Europium(III) and terbium(III) luminescent lanthanidomesogens

Article abstract of DOI:10.1080/15421406.2011.581149

Liquid-crystalline columnar phenanthroline-based ligand, for the first time substituted in 4,7-positions, is synthesized and used to induce low temperature mesomorphism in his corresponding lanthanide complexes. Stable liquid crystalline Eu(III) and Tb(II

Full text of DOI:10.1080/15421406.2011.581149

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Europium(III) and Terbium(III)
Luminescent Lanthanidomesogens
Elisabeta I. Szerb a , Alessandra Crispini b , Massimo La Deda b
Daniela Pucci a , Paola F. Liguori a & Claudio Pettinari c
,
a (Elisabeta I. Szerb, Alessandra Crispini, Daniela Pucci, Massimo La
Deda) Centro di Eccellenza CEMIF.CAL-LASCAMM , CR-INSTM Unità
della Calabria, Dipartimento di Chimica, Università della Calabria ,
Via P. Bucci Cubo 14C Italy
b (Alessandra Crispini, Massimo La Deda) Centro di Eccellenza
CEMIF.CAL-LASCAMM, CR-INSTM Unità della Calabria , Dipartimento
di Chimica, Dipartimento di Scienze Farmaceutiche, Università della
Calabria , Edificio Polifunzionale, Italy
c (Claudio Pettinari) Dipartimento di Scienze Chimiche , Università
degli Studi , via S. Agostino, 1, 62032 Camerino (MC), Italy
Published online: 07 Oct 2011.
To cite this article: Elisabeta I. Szerb , Alessandra Crispini , Massimo La Deda , Daniela Pucci , Paola
F. Liguori & Claudio Pettinari (2011) Europium(III) and Terbium(III) Luminescent Lanthanidomesogens,
Molecular Crystals and Liquid Crystals, 549:1, 86-99, DOI: 10.1080/15421406.2011.581149
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Mol. Cryst. Liq. Cryst., Vol. 549: pp. 86–99, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2011.581149
Europium(III) and Terbium(III) Luminescent
Lanthanidomesogens
ELISABETA I. SZERB,1,∗ ALESSANDRA CRISPINI,2
MASSIMO LA DEDA,2 DANIELA PUCCI,1
PAOLA F. LIGUORI,1 AND CLAUDIO PETTINARI3
1(Elisabeta I. Szerb, Alessandra Crispini, Daniela Pucci, Massimo La Deda)
Centro di Eccellenza CEMIF.CAL-LASCAMM, CR-INSTM Unita` della
Calabria, Dipartimento di Chimica, Universita` della Calabria, Via P. Bucci Cubo
14C Italy
2(Alessandra Crispini, Massimo La Deda) Centro di Eccellenza
CEMIF.CAL-LASCAMM, CR-INSTM Unita` della Calabria, Dipartimento di
Chimica, Dipartimento di Scienze Farmaceutiche, Universita` della Calabria,
Edificio Polifunzionale, Italy
3(Claudio Pettinari) Dipartimento di Scienze Chimiche, Universita` degli Studi,
via S. Agostino, 1, 62032 Camerino (MC), Italy
Liquid-crystalline columnar phenanthroline-based ligand, for the first time substituted
in 4,7-positions, is synthesized and used to induce low temperature mesomorphism in
his corresponding lanthanide complexes. Stable liquid crystalline Eu(III) and Tb(III)
complexes with low transition temperatures and low viscosity mesophases are obtained
and their thermal and photophysical properties investigated as a function of their
different solid, soft and liquid crystalline organisations. The eight-coordination around
the metal lanthanide centre is further fulfilled by six oxygen atoms of three bidentate
1-phenyl-3-methyl-4-benzoylpyrazol-5-one proligands.
Keywords Coordination chemistry; lanthanidomesogens; phenanthroline mesogenic
ligand; acylpyrazolone proligands; luminescence.
Introduction
Currently lanthanide luminescent complexes are essential for a landscape of applications
ranging from telecommunications to life sciences, due to their ability to emit with high
quantum yields and narrow bandwidth lines, spanning the visible and NIR spectral re-
gions [1–9]. Therefore the design of lanthanide compounds with increased thermal and
photophysical stabilities is a living matter, different strategies being used to circumvent
the limited applicability arising from the presence of solvent molecules in the coordination
sphere of these systems.
∗Corresponding author. Fax: +39 0984 492066. E-mail: e.szerb@unical.it
86

