The role of the intermolecular π···π interactions in the luminescence behavior of novel coumarin-based pyrazoline materials

Article abstract of DOI:10.1016/j.dyepig.2020.108942

Novel nine coumarin-based pyrazolines have been synthesized and fully characterized in search of new fluorescent compounds for design stimuli-responsive chromic materials. All reported compounds behave as highly fluorescent materials, both in solution and

Full text of DOI:10.1016/j.dyepig.2020.108942

Journal Pre-proof
The role of the intermolecular π···π interactions in the luminescence behavior of novel
coumarin-based pyrazoline materials
V.F. Traven, D.A. Cheptsov, J.I. Svetlova, I.V. Ivanov, Cristián Cuerva, Carlos
Lodeiro, Frederico Duarte, S.F. Dunaev, V.V. Chernyshev
PII:
S0143-7208(20)31639-9
DOI:
https://doi.org/10.1016/j.dyepig.2020.108942
DYPI 108942
Reference:
To appear in: Dyes and Pigments
Received Date: 6 September 2020
Revised Date: 12 October 2020
Accepted Date: 13 October 2020
Please cite this article as: Traven VF, Cheptsov DA, Svetlova JI, Ivanov IV, Cuerva C, Lodeiro C, Duarte
F, Dunaev SF, Chernyshev VV, The role of the intermolecular π···π interactions in the luminescence
behavior of novel coumarin-based pyrazoline materials, Dyes and Pigments, https://doi.org/10.1016/
j.dyepig.2020.108942.
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The role of the intermolecular π···π interactions in the luminescence
behavior of novel coumarin-based pyrazoline materials
a
a
a
a
V.F. Traven* , D.A. Cheptsov , J.I. Svetlova , I.V. Ivanov ,
b
b,c
b
Cristián Cuerva , Carlos Lodeiro* , Frederico Duarte ,
d
d,e
S.F. Dunaev , V.V. Chernyshev
a
D. Mendeleev University of Chemical Technology of Russia, Miusskaya sq., 9, Moscow
25047, Russian Federation
1
b
BIOSCOPE Research Group, LAQV@REQUIMTE Chemistry Department, NOVA School of
Science and Technology, NOVA University Lisbon, 2829-516 Caparica (Portugal)
c
PROTEOMASS Scientific Society, Rua dos Inventores, Madam Parque, Caparica Campus,
2
829-516 Caparica (Portugal)
d
Department of Chemistry, M.V. Lomonosov Moscow State University, 1-3 Leninskie Gory,
Moscow 119991, Russian Federation
e
A.N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS, 31 Leninsky
prospect, Moscow 119071, Russian Federation
*
Corresponding authors:
V.F. Traven (valerii.traven@gmail.com), Carlos Lodeiro (cle@fct.unl.pt)
CRediT authorship contribution statement
V.F. Traven. Conceptualization, Methodology, Validation, Investigation, Resources,
Data Curation, Writing-Original Draft and Review&Editing, Visualization, Supervision,
Project administration and Funding Adquisition.
D. A. Cheptsov: Synthesis and characterization, NMR-,mass spectra, elemental
analysis.
J.I. Svetlova, Synthesis and characterization
I.V. Ivanov: Quantum chemical calculations, Data Curation, Visualization.
S. F. Dunaev: Powder X-Ray studies Visualization Data Curation
V.V. Chernyshev: Powder X-Ray studies Visualization Conceptualization, Methodology,
Validation

Carlos Lodeiro: Conceptualization, Methodology, Validation, Investigation, Resources,
Data Curation, Writing-Original Draft and Review&Editing, Visualization, Supervision,
Project administration and Funding Adquisition.
Cristian Cuerva: Conceptualization, Methodology, Validation, Investigation, Data
Curation, Writing-Original Draft and Review&Editing, Visualization, Supervision.
F. Duarte: Validation, Investigation, Data Curation, Visualization.

The role of the intermolecular π···π interactions in the luminescence
behavior of novel coumarin-based pyrazoline materials
a
a
a
a
V.F. Traven* , D.A. Cheptsov , J.I. Svetlova , I.V. Ivanov ,
b
b,c
b
Cristián Cuerva , Carlos Lodeiro* , Frederico Duarte ,
d
d,e
S.F. Dunaev , V.V. Chernyshev
a
D. Mendeleev University of Chemical Technology of Russia, Miusskaya sq., 9, Moscow
25047, Russian Federation
1
b
BIOSCOPE Research Group, LAQV@REQUIMTE Chemistry Department, NOVA School of
Science and Technology, NOVA University Lisbon, 2829-516 Caparica (Portugal)
c
PROTEOMASS Scientific Society, Rua dos Inventores, Madam Parque, Caparica Campus,
2
829-516 Caparica (Portugal)
d
Department of Chemistry, M.V. Lomonosov Moscow State University, 1-3 Leninskie Gory,
Moscow 119991, Russian Federation
e
A.N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS, 31 Leninsky
prospect, Moscow 119071, Russian Federation
*
Corresponding authors:
V.F. Traven (valerii.traven@gmail.com), Carlos Lodeiro (cle@fct.unl.pt)
Abstract
Novel nine coumarin-based pyrazolines have been synthesized and fully characterized
in search of new fluorescent compounds for design stimuli-responsive chromic
materials. All reported compounds behave as highly fluorescent materials, both in
solution and in the solid state, the intermolecular interactions playing a key role in their
photophysical properties. In particular, compound 1a exhibits non-reversible thermo-,
mechano-, solvato- and vapochromic behaviors as a result of the establishment and/or
the rupture of intermolecular π···π transitions, and additionally, ionochromic properties
due to the complexation upon the addition of several metal salts. Powder XRD studies
have been performed to explain the noted stimuli-responsive effects. The compound 1a
molecules have π···π interactions proved by short distance of 3.61(2) Å between the
centroids of six-membered cycles and weak intermolecular C–H…O hydrogen bonds,
which link the π···π dimers into columns. According to quantum chemical calculations
by TD DFT method with the B3LYP functional, in the def2-TZVP basis, intermolecular
π···π interactions lead to strong red-shift (around 63 nm) of the electron absorption
(EA) of the 1a in solid state. On the contrary, in the 2a structure, there are no any hint
for the π···π stacking and no changes in EA spectra from solution to solid state. Results
show clear evidences of the usefulness of this compound in the field of sensors.

1
. INTRODUCTION
There is an increasing interest in the molecular packing arrangement in the solid state
which plays a very important role in determining the organic optoelectronic device
performance [1–3]. Among various optoelectronic properties, fluorescence is considered
to be the most sensitive and efficient method in monitoring of the molecular packing
arrangement. Even slight changes in the molecular packing can generate a notable
change in the luminescent properties of the material. Recently, various examples of
fluorescence color change related to the molecular aggregation [4-6] and/or stacking [7-
1
2] have been reported. Among them, compounds showing mechanochromic
modulation of luminescence [13, 14, 15-22] are drawing special attention in view of
developing functional sensors, security papers, optoelectronic devices and data storage,
which can respond to the input analyte signal. In general, packing process in the
molecular solid is governed by certain secondary intermolecular interactions, such as
π···π stacking, heteroatom···H and C–H···π bonding, dipole···dipole interactions [23-
2
5]. The fine-tuning of these intermolecular effects by the relate molecular design is a
promising approach to control the optoelectronic properties of functional molecular
solids and sensory materials. Some examples are considered below in more detail.
Strong dependence of emission characteristics of 9,10-bis((E)-2-(pyrid-2-
yl)vinyl)anthracene on π···π stacking efficiency has been explained be its molecular
aggregation [26].
9
,10-bis((E)-2-(pyrid-2-yl)vinyl)anthracene
This compound is crystallized into three different crystal forms: C1, C2 and C3. The
overlap of anthracene planes between the adjacent molecules has been proved to
increase from C1 to C3. The different stacking modes in C1, C2, and C3 reasonably
result in different molecular aggregation states and thus lead to different fluorescence
colors. The anthracene planes of two adjacent molecules in C1 hardly overlapped at all,
so there was nearly no π···π interaction in C1, which therefore exhibited green emission
with λmax = 527 nm. As for C2, the adjacent anthracene planes overlapped with each
other by about 40%, and the vertical distance between them was measured to be

