The effect of the molecular structures of dicyanomethylene compounds on their supramolecular assembly, photophysical and electrochemical properties

Article abstract of DOI:10.1039/c3cp51957k

Two series of flexible dicyanomethylene compounds, specifically, class 1 and class 2 compounds, have been designed and synthesised. In class 1 compounds, the dicyanomethylene groups are separated by glycol chain spacers of different lengths, whereas, in class 2 compounds, the spacers are alkyl linkers of different lengths. The notion underlying the design of these compounds is that in class 1 molecules, the spacers contain donor oxygen atoms that could not only form hydrogen bonds during the course of crystal packing but also promote withdrawing effects that modify the photophysical and electrochemical properties of these molecules in solution; in contrast, these effects would be absent for class 2 molecules. However, this study revealed that, with respect to crystal packing, the size of the spacers and their even and odd numbers of atoms are more important than their chemical nature. All of the synthesised compounds exhibited blue emission in the solid state and in CH₂Cl₂ solutions. The photophysical and electrochemical properties of these compounds in solution were not significantly affected by the type and length of the spacer that was used in each molecule. In the solid state, however, the compound with the shortest spacer showed the highest Stokes shift. The electronic transitions for the synthesized compounds in solution were explained by density functional theory and time-dependent density functional theory calculations, which indicated that the methylene moieties control the properties of both classes of compounds and that the spacers do not conjugate with the end groups. These two series of flexible dicyanomethylene compounds could be utilised as molecular building blocks for the development of new solids with novel properties. the Owner Societies 2013.

Full text of DOI:10.1039/c3cp51957k

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The effect of the molecular structures of
dicyanomethylene compounds on their supramolecular
assembly, photophysical and electrochemical
properties†
Cite this: Phys. Chem. Chem. Phys., 2013,
15, 13013
a
a
a
´
Catiu´cia R. M. O. Matos, Fabio S. Miranda, Jose W. de M. Carneiro,
b
a
´
Carlos B. Pinheiro and Celia M. Ronconi*
Two series of flexible dicyanomethylene compounds, specifically, class 1 and class 2 compounds, have been
designed and synthesised. In class 1 compounds, the dicyanomethylene groups are separated by glycol chain
spacers of different lengths, whereas, in class 2 compounds, the spacers are alkyl linkers of different lengths.
The notion underlying the design of these compounds is that in class 1 molecules, the spacers contain donor
oxygen atoms that could not only form hydrogen bonds during the course of crystal packing but also
promote withdrawing effects that modify the photophysical and electrochemical properties of these
molecules in solution; in contrast, these effects would be absent for class 2 molecules. However, this study
revealed that, with respect to crystal packing, the size of the spacers and their even and odd numbers of
atoms are more important than their chemical nature. All of the synthesised compounds exhibited blue
emission in the solid state and in CH2Cl2 solutions. The photophysical and electrochemical properties of these
compounds in solution were not significantly affected by the type and length of the spacer that was used in
each molecule. In the solid state, however, the compound with the shortest spacer showed the highest Stokes
shift. The electronic transitions for the synthesized compounds in solution were explained by density
functional theory and time-dependent density functional theory calculations, which indicated that the
methylene moieties control the properties of both classes of compounds and that the spacers do not
conjugate with the end groups. These two series of flexible dicyanomethylene compounds could be utilised
as molecular building blocks for the development of new solids with novel properties.
Received 8th May 2013,
Accepted 31st May 2013
DOI: 10.1039/c3cp51957k
www.rsc.org/pccp
In principle, the introduction of chemically or electrostatically
active regions into organic ligands can govern the formation of
Introduction
The crystal engineering of new structures with target properties
is a challenging research area in modern chemistry.1 In the
field of coordination chemistry, particularly with respect to the
study of coordination polymers, the design and preparation of
molecular building blocks (MMBs) with covalent frameworks
that incorporate the capacity to achieve a directed connectivity
between subunits for the assembly of supramolecular structures is
the key approach for obtaining desired structures and functions.2,3
supramolecular arrays. Several strategies to obtain predetermined
ordered structures have been developed, such as the directional-
bond approach,4,5 the symmetry interaction model6,7 and methods
that utilise reticular chemistry.8 These strategies typically function
best if rigid ligands and preferred coordination motifs of the metal
cations are used to improve the predictability of supramolecular
structures.8 However, in practice, many subtle considerations, such
as the solvent system,9 the temperature,10 the nature of the counter
anions,11 the coordination properties of the metal cations12 and the
functionality of the ligands13 can also affect the self-assembly of
these supramolecular architectures.
a
´
Instituto de Quımica, Universidade Federal Fluminense, Campus do Valonguinho,
´
CEP 24020-141, Niteroi, RJ, Brazil. E-mail: cmronconi@id.uff.br;
Fax: +55 21 26292136; Tel: +55 21 26292164
The structures formed between flexible ligands and metals
are less predictable than the structures produced between rigid
ligands and metals because of the conformational freedom of
flexible ligands.10,14 Polydentate flexible ligands have been
extensively used for the construction of polynuclear compounds
b
´
ˆ
Departamento de Fısica, ICEX, Universidade Federal de Minas Gerais, Av. Antonio
Carlos, 6627 Pampulha, CEP 31270-901, Belo Horizonte, MG, Brazil
† Electronic supplementary information (ESI) available. CCDC 908002–908004
and 929360. For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/c3cp51957k
c
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and for the transmission of magnetic exchanges because of their Scheme 1. Compounds 3 and 4 were obtained through the
versatile coordination modes and conformations.15,16 Therefore, reaction of 1 equiv. of the appropriate bis-tosylate with 2 equiv.
one interesting research direction involves attempting to achieve of salicylic aldehyde in dry MeCN in the presence of K2CO3.
a better understanding of the ways in which the molecular Compounds 7, 8 and 9 were obtained through the addition of
properties of flexible ligands can affect the supramolecular 1 equiv. of dibromoalkanes to 2 equiv. of salicylic aldehyde in
structures and properties of compounds.
dry MeCN in the presence of K2CO3. Addition of dinitriles to the
To obtain insights into this topic, we have synthesised a dialdehydes in the presence of NH4OAc by mechanochemical
series of flexible dicyanomethylene compounds and have inves- reactions, without solvent, yielded compounds 5, 6, 10, 11 and
tigated their crystallisation and optical properties in the solid 12 as yellow crystalline powders. The compounds were fully
state and in solution. This study was conducted in an effort to characterised through both 1H and 13C nuclear magnetic
understand their supramolecular assembly in the solid state resonance (NMR), Fourier transform infrared (FTIR) spectro-
and the relationship with their photophysical properties in both scopy (see ESI,† Fig. S1–S15) and elemental analysis.
solid state and solution. This understanding will be applied to
X-ray crystallography
the design of new solids with desirable physical and chemical
properties. The synthesised compounds include in their struc-
tural components: (i) two dicyanomethylene moieties that are
symmetrically distributed on the molecule and separated by (ii)
highly flexible (–CH2OCH2–)n or (–CH2CH2–)n spacers of different
lengths. The dicyanomethylene groups are interesting because
they can act as p-acceptors and also present remarkable coordi-
nation properties which make these compounds potentially
useful in the field of coordination polymers.10,17–19 The oxygen
atom in the ligands that contain glycol spacers can also behave as
a donor atom in the formation of hydrogen bonds. The com-
pounds with glycol chain spacers of different lengths will be
referred to as class 1 compounds whereas in class 2 compounds,
the spacers are alkyl linkers of different lengths. All of the
synthesised compounds have interesting photochemical and
electrochemical properties. We also discuss a detailed theoretical
investigation of the electronic properties in the ground and
excited states that utilises density functional theory (DFT) and
time-dependent DFT (TD-DFT).
