Coordination induction of nonlinear molecular shape in mesomorphic and luminescent ZnII complexes based on salen-like frameworks

Article abstract of DOI:10.1002/ejic.200900536

A series of tetradentate dimeric salicylaldimine ligands (H ₂L_nR_m) with terminal chains of variable length (R_m) and a central flexible (CH₂)_n spacer (L_n = 10 and 12) was synthesi

Full text of DOI:10.1002/ejic.200900536

FULL PAPER
DOI: 10.1002/ejic.200900536
Coordination Induction of Nonlinear Molecular Shape in Mesomorphic and
Luminescent ZnII Complexes Based on Salen-Like Frameworks
Daniela Pucci,*[a] Iolinda Aiello,[a] Anna Bellusci,[a] Alessandra Crispini,[b] Mauro Ghedini,[a]
and Massimo La Deda[b]
Keywords: Zinc / Schiff bases / Metallomesogens / Nonlinear shape / Intercalated smectic phase
A series of tetradentate dimeric salicylaldimine ligands
(H2LnRm) with terminal chains of variable length (Rm) and a
central flexible (CH2)n spacer (Ln = 10 and 12) was synthe-
sized. For all ligands, according to their rod-like molecular
shape, mesomorphism characteristic of calamitic systems
(nematic and smectic C phases) is observed. The reaction
in the central part of the molecule, responsible for the ap-
pearance of an intercalated smectic C mesophase. Moreover,
the coordination of the ZnII ion to the salen-like framework
induces, in all the corresponding complexes, interesting
blue-light-emitting properties at room temperature in dichlo-
romethane solution (EQY in the 19–22% range at about
with ZnII acetate dihydrate afforded a series of ZnLnRm deriv- 450 nm), as well as in the solid (EQY: 9% at about 450 nm)
atives (1–6) that show mesomorphic behaviour only in the
presence of the longest terminal tails (R12). Interestingly, the
flexibility of the very long spacer in the central core and the
presence of the tetrahedral ZnII centre introduce nonlinearity
or, when present, in the mesophase (EQY 8% at 440 nm).
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
of nonconventional shapes and supramolecular assemblies
allowed the first examples of mesomorphic ZnII species
showing lamellar or columnar liquid crystalline phases to
be obtained.[3]
In particular, ZnII complexes based on versatile salen
(N,NЈ-bis-salicylidene ethylenediamine) frameworks are re-
ceiving growing interest as cheap and accessible building
blocks for the synthesis of new molecular materials working
as the light-emitting layer in OLEDs (organic light-emitting
devices).[4]
In a recent paper we reported on the excellent emission
quantum yield displayed by the blue-emitting chromophore
obtained through ZnII complexation with the salen-like li-
gand H2L12 containing a very long, central alkyl backbone
(Scheme 1).[5] From this study it appears evident that the
emission performances are strongly related to the nature of
the bridging diamine and therefore to the molecular struc-
ture of the resulting coordination compound.
In order to combine the emissive properties of these sys-
tems with the development of softness through mesomor-
phic induction, promesogenic building blocks have been in-
troduced[6] as alkoxy substituents in the 4-position of the
aromatic rings connected to the salicylaldimine moiety
through an ester link (H2L12Rm in Scheme 1) in analogy
with reference ligands containing shorter central bridges.[7]
Our first attempts to obtain metal-containing salen-like li-
quid crystals by using these new ligands involved the use of
NiII and CuII metal ions. Interestingly, such MII complex-
ation afforded 1:1 metal-to-ligand compounds (with a
square planar MII coordination geometry, regular for NiII
Introduction
ZnII complexes displaying physical properties such as
thermal stability, luminescence in the visible region of the
electromagnetic spectrum and/or charge transporting abil-
ity are very attractive species for applications in electroptic
devices.[1] The different practical applications involving mo-
lecular materials processed as amorphous thin films imply
the use of technological approaches able to obtain useful
thin layers such as high-vacuum evaporation or solutions,
the latter way being less expensive and more suitable for
large area devices. In this context, the synthesis of ZnII
compounds featuring good solubility in appropriate sol-
vents is required. However, the performances of these de-
vices are also strongly dependent on the efficiency of the
charge transport and the emission, both properties ulti-
mately depending on the molecular arrangement inside the
amorphous films. Therefore, in order to optimize properly
the devices, the development of new soft materials such as
liquid crystals, showing at the same time order and charge
mobility, seems to be a good strategy.[2] Indeed, in the last
years it has been proven that the opportune combination
[a] Centro di Eccellenza CEMIF.CAL, LASCAMM - CR INSTM,
Unità INSTM della Calabria and LiCryl, CNR-INFM, Dipart-
imento di Chimica - Università della Calabria,
87036 Arcavacata di Rende (CS), Italy
Fax: +39-984-492066
E-mail: d.pucci@unical.it
[b] Centro di Eccellenza CEMIF.CAL, LASCAMM - CR INSTM,
Unità INSTM della Calabria and LiCryl, CNR-INFM, Dipart-
imento di Scienze Farmaceutiche – Università della Calabria,
87036 Arcavacata di Rende (CS), Italy
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Mesomorphic and Luminescent ZnII Complexes
Scheme 1.
