Aromatic Schiff Bases Multiply Substituted with Terminal Ethynyl Groups: Potential Building Blocks for Conjugated Polymers and Oligomers

Article abstract of DOI:10.1071/CH14639

Nine mostly novel aromatic Schiff bases containing from two-to-four terminal ethynyl groups and one or two methanimine groups per one molecule are reported. The spectral and density functional theory characteristics and the extent of conjugation are discu

Full text of DOI:10.1071/CH14639

CSIRO PUBLISHING
Aust. J. Chem. 2015, 68, 1237–1248
Full Paper
http://dx.doi.org/10.1071/CH14639
Aromatic Schiff Bases Multiply Substituted with Terminal
Ethynyl Groups: Potential Building Blocks for
Conjugated Polymers and Oligomers
A
A
A
B
Sabina Stahlova´, Jan Sedla´cˇek, Jan Svoboda, Miroslav Pola´sˇek,
and Jirˇ´ı Zedn´ık
A C
,
A
Department of Physical and Macromolecular Chemistry, Faculty of Science,
Charles University in Prague, Hlavova 2030, CZ-128 43 Prague 2, Czech Republic.
J. Heyrovsky´ Institute of Physical Chemistry, v.v.i., Academy of Sciences
of the Czech Republic, Dolejsˇkova 3, 182 23 Prague 8, Czech Republic.
B
C
Corresponding author. Email: jiri.zednik@natur.cuni.cz
Nine mostly novel aromatic Schiff bases containing from two-to-four terminal ethynyl groups and one or two methanimine
groups per one molecule are reported. The spectral and density functional theory characteristics and the extent of
conjugation are discussed in connection with the structure and architecture of the prepared compounds. The applicability
of compounds as building blocks for conjugated polymers is shown in TaCl5-catalyzed polycyclotrimerization (proceed-
ing in ethynyl groups) yielding either soluble luminescent or insoluble microporous polymers.
Manuscript received: 28 October 2014.
Manuscript accepted: 17 December 2014.
Published online: 31 March 2015.
the networks.[8,15–17] The functionality f ¼ 2 is reliably sufficient
to achieve (hyper)cross-linked networks via polycyclotrimeriza-
tion[18,19] and chain-growth polymerization[9,20] of MEAs,
although in this case, MEAs with f . 2 are also sometimes
used.[18,21] The networks derived from MEAs are investigated
for their optoactive properties,[22,23] porosity, and correspond-
ing applicability in catalysis and the capture of gases and small
molecules.[16,24–26]
Introduction
Arenes substituted with several terminal ethynyl groups
(referred to here as multiethynylarene, MEA) are excellent
building blocks (monomers) for the synthesis of conjugated
polymers and oligomers of various structures, architectures, and
functions.[1–9] The number of ethynyl groups per one MEA
molecule (i.e. the monomer functionality, f ) ranges mostly from
two to four. Various synthetic paths from MEAs to conjugated
polymers are described in the literature. Homocoupling of die-
thynylarenes leads to linear poly(arylenebutadiynylene)s.[1,10]
Cross-coupling of diethynylarenes with dibromo- or diiodo-
arenes provides linear poly(aryleneethynylene)s chain length
and end-capping of which can be controlled by composition
of the polymerization feed.[4,7,11] Linear polymers are also
obtained via Huisgen cycloaddition from diethynylarenes and
diazidoarenes.[1] The polycyclotrimerization of mixtures of
diethynylarene and alkylacetylene catalyzed by TaCl5 provides
soluble hyperbranched polyarylenes and oligoarylenes in which
the original arene cores of the monomer molecules are inter-
connected by benzenetriyl linkers formed via cyclotrimerization
of three ethynyl groups.[1,2,12] The soluble branched polymers
have also been obtained via chain-growth polymerization from
a diethynylarene and monoethynylarene feed (polyacetylene-
type polymers).[13,14] The luminescence, response to stimuli,
molecular recognition, and other properties are studied on
soluble MEA-derived polymers.[1] If MEAs of a higher func-
tionality are polymerized by the above approaches, the insoluble
highly cross-linked conjugated networks are obtained. MEAs
and corresponding halo- or azidoarenes of an average func-
tionality from 2.5 to 4 are used in the step-growth synthesis of
Arene cores of MEAs mostly consist of isolated or C–C
interconnected aromatics.[1–4,18,19] Besides, MEAs have been
reported to contain cores in which two or three arene rings are
connected by conjugated ethene-1,2-diyl, ethyne-1,2-diyl or azo
linker(s) (e.g. 1,4-bis[(4-ethynylphenyl)ethenyl]benzene and
2,5-bis[(4-ethynylphenyl)ethynyl]thiophene MEAs).[27,28] One
may assume that the choice of arene cores of MEAs is limited
by the requirement of sufficient solubility of MEA. From
this point of view, interconnecting arene rings in the MEA core
by methanimine (azomethine) –CH¼N– group[29] may be a
promising step. This group should (1) decrease the rigidity and
(2) slightly increase the polarity of the molecules of MEA. Both
of these factors should positively contribute to the solubility of
MEA. Moreover, the polymers and oligomers prepared from
such MEAs may be suitable for post-polymerization modifica-
tions involving reactions in the methanimine group. Only several
reports can be found in the literature on the Schiff base-type
MEAs. Wei et al.[30] used condensation of 3-ethynylaniline
with either 1,4- or 1,3-phthaldehyde and 4-ethynylaniline with
1,4-phthaldehyde and prepared respective positional isomers of
1,10-(phenylene)bis[N-(4-ethynylphenyl)methanimine]s. Mono-
mer 1,10-(1,4-phenylene)bis[N-(4-ethynylphenyl)methanimine]
Journal compilation Ó CSIRO 2015
www.publish.csiro.au/journals/ajc

1238
S. Stahlova´ et al.
N
C
H
N
C
H
C
H
N
D1
T1
T2
C
H
N
C
H
N
N C
H
D2
N
N
CH
CH
N
C
H
D3
T3
N
C
H
D4
C
H
N
C
H
N
N
C
H
D5
T4
Chart 1. Structure formulae and codes of the prepared MEAs.
was polymerized via Glaser–Hahn oxidative coupling into well-
defined –CH¼N–groups containingpoly(arylenebutadiynylene)-
type polymer. Other isomers were applied in the preparation of
thermosets via hot-melt processing.[31] 1,10-(1,4-Phenylene)bis
[N-(4-ethynylphenyl)methanimine] was also used by Lavastre
et al. in a combinatorial chemistry screening in which eight
various diethynylarenes were polymerized by Sonogashira
cross-coupling with a series of dibromoarenes into (arylene-
ethynylene)s.[28] Various monoethynylarenes ( f ¼ 1) with the
methanimine group in the substituent (e.g. N-(benzylidene)-4-
ethynylanilines and N-(4-ethynylbenzylidene)anilines) have
also been prepared and characterized.[32,33] With respect to the
monofunctionality of these monomers, only the chain-growth
mode was possible for their polymerization.[34–37] Linear poly-
acetylenes containing methanimine groups as parts of the
pendant groups were achieved by this approach.