Europium(III) and Terbium(III) Luminescent Lanthanidomesogens
87
The best strategy seems to be the synthesis of highly coordinated heteroleptic com-
plexes where the lanthanide ions are coordinated in the same time to a neutral chelating
nitrogen ligand and to three β-diketonate units [10], protecting the metal centre from vi-
brational coupling and thus increasing their light absorption cross section by the “antenna
effect”. In particular 1,10-phenanthrolines have been proposed as the most versatile and ap-
pealing partners for lanthanide centers, whereas Eu(III) and Tb(III) derivatives were found
to be the strongest emitters, red and green respectively [11]. Recently, increasing interest
has been shown in the use of the acylpyrazolones, a class of asymmetrical heterocyclic
ligands analogues of β-diketones, since their presence as ancillary ligands in rare earth
metal complexes is beneficial for both luminescence and stability properties, offering new
possibilities in their application [12].
Furthermore, the possibility of conjugating the unique electronic, magnetic and opti-
cal properties of lanthanide complexes with the advantages of anisotropic soft materials
such as liquid crystals, opens new perspectives in the application of lanthanide complexes
as molecular components for more efficient probes or devices. Thus, a lot of work in
the field of thermotropic lanthanide containing metallomesogens, namely lanthanidome-
sogens, has been performed in the last years, and different mesomorphic organisations
from lamellar to cubic and columnar ones were obtained [13–15]. From the beginning
it was a challenge to obtain lanthanide complexes with low temperature and low viscos-
ity mesophases in order to perform luminescence studies in the liquid crystalline phase
[16], the polarized luminescence from oriented materials being a strategic goal in different
fields [17, 18].
Some recent crucial contributions in this direction have been reported by Binnemanns
[19] on nematogenic complexes based on imidazo 1,10 phenanthroline ligands and thenoyl-
trifluoroacetonate as coligands (A in Chart 1) whose luminescence has been measured in a
solution of liquid crystal host, followed by compounds of 5,5’-substituted 2,2’-bipiridines
and tris-diketonates (B in Chart 1) [20] for which polarized emission has been observed for
aligned samples of the supercooled nematic phase.
As part of our research in exploring the potential of forming luminescent and liq-
uid crystalline complexes of lanthanide complexes with aromatic N-donor and suitable
β-diketonate ligands [21] herein we report the synthesis of a new 1,10-phenanthroline
functionalized in 4,7-positions with groups containing several long peripheral alkyl chains
(phen-16), used to induce liquid-crystalline properties in their Eu(III) and Tb(III) com-
plexes containing as ancillary O,O ligands the 1-phenyl-3-methyl-4-benzoylpyrazol-5-one
(HQ). Furthermore, a similar ligand but lacking of alkyl chains (phen) was synthesized
and used to obtain model Eu(III) and Tb(III) complexes.
Chart 1.

88
E. I. Szerb et al.
Results and Discussion
Synthesis and Characterization
The proligand 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (HQ) was synthesized as previ-
ously reported [22].
The phenanthroline-based ligands (phen) and (phen-16), were prepared through a
three step synthesis as shown in Scheme 1. In particular, precursor II was obtained by a
synthetic methodology reported for similar derivatives [23], starting from the commercially
available 4,7-dimethyl-1,10-phenantroline which was first oxidized to dicarboxaldehyde (I)
with selenium dioxide, and successively reduced with sodium borohydride. In the final step,
the hydroxymethyl compound II reacts with the appropriate benzoic acid by a DCC-PPY
esterification, to give (phen) and (phen-16) ligands, which were separated in satisfactory
yields as white solids [24].
Scheme 1. Synthesis of ligands (phen) and (phen-16): i) SeO2, dioxane, ꢀT, ii) NH4BF4, EtOH,
ꢀT; iii) DCC, Ppy, CH2Cl2, r.t.
The synthesis of the lanthanide model complexes [Ln(Q)3(phen)], 1–2 and the highest
homologues [Ln(Q)3(phen-16)], 3–4 (Ln = Eu(III) and Tb(III)), requires a previous prepa-
ration of tris-pyrazolonate eight-coordinated lanthanide precursors [Ln(Q)3(H2O)(EtOH)]
using a method described for similar complexes (Scheme 2) [25]. In particular, the appro-
priate lanthanide nitrate is reacted with the ligand HQ in presence of KOH to give the
lanthanide precursor [Ln(Q)3(H2O)(EtOH)], that was subsequently reacted with the lig-
and (phen) in refluxing ethanol for 3 hours, to obtain the model complexes [Ln(Q)3(phen)],
1 and respectively 2, in high yields (Experimental Section). Because of the insolubility of
(phen-16) ligand in ethanol, the synthesis of complexes [Ln(Q)3(phen-16)], 3 and 4, was
conducted in toluene, increasing the reaction time to 7–8 days.
The structural characterization and purity of the new derivatives reported herein, re-
spectively the phenanthroline-based ligands (phen) and (phen-16), the lanthanide precur-
sors [Ln(Q)3(H2O)(EtOH)], and the final heteroleptic complexes 1–4, were investigated