or slightly distorted for CuII) showing the same mesomor- used for H2L12R6 and H2L12R12.[6] Because the overall geo-
phism (nematic or smectic phases) of their precursors, sug- metries and the subsequent thermal properties of these
gesting that an overall rod-like molecular shape is main- types of dimeric liquid crystals are strongly dependent on
tained after complexation.[6] However, in order to get the the ratio between the length of the terminal chains and the
desired luminescence properties not present in the NiII and spacers,[7,8] Ln and Rm in the present case, for the synthesis
CuII derivatives, we focused on the ZnII ion as coordinating of this new series of ligands N,NЈ-bis[(4Ј-alkoxy)benzoyloxy-
metal able to act as a luminophore centre in such systems. benzylidene]-1,10-diaminodecane H2L10Rm and N,NЈ-bis-
In this paper the synthesis and characterization of a new [(4Ј-alkoxy)benzoyloxybenzylidene]-1,12-diaminododecane
series of H2LnRm ligands and their corresponding ZnII H2L12Rm terminal chains of comparable length or shorter
complexes and the role exerted by the different central spa- than the spacer length were selected (Scheme 2).
cers (Ln) and terminal chains (Rm) on the overall molecular
shape, molecular packing and nature of the potential me-
sophases in the ZnII derivatives are reported.
The reaction of the H2LnRm ligands with an equimolar
amount of ZnII acetate dihydrate in ethanol under reflux
leads to the formation of the corresponding ZnLnRm com-
plexes 1–6 in very good yields, whose 1:1 ligand to metal
stoichiometry and purity were confirmed by elemental
Results and Discussion
1
analyses, IR and H NMR spectroscopy (Scheme 3).
In particular, the success of the coordination to the ZnII
Synthesis and Characterization
ion was evidenced, in the IR spectra of 1–6, by the disap-
The series of dimeric ligands H2LnRm containing two pearance of the OH signal and by the shift of the CN
identical salicylaldimine fragments connected by long even- stretching band to lower wavenumbers with respect to the
1
numbered alkylene spacer were prepared as yellow solids organic ligand and, in the H NMR spectra, from the lack
in high yields in a two-step reaction starting from the 2,4- of OH signals and from the upfield shift of the signal attrib-
dihydroxybenzaldehyde and the appropriate 4-alkoxyben- utable to the iminic hydrogen. Moreover, for complexes 1–
zoic acid, according to the previously reported procedure 6, in the IR spectra two different absorption bands centred
Scheme 2.
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Figure 1. (a) UFF-optimized molecular structure of complex 3 in
the fully extended all-trans chain conformation and (b) pseudobent
core of about 120.4° (chains omitted for clarity).
Thermal Behaviour
All the H2LnRm ligands show, after a crystal-to-crystal
transition, mesomorphism typical of calamitic systems, un-
ambiguously recognized by polarized optical microscopy
(POM), differential scanning calorimetry (DSC) and tem-
perature-dependent powder X-ray diffraction (PXRD) mea-
Scheme 3.
at about 1530 and 1550 cm–1 are observed for the phenolic surements. Thermal data are summarized in Table 1.
oxygen atoms and, in the 1H NMR spectra, two singlets for
In particular, for the lower homologues the results from
both the imine groups and the protons in the ortho position POM observations suggested the presence of only a nematic
to the coordinated phenolic oxygen atoms are present, sug- mesophase, as indicated by the typical schlieren (H2L10R1,
gesting a loss of symmetry with respect to the starting li- H2L10R6, H2L12R6) or marbled (H2L12R1) textures. As re-
gands.
gards the ligands with the longest terminal chain R12,
As regards the possible molecular organization and coor- H2L10R12 shows only a smectic C phase with an unusual,
dination geometry around the zinc(II) centre, in the arche- simultaneous occurrence of schlieren and fun-shaped tex-
typal Zn(salen) framework the presence of the short central tures (Figure 2), whereas H2L12R12 exhibited a smectic C
bridge prevents the formation, in the solid state, of a tetra- phase followed by the nematic one, both identified with a
hedral environment, leading to two interchangeable forms: schlieren texture showing only four-brush defects.
a five-coordinate distorted planar geometry for the mono-
All the mesophases are enantiotropically exhibited for
meric [Zn(salen)L] species[9,10] and a bipyramidal geometry several heating/cooling cycles. As expected, the clearing
for the [Zn(salen)]2 anhydrous dimeric form.[11] Interest- points decreased with the elongation of the terminal chains
ingly, when the alkyl chain between the two imine moieties Rm.