In this contribution, we report the preparation of a series of
mostly new MEAs containing in a molecule from two-to-four
terminal ethynyl groups on benzene rings interconnected by
either one or two methanimine groups. The influence of the
molecular structure and architecture (the size of MEA core,
positional isomerism on benzene rings, functionality) on the
spectral properties and overall conjugation extent of MEAs is
discussed on the basis of experimental spectral data and results
of density functional theory (DFT) computation. The applica-
bility of the prepared MEAs is demonstrated by TaCl5-catalyzed
polymerizations yielding (depending on the conditions) either
soluble luminescent or insoluble microporous polycyclotrimers.
prepared. Structural formulae, names, and codes of MEAs are
given in Chart 1 and the Experimental section. The MEAs were
synthesized by one-step condensation from respective amines
and aldehydes performed in a minimum amount of methanol
at room temperature (Experimental section). The use of the
smallest possible amount of methanol was crucial because it
supported the precipitation of the products, which are less sol-
uble than the starting amines and aldehydes. The precipitation
resulted in a shift in the condensation equilibrium in favour of
the product. MEAs were prepared in isolated yields ranging
from 62 % to 90 % (see Experimental section); the yield loss is
mainly attributed to the purification of the products by their
washing with (cold) methanol.
The MEAs with two (ethynyl-substituted) benzene rings
connected by one methanimine link are referred to as dimers
(D). The functionality, f, (i.e. the number of ethynyl groups per
one MEA molecule) of the dimer-type MEAs is either 2 (D1, D2,
D4, D5) or 3 (D3). The prepared MEAs containing three benzene
rings connected by two methanimine links are referred to as
trimers (T). Trimers T1, T2, and T4 contain ethynyl groups on
terminal benzene rings only (one ethynyl group on each terminal
benzene ring, f ¼ 2, in T1 and T2, or two ethynyl groups on
each terminal benzene ring, f ¼ 4, in T4). Trimer T3 has been
designed such that each benzene ring (including the central one)
bears one ethynyl group ( f ¼ 3). The ethynyl groups of MEAs are
either para- or meta-positioned with respect to the methanimine
group. The compounds D1, T1, and T2 possess only para-
positioned ethynyl groups. Only meta-positioned ethynyl groups
are present in D5 and T4. The compounds D2, D3, D4, and T3
contain both para- and meta-positioned ethynyl groups. Both the
para- and meta- positioning of the ethynyl groups with respect to
the methanimine group was realised (particularly in the D series
of MEAs) with the aim of evaluating the influence of this
positional isomerism on the MEA conjugation.
Results and Discussion
Synthesis of Schiff Base-Type MEAs
A series of mostly new MEAs with cores containing benzene
rings connected by methanimine (azomethine) link(s) have been

Aromatic Schiff Bases with Terminal Ethynyl Groups
1239
Table 1. 13C NMR shifts of HC5N and CꢁCH carbons and 1H NMR shifts of HC5N and CꢁCH hydrogens in MEAs. Charges of CꢁCH carbons by
NBO method and dihedral angles between the aniline ring plane and the plane defined by a benzylidene ring and the C5N unit (by DFT computation)
MEA
13C NMR
1H NMR
13C NMR
13C NMR
1H NMR
1H NMR
Charge
Charges
of CꢁCH
benzylidene
part
Dihedral
angle
[8]
shift of HC¼N shift of HC¼N shift of CꢁCH shift of CꢁCH shift of CꢁCH shift of CꢁCH of CꢁCH
[ppm]
[ppm]
aniline part
[ppm]
benzylidene
part
aniline part
[ppm]
benzylidene
part
aniline
part
[ppm]
[ppm]
D1
D2
D3
D4
D5
T1
T2
T3
160.3
160.6
159.1
160.3
160.4
160.1
159.1
160.5
8.45
8.45
8.39
8.43
8.43
8.52
8.53
8.50
77.9
77.9
78.0
77.9
77.9
78.0
–
80.0
80.0
79.2
78.4
78.5
–
3.17
3.17
3.18
3.17
3.17
3.18
–
3.30
3.30
3.23
3.20
3.20
–
ꢀ0.213
ꢀ0.211
ꢀ0.211
ꢀ0.213
ꢀ0.211
ꢀ0.211
–
ꢀ0.199
ꢀ0.198
ꢀ0.196
ꢀ0.203
ꢀ0.203
–
37.78
39.59
38.28
39.17
40.09
37.50
35.28
38.40;
38.04
35.45
79.9
79.2
3.29
3.27
ꢀ0.200
ꢀ0.196
78.1
3.18
ꢀ0.210
T4
157.9
8.48
–
79.1
–
3.23
–
ꢀ0.197
conclusion results for the 13C NMR signals of terminal carbon
of the ethynyl groups: CꢁCH signals of the ethynyl groups
connected to the aniline part of the molecules (d ¼ 77.9–
78.1 ppm) are shifted upfield compared with CꢁCH signals of
the ethynyl groups connected to the benzylidene part of the
molecules (d ¼ 78.4–80.0 ppm). The influence of the meta or
para positioning of the ethynyl groups (relative to the methani-
mine link) on the NMR shifts of their terminal hydrogen and
carbon can be well followed in the D-type series of MEAs. The
1H NMR (CꢁCH) and 13C NMR (CꢁCH) chemical shifts of
ethynyl groups connected to the aniline part of MEAs are not
sensitive to the meta or para positional isomerism of ethynyl
groups (Table 1). On the contrary, both 1H NMR (CꢁCH) and
13C NMR (CꢁCH) chemical shifts reflect the meta or para
positional isomerism in the case of ethynyl groups connected to
the benzylidene part of MEAs: CꢁCH and CꢁCH signals of the
para-positioned ethynyls are at 80.0 and 3.30 ppm, respectively
(D1, D2), whereas the corresponding signals of the meta-
positioned ethynyls are in the intervals d 78.4–79.2 ppm and
3.20–3.23 ppm, respectively (D3, D4, D5). The downfield shift
of CꢁCH and CꢁCH signals of the para-positioned ethynyls
may indicate that the para-positioned ethynyl groups are more
conjugated with the benzylidene moiety than the ethynyl groups
in the meta position(s) (see below). The observed behaviour is
caused by the junction of the mesomeric effects of ethynyl and
azomethine groups. The 13C NMR chemical shifts of CꢁCH
carbons (ethynyl groups on both aniline and benzylidene parts of
MEAs) are plotted as a function of the charge on these carbons
(by NBO computation) in Fig. 1. A certain correlation between
these parameters is apparent from Fig. 1. Nevertheless, besides
the partial charge, other factors most probably affected the
13C NMR chemical shifts of CꢁCH carbons (e.g. the chemical
neighbouring of the ethynyl group, overall geometry, and
electron density of the MEA molecule).