Europium(III) and Terbium(III) Luminescent Lanthanidomesogens
89
Scheme 2. Synthesis of complexes 1–4: i) Ln(NO3)3·5H2O, KOH, EtOH, 2h, r.t.; ii) (phen), EtOH,
ꢀT, 3h; iii) (phen-16), Toluene, r.t., 9 days.
by combined elemental analysis, IR and UV spectroscopies. Moreover, the diamagnetic
Eu(III) compounds 1 and 3 were characterized by 1H NMR spectroscopy.
The IR spectra of the heteroleptic complexes 1–4 show the C O bands of both the
N,N (1720–1730 cm−1) and O,O ligands (1645–1630 cm−1), shifted with respect to their
corresponding precursors (Experimental Section).
The absorption spectra of the Eu(III) and Tb(III) complexes in dichloromethane so-
lution are very similar, being the change of the metal irrelevant on the spectral shape,
therefore, as an example, in Figure 1 is reported only the electronic spectra of the Eu(III)
complex 3 and its precursors HQ, (phen-16) and [Eu(Q)3(H2O)(EtOH)]. In particular,
the starting complex [Eu(Q)3(H2O)(EtOH)] shows two bands at 250 and 297 nm, clearly
reminiscent of the two analogues bands of the parent ligand HQ, which are attributed to
π-π∗ transitions on the aromatic rings. In the spectrum of complex [Eu(Q)3(phen-16)],
3, an intense band at 275 nm and a shoulder at about 305 nm are detected; these features,
which are due to transitions localized on the phenanthroline ligand, superimpose the bands
originated from the Q excitations.
The coordination mode of the diamagnetic Eu(III) derivatives in solution was exam-
1
1
ined through proton H NMR measurements. In the H NMR spectrum of the precur-
sor [Eu(Q)3(H2O)(EtOH)] very broad signals are found due to the presence of solvent
molecules (water and/or ethanol) [26]. Therefore the spectral patterns of the Eu(III) com-
plexes 1 and 3 were compared with those of the parent ligands, HQ and (phen) or (phen-16).
The 1H NMR spectra of either 1 or 3 contain signals related to both ligands (Q and (phen),
or Q and (phen-16) respectively), shifted with respect to the uncomplexed ligands, con-
firming once again their successful coordination to the Eu(III) metal centers. Indeed, upon
coordination, the signals of the phenanthroline protons (H2,3,6,8,9) are shifted about 1.0–
2.0 ppm downfield with respect to the uncomplexed ligand. Also the protons related to the
pyrazolonate ligand Q suffer a sizeable shift with respect to the neutral HQ, downfield of
about 0.2–0.7 ppm for Ha, He and Hf-j or upfield of aproximatively 0.7 ppm for Hb-d
.
Furthermore, for all complexes 1–4, the absence of any co-crystallized solvent
molecules in their structures was verified by TGA analysis, whose traces showed no weight
loss until decomposition, which occurs at ca. 300◦C for [Ln(Q)3(phen)] complexes 1 and
2 and at about 200◦C for [Ln(Q)3(phen-16)] complexes 3 and 4.

90
E. I. Szerb et al.
Figure 1. Absorption spectra of ligand HQ (solid line), ligand (phen-16) (dash dot dot) precursor
[Ln(Q)3(H2O)(EtOH)] (dot) and complex 3 -[Eu(Q3)(phen-16)] (short dash dot).
These results and a comparison with related structures previously reported on similar
neutral lanthanide complexes [21], suggest an eight-coordination around the metal centre
fulfilled by six oxygen atoms of the three bidentate Q ligands and two nitrogen atoms of
the bidentate (phen) or (phen-16) ligand respectively, as presented in Scheme 2.
Mesomorphism
The thermal behaviour of the ligand (phen-16), decorated with 6 long peripheral alkyl
chains, as well as that of the corresponding lanthanide complexes 3 and 4 was investigated
by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and
small-angle X-ray diffraction on powder samples (PXRD). An overview of the transition
temperatures and the corresponding detectable enthalpies is given in Table 1.
The substituents on the 4 and 7 positions of the 1,10-phenanthroline skeleton confers
the anisotropy necessary for inducing liquid crystalline properties on the ligand (phen-16)
and on the corresponding complexes [Ln(Q)3(phen-16)], 3 and 4.
The ligand (phen-16) exhibits an enantiotropic liquid crystalline phase from 46◦C to
100◦C, with a non-typical schlieren texture observed by POM (Figure 2a). The identification
of the mesophase, with reference to both its nature and symmetry, was made by PXRD. The
X-ray pattern of the ligand (phen-16) (Figure 2b) consists at small angle in four reflections
√
√
√
in the ratio 1 : 3 : 4 : 9 characteristic of a 2D lattice of a hexagonal columnar phase,
corresponding to the indexation (hk) = (10), (11), (20) and (30), with a cell parameter a =
50.1 Å. The fluid-like nature of the phase is confirmed by the diffuse and broad-scattering