increases in length (3 Ͻ n Ͻ 8) a greater propensity to form
The definitive mesophase identification was achieved by
bimetallic or polymeric systems through oxygen-bridging temperature-dependent PXRD analysis on nonaligned sam-
was observed, allowing again the ZnII ion to adopt a five- ples. The nematic nature of the mesophase was confirmed:
coordinate environment, but no structural information in in all cases, the diffuse in the small-angle region arises from
the solid state have been reported for ZnII complexes with correlations in the molecular arrangement along the direc-
alkyl backbones longer than three CH2 groups, suggesting tor. In the case of the highest homologues H2L10R12 and
that the structural preferences of the ZnII ion in such Schiff H2L12R12, the PXRD patterns revealed the presence of a
base environments are more complex than thought.[10,12] In lamellar smectic phase. In particular, both spectra show
the case of complexes 1–6, it appears from all the spectro- three sharp peaks in the low-angle region (46.8, 23.3, 15.7 Å
scopic evidence that the new species show an asymmetric for H2L10R12; 50.4, 25.8, 16.2 Å for H2L12R12) with a recip-
ligand environment around the ZnII, which coupled with rocal space ratio of 1:2:3. The maxima can be assigned to
the presence of the flexible spacer between the nitrogen do- the (001), (002) and (003) reflections typical of a layered
nor atoms, direct towards the formation of monomeric de- arrangement. In both cases, the wide angle region displayed
rivatives with a distorted tetrahedral geometry. In the ab- a broad halo centred at 4.6–4.7 Å, typical of disordered
sence of experimental structure determination, a model is smectic structures and associated with short-range liquid-
proposed on the basis of molecular modelling calculations like positional order within the layer. The layer thickness d
made through the Universal Force Field (UFF) method[13] of 46.8 and 50.2 Å, deduced from the Bragg spacings of the
and performed on complex 3 (Figure 1).
low-angle reflections, is significantly smaller than the length
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Mesomorphic and Luminescent ZnII Complexes
Table 1. Thermal behaviour of the H2LnRm, ligands.
L of the molecules, as calculated from the modelled lowest
energy conformation of the molecule of H2L10R12 (Fig-
ure 3a) of 65 Å. In agreement with the POM observations,
the mesophase can be assigned as a tilted smectic C type,
with an estimate tilt angle of 43° in the case of H2L10R12,
assuming no interdigitation of molecules in adjacent layers
(Figure 3b).
Figure 3. (a) UFF-optimised[13] molecular structure of H2L10R12 in
a linear conformation suitable for an overall rod-like shape and (b)
schematic representation of the possible arrangements of molecules
of H2L10R12 in a tilted layered structure.
Therefore, the presence of nematic and/or smectic C
phases in this series of dimeric molecules containing an
even number of flexible spacers is an indication of their
overall rod molecular geometry, as recently reported in the
literature for similar salicylaldimine derivatives.[7]
The thermal behaviour of the ZnLnRm complexes
(Table 2) was found to be strongly dependent on the ratio
between the carbon atom number of the spacer Ln and the
terminal chains Rm. Indeed, when Ln/Rm Ͼ 1 the complexes
completely lack mesomorphism, melting directly into an
isotropic liquid at very high temperatures, whereas for the
higher homologues with Ln/Rm Յ 1 a mesophase charac-
terized by a very fine focal conic fan-shaped texture slowly
formed from batonnets emerging from the isotropic liquid
was observed by POM (Figure 4).
[a] Cr: Crystal; SmC: smectic C; N: nematic, I: isotropic liquid.
[b] Temperature data as onset peak.
The nature of the mesophase displayed by complexes 3
or 6 was clarified through PXRD measurements performed
on nonaligned samples. The PXRD patterns of complexes
3 and 6, very similar, exhibited sharp inner reflections (22.8,
11.1, 7.3 Å for 3; 24.8, 11.9, 8.9 Å for 6) that are consistent
with (001), (002), (003) reflections of a layered structure.
Furthermore, both spectra showed a diffuse halo centred
at 4.6–4.8 Å and associated with the short-range liquid-like
positional ordering of the chains. The reduction of the lam-
ellar periodicity d in the zinc complexes with respect to the
corresponding ligands evidences a strong interdigitation of
the chains as a result of the increase in the molecular area
of the core after complexation. Moreover, according to the
modelled structure of complex 3, the coordination of the
Figure 2. Polarized-light optical photomicrograph of the texture ex-
hibited by H2L10R12 at 130 °C.
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Table 2. Thermal behaviour of ZnLnRm complexes.
Figure 5. Proposed molecular packing mode in the intercalated
smectic C phase.
[a] Cr: crystal; Sm: smectic; N: nematic, I: isotropic liquid. [b] Tem-
perature data as onset peak. [c] Data from POM.
Photophysical Studies
The photophysical properties of all species were investi-
gated in dichloromethane solution at room temperature.