Characterization of MEAs
All the MEAs prepared are yellowish solids soluble in tested
solvents: CH2Cl2, toluene, THF. The solubility of MEAs in
CH2Cl2 at room temperature was studied in detail. The solubility
of 1 mol Lꢀ1 was achieved for all the D-type MEAs. The solu-
bility of T-type MEAs in CH2Cl2 was as follows: 0.6 mol Lꢀ1
(T3); 0.3 mol Lꢀ1 (T1 and T2); and 0.1 mol Lꢀ1 (T4). The
MEAs prepared were characterized by high-resolution mass
1
spectrometry (HRMS), H and 13C NMR, infrared (IR) spec-
troscopy, and Raman spectroscopy (see Experimental).
The presence of the methanimine group in the prepared
MEAs was evidenced by means of H NMR and 13C NMR
1
spectroscopy techniques. The respective signals are in narrow
intervals (d ¼ 8.39–8.50 ppm, HC¼N and d ¼ 157.9–
160.6 ppm, HC ¼ N, see Table 1) regardless of the functionality,
positional isomerism, and architecture of individual MEAs. The
positions of the signals are close to the positions of HC¼N
signals in unsubstituted N-benzylideneaniline (d ¼ 8.43 ppm,
HC¼N and d ¼ 160.34 ppm, HC¼N, refs[38,39]). This finding
can be discussed in connection to the work of Neuvonen et al.[39]
who investigated the influence of various substituents in para
positions of N-benzylideneaniline rings on the 13C NMR chemi-
cal shifts of carbon of the methanimine group (however,
ꢀCꢁCH substituent had not been involved in this study). The
authors revealed the inductive effect of the substituents as a
crucial factor influencing the 13C NMR chemical shifts of
HC¼N. Because the ethynyl group possesses only a low
electron-withdrawing inductive effect, consequently, the
1H NMR and 13C NMR chemical shifts of MEAs methanimine
groups are similar to those of the methanimine group of
unsubstituted N-benzylideneaniline. The main aspect of the
terminal ethynyl groups influencing electron densities is the
resonance (mesomeric) effect.
The 13C NMR chemical shifts and values of charges (by
natural bond orbital, NBO, analysis) of terminal carbon of the
ethynyl groups (CꢁCH) are summarized in Table 1 together
with the values of 1H NMR chemical shifts of hydrogen of the
ethynyl groups (CꢁCH). The 1H NMR signals of hydrogens of
the ethynyl groups connected to the aniline part of MEAs
(d ¼ 3.17–3.18 ppm) are slightly shifted upfield compared with
the signals of hydrogens of the ethynyl groups connected to the
benzylidene part of MEAs (d ¼ 3.20–3.30 ppm). The same
The dihedral angle between the aniline ring plane and the
plane defined by the benzylidene ring and the C¼N unit is a
structural parameter that is often studied in ring-substituted
N-benzylideneanilines.[39,40] The dihedral angles obtained by
DFT for the optimized ground state geometry of MEAs are given
in Table 1. All the values are in a narrow range from 35.288 to
40.098. A weak influence of the meta or para positioning of the
ethynyl groups on the dihedral angle is evident in the series of

1240
S. Stahlova´ et al.
35
30
25
20
15
10
5
1.0
D1
D2
D3
D4
D5
80.0
79.5
79.0
78.5
78.0
77.5
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
260 280 300 320 340 360 380 400 420
Wavelength [nm]
Ϫ0.212
Ϫ0.208
Ϫ0.204
Ϫ0.200
Ϫ0.196
NBO partial charges on terminal acetylenic carbon
Fig. 2. UV-Visible spectra of D-type MEAs. Computed positions of
HOMO–LUMO transitions are presented as perpendiculars to the wave-
length axis; the length of perpendiculars is related to the oscillator
strength axis.
Fig. 1. 13C NMR chemical shifts vs NBO partial charges for CꢁCH
carbons of MEAs.
1.6
60
50
40
30
20
10
0
T1
T2
T3
T4
the bifunctional D-type MEAs in which the dihedral angle
increases in the order: D1(pp) , D4(pm) E D2(pm) , D5
(mm); letters p and m in the parentheses represent one ethynyl
group in either the para (p) or meta (m) position. Evidently, each
replacement of the para-positioned ethynyl group by the meta-
positioned one leads to the (small) increase in the dihedral angle,
most probably due to the steric effect of the meta-positioned
ethynyl group(s). Dihedral angles of the T-type MEAs depend
mainly on the composition of the MEA core. The T-type MEAs
with a central ring derived from p-phenylenediamine exhibit
dihedral angles of 35.288 (T2) and 35.458 (T4). Slightly higher
dihedral angles result for the T-type MEAs with a central ring
derived from benzenedicarboxaldehydes: 37.508 (T1); 38.048
and 38.408 (T3).
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
260 280 300 320 340 360 380 400 420 440
Wavelength [nm]
The Fourier transform infrared (FT-IR) and Raman spectra of
MEAs are given in Figs S1 and S2 (Supplementary Material),
respectively, and the representative FT-IR and Raman bands are
summarized in Table S1 (Supplementary Material). Bands
around 1620 cmꢀ1 observed in both FT-IR and Raman spectra
of all the MEAs have been ascribed to the stretching vibration of
C¼N bonds. The stretching vibration of NC–H bond was
manifested by an FT-IR band at 2880–2900 cmꢀ1. The stretch-
ing vibration of CꢁC bonds was well apparent in the Raman
spectra (2100 cmꢀ1), but barely noticeable in the FT-IR spectra.
The bands due to the stretching vibrations of ꢁC–H bonds were
observed in the FT-IR spectra only (3205–3293 cmꢀ1). An
interesting phenomenon was observed in the FT-IR spectra of
D2, D3, D5, T3, and T4. A huge difference (up to 75 cmꢀ1) was
Fig. 3. UV-Visible spectra of T-type MEAs. Computed positions of
HOMO–LUMO transitions are presented as perpendiculars to the wave-
length axis; the length of perpendiculars is related to the oscillator
strength axis.
The shapes of the HOMO and LUMO orbitals of individual
MEAs obtained by DFT computation are given in Fig. 4.
Table 2 and Fig. 2 clearly show that the lmax, ledge, and emax
values of the D-type MEAs decrease in the following order:
D1 . D3 E D4 E D2 . D5. The wavelengths of the HOMO–
LUMO transition computed by DFT (lDFT) as well as the values
of oscillator strength exhibit the same trend (see Table 2 and
Fig. 2) although all the values of lDFT are systematically red-
shifted from the values of lmax. The above-outlined trends show
that the meta or para positioning of the ethynyl groups signifi-
cantly affects the overall conjugation of the D-type MEA. The
MEA with all ethynyl groups in the meta positions (D5)
possesses UV-visible spectral characteristics nearly equal to
those of unsubstituted N-benzylideneaniline (see Table 2 and
compare with values for N-benzylideneaniline: lmax ¼ 315 nm,
ledge ¼ 370 nm, lDFT ¼ 331 nm). Evidently, the meta-positioned
ethynyl groups in D5 only marginally extended the conjugation
of the N-benzylideneaniline core. On the other hand, each
replacement of the meta-positioned ethynyl group(s) by the
para-positioned group leads to the red shift in the UV-visible
spectrum most probably due to the extension of the conjugation
of the N-benzylideneaniline core to the para-positioned ethynyl
found between the positions of the FT-IR n
bands corre-
ꢁC–H
sponding to individual (non-equivalent) ethynyl groups of one
molecule although the positions of these bands should differ by
only 2 cmꢀ1 according to the DFT computation. This phenome-
non could probably be caused by the Fermi resonance.
