Structure impact in antenna effect of novel upper rim substituted tetra-1,3-diketone calix[4]arenes on Tb(III) green and Yb(III) NIR-luminescence

Article abstract of DOI:10.1016/j.tet.2016.03.068

Two novel calix[4]arene macrocyclic ligands functionalized with four 1,3-diketone groups at the upper and hydroxyl (3) or propyloxy-groups (6) at the lower rims were synthesized and characterized using NMR, IR spectroscopy, mass spectrometry, and elemental analysis. UV-vis spectrophotometry and ESI mass spectrometry studies indicate 1:1 complex formation of ligands 3 and 6 with Ln(III) (Ln=Tb, Yb) in alkaline DMF solutions resulted from coordination of Ln(III) with 1,3-diketonate groups. Luminescence study of Ln(III) complexes with 3 and 6 reveals significant difference in antenna effects of their deprotonated forms on both Tb(III)- and Yb(III)-centered luminescence. Comparison of ligand-centered emission for ligands 3 and 6 points to the latter as more efficient antenna for Tb(III) and Yb(III). Different conformational behavior of ligands 3 and 6 in alkaline media is assumed as a reason for the experimentally observed difference in sensitization pathways in Ln(III) complexes with 3 and 6.

Full text of DOI:10.1016/j.tet.2016.03.068

Accepted Manuscript
Structure impact in antenna effect of novel upper rim substituted tetra-1,3-diketone
calix[4]arenes on Tb(III) green and Yb(III) NIR-luminescence
Rustem Zairov, Nataliya Shamsutdinova, Sergey Podyachev, Svetlana Sudakova,
Gulnaz Gimazetdinova, Ildar Rizvanov, Victor Syakaev, Vasily Babaev, Rustem
Amirov, Asiya Mustafina
PII:
S0040-4020(16)30199-5
10.1016/j.tet.2016.03.068
TET 27608
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 7 January 2016
Revised Date: 8 March 2016
Accepted Date: 21 March 2016
Please cite this article as: Zairov R, Shamsutdinova N, Podyachev S, Sudakova S, Gimazetdinova G,
Rizvanov I, Syakaev V, Babaev V, Amirov R, Mustafina A, Structure impact in antenna effect of novel
upper rim substituted tetra-1,3-diketone calix[4]arenes on Tb(III) green and Yb(III) NIR-luminescence,
Tetrahedron (2016), doi: 10.1016/j.tet.2016.03.068.
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ACCEPTED MANUSCRIPT

1
ACCEPTED MANUSCRIPT
Structure impact in antenna effect of novel upper rim substituted tetra-1,3-diketone
calix[4]arenes on Tb(III) green and Yb(III) NIR-luminescence
a,b*
a,b
a
a
Rustem Zairov , Nataliya Shamsutdinova , Sergey Podyachev , Svetlana Sudakova ,
c
a
a
a,c
b
Gulnaz Gimazetdinova , Ildar Rizvanov , Victor Syakaev , Vasily Babaev , Rustem Amirov ,
a,b
Asiya Mustafina
a
A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center of Russian
Academy of Sciences, Arbuzov str., 8, 420088, Kazan, Russia.
b
Kazan (Volga region) Federal university, Kremlyovskaya str., 18, 420008, Kazan, Russia.
c
Kazan National Research Technological University, K. Marks str., 68, 420015, Kazan, Russia.
Abstract
Two novel calix[4]arene macrocyclic ligands functionalized with four 1,3-diketone groups
at the upper and hydroxyl (3) or propyloxy-groups (6) at the lower rims were synthesized and
characterized using NMR, IR spectroscopy, mass spectrometry and elemental analysis. UV-Vis
spectrophotometry and ESI mass spectrometry studies indicate 1:1 complex formation of ligands
3
and 6 with Ln(III) (Ln=Tb, Yb) in alkaline DMF solutions resulted from coordination of
Ln(III) with 1,3-diketonate groups. Luminescence study of Ln(III) complexes with 3 and 6
reveals significant difference in antenna effects of their deprotonated forms on both Tb(III)- and
Yb(III)-centered luminescence. Comparison of ligand-centered emission for ligands 3 and 6
points to the latter as more efficient antenna for Tb(III) and Yb(III). Different conformational
behavior of ligands 3 and 6 in alkaline media is assumed as a reason for the experimentally
observed difference in sensitization pathways in Ln(III) complexes with 3 and 6.
Keywords: calix[4]arene, 1,3-diketone, luminescence, NIR-emission, ytterbium(III),
terbium(III), complexation.
*
Author for correspondence. Tel.: +7 843 2739365; fax: +7 843 2731872.
E-mail address: rustem02@yandex.ru (R. Zairov).