Europium(III) and Terbium(III) Luminescent Lanthanidomesogens
91
Table 1. Optical and thermal data.
Compound
Transition[a]
T/◦C[b]
ꢀH/kJ · mol−1
(phen-16)
C – Colh
Colh – I
I – Colh
Colh – C
Slam – Lam
Lam – I
46.3
100.4
79.7
54.8
45.7
75.0[c]
70.0
26.0
33.5
75.0
70.0
26.2
45.6
80.0[c]
75.0
24.4
31.8
80.0
75.0
24.9
13.7
40.8
42.2
14.3
107.6
—
—
9.5
26.1
—
—
[Eu(Q3)(phen-16)],3
[Tb(Q3)(phen-16)],4
I – Slam
Lam – Slam
Slam – Lam
Lam – I
I – Lam
Lam – Slam
Slam – Lam
Lam – I
9.8
89.0
—
I – Lam
—
Lam – Slam
Slam – Lam
Lam – I
I – Lam
Lam – Slam
16.8
16.1
—
—
26.9
[a] C: crystal; Colh: columnar hexagonal mesophase, Slam: ‘soft’ lamellar crystal phase; Lam:
lamellar liquid crystalline phase I: isotropic liquid.
[b] Temperature data as onset peaks obtained on second heating and cooling cycle;
[c] POM observations.
Figure 2. a) POM micrograph of the texture developed by ligand (phen-16) on cooling at 70◦C; b)
PXRD pattern of Colh phase of ligand (phen-16) on cooling at 70◦C.

92
E. I. Szerb et al.
Figure 3. Shape of the a) bipyridine-based analogues ligand previously reported; b) ligand (phen-16)
and the arrangement for the latter in the columnar slice.
halo h centred at 4.4 Å at wide angles of the X-ray pattern. This columnar mesophase is
well organised by relatively strong π-π interactions, as indicated by the existence in the
wide angle region of the PXRD pattern of a broad reflection centred at 3.6 Å and the high
transition Colh – I enthalpy detected by DSC measurements.
The analogues 2,2’-bipyridine-based ligand previously reported [24], bearing the same
tri-hexadecyloxy-benzoyloxymethyl groups in 4,4’-position, is a solid crystalline that melts
directly into isotropic liquid at 90◦C, and has excellent promesogenic properties for a series
of bulky metal centres like Zinc(II) [24], Ruthenium(II) [27] or Iridium(III) [28]. Despite
of the rod-like shape of the uncomplexed bipyridines that have the nitrogen atoms in cis-
configuration (therefore a transoid molecular shape) (Figure 3a), more compatible with
liquid crystalline formation than the shape of the polycatenar phenanthroline (phen-16),
the planarity and rigidity of the aromatic system of the latter assures the proper interactions
that favours the π-π stacking of the aromatic cores forming discs that furthermore assemble
into columns. Indeed, when compared with 2,2’-bipyridines, the 1,10-phenantrolines have
increased rigidity, extended planar aromatic cores and the two nitrogen atoms held in
juxtaposition [29].
The number of the molecules forming a columnar stratum given by h, may be esti-
mated taking into account the relationship between the columnar cross-section Scol and the
molecular volume Vmol calculated at 70◦C, method commonly used in LCs. [30] From this
analysis we obtain that 3 molecules of ligand (phen-16) form the columnar cross-section
with a mean stacking distance of 4.4 Å (Figure 3b).
Both complexes have similar thermal behaviour, the type and size of the lanthanide
ions having no noticeable effect on the transition temperatures, or the organizations in the
different soft or liquid-crystalline phases. At room temperature both complexes are waxy
soft solids, whose lamellar nature was evidenced by PXRD analysis. Indeed, the powder
patterns of the pristine solids recorded at room temperature consist at small angle in three
reflections with reciprocal spacings in the ratio 1 : 2 : 3 indexed as (001), (002) and (003)
with d001 of 36.4 Å for complex [Eu(Q)3(phen-16)], 3 (Figure 4b—bottom) and 36.3 Å
respectively for complex [Tb(Q)3(phen-16)], 4 having a certain degree of intralayer order
as revealed in the wide angle of the spectra by the relatively intense and broad reflection
centred for both complexes at 4.1 Å. This reflection superimposed to the diffuse halo
corresponding to the molten chains order, centred at 4.3 Å, whose intensity is low, indicates
that these phases can be classified as ‘soft’ crystalline phases (Slam in Table 1).

Europium(III) and Terbium(III) Luminescent Lanthanidomesogens
93
Figure 4. a) POM micrograph of the texture developed by complex [Eu(Q3)( phen-16)], 3 after
mechanical stress at 60◦C; b) PXRD pattern of Slam phase of complex [Eu(Q3)( phen-16)], 3 at room
temperature (bottom) and Lam mesophase at 60◦C on first heating (top).
The transition to the true liquid crystalline phase (Lam) at 45◦C, is accompanied by
high transition enthalpies, for both complexes (Table 1). This mesophase has no recog-
nizable textures. On heating, the samples orient nearly perpendicular to the glass surface
giving rise to homeotropic textures whose order is disrupted by mechanical stress. A cer-
tain birefringence can be induced by pressing on the glass cover slips of the microscope
preparations, as showed in Figure 4a. The textures obtained on POM are mantained until
room temperature.
The PXRD analysis reveals that the wide-angle pattern contains only the wide halo
corresponding to the molten alkyl chains with the total loss of the intralayer correlation.
In the small angle, a variation of d001 to 33.5 Å for complex 3 (Figure 4b—top) and 35.5
Å respectively for complex 4 is observed, accompanied by a broadening of the reflections,
whereas the second and third harmonics are hided under a broad halo. Nevertheless, the
existence of these broad halos implies that the molecules are organised into lamellar liquid
crystalline phases, with no intralayer order.
Complexes 3 and 4 melt into the isotropic liquid at 75◦C and 80◦C respectively. The
values for the enthalpy and the corresponding entropy changes of the lamellar mesophase
– isotropic state transitions are very small and these transitions are not detected by DSC,
confirming once again the low order of the lamellar mesophase.
Photophysical Behaviour
All the complexes 1–4 show appreciable luminescence at room temperature in their pristine
solid and soft states (Figure 5 and 6). As well known, the emission spectra of lanthanide
complexes can be assigned simply on the basis of the spectroscopic terms of the free Tb(III)
or Eu(III) ions, due to the lack of significant crystal field effects in their complexes, and thus
the shape and peak position are characteristic of the ion, regardless of the ligands. However,