The UV-visible spectra of the MEAs are shown in Fig. 2
(D-type MEAs) and Fig. 3 (T-type MEAs). All MEAs featured
spectra that contain a higher energy band and a lower energy
band that correspond to the HOMO–LUMO transition and
is discussed in detail. The wavelengths of the absorption
maximum and low-energy edge of this band, lmax and ledge
,
respectively, molar absorption coefficients, emax, corresponding
to lmax, and band gap values obtained from the edge of the
UV-visible spectra are given in Table 2.

Aromatic Schiff Bases with Terminal Ethynyl Groups
1241
Table 2. Characteristics of HOMO–LUMO transitions in MEAs as obtained by UV-visible spectroscopy and DFT computation
lmax, absorption maximum of lower energy band ascribed to HOMO–LUMO transition; lDFT, absorption maximum of lower energy band ascribed to
HOMO–LUMO transition from DFT calculation; emax, molar absorption coefficient determined from absorption maxima; ledge, absorption edge
MEA
lmax [nm]
emax
ledge [nm]
Band gapA [eV]
lDFT [nm]
Oscillator strength
Band gapB [eV]
[ꢂ103 molꢀ1 dm3 cmꢀ1
]
D1
D2
D3
D4
D5
T1
T2
T3
T4
338
329
331
330
320
361
371
335
364
19
12
11
13
6.3
33
33
30
29
408
389
395
391
366
432
438
408
428
3.04
3.19
3.12
3.17
3.38
2.87
2.83
3.04
2.89
371
351
360
354
335
416
417
368
396
0.917
0.622
0.684
0.674
0.379
1.567
1.625
0.886
1.274
3.76
4.02
3.92
3.96
4.25
3.37
3.44
3.78
3.65
AObtained from the UV-vis spectra from ledge
.
BObtained by DFT computation.
groups. Consequently, the D1 MEA (two ethynyl groups in the
para positions) exhibits (1) experimental lmax ,18 nm red-
shifted from that of D5 and (2) emax about three times as high as
that of D5. The finding that D1 is the most conjugated MEA
from the D-type series is consistent with the shapes of HOMO
and LUMO (Fig. 4): among all the D-type MEAs, only D1 has
both HOMO and LUMO delocalized over the whole molecule
including both ethynyl groups. The values of the band gap of the
D-type MEAs (whether obtained from ledge or by DFT compu-
tation) are increasing with decreasing values of lmax. It should
be noted that DFT computation provided systematically higher
values of the band gaps when compared with those obtained
from the experimental UV-visible spectra (the differences are
,0.8 eV, see Table 2).
HOMO
LUMO
D1
D2
D3
The HOMO–LUMO transitions in T1, T2, and T4 (T-type
MEAs with 1,4-phenylene central ring) are shifted to a lower
energy when compared with the HOMO–LUMO transitions in
the D-type MEAs (compare lmax, lDFT, and band gap values of
T1, T2, and T4 with those of D-type MEAs in Table 2). This
most probably reflects that the cores of T1, T2, and T4 are one
1,4-phenylene-azomethine segment longer compared with the
cores of the D-type MEAs. The UV-visible spectral character-
istics of T1, T2, and T4 exhibited only a weak influence on
(1) the orientation of azomethine links between 1,4-phenylene
rings (compare data for T1 and T2 in Table 2) and (2) meta or
para positioning of ethynyl groups (compare data for T2 and T4
in Table 2).
D4
D5
T1
As evident from Fig. 4, the HOMO and LUMO of T1, T2,
and T3 (MEAs with a 1,4-phenylene central ring) are deloca-
lized over the whole MEA core. On the contrary, the HOMO
and LUMO delocalization is interrupted on the central 1,3-
phenylene ring of T3. This is manifested by a blue shift of the
low-energy UV-visible band of T3 in comparison with the
position of this band in the spectra of T1, T2, and T4
(see Fig. 3 and Table 2). The incorporations of 1,3-phenylene
as the central ring into the T-type MEA allowed the substitution
of this central ring into a sterically unhindered position 5. On the
other hand, the replacement of the 1,4-phenylene central ring
by the 1,3-phenylene ring led to the decrease in the conjugation
extent of the T-type MEA. The DFT computation of electronic
transitions in the T3 molecule revealed that two other electronic
transitions occur energetically close to the HOMO–LUMO
transition (l ¼ 360 and 348 nm). This is most probably respon-
sible for an apparent discrepancy between a relatively high value
T2
T3
T4
Fig. 4. Electronic density contours for LUMO and HOMO of MEAs
obtained using DFT computation.

1242
S. Stahlova´ et al.
of emax and a relatively low value of oscillator strength ascer-
tained for T3 (see Table 2).
feed, D1/1-hexyne ¼ 0.5) according to Scheme 2 into a poly-
arylene-type product labelled as Pc(D1/hexyne).
The compounds D1and D2 exhibit photoluminescence when
excited by radiation of wavelength of 340 nm. The wavelengths
of the photoluminescence emission maxima, lPLmax, are 428 nm
(D1) and 419 nm (D2). The photoluminescence emission spectra
of D1 and D2 and corresponding photoluminescence lifetimes
are given in Fig. S3 and Table S2 (Supplementary Material),
respectively.
The growth of the polymers proceeded via interconnecting
N,1-bis(phenyl)methanimine cores of D1 (labelled as D1C) with
benzene-1,3,5-triyl and benzene-1,2,4-triyl linkers formed by
[2þ2þ2] cyclotrimerization of ethynyl groups.[12,19] Homo-
polycyclotrimerization of D1 gave insoluble (toluene, CH2Cl2,
THF) hyperbranched Pc(D1) with a yield of 68 %. The elemen-
tal analysis of Pc(D1) provided a C/N mole ratio of 18.10 that is
in good agreement with the C/N mole ratio of D1 (C/N ¼ 17). To
reduce the degree of polymerization and to achieve a soluble
product, 1-hexyne was applied as a monofunctional co-monomer
for the copolycyclotrimerization with bifunctional D1. The
copolycyclotrimerization gave Pc(D1/hexyne) with a yield of
62 % with respect to D1. The product was soluble in toluene,
CH2Cl2, and THF although the solubility deteriorated with the
Pc(D1/hexyne) ageing in both solid state and solution. Size
Polycyclotrimerization of D1
The polymerizability of Schiff base-type MEAs via poly-
cyclotrimerization was investigated with the use of the
compound (monomer) D1 and TaCl5/Ph4Sn catalyst system.