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Introduction
Luminescent Ln(III) complexes attract great research attention due to their wide
1
2-4
application as fiber amplifiers operating at telecommunication wavelength, OLEDs as well as
5
UV light converters transforming high energy UV irradiation to visible or NIR-emission,
6
7
immune-fluorescent analysis and therapy, and information security. Usually, the small
absorption of Ln(III) ions due to Laport forbiddance of 4f-4f transitions results in poor emission
from the excited 4f levels under direct excitation unless powerful lasers are used. One of the
most popular ways to overcome this limitation is complexation of Ln(III) ions with organic
8
ligands that sensitize emission of the metal ion by the well-known antenna effect. However,
NIR emitting lanthanide complexes with organic ligands often show low emission efficiencies
compared to inorganic and cluster systems. Radiationless decay through high-frequency
oscillators (O–H, N–H and C–H) resulting from organic ligands or the solvent molecules is the
9
reason for quenching NIR luminescence.
Many recent efforts have been made to synthesize the appropriate antenna-ligands for the
Er(III) and Yb(III) NIR-luminescence according to the general requirements of the organic
antenna – an energetically well-matched triplet state of the ligand or d-block chromophore to the
first Ln(III) excited state, a rigid structure, and the number of O–H, N–H, C–H oscillators
1
0
minimized via chelating or fluorination processes (for C-H bonds).
1,3-Diketones have been reported as very promising antenna-ligands for Ln(III)-centered
11,12
emission,
where the rigidity of the complex structure is a reason for lesser radiationless
1
3-16
decay.
was found to be 11 times more intense than the luminescence of mononuclear analogues.
For example, the luminescence of the Ln(III) bis(1,3-diketone) dinuclear complex
1
3
Anchoring 1,3-diketone fragments to a cyclic calix[4]resorcinarene backbone was recently
documented as a route for efficiently sensitizing Tb(III)-centered luminescence due to the
rigidity of the complex structures or/and additional antenna effect provided by the cyclophane-
1
7
based platform. The impact of the thiacalix[4]arene backbone in the antenna effect of its
1
8,19
derivatives is exemplified in the literature.
From this point of view, 1,3-diketone groups anchored to the cyclophane platform is a
prospective direction for the design of novel ligands for luminescent lanthanide(III) complex
synthesis. However, there are only few papers devoted to synthesis of cyclophane-based 1,3-
diketones. The recent report by Senthilvelan et al. introduces the synthesis of lower and upper
rim substituted calix[4]arene derivatives with one 1,3-diketone group from an isoxazoline
2
0
precursor in the presence of Mo(CO) as a catalyst. Low reaction yield, necessity for proper
6
catalyst selection and disproportionation of the initial compounds can be noted as the main
drawbacks of this synthetic route, restricting its application for the synthesis of poly-1,3-

3
ACCEPTED MANUSCRIPT
diketones. A penta-substituted calix[5]arene with five 1,3-diketone groups attached to methylene
carbon atoms is another example of a poly-1,3-diketone ligand. This ligand was obtained by
heating pentabromine-substituted calix[5]arene with an excess of acetylacetone or
2
1
22
dibenzoylacetone. The corresponding calix[6]arene ligand was synthesized in a similar way.
It is worth noting that this synthesis requires the use of the ionizing solvent 2,2,2-
trifluoroethanol, and results in a low yield (10-23%). An upper rim substituted calix[4]arene with
four 1,3-diketone groups was obtained through the reaction of 2,2,2-trimethoxy-4,5-dimethyl-
5
1
,3,2λ -dioxaphosphole with the tetraformylated calix[4]arene, followed by molecular
2
3
rearrangement in methanol in 40% yield. Reaction of chloromethylated calix[4]arene with
acetylacetone in the presence of potassium tert-butylate results the 1,3-distal calix[4]arene with
2
4
1
,3-diketone groups at the upper rim, in a higher yield (74%) than the above mentioned
1
7
synthetic procedures. Our recent article reports the synthesis and luminescent properties of
Tb(III) complexes of calix[4]resorcine cavitand, bearing four (acetylaceton-3-yl)methylene
groups obtained through the corresponding tetrabromomethylated calix[4]resorcine cavitand,
with a good yield (63%).
Herein, we report a synthetic route for novel tetra-substituted calix[4]arenes with 1,3-
diketone groups on the upper rim, and alkylated(6) or nonalkylated(3) on the lower rim of the
macrocycle. Complex formation of 3 and 6 with Tb(III) and Yb(III) in alkaline DMF solution is
also introduced in correlation with Tb(III)- and Yb(III)-centered luminescence of the complexes.
The reasons for the different antenna effect of the ligands are also discussed. In particular, the
impact of the macrocyclic backbone in the sensitizing effect of calix[4]arene tetra-diketone
derivatives is not clear. Thus, comparison of the sensitizing effects of two structural counterparts
3
and 6 exhibiting different conformational flexibility is aimed at highlighting the impact of the
calix[4]arene backbone in antenna effects of the tetra-1,3-diketone derivatives.
Results and discussion
Synthesis and characterization of tetra-1,3-diketone calix[4]arenes 3 and 6.
The synthetic routes for tetra-1,3-diketone calix[4]arenes 3 and 6 are presented in Scheme
1
. This approach has been successfully applied earlier for the preparation of tris-(1,3-
2
5
17
diketonyl)benzenes, and tetra-1,3-acetylacetone derivative of calix[4]resorcinarene cavitand.
According to the procedure, the prepared sodium salt of acetylacetone (NaAA) was added to
corresponding tetrakis(halogenomethyl) derivative 2 or 5 in 1,4-dioxane and the reaction mixture
was heated with stirring for several hours. The obtained new tetra-1,3-diketone derivatives 3 and
1
13
6
were characterized by H NMR, С NMR, IR spectroscopy and MALDI-MS techniques.