The absorption spectra of the H2LnRm ligands are very sim-
ilar, showing two peaks centred at 265 and 310 nm and a
very-low intensity band at 400 nm. The 265 and 310 nm
bands are ascribed to a π–π* transition localized on the
aromatic rings, whereas the 400 nm band is due to an n–π*
excitation between the lone pair on the iminic nitrogen
atom and a π* orbital on the C=N fragment. Complexes
1–6 show two intense bands at 275 nm and in the 355–
370 nm range resulting from metal-perturbed ligand-
centred transitions, which have the same origin as the two
principal bands of the ligand spectrum, so proving that ZnII
complexation to H2LnRm lowers the energy states of the
ligands, leading to a bathochromic shift of the absorption
peaks of the complexes. Moreover, as expected, the n–π*
transition, which gives rise to a low-intensity band in the
H2LnRm spectra, is not detected in the spectra of the corre-
sponding complex because of the involvement of the nitro-
gen lone pair in the coordination to the ZnII ion.
Figure 4. Polarized-light optical photomicrograph of the interca-
lated smectic C phase appearing just below the isotropic phase in
complex 6.
With reference to the emission properties, whereas the
dimeric ligand to the ZnII ion gives rise to an almost regular H2LnRm compounds are nonemissive, their corresponding
tetrahedral geometry around the metal ion and an overall ZnII complexes show the typical large fluorescence band
pseudobent conformation of the molecule with a reduced usually observed in similar Schiff-based metal complexes,[4a]
length (L ≈ 53 Å) compared to the free ligand. Therefore, with the emission maximum centred at 432 nm originating
the observed layer spacings d are also less than half of the from π–π* singlet ligand-centred excited state.
molecular length of the complex molecules (d/L about 0.4).
Emission quantum yields (EQY) values were determined
As a result of the d/L ratio found and the possibility of by using the optically dilute method[15] on aerated dichloro-
efficiently packed molecules with strong chain interdigi- methane solutions whose absorbance at excitation wave-
tation between layers, it is possible to propose the formation lengths was Ͻ0.1; 9,10-diphenylanthracene in cyclohexane
of an intercalated smectic C phase (Figure 5; designed as was used as a standard (EQY = 0.96).[16] The EQY of com-
B6 in the case of bent-core structures[14]), often observed for plexes 1–6 are in the 19–22% range and are not significantly
bent-core dimers.[7b,8] Moreover, the quite unusual thermal affected by the length of the Ln bridge or the Rm substitu-
behaviour including pronounced hysteresis and high vis- ents.
cosity observed for complexes 3 and 6 is in line with the
packing of such nonlinear molecules, which induces strong also recorded in the solid crystalline state by placing a uni-
intermolecular dipole–dipole interactions. form powder sheet between two quartz plates. The charac-
Emission and excitation spectra of complexes 1–6 were
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Mesomorphic and Luminescent ZnII Complexes
teristic large fluorescent band of Schiff-based metal com- molecular shape, mesomorphism characteristic of calamitic
plexes was detected in all cases at 452 nm, considerably red- systems is observed, whose nature is strongly influenced by
shifted with respect to that recorded in solution. The EQY the ratio between the length of the central bridge Ln and
measurements of complexes 1–6 were performed by means the terminal chains Rm. Indeed, when the Rm length is
of an integrating sphere, and a value of about 9% was ob- smaller then the Ln spacer, only a nematic phase is shown,
tained in all cases. Moreover, for mesomorphic ZnL12R12 whereas the smectic C is added or replaces the nematic one
complex 6, whose mesophase is frozen, on cooling into a when the two lengths are comparable.
glassy state until room temperature, the emission maximum
The addition of ZnII acetate to this series of dimers af-
in this aggregation state was found at 440 nm, with an EQY forded the corresponding ZnLnRm derivatives, for which the
of about 8%. The emission spectra of 6, recorded in solu- intrinsic flexibility of the very long spacer and the presence
tion and in the different phases, are summarized in Figure 6 of the tetrahedral centre induce a bent core geometry fav-
and comparing the different traces it is worthy to note that ouring, in the homologues with the longest terminal chains,
the maximum emission wavelength with the associated red- the onset of an intercalated tilted smectic C phase (or B6 in
shift in the excitation spectrum increases on going from the the banana phases nomenclature), with the molecules in-
solution to the mesophase and to the microcrystalline pow- tercalated and tilted within the layers. This is a phase nor-
der, so evidencing a trend which can be related to a pro- mally observed for organic dimers formed by two rod-like
gressive reinforcement of the intermolecular aromatic inter- segments covalently linked to a central angular aromatic
actions. This gives rise to a larger electronic delocalization, core when the length of the terminal chains is smaller or
resulting in an energy lowering of the electronic states.
comparable to the length of the spacer in the dimers. In the
present case, it is the metal scaffold that promotes the
space-filling interactions, which originate from the bent
core structure and which result in the formation of a B
phase.