Monomer D1 was (1) homopolycyclotrimerized according to
Scheme 1 into a polyarylene-type product labelled as Pc(D1)
and (2) copolycyclotrimerized with 1-hexyne (mole ratio in the
D1C
D1C
D1C
D1C
D1C
D1C
D1C
TaCl5/Ph4Sn
D1C
D1C
D1C
D1C
D1C
D1C
CH
N
D1C ϭ
D1C
D1C
D1C
D1C
Scheme 1. Homopolycyclotrimerization of D1.
D1C
D1C
D1C
D1C
TaCl5/Ph4Sn
D1C
ϩ
D1C
D1C
D1C
CH
D1C ϭ
N
Scheme 2. Copolycyclotrimerization of D1 with 1-hexyne.

Aromatic Schiff Bases with Terminal Ethynyl Groups
1243
exclusion chromatography (SEC) analysis of the freshly
prepared Pc(D1/hexyne) provided apparent molecular weight
averages, Mw ¼ 2000 and Mn ¼ 1100. Because the hyper-
branched architecture of Pc(D1/hexyne) is assumed, the abso-
lute molecular weight averages of Pc(D1/hexyne) are most
probably higher than the apparent molecular weight averages,
which are based on the calibration of SEC columns by linear
polystyrene standards. The C/N mole ratio of 22.29 was deter-
mined for Pc(D1/hexyne), i.e. the mole ratio of monomeric units
in Pc(D1/hexyne), (D1)MU/(1-hexyne)MU, is 1.13. The results of
elemental analysis of Pc(D1) and Pc(D1/hexyne) are given in
Table S3 (Supplementary Material). Fig. 5 shows the FT-IR
spectra of D1, Pc(D1), and Pc(D1/hexyne). The band at
1607 cmꢀ1 corresponding to the stretching vibration of C¼N
bonds is well apparent in the spectra of both polymers. Soluble
Pc(D1/hexyne) was characterized by 1H NMR spectroscopy in
CD2Cl2 (see Fig. S4 in Supplementary Material for the spec-
trum). Also, the 1H NMR spectroscopy confirms the presence of
the azomethine groups in the Pc(D1/hexyne) sample (signal
region 8.4–8.7 ppm). Nevertheless, the inspection of the
1H NMR spectrum also reveals a minor signal at ,10 ppm that
most probably corresponds to aldehyde groups formed by partial
hydrolysis of the azomethine groups. The hydrolysis may reflect
the Lewis acidity of TaCl5 cyclotrimerization catalyst. We have
estimated the degree of hydrolysis of the CH¼N groups in
Pc(D1/hexyne) to be 25–35 % on the basis of the intensities
of signals of CH¼N and CH¼O groups in the 1H NMR
spectrum. Both Pc(D1) and Pc(D1/hexyne) contain a certain
amount of non-transformed ethynyl groups (see FT-IR bands
corresponding to the stretching vibration of CꢁC and ꢁC–H
bonds at 2106 cmꢀ1 and 3295 cmꢀ1, respectively). The presence
of ethynyl groups in Pc(D1/hexyne) and their slow spontaneous
reaction leading to the polymer cross-linking may be respon-
sible for the gradual deterioration of the solubility of
Pc(D1/hexyne). The performed polycyclotrimerizations of D1
confirmed the possibility to transform this type of MEA into
hyperbranched polyarylenes with various degrees of
polymerization.
D1
Pc(D1)
Pc(D1/hexyne)
3500
3000
2500
2000
1500
1000
500
Wavenumber [cmϪ1
]
Fig. 5. FT-IR spectra of D1, Pc(D1), and Pc(D1/hexyne).
D1
Pc(D1/hexyne)
Homopolycyclotrimer Pc(D1) was analyzed by nitrogen
adsorption at 77 K (see Fig. S5 in Supplementary Material for
the adsorption isotherm). The analysis revealed the microporous
character of Pc(D1) with a Brunauer–Emmett–Teller surface
area, SBET, of 65 m2 gꢀ1. This value is lower than SBET values of
purely hydrocarbon microporous polyarylenes.[18,19] On the
other hand, the ethynyl and methanimene groups present in
Pc(D1) are promising for post-polymerization modification of
microporous polymers of this type.[5]
The UV-visible spectrum of soluble Pc(D1/hexyne) (see
Fig. S6 in Supplementary Material) provides the following
parameters: lmax ¼ 350 nm and ledge ¼ 420 nm. These values
are slightly red-shifted from those of D1 monomer (lmax ¼ 338 nm
and ledge ¼ 408 nm). Likewise to D1, Pc(D1/hexyne) exhibits
photoluminescence when excited by radiation of a wavelength
of 350 nm. The photoluminescence emission spectra of D1
and Pc(D1/hexyne) and the corresponding photoluminescence
lifetimes are given in Fig. 6 and Table 3, respectively.
400
450
500
550
600
650
Wavelength [nm]
Fig. 6. Normalized photoluminescence emission spectra of D1 (excitation
wavelength: 340 nm) and Pc(D1/hexyne) (excitation wavelength: 350 nm).
Table 3. Photoluminescence emission characteristics of D1 and Pc(D1/hexyne)
PLmax, wavelength of the photoluminescence emission maximum; t1, t2, and t3, lifetimes of the photoluminescence
components (their contributions are given in parentheses)
l
Sample
l
PLmax [nm]
Stokes shift [nm]
t1 [ns]C
t2 [ns]C
t3 [ns]C
D1
428A
490B
88
3.2 (10 %)
7.5 (46 %)
1.1 (52 %)
2.9 (44 %)
0.06 (38 %)
0.5 (10 %)
Pc(D1/hexyne)
140
AExcitation wavelength: 340 nm.
BExcitation wavelength: 350 nm.
CExcitation wavelength: 378 nm.

1244
S. Stahlova´ et al.
Fig. 6 clearly shows that the photoluminescence emission
All FT-IR spectra were measured on a Nicolet Magna IR 760
using the diffuse reflection mode (DRIFT; diffuse reflectance
infrared Fourier transform). Samples were diluted with KBr.
Raman spectra were recorded on a DXR Raman microscope
(Thermo Scientific) using excitation at 780 nm and undiluted
samples.
UV-visible spectra were measured in a dichloromethane
solution of known concentration (10ꢀ5 mol dmꢀ3) on a Shimadzu
PC-2401 UV-vis spectrometer.
Steady-state fluorescence was measured on a Spex 3 Jobin
Yvon fluorescence spectrometer using 340 nm as an excitation
wavelength. The time-resolved fluorescence decay was mea-
sured on the same apparatus using a laser (378 nm) diode as an
excitation monochromator. The emission monochromator was
set to luminescence maxima according to the steady-state
emission spectra of the appropriate sample.
band of Pc(D1/hexyne) is significantly red-shifted from that of
D1 as a result of D1 copolycyclotrimerization. Simultaneously,
the photoluminescence lifetimes of Pc(D1/hexyne) are signifi-
cantly prolonged compared with photoluminescence lifetimes
of D1 (Table 3). Values of lPLmax of D1 and Pc(D1/hexyne) are
428 nm and 490 nm, respectively, and the corresponding Stokes
shifts are 88 nm in the case of D1 and 140 nm in the case of
Pc(D1/hexyne). Although the photoluminescent polyarylenes
prepared by copolycyclotrimerization of diethynylarenes (with
bulky arene cores) and 1-alkynes often exhibit large Stokes
shifts, the value of 140 nm determined for Pc(D1/hexyne)
represents an exceptionally large Stokes shift among this type
of polymers.[41]
Conclusions
Low-resolution electron ionization mass spectra were mea-
sured on a ZAB2-SEQ double focusing mass spectrometer. Ion
source conditions were as follows: electron energy, 70eV;
electron current, 50 mA; and source temperature, 2508C. Accu-
rate mass measurements were performed at a resolution
of 10000 (10 % valley definition) using a peak matching tech-
nique with perfluorokerosene as the internal standard. Samples
were introduced using a direct inlet probe heated up to a
temperature enabling evaporation.