approximately 3.65 Å, which corresponds to the formation of weak π···π interaction
between the anthracene planes. Thus, C2 was an orange-emissive crystal (λmax = 579
nm). In the case of C3, molecules were bound together by a strong π···π interaction to
form pairs in which the adjacent anthracene planes overlapped almost in a face-to-face
stack with a distance between them of approximately 3.52 Å. This strong π···π
interaction induced the red emission of C3 with λmax = 618 nm. The red shift of the C3
emission relative to those of C1 and C2 has been ascribed to the smaller band gap of the
9
,10-bis((E)-2-(pyrid-2-yl)vinyl)anthracene molecule in C3 owing to the increased band
widths of both the HOMO- and the LUMO-derived band as a result of the increased
π···π interaction, according to a tight binding model. Nonetheless, another important
factor for the red-shifted fluorescence should be taken into consideration, that is, the
increase in exciton coupling and orbital overlap between neighboring molecules from
C1 to C2 to C3. These results clearly indicate that 9,10-bis((E)-2-(pyrid-2-
yl)vinyl)anthracene forms three or even more different aggregation structures in the
solid state. Dependencies of emission characteristics on π···π stacking efficiency have
been also discussed in [27-33].
A series of boron ketoiminate derivatives a-c were prepared by the reactions of
the 1,3-enaminoketone derivatives with a boron trifluoride–diethyl etherate [29].
The 99a-c exhibit efficient AIE characteristics (in THF: Φ ≤ 0.01; in the solid
PL
state: Φ = 0.30-0.76) that resulted from molecular motions of boron-chelating
PL
rings with a boron-nitrogen (B–N) bond. The low emissions of boron ketoiminate
derivatives in the solution states were derived from quenching through the
molecular motions of the boron-chelating ring. The 99a-c show low planarity:
dihedral angle a: N1-C2-C3-C8= 20.7°, b: N1-C2-C3-C8=47.1°, c: N1-C2-C3-
C8=75.9°. The packing structures of a and b have short intermolecular distances
of approximately 3.5 Å between each boron-chelating ring. The distances

indicate an effective intermolecular π–π stacking, which usually causes red shifts
of PL spectra and quenching. Compound c has the longest intermolecular
distance between each boron-chelating ring (5.0 Å) in the synthesized boron
ketoiminate derivatives since the intermolecular π–π stacking was suppressed by
the poor planarity of c. These results from X-ray analysis also clearly correspond
to their optical properties. The emission maxima in the PL spectra from the
solutions with a-c were observed at similar positions (λ =424–429 nm). In
PL
contrast, the largely redshifted emission maxima were detected in the solid
samples of the complexes except c (a: λ = 471 nm; b: λ = 470 nm; c: λ =
PL
PL
PL
4
43 nm). In addition, in the solid states, a and b showed higher quantum yields
than that of c. These data suggest that the molecular motions of the boron-
chelating rings in a and b should be strongly suppressed by intermolecular
stacking between each boron-chelating ring. In particular, the more planar
structure of a is favorable to the stacking formation at the boron-chelating rings,
thus leading to the larger quantum yields of the boron ketoiminates. The
substituents on the nitrogen atom in b and particularly c can disturb the stacking
formation at the boron-chelating rings. Therefore, the AIE should be significantly
induced from the solid sample of a. These results also indicate that the molecular
motions at the boron-chelating rings play the most important role in the AIE
behavior of this system.
New luminogen, (E)-dimethyl-5-((4-(diethylamino)-2-hydroxybenzylidene)-
amino)isophthalate has been synthesized by a simple one-step reaction [31]. Its
absorption peak appears at around 375 nm in hexane corresponding to the π–π*
transition. With an increase in the solvent polarity, it shifts from 375 to 398 nm.
Similarly, the luminescence behaviors of solutions also vary slightly with solvent
polarity. When excited at 388 nm, it shows weak fluorescence at 435 nm in
hexane, while in a polar solvent, DMSO, the maximum emission shifts to 475
nm. There is a huge difference in the PL intensity between the crystalline and

amorphous phases (as high as 28 times) that can be easily distinguished by the
naked eye. Intramolecular hydrogen bonds are formed between the OH group
and the CN bond. They enhance the planarity of the diethylaminobenzene moiety
and consequently redshift the emission wavelength of the crystalline sample. In
addition to the π–π interactions, multiple intermolecular weak interactions such
as C–H···O, N–C···H, O–C···H and C=O···C are observed in the crystals. These
weak forces help the molecules to further rigidify their conformation and reduce
the energy loss via the nonradiative relaxation channel and thus enhance the
emission efficiency. Based on the above crystallographic analysis, the CIEE
phenomenon probably results from a combined effect of J-aggregates and close
packing.
Derivatives of coumarin, one of the most prominent organic fluorophores, have been
widely and extensively used in both material and biological sciences due to their
inherent physicochemical and photophysical characteristics, such as reasonable stability
and relative ease of synthesis [34]. However, in comparison with abundant reports about
the photoluminescent researches of coumarins in solution, the investigation of
fluorescent properties as well as potential utilization in the solid state is still rare [35]. In
this paper we report the synthesis of novel coumarin-based pyrazolines in search of
fluorescent compounds for design of new stimuli-responsive sensory chromic materials.
2
2
. EXPERIMENTAL SECTION
.1. Materials
The deuterated solvent (DMSO‐d ) for NMR spectroscopy was obtained from Merck.
6
All other commercial chemicals, solvents and polymers were purchased from Sigma-
Aldrich and used without further purification. The metal ions used in the titrations were
obtained from their corresponding metal salts Hg(ClO ) ·xH O, Zn(ClO ) ·6H O,
4
2
2
4 2
2
CuNO ·3H O, FeCl ·xH O, Cd(ClO ) ·H O, CoCl ·6H O, Ag(NO ), Pb(ClO ) ·3H O,
3
2
2
2
4 2
2
2
2
3
4 2
2
Ca(CF SO ) , Ni(NO ) ·6H O.
3
3 2
3 2
2
2
.2. Physical measurements
1
The NMR spectra were recorded on a «Bruker Avance» spectrometer in DMSO‐d : H
6
13
NMR spectra at 500 MHz and C NMR spectra at 126 MHz. As an internal standard
1
3
was used tetramethylsilane (SiMe ) or a signal of residual protons and carbon of C
4