94
E. I. Szerb et al.
Figure 5. Emission spectra of pristine solid of a) complex [Eu(Q3)( phen-16)],3 and b) complex
[Tb(Q3)( phen-16)], 4.
a direct excitation of the lanthanide ions is very difficult, due to the low intensities and
narrowness of their f-f absorption bands; a viable excitation mechanism is provided by the
indirect excitation of the lanthanide ions through energy transfer from an excited state of
a ligand, which act as an antenna system, to the emissive central ion. Thus, the spectra of
both Eu(III) complexes (1 and 3) are superimposable and display characteristic sharp peaks
Figure 6. Emission spectra of complex [Eu(Q3)( phen-16)],3 on first cooling at variable tempera-
tures.

Europium(III) and Terbium(III) Luminescent Lanthanidomesogens
95
5
7
in the 593–700 nm region associated with the D0 → FJ (J = 0 ÷ 4) transitions of the
Eu3+ ion [30]. Interestingly, at 537 nm is detected a low-intensity band due to the electric
7
dipole 5D1 → F1 transition sensitive to the coordination environment (Figure 5a). Also the
emission spectra of Terbium(III) complexes 2 and 4 are superimposable with each other
in their initial pristine condensed states, and show a series of a well defined peaks in the
5
7
492–622 nm range, attributed to the D4 → FJ (J = 6 ÷ 3) transitions of the lanthanide
ion (Figure 5b).
Moreover, both mesomorphic complexes [Eu(Q)3(phen-16)], 3 and [Tb(Q)3(phen-
16)], 4 show luminescence in their mesomorphic state and their photophysical behaviour
were investigated at different temperatures. The pristine samples were heated until the
isotropic transition, then cooled slowly to room temperature and their emission spectra col-
lected during the cooling phase, at different temperatures. For both complexes, the emission
intensity increases by decreasing temperature, and, at 30◦C, the spectral features are well
defined; this behaviour is probably due to the competitive non-radiative deactivations, which
are favoured by increased temperature. For Terbium(III) complex [Tb(Q)3(phen-16)], 4,
the spectra features remain essentially unchanged with respect to the pristine sample. For
7
the Eu(III) complex [Eu(Q)3(phen-16)], 3, two changes may be observed: the 5D1 → F1
transition, positioned at 537 in the solid sample spectrum (Figure 5), is red-shifted at 577
nm in the mesophase spectrum (Figure 6), and this behaviour is attributed to the band
sensitivity on passing from the solid to the mesophase. Furthermore, the liquid-crystalline
spectrum of complex [Eu(Q)3(phen-16)],3 shows a peak at 691 nm; this features is as-
7
signed to a satellite of the 5D1 → F4 transition (which, in turn, is centred at 700 nm), due
to an electron/phonon coupling that occurs because, with respect to the pristine sample, in
the mesophase the ions or ligands are not fixed in the crystal lattice but oscillate around
an equilibrium position. This interaction between the phonon density of states and the
electronic sublevels splits the electronic sublevels by a few cm−1 [31].
Conclusions
The new phenantroline-based ligand (phen-16), for the first time functionalised in 4,7-
position with promesogenic groups, has intrinsic liquid crystalline properties. The pla-
narity and rigidity of the aromatic system of the phenantroline ligand (phen-16), when
compared with analogues bipyridine-based ligands, assures the proper interactions that
favours the π-π stacking of the aromatic cores into columnar mesomorphic structures, with
3 phenanthroline molecules forming a columnar slice.
Furthermore, (phen-16) resulted to be a versatile ligand for the synthesis of low tem-
perature mesomorphic lanthanide complexes. The high capacity of metal binding of the
phenanthroline ligands (phen) and (phen-16), yielded stable Eu(III) and Terbium(III) eight
coordinated complexes (1–4). The coordination around the metal centre is furthermore
fulfilled by three O,O-proligands, yielding stable neutral lanthanide derivatives. The pho-
tophysical properties of the complexes were investigated in their different mesomorphic
states at variable temperatures. All complexes show appreciable luminescence in their con-
densed states, having the characteristic spectral features of the corresponding lanthanide
metal centre.
Experimental
Materials and methods: All commercially available starting materials were used as re-
ceived without further purification. The proligand HQ and the corresponding lanthanide