4
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It is worth noting that the nucleophilic substitution of calix[4]arene 2 proceeds even at
17,25
room temperature, and completes in a rather short time in contrast to compound 5.
The
chlorine analogue of 2 is known to be a highly reactive compound, especially under basic
26,27
conditions.
It easily loses HCl to give the corresponding p-quinone methide which undergoes
further transformations. The intensive reddening of the reaction mixture observed in 10-15
minutes after adding NaAA to calix[4]arene 2, is followed by the disappearance of color when
the reaction was completed. These facts clearly indicate formation of an intermediate quinone
structure in the solution. In spite of the differences in the reactive behavior of the initial
compounds 2 and 5, the applied synthetic protocol afforded the target products 3 and 6 with high
yields (65% and 77% respectively).
Scheme 1. Synthetic routes and structures of compounds 3 and 6. The similar numbering system
of atoms is used in the experimental section.
The IR spectra of both tetra-1,3-diketones contain the doublet bands assigned to the
–
1
–1
ν(C=O) vibrations (1724 and 1698 cm for 3, 1720 and 1699 cm for 6). The doublet character
of the keto-carbonyl bands with similar intensities is caused by the syn- and anti-phase stretching
2
8,29
vibrations of the carbonyl groups in the 1,3-diketone fragments.
The absorption band at
–
1
∼
1600 cm , reflecting both the stretching vibrations of multiple bonds of aromatic rings and the
resonance vibrations of enol structures (ν(С=О) and ν(С=С)) is noticeably broadened and its
intensity in both cases is ~0.5-0.7 of ν(C=O) absorbance in Nujol. It is worth noting the lower
intensity peak in this region (~0.1) in the IR spectrum of the previously reported
calix[4]resorcine tetra-1,3-diketone, which results from the 5-10% of enol contribution according

5
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1
17
to H NMR spectroscopic data. Taking this into account, the IR spectra of 3 and 6 indicate the
presence of a considerably higher percentage of enol form.
Stretching vibrations ν(ОH) for 6 are detected as a broad diffuse base under the ν(СH)
–
1
lines in the interval 2400—3300 cm with an uncertain maximum, which is characteristic for
3
0,28
enol structures.
In the case of calix[4]arene 3 having the non-substituted lower rim, this
absorption is additionally masked under the broad and intensive dome-shaped ν(OH) band with
-1
the maximum at ~ 3183 cm , caused by vibrations of the hydroxyl groups of the calix[4]arene
-1
scaffold. The underfrequency for this band in comparison with ν(ОH)free ~ 3500-3600cm
2
8
reveals the participation of these groups in strong hydrogen bonding.
1
Assignment of signals in the NMR spectra was accomplished by means of 2D COSY, H–
1
3
1
13
C HSQC and H– C HMBC experiments. The embedding of four 1,3-diketone fragments on
the calix[4]arene backbone leads to a large number of spatial forms for these compounds. Keto-
enol tautomerism of 1,3-diketone moieties is one more reason for the complication of spectral
patterns in compounds 3 and 6. Each of 1,3-diketone fragments in the compounds can exist both
in enol and keto form. Furthermore, these tautomers may occupy different positions relative to
each other, which undoubtedly lead to multiplication of peaks in the NMR spectra of compounds
3
and 6 in CDCl . Nevertheless, the use of two-dimensional NMR correlation spectroscopy
3
techniques results in accurate identification of compounds 3 and 6.
Calix[4]arenes and their derivatives can adopt four conformations, namely cone, partial
3
1,32
cone, 1,3- and 1,2-alternates.
The single narrow peak assigned to the methylene-bridged
1
3
carbon atom is observed in the C NMR spectra of compounds 3 and 6. This behavior is peculiar
for cone or 1,3-alternate conformations. The choice between these spatial forms may be realized
3
3
13
by the using “de Mendoza rule”. The obtained С chemical shifts determined for the bridged
1
3
carbon atoms of 3 and 6 (δ С = 33.4 and 30.9 ppm respectively) evidence the cone isomer for
1
the synthesized compounds. The chemical shift for the hydroxyl protons in the H NMR
spectrum of calix[4]arene 3 in CDCl is 10.1 ppm and is almost the same as in the parent
3
3
4
calix[4]arene 1 (10.19 ppm). Thus, both the IR and NMR data indicate a circular hydrogen
3
5
bond realized at the low rim of the compound 3, similar to calix[4]arene 1.
The chemical shifts of the OH groups protons (∼16.7 - 16.9 ppm), belonging to 1,3-
diketone fragments of the compounds 3 and 6, testify for a strong intramolecular hydrogen
bonding. The amount of enol tautomer in CDCl solution reaches 40% for 3 and 50% for 6,
3
essentially higher than for the mentioned above calix[4]resorcine derivative. This difference is
obviously caused by the rigidity of the cavitand structure, and the sterical hindrances realized for
the latter compound, which prevents the stabilization of the enol form.