solvent with respect to SiMe (DMSO‐d : δ 2.50 ppm, δ 39.5 ppm). The mass spectra
4
6
H
C
were obtained using the «Thermo Scientific» mass spectrometer (ISQ LT Single
Quadrupole Mass Spectrometer) by electron impact with ionizing electron energy of
7
0 eV. High‐resolution mass spectra were recorded on the «Bruker micrOTOF II»
instrument using electrospray ionization (ESI).
Melting points were measured on a «Stuart» melting point apparatus SMP30 and are
uncorrected.
2
.3. Photophysical measurements
UV-Vis absorption spectra were recorded on a Jasco V-650 spectrophotometer and the
luminescence emission by using a Horiba-Jobin-Yvon Fluoromax-4 spectrofluorimeter
in the PROTEOMASS-BIOSCOPE facilities. The stock solutions of the complexes (ca.
-3
1
0 M) were prepared by dissolving an appropriate amount of the corresponding
compound in a 10 mL volumetric flask and diluting to the mark with chloroform. The
-
studied solutions were prepared by appropriate dilution of the stock solutions up to 10
5
-6
-
10 M. All measurements were performed at 298 K.
The relative luminescence quantum yields were determined using as the standard a
solution of coumarin 343 in ethanol (φ = 0.63).
F
Luminescence spectra of solid samples were recorded on the Horiba Jobin-Yvon
Fluoromax-4 spectrofluorimeter using a fiber-optics device connected to the
spectrofluorimeter, exciting the solid compounds at appropriated wavelength. The
emission spectra at variable temperature were recorded by heating the samples over a
hotplate with temperature control.
Titrations were carried out by the addition of microliter amounts of standard solutions
2
+
2+
2+
2+
2+
+
2+
2+
2+
2+
of the metal ions Hg , Zn , Cu , Cd , Co , Ag , Ca , Pb , Ni and Fe in
chloroform or acetonitrile. All measurements were performed at 298 K.
2
.4. Powder X-Ray studies, experimental
Powder X-ray diffraction patterns were obtained using a X’Pert PRO diffractometer
from 2θ = 5−80° with Cu K radiation (λ = 1.5406 Å) under room temperature. In the
α
absence of single-crystals suitable for standard X-ray analysis, the crystal structures of
1
a and 2a were determined with the use of SDPD methods [36-40]. The powder
patterns, measured at room temperature on the laboratory diffractometer Huber G670
Guinier сamera equipped with curved germanium monochromator (Cu K radiation, λ
α1

=
1.54059 Å) and imaging plate detector, were indexed in triclinic (1a) and monoclinic
(2a) unit cells. The crystal structures 1a and 2a were solved in space groups P-1 and
P2 /c, respectively, with the use of simulated annealing technique [41] and refined with
1
the program MRIA [42] following the known procedures described by us earlier [43-
4
5].
2
.5. The synthesis of N-acetylpyrazolines 1a-c, 2a-d
A 4-fold excess (mol) of hydrazine as an 85% hydrazine hydrate solution is added with
stirring to a solution or suspension of 0.58 mmol of 3-cinnamoylcoumarin in glacial
acetic acid (10 ml). The reaction mixture is then heated at boiling for 2-3 hours (1a-c)
or 15 hours (2a-d). The reaction mixture is poured into 30 ml of ice water, neutralized
with 10% sodium carbonate solution. The precipitate is filtered off, washed with water
and dried. The final compound is purified by column chromatography with gradient
elution (eluent – petroleum ether - ethyl acetate from 4 : 1 to 0 : 1) or recrystallized
(toluene or ethanol).
3
-(1-Acetyl-5-phenyl-4,5-dihydro-1H-pyrazol-3-yl)coumarin (1a). Yield 59%, mp.
2
17-217,5°C (lit. [46] mp. 199-200°C). MS (ES+) calcd for C H N O m/z: 332.12,
2
0
16
2
3
1
found m/z: 332.31. H NMR (DMSO-d ), δ (ppm): 2.33 (s, 3H, COCH ); 3.20 (dd, 1H,
6
3
2
3
2
3
Н (19), J=18.3 Hz, J=4.6 Hz); 3.91 (dd, 1H, Н (19), J=18.3 Hz, J=11.9 Hz); 5.54
A
B
3
3
(
dd, 1H, H(12), J=4.6 Hz, J=11.9 Hz); 7.19-7.35 (m, 5H, H(14-18)); 7.38-7.44 (m,
3
2
H, H(6,8)); 7.65-7.68 (m, 1H, H(7)); 7.86 (d, 1H, H(5), J=7.5 Hz); 8.58 (s, 1H, H(4)).
1
3
С NMR (DMSO-d ), δ (ppm): 21.6; 43.9; 59.3; 116.0; 118.6; 119.0; 124.8; 125.4
6
(2C); 127.2; 128.6 (2C); 129.3; 132.9; 141.8; 142.2; 150.7; 153.4; 157.9; 167.6. For
1
13
compound 1a, the H and C NMR spectra are identical to the spectra given in [46,47].
3
4
3
-[1-Acetyl-5-(4-methylphenyl)-4,5-dihydro-1H-pyrazol-3-yl]coumarin (1b). Yield
0%, mp. 185-185,5°C (lit. [47] mp. 200-201°C). MS (ES+) calcd for C H N O m/z:
2
1
18
2
3
1
46.13, found m/z: 346.32. H NMR (DMSO-d ), δ (ppm): 2.26 (s, 3H, CH ); 2.31 (s,
6
3
2
3
3
H, COCH ); 3.18 (dd, 1H, Н (19), J=18.6 Hz, J=4.6 Hz); 3.88 (dd, 1H, Н (19),
3 A B
2
3
3
3
J=18.6 Hz, J=11.9 Hz); 5.49 (dd, 1H, H(12), J=4.6 Hz, J=11.9 Hz); 7.07-7.14 (m,
4
H, H(14,15,17,18)); 7.38-7.44 (m, 2H, H(6,8)); 7.65-7.68 (m, 1H, H(7)); 7.86 (dd, 1H,
3
4
13
H(5), J=7.6 Hz, J=1.2 Hz); 8.57 (s, 1H, H(4)). С NMR (DMSO-d ), δ (ppm): 20.6;
6
2
1.6; 43.8; 59.1; 116.0; 118.7; 119.1; 124.8; 125.4 (2C); 129.1 (2C); 129.3; 132.9;