96
E. I. Szerb et al.
precursors [Ln(Q)3(H2O)(EtOH)] derivatives were synthesized according to the procedure
previously described [25].
1
The H NMR spectra were recorded on a Bruker Avance AC-300 spectrometer in
[D6]DMSO, CDCl3 orCD3ODsolution, usingtetramethylsilane(TMS)asinternalstandard.
Elemental analyses (CHN) were performed with a Perkin Elmer 2400 microanalyzer by
the Microanalytical Laboratory at the University of Calabria. Infrared spectra (KBr) in the
range 4000–400 cm−1 were recorded on a Spectrum One FT-IR Perkin Elmer spectrometer.
Mesomorphism: The textures of the mesophases were examined with a Leica DMLP
polarising microscope equipped with a Leica DFC280 camera and a CalCTec (Italy) heating
stage. The thermal stability was measured on a Perkin-Elmer Thermogravimetric Analyser
Pyris 6 TGA, respectively the transition temperatures and enthalpies were measured on a
Perkin-Elmer Pyris1 Differential Scanning Calorimeter with a heating and cooling rate of
10 ◦C/min. The apparatus was calibrated with indium. Three heating/cooling cycles were
performed on each sample. The powder X-Ray diffraction patterns were obtained using
a Bruker AXS General Area Detector Diffraction System (D8 Discover with GADDS)
with Cu-Kα radiation (λ = 1.54056 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) heating
◦
stage was used to heat the samples at a rate of 5 C/min to the appropriate temperature.
Measurements were performed by placing the samples in Lindemann capillary tubes with
an inner diameter of 0.5 mm.
Photophysical Measurements. Spectrofluorimetric grade solvents were used for the
photophysical investigations in solution, at room temperature. A Perkin Elmer Lambda
900 spectrophotometer was employed to obtain the solution absorption spectra. The ex-
amined compounds are fairly stable in solution, as demonstrated by the constancy of their
absorption spectra over a week. Steady-state emission spectra were recorded on a HORIBA
Jobin-Yvon Fluorolog-3 FL3–211 spectrometer equipped with a 450 W xenon arc lamp,
double-grating excitation and single-grating emission monochromators (2.1 nm/mm dis-
persion; 1200 grooves/mm), 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. Powder samples
have been prepared by placing the powder between two quartz plates, in such a position
that the luminescence has been measured in reflection mode, in front-face arrangement to
reduce the scattered light. The emission quantum yields of the solid samples were obtained
by means of a 102 mm diameter integrating sphere coated with SpectralonꢀR and mounted
in the optical path of the spectrofluorimeter. The experimental uncertainty on the emission
quantum yields is 5%.
To reach the mesophase, the two quartz plates were heated in the sample compartment
of the spectrofluorimeter by means a customized hot stage realized by CaLCTec s.r.l.
(Rende, Italy).
Synthesis
4,7-dicarboxaldehyde-1,10-phenanthroline (I): To solution of selenium dioxide (2.92 g,
26.52 mmol) in dioxan containing 4% water (40 ml), was added dropwise a solution of
4,7-dimethyl-1,10-phenanthroline (2 g, 8.84 mmol) in dioxan (140 ml). The mixture was
heated under reflux for 5 h, and then filtered through celite while still hot. The filtrate
was evaporated to dryness and the residue was recrystallized from chloroform/hexane to
give the aldehyde I (1,253 g, 60%) as a yellow powder. M.p. > 300◦C; Anal. Calcd. for
C14H8N2O2 (236.23 gmol−1): C, 71.10; H, 3.40; N, 11.80; Found: C, 71.60; H, 3.50; N,

