Donor-(π-bridge)-azinium as D-π-A+ one-dimensional and D-π-A+-π-D multidimensional V-shaped chromophores

Article abstract of DOI:10.1039/c2ob06427h

Heteroaromatic cations reacted with N-heteroarylacetylenes under Sonogashira conditions to allow easy access to potential single donor D-π-A⁺ and V-shaped D-π-A⁺-π-D chromophores, where the acceptor moiety A is the π-deficient pyridi

Full text of DOI:10.1039/c2ob06427h

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PAPER
Donor-(π-bridge)-azinium as D-π-A+ one-dimensional and D-π-A+-π-D
multidimensional V-shaped chromophores†
Marco Antonio Ramírez,a Ana M. Cuadro,*a Julio Alvarez-Builla,a Obis Castaño,b Jose L. Andrés,b
Francisco Mendicuti,b Koen Clays,c Inge Asselberghsc and Juan J. Vaquero*a
Received 22nd August 2011, Accepted 28th November 2011
DOI: 10.1039/c2ob06427h
Heteroaromatic cations reacted with N-heteroarylacetylenes under Sonogashira conditions to allow easy
access to potential single donor D-π-A+ and V-shaped D-π-A+-π-D chromophores, where the acceptor
moiety A is the π-deficient pyridinium cation and the donor moiety is represented by different π-excessive
N-heterocycles. The β hyperpolarizabilities were measured using hyper-Rayleigh scattering experiments
and the experimental data are supported by a theoretical analysis that combines a variety of computational
procedures, including Density Functional Theory (DFT) and correlated Hartree–Fock-based methods
(RCIS(D)).
octopolar,5 star-shaped,6 H-shaped,7 Λ-shaped (also called V-
Introduction
shaped),8 X-shaped,9 Y-shaped10 and U-shaped11 systems, with
In recent years a great deal of effort has been focused on the
the aim of increasing the number of significant components of β.
design and synthesis of conjugated donor–acceptor (D–A)
organic molecules in the search for new materials with non-
linear optical (NLO)1 properties due to their application in opto-
electronics,2 all-optical data processing technology, biological
imaging3 and dye-sensitized solar cells,4 inter alia. In this area, a
number of organic compounds have been studied as possible
NLO materials and it is widely accepted that active chromo-
phores are usually composed of electron-donor and electron-
acceptor moieties linked by a π-conjugated bridge, with large
second-order polarizabilities related to an electronic intramolecu-
lar charge transfer effect. Chromophores of this type usually
exhibit a single and intense low-lying longitudinal charge-trans-
fer (CT) excitation and possess optical nonlinearities that are
essentially dominated by a single β tensor component. However,
a major problem associated with these one-dimensional (1D)
dipolar chromophores is the optimization of the nonlinearity-
transparency trade-off, such that the increase in the second-order
hyperpolarizability β is usually accompanied by a bathochromic
shift in the electronic transition.
Thus, different multi-dimensional (MD) chemical systems have
emerged that offer potential advantages over classical 1D linear
chromophores due to the contribution of the large off-diagonal
component,12 which provides increased β responses, with the
possibility of overcoming the nonlinearity-transparency trade-
off.13 Dipolar 2D NLO chromophores are primarily V-shaped (or
Λ-shaped) molecules with either D–A–D or A–D–A structures.
Such C2v symmetric species display electronic transitions for
which the direction of the transition dipole moment μ12 is per-
pendicular to the C2(z) axis, and these are associated with sub-
stantial off-diagonal tensor components βzyy if the molecule lies
in the yz plane.
In this context, organic chromophores that use charged moi-
eties as acceptor units are restricted to diazonium salts14 and
some heteroaromatic cations such as benzothiazolium15 and pyri-
dinium salts,16 which have been studied as cationic and dicatio-
nic acceptor 1D chromophores. However, very few charged 2D
chromophores have been reported to date,17 even including
dipolar 2D metal-based NLO charged chromophores studied by
Coe et al. and, more recently, a new V-shaped quinolizinium
chromophore as a marker in nonlinear optical bioimaging18
(Fig. 1) by multiphotonic interaction as TPA (two-photon
absorption).