Moreover, the complexation with ZnII turns on, in solu-
tion, an intense luminescence in the ZnLnRm complexes at
432 nm with a valuable high emission quantum yield of
about 20%. This emission, centred on the ZnII salicylald-
imine core, is successfully preserved in the mesogenic phase
of complex 6, which emits in the blue spectral range (CIE
1931 chromaticity coordinates x = 0.2025, y = 0.1827) with
a considerable EQY value of 8%.
The described liquid crystalline compounds are interest-
ing blue emitters that combine fluidity and orientational
ability so proving that these easy-to-synthesize ZnII com-
plexes can actually form an interesting class of multifunc-
tional materials whose properties are easily modulated
through little changes in the single molecular tectons.
Figure 6. Emission spectra of complex 6.
In order to comment on the EQY values calculated for
6, which were found to be 22% in solution, 8% in the meso-
phase and 9% in the crystalline state, it is reasonable to
assume that they could originate from a delicate balance
between an enhancement in the intermolecular interactions,
which reduces the luminescence intensity (as can be ob-
served on going from the solution to the mesophase), and
a reduction in the local mobility, which, on the contrary,
favours the radiative deactivation efficiency (as can be ob-
served on going from the mesophase to the crystalline
state).
Experimental Section
General Methods: Infrared spectra in KBr were recorded with a
Perkin–Elmer Spectrum One FTIR spectrometer equipped for re-
flectance measurements. 1H NMR spectra were recorded with a
Bruker WH-300 spectrometer in CDCl3 solutions, with TMS as an
internal standard. Elemental analyses were performed with a Per-
kin–Elmer 2400 analyzer. The textures of the mesophases were
studied with a Zeiss Axioscope polarizing microscope equipped
with a Calctec C0 600 heating stage. The transition temperatures
and enthalpies were measured with a Perkin–Elmer Pyris 1
Differential Scanning Calorimeter with a heating and cooling rate
of 10 °Cmin–1. The apparatus was calibrated with indium. Two or
more heating/cooling cycles were performed on each sample. The
X-ray powder diffraction patterns were obtained by using a Bruker
AXS General Area Detector Diffraction System (D8 Discover with
GADDS) with monochromated Cu-Kα radiation (λ = 1.5406 Å).
The highly sensitive area detector was placed at a distance of 20 cm
from the sample and at an angle 2θD of 14°. A CalCTec (Italy)
Conclusions
A series of mesogenic tetradentate Schiff bases, H2LnRm,
containing two identical salicylaldimine fragments (bearing
alkoxy substituents of variable length in the 4-position of
the terminal aromatic ring) connected through a long,
highly flexible even-numbered spacer of variable length was
successfully synthesized and characterized. For all these di-
meric H2LnRm compounds, according to the global rod-like variable heating stage was used to heat the samples at a rate of
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D. Pucci et al.
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5.0 °Cmin–1 to the appropriate temperature. Measurements were
performed by charging samples in Lindemann capillary tubes with
inner diameters of 0.5 mm. Steady-state emission spectra were re-
corded with a HORIBA Jobin–Yvon Fluorolog-3 FL3-211 spec-
trometer equipped with a 450 W xenon arc lamp, double-grating
N,NЈ-Bis[(4Ј-dodecyloxy)benzoyloxybenzylidene]-1,10-diaminode-
cane (H L R ): Yellow solid. Yield: 0.32 g (79%). IR (KBr): ν =
˜
2
10 12
2920–2849 (stretching aliphatic CH), 1728 (stretching C=O), 1640
(stretching C=N), 1606, 1254 cm–1. 1H NMR (300 MHz, CDCl3,
25 °C): δ = 14.10 (s, 2 H, OH), 8.31 (s, 2 H, CH=N), 8.13 (d, J =
8.80 Hz, 4 H, H2Ј,6Ј), 7.26 (d, J = 8.27 Hz, 2 H, H6), 6.97 (d, J =
8.80 Hz, 4 H, H3Ј,5Ј), 6.79 (d, J = 1.87 Hz, 2 H, H3), 6.72 (dd, J3,5
= 1.87 Hz, J = 8.54 Hz, 2 H, H5), 4.04 (t, J = 6.95 Hz, 4 H, OCH2),
3.58 (t, J = 6.90 Hz, 4 H, C=N-CH2), 1.86–0.90 (m, 62 H, aliphatic
protons) ppm. UV/Vis (CH2Cl2): λabs. = 400, 310, 265 nm.
C62H88N2O8 (989.37): calcd. C 75.27, H 8.97, N 2.83; found C
75.33, H 8.88, N 3.16.
excitation and single-grating
emission monochromators
(2.1 nmmm–1 dispersion; 1200 groovesmm–1) and a Hamamatsu
R928 photomultiplier tube. Emission and excitation spectra were
corrected for source intensity (lamp and grating) and emission
spectral response (detector and grating) by standard correction
curves. The molar extinction coefficients determination was not
performed cause a nonoptimal solubilization of the compounds.