Europium(III) and Terbium(III) Luminescent Lanthanidomesogens
97
11.90); νmax/cm−1: 1700–1684 (C O), 1385 (CHO); δH (300 MHz, DMSO-d6) 10.71 (2H,
s, CHO), 9.48 (2H, d, J(H,H) = 4.78 Hz, H2,9), 9.14 (2H, s, H5,6), 8.30 (2H, d, J(H,H) = 4.43
Hz, H5,8).
4,7-Bis(hydroxymethyl)-1,10-phenanthroline (II): A solution of I (2.00 g,
8.47 mmol) and NaBH4 (4.80 g, 126.9 mmol) in ethanol (200 ml) was heated under reflux
for 5 h. The mixture was then concentrated and diethyl ether was added to the solution.
The precipitate formed was filtrated out and dried to give the pure hydroxymethyl com-
pound II as a yellow powder (1,322 g, 65%). M.p. > 300◦C. Anal. Calc. for C14H12N2O2
(240.2 gmol−1): C, 70.00; H, 5.03; N, 11.66; Found: C, 70.10; H, 5.20; N, 12.10;
νmax(KBr)/cm−1: 3290–3234 (OH), 2898–2878 (C H), 1618–1423 (C = C); δH (300 MHz,
DMSO-d6) 9.07 (2H, d, J(H,H) = 4.43 Hz, H2,9), 8.10 (2H, s, H5,6), 7.82 (2H, d, J(H,H)
=
4.43 Hz, H3,8), 5.72 (2H, s, OH), 5.13 (4H, s, CH2OH).
4,7-Bis(benzoyloxymethyl)-1,10-phemanthroline (phen): 4,7-Bis(hydroxymethyl)-
1,10-phenanthroline (II) (0.150 g, 0.62 mmol), benzoic acid (0.167 g, 1.36 mmol) and 4-
pyrrolidinopyridine (PPY) (0.203 g, 1.36 mmol) were suspended in dry dichloromethane
(20 mL). The reaction mixture was cooled down to 0◦C and N,N-dicyclohexylcarbodiimide
DCC (0.228 g, 1.36 mmol) dissolved in 5 mL dichloromethane was added slowly. The re-
action was left under stirring at room temperature for 72 h. The colorless precipitate
formed was separated by filtration, and recrystallized from chloroform/methanol to give
ligand (phen) (0.551g, 74%) as a colorless solid. Anal. Calc. For C28H20N2O4
(448.14 gmol−1): C, 74.99; H, 4.50; N, 6.20; Found: C, 74.86; H, 4.35; N, 6.30);
νmax(KBr)/cm−1: 2946 (C H), 1729 (C O); δH (300 MHz, CDCl3): 9.25 (2H, d, J(H,H)
4.77 Hz, H2,9), 8.13 (6H, t, J(H,H) = 7.52 Hz, H5,6 and Hα,α’), 7.81 (2H, d, J(H,H) = 4,40 Hz,
H3,8), 7.60 (2H, t, J(H,H) = 7.53 Hz, Hγ ,γ ’),7.47 (4H, t, J(H,H) = 7.52 Hz, Hβ,β’), 5.93 (4H,
s, CH2).
=
4,7-Bis[3,4,5-(trihexadecyloxy)benzoyloxymethyl]-1,10-phenanthroline (phen-
16): 4,7-Bis(hydroxymethyl)-1,10-phenanthroline (II) (0.129 g, 0.54 mmol), 3,4,5-
trihexadecyloxy benzoic acid (1.0 g, 1.186 mmol) and 4- pyrrolidinopyridine (PPY)
(0.176 g, 1.186 mmol) were suspended in dry dichloromethane (20 mL) under N2 atmo-
sphere. The reaction mixture was cooled down to 0◦C and N,N-dicyclohexylcarbodiimide
DCC (0.245 g, 1.186 mmol) dissolved in 5 mL dichloromethane was added slowly. The
reaction was left under stirring at room temperature for 72 h. The solution was filtrated
through Celite, concentrate and precipitate with methanol, to give the ligand (phen-16)
as a colorless solid (0,611 g, 60%). Thermal behaviour in Table 1. Anal. Calc. For
C124H212N2O10 (1891.17 g mol−1): C, 78.75; H, 11.30; N, 1.50; Found: C, 78.90; H, 11.50;
N, 1.60; νmax(KBr)/cm−1: 2919–2851 (C H), 1720 (C O); δH (300 MHz, CDCl3): 9.24
(2H, d, J(H,H) = 4.38 Hz, H2,9), 8.12 (2H, s, H5,6), 7.76 (2H, d, J(H,H) = 4.38 Hz, H3,8),
7.33 (4H, s, Hα,α’), 5.92 (4H, s, CH2), 4.02 (12H, m, OCH2(CH2)14CH3), 1.77 (12H, m,
CH2(CH2)13CH3), 1.36 (156H, m, (CH2)13CH3), 0.87 (18H, t, J(H,H) = 6.58, CH3).
General synthesis of lanthanide precursors, [Ln(Q)3(H2O)(EtOH)]: To a colorless
solution of proligand HQ (1.76 mmol) in 15 mL of ethanol was added a solution of the
appropriate lanthanide salt Ln(NO3)3 · 5H2O (0.59 mmol) in 5 mL ethanol and KOH
(1.76 mmol). The resulting mixture was stirred at room temperature for 2 hours. The
yellow precipitate formed was filtered out and washed with water. The pure products were
obtained after recrystallisation from chloroform/petroleum ether as yellowish solids.
[Eu(Q)3(H2O)(EtOH)]: Yield: 70%. M. p. 228◦C. Anal. Calc. For EuC53H47N6O8
(1048.27) g mol−1): C, 60.74; H, 4.52; N, 8.02; Found: C, 60.30; H, 4.32; N, 8.10.
νmax(KBr)/cm−1: 3200–2800 (O-H), 2948–2865 (C H), 1623 (C O).