X-ray diffraction measurements were performed on compounds 5, 6,
10, 11 and 12 at temperatures indicated in Table 1. For compounds
5, 10, 11 and 12, data collection and structure refinement processes
of the X-ray diffraction experiments are summarised in Table 1.
Compound 6 provided single crystals of poor quality and X-ray
diffraction data were used only to identify its molecular shape.
Compounds 5 and 11 possess the same number of atoms
(seven) in their spacers; compound 5 contains one oxygen atom
in the middle of its spacer, whereas compound 11 contains a
carbon atom at this location. In principle, this extra oxygen
atom in compound 5 could serve as a donor atom to form
hydrogen bonds. However, 5 and 11 crystallize in the same
space group, P2/c, and both possess the same molecular
geometry and crystal packing as evidenced by the juxtaposition
of the structures (see ESI,† Fig. S16). In both compounds, the
three-dimensional packing involves three different kinds of
hydrogen-bond-like short contacts, C–Hꢀ ꢀ ꢀN, labelled I, II and
III (Fig. 1 and Table 2; see also ESI,† Fig. S17). The short contact
I involves the hydrogen atom of the methylene group and the
N atom of the cyano group. Interaction I regulates compounds
5 and 11 into end-to-end assemblies. In the short contact II, the
hydrogen atom of the benzene ring carbon and N atom of the
Results and discussion
Synthesis
The synthetic routes for obtaining compounds 5, 6, 10, 11 and cyano group are involved. Finally, the short contact III arises
12 and their intermediates 3, 4, 7, 8 and 9 are outlined in from an electrostatic interaction between the N atom of the
Scheme 1 The synthesis of dicyanomethylene compounds.
c
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Table 1 Crystallographic data and structure refinement
Identification code
5
10
11
12
Empirical formula
Formula weight
Temperature (K)
C24H18N4O3
410.42
123(2)
C12H9N2O
197.21
140(2)
C25H20N4O2
412.48
293(2)
C26H22N4O2
422.48
120(2)
Wavelength (Å)
Crystal system, space group
Unit cell dimensions (Å, 1)
1.54178
0.71073
Triclinic, P1
a = 4.1838(3), b = 9.5667(6), a = 27.4442(16), b =
c = 12.2486(8), a =
96.676(5), b = 91.076(5),
g = 93.139(6)
486.04(6)
2, 1.348
0.089
0.71073
Monoclinic, P2/c
0.71073
Monoclinic, P21/n
a = 4.3137(2), b = 9.9807(4),
%
Monoclinic, P2/c
a = 27.6303(10), b =
4.1076(2), c = 19.1097(6),
b = 110.163(3)
4.3997(3), c = 19.1278(12), b = 94.618(3), c = 25.5817(8)
b = 110.361(6)
Volume (Å3)
2035.92(14)
2165.3(2)
4, 1.265
0.082
1097.81(8)
2, 1.278
0.083
Z, calculated density (Mg mꢁ3) 4, 1.339
Absorption coefficient (mmꢁ1) 0.741
F(000)
Crystal size (mm)
y range for data collection (1) 2.46 to 66.61
856
206
872
444
0.45 ꢂ 0.15 ꢂ 0.10
0.61 ꢂ 0.27 ꢂ 0.10
0.64 ꢂ 0.21 ꢂ 0.10
0.48 ꢂ 0.38 ꢂ 0.15
2.15 to 26.37
2.97 to 25.19
2.19 to 26.37
Limiting indices
ꢁ32 r h r 31; ꢁ4 r k r 4; 5 r h r 5, ꢁ11 r k r 10, ꢁ32 r h r 32; ꢁ4 r k r 5; ꢁ5 r h r 5; ꢁ12 r k r 12;
ꢁ22 r l r 22
22 251/3559, [R(int) =
0.0336]
ꢁ15 r l r 15
ꢁ22 r l r 21
ꢁ31 r l r 31
17 312/2259, [R(int) =
0.0247]
Reflections collected/
independent
5801/1985, [R(int) = 0.0381] 15 433/3447, [R(int) =
0.0569]
Completeness
Max. and min. transmission
Refinement method
(ymax = 66.611), 99.5%
1.00 and 0.860
Full-matrix least-squares
on F2
(ymax = 26.371), 99.7%
0.993 and 0.970
Full-matrix least-squares
on F2
(ymax = 25.191), 88.1%
0.990 and 0.954
Full-matrix least-squares
on F2
(ymax = 26.371), 100.0%
0.988 and 0.964
Full-matrix least-squares
on F2
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices
3559/0/282
1985/0/136
1.057
3447/0/282
1.030
2259/0/145
1.039
1.065
R1 = 0.0434, wR2 = 0.1136 R1 = 0.0464, wR2 = 0.1126 R1 = 0.0556, wR2 = 0.1366 R1 = 0.0366, wR2 = 0.0916
[I > 2s(I)]
R indices (all data)
R1 = 0.0441, wR2 = 0.1151 R1 = 0.0678, wR2 = 0.1303 R1 = 0.0792, wR2 = 0.1550 R1 = 0.0400, wR2 = 0.0942
Table 2 Short contacts [measured in Å and 1]
Type of
Angle inter-
d
d
d
Compounds D–Hꢀ ꢀ ꢀAa
(D–H) (Hꢀ ꢀ ꢀA) (Dꢀ ꢀ ꢀA) (DHA) action
5
C4–H4ꢀ ꢀ ꢀN2i
0.95 2.53
C16–H16ꢀ ꢀ ꢀN4ii 0.95 2.51
C19–H19ꢀ ꢀ ꢀN1iii 0.95 2.58
C11–H11Bꢀ ꢀ ꢀN1iv 0.99 2.74
3.413(3) 154.2
3.389(3) 153.1
I
I
3.402(3) 144.5 II
3.493(3) 132.8 III
10
11
C4–H4ꢀ ꢀ ꢀN2v
0.95 2.64
3.545(2) 158.4
I
C11–H11Aꢀ ꢀ ꢀN1vi 0.99 2.70
3.491(2) 137.5 III
C4–H4ꢀ ꢀ ꢀN2i
0.93 2.64
3.502(6) 154.4
3.459(5) 151.7
I
I
C16–H16ꢀ ꢀ ꢀN4ii 0.93 2.61
C19–H19ꢀ ꢀ ꢀN1iii 0.93 2.63
C11–H11bꢀ ꢀ ꢀN1iv 0.97 2.77
C12–H12Bꢀ ꢀ ꢀN2vii 0.99 2.60
3.436(6) 145.1 II
3.607(6) 144.7 III
3.434(2) 141.4 III
12
a
The following symmetry transformations were used to generate
equivalent atoms: (i) ꢁx + 1, ꢁy, ꢁz + 1; (ii) ꢁx, ꢁy + 1, ꢁz; (iii) x, y
ꢁ 1, z; (vi) x, 1 ꢁ y, 0.5 ꢁ z; (v) ꢁx ꢁ 1,ꢁy + 1, 1 ꢁ z + 1; (vi) x ꢁ 1, y ꢁ 1, z
and (vii) ꢁx + 1, ꢁy + 1, ꢁz.
Fig. 1 Representation of the crystal packing of compound 5. Oxygen atoms are
indicated in red and nitrogen in blue. Displacement ellipsoid parameters are
drawn at the 50% probability level. Symmetry codes (i) =ꢁx, y, 0.5 ꢁ z; (ii) =x, 1 ꢁ
y, 0.5 + z; (iii) =x, 2 ꢁ y, 0.5 + z; (iv) x, 1 + y, z.
%
Compound 10 crystallises in a triclinic P1 space group. The
unit cell has a volume that is a quarter of that of the unit cells of
cyano group and the hydrogen atom of the carbon adjacent to 5 and 11. The three-dimensional packing involves the short
the oxygen atom of the spacer.
contacts I and III (Fig. 2 and Table 2).