The emission quantum yields of the pure samples were obtained
by means of a 102 mm diameter integrating sphere coated with
Spectralon® and mounted in the optical path of the spectrofluorim-
eter by using, as excitation source, a 450 W Xenon lamp coupled
with a double-grating monochromator for selecting wavelengths.
The experimental uncertainties were 1 nm for the band maxima for
the luminescence spectra, 10% for EQY in solution and 5% for
EQY in pure samples.
N,NЈ-Bis[(4Ј-methoxy)benzoyloxybenzylidene]-1,12-diaminodode-
cane (H L R ): Yellow solid. Yield: 0.29 g (77%). IR (KBr): ν =
˜
2
12 1
2927–2853 (stretching aliphatic CH), 1731 (stretching C=O), 1637
(stretching C=N), 1606, 1256 cm–1. 1H NMR (300 MHz, CDCl3,
25 °C): δ = 14.12 (s, 2 H, OH), 8.32 (s, 2 H, CH=N), 8.14 (d, J =
8.79 Hz, 4 H, H2Ј,6Ј), 7.26 (d, J = 8.47 Hz, 2 H, H6), 6.98 (d, J =
8.79 Hz, 4 H, H3Ј,5Ј), 6.78 (d, J = 2.48 Hz, 2 H, H3), 6.72 (d, J3,5
= 2.48 Hz, J = 8.47 Hz, 2 H, H5), 3.90 (s, 6 H, OCH3), 3.58 (t, J
= 7.38 Hz, 4 H, C=N-CH2), 1.71–1.28 (m, 20 H, aliphatic protons)
ppm. UV/Vis (CH2Cl2): λabs. = 400, 310, 265 nm. C42H48N2O8
(708.34): calcd. C 71.17, H 6.83, N 3.95; found C 71.49, H 6.71, N
3.64.
Synthesis of the Ligands: The preparation of I2,3 precursors and
H2L12R6 and H2L12R12 ligands was accomplished as previously re-
ported.[7] The synthesis of I1 and other H2LnRm compounds was
performed by following the same method.
4-Formyl-3-hydroxyphenyl 4-Methoxybenzoate (I1): White solid.
ZnL10R1 (1): Zinc acetate dihydrate (0.05 g, 0.02 mmol) was added
to a hot solution of HL1 (0.15 g, 0.21 mmol) in ethanol (15 mL).
The reaction mixture was stirred at reflux for 5 h and then cooled
to room temperature. The solid, collected by filtration, was purified
Yield: 0.86 g (69%). M.p. 117 °C. IR (KBr): ν = 2951–2846
˜
(stretching aliphatic CH), 1735 (ester stretching C=O), 1658 (al-
dehydic stretching C=O), 1606, 1254 cm–1. 1H NMR (300 MHz,
CDCl3, 25 °C): δ = 11.26 (s, 1 H, OH), 9.89 (s, 1 H, CH=O), 8.13 by recrystallization from chloroform/acetonitrile and then dried in
(d, J = 9.04 Hz, 2 H, H2Ј,6Ј), 7.61 (d, J = 9.04 Hz, 1 H, H6), 6.99
(d, J = 9.04 Hz, 2 H, H3Ј,5Ј), 6.93 (dd, J = 2.44 Hz, J = 8.54 Hz, 1
vacuo. White solid. Yield: 0.14 g (89%). IR (KBr): ν = 2932–2856
˜
(stretching aliphatic CH), 1725 (stretching C=O), 1605 (stretching
H, H5), 6.87 (d, J = 2.44 Hz, 1 H, H3), 3.90 (s, 3 H, OCH3) ppm. C=N), 1255 cm–1. 1H NMR (300 MHz, CDCl3, 25 °C): δ = 8.18 (s,
C15H12O5 (272.25): calcd. C 66.17, H 4.44; found C 65.81, H 4.16.
2 H, CH=N), 8.14 (d, J = 8.83 Hz, 4 H, H2Ј,6Ј), 7.15 (t, J = 8.51 Hz,
2 H, H6), 6.98 (d, J = 8.83 Hz, 4 H, H3Ј,5Ј), 6.65 (d, J = 1.89 Hz,
2 H, H3), 6.51 (dd, J = 1.89 Hz, J = 8.51 Hz, 2 H, H5), 4.05 (s, 6
H, OCH3), 4.15, 3.82 (m, 4 H, C=N-CH2), 1.34-1.16 (m, 16 H,
aliphatic protons) ppm. UV/Vis (CH2Cl2): λabs. = 370, 275 nm; λem.
= 432 nm. C40H42N2O8Zn (744.16): calcd. C 64.56, H 5.69, N 3.76;
found C 64.78, H 5.52, N 3.89.
N,NЈ-Bis[(4Ј-methoxy)benzoyloxybenzylidene]-1,10-diaminodecane
(H2L10R1): 1,10-Diaminodecane (0.08 g, 0.46 mmol) was added to
a hot solution of I1 (0.25 g, 0.92 mmol) in methanol (15 mL). The
precipitate, which immediately formed, was stirred under reflux for
4 h, then filtered and washed with ethanol. The crude product was
purified by recrystallization from acetone and then dried in vacuo.