98
E. I. Szerb et al.
[Tb(Q)3(H2O)(EtOH)]: Yield: 68%. M. p. 240◦C. Anal. Calc. For TbC53H47N6O8
(1054.91 g mol−1): C, 60.34; H, 4.49; N, 7.97; Found: C, 60.53; H, 4.23; N, 7.71;
νmax(KBr)/cm−1: 3200–2800 (O-H), 2948–2865 (C H), 1624 (C O).
Synthesis of Lanthanide Complexes 1–4:
Complex 1, [Eu(Q)3(phen)]: A solution of the ligand (phen) (0.064 g, 0.143 mmol) in
hot EtOH (20 ml) was added to a stirred solution containing a stoichiometric quantity
of [Eu(Q)3(H2O)(EtOH)] (0.150 g, 0.143 mmol) in EtOH (10 ml). A yellow precipi-
tate is formed. The reaction mixture was heated under reflux for 3 h and then cooled to
room temperature. The yellow precipitate was separated by filtration, washed with hot
◦
ethanol and dried under vacuum. Yield 0.174 g (85%). M.p. 226 C; Anal. Calc. For
EuC79H59N8O10 (1432.34 g mol−1): C, 66.25; H, 4.15; N, 7.82; Found: C, 66.10; H, 4.30;
N, 7.56); νmax(KBr)/cm−1: 1724 (C O (phen)), 1633 (C O Q); δH (300 MHz, CDCl3):
11.1 (2H, s, H2,9); 9.21 (2H, s, H5,6); 8.52 (8H, t, J(H,H) = 7.7 Hz, Ha,e and H3,8); 8.19 (4H,
s, Hα,α’); 7.76 (21H, m, Hf,g,h,i,j, and Hβ,β’, γ ,γ ’); 6.71 (9H, s, Hb,c,d); 4.74 (4H, S, CH2); 0.44
(9H, S, CH3 QPh); λmax(CH2Cl2)/nm 254 (ε/mol−1 dm3 cm−1 74467.89); 275 (103018.5);
298.80 (60377.73).
Complex 2, [Tb(Q)3(phen)]: A solution of the ligand (phen) (0.064 g, 0.143 mmol)
in hot EtOH (20 ml) was added to a stirred solution containing a stoichiometric quantity
of [Tb(Q)3(H2O)(EtOH)] (0.150 g, 0.143 mmol) in EtOH (10 ml). A yellow precipi-
tate is formed. The reaction mixture was heated under reflux for 3 h and then cooled to
room temperature. The yellow precipitate was separated by filtration, washed with hot
◦
ethanol and dried under vacuum. Yield 0.163 g (80%). M.p. 260 C; Anal. Calc. For
TbC79H59N8O10 (1439.30 g mol−1): C, 65.93; H, 4.13; N, 7.79; Found: C, 65.78; H, 4.03;
N, 7.81; νmax(KBr)/cm−1: 1724 (C O (phen)), 1634 (C O Q).
Complex 3, [Eu(Q)3(phen-16)]: A solution of the ligand (phen-16) (0.100 g,
0.053 mmol) in toluene (10 ml) was added to a solution containing a stoichiometric quan-
tity of [Eu(Q)3(H2O)(EtOH)] (0.055 g, 0.053 mmol) in Toluene (5 ml). The solution was
stirred at room temperature for 9 days. The solvent was then removed by evaporation, and
the residue was dissolved in hexane and filtered through celite. Complex 3 was obtained
after recrystallization from chloroform/acetone as yellow solid. Yield 0.100 g (66%). Ther-
mal behaviour in Table 1. Anal. Calc. For EuC175H251O16N8 (2874.91 g mol−1): C,73.11;
H, 8.80; N, 3.90; Found: C, 73.30; H, 9.05; N, 3.68; νmax(KBr)/cm−1: 1724 (C O L16),
1632 (C O Q); δH (300 MHz, CDCl3): 11.3 (2H, s, H2,9); 9.32 (2H, s, H5,6); 8.38 (2H, s,
H3,8); 8.16 (6H, s, Ha,e); 7.79 (19H, m, Hf,g,h,i,j, and Hα,α’); 6.69 (9H, s, Hb,c,d); 4.79 (4H, S,
CH2); 4.08 (12H, m, OCH2(CH2)14CH3); 1.82 (12H, s, CH2(CH2)13CH3), 1.37 (156H, m,
(CH2)13CH3); 0.86 (18H, s, CH3 (phen-16)); 0.43 (9H,s, CH3 Q).
Complex 4, [Tb(Q)3(phen-16)]: A solution of the ligand (phen-16) (0.100 g, 0.053
mmol) in toluene (10 ml) was added to a solution containing a stoichiometric quantity of
[Tb(Q)3(H2O)(EtOH)] (0.056 g, 0.053 mmol) in Toluene (5 ml). The solution was stirred
at room temperature for 10 days. The solvent was then evaporated, the residue dissolved
in hexane and filtered through Celite. After recrystallization from chloroform/acetone,
complex 4 was obtained as a yellow solid. Yield 0.090 g (59%);. Thermal behaviour in
Table 1. Anal. Calc. For TbC175H251O16N8 (2881.88 g mol−1): C, 72.93; H, 8.78; N,
3.89; Found: C, 73.10; H, 9.00; N, 3.52; νmax(KBr)/cm−1: 1725 (C O (phen-16)), 1634
(C O Q).

Europium(III) and Terbium(III) Luminescent Lanthanidomesogens
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