1
13
1
36.3; 139.2; 141.7; 150.7; 153.4; 157.9; 167.5. For compound 1b, the H and C
NMR spectra are identical to the spectra given in [47].
3
-(1-Acetyl-5-phenyl-4,5-dihydro-1H-pyrazol-3-yl)-7-(diethylamino)coumarin
+
(
1c). Yield 36%, mp. 167-169°C. HRMS (ESI), m/z: 426.1790 (M+Na) (calcd for
+
C H N O Na : 426.1788). MS (ES+) calcd for C H N O m/z: 403.19, found m/z:
24
25
3
3
24 25
3
3
1
3
4
03.45. H NMR (DMSO-d ), δ (ppm): 1.14 (t, 6H, N(CH CH ) , J=7.0 Hz); 2.30 (s,
6 2 3 2
2
3
3
H, COCH ); 3.16 (dd, 1H, Н (19), J=18.6 Hz, J=4.6 Hz); 3.46 (q, 4Н, N(CH CH ) ,
3 A 2 3 2
3
2
3
3
J=7.0 Hz); 3.85 (dd, 1H, Н (19), J=18.6 Hz, J=11.9 Hz); 5.48 (dd, 1H, H(12), J=4.6
B
3
4
3
4
Hz, J=11.9 Hz); 6.55 (d, 1H, H(8), J=2.1 Hz); 6.76 (dd, 1H, H(6), J=8.9 Hz, J=2.1
3
Hz); 7.16-7.34 (m, 5H, H(14-18)); 7.58 (d, 1H, H(5), J=8.9 Hz); 8.38 (s, 1H, H(4)).
1
3
С NMR (DMSO-d ), δ (ppm): 12.3 (2C); 21.6; 44.2 (3C); 59.0; 96.1; 107.7; 109.7;
6
1
1
10.0; 125.3 (2C); 127.1; 128.6 (2C); 130.6; 142.3; 142.4; 151.55; 151.60; 156.7;
58.9; 167.1.
3
4
3
-(1-Acetyl-5-phenyl-4,5-dihydro-1H-pyrazol-3-yl)-4-hydroxycoumarin (2a). Yield
+
+
2%, mp. 247-249°C. HRMS (ESI), m/z: 349.1182 (M+H) (calcd for C H N O H :
2
0
16
2
4
1
49.1183). MS (ES+) calcd for C H N O m/z: 348.11, found m/z: 348.36. H NMR
2
0
16
2
4
2
3
(
DMSO-d ), δ (ppm): 2.32 (s, 3H, COCH ); 3.32 (dd, 1H, Н (19), J=18.9 Hz, J=4.6
6 3 A
2
3
3
Hz); 4.02 (dd, 1H, Н (19), J=18.9 Hz, J=11.9 Hz); 5.49 (dd, 1H, H(12), J=4.6 Hz,
B
3
J=11.9 Hz); 7.20-7.37 (m, 5H, H(14-18)); 7.39-7.47 (m, 2H, H(6,8)); 7.73 (t, 1H,
3
3
13
H(7), J=7.8 Hz); 8.01 (d, 1H, H(5), J=7.8 Hz); 13.27 (br. signal, 1H, OH). С NMR
DMSO-d ), δ (ppm): 21.8; 45.4; 57.6; 95.8; 113.9; 116.5; 124.1; 124.6; 125.5 (2C);
(
6
1
27.3; 128.6 (2C); 134.1; 142.0; 152.8; 155.3; 159.9; 166.6; 166.7.
3
-[1-Acetyl-5-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol-3-yl]-4-
hydroxycoumarin (2b). Yield 47%, mp. 236-237°C. HRMS (ESI), m/z: 401.1103
+
+
(
M+Na) (calcd for C H N O Na : 401.1108). MS (ES+) calcd for C H N O m/z:
21 18 2 5 21 18 2 5
1
3
78.12, found m/z: 378.40. H NMR (DMSO-d ), δ (ppm): 2.30 (s, 3H, COCH ); 3.33
6 3
2
3
(
dd, 1H, Н (19), J=18.9 Hz, J=4.3 Hz); 3.73 (s, 3H, OCH ); 3.99 (dd, 1H, Н (19),
A 3 B
2
3
3
3
J=18.9 Hz, J=11.9 Hz); 5.44 (dd, 1H, H(12), J=4.3 Hz, J=11.9 Hz); 6.85-7.21 (m,
3
4
H, H(14,15,17,18)); 7.41-7.48 (m, 2H, H(6,8)); 7.74 (t, 1H, H(7), J=7.8 Hz); 8.01 (d,
3
13
1
H, H(5), J=7.8 Hz); 13.33 (br. signal, 1H, OH). С NMR (DMSO-d ), δ (ppm): 21.8;
6

4
1
5.2; 55.1; 57.1; 95.9; 113.9; 116.5; 124.1 (2C); 124.6 (2C); 126.8 (2C); 134.1; 142.1;
52.7; 155.3; 158.5; 159.8; 166.4; 166.6.
3
-[1-Acetyl-5-(4-methylphenyl)-4,5-dihydro-1H-pyrazol-3-yl]-4-hydroxycoumarin
+
(
2c). Yield 34%, mp. 237-239°C. HRMS (ESI), m/z: 385.1151 (M+Na) (calcd for
+
C H N O Na : 385.1159). MS (ES+) calcd for C H N O m/z: 362.13, found m/z:
21
18
2
4
21 18
2
4
1
3
62.44. H NMR (DMSO-d ), δ (ppm): 2.27 (s, 3H, CH ); 2.30 (s, 3H, COCH ); 3.30
6 3 3
2
3
2
3
(
dd, 1H, Н (19), J=18.6 Hz, J=4.2 Hz); 4.00 (dd, 1H, Н (19), J=18.6 Hz, J=11.9
A
B
3
3
Hz); 5.45 (dd, 1H, H(12), J=4.2 Hz, J=11.9 Hz); 7.07-7.25 (m, 4H, H(14,15,17,18));
3
7
.39-7.49 (m, 2H, H(6,8)); 7.71-7.77 (m, 1H, H(7)); 8.01 (dd, 1H, H(5), J=7.9 Hz,
4
13
J=1.2 Hz); 13.37 (br. signal, 1H, OH). С NMR (DMSO-d ), δ (ppm): 20.6; 21.8;
6
4
5.3; 57.4; 95.9; 115.5; 116.5; 124.1; 124.6; 125.4 (2C); 129.1 (2C); 134.1; 136.5;
39.0; 152.7; 155.3; 159.8; 166.4; 166.6.
1
3
-[1-Acetyl-5-(3-ethoxy-4-hydroxyphenyl)-4,5-dihydro-1H-pyrazol-3-y]-4-
hydroxycoumarin (2d). Yield 46%, mp. 247-250°C. HRMS (ESI), m/z: 447.0945
+
+
(
M+K) (calcd for C H N O K : 447.0953). MS (ES+) calcd for C H N O m/z:
22 20 2 6 22 20 2 6
1
4
08.13, found m/z: 408.41. H NMR (DMSO-d ), δ (ppm): 1.30 (t, 3H, OCH CH ,
6 2 3
3
J=7.1 Hz); 2.30 (s, 3H, COCH ); 3.30-3.50 (m, 1H, Н (19)); 3.90-4.05 (m, 3H,
3
A
3
3
Н (19), OCH CH ); 5.38 (dd, 1H, H(12), J=4.2 Hz, J=11.9 Hz); 6.55-6.84 (m, 3H,
B
2
3
3
H(14,17,18)); 7.37-7.51 (m, 2H, H(6,8)); 7.75 (t, 1H, H(7), J=7.9 Hz); 8.01 (dd, 1H,
3
4
H(5), J=7.9 Hz, J=1.2 Hz); 8.86 (br. signal, 1H, OH (phenyl)); 13.39 (br. signal, 1H,
1
3
OH (coumarinyl)). С NMR (DMSO-d ), δ (ppm): 14.7; 21.9; 45.2; 57.5; 64.0; 96.1;
6
1
11.6; 114.8; 115.5; 116.5; 117.7; 124.1; 124.7; 132.8; 134.2; 146.1; 146.7; 152.7;
55.4; 159.7; 166.1; 166.7.
1
2
.6. The synthesis of pyrazolines 3a-c
A 4-fold excess (mol) of hydrazine in the form of an 85% solution of hydrazine hydrate
is added with stirring to a hot solution or suspension of 0.96 mmol of 4-hydroxy-3-
cinnamoylcoumarin in ethanol (15 ml). The reaction mixture was refluxed for 3 hours.
After cooling, the precipitate formed was filtered off and recrystallized from ethanol.
4
-Hydroxy-3-(5-phenyl-4,5-dihydro-1H-pyrazol-3-yl)coumarin (3a). Yield 34%,
mp. 167-168°C (lit. [48] mp. 168°C). MS (ES+) calcd for C H N O m/z: 306.10,
1
8
14
2
3
found m/z: 306.32.