Recently, a new synthetic strategy based on introducing mul-
tiple D and/or A substituents has been developed, including
aDepartamento de Química Orgánica, Universidad de Alcalá, 28871
Alcalá de Henares, Madrid, Spain. E-mail: ana.cuadro@uah.es, juan-
jose.vaquero@uah.es; Fax: +34-91-8854686; Tel: +34-91-8854628e
bDepartamento de Química Física, Universidad de Alcalá, 28871
Alcalá de Henares, Madrid, Spain
As a part of a project focused on the development of the
chemistry and applications of heteroaromatic cations,19 we con-
sidered the use of charged moieties as acceptor units in the
design of NLO-active cations and the feasibility of Sonogashira20
cross-coupling reactions as a basic strategy to obtain D-π-A+ and
D-π-A+-π-D architectures as potentially bioactive compounds or
new materials. From this perspective, our research with 1D and
2D chromophores is based on the pyridinium cation as the
cDepartment of Chemistry, University of Leuven, Celestijnenlaan 200 D,
3001 Leuven, Belgium. E-mail: Koen.Clays@fys.kuleuven.be
†Electronic supplementary information (ESI) available: Copies of 1H
and 13C NMR for all new compounds reported and general information
of OL and NLO. See DOI: 10.1039/c2ob06427h
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Fig. 3
different behaviour from an electronic point of view at the C2/
C4 and C3 positions. The target 1D chromophores could be
obtained by the two alternative routes shown in Fig. 3 by Sono-
gashira reactions. Route A would involve a Sonogashira reaction
of a halo-N-heterocycle and an ethynylpyridinium whereas route
B involves a pyridinium halide and an ethynylheterocycle.
All attempts to obtain the corresponding chromophores by
route A failed with pyrrole and indole heterocycles on using
either the parent bromoheterocycle or the corresponding N-pro-
tected derivatives. Although the trimethylsilylethynyl pyridinium
derivatives could be obtained in the coupling reaction between
2-, 3- and 4-brompyridinium bromides and trimethylsilylacety-
lene, the desilylation process could not be achieved under a
variety of conditions, particularly from ethynyl derivatives at the
C3- and C4-positions. Consequently, we focused our attention
on the coupling of the corresponding bromopyridinium salt
(1–3) with heteroaryl-acetylenes (route B).
Initially, considering the conditions recently described by
us,18 the cross-coupling reaction of 3-bromopyridinium bromide
(1a) with protected N-heteroaryl acetylenes24 was carried out in
the presence of 10 mol% of copper(I) iodide, 5 mol%
PdCl2(PPh3)2 and 1.5 equiv. of Et3N in DMF, with the reaction
mixture stirred for 8 h at room temperature. Under these con-
ditions coupling of 1a with pyrazole and indazole gave 4c and
4d in 48% and 57% yields, respectively (Table 1, entries 3 and
4). The same yields could also be obtained by heating the mix-
tures at 65 °C for 4 h (Method A). However, under the same
conditions the preparation of derivatives 4a and 4b from pyrrole
and indole was unsuccessful, giving rise the homocoupling
product of the corresponding ethynyl acetylene and the dehalo-
genated N-methyl pyridinium iodide. The homocoupling reac-
tion with pyrrole and indole derivatives was avoided by adding
10 mol% of LiCl25 in the presence of the same catalytic system
[PdCl2(PPh3)2 (5 mol%), CuI (10 mol%)] and Et3N in DMF.
Under these conditions the expected coupling compounds 4a
and 4b were obtained at room temperature after 20 h (Method B)
in 63% and 61% yields, respectively. As was the case for 4c,d,
heating at 65 °C reduced the reaction time without affecting
yields. It is noteworthy that deprotection (TIPS) of the pyrrole
ring in isolated compound 4a was observed, but all attempts to
deprotect isolated compounds 4b–d were unsuccessful, with
extensive recovery of the protected compounds under acidic con-
ditions and decomposition under basic conditions. Furthermore,
the attempted formation of a heterobetainic structure for chromo-
phore 4a under basic conditions resulted in decomposition.
We next examined the coupling at the C-2 and C-4 positions
of the pyridinium ring. On examining the two methods (Method
Fig. 1 Examples of 1D (D-π-A+) and 2D (D-π-A+-π-D) chromophores
based on heteroaromatic cations as acceptor units.
acceptor unit due to the interest in organic compounds21 that
contain this unit in recent fields22 and the use of pyridinium salts
(crystals of DAST) and related species for terahertz (THz) wave
generation using difference frequency mixing of two lasers.23
These systems have potential applications in security scanning,
biomedical analysis and space communication.
