He and P. N. Prasad, J. Mater. Chem. 2005, 15, 579–
587.
[24] F. Bestvater, E. Spiess, G. Stobrawa, M. Hacker, T. Feurer, T.
Porwol, U. Berchner-Pfannschmidt, C. Wotzlaw, H. Acker, J. Mi-
crosc. 2002, 208, 108–115.
[30] See Supporting Information.
[25] W. Denk, D. W. Piston, W. W. Webb in Multi-Photon Molecular Ex-
citation in Laser-Scanning Microscopy, Chapter 28: Handbook of
Biological Confocal Microscopy, 3rd revised ed. (Ed.: J. B. Pawley),
Springer, 2006, pp. 535–549.
[31] K. G. Ragunathan, P. K. Bharadwaj, Tetrahedron Lett. 1992, 33,
7581–7584.
[32] P. Mukhopadhyay, P. K. Bharadwaj, G. Savitha, A. Krishnan, P. K.
Das, J. Mater. Chem. 2002, 12, 2237–2244.
[26] X.-B. Zhang, J.-K. Feng, A.-M. Ren, J. Phys. Chem. A 2007, 111,
1328–1338.
[33] H. Adams, R. Bastida, D. E. Fenton, B. E. Mann, L. Valencia, Eur.
J. Org. Chem. 1999, 1843–1846.
[27] Gaussian 03, Revision C.02, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomer-
Received: July 9, 2008
Published online: October 16, 2008
10638
www.chemeurj.org
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Chem. Eur. J. 2008, 14, 10628 – 10638