4
-Hydroxy-3-[5-(4-methylphenyl)-4,5-dihydro-1H-pyrazol-3-yl]coumarin
(3b).
+
Yield 49%, mp. 219-220°C. HRMS (ESI), m/z: 321.1231 (M+H) (calcd for
+
C H N O H : 321.1234). MS (ES+) calcd for C H N O m/z: 320.12, found m/z:
19
16
2
3
19 16
2
3
1
3
4
2
7
20.20. H NMR (DMSO-d ), δ (ppm): 2.29 (s, 3H, CH ); 3.30-3.40 (m, 1H, Н (19));
6 3 A
2
3
3
.07 (dd, 1H, Н (19), J=18.6 Hz, J=9.8 Hz); 4.82 (t, 1H, Н(12), J=9.8 Hz); 7.17 (d,
B
3
H, H(15,17), J=7.6 Hz); 7.24-7.33 (m, 5H, H(6,8,11,14,18)); 7.58-7.63 (m, 1H, H(7));
3
4
13
.93 (dd, 1H, H(5), J=7.9 Hz, J=1.5 Hz); 13.36 (br.signal, 1H, OH). С NMR
(
DMSO-d ), δ (ppm): 20.6; 43.8; 58.4; 91.5; 116.4; 120.0; 123.6; 125.2; 126.5 (2C);
6
1
29.1 (2C); 133.5; 136.7; 137.9; 153.4; 160.3; 161.7; 176.2.
4
-Hydroxy-3-[5-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol-3-yl]coumarin (3c).
Yield 60%, mp. 194-195°C (lit. [49] mp. 196-198°C). MS (ES+) calcd for C H N O
4
19
16
2
m/z: 336.11, found m/z: 336.33.
2
.7. The synthesis of N-formylpyrazolines 4a-c
A mixture of formic acid (3.6 ml) and acetic anhydride (7.2 ml) was stir for 1.5 hours at
room temperature. Then mixture was cooled on ice bath and compound 3 (1.8 mmol)
was added. The reaction mixture was stirred for 0.5 hours when cooled, and then for 1
hour at room temperature. The resulting precipitate was filtered off and recrystallized
from ethanol.
3
-(4-Hydroxycoumarin-3-yl)-5-phenyl-4,5-dihydro-1H-pyrazole-1-carbaldehyde
+
(
4a). Yield 37%, mp. 254-256°C. HRMS (ESI), m/z: 335.1021 (M+H) (calcd for
+
C H N O H : 335.1026). MS (ES+) calcd for C H N O m/z: 334.10, found m/z:
19
14
2
4
19 14
2
4
1
2
3
3
34.27. H NMR (DMSO-d ), δ (ppm): 3.40 (dd, 1H, Н (19), J=19.0 Hz, J=4.6 Hz);
6 A
2
3
3
4
.06 (dd, 1H, Н (19), J=19.0 Hz, J=11.9 Hz); 5.47 (dd, 1H, H(12), J=4.6 Hz,
B
3
J=11.9 Hz); 7.21-7.49 (m, 7H, H(6,8,14-18)); 7.70-7.80 (m, 1H, H(7)); 8.00 (dd, 1H,
3
4
13
H(5), J=7.9 Hz, J=1.2 Hz); 9.02 (s, 1H, CHO). С NMR (DMSO-d ), δ (ppm): 45.6;
6
5
1
3
6.7; 95.7; 115.1; 116.5; 124.2; 124.6; 125.7 (2C); 127.5; 128.7 (2C); 134.2; 141.0;
52.7; 156.4; 159.8; 159.9; 166.3.
-(4-Hydroxycoumarin-3-yl)-5-(4-methylphenyl)-4,5-dihydro-1H-pyrazole-1-
+
carbaldehyde (4b). Yield 48%, mp. 213-215°C. HRMS (ESI), m/z: 349.1180 (M+H)
+
(
calcd for C H N O H : 349.1183). MS (ES+) calcd for C H N O m/z: 348.11,
2
0
16
2
4
20 16
2
4

1
found m/z: 348.32. H NMR (DMSO-d ), δ (ppm): 2.27 (s, 3H, CH ); 3.36 (dd, 1H,
6
3
2
3
2
3
Н (19), J=18.9 Hz, J=4.6 Hz); 4.04 (dd, 1H, Н (19), J=18.9 Hz, J=11.9 Hz); 5.43
A
B
3
3
(
dd, 1H, H(12), J=4.6 Hz, J=11.9 Hz); 7.09-7.27 (m, 4H, H(14,15,17,18)); 7.40-7.49
3
4
(
m, 2H, H(6,8)); 7.71-7.78 (m, 1H, H(7)); 8.00 (dd, 1H, H(5), J=7.9 Hz, J=1.4 Hz);
1
3
9
4
1
.00 (s, 1H, CHO); 13.07 (br. signal, 1H, OH). С NMR (DMSO-d ), δ (ppm): 20.6;
6
5.5; 56.5; 95.8; 115.0; 116.5; 124.2; 124.7; 125.7 (2C); 129.2 (2C); 134.2; 136.8;
38.0; 152.7; 156.4; 159.7; 159.8; 166.1.
3
-(4-Hydroxycoumarin-3-yl)-5-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazole-1-
+
carbaldehyde (4с). Yield 40%, mp. 206-208°C. HRMS (ESI), m/z: 387.0951 (M+Na)
+
(
calcd for C H N O Na : 387.0951). MS (ES+) calcd for C H N O m/z: 364.11,
2
0
16
2
5
20 16
2
5
1
2
found m/z: 364.35. H NMR (DMSO-d ), δ (ppm): 3.35 (dd, 1H, Н (19), J=19.0 Hz,
6
A
3
2
3
J=4.9 Hz); 3.71 (s, 3H, OCH ); 4.00 (dd, 1H, Н (19), J=19.0 Hz, J=11.9 Hz); 5.39
3
B
3
3
3
(
dd, 1H, H(12), J=4.9 Hz, J=11.9 Hz); 6.89 (d, 2H, H(15,17), J=8.6 Hz); 7.18 (d, 2H,
3
H(14,18), J=8.6 Hz); 7.35-7.48 (m, 2H, H(6,8)); 7.66-7.77 (m, 1H, H(7)); 7.98 (dd,
3
4
13
1
4
1
H, H(5), J=7.9 Hz, J=1.2 Hz); 8.93 (s, 1H, CHO). С NMR (DMSO-d ), δ (ppm):
6
5.9; 55.4; 56.5; 95.8; 114.4 (2C); 114.9; 116.7; 124.6; 125.0; 127.4 (2C); 133.3;
34.5; 153.0; 153.6; 156.9; 158.6; 158.9; 160.1.
2
.8. Fabrication of polymer thin films
The PMMA, PVP and SBS polymer thin films were obtained by slow evaporation (24
h at 20 ºC) of a chloroform solution containing 100 mg of the corresponding polymer
matrix and 1 mg of the selected compound.
3
3
. DISCUSSION AND RESULTS
.1. Synthesis and characterization
The synthesis of N-acylpyrazolines – coumarin derivatives has been previously reported
starting both from 3-cinnamoylcoumarins and from 3-(3-pyrazolinyl)coumarins [46-51].
Syntheses involving 3-cinnamoylcoumarins were carried out with an excess of
hydrazine hydrate when heated both in acetic acid [46,47] and in propionic acid [47].
Thus, N-acetylpyrazolines as well as N-propionylpyrazolines have been obtained with a
yield up to 67-80% [47].