As a contribution to this field, and as part of our study on the
chemistry of these heteroaromatic cations, their applications as
molecular markers or in second harmonic generation, we report
here our results on the synthesis and linear and NLO properties
of both 1D and 2D charged chromophores (Fig. 2). The donor
moiety is represented by π-excessive N-heterocycles that have
different electron densities, which will, in turn, lead to larger β
values for 2D chromophores and determine the relative magni-
tude between diagonal and off-diagonal β tensor components.
Furthermore, the first hyperpolarizabilities of 1D and 2D cations
were studied by hyper-Rayleigh scattering experiments and the
experimental data were supported by theoretical analysis. The
goal of this study was to relate the nonlinear optical responses to
the molecular properties in order to gain a better understanding
of molecular markers, where biological affinity and compatibility
are the most critical issues for the appropriate use of NLO
molecules.
Fig. 2 Linear 1D (D-π-A+) and 2D V-shaped (D-π-A+-π-D) charged
chromophores.
Results and discussion
Synthesis
The pyridinium system offers three possible positions to explore
the scope of these charged heterocycles, because they exhibit
1660 | Org. Biomol. Chem., 2012, 10, 1659–1669
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Table 1 Synthesis of chromophores 4–7 by Sonogashira reaction on bromo pyridinium salts
aMethod A: PdCl2(PPh3)2 (5 mol%), CuI (10 mol%), DMF, Et3N, 65 °C bMethod B: PdCl2(PPh3)2 (5 mol%), CuI (10 mol%), LiCl (10 mol%) DMF,
Et3N, r.t. cMethod C: PdCl2(PPh3)2 (5 mol%), CuI (10 mol%), THF, Et3N, r.t.
A or B) for the coupling on 1D, it was found that method A was
efficient with pyrazole and indazole at the C2/C4 positions and
Method B for pyrrole and indole, with moderate to good yields
obtained at room temperature for compounds 5a–d and 6a–d
(see Table 1). Regarding the reactivity of the different haloge-
nated positions in the pyridinium ring and the yield of the coup-
ling product, the electronic character of the less activated
position at C3 did not have a significant effect on the yield.
However, in 2- and 4-bromopyridinium the different yields
obtained could be related not only with the activation of α and γ
positions but also with the instability of the alkyne.
The use of a double substitution strategy enabled the synthesis
of different V-shaped molecules with the aim of understanding
the NLO properties of charged chromophores by hyper-Rayleigh
scattering experiments.26 Initially, chromophores 7 (D-π-A+-π-D)
were synthesized from 3,5-dibromo-1-methylpyridinium iodide
by a double Sonogashira reaction, under the optimized con-
ditions found for monoderivatives 1D, with a change in the
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corresponding equivalents of alkyne (2.4 equiv) and the base (3
equiv). However, yields of the coupling products were low,
mainly due to problems encountered in the work-up and purifi-
cation of the products. To overcome these problems, the PF6
salt27 of 3,5-dibromo-1-butylpyridinium was employed instead
of the corresponding methylpyridinium derivative. This salt has
the advantage of solubility in THF, thus facilitating the work-up.
In this way, compound 1b was reacted with different heteroaryla-
cetylenes to afford the corresponding coupling products 7a–d as
hexafluorophosphates under Sonogashira conditions (Method C)
similar to those used for compounds 4–6. The results are sum-
marized in Table 1. Compounds 7b–d were obtained in good
yields but only a moderate yield was achieved for 7a, which was
also isolated with both pyrrole rings deprotected.
Linear optical properties
Absorption spectra of the 1D (4–6) and 2D V-shaped (7) com-
pounds were monitored in the 230–800 nm range. The absorp-
tion spectra for these compounds are shown in Fig. 4 and did not
exhibit significant absorption above 450 nm. The relatively
intense peak at the longest wavelengths is ascribed to the π–π*
intramolecular charge transfer (ITC) absorption band from the
pyridinium acceptor moiety. The positioning of the maxima for
these bands is usually rather sensitive to the degree of conju-
gation and to the electron-donating characteristics of the substitu-
ent. Most of the chromophores, with the exception of 4a, 4c, 6d
and 7b, which exhibit a weak overlapping band, show a sharp
cut-off for the π–π* transition band. The overlapping band,
which is observed at a longer wavelength relative to the
maximum for the π–π* band, may be ascribed to the n–π* tran-
sition due to the presence of N heteroatoms and the triple bond.