6
ACCEPTED MANUSCRIPT
Electronic absorption spectroscopy
Electronic absorption spectra of both ligands are characterized by the main absorption peak
at 290 nm arising from the π→π* transition and a shoulder at 310-320 nm, which should be
assigned to enolic forms of the 1,3-diketone groups (Fig. 1). Changes in electronic absorption
spectra of the ligands under basification and complex formation with lanthanides are exemplified
in Figure 1 by Tb(NO ) .
3
3
Fig. 1. Absorption spectra of L (C =0.025 mM) in DMF (1); L in alkalized DMF (CTEA=0.1mM)
L
(
2); L with Tb(NO ) (C =C =0.025 mM) in alkalized DMF: CTEA=0.1 mM (3). L = 3 (a) and 6
3 3 L Tb
(b).
The basification of DMF solutions of the both calixarenes with triethylamine (TEA) affects
their absorption spectra (Fig.1). This effect significantly increases when both Tb(NO ) and TEA
3
3
are added to the ligands 3 and 6 (Fig.1). A similar tendency is observed for Yb(NO ) (Fig. S1 in
3
3
ESI). The observed changes clearly point to complex formation of the lanthanide ions with 3 and
in alkaline conditions. The spectral changes at various ligand:TEA ratios were measured in
6
order to optimize this value for efficient complex formation of the ligands with Tb(III) and
Yb(III). This would avoid any interference caused by their hydrolysis at higher pH. The obtained
spectral data are analysed graphically by means of absorption intensities at 320 and 306 nm for 3
and 6, respectively (Fig. S2 in ESI). The optimal ligand:TEA ratio is 1:4 for Tb(III) and 1:2 for
Yb(III). This agrees well with their coordination capacities and hydrolysis constants, which both
tend to increase from Tb(III) to Yb(III) in accordance with the lanthanide contraction effect.
The spectral data measured at various concentrations of the ligands were analyzed by Job
plotting (Fig. 2) in order to evaluate the stoichiometry of the complex formation in DMF
solutions of the ligands at constant TEA:ligand ratio. The obtained results indicate the
predominance of 1:1 stoichiometry for both ligands (Fig.2).

7
ACCEPTED MANUSCRIPT
Fig. 2. The Job plot profiles for the DMF solutions at varied Ln:L molar ratio [Ln]+[L]=0.15
mM. L:TEA concentration ratio remaining at the 1:2 (a) and 1:4 (b) level. Ln=Yb (a), Tb (b). L =
3
(1), 6 (2).
ESI mass spectrometry
Mass spectrometry is another useful tool for the complex formation study. ESI spectra
provide evidence of 1:1 complexes of Tb(III) and Yb(III) in alkaline DMF solutions of 6 (Fig.3).
-
-
In particular, the signals at m/z 1336.5 and m/z 1321.6 are revealed in the spectra of alkaline
DMF solutions of 6 in the presence of Yb(NO ) and Tb(NO ) , respectively (Fig.3). The signals
3
3
3 3
2
-
are related to 1:1 anionic complexes with dianion (6 ) and two nitrate anions, namely
3+
2-
-
3+
2- -
[
Yb (NO ) (6 )] and [Tb (NO ) (6 )] . The changes in the electronic absorption spectra of
3 2 3 2
DMF solutions of 6 and the lanthanide nitrates under the basification (Fig.1b) point to
deprotonation of two 1,3-diketone groups as the reason for the complex formation with the
-
3+
- -
lanthanide ions. The smaller peak at m/z 1384.6 assigned to [Tb (NO ) (6 )] indicates the
3
3
equilibrium between various 1:1 complexes in solution. The isotopic patterns for all peaks are in
good agreement with the predicted isotopic distribution patterns (see insets).

8
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Fig. 3. ESI spectra of calix[4]arene 6 with Yb(NO ) (a) and Tb(NO ) (b) in alkaline DMF
3
3
3 3
solutions (C =C
=0.05 mM at 0.1 mM TEA; C =CTb(III)=0.05 mM at 0.2 mM TEA) at
L
Yb(III)
L
negative mode. Inset represents isotopic distribution patterns.
In the case of 3 and the lanthanide nitrates in alkaline DMF solution, ESI spectra (Fig. 4)
reveal no peaks in negative mode, which can be assigned to the complexes. Nevertheless, peaks
+
+
at m/z 1102.4 and m/z 1117.4 in the ESI spectra of the solutions indicate the formation of
3
+
2-
+
3+
2- +
[
(Tb DMF)(3 )] and [(Yb DMF)(3 )] in alkaline DMF solutions.
Thus, the ESI spectra confirm the 1:1 complex formation of ligands 3 and 6 with
lanthanide ions in alkalized DMF solutions.