The electrostatic potential surfaces were obtained for all
Compound 12 crystallises in the monoclinic space group
compounds (see ESI,† Fig. S18). The charge distribution in the P21/n. The unit cell has a volume that is half that of the unit
dicyanomethylene compounds showed that the nitrogen atoms cells for 5 and 11. A number of short electrostatic contacts,
from the cyano groups are negatively charged, as expected, and namely III, and phenyl-ring p-stacking are responsible for the
the hydrogen atoms adjacent to the oxygen atoms in the 3D packing of compound 12 (Fig. 3 and Table 2).
spacers are positively charged, showing that these atoms can
electrostatically interact as observed in Fig. 1–3.
A comparison of the structures of compounds 5, 6, 10, 11
and 12 (Fig. 4) reveals a V-shaped arrangement of the phenyl
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Fig. 2 Representation of the crystal packing of compound 10. Oxygen atoms
are indicated in red and nitrogen in blue. Displacement ellipsoid parameters are
drawn at the 50% probability level. Symmetry codes (v) =ꢁx ꢁ 1, ꢁy + 1, 1 ꢁ z + 1;
(vi) = x ꢁ 1, y ꢁ 1, z.
Fig. 3 Representation of the crystal packing of compound 12. Oxygen atoms
are indicated in red. Displacement ellipsoid parameters are drawn at the 50%
probability level. Symmetry codes (vii) = ꢁx + 1, ꢁy + 1, ꢁz.
rings for the compounds containing an odd number of atoms
in the spacer (5 and 11) and a parallel arrangement of the
phenyl rings for the compounds containing an even number of
atoms in the spacer (6, 10 and 12). The angle between the
normal vectors of the least square planes defining the aromatic
rings in 5 and 11 is approximately 1211 and 1141, respectively.
Interestingly, the distances between the parallel phenyl rings
are 1, 3 and 5 Å for compounds 6, 10 and 12, respectively.
Based on these results, it is likely that the size and also the
even and odd number of atoms in the spacers are more relevant
for the conformations of the dicyanomethylene compounds
than the spacers’ chemical composition.20
Fig. 4 The conformations of compounds 5, 6, 10, 11 and 12. Oxygen atoms are
indicated in red and nitrogen atoms are represented in blue. Atomic displace-
ment parameters are represented at 50% of probability. f angles are defined as
the angle between the normal vectors of the least square planes defining the
aromatic rings.
Photophysical properties in the solid state
Normalised diffuse reflectance UV-Vis and photoluminescence
spectra of compounds 5, 6, 10, 11 and 12 in the solid state at
room temperature are presented in Fig. 5. The photophysical
data for these compounds in the solid state are summarised in
Table 3. Two absorption bands were observed for all of the
examined compounds. The absorption at high wavelength is
slightly red shifted for compounds 11 and 12 (class 2). To obtain
the precise bandgap values from absorption edges, the inflection
Fig. 5 Normalised absorption (full lines) and emission spectra (dashed lines) of
the examined dicyanomethylene compounds, measured in solid state.
The compounds are highly fluorescent in the solid state.
point in the first derivatives of the absorption spectra was used.21 Greenish-blue emissions were observed upon irradiation of the
The bandgap values are similar for all of the examined compounds, solids at the absorption maximum lmax(2) (Table 3). The
indicating that the different types of spacers and crystal packing do emission maximum is blue shifted for class 1 (5 and 6) relative
not significantly affect the bandgap size.
to class 2 compounds (10, 11 and 12). Compound 10 exhibits
c
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Table 3 Optical properties of the dicyanomethylene compounds in the solid
also observed for all of the examined compounds in solution:
one at approximately 303 nm and the other near the visible
region at ca. 368 nm. The observed molar extinction coefficients
for these peaks range from 19 500 to 30 100 and from 16 000 to
26 400 molꢁ1 Lꢁ1 cmꢁ1, respectively (Table 4). The primary
feature of these spectra is a slight blue shift observed for class 1
compounds (5 and 6) relative to class 2 compounds (10, 11 and
12). The LUMO/HOMO energy gap was estimated from the
absorption edge of the optical absorption spectra (Table 4).21,22
All compounds exhibit blue emissions in CH2Cl2 when
excited at the absorption maximum lmax(2) (Table 4). Among
state
a
l
nm
max(1)/
l
nm
max(2)/
lem
nm
/
Stokes
shift/eV
Bandgapb/
eV
Compounds
5
6
10
11
12
307
303
310
311
312
382
380
382
388
392
465
454
483
470
468
0.58
0.53
0.68
0.56
0.51
2.69
2.68
2.62
2.67
2.67
a
b
Excited at lmax(2). Estimated from the optical absorption edge.
the largest Stokes shift in the series. This compound might be the examined molecules, compound 6 exhibited the highest
experiencing a larger geometry change upon excitation. A quantum yield and fluorescence lifetime (F = 0.06 and ts = 6.1 ns;
comparison of the crystal structures of all compounds (Fig. 1–3 Table 4). In contrast to the absorption spectra, the emission
and Tables 1 and 2) shows that the crystal packing of compound maximum is blue shifted for class 2 compounds relative to that
10 involves two types of short contacts (Table 2), whereas the of class 1 compounds. Inversely, in the solid state, the emission
compounds 5, 11 and 12 have additional weak interactions maximum was blue shifted for class 1. The Stokes shifts of the
such as, phenyl-ring p-stacking (compound 12) and hydrogen- compounds in solution were 0.58 and 0.52 eV for class 1 and 2,
bond-like short contacts (type III in compounds 5 and 11). These respectively. Class 1 molecules exhibited larger Stokes shifts
additional weak interactions in compounds 5, 11 and 12 may than class 2 molecules; behaviour that is not observed in the
cooperatively increase the structural rigidity in the solid state, solid state (Table 3). The larger Stokes shifts for class 1
leading to a smaller Stokes shift for these compounds than for compounds in solution may be related to the fact that, relative
compound 10.
to class 2 molecules, class 1 molecules may display better
To gain further insight into the photophysical process reorganisation of their excited states because of the withdrawing
within the five examined compounds, we also investigated their effects of the glycol spacers. The larger Stokes shifts for class 1
absorption and emission behaviour in solution (CH2Cl2).
can also arise from different solvation of the excited state relative
to the ground state.23
Photophysical properties in solution
Electrochemical properties
Normalised absorption and photoluminescence spectra of
compounds 5, 6, 10, 11 and 12 in CH2Cl2 solution at room
temperature are presented in Fig. 6. Two absorption bands were
Cyclic voltammetry (CV) (see ESI,† Fig. S19) was used to identify
the electrochemical behaviour and also to obtain HOMO/LUMO
energies of the dicyanomethylene compounds in solution
(Table 4). The experiments were performed in argon-purged
CH2Cl2/TBAClO4, at room temperature. The cyclic voltammo-
grams were obtained in the potential range of +1.00 to ꢁ1.50 V
vs. Ag/AgCl (in organic medium) quasi-reference electrode. For
all of the examined compounds, the potential was scanned
from the open-circuit potential. The onsets were referenced to
Fc/Fc+.24,25 The reduction potentials, the electron affinity (EA)
(LUMO level), the ionisation energy (IE) (HOMO level) and the
optical gap for these compounds are presented in Table 4. The
LUMO level was determined using the ELUMO = ꢁ4.8 ꢁ Ered
(vs. SCE) equation.26–31 The HOMO energy levels of all of these
Fig. 6 Normalised absorption (full lines) and emission spectra (dashed lines) of compounds were calculated by subtracting the optical gap from
the examined dicyanomethylene compounds, measured in CH2Cl2 solutions.
the electrochemical LUMO levels (Table 4).