These bands are characterized by molar absorptivities that are
usually somewhat smaller than those for π–π* transitions.
Fig. 4 Absorption spectra for compounds 4–7 in methanol at 25 °C.
transitions between HOMO-2 and LUMO and HOMO-4 and
LUMO band rather than the in-plane heteroatom lone pairs.
In general, little correlation was found between the electron
donating characteristics of the different pyrrole (a), indole (b),
pyrazole (c) and indazole (d) substituents of the pyridinium
acceptor and the location of the wavelength for the π–π* ITC
absorption band for all the different systems. Compounds 4,
The molecular orbitals involved in these transitions for 6a and
7a are shown in Fig. 5 and 6 and were calculated at the HF/6-
31G(d) level of theory. These MOs represent the main com-
ponent of the π–π* band due to a HOMO–LUMO transition and
the in-plane n–π* triple bond molecular orbitals involved in the
Fig. 5 HOMO, LUMO and HOMO-2 for compound 6a at the HF/6-31G(d) level of theory.
Fig. 6 HOMO, LUMO and HOMO-4 for compound 7a at the HF/6-31G(d) level of theory.
1662 | Org. Biomol. Chem., 2012, 10, 1659–1669 This journal is © The Royal Society of Chemistry 2012

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Table 2 Linear optical data for 4–7
Compound
λmax
λexc
λem
ε (M−1cm−1
)
Φf (×102)
<τ>, ns
4a
4b
4c
4d
5a
5b
5c
5d
6a
6b
6c
6d
7a
7b
7c
7d
297
319
293
317
348
345
374
366
348
372
380
372
317
332
338
341
310
—
—
—
370
345
350
345
—
370
—
365
—
—
330
325
434
—
—
—
526
537
495
492
—
459
—
495
—
—
494
496
5500
8.9
—
—
—
0.04
0.9
9.0
3.0
—
0.25
—
0.8
—
—
17.0
30.4
1.1
—
—
—
1.0
0.7
2.5
2.0
—
2.7
—
1.0
—
—
2.3
2.0
16 700
15 750
15 800
10 750
15 600
23 700
10 100
14 300
10 900
27 200
15 450
21 450
28 600
16 250
36 700
Wavelength for the maximum of the π–π* charge transfer absorption band (λmax) and emission band (λem) upon excitation of λexc, molar absorptivity
(ε), fluorescence quantum yields Φf, and lifetime averages <τ> for compounds 4 and 7 in methanol at 25 °C.
where donors are substituted at the C3(β) (meta substitution) and
the conjugation is less efficient, is the only compound which
follows the expected trend. For the latter compounds the pyra-
zole substituent, which is the weakest donor, yields the shortest
λmax for the π–π* transition. The indole and indazole are the best
donors and yield the highest λmax. Wavelengths for the absorp-
tion maxima (λmax) of the π–π* band are collected in Table 2
along with the molar absorptivities (ε) at these wavelengths.
Greater influence of the position of the donor substituent at
the pyridinium acceptor on the placement of the absorption
bands, however, were observed. A substituent at the C4(γ) pos-
ition of the pyridinium resulted in the most efficient conjugation,
while the one at C3(β) was the least efficient. The effect at the
C2(α) position is usually somewhere between both due to elec-
tronic and steric effects. Therefore longer wavelengths for the
absorption maximum are detected for compounds 6, and 5
(λmax,6 ≥ λmax,5) in comparison with 4. Thus, the λmax values for
5a, d and 6a, d are ∼50 nm higher than those for 4a, d. These
differences are, however, larger than 80 nm when comparing
compounds that contain the weakest donor pyrazole substituent,
i.e. 5c and 6c with 4c.
The addition to 1D compounds named 4 of a second hetero-
cyclic donor group linked to the pyridinium acceptor moiety at
C(5) by a triple bond to give 2D V-shaped 7 compounds, con-
tributes to extending the π-delocalization and ICT stabilization.