9
ACCEPTED MANUSCRIPT
Fig. 4. ESI spectra of calix[4]arene 3 with Yb(NO ) (a) and Tb(NO ) (b) in alkaline DMF
3
3
3 3
solutions (C =C
=0.05 mM at 0.1 mM TEA; C =CTb(III)=0.05 mM at 0.2 mM TEA) in
L
Yb(III)
L
positive mode. Inset represents isotopic distribution patterns.
Modeling of possible coordination modes of lanthanide ions with 3 and 6 in alkaline media
Structural diversity of the ligands (Scheme 1) may be the reason for different coordination
environment of lanthanide ions in their complexes with 3 and 6. As it was abovementioned the
lower rim of 3 is phenolic, while it is alkyl-substituted for 6, which is the only structural
difference between the ligands. It is worth noting that coordination of lanthanide ions via 1,3-
diketone groups is more thermodynamically favorable than the coordination via phenolate
groups in alkaline media. Nevertheless, deprotonation of lower phenolic rim is the well-known
36,37
reason for conformational shift of calix[4]arenes.
The cone conformation of calix[4]arenes in
neutral media is favored by the efficient hydrogen bonding of the phenolic groups, while their
deprotonation in alkaline media induces the conformation shift towards partial cone, 1,2- and
1
,3-alternates.

1
0
ACCEPTED MANUSCRIPT
Structural modeling of complexes was performed with the use of MOPAC 2012 software
with the aim to illustrate diversity of binding modes of lanthanide ions via 1,3-diketonate groups,
when calix[4]arene backbone is in different conformations. The possible complex structures
represented in Scheme 2 indicate the similar coordination of lanthanide ions via two chelating
1
,3-diketonate groups for all calix[4]arene conformers.
Scheme 2 Possible modes of binding of Tb(III) cations to molecule 3. The structures are
obtained after SPARKLE/PM7 optimization (for details see subsection ‘Quantum-chemical
computations’).
Luminescence spectroscopy
The electronic absorption spectra of the Tb(III) and Yb(III) complexes (Fig.1) indicate
efficient feeding of the singlet excited levels, while the energy from singlet levels can be
transferred to lanthanide-centered excited level through the intersystem crossing. Triplet excited
state is considered as the main pathway in ligand-to-lanthanide energy transfer in 1,3-diketonate
3
8
complexes of lanthanides.
The energy gap between triplet level of ligand and excited state of Tb(III) is of great
impact in sensitizing Tb(III)-centered luminescence. Thus, the sensitizing abilities of ligands 3
and 6 were confirmed by measuring intra-ligand emission for Gd(III) counterparts of the Tb(III)

1
1
ACCEPTED MANUSCRIPT
complexes in alkaline DMF solutions (Fig. 5). The emission bands of Gd(III) complexes with
ligands 3 and 6 arise from ligand-centered luminescence. Although both emission bands are
widened the energy of the triplet levels for ligands 3 and 6 can be compared. The results indicate
that the triplet levels of 3 are underlying those of ligand 6 (Fig. 5). Moreover, the intensity of the
intra-ligand emission is significantly greater for ligand 6 than for 3, while the intensity of the
intraligand electronic absorption is greater for 3 than for 6 (Fig.1). This disagreement indicates
that intersystem crossing is more efficient for 6 versus 3 in their complexes with Gd(III). Taking
into account that intersystem crossing is the main pathway of triplet levels excitation, the
different antennae effects of ligands 3 and 6 on Tb(III)-centered luminescence is rather
anticipated.
Fig. 5. Luminescence spectra of Gd-L alkalized DMF solutions. L=3 (2), 6 (1). C =CGd(III)=4.5
L
mM, CTEA=18 mM, λ =350 nm. The red color Y axis refers to emission magnitude for the
ex
spectrum of Gd-3.
Luminescence spectra of the alkalized DMF solutions of ligands 3 and 6 in the presence of
Tb(NO ) are characterized by the peaks peculiar to Tb(III)-centered emission (emission bands at
3
3
5
7
5
7
5
7
4
94 nm, 545 nm and 587 nm, which are assigned to D → F , D → F , D → F transitions)
4 6 4 5 4 4
under the excitation at λ=325 nm (Fig. 6). The luminescence spectra reveal the difference
between ligands 3 and 6 in their antenna-effects on Tb(III)-centered luminescence.

1
2
ACCEPTED MANUSCRIPT
Fig. 6. Excitation (a) and luminescence spectra (b) of alkalized DMF solutions of Tb(III) with
ligands 3 (1) and 6 (2). C =CTb(III)=0.1 mM, CTEA=0.4 mM, λ =325 nm.
L
ex
The results (Figs. 6, 7) point to ligand 6 being the more efficient antenna for Tb(III)-
centered luminescence than ligand 3 due to higher lying triplet levels, which facilitates the
5
energy transfer to D level of Tb(III). The lower lying triplet levels of 3 versus 6 should be
4
5
noted as a reason for less efficient feeding of D level in Tb(III) complexes with 3 versus 6. It is
4
worth noting that measurements of excited state lifetimes (τ) confirm the difference in the steady
state luminescence. In particular, τ is about 0.15 ms for Tb(III) complexes with 6, while it
decreases to 0.09 ms in the case of 3 (the corresponding luminescence decay curves are
represented in Fig. S3 in ESI).
2
5
It is well-known that F5 level of Yb(III) is much lower than D level of Tb(III). Thus,
/2
4
abilities of the ligands to sensitize Yb(III)-centered luminescence may differ from those for
Tb(III). The luminescence measurements in alkaline DMF solutions of Yb(III) complexes with
2
2
ligands 3 and 6 reveal Yb(III)-centered NIR-luminescence at 976 nm arisen from F → F
7/2
5
/2
transition (Fig. 7). The results indicate rather poor Yb(III)-centered luminescence in the solutions
of 3, while the antenna effect of ligand 6 is more significant.
Fig. 7. Excitation (a) and luminescence spectra (b) of alkalized DMF solutions of Yb(III) with
ligands 3 (1) and 6 (2). C =CYb(III)=0.1 mM, CTEA=0.4 mM, λ =325 nm.
L
ex