Similarly, we obtained N-acetylpyrazolines 1a-c and 2a-d by the reaction of 3-
cinnamoylcoumarins with an excess of hydrazine hydrate in glacial acetic acid (Scheme
1
). The synthesis of the 3-cinnamoylcumarins has been earlier reported [52-55].
Scheme 1. Synthesis of N-acetylpyrazolines
The structures of the new N-acetylpyrazolines (1c, 2a-d) were confirmed by NMR
spectroscopy and mass spectrometry. The melting points of compounds 1a and 1b were
refined after purification by recrystallization, and their structures were also confirmed by
the mass and NMR spectra (see the supporting information).
N-Formylpyrazolines (4a-c) were also obtained with use of mixed anhydride of formic
and acetic acids, then isolated and characterized (Scheme 2).
OH
O
NH
OH
N
NH NH
H O
2
2
2
R2
EtOH, reflux
R1
O
O
R2
R1
O
O
3
a-c
1
2
3
3
3
a: R = R = H (yield 34%);
1
2
b: R = H, R = Me (yield 49%);
1
2
c: R = H, R = OMe (yield 60%)
HCOOAc, RT
O
N
N
OH
R2
R1
O
O
4a-c
1
2
4
4
4
a: R = R = H (yield 37%);
1
2
b: R = H, R = Me (yield 48%);
1
2
c: R = H, R = OMe (yield 40%)
Scheme 2. Synthesis of N-formylpyrazolines

The structures of 4a-c were confirmed by NMR spectroscopy and mass spectrometry
see the supporting information).
When analyzing NMR spectra of the DMSO-d -solutions, the new N-acylpyrazolines
(
6
2
a-d and 4a-c have been found to exist mostly in the tautomeric imino-form. However,
the presence of minor amount (≤ 10%) of their second tautomeric enamino-form can be
also suggested (Scheme 3):
Scheme 3.
1
For example, in the H NMR spectrum of compound 2b in a DMSO-d6 solution at room
temperature, a slight doubling of their signals is observed for protons H(12), H (19),
B
H(14,18), and H(15,17). This is evidenced by low-intensity signals at 4.18 m. d., 5.62
m. d., 6.96 m. d. and 7.25 m. d. Heating of the solution to 90°C leads to the fusion of
paired signals of the above protons since the mutual transition of tautomeric forms is
1
accelerated. The H NMR spectrum and the two dimensional COSY spectrum of the 2b
recorded at 90 ° C are shown in the Supporting information. Tautomeric transformations
of new N-acylpyrazolines 2a-d and 4a-c are studied now in more detail and the results
will be published elsewhere.
The proton signal Н (19) of most of the studied N-acylpyrazolines, overlaps with the
A
solvent water signal. The values of the spin-spin interaction constants for this signal
were determined from signals Н (19) and Н(12). The values of the chemical shifts of
B
the proton Н (19) were determined from the HSQC spectra (see Supporting
A
information). The OH proton signals for compounds 4a and 4c are broadened to the
zero line due to fast exchange processes with water from the solvent.
The compounds 1c, 2a-d and 4a-c are new ones. Melting points of the compounds 1a
and 1b have been corrected.

3
.2. Photophysical behavior
Most of the new compounds exhibit luminescence properties both in solution and in the
solid state. Table 1 collects the photophysical data of all compounds, and Fig. 1 displays
the UV-Vis and emission spectra for the prototype compounds 1a, 1c and 2a. The
photophysical characterization of the remaining compounds is shown in Fig. S57.
The UV-Vis spectra of compounds 1a, 1b, 2a-d, 4a-c in chloroform solution show two
or three absorption bands in the range of 230 – 400 nm that can be attributed to π···π*
transitions between aromatic groups, the maximum generally appearing at around 360–
3
2
66 nm. In the particular case of 1c, the absorption bands are recorded ranging between
30 – 500 nm, with the maximum centered at 440 nm.
After excitation at the appropriated wavelength, most of the compounds emit a highly-
intense bluish light in chloroform solution, and the corresponding emission spectra
appear centered at around 473 nm for 1a and 1b, and at ca. 430-440 nm for 2a-d, 4a-c
(Table 1). Obviously, the presence of a diethyl amine group in 1c generates a red-shift
of the emission band, which appears at 501 nm.
Fig. 1 Photophysical characterization of compounds (a) 1a, (b) 1c and (c) 2a in CHCl solution
3
-5
(
1 x 10 M), in the solid state and in film. The insets show images of the CHCl solutions of
3
each compound taken under UV light (λexc. = 365 nm).
The luminescence behavior of these compounds was also studied in the solid state and
in thin films obtained by dip-coating. All the compounds behave as luminescent
materials with the exception of 2d. As observed in Table 1 and Fig. 1, the emission
bands recorded for 1a-c are remarkably red-shifted in comparison with those recorded
in solution, and the compounds emit a yellowish light, which suggests the formation of
intermolecular π···π interactions. It is also interesting to note that the emission bands in
the solid state and in film are practically coincident for all the compounds, indicating no

changes in the molecular packing. However, the solid-state fluorescence band of 1a
displays a small red-shift of ca. 23 nm respects to that recorded in film. The origin of
this shift can be associated with a reorganization of molecules, and it is a clear
indication of the structural order and the strength of the contacts established [18]. Thus,
intermolecular π···π interactions are weak in solution (λ = 473 nm), whereas they are
em
well-stablished in thin film (λ = 513 nm) and in the solid state (λ = 536 nm), where
em
em
the degree of molecular order is higher.
Table 1. Photophysical data of compounds 1a-c, 2a-d, 4a-c.
max
4
-1
-1
a
max
a
max
a
max
a
b
Comp.λabs [nm] (ε/10 [Lmol cm ]) λ
[nm] λem(solid) [nm] λem (film) [nm] ΦF
em
1
1
1
2
2
2
2
4
4
a
b
c
244 (1.2), 366 (1.3)
473
536
513
0.53
0.50
0.40
0.17
0.20
0.06
0.09
0.07
0.06
0.07
244 (1.8), 366 (1.6)
473
505
505
242 (2.1), 278 (1.6), 440 (5.0)
244 (1.5), 256 (1.5), 358 (2.0)
244 (2.2), 256 (2.1), 358 (2.7)
244 (2.1), 259 (1.9), 358 (2.6)
244 (3.6), 258 (3.2), 359 (4.2)
245 (2.2), 354 (2.2)
501
544
542
a
b
c
439, 458
440, 459
440
447, 473
443, 469
441, 466
NA
450
445
442, 464
NA
d
a
b
c
440
431
436, 459
441, 461
444, 468
449
433, 454
432, 450
449
2
44 (1.9), 257 (1.6), 356 (2.1)
4
244 (3.1), 355 (1.9)
448
a
b
Estimated error: ± 1 nm. Estimated error: ± 5 %.
To confirm that intermolecular contacts are responsible of the changes observed in the
emission spectra of the pyrazoline compounds, several polymer supports were prepared
by using PMMA, PVP and SBS polymers as matrixes. Compound 1a was selected as
the dopant agent since its luminescence properties shows remarkable changes in
solution and in the solid state. The dispersion of 1a in the polymer matrix should totally
separate the molecules and prevent any short contact among them if the concentration of
the dye is low enough. Thus, the three polymers were doped with only just 1% 1a.
Fig. 2 shows the emission spectra of these polymer supports together with the
corresponding ones in film and in the solid state. As expected, the fluorescence band is
blue-shifted in all cases (λem = 468 – 472 nm), which is in agreement with the results
obtained in solution (λem = 473 nm). This demonstrates that the formation of π···π
interactions causes a red-shift of the fluorescence emission in these systems.