Table 4 Optical and electrochemical properties of the dicyanomethylene compounds in CH2Cl2
Ered/V vs. HOMOb/ LUMOc/ Gapopt
/
d
e1/
e2/
Compounds
l
max(1)/nm 104 Mꢁ1 cmꢁ1
l
max(2)/nm 104 Mꢁ1 cmꢁ1
F
l
em/nm Dla/eV ts/ns Ag/AgCl eV
eV
eV
5
6
10
11
12
303
303
303
303
303
3.01
1.95
3.02
2.82
2.64
365
366
369
369
371
2.47
1.60
2.64
2.50
2.35
0.02 440
0.06 441
0.04 436
0.03 436
0.03 439
0.58
0.58
0.52
0.52
0.52
5.6
6.1
5.8
5.8
5.8
ꢁ1.17
ꢁ1.17
ꢁ1.22
ꢁ1.16
ꢁ1.19
ꢁ6.81
ꢁ6.81
ꢁ6.76
ꢁ6.81
ꢁ6.75
ꢁ3.63
ꢁ3.63
ꢁ3.58
ꢁ3.65
ꢁ3.61
3.18
3.18
3.18
3.16
3.14
a
b
c
d
The Stokes shift. HOMO = LUMOelec. ꢁ gapopt
. Calculated from the irreversible reduction process. Estimated from the optical absorption
edge. The inflection point in the first derivatives of the absorption spectrum was used.
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All of the examined compounds are characterised by an HOMOs involve the O11 atom and one of the e1g orbitals of the
irreversible cathodic reduction process that is slightly shifted benzyl ring, whereas the LUMOs involve mainly the C7–C8 double
to more negative potentials for compounds 10 and 12 (which are bonds (Fig. 7). Although these calculations were performed in
both class 2 compounds) relative to the potentials of compounds CH2Cl2, the same orbitals may be involved in the electronic
5, 6, and 11 (see ESI,† Fig. S19). An irreversible anodic oxidation transitions observed in the solid state absorption spectra (Fig. 5),
process that occurs after the reduction process is also observed because the spectra in solution and in solid state are similar.
for all of the examined compounds. This anodic oxidation may The theoretical absorption spectra calculated for both the
be related to the oxidation of the reduced product that has been experimental (obtained from CIF files) and the planar structures
adsorbed onto the surface of the working electrode.
show a systematic underestimation of the excitation energies (see
ESI,† Fig. S20–S24), a result that can possibly be attributed to the
limitation of TD-DFT methods for calculation of excitation energies
of charge-transfer excited states.34,35 In spite of this limitation, the
important features of the spectra were correctly simulated. To our
present discussion this is adequate, as the TD-DFT calculation has
been used mainly to assign the electronic transitions observed in
the experimental spectra36,37 (see ESI,† Fig. S20–S24 and Tables S5
and S6), rather than to calculate the excitation energies.
Theoretical calculations
To better understand the photophysical properties of the newly
synthesised dicyanomethylene compounds, density functional
theory (DFT) was used to perform theoretical calculations at the
B3LYP/6-31G(d,p) level.32,33 Two sets of geometries were optimized
for each compound: (i) one starting from the CIF files obtained
from the X-ray diffraction experiments and (ii) the other one with a
fully planar geometry in a zig-zag arrangement of the spacers.
Relative energies for the two sets of structures are given in Table S1
(ESI†). Considering the final free energy in solution ðDGsolÞ, the
relative energies are below 2 kcal molꢁ1. The structures obtained
from the CIF files for class 1 compounds (compounds 5 and 6) are
more stable than the planar structures (see ESI,† Table S1). In
contrast, the planar arrangements are more stable for class 2
compounds (10, 11 and 12) (see ESI,† Table S1). Considering the
low energy differences between the two sets of structures, in the
following analysis only the structures obtained from the X-ray
experiments will be discussed.
To assign the absorption bands observed in the UV-Vis spectra,
we calculated the molecular orbitals of the compounds in CH2Cl2.
Fig. 7 displays the contour plots of the frontier orbitals (HOMOs
and LUMOs) and their corresponding energy levels and gaps. The
HOMOs have p-symmetry and reside mainly on the aromatic rings,
whereas the LUMOs have higher amplitude on the double bonds
conjugated to the aromatic rings. The conjugation patterns of the
The natural transition orbitals (NTOs)38 involved in the
electronic transitions of compound 6 are presented in Fig. 8.
These calculations were performed only for this compound
because the absorption and emission spectra of all of the
examined compounds exhibit similar patterns (Fig. 6).
The NTOs are similar to the previously discussed canonical
orbitals and feature the same distribution pattern as the
canonical orbitals. The NTOs are also associated with either
the aromatic system or the adjacent unsaturated group. Thus, the
two transitions in the absorption spectra are due to p–p* electron
transfer from the aromatic ring to the unsaturated group. For the
excitation at low energies (Fig. 8), which involves transitions
from the HOMO and HOMO ꢁ 1 orbitals, there is no amplitude
on the C7 carbon (atom labels are shown at the top of Fig. 7).
Fig. 7 Calculated HOMOs, LUMOs, energy levels and gaps for the synthesised
Fig. 8 The NTO contours (isosurface = 0.02 a.u.) for the main components of the
electronic transitions of compound 6.
dicyanomethylene compounds.
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In contrast, for the second excitation, which involves transi- and electrochemical properties. X-ray single-crystal structure
tions from the HOMO ꢁ 2 and HOMO ꢁ 3 orbitals, there is analyses of 5, 10, 11 and 12 revealed that the 3D crystal packing
amplitude on carbon C7. The conjugation between the orbitals for all of the examined structures is governed by a number of
involved in the transition is higher in the latter case than in the weak hydrogen bonds. The compounds containing an odd
former case.
number of atoms in the spacer (5 and 11) revealed a V-shaped
The selected bond lengths obtained from the optimised arrangement of the phenyl rings and the compounds contain-
structure for the ground state (GS) and excited state (ES) forms ing an even number of atoms in the spacer (6, 10 and 12)
of compound 6 are presented in Table S7 (see ESI†). A compar- showed a parallel arrangement of the phenyl rings. All synthe-
ison of the GS and ES structures reveals that, in the excited sised compounds showed blue emissions in the solid state and
state, the double-bond length C7–C8 (see ESI,† Table S7; atom in solution. Stokes shift range from 0.51 to 0.58 eV in solution.
labels are shown on the top of Fig. 7) increases from 1.373 to Compound 10, with the shortest spacer, exhibited the highest
1.416 Å (3.1%). Several bonds in the phenyl ring also increase in Stokes shift in the solid state, 0.68 eV, suggesting that this
length, most notably C2–C3 (0.038 Å; 2.74%) and C1–C6 (0.027 Å; compound might be experiencing a larger geometry change
1.9%). In contrast, the C1–C2 (ꢁ0.022 Å; ꢁ1.49%) and C6–O11 upon excitation.