1
3
ACCEPTED MANUSCRIPT
This tendency is in good agreement with the observation that revealed for the Tb(III)-
centered luminescence. The worse feeding of the triplet level of 3 versus 6, which is evident
from intensities of the corresponding ligand-centered luminescence (Fig. 5) is a main reason for
the difference in antenna effects of 3 and 6. Moreover, radiationless decay arisen from energy
stock to high-frequency oscillators of the ligand is more important for Yb(III) than for Tb(III)
complexes. Thus, the increase of radiationless decay in Yb(III) complexes with 3 versus 6 due to
more conformation flexibility in alkaline media should be assumed as one more cause for the
observed difference. It is also worth noting that Yb(III)-centered emission spectra are resolved
2
with additional transitions at lower energy that correspond to the degeneracy of the F ground
7
/2
3
9,40
state due to crystal field effects of the ligands.
The probability of the intersystem crossing is more favorable when the vibrational levels of
the two excited states overlap. Since the overlapping is greatly affected by structural or
4
1
conformational changes the reasons for different conformation behavior of structurally similar
ligands 3 and 6 are worth discussing. Both ligands 3 and 6 adopt cone-conformation in neutral
solutions, while their conformation behavior tends to differentiate in alkaline solutions. The lack
of intermolecular hydrogen bonding along with more easy conformation transformations make
ligand 3 in alkaline media adopting alternate to cone conformations, which are represented by
Scheme 2 c,d,e. Bulky substituents of ligand 6 restrict conformation shifts from cone (Scheme 2
3
1,42
a,b) to alternate conformations (Scheme 2 c,d,e).
These tendencies are in good agreement
with the experimentally observed difference in ligand-centered luminescence for Gd(III)
1
9
complexes of ligands 3 and 6. The work of Iki should be mentioned for accurate correlation
between the conformation of calix[4]arene backbone and its triplet level energy. Unfortunately,
all precipitates separated from the solutions of lanthanide complexes are amorphous, which
excludes the structure evaluation by X-ray analysis. Nevertheless, difference in the intraligand
emission for ligands 3 and 6 correlates with the well-known effects of lower rim deprotonation
or alkoxy-substitution on conformation behavior of calix[4]arene derivatives. Moreover, the
obtained results highlight conformation shift of calix[4]arene backbone as convenient tool to
tune antenna effect of calix[4]arene derivatives.
Summary
The obtained results introduce facile synthetic route for novel calix[4]arene macrocyclic
ligands functionalized with four 1,3-diketone groups at the upper rim and hydroxyl (3) or propyl
(6) groups at the lower rim on the basis of nucleophilic substitution of calix[4]arene. Their
ability to form 1:1 complexes with Tb(III) and Yb(III) in alkaline DMF solutions through
coordination via 1,3-diketonate groups is revealed from spectroscopic measurements. The
sensitizing of Tb(III)-centered luminescence confirms the complex formation of both ligands