SEC analysis of D1/1-hexyne copolycyclotrimer was per-
formed on an Agilent Technologies 1100 Series apparatus fitted
with a UV-visible detector operating at 254 nm. A series of three
PL-gel columns (Mixed B and Mixed C and Mixed E, Polymer
Laboratories, UK) and THF as the mobile phase (flow rate
0.7 mL minꢀ1) were used. Apparent (relative to polystyrene)
number-average molecular weight Mn and weight-average
molecular weight Mw are reported.
A series of mostly novel aromatic Schiff bases containing from
two-to-four terminal ethynyl groups have been prepared. The
condensation of respective amines and aldehydes, performed in
a minimum amount of methanol, was used as a synthetic tool.
The spectral characteristics of Schiff bases as well as the results
of DFT computation are discussed in connection with the
composition and architecture of the prepared compounds. The
extent of conjugation depends on the size and architecture of
the arene cores; mainly, the Schiff bases containing the short
N-benzylideneaniline core exhibit a lower extent of conjugation
than those with prolonged (1,4-phenylene)bis[N-(phenyl)
methanimine] and (1,4-phenylene)bis[1-(phenyl)methanimine]
cores. The extent of conjugation of the Schiff bases with a
N-benzylideneaniline core further depends on the meta or para
positioning of ethynyl groups on both benzene rings, whereby
each ethynyl group in the para position (with respect to
methanimine group) enhances the conjugation and the meta-
positioned ethynyl groups affect the conjugation only margin-
ally. The prepared multi-substituted Schiff bases are promising
building blocks for the synthesis of conjugated polymers via
polymerization of their ethynyl groups. An example is reported
in which N,1-bis(4-ethynylphenyl)methanimine has been
catalytically polycyclotrimerized into hyperbranched poly-
arylenes of various degrees of polymerization exhibiting either
microporosity or photoluminescence.
Nitrogen adsorption isotherm on polycyclotrimer of D1 was
recorded at 77 K using an ASAP 2020 (Micromeritics) volu-
metric instrument as described elsewhere.[9]
Computation
The geometry of ground states was optimized using DFT;
transition energies of absorption were calculated by time
dependent-DFT using optimized ground state geometry. In all
the computations, Becke’s three-parameter functional with the
non-local Lee–Yang–Parr correlation functional (B3LYP) with
the standard 6–31G(2d,p) basis set as implemented in Gaussian
was used.[42]
Experimental
Materials
4-Ethynylaniline, 3-ethynylaniline, 4-ethynylbenzaldehyde, 3-
ethynylbenzaldehyde, terephthalaldehyde, p-phenylenediamine,
tantalum(V) chloride (TaCl5), tetraphenyltin (Ph4Sn), and
methanol (Sigma-Aldrich), and 3,5-diethynylbenzaldehyde and
5-ethynyl-1,3-benzenedicarboxaldehyde (Spectra Group Lim-
ited, Inc.) were used as obtained. 1-Hexyne (Sigma-Aldrich)
was distilled from CaH2 under reduced pressure just before use.
Toluene (Lach-Ner, Czech Rep.) was distilled from a sodium/
acetophenone drying system under nitrogen just before use.
Synthesis of Dimer-Type MEAs
Dimers D1, D2, D3, D4, and D5 (see below) were prepared by
reaction of respective ethynyl(s)benzaldehyde (2 mmol) with
respective ethynylaniline (2 mmol). Reactions were started by
mixing reactant solutions (solutions were prepared by dissol-
ving the reactants in minimum amounts of methanol, 3-ethynyl-
aniline, which is liquid, and used undiluted). The first crystals of
the product appeared in the reaction mixture within a 5–30 min
interval. After 3 h, a yellowish microcrystalline precipitate was
separated by filtration, washed with cold methanol to remove
non-reacted starting compounds, and dried in a vacuum at room
temperature to a constant weight.
Techniques
1H NMR and 13C NMR measurements were performed using
a Varian Unity Inova 400 spectrometer. Chemical shifts of
signals in the spectra were referenced to the solvent peaks
(1H NMR (CD2Cl2, 400 MHz): d ¼ 5.32 ppm; 13C NMR
(CD2Cl2, 101 MHz): d ¼ 54 ppm). First-order analysis was used
to evaluate all the NMR spectra received.
Synthesis of Trimer-Type MEAs
Trimers T1 and T3 (see below) were prepared by reaction of
respective (ethynyl)benzenedicarboxaldehyde (1 mmol) with

Aromatic Schiff Bases with Terminal Ethynyl Groups
1245
4-ethynylaniline (2.4 mmol). Trimers T2 and T4 (see below)
were prepared by reaction of respective ethynyl(s)benzaldehyde
(2.4 mmol) with p-phenylenediamine (1 mmol). Reactions were
started by mixing reactant solutions (solutions were prepared by
dissolving the reactants in minimum amounts of methanol). If a
yellowish microcrystalline precipitate of the desired product
was not formed within 3 h, the reaction mixture was cooled at
ꢀ58C to induce product crystallization. The solid product was
separated by filtration, washed with cold methanol to remove
non-reacted starting compounds, and dried in a vacuum at room
temperature to a constant weight.
dC (CD2Cl2, 101 MHz) 160.6 (C5), 152.4 (Carom), 136.8
(Carom), 133.0 (Carom), 130.0 (Carom), 129.9 (Carom), 129.3
(Carom), 125.7 (Carom), 124.8 (Carom), 123.5 (Carom), 122.4
(Carom), 83.7 (C14), 83.6 (C12), 80.0 (C15), 77.9 (C13).
m/z (HRMS EI) 229.0899; Mþꢃ requires 229.0891.
1-(3,5-Diethynylphenyl)-N-(4-ethynylphenyl)
methanimine (D3) (Chart 4)
11
10
7
2
2
3
8
N,1-Bis(4-ethynylphenyl)methanimine (D1) (Chart 2)
5
C
H
1
12
4
6
9
13
N
7
7
8
8
2
3
3
8
13
7
11
1
5
C
H
3
9
4
N
6
12
10
10
2
11
Chart 2. Structure and group numbering of D1.
Chart 4. Structure and group numbering of D3.
Yield 80 %.
nmax (KBr)/cmꢀ1 552s, 636m, 710m, 845v., 1105vw,
1165w, 1365w, 1502w, 1556w, 1587w, 1622w, 2102w,
2881w, 3269v.