(ꢁ0.019 Å; ꢁ1.40%) bond lengths decrease. The calculated
The electronic transitions for the synthesized compounds in
structural changes for the excited state are consequences of solution could be assigned on the basis of DFT calculations and
the electronic transitions that occur during the excitation revealed that the main transitions involve the e1g orbital of the
process, as indicated by the HOMO and LUMO surfaces phenyl ring (HOMO) and the double bonds of the methylenic
(Fig. 8). The transition from the HOMO (the e1g bonding orbital group (LUMO). These electronic transitions influence both the
of the phenyl ring) to the LUMO (an antibonding orbital that is geometrical and electronic properties of the groups involved in
primarily located on the methylene group) results in an the transitions. The electronic transitions observed in the solid
increase in the C7–C8 bond length. In addition, as shown in state most likely involve the same orbitals considering the
Fig. 8, the C6–O11 bond possesses an antibonding character in similar patterns of the spectra in solution and in the solid
the occupied orbitals. Therefore, a HOMO–LUMO electron state. TD-DFT simulations of the emission spectra indicate that
transfer results in a decrease in the C6–O11 bond length. One the fluorescence of these compounds originates from electronic
additional consequence of the excitation process is a decrease transitions from the aromatic system of the methoxyphenyl
in the electronic charge densities on O11 and C1 and an increase moiety to the adjacent propanedinitrile group. The simulation
in the negative charge on C7 (see ESI,† Table S9).
of the electrochemical process in solution demonstrated that
To help rationalise the reduction process, geometry optimi- the one-electron reduction involves only one of the [(2-methoxy-
sations at the B3LYP/6-31+G(d,p) level were performed for one phenyl)methylene]propanedinitrile fragments.
electron reduction in a vacuum and CH2Cl2, using the PCM
solvation model.39,40 The diffuse functions were added to
appropriately describe the resulting anions. Geometrical para-
Experimental
meters for the first reduced form are also given in Table S7 (see All of the chemicals used in this study were purchased from
ESI†). The geometries found for the anions are similar to the Aldrich and were used without further purification. Solvents
geometry of the neutral form. The charge and spin densities for were purchased from Vetec (Brazil) and were purified according
the one-electron reduced form are provided in Table S9 (see to procedures in the extant literature. Thin-layer chromato-
ESI†). The spin densities for the gas phase geometries show a graphy (TLC) was performed on aluminium sheets coated with
symmetrical distribution of the spin densities between the two silica gel 60F (Merck 5554). The plates were inspected under UV
dicyanomethylene moieties (see ESI,† Fig. S27 and S28). In light and, if necessary, developed in I2 vapour. Column chro-
contrast, calculation in the solvent promotes the localization matography was performed on silica gel 60 (Merck; 40–60 nm,
of the spin density in one side (see ESI,† Fig. S27 and S28). Most 230–400 mesh). Melting points were determined on a Thermo
likely this difference may be related to the polarization of the Scientific 9100 and were reported without corrections. Infrared
molecules promoted by the solvent. In both phases the spin spectra were recorded on a Perkin Elmer FT-IR spectrometer
1
density distribution in the reduced form follows a pattern very using KBr pellets. H and 13C NMR spectra were recorded on a
similar to that found for the LUMOs (Fig. 8 and see ESI,† Fig. Bruker instrument (at 500 and 125 MHz, respectively), using
S28), with spin concentration on the C7 and C8 carbon atoms, residual solvents as internal standards. Samples were prepared
and some polarisation to the aromatic ring and the nitrile using CDCl3 purchased from Cambridge Isotope Laboratories.
groups. This result clearly indicates that the methylene moiety Elemental analyses were conducted on a Perkin Elmer CHN
´
controls both the spectroscopic features and the electrochem- 2400 analyser at the Central Analıtica of the Instituto de
´
˜
istry of the examined compounds.
Quımica at the Universidade de Sao Paulo in Brazil.
Absorption and emission spectroscopy
Conclusions
Absorption spectra were obtained on a Cary 50 spectrophoto-
The five new dicyanomethylene compounds characterised in meter using spectroscopic-grade CH2Cl2. The photoluminescence
the present study possess interesting structural, spectroscopic (PL) spectroscopy measurements were carried out at room
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temperature using a Photon Technology International (PTI) existence of two domains that were related by a non-crystallographic
fluorescence spectrophotometer. Diffuse Reflectance UV-Visible lattice rotation. Because the single crystals are described
spectra (DR UV-Vis) were recorded using a Varian Cary 5000 spectro- by monoclinic symmetry, this rare case is only possible for
meter using Cary win-UV/scan software. Fluorescence quantum particular combinations of lattice parameters and monoclinic
yields were determined using a quinine bisulphate (QB) solution angles. The details regarding the refinement of these mono-
in 0.5 M H2SO4 (F = 0.546)41 as a reference material. The quantum clinic samples will be published elsewhere.
yield was determined using the following equation:42,43
Electrochemistry
Fem,S = Fem,R (fR/fS)(IS/IR)(nS/nR)
Cyclic voltammetric (CV) experiments were performed in argon-
where Fem,S represents the fluorescence quantum yield of the purged CH2Cl2 (Aldrich) at room temperature using a micro
sample; fS and fR are the absorption factors (f = 1ꢁ10ꢁAbs, where Autolab Type III system that was interfaced with a personal
Abs = absorbance) for the sample and the reference, respectively, computer. A glassy carbon working electrode was utilised for
at the excitation wavelength; IS and IR denote the integrated these experiments, and its surface was polished with 0.3 mm
areas of the corrected emission spectra for the sample and the alumina–water slurry on a felt surface prior to each use. The
reference, respectively; and nS and nR are the refractive indices of counter electrode was a Pt wire that was separated from the bulk
the sample and reference solvents, respectively.
solution by a fine glass frit, and the reference for these experi-
All fluorescence lifetime measurements were carried out in a ments was an Ag/AgCl electrode in organic media. Ferrocene was
homemade laser table. A quartz cuvette (10 mm pathlength) used as an internal standard (E1/2 of 0.40 V vs. NHE). Under all of
containing a solution of the dicyanomethylene compounds at the tested conditions, the concentration of each compound was
the concentration of 10ꢁ5 mol dmꢁ3 was irradiated using a 6.6 ꢂ 10ꢁ4 mol dmꢁ3, and 0.1 mol dmꢁ3 tetrabutylammonium
third harmonic (355 nm, 185 mJ) Nd-YAG pulsed laser (Quantel perchlorate (TBAClO4, Fluka) was added to the solutions as a
BRILLIANT-B). The emissions were collected at 901 to the supporting electrolyte. Cyclic voltammograms were obtained at
excitation on an Oriel Cornerstonet 260 1/4 m monochromator sweep rates in the range of 0.02–1.0 V sꢁ1
.
at the selected wavelengths (440 nm) and detected using a PMT
(Oriel 77360, risetime = 1.2 ns). The signals were captured using
Theoretical calculations
an oscilloscope (LeCroy Wavesurfer 44MXs-B, 400 MHz).
DFT calculations were performed using the Gaussian 09 (Rev.
B.01) software package.49 All geometries were fully optimized
starting from two initial arrangements, one using the geometry
Single crystal structure determination
Single crystals of 5, 10, 11, and 12 that were suitable for X-ray obtained in the solid state measurements and the second one
diffraction experiments were obtained by the slow evaporation starting from a fully planar geometry, with the spacer chain in a
of solutions of these compounds (at 1.0 mmol dmꢁ3) in CH2Cl2/ zig-zag arrangement. For the geometry optimization calculation
C6H6. X-ray diffraction data were collected on an Oxford the B3LYP functional together with the 6-31G(d,p) basis set was
Diffraction Gemini diffractometer using a graphite-enhanced employed.50,51
source of MoKa radiation (l = 0.7107 Å) for compounds 10, 11
Harmonic frequency calculations were performed for the
and 12 and an enhanced source of CuKa radiation (l = 1.5418 Å) optimised geometries and revealed that these geometries represent
for compound 5. The data integration and scaling of the reflec- genuine minimum energy points (with no negative eigenvalue)
tions for all of the compounds were performed using the on the potential energy surface. Based on the B3LYP/6-31G(d,p)
Chrysalis software suite.44 The final unit-cell parameters were optimised geometries, TD-DFT approaches were used to simu-
based on the fitting of all of the reflection positions. Analytical45 late vertical excitations with linear responses to verify the
and semi-empirical46 absorption corrections were performed effects of these excitations on the absorption spectra of the
using the Chrysalis software suite.44 The XPREP47 program was examined compounds.
used for space-group identification. The structures of all of the
The polarised continuum (overlapping spheres) solvation
examined compounds were solved by direct methods using the model (PCM) was used to ensure that solvent effects (CH2Cl2)
SHELXS47 software program. The positions of all of the atoms were incorporated into all of the aforementioned calculations.