1
4
ACCEPTED MANUSCRIPT
with Tb(III) in the solutions, although points to significant difference in antenna-effects of 3 and
6
. The intra-ligand emission revealed from luminescence measurements of Gd(III) complexes
5
with 3 and 6 indicates the inconvenient energy gap between triplet level of ligand 3 and D level
4
of Tb(III) as main reason for worse antenna-effect of 3 versus 6. Ligands 3 and 6 exhibit
different conformation behavior in alkaline DMF solutions due to well-known effects of lower
rim deprotonation and alkoxy-substitution on conformation behavior of calix[4]arene
derivatives. Structural modeling of the complexes illustrates that bis-chelating of the lanthanide
ions via two diketonate-groups is favorable coordination mode for all conformations of
calix[4]arene backbone. In the case of Yb(III)-centered luminescence the ligand 6 is also a better
2
sensitizer than 3, although the feeding of lower energy level F of Yb(III) must be insensitive
5
/2
to the difference in triplet level energy of 3 and 6. Both greater radiationless decay contribution
and less efficient feeding of the triplet level of 3 should be assumed as reasons for the observed
tendency. The obtained results point to conformation behavior of calix[4]arene backbone as one
more cause affecting lanthanide-centered luminescence in lanthanide complexes with
calix[4]arene derivatives and can be utilized for the design of new highly luminescent lanthanide
complexes.
Experimental
Reagents and materials
Acetylacetone was distilled before use. 1,4-Dioxane and toluene were purified by
distillation over metallic sodium. N,N-Dimethylformamide (DMF) (Acros Organics) was
distilled over P O . CDCl (99.8% isotopic purity) from Aldrich was used for NMR
2
5
3
spectroscopy. Ytterbium(III) nitrate pentahydrate (Yb(NO ) ꢀ5H O) (Aldrich Chemistry),
3
3
2
triethylamine (TEA) (Acros Organics) were used as commercially received without further
purification. Other commercial reagents were used as received.
The sodium salt of acetylacetone was synthesized by addition of excess Na (metal plates)
to acetylacetone in absolute toluene. After stirring the mixture at 50 ºC for 4 h the precipitate was
decanted from residues of unreacted sodium, washed with diethyl ether, and dried in vacuo.
Tdecomp.> 198 ºC.
Methods
Microanalyses of C and H were carried out with a EuroVector CHNS-O Elemental
Analyser EA3000. Melting points of compounds were measured with a Boetius hotstage
apparatus. MALDI mass spectra were detected on a Bruker Ultraflex III MALDI-TOF/TOF mass
spectrometer. ESI measurements were performed using an AmazonX ion trap mass spectrometer
in positive and negative mode. NMR experiments were performed on a Bruker AVANCE-600

1
5
ACCEPTED MANUSCRIPT
spectrometer at 303K equipped of a 5 mm diameter broadband probe head working at 600.13
1
13
1
13
MHz in H and 150.864 MHz in C experiments. Chemical shifts in H and C spectra were
1
13
reported relative to the solvent as internal standard (CDCl δ( H) 7.27 ppm, δ( C) 77.2 ppm).
3
1
13
1
Assignment of NMR signals was accomplished by means of 2D COSY, H– C HSQC and H–
1
3
C HMBC experiments. The pulse programs of the COSY, HSQC and HMBC experiments were
taken from Bruker software library. IR absorption spectra were recorded on a Vector-22 Bruker
-1
FT-IR spectrophotometer with a resolution of 4 cm as Nujol emulsions and KBr pellets of
compounds.
The steady-state luminescence spectra were recorded on a spectrofluorometer Cary Eclipse
(Agilent Technologies) in 10 mm quartz cuvettes. Excitation of samples was performed at 325
nm, and emission detected at 545 nm (for terbium luminescence) and 976 nm (for ytterbium
luminescence) with a 6 nm slit width for both excitation and emission. Time-resolved
measurements were performed using the following parameters: time per flash-49.00 ms, flash
count-200 ms, initial delay-0.05 ms and sample window-2 ms. The normalized fluorescence
decay curves are presented in Fig. S3 in ESI.
UV-VIS spectra were recorded on a Lambda 35 spectrophotometer (Perkin-Elmer) in 10
mm quartz cuvettes. The Job plotting was done from monitoring of the absorbance at (А - А ),
λ
λL
where А is absorbance at 320 nm for 3 and 306 nm for 6.
λL
Quantum-chemical computations. Structural modeling of complexes was performed with the
4
3
43
use of MOPAC 2012 software. The PM7 semiempirical method was applied using of
4
4
Sparkle/PM7 Lanthanide Parameters for the Modeling of Tb(III) complexes, which allowed us
to minimize computational time and resources and to maintain the accuracy comparable to non-
empirical approaches.
Synthesis
The synthetic routes, the structural formulae and numbering of atoms of the investigated
34
compounds are shown in Scheme 1. The calix[4]arene 1,
25,26,27,28-tetra-
4
5
36
46
propoxycalix[4]arene 4, and their 5,11,17,23-tetrakis(halogenomethyl) derivatives 2 and 5
were obtained as described in the literature.
Synthesis of 5,11,17,23-tetrakis[(acetylaceton-3-yl)methyl)]-25,26,27,28-tetrahydroxy-
calix[4]arene (3). A mixture of the sodium salt of acetylacetone (NaAA) (0.92 g, 7.5 mmol) and
5
,11,17,23-tetrakis(bromomethyl)-25,26,27,28- tetrahydroxycalix[4]arene 2 (1.19 g, 1.5 mmol)
in anhydrous dioxane (40 mL) was stirred at 35 ºC under an argon atmosphere for 3 h.
Thereafter, dioxane was distilled off under reduced pressure. The residue was acidified with 1 M
HCl (40 mL). After addition of CH Cl (40 mL) the mixture was vigorously stirred. The organic
2
2
layer was separated, washed several times with water, dried over MgSO and concentrated by
4