The effect on λmax for these V-shaped compounds can be
seen as the balance of a meta substitution that provides a less
effective conjugation and di-substitution which contributes to
extend it. As a results, an intermediate effect on λmax between
compounds 4 and 5 or 6 was obtained for 7. This situation
is consequently reflected in a bathochromic displacement of
the π–π* band by about 13–45 nm for compounds 7 relative to
compounds 4. Nevertheless, this stabilization does not permit
reaching the absorption wavelengths for 5 and 6. It is also
remarkable that molar absorptivities at λmax are significantly
higher for V-shaped compounds 7 (15 000–37 000 M−1cm−1
range) than for 4 (5500–16 700 M−1cm−1 range) and other 1D
(5, 6) systems.
Fluorescence data, obtained from the analysis of the emission
spectra in the 350–700 nm range upon excitation of the π–π*
band at the λexc, are also collected in Table 2. All spectra – with
the exception of those for compounds 4b–d, 6a,c and 7a,b,
which did not fluoresce – exhibit single bands, the maxima (λem
)
of which depend on the nature of the compound. However,
among the fluorescent systems, discrete correlations between λem
and the electron-donating characteristics of the substituent (5a–
d) and/or its position at the pyridinium acceptor (5d, 6d and 7d)
were observed.
Something similar occurs for fluorescence quantum yields and
lifetimes. In general, 1D systems exhibit zero or very low fluor-
escence quantum yields. 2D systems 7c,d are the only ones that
have a noticeable fluorescence. Low fluorescence in polar sol-
vents is usually attributed to the stabilization of the ICT excited
state and thus increases the probability of deactivations through
other non-radiative pathways.28 All the fluorescence intensity
profiles for the fluorescent samples, measured at λem upon λexc
,
were fitted to bi-exponential decays This denotes the involve-
ment of some processes other than the simple radiative emission
from a singlet to the ground state. As stated before, it is quite
difficult to assign any correlation between the quantitative values
for Φf and lifetime averages (<τ>), collected in Table 2, and the
electron-donating character, the location of the substituent or the
number of substituents for these systems where several complex
deactivation excited state processes were involved. The low flu-
orescence quantum yields and subsequently the uncertainty in
both Φf and <τ> measurements also contribute to this.
Nonlinear optical properties: Hyper-Rayleigh Scattering (HRS)
measurements and computational details
Femtosecond hyper-Rayleigh scattering measurements per-
formed at 800 nm for all compounds presented in Table 3
confirm the potential of these small ionic compounds for
second-order nonlinear optics. The second-order nonlinear
optical properties reflect the observations already made in linear
optics in terms of the nature of the conjugation. According to the
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Table 3 Experimental nonlinear optical properties of 1D and 2D
chromophores
Table 4 Theoretical values for the optical properties of 1D and 2D
chromophores. Wavelength of maximum absorption λmax (nm), HRS
first hyperpolarizability at 800 nm βHRS,800, diagonal averaged first
hyperpolarizability at 800 nm βzzz,800, depolarization ratio at 800 nm
ρ800, off-resonance components of the molecular first hyperpolarizability
βzzz and βzxx (10−30 esu), dipole moment in Debye and the reduced
vector component of molecular first hyperpolarizability βz (10−30 esu)
Compound
λmax
βHRS
βzzz
βzzz, 0
τ
4a
4b
4c
4d
4e
5b
5c
5d
5e
6a
6b
6c
6d
6e
7a
7b
7d
297
319
293
317
292
345
374
366
346
348
372
380
372
360
317
332
341
42
25
18
13
16
3
103
60
44
32 18
40 16
267 35
148
39 22
90
7
32
18
17
9
16
32
29
8
2
2
2
1.4 0.4
—
2.7 1.3
0.3 0.2
—
3
2
7
6
8
6
5
4
λmax
6
4
2
Comp. CIS(D) βHRS,800 βZZZ, 800 ρ800 βzzz,0 βzxx,0 μz
βz
−66
88
165
51
110 14
—
61
16
37
112 16
113 13
NLR
125 20
67
NLR
NLR
68 21
3
9
4
6
1.0 0.3
—
—
—
—
4a
5a
6a
7a
5d
4d
6d
7d
317
323
354
327
314
287
344
306
46
61
115
47
69
44
42
55
105
40
63
40
5.2
4.9
4.8
2.8
4.9
5.1
−51 −1
59
99 −1
−3.1
1.7
2.9
3.8
6.7
8.4
0
9
18
64
31
2
9
3
270 40
274 32
5
65
47
39
3
2
99
62
303 49
163 16
32
27
5
3
—
—
119
49
109
42
4.8 −107
2.7
2
−8.3 −171
4.4 57
6
3
45
164 51
64 14
1.5 0.6
chromophores, have a higher nonlinear response (cf. 7d and 4d)
in accordance with the progression in absorption maxima to
higher wavelengths and the increase in the molar adsorptivities.