Fig. 2. (a) Normalised emission spectra of the polymer supports doped with 1a.
b,c) Images of the fluorescent and flexible PMMA support doped with 1a taken upon UV light
by excitation at 365 nm.
(
3
.3. Thermo-, mechano-, solvato- and vapochromic properties
Since the establishment of intermolecular π···π interactions generates remarkable
changes in the photophysical nature of these compounds, it is possible that the packing
of molecules in the solid state can be modified by the application of certain external
stimuli, which could induce a fluorescence response in the materials. On the basis of
this hypothesis, we have investigated the effect of some stimuli that usually cause the
formation and rupture of intermolecular contacts, such as the temperature, the
mechanical grinding or the presence of certain solvents and vapors [13,15].
Fig. 3a displays the temperature-dependent emission spectra of 1a. Note that the
yellowish emission is progressively quenched by increasing the temperature from 25 to
1
30 ºC. This is a usual behavior on molecular materials associated with the existence of
thermally-activated non-radiative processes. However, by further heating the sample,
the intensity of the fluorescence band increases and, concomitantly, the emission
maximum is blue-shifted from 536 to 503 nm. The rupture of the intermolecular π···π
interactions by increasing the temperature probably originates this chromic response
that is able to suppress the effect of the non-radiative processes (Fig. 3b). Thus, 1a
adopts a new packing and, when it is cooled back to room temperature, the intensity of
the emission band continues to increase until almost doubling its initial value (Fig. S58
and 4).

Fig. 3. (a) Emission spectra of 1a recorded in the solid state upon heating.
b) Images of 1a at selected temperatures taken under UV light (λexc = 365 nm).
(
6
Initial
After heat treatment
6
5
4
3
2
1
10
6
10
6
10
6
10
6
10
6
10
0
4
00 450 500 550 600 650 700
λ
/nm
Fig. 4. Solid-state emission spectra of 1a as prepared (blue line) and after heat treatment (black
line).
The analogous compounds 1b and 1c were subjected to thermal treatments under the
same conditions since their luminescence properties also exhibit remarkable changes in
solution and in the solid state. In both cases it was observed a total quenching of the

fluorescence during the heating cycle (Fig. 5a and S59). On cooling, the compounds did
not achieve to recover the initial emission intensity, this feature suggesting the existence
of a partial decomposition as a result of the high temperatures reached (Fig. 5b). By
contrast, compounds 2a and 2b showed a slight boost of the emission intensity with the
increase of the temperature, which was maintained by cooling back to room temperature
(Fig. 5c-f).
6
6
3
10
4 10
6
(
a)
(b)
(c) 3.2 10
6
3.5 10
6
6
2.8 10
2
1
.5 10
30 ºC
1
00 ºC
200 ºC
25 ºC
6
3
10
6
2
.4 10
6
2
10
6
2
.5 10
2 10
6
6
6
200 ºC
5 ºC
6
.5 10
2 10
1.6 10
1
75 ºC
6
1.5 10
2
1.2 10
6
6
1
5
10
6
5
1
5
10
8 10
5
10
5
5
10
4 10
0
0
0
4
00 450 500 550 600 650 700
400 450 500 550 600 650 700
400 450 500 550 600 650 700
λ
/nm
λ
/nm
λ/nm
d) 3 106
Initial
After heat treatment
(e) 3.5 106
(f) 5 10
6
(
6
Initial
After heat treatment
Initial
After heat treatment
6
3 10
2.5 10
6
4
10
6
6
2.5 10
2
10
6
6
3 10
2
10
6
1
.5 10
6
1
.5 10
6
2
10
6
1
5
10
6
1
5
10
6
5
1 10
10
5
10
0
0
0
4
00 450 500 550 600 650 700
400 450 500 550 600 650 700
400 450 500 550 600 650 700
λ
/nm
λ
/nm
λ/nm
Fig. 5. Solid-state emission spectra at variable temperature for compounds (a) 1b, (b) 2a and (c)
2
b, upon heating. (d,e,f) Emission spectra of 1b, 2a and 2b, respectively, as prepared and after
heat treatment, recorded at room temperature.
Mechanical grinding is another process that allows breaking weak contacts between
molecules [15]. Thus, all the compounds were scrapped with a mortar and pestle and
then, the emission spectra were recorded in order to analyze the effect of this external
stimulus. Among all of them, only 1a showed a remarkable mechanochromic behavior,
as demonstrated in Fig. 6a-c. The yellowish fluorescence turns greenish after grinding
the sample during a few seconds. Note in Fig. 6a how the emission maximum is blue-
shifted from 536 to 513 nm, which evidences the rupture of π···π interactions. It is also
interesting to observe the presence of a small shoulder at ca. 472 nm, both in the
spectrum obtained for the initial powder, and in the spectrum recorded after the
mechanical grinding. The origin of this peak seems to be associated with a packing of
molecules in which they do not interact with each other. To confirm this fact, the
grinded sample was heated at ca. 100 ºC and then, it was again cooled back to room

temperature. Now, the shoulder at 472 nm appears as the emission maximum, so that
thermal treatment of the sample causes the rupture of the stronger π···π interactions that
resisted to the previous mechanical grinding and as a result, the greenish emission of 1a
turns bright blue (Fig. 6d).
Fig. 6. (a) Solid-state normalised emission spectra of 1a upon the application of several external
stimuli. (b,c,d) Images of 1a (b) as prepared, (c) upon mechanical grinding, and (d) after
heating.
A similar behavior than that found by the effect of temperature is also originated when
the grinded sample is exposed to certain solvents or to their vapours. For vapochromic
studies, we fabricated two closed systems whose atmospheres were saturated with the
corresponding vapour, which was generated from 5-10 mL of the solvent. The solvent
molecules can be intercalated between the 1a ones, so causing the rupture of the
intermolecular π···π interactions that are still present in the material. As a result, the
emission intensity of the shoulder located at 472 nm is increased slightly with the
increase of solvent polarity but enough for the fluorescence of 1a turns bluish (Fig. 7
and S60).

As prepared
After grinding
Acetonitrile
Methanol
1
.8
.6
.4
.2
0
Acetone
Chloroform
Dichloromethane
THF
Hexane
Ciclohexane
Ethanol
0
0
0
0
Ethyl acetate
Dietyl ether
4
00 450 500 550 600 650 700
λ
/nm
Fig. 7. Vapochromic properties of 1a in the presence of acetonitrile, methanol, acetone,
chloroform, dichloromethane, tetrahydrofuran, hexane, cyclohexane, ethanol, ethyl acetate and
diethyl ether.
Regarding to the compounds 1b,c and 2a,b, no remarkable changes were detected in
their fluorescence properties upon the application of mechanical grinding, as
demonstrated in Fig. S61.
3
.4. Ionochromic behavior
Another external stimulus that can modify the luminescence properties of organic
2
+
2+
2+
compounds is the presence of metal cations such as Zn , Cd or Hg , among others.
Complexation can occur in solution and therefore, metal-to-ligand charge transfers can
be originated, so that these compounds may exhibit ionochromic properties.
To study the ionochromism of the synthesized pyrazolines, several titrations of 1a were
2
+
2+
2+
+
2+
2+
2+
carried out by the addition of small amounts of Zn , Ca , Cd , Ag , Ni , Cu , Co ,
2
+
3+
2+
2+
Hg , Tb , Fe and Pb ions. As a result of the interaction of the metal cations with
1
a, we could observe two different behaviors, as demonstrated in Fig. 8 and S62. On
2
+
2+
2+
one hand, the addition of Cd , Zn and Ca produces a blue-shift of the emission band
centered at 473 nm, as well as an increase of the fluorescence intensity (Fig. 9a-c). This
can be associated with the formation of metal-to-ligand charges transfers as a result of
the metal coordination. Note that the most remarkable increase of the fluorescence
2
+
emission is achieved after adding 10 equiv. of Ca .