could be unambiguously assigned on consecutive difference The PCM computations used the UFF radii and all of the
Fourier maps. No solvent molecules were observed in the standard specifications of the Gaussian package. The thermo-
structures of the assessed compounds. SHELXL47 was used to dynamic calculations in solution were performed as described
apply a full-matrix least-squares approach to perform refine- by Pliego and Riveros52 using the Gibbs free energy of solvation
ments that were based on F2. All of the hydrogen atoms were as described by Ben-Naim.53 All values reported are those
refined with anisotropic atomic displacement parameters. The obtained in solution (CH2Cl2).
hydrogen atoms in the compounds were added to the structure
The photophysical properties of compound 6 were explored
in idealised positions and were further refined according to a in detail. The geometry of the first excited state was optimized,
riding model.48
followed by frequency calculations. This procedure permitted a
All single-crystal samples of compounds 5 and 11 were Franck–Condon analysis54,55 and the generation of simulated
merohedrally twinned, i.e., the complete superpositions of all emission spectra. State-specific56,57 TD-DFT was performed at
of the reflections in the reciprocal space were caused by the the ground- and excited-state geometries to obtain a more
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accurate emission value that corresponded to the S1 - S0 13C NMR (125 MHz, CDCl3) d: 158.5, 154.7, 136.7, 128.9, 121.8,
transition. The emission band shape was calculated using FC 120.7, 114.6, 113.1, 81.5, 71.0, 69.5 and 68.7. IR (KBr) n(cmꢁ1):
analysis parameters of a half-width at half-maximum (HWHM) 3043(w), 2970(w), 2916(w), 2221(m), 1600(m), 1579(s), 1480(m),
of 2000 cmꢁ1 and a spectral resolution of 1 cmꢁ1
.
1462(m), 1367(m), 1257(s), 1137(s) and 751(m). Elemental
To evaluate the orbitals that are involved in the electronic analysis for C26H22O4N4: calculated: 68.71% C, 4.88% H and
transitions, a NTO analysis was performed for compound 6. 12.33% N; experimentally determined: 67.56% C, 4.62% H and
The TD results were analysed using the GaussSum software.58 11.70% N.
The absorption spectra were fitted with a Gaussian function
Compound 7. A mixture of salicylic aldehyde (8.00 g,
65.5 mmol), K2CO3 (9.00 g, 65.5 mmol), KI (5.66 g, 26.20 mmol)
and 1,4-dibromobutane (5.66 g, 26.204 mmol) in dry MeCN
(50 mL) was heated for 12 h under reflux. After the reaction
with a FWHM of 3000 cmꢁ1
.
Synthesis
Compound 3. The synthesis of compound 3 has been mixture was cooled to room temperature, the solid was filtered
described elsewhere.59
away, and the solvent was removed under vacuum. The residue
Compound 4. The synthesis of compound 4 was analogous was then dissolved in CH2Cl2 and washed with cold water and
to the synthesis of 3, using 2 (1.50 g, 3.27 mmol), salicylic saturated brine. After this solution was dried over anhydrous
aldehyde (0.957 g, 7.85 mmol) and K2CO3 (2.16 g, 15.70 mmol) sodium sulphate, the solvent was removed under reduced
in dry MeCN (80 mL). After the reaction mixture was cooled to pressure to produce the desired product in the form of pale
room temperature, the solid was filtered away, and the solvent crystals (3.26 g, 40.8% yield). m.p.: 112–116 1C. 1H NMR
was removed under vacuum. The residue was purified by (500 MHz, CDCl3) d: 10.5 (s, 2H), 7.82 (dd, J = 7.5 and 1.5 Hz,
column chromatography (SiO2; hexane : EtOAc 1 : 1) to produce 2H), 7.56–7.52 (m, 2H), 7.04–6.97 (m, 4H), 4.19 (t, J = 5.5 Hz, 4H)
the desired product (0.850 g, 73% yield) as a light-yellow solid and 2.11–2.09 (m, 4H). 13C NMR (125 MHz, CDCl3) d: 189.3,
with the following properties: m.p.: 44–46 1C. 1H NMR 161.0, 135.8, 128.3, 124.7, 120.6, 112.2, 67.7 and 25.7. IR (KBr)
(500 MHz, CDCl3) d: 10.50 (s, 2H), 7.81 (dd, J = 8.0 Hz and n(cmꢁ1): 3107(w), 3078(w), 2952(m), 2876(m), 2759(w), 1679(s),
J = 2.0 Hz, 2H), 7.53–7.50 (m, 2H), 7.03–6.97 (m, 4H), 4.24 1595(w), 1493(s), 1461(s), 1382(s), 1287(s), 1237(s), 1195(m),
(t, J = 4.5 Hz, 4H), 3.91 (t, J = 4.5 Hz, 4H) and 3.74 (s, 1145(m), 1006(m), 846(s), 754(s), 657(m) and 609(m). Elemental
4H).13C NMR (125 MHz, CDCl3) d: 190.1, 161.4, 136.1, 128.5, analysis for C18H18O4: calculated: 72.47% C and 6.08% H;
125.3, 121.1, 113.0, 71.2, 69.8 and 68.4. IR (KBr) n(cmꢁ1): experimentally determined: 73.43% C and 6.29% H.
2924.51(w), 2869.20(w), 2761.22(w), 1678.74(s), 1599.72(s),
Compound 8. The synthesis of 8 was analogous to the
1481.20(m), 1453.55(m), 1391.65(w), 1348.20(w), 1287.62(s), synthesis of 7 using 1,5-dibromopentane (1.51 g, 6.56 mmol),
1240.21(s), 1184.90(w), 1105.89(s), 1042.68(m), 916.26(w), salicylic aldehyde (2.00 g, 16.4 mmol), K2CO3 (2.26 g,
829.34(m), 758.23(s), 647.61(m) and 598.89(w). Elemental analysis 16.4 mmol) and KI (2.18 g, 13.1 mmol) in dry MeCN (50 mL).
for C20H22O6: calculated: 67.07% C and 6.19% H; experimentally Pale crystals were obtained after the solvent was removed under
determined: 66.94% C and 6.08% H.
reduced pressure (2.38 g, 90% yield). m.p.: 54.6 1C. 1H NMR
Compound 5. A mixture of 3 (0.996 g, 3.13 mmol), CH2(CN)2 (500 MHz, CDCl3) d: 10.48 (s, 2H), 7.80 (dd, J = 7.5 and 2.0 Hz,
(0.500 g, 7.82 mmol) and NH4OAc (0.0024 g, 0.03 mmol) was 2H), 7.53–7.49 (m, 2H), 7.03–6.97 (m, 4H), 4.10 (t, J = 6.5 Hz,
ground in a mortar. The product was purified by column 4H), 1.97–1.91 (m, 4H) and 1.74–1.67 (m, 2H). 13C NMR
chromatography (SiO2, CH2Cl2) to generate a yellow solid (125 MHz, CDCl3) d: 189.54, 161.18, 135.79, 128.23, 124.76,
(1.00 g, 78% yield) with the following properties: m.p.: 120.50, 112.33, 68.08, 28.70 and 22.66. IR (KBr) n(cmꢁ1):
148–150 1C. 1H NMR (500 MHz, CDCl3) d: 8.28 (s, 2H), 8.18 2949(w), 2868(w), 1678(s), 1480(m), 1459(s), 1460(m), 1292(m),
(dd, J = 8.0 Hz and J = 1.0 Hz, 2H), 7.58–7.55 (m, 2H), 7.1 1240(s), 1185(w), 1155(m), 1112(w), 1076(w), 1011(w), 1008(m),
(t, J = 8.0 Hz, 2H), 7.01 (d, J = 8.5 Hz, 2H), 4.27 (t, J = 4.5 Hz, 4H) 984(w), 917(w), 839(m), 764(s) and 656(m). Elemental analysis
and 3.96 (t, J = 4.5 Hz, 4H). 13C NMR (125 MHz, CDCl3) d: 158.0, for C19H20O4: calculated: 73.06% C and 6.45% H; experimen-
154.3, 136.4, 128.7, 121.6, 120.4, 114.2, 112.7, 81.4, 69.4 and tally determined: 73.22% C and 6.74% H.