Yellow solid. Yield: 0.25 g (80 %). IR (KBr): ν = 2921–2850 ZnL R (2): White solid. Yield: 0.16 g (85%). IR (KBr): ν = 2924–
˜
˜
10
6
(stretching aliphatic CH), 1728 (stretching C=O), 1635 (stretching
2848 (stretching aliphatic CH), 1730 (stretching C=O), 1606
1
C=N), 1606, 1254 cm–1. H NMR (300 MHz, CDCl3, 25 °C): δ = (stretching C=N), 1267 cm–1. 1H NMR (300 MHz, CDCl3, 25 °C):
14.11 (s, 2 H, OH), 8.31 (s, 2 H, CH=N), 8.14 (d, J = 8.95 Hz, 4
δ = 8.17 (s, 2 H, CH=N), 8.12 (d, J = 8.86 Hz, 4 H, H2Ј,6Ј), 7.14
(t, J = 8.60 Hz, 2 H, H6), 6.95 (d, J = 8.86 Hz, 4 H, H3Ј,5Ј), 6.65
H, H2Ј,6Ј), 7.26 (d, J = 8.67 Hz, 2 H, H6), 6.99 (d, J = 8.95 Hz, 4
H, H3Ј,5Ј), 6.79 (d, J = 2.31 Hz, 2 H, H3), 6.72 (d, J = 2.31, J = (d, J = 1.89 Hz, 2 H, H3), 6.51 (dd, J = 1.89 Hz, J = 8.33 Hz, 2 H,
8.67 Hz, 2 H, H5), 3.89 (s, 6 H, OCH3), 3.59 (t, J = 7.51 Hz, 4 H, H5), 4.04 (t, J = 6.45 Hz, 4 H, OCH2), 3.83, 3.32 (m, 4 H,
C=N-CH2), 1.72–1.30 (m, 16 H, aliphatic protons) ppm. UV/Vis
C=NCH2), 1.86–0.89 (m, 38 H, aliphatic protons) ppm. UV/Vis
(CH2Cl2): λabs. = 400, 310, 265 nm. C40H44N2O8 (680.31): calcd. C (CH2Cl2): λabs. = 355, 275 nm; λem. = 432 nm. C50H62N2O8Zn
70.57, H 6.51, N 4.11; found C 70.71, H 6.18, N 4.14.
(884.43): calcd. C 67.90, H 7.07, N 3.17; found C 67.58, H 7.25, N
2.92. Thermal behaviour is reported in Table 2.
N,NЈ-Bis[(4Ј-hexyloxy)benzoyloxybenzylidene]-1,10-diaminodecane
(H L R ): Yellow solid. Yield: 0.28 g (82%). IR (KBr): ν = 2925–
ZnL10R12 (3): White solid. Yield: 0.11 g (82%). IR (KBr): ν =
˜
˜
2
10 6
2846 (stretching aliphatic CH), 1728 (stretching C=O), 1635
2946–2853 (stretching aliphatic CH), 1732 (stretching C=O), 1605
(stretching C=N), 1254 cm–1. 1H NMR (300 MHz, CDCl3, 25 °C):
δ = 8.17 (s, 2 H, CH=N), 8.12 (d, J = 8.84 Hz, 4 H, H2Ј,6Ј), 7.13
(t, J = 8.55 Hz, 2 H, H6), 6.95 (d, J = 8.84 Hz, 4 H, H3Ј,5Ј), 6.64
(d, J = 2.49 Hz, 2 H, H3), 6.51 (dd, J = 2.49 Hz, J = 8.55 Hz, 2 H,
H5), 4.03 (t, J = 6.36 Hz, 4 H, OCH2), 3.83, 3.33 (m, 4 H, C=N-
1
(stretching C=N), 1608, 1255 cm–1. H NMR (300 MHz, CDCl3,
25 °C): δ = 14.12 (s, 2 H, OH), 8.31 (s, 2 H, CH=N), 8.12 (d, J =
8.52 Hz, 4 H, H2Ј,6Ј), 7.26 (d, J = 8.52 Hz, 2 H, H6), 6.96 (d, J =
8.83 Hz, 4 H, H3Ј,5Ј), 6.79 (d, J = 2.18 Hz, 2 H, H3), 6.71 (dd, J =
2.18 Hz, J = 8.20 Hz, 2 H, H5), 4.04 (t, J = 6.62 Hz, 4 H, OCH2),
3.58 (t, J = 6.62 Hz, 4 H, C=N-CH2), 1.86–0.89 (m, 38 H, aliphatic CH2), 1.83–0.86 (m, 62 H, aliphatic protons) ppm. UV/Vis
protons) ppm. UV/Vis (CH2Cl2): λabs. = 400, 310, 265 nm.
C50H64N2O8 (821.05): calcd. C 73.14, H 7.86, N 3.41; found C
72.98, H 8.01, N 3.32.