Raman shift (780 nm, 15 mW)/cmꢀ1 1166s, 1190w, 1556m,
1587s, 2099s.
dH (CD2Cl2, 400 MHz) 8.45 (s, 1H5), 7.88 (d, J 8.3, 2H7),
7.60 (d, J 8.3, 2H2), 7.53 (d, J 8.5, 2H8), 7.18 (d, J 8.6, 2H3), 3.30
(s, 1H13), 3.17 (s, H11).
Yield 64 %.
nmax (KBr)/cmꢀ1 634s, 673s, 726w, 839s, 856m, 886s,
1501m, 1580m, 1593m, 1624m, 2104w, 2888vw, 3212v.,
3282v.
Raman shift (780 nm, 15 mW)/cmꢀ1 1144w, 1167w, 1211w,
1580s, 1594m, 1624m, 2105s.
dH (CD2Cl2, 400 MHz) 8.39 (s, 1H5), 8.00 (d, J 1.5, 2H7),
7.71 (t, J 1.5, 1H9), 7.53 (d, J 8.5, 2H2), 7.18 (d, J 8.5, 2H3), 3.23
(s, 2H11), 3.18 (s, 1H13).
dC (CD2Cl2, 400 MHz) 160.3 (C5), 152.7 (Carom), 136.5
(Carom), 133.6 (Carom), 133.0 (Carom), 129.3 (Carom), 125.7
(Carom), 121.5 (Carom), 120.3 (Carom), 83.9 (C10), 83.6 (C12),
80.0 (C13), 77.9 (C11).
dC (CD2Cl2, 101 MHz) 159.1 (C5), 152.3 Carom), 138.4
(Carom), 137.3 (Carom), 133.8 (Carom), 133.0 (Carom), 123.8
(Carom), 121.5 (Carom), 120.6 (Carom), 83.8 (C12), 82.2 (C13),
79.2 (C11), 78.0 (C10).
m/z (HRMS EI) 229.0892; Mþꢃ requires 229.0891.
m/z (HRMS EI) 253.0887; Mþꢃ requires 253.0891.
N-(3-Ethynylphenyl)-1-(4-ethynylphenyl)methanimine
(D2) (Chart 3)
1-(3-Ethynylphenyl)-N-(4-ethynylphenyl)methanimine
(D4) (Chart 5)
7
8
2
2
3
3
2
3
11
10
12
5
C
H
1
4
14
5
C
H
1
4
9
N
9
N
13
6
6
15
10
11
8
2
3
7
14
12
15
13
Chart 5. Structure and group numbering of D4.
Chart 3. Structure and group numbering of D2.
Yield 62 %.
nmax (KBr)/cmꢀ1 419m, 535m, 559m, 654s, 677v., 685v.,
767m, 794m, 838s, 888s, 940s, 1145m, 1174m, 1211m, 1284m,
1307m, 1414m, 1476m, 1558m, 1575m, 1584m, 1602m, 1619s,
2102w, 2895w, 3221s, 3263v.
Yield 74 %.
nmax (KBr)/cmꢀ1 419m, 535m, 559m, 654s, 677v., 685v.,
767m, 794m, 838s, 888s, 940s, 1145m, 1174m, 1211m, 1284m,
1307m, 1414m, 1476m, 1558m, 1575m, 1584m, 1602m, 1619s,
2102w, 2895w, 3221s, 3263v.
Raman shift (780 nm, 15 mW)/cmꢀ1 972w, 999w, 1140m,
1168w, 1365w, 1590s, 1631m, 2107m.
Raman shift (780 nm, 15 mW)/cmꢀ1 1144w, 1175m, 1211w,
1557w, 1574m, 1602s, 1621s, 2013s.
dH (CD2Cl2, 400 MHz) 8.45 (s, 1H5), 7.88 (d, J 8.3, 2H3),
7.60 (d, J 8.3, 2H2), 7.37 (m, 2H9,11), 7.33 (bs, 1H7), 7.25–7.19
(m, 1H10), 3.30 (s, 1H15), 3.17 (s, 1H13).
dH (CD2Cl2, 400 MHz) 8.43 (s, 1H5), 8.03 (m, 1H11), 7.91
(dt, J1 7.8, J2 1.4, 1H7), 7.62 (dt, J1 7.7, J2 1.4, 2H9), 7.54 (dm, J
2.2, 2H2), 7.47 (t, J 7.7, 1H8), 7.17 (dm, J 8.6, 2H3), 3.20 (s,
1H15), 3.17 (s, 1H13).

1246
S. Stahlova´ et al.
dC (CD2Cl2, 101 MHz) 160.3 (C5), 152.6 (Carom), 136.9
dH (CD2Cl2, 400 MHz) 8.52 (s, 2H3), 8.03 (s, 4H1), 7.55 (d, J
8.5, 4H6), 7.21 (d, J 8.5, 4H5), 3.18 (s, 2H9).
(Carom), 135.4 (Carom), 133.7 (Carom), 132.9 (Carom), 129.6
(Carom), 129.5 (Carom), 123.4 (Carom), 121.5 (Carom), 120.3
(Carom), 83.9 (C12), 83.2 (C10), 78.4 (C13), 77.9 (C13).
m/z (HRMS EI) 229.0888; Mþꢃ requires 229.0891.
dC (CD2Cl2, 101 MHz) 160.1 (C3), 152.7 (Carom), 139.1
(Carom), 133.6 (Carom), 129.6 (Carom), 121.6 (Carom), 120.4
(Carom), 83.8 (C8), 78.0 (C9).
m/z (HRMS EI) 332.1311; Mþꢃ requires 332.1313.
N,1-Bis(3-ethynylphenyl)methanimine (D5) (Chart 6)
N,N0-(1,4-Phenylene)bis(1-(4-ethynylphenyl)
methanimine) (T2) (Chart 8)
3
4
11
10
Yield 83 %.
nmax (KBr)/cmꢀ1 567m, 625m, 652m, 831m, 850s, 1107w,
1363m, 1616m, 2103vw, 2879w, 3288s.
Raman shift (780 nm, 15 mW)/cmꢀ1 1156m, 1171w, 1191w,
1554m, 1578s, 1604w, 2106m.
dH (CD2Cl2, 400 MHz) 8.53 (s, 2H3), 7.90 (d, J 8.3, 4H6),
7.61 (d, J 8.2, 4H5), 7.30 (s, 4H1), 3.29 (s, 2H).
dC (CD2Cl2, 101 MHz) 159.1 (C3), 150.5 (Carom), 137.4
(Carom), 133.1, 128.9, 122.3, 125.3, 83.7 (C8), 79.9 (C9).
m/z (HRMS EI) 332.1320; Mþꢃ requires 332.1313.
H
C
7
5
2
9
N
12
1
8
6
13
16
14
17
15
Chart 6. Structure and group numbering of D5.