1
6
ACCEPTED MANUSCRIPT
distillation. Solvent residues were removed at 80 °C in vacuo. After foaming, the product 3 was
1
obtained as a straw color powder (0.84 g) in 65% yield. Mp: 89-90 ºC. H NMR (600.13 MHz,
CDCl , 303K, ppm), δ: 16.7-16.9 (m, OHenol), 10.10 (4H, H(10)), 6.80 (8H, H(6)), 4.19 (4H,
3
3
H(9)eq), 3.93ket (t, J=5.3 Hz, 4H for keto form, H(3) ), 3.46 (4H, H(9) )), 3.44en(s, 4H for
ket
ax
3
enolic form H(4)) and 2.95ket (d, J = 5.3 Hz, 8H for keto form, H(4)), 2.12 , 2.03 (m, 24 H,
ket
en
1
3
H(1)). С NMR (150.9 MHz, CDCl , 303 K, ppm) δ: 203.5 , 191.9 С(2); 147.6 С(8); 129.3
3
ket
en
С(6); 128.6 С(7); 129.7 С(5); 108.4 70.5 С(3); 33.3 32.1 C(4); 31.9 С(9); 29.8 , 23.4
en
en,
ket
ket,
en
ket
-1
С(1). IR (nujol, cm ): ν = 3183 (vbr, ν(ОH)), 3000-2800 (ν(СH), (ν(СH ) and (ν(СH ) for KBr
2
3
pellet), 1724, 1698 (ν(С=О)), 1603 (ν(С=О) and ν(С=С)), 1458 (ν(Ph)), 1377, 1357, 1245,
+
1
224, 1147 (ν (CCC)), 1077, 1021, 950 (ν (CCC)). HR-MALDI-MS: m/z calcd for С H O
as s 52 56 12
+
[
M+Na] 895.3664, found 895.3670. Calcd for С H O : С, 71.54; H, 6.47. Found: C, 71.86;
52 56 12
H, 6.43.
Synthesis of 5,11,17,23-tetrakis[(acetylaceton-3-yl)methyl)]-25,26,27,28-tetrapropoxy-
calix[4]arene (6). 5,11,17,23-Tetrakis(chloromethyl)-25,26,27,28-tetra-propoxycalix[4]arene 5
(0.4 g, 0.5 mmol) and the sodium salt of acetylacetone (NaAA) (0.38 g, 3.1 mmol) were mixed
in anhydrous dioxane (30 mL). The suspension was refluxed with stirring for 24h under argon.
Then dioxane was distilled off and the residue acidified with 1 M HCl (20 mL). After addition of
CH Cl (40 mL), the mixture was vigorously stirred. The organic layer was separated, washed
2
2
twice with water, dried over MgSO and concentrated. Solvent residues were removed at 80 °C
4
in vacuo. After foaming, the product 6 was obtained as a straw color powder (0.41g) with the
1
yield 77%. Mp: 80-83 ºC. H NMR (600.13 MHz, CDCl , 303 K, ppm), δ: for enol form: 16.7-
3
1
8
6.9 (m, ОН ), 6.4-6.6 (8H, H(6)), 4.41 (4Н, H(9) ), 3.82 (4Н, for keto form H(3)), 3.79 (m,
en eq
H, H(10)), 3.39 (m, 4H for enolic form H(4)) and 2.85 (m, 8H for keto form, H(4)), 3.09 (4Н,
ket
H(9) ), 2.14 and 2.09 (m, 24 Н for keto and enolic forms, H(1)), 1.94 (m, 8H, H(11)); 1.01
ax
en
ket
1
3
(
m, 12H, H(12)). С NMR (150.9 MHz, CDCl , 303 K, ppm) δ, enol form: 204.1 , 191.9
3 ket en
C(2), 155.4 С(8), 135.2 С(7), 131.3 (C6) and 128.2 С(6)ket , 128.5 С(5), 109.2 , 70.3 С(3),
en
en
ket
7
7.8 C(10), 34.0 , 31.1 C(4); 29.8 С(9), 29.7 , 23.4 C(1); 23.3 C(11), 10.5 C(12). IR (nujol,
ket en ket en
-1
cm ): ν = 3405 (overtone (ν(С=О)), 3000-2800 (ν(СH), (ν(СH ) and (ν(СH ) for KBr pellet),
2
3
1
1
720, 1699 (ν(С=О)), 1603 (ν(С=О) and ν(С=С)), 1465 (ν(Ph)), 1378, 1359, 1304, 1254, 1221,
+
146 (ν (CCC)), 1067, 1041, 1007, 964 (ν (CCC)). HR-MALDI-MS: m/z calcd for С H O
as
s
64 80 12
+
[
M+Na] 1063.5542, found 1063.5553. Calcd for C H O : С, 73.82; H, 7.74. Found: C, 73.94;
64
80 12
H, 7.98.

1
7
ACCEPTED MANUSCRIPT
Acknowledgement. This work is supported by the Russian Fund for basic Research (grant
1
6-03-00007 A). R. Zairov, N. Shamsutdinova and G. Gimazetdinova thank the President of
Russian Federation grant for young scientists (МК-4456.2015.3) for financial support. R. Zairov,
N. Shamsutdinova, A. Mustafina and R. Amirov are grateful for financial support of the part of
the work from the Russian Government Program of Competitive Growth of Kazan Federal
University and for subsidy allocated to Kazan Federal University for the project part of the state
assignment in the sphere of scientific activities.

1
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ACCEPTED MANUSCRIPT
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