(CH2Cl2): λabs. = 360, 275 nm; λem. = 432 nm. C62H86N2O8Zn
(1052.74): calcd. C 70.74, H 8.23, N 2.66; found C 70.88, H 8.15,
N 2.49. Thermal behaviour is reported in Table 2.
4280
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Eur. J. Inorg. Chem. 2009, 4274–4281

Mesomorphic and Luminescent ZnII Complexes
ZnL R (4): White solid. Yield: 0.13 g (75%). IR (KBr): ν = 2931–
2855 (stretching aliphatic CH), 1735 (stretching C=O), 1607
(stretching C=N), 1258 cm–1. 1H NMR (300 MHz, CDCl3, 25 °C):
δ = 8.18 (s, 2 H, CH=N), 8.13 (d, J = 8.79 Hz, 4 H, H2Ј,6Ј), 7.13
(t, J = 8.79 Hz, 2 H, H6), 6.97 (d, J = 8.82 Hz, 4 H, H3Ј,5Ј), 6.64
(d, J = 2.19 Hz, 2 H, H3), 6.48 (dd, J = 2.19 Hz, J = 8.79 Hz, 2 H,
H5), 3.90 (s, 6 H, OCH3), 3.83, 3.32 (m, 4 H, C=N-CH2), 1.28–
chat, A. Baro, N. Steinke, F. Giesselmann, C. Hoegele, G.
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ama, K. Minoura, M. Funahashi, T. Shimomura, T. Kato, Adv.
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˜
12
1
0.95 (m, 20 H, aliphatic protons) ppm. UV/Vis (CH2Cl2): λabs.
=
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360, 275 nm; λem. = 432 nm. C42H46N2O8Zn (772.21): calcd. C
65.33, H 6.00, N 3.63; found C 65.18, H 6.15, N 3.89. Thermal
behaviour is reported in Table 2.
ZnL R (5): White solid. Yield: 0.13 g (80%). IR (KBr): ν = 2926–
˜
12
6
2854 (stretching aliphatic CH), 1732 (stretching C=O), 1606
(stretching C=N), 1535, 1255 cm–1. 1H NMR (300 MHz, CDCl3,
25 °C): δ = 8.17 (s, 2 H, CH=N), 8.11 (d, J = 8.54 Hz, 4 H, H2Ј,6Ј),
7.14 (t, J = 8.54 Hz, 2 H, H6), 6.95 (d, J = 8.54 Hz, 4 H, H3Ј,5Ј),
6.65 (d, J = 2.44 Hz, 2 H, H3), 6.51 (dd, J = 2.44 Hz, J = 8.54 Hz,
2 H, H5), 4.04 (t, J = 6.10 Hz, 4 H, OCH2), 3.81, 3.33 (m, 4 H,
C=NCH2), 1.87–0.88 (m, 42 H, aliphatic protons) ppm. UV/Vis
(CH2Cl2): λabs. = 360, 275 nm; λem. = 432 nm. C52H66N2O8Zn
(912.48): calcd. C 68.45, H 7.29, N 3.07; found C 68.28, H 7.25, N
2.89. Thermal behaviour is reported in Table 2.
ZnL12R12 (6): White solid. Yield: 0.12 g (76%). IR (KBr): ν =
˜
2924–2853 (stretching aliphatic CH), 1732 (stretching C=O), 1606
(stretching C=N), 1535, 1254 cm–1. 1H NMR (300 MHz, CDCl3,
25 °C): δ = 8.17 (s, 2 H, CH=N), 8.11 (d, J = 8.54 Hz, 4 H, H2Ј,6Ј),
7.14 (t, J = 8.54 Hz, 2 H, H6), 6.95 (d, J = 8.54 Hz, 4 H, H3Ј,5Ј),
6.65 (d, J = 2.44 Hz, 2 H, H3), 6.50 (dd, J = 2.44 Hz, J = 8.54 Hz,
2 H, H5), 4.03 (t, J = 6.10 Hz, 4 H, OCH2), 3.79, 3.31 (m, 4 H,
C=N-CH2), 1.85–0.83 (m, 66 H, aliphatic protons) ppm. UV/Vis
(CH2Cl2): λabs. = 355, 275 nm; λem. = 432 nm. C64H90N2O8Zn
(1080.80): calcd. C 71.12, H 8.39, N 2.59; found C 71.28, H 8.45,
N 2.28. Thermal behaviour is reported in Table 2.
Acknowledgments
Financial support received from the Ministero dellЈIstruzione,
dellЈUniversità e della Ricerca Scientifica (MIUR) through the
Centro di Eccellenza CEMIF.CAL (CLAB01TYEF) and the PRIN
projects 2006038447 and 2007WJMF2W is gratefully acknowl-
edged.
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Received: June 15, 2009
Published Online: August 31, 2009
Eur. J. Inorg. Chem. 2009, 4274–4281
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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