I /a.u.
6
2
1
.5 10
1a
Hg2+
Zn2+
Cd2+
Fe2+
Pb2+
Co2+
Cu2+
Ni2+
Ca2+
Ag+
6
2
10
6
.5 10
6
1
5
10
5
10
0
4
10
460
510
560
610
λ
/nm
Fig. 8. Ionochromic behavior of compound 1a.
2
+
2+
2+
On the other hand, the presence of Hg , Fe and Pb causes a chelation enhanced
fluorescent quenching (CHEQ) effect (Fig. 9d-f), which is commonly observed for these
ions because of the heavy-atom effect. It is interesting to noteworthy that only the
2
+
addition of 3 equiv. of Hg originates a total quenching of the emission band, whereas
2
+
2+
8
and 15 equiv. of Pb and Fe are required to achieve a similar effect.
Non-remarkable changes in the initial emission of 1a were noted upon the addition of
+
2+
2+
2+
Ag , Ni , Cu and Co ions.

I /a.u.
I /a.u.
I /a.u.
6
2
10
6
(a)
(b)
2.5 10 (c)
2+
2+
2+
6
1a + 5 equiv Zn
1a
1
a + 6 equiv Cd
2 10
1a + 10 equiv Ca
6
6
2 10
1
.5 10
6
1a
1
.5 10
6
1
.5 10
1a
6
1
5
10
6
1
5
10
6
1
5
10
5
10
5
10
5
10
0
0
0
4
10
460
510
560
610
410
460
510
560
610
410
460
510
/nm
560
610
λ
/nm
λ
/nm
λ
I /a.u.
I /a.u.
I6/a.u.
1.6 10
6
6
1.6 10
1
1
1
.6 10
(d)
1a
(e)
1a
6
(f)
1a
6
1.4 10
6
1.4 10
.4 10
6
6
6
1.2 10
.2 10
1.2 10
6
6
6
1 10
1
8
6
4
2
10
1 10
2+
1
a + 15 equiv Fe
5
5
2+
5
8 10
10
1a + 3 equiv Hg
8 10
2+
1a + 8 equiv Pb
5
5
5
10
6 10
6 10
5
5
5
10
4 10
4 10
5
5
5
10
2 10
2 10
0
0
0
4
10
460
510
/nm
560
610
410
460
510
/nm
560
610
410
460
510
560
610
λ
λ
λ
/nm
2
+
2+
2+
2+
Fig. 9. Emission spectra of 1a upon the addition of (a) Cd , (b) Zn , (c) Ca , (d) Hg , (e)
2
+
2+
Fe , and (f) Pb metal cations.
3
.5. Powder X-Ray studies
The experimental and calculated diffraction profiles after the final bond-restrained
Rietveld refinement are shown on Fig. S55 and S56 (see the supporting information).
The crystal data, data collection and refinement parameters are given in Table 2.
Table 2. Crystal data for 1a and 2a.
1
a
2a
empirical formula
C H N O
C H N O
20 16 2 4
2
0
16
2
3
Mr
332.35
348.35
crystal system
Triclinic
Monoclinic
space group
P -1
P 2 /c
1
unit cell dimensions
a, Å
b, Å
c, Å
9.3137(10)
10.8089(12)
8.3672(8)
7.1258(7)
28.145(2)
8.5345(9)

o
α
β
,
95.685(14)
98.688(11)
97.139(15)
820.23(15)
2
90
o
,
103.577(17)
o
γ,
90
3
volume, Å
Z
1663.8(3)
4
-
3
D (Mg m )
1.346
1.391
x
-
1
µ, mm
0.748
0.810
o
2
θmin - 2θmax , ∆2θ ( )
5.00 – 80.00, 0.01
135/97
5.00 – 80.00, 0.01
147/103
no. params/restraints
R , R , R
0.0260, 0.0333, 0.0227
0.0351, 0.0460, 0.0192
p
wp
exp
The molecular structures are shown on Fig. 10 and 11, prepared with PLATON, [56] and
portion of the crystal packing of 1a is shown on Fig. 10, prepared with Mercury [57]. In
molecules 1a and 2a all bond lengths and angles are normal corresponding to those
found in the Cambridge Structural Database (ConQuest, version 2.0.4) [58] for related
compounds.
Fig. 10. The molecular structure of 1a, showing the atomic numbering and 50% probability
displacement spheres.

Fig. 11. The molecular structure of 2a, showing the atomic numbering and 50% probability
displacement spheres. Intramolecular O21–H21···N10 hydrogen bond is shown by dotted line
In 1a, two types of intermolecular interactions are observed. Specifically, there are π···π
interactions between the bicycles of two molecules related by inversion center (Fig. 12),
proved by short distance of 3.61(2) Å between the centroids of six-membered cycles,
Fig. 12. Centrosymmetric dimer in 1a formed by π-π interactions between the bicycles.
Pink circles denote the centroids of six-membered rings in the bicycles. H atoms
omitted for clarity.
i
i
and weak intermolecular C–H···O hydrogen bonds [C8···O20 3.386(12) Å, H8···O20
i
o
2
.46 Å, C8–H8···O20 , 174 ; (i) 1-x, -y, 2-z], which link the π···π dimers into columns

extended in [001] (Fig. 13). In both structures, the crystal packings are further stabilized
by the weak Van der Waals interactions.
Fig. 13. A portion of the crystal packing in 1a showing centrosymmetric dimer formed
by the weak intermolecular C–H···O hydrogen bonds (thin blue lines)
The hydroxy group in 2a is involved in formation of intramolecular O21–H21···N10
hydrogen bond (Fig. 13) with O21···N10 distance of 2.535(11) Å and O21–H21···N10
o
angle of 126 . In the 2a structure, there is no any hint for the π···π stacking, The
shortest distance between the centroids of six-membered cycles in the 2a dimer is equal
to 4.18(3) A.
Crystallographic data for 1a and 2a have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication CCDC nos. 1983112 and
1
983113, respectively. Copies of data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax: (44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
3
.6. Quantum chemical calculations
To get more understanding the role of the intermolecular π···π interactions in the
luminescence behavior of novel coumarin-based pyrazoline 1a, quantum chemical
calculations were performed using the software package for quantum chemical
calculation Orca version 4.1.1 [59], by TD DFT method, the B3LYP functional, in the
def2-TZVP basis [58,60-63]. The coordinates of the monomeric and dimeric forms of
1
a were taken from the results of X-Ray diffraction analysis.

The calculated absorption spectral characteristics for the monomer correlate well with
the experimental results (Table 3). The main absorption maximum for the monomer
according to the calculation results should be observed at 360-390 nm, which is a
consequence of the transition S → S .
0
1
Table 3. Comparison of experimental (solvent-toluene) and calculated electron absorption
spectral data of compound 1
Experimental
Calculated
Form
comp. 1a)
max
max
Assignment
λabs [nm]
λabs [nm]
(
4
-1
-1
(
ε/10 [L·mol ·cm ])
(f 0
osc
Monomer
Solid
371 (1.3)
379 (0.55)
HOМО → LUМО
Film
3
4
3
69 (0.73)
22 (0.25)
58 (1.05)
HOМО → LUМО+1
HOМО → LUМО
HOМО → LUМО+1
HOМО → LUМО
Dimer 1
Dimer 2
4
01 (0.00005)
As can be seen from the Table 3, for dimer 1, in which coumarin fragments are located
parallel to each other, providing effective intermolecular π···π interactions is
characterized by the presence of longer-wave absorption maxima, which is a
consequence of the interaction between the π-electron shells of two molecules (Fig. 14).
Shapes of the frontier MO-s involved into calculated long-wave electron transitions in
EAS of the dimer 1 are shown in the Fig. 14. One can see the distance between the
planes of two 1a molecules around 3.6 Å is well fitted to provide effective exciton
interactions that lead to red-shift of the electron absorption of the 1a in solid state.