68.4. IR (KBr) n(cmꢁ1): 3039(w), 2953(w), 2933(w), 2226(m),
Compound 9. The synthesis of 9 was analogous to the
1601(s), 1582(s), 1484(s), 1262(s), 1139(m) and 748(s). Elemental syntheses of 7 and 8 using 1,6-dibromohexane (6.39 g,
analysis for C24H18O3N4: calculated: 70.23% C, 4.42% H and 26.20 mmol), salicylic aldehyde (8.00 g, 65.5 mmol), K2CO3
13.65% N; experimentally determined: 69.84% C, 3.94% H and (9.04 g, 65.50 mmol) and KI (8.60 g, 52.4 mmol) in dry MeCN
13.60% N.
(50 mL). Pale crystals were obtained after the solvent was
Compound 6. The synthesis of 6 was analogous to the removed under reduced pressure (7.24 g, 67% yield). m.p.:
1
synthesis of 5 using 4 (0.850 g, 2.4 mmol), CH2(CN)2 (0.634 g, 76.6 1C. H NMR (500 MHz, CDCl3) d: 10.51 (s, 2H), 7.83 (dd,
9.6 mmol) and NH4OAc (0.740 g, 9.6 mmol). A yellow solid was J = 7.5 and 1.5 Hz, 2H), 7.55–7.52 (m, 2H), 7.03–6.97 (m, 4H),
obtained after purification (0.792 g, 74% yield) that possessed 4.10 (t, J = 6.5 Hz, 4H), 1.93–1.88 (m, 4H) and 1.62–1.59 (m, 4H).
the following properties: m.p.: 149–151 1C. 1H NMR (500 MHz, 13C NMR (125 MHz, CDCl3) d: 189.6, 158.3, 154.2, 136.47, 128.7,
CDCl3) d: 8.31(s, 2H), 8.16 (dd, J = 8.0 Hz and J = 1.5 Hz, 2H), 125.0, 121.1, 112.17, 68.6, 68.3, 28.7 and 25.7. IR (KBr) n(cmꢁ1):
7.58–7.54 (m, 2H), 7.08 (t, J = 8.0 Hz, 2H), 6.7 (d, J = 8.5 Hz, 2H), 3072(w); 2955(w), 2933(w), 2850(w), 2760(w), 1685(s), 1602(s),
4.24 (t, J = 4.5 Hz, 4H), 3.90 (t, J = 5.0 Hz, 4H) and 3.76 (s, 4H). 1486(m), 1459(s), 1395(m), 1291(s), 1246(s), 1164(w), 1110(w),
c
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1081(w), 1037(w), 999(w), 833(m) and 758(m). Elemental analysis Dr Marco Cremona (IF-PUC, Rio de Janeiro, Brazil) for PL
for C20H22O4: calculated: 73.60% C and 6.79% H; experimentally spectroscopy measurements.
determined: 73.40% C and 7.00% H.
Compound 10. 7 (2.00 g, 6.7 mmol), CH2(CN)2 (1.32 g,
20 mmol) and AcONH4 (1.54 g, 20 mmol) were mixed. A yellow
solid was obtained after purification (0.785 g, 30% yield). m.p.:
Notes and references
212–215 1C. 1H NMR (500 MHz, DMSO) d: 8.19 (s, 2H), 8.17 (dd,
J = 8.0 and 1.0 Hz, 2H), 7.59–7.55 (m, 2H), 7.06 (t, J = 8.0 Hz,
2H), 6.96 (d, J = 8.5 Hz, 2H), 4.17 (t, J = 5.0 Hz, 4H) and 2.07–206
(m, 4H). 13C NMR (125 MHz, DMSO) d: 156.7, 154.4, 128.5,
128.1, 120.2, 114.3, 113.1, 87.2, 68.4 and 25.0. IR (KBr) n(cmꢁ1):
3039(w), 2949(w), 2888(w), 2224(m), 1598(m), 1578(m), 1485(m),
1454(m), 1392(w), 1365(m), 1312(m), 1256(s), 1200(w), 1156(m),
1042(m), 980(m), 751(m) and 616(w). Elemental analysis for
C24H18O2N4: calculated: 73.08% C, 4.60% H and 14.20% N; experi-
mentally determined: 72.54% C, 4.70% H and 14.05% N.
1 N. A. J. M. Sommerdijk, Angew. Chem., Int. Ed., 2003,
42, 3572.
2 J.-P. Zhang, Y.-B. Zhang, J.-B. Lin and X.-M. Chen, Chem.
Rev., 2012, 112, 1001.
3 A. Schoedel, L. Wojtas, S. P. Kelley, R. D. Rogers,
M. Eddaoudi and M. J. Zaworotko, Angew. Chem., Int. Ed.,
2011, 50, 11421.
4 B. J. Holliday and C. A. Mirkin, Angew. Chem., Int. Ed., 2001,
40, 2022.
5 P. J. Stang and B. Olenyuk, Acc. Chem. Soc., 1997, 30, 502.
6 D. L. Caulder and K. N. Raymond, J. Chem. Soc., Dalton
Trans., 1999, 1185.
7 M. Albrecht, Chem. Soc. Rev., 1998, 27, 281.
8 O. M. Yaghi, M. O’Keeffe, N. W. Ockwig, H. K. Chae,
M. Eddaoudi and J. Kim, Nature, 2003, 423, 705.
9 S. Subramanian and M. J. Zaworotko, Angew. Chem., Int. Ed.
Engl., 1995, 34, 2127.
Compound 11. The synthesis of 11 was analogous to the
syntheses of 5, 6 and 10 using 8 (0.290 g, 0.9 mmol), CH2(CN)2
(0.182 g, 2.76 mmol), and AcONH4 (0.213 g, 2.7 mmol). A yellow
solid was obtained after purification (0.172 g, 46% yield). m.p.:
1
178 1C. H NMR (500 MHz, CDCl3) d: 8.29 (s, 2H), 8.20 (dd, J =
8.0 Hz and 1.5 Hz, 2H), 7.59–7.55 (m, 2H), 7.08 (t, J = 7.5 Hz,
2H), 6.99 (d, J = 8.5 Hz, 2H), 4.13 (t, J = 6.5 Hz, 4H), 1.98 (m, 4H)
and 1.68 (m, 2H). 13C NMR (125 MHz, CDCl3) d: 158.2, 154.2, 10 Y.-B. Dong, Y.-Y. Jiang, J. Li, J.-P. Ma, F.-L. Liu, B. Tang,
136.4, 128.8, 120.1, 114.3, 112.8, 112.16, 81.3, 68.5, 28.6 and
R.-Q. Huang and S. R. Batten, J. Am. Chem. Soc., 2007,
129, 4521.
22.7. IR (KBr) n(cmꢁ1): 3041(w), 2957(w), 2934(w), 2222(m),
1581(m), 1483(m), 1478(w), 1456(w), 1389(m), 1367(w), 11 H.-J. Kim, W.-C. Zin and M. Lee, J. Am. Chem. Soc., 2004,
1309(w), 1262(s), 1168(w), 1100(w), 1059(w), 1019(w), 987(w) 126, 7009.
and 743(s). Elemental analysis for C25H20O2N4: calculated: 12 A. S. Abd-El-Aziz and E. A. Strohmb, Polymer, 2012, 53, 4879.
73.51% C, 4.94% H and 13.72% N; experimentally determined: 13 G. K. Patra and I. Goldberg, Cryst. Growth Des., 2003, 3, 321.
73.47% C, 5.07% H and 13.59% N.