1,10-(5-Ethynyl-1,3-phenylene)bis[N-(4-ethynylphenyl)
methanimine] (T3) (Chart 9)
Yield 62 %.
nmax (KBr)/cmꢀ1 434m, 539m, 615s, 637s, 689v., 766s,
804v., 896s, 910m, 987m, 1091m, 1134s, 1224m, 1269s,
1368s, 1476s, 1567s, 1589s, 1629s, 2103m, 2918w, 3004w,
3060m, 3213s, 3280s.
Yield 68 %.
nmax (KBr)/cmꢀ1 544m, 627m, 646s, 668s, 684m, 729m,
838v., 856m, 864m, 887m, 972m, 1108w, 1143m, 1157m,
1405m, 1499s, 1582s, 1596m, 1627s, 2101w, 2900w, 3205s,
3280s.
Raman shift (780 nm, 15 mW)/cmꢀ1 998s, 1136s, 1224s,
1432w, 1568s, 1590s, 1628s, 2103s.
dH (CD2Cl2, 400 MHz) 8.43 (s, 1H7), 8.02 (t, J 1.6, 1H6), 7.91
(dt, J1 7.8, J2 1.4 Hz, 1Harom), 7.62 (dt, J 1 7.7, J2 1.4, 1Harom),
7.47 (t, J 7.7, 1Harom), 7.41–7.35 (m, 2Harom), 7.33 (dt, J1 2.0,
J2 1.0, 1H13), 7.25–7.19 (m, 1H), 3.20 s (s, 1H17), 3.17 (s, H15).
dC (CD2Cl2, 101 MHz) 160.5 (C7), 152.4 (Carom), 136.9
(Carom), 135.4 (Carom), 132.9 (Carom), 130.2 (Carom), 129.9
(Carom), 129.6 (Carom), 129.5 (Carom), 124.7 (Carom), 123.5
(Carom), 123.3 (Carom), 122.4 (Carom), 83.6 (C14), 83.2 (C16),
78.5 (C17), 77.9 (C15).
Raman shift (780 nm, 15 mW)/cmꢀ1 1141w, 1157w, 1169w,
1209w, 1308w, 1585s, 1624m, 2097m.
dH (CD2Cl2, 400 MHz) 8.50 (s, 2H7), 8.43 (s, 1H6), 8.15 (s,
2H4), 7.55 (d, J 8.5, 4H10), 7.21 (d, J 8.6, 4H9), 3.27 (s, 1H1),
3.18 (s, 2H13).
dC (CD2Cl2, 101 MHz) 159.5 (C7), 152.2 (Carom), 137.6
(Carom), 135.3 (Carom), 133.7 (Carom), 129.6 (Carom), 124.0
(Carom), 121.6 (Carom), 120.7 (Carom), 83.8 (C12), 82.5 (C2),
79.2 (C1), 78.1 (C13).
m/z (HRMS EI) 229.0883; Mþꢃ requires 229.0891.
m/z (HRMS EI) 356.1294; Mþꢃ requires 356.1313.
1,10-(1,4-Phenylene)bis[N-(4-ethynylphenyl)
methanimine] (T1) (Chart 7)
N,N0-(1,4-Phenylene)bis[1-(3,5-diethynylphenyl)
methanimine] (T4) (Chart 10)
Yield 65 %.
nmax (KBr)/cmꢀ1 561m, 852s, 1617w, 2104vw, 2875w,
3284s.
Raman shift (780 nm, 15 mW)/cmꢀ1 1160s, 1190w, 1556s,
1585s, 1624w, 2103m.
Yield 90 %.
nmax (KBr)/cmꢀ1 628s, 655m, 680s, 846s, 880s, 1498s,
1584m, 1624s, 2104w, 2885w, 3221s, 3280s.
Raman shift (780 nm, 15 mW)/cmꢀ1 1143w, 1162w, 1215w,
1288w, 1578s, 1596m, 1628m, 2109w.
6
1
1
5
5
6
3
3
C
H
8
2
8
4
2
C
N
N
7
4
7
9
H
9
1
1
6
5
5
6
Chart 7. Structure and group numbering of T1.
1
1
6
5
6
5
5
3
8
3
C
H
8
2
2
4
N
N
C
4
7
7
9
9
H
6
1
1
5
6
Chart 8. Structure and group numbering of T2.

Aromatic Schiff Bases with Terminal Ethynyl Groups
1247
1
2
3
4
4
9
9
10
9
9
10
7
7
CH
5
5
CH
12
8
11
6
13
N
N
13
11
8
12
10
10
Chart 9. Structure and group numbering of T3.
9
9
8
8
1
1
1
1
6
5
6
6
5
3
C
H
3
C
H
2
4
7
7
N
N
2
4
5
6
5
8
8
9
9
Chart 10. Structure and group numbering of T4.
dH (CD2Cl2, 400 MHz) 8.48 (s, 2 H3), 8.02 (s, 4 H5), 7.70 (s,
a vacuum at room temperature to a constant weight. The
yields of homo- and copolycyclotrimers were determined
gravimetrically.
2 H7), 7.30 (s, 4H1), 3.23 (s, 4 H9).
dC (CD2Cl2, 101 MHz) 157.9 (C3 150.2 (Carom), 138.2
,
(Carom), 137.5 (Carom), 132.8 (Carom), 123.7 (Carom), 122.5
(Carom), 82.3 (C8), 79.1 (C9).
Supplementary Material
m/z (HRMS EI) 380.1322; Mþꢃ requires 380.1313.
IR and Raman spectroscopic characteristics of prepared MEAs,
UV-visible and luminescence spectra of Pc(D1/hexyne) and N2
adsorption isotherm on Pc(D1) are available on the Journal’s
website.
Homopolycyclotrimerization of D1 and
copolycyclotrimerization of D1 with 1-Hexyne
Polycyclotrimerizations were performed in toluene at 508C
under a nitrogen atmosphere in a drybox (PlastLabs) combined
with a standard Schlenk technique. The polycyclotrimerization
catalyst TaCl5/Ph4Sn (prepared by mixing toluene solutions of
TaCl5 and Ph4Sn in a round-bottom flask, equipped with a
Schlenk stopper) was left to ripen for 10–15 min before use.
The polycyclotrimerizations were started by mixing TaCl5/
Ph4Sn and monomer(s) solutions. The initial concentrations of
the reaction components in the polycyclotrimerization mixtures
Acknowledgements
Financial support from the Czech Science Foundation (Project No. P108–
12–1143) and the Science Foundation of Charles University (Project No.
574612 B-CH) is gratefully acknowledged. Access to computing and storage
facilities owned by parties and projects contributing to the National Grid
Infrastructure MetaCentrum, provided under the program ‘Projects of Large
Infrastructure for Research, Development, and Innovations’ (LM2010005),
is greatly appreciated.
were [TaCl5]0 ¼ 0.015 mol Lꢀ1
,
[Ph4Sn]0 ¼ 0.015 mol Lꢀ1
,
[D1]0 ¼ 0.6 mol Lꢀ1 in the case of homopolycyclotrimerization
References
and [TaCl5]0 ¼ 0.015 mol Lꢀ1
,
[Ph4Sn]0 ¼ 0.015 mol Lꢀ1
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