According to the HRS theory (see eqn (1), (2) and (3) in the
ESI†), for a typical experiment a clear linear dependence of the
HRS response QC (quadratic coefficient) is observed as a func-
tion of concentration and the ratio of the slopes is directly pro-
portional to the ratio of their orientationally averaged
hyperpolarizabilities squared. However, for compounds 6c, 7a,
7b and 7c the data obtained for the samples were plotted, with
the Y-axis representing the quadratic coefficient QC of the HRS
signal and the X-axis the concentration of the sample. A linear
fitting was not obtained and the data could not be used to calcu-
late any hyperpolarizability (see ESI†).
On the other hand, because of the two-photon resonance
enhancement that varies with the wavelength of the charge trans-
fer, all of which are relatively close to the second-harmonic
wavelength, the dynamic values for the first hyperpolarizability
measured at 800 nm are not directly comparable. Taking into
account this resonance enhancement by using the simple two-
level formalism REF, it is possible to compare values for the
static first hyperpolarizability, βo. These values are the most rel-
evant ones for comparison. It is clear that the largest, corrected
nonlinearities are found for the better C4 substituents or for the
V-shaped compounds 7d.
Theoretical calculations were performed using the Gaussian
suite of quantum chemical programs.29 For all the studied cat-
ionic chemical systems, the molecular structures used to
compute optical properties correspond to energy minima calcu-
lated at the HF/6-31G(d) level of theory. These structures were
confirmed to be minima by evaluation of the harmonic
vibrational frequencies, which all proved to have real values.
Calculated wavelengths (λmax, in nm) were estimated from
CIS(D)30 and DFT methods and theoretically predicted values of
the second harmonic generation (SHG) of hyperpolarizability
β(2ω;ω,ω) was obtained including the electron correlation effect
by the MP2/6-31G(d) level. This property βMP2(-2ω;ω,ω) was
estimated from the resonant or dynamic β(-2ω;ω,ω) at the HF/6-
31G(d) level, and the static or non-resonant β(0;0,0) was calcu-
lated at both HF/6-31G(d) and MP2/6-31G(d) levels following
the multiplicative approximation scheme, where the frequency
dispersion is estimated to be similar at these two levels of
NLR: non-linear relation. Wavelength of maximum absorption λmax
(nm), resonant enhanced HRS experimental first hyperpolarizability
βHRS (10−30 esu), resonance enhanced diagonal component of the
molecular first hyperpolarizability βzzz (10−30 esu), off-resonance
diagonal component of the molecular first hyperpolarizability βzzz,0
(10−30 esu). The values of the fluorescence lifetime, τ (ns), are also
included for molecules that showed demodulation.
trends already observed in the linear optical (absorption) exper-
iments, the largest first hyperpolarizability values were found for
some indole (5b: β = 110 × 10−30 esu, 6b: 113 × 10−30 esu) and
indazole (6d: β = 125 × 10−30 esu) derivatives, but also for
pyrrole (6a: β = 112 × 10−30 esu). In agreement with the greater
influence of the position of the donor substituent at the pyridi-
nium acceptor – more than their relative electron donating
strength characteristics – and the better conjugation and stabiliz-
ation, the largest β values correspond to the compounds whose
substituents are at the C4(γ) and C2(α) positions on the pyridi-
nium system, confirming that the best conjugation and charge
transfer from donor to acceptor is achieved in these positions.
The subtle differences between C2(α) and the C4(γ) positions
are attributed to steric effects, leading to shorter wavelength of
maximum absorption and smaller hyperpolarizabilities for C2(α)
if differences are observed, pointing to torsional angle effects in