14 Q. Yang, X. Chen, Z. Chen, Y. Hao, Y. Li, Q. Lu and
Compound 12. 9 (5.06 g, 15.5 mmol), CH2(CN)2 (3.07 g,
H. Zheng, Chem. Commun., 2012, 48, 10016.
46.5 mmol) and AcONH4 (3.59 g, 46.5 mmol) were mixed. A 15 L.-F. Ma, X.-Q. Li, Bin-Liu, L.-Y. Wang and H.-W. Hou,
yellow solid was obtained after purification (4.20 g, 64% yield). CrystEngComm, 2011, 13, 4973.
m.p.: 169 1C. H NMR (500 MHz, CDCl3) d: 8.26 (s, 2H), 8.18 16 S. Konar, P. S. Mukherjee, M. G. B. Drew, J. Ribas and
(dd, J = 7.8 and 1.5 Hz, 2H), 7.59–7.53 (m, 2H), 7.06 (t, J = 7.5 Hz, N. R. Chaudhuri, Inorg. Chem., 2003, 42, 2545.
2H), 6.97 (d, J = 8.4 Hz, 2H), 4.09 (t, J = 6.3 Hz, 4H), 1.91–1.86 17 R. J. Angelici, M. H. Quick, G. A. Kraus and D. T. Plummer,
(m, 4H) and 1.60–1.58 (m, 4H). 13C NMR (125 MHz, CDCl3) d:
Inorg. Chem., 1982, 21, 2178.
158.2, 154.1, 136.4, 128.4, 121.0, 114.3, 112.8, 112.2, 81.0, 68.6, 18 V. E. de Oliveira, R. Diniz and L. F. C. de Oliveira, Quim.
28.7 and 25.6. IR (KBr) n(cmꢁ1): 3034(w), 2952(w), 2944(w),
Nova, 2009, 32, 1917.
2854(w), 2225(m), 1598(m), 1578(m), 1485(m), 1447(m), 19 L. Carlucci, G. Ciani, P. Macchi, D. M. Proserpio and
1388(w), 1358(w), 1309(m), 1258(s), 1156(m), 993(m) and S. Rizzato, Chem.–Eur. J., 1999, 5, 237.
750(s). Elemental analysis for C26H22O2N4: calculated: 73.92% 20 C. T. Imrie and P. A. Henderson, Chem. Soc. Rev., 2007,
1
C, 5.25% H and 13.26% N; experimentally determined: 73.91%
C, 5.40% H and 13.13% N.
36, 2096.
21 H. Qu, L. Qiu, X.-K. Leng, M.-M. Wang, S.-M. Lan, L.-L. Wen
and D.-F. Li, Inorg. Chem. Commun., 2011, 14, 1347.
22 L. Shi, Z. Liu, G. Dong, L. Duan, Y. Qiu, J. Jia, W. Guo,
D. Zhao, D. Cui and X. Tao, Chem.–Eur. J., 2012, 18, 8092.
23 E. V. Anslyn and D. A. Dougherty, Modern Physical Organic
Chemistry, University Science Books, Sausalito, CA, 2006.
Acknowledgements
The authors gratefully acknowledge FAPERJ (JCNE grant num-
´
ber E-26/103.213/2011 and Pensa Rio grant number E-26/ 24 R. R. Gagne, C. A. Koval and G. C. Lisensky, Inorg. Chem.,
110.692/2012) and CNPq (the C.R.M.O. Matos fellowship and 1980, 19, 2854.
Universal grant number 478302/2012-6) for financial support. 25 V. V. Pavlishchuk and A. W. Addison, Inorg. Chim. Acta,
C.M.R., J.W.M.C. and C.B.P. are recipients of CNPq research 2000, 298, 97.
fellowships. We thank Dr E. A. Ponzio (IQ-UFF, Brazil) for 26 Y. Liu, M. S. Liu and A. K.-Y. Jen, Acta Polym., 1999, 50, 105.
assistance with the cyclic voltammetry experiments and 27 S. C. Chang and M. J. Weaver, J. Phys. Chem., 1991, 95, 5391.
c
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Paper
28 E. M. Stuve, A. Krasnopoler and D. E. Sauer, Surf. Sci., 1995, 49 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
335, 177.
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin,
V. N. Staroverov, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
29 L. L. Miller, G. D. Nordbloman and E. A. Maybda, J. Org.
Chem., 1972, 37, 916.
¨
30 P. Posch, M. Thelakkat and H. W. Schmidt, Synth. Met.,
1999, 102, 1110.
31 J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt,
H. Bassler, M. Porsch and J. Daub, Adv. Mater., 1995, 7, 551.
32 A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
33 R. Ditchfield, W. J. Hehre and J. A. Pople, J. Chem. Phys.,
1971, 54, 724.
34 A. Dreuw and M. Head-Gordon, J. Am. Chem. Soc., 2004,
126, 4007.
35 A. Dreuw and M. Head-Gordon, Chem. Rev., 2005, 105, 4009.
36 R. Bauernschmitt and R. Ahlrichs, Chem. Phys. Lett., 1996,
256, 454.
¨
J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas,
37 F. Furche and R. Ahlrichs, J. Chem. Phys., 2002, 117, 7433.
38 R. L. Martin, J. Chem. Phys., 2003, 118, 4775.
J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox,
Gaussian 09, Revision B.01, Gaussian, Inc., Wallingford,
CT, 2009.
ˇ
39 S. Miertus, E. Scrocco and J. Tomasi, Chem. Phys., 1981, 55, 117.
40 J. Tomasi, B. Mennucci and R. Cammi, Chem. Rev., 2005, 50 A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
105, 2999.
51 R. Ditchfield, W. J. Hehre and J. A. Pople, J. Chem. Phys.,
1971, 54, 724.
41 G. F. Kirkbright, Anal. Chem., 1977, 49, 1850.
42 J. B. Birks, Photophysics of Aromatic Molecules, Wiley-Interscience, 52 J. R. Pliego and J. M. Riveros, Phys. Chem. Chem. Phys., 2002,
London, 1st edn, 1970.
4, 1622.
43 A. M. Brouwer, Pure Appl. Chem., 2011, 83, 2213.
53 A. Ben-Naim, J. Phys. Chem., 1978, 82, 792.
44 Agilent Technologies, Xcalibur CCD system, CrysAlisPro 54 F. Santoro, A. Lami, R. Improta, J. Bloino and V. Barone,
Software system, Version 1.171.35.21, Agilent Technologies
UK Ltd., Oxford, UK, 2011.
45 Analytical numeric absorption correction using a multi-
J. Chem. Phys., 2008, 128, 224311.
55 M. Dierksen and S. Grimme, J. Phys. Chem. A, 2004,
108, 10225.
faceted crystal model based on expressions derived by 56 R. Improta, V. Barone, G. Scalmani and M. J. Frisch, J. Chem.
R. C. Clark and J. S. Reid. (R. C. Clark and J. S. Reid, Acta
Crystallogr., Sect. A: Fundam. Crystallogr., 1995, 51, 887).
46 Empirical absorption correction using spherical harmonics,
implemented in the SCALE3 ABSPACK scaling algorithm.
47 G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystallogr.,
2008, 64, 112.
Phys., 2006, 125, 054103.
57 R. Improta, G. Scalmani, M. J. Frisch and V. Barone, J. Chem.
Phys., 2007, 127, 074504.
58 N. M. O’Boyle, A. L. Tenderholt and K. M. Langner,
J. Comput. Chem., 2008, 29, 839.
59 N. C. F. Dionysio, J. Bordinhao, L. C. Visentin and
˜
48 C. K. Johnson, in Crystallographic Computing, ed. F. R. Ahmed,
Munksgaard, Copenhagen, 1970, pp. 207–219.
C. M. Ronconi, Acta Crystallogr., Sect. E: Struct. Rep. Online,
2008, 64, o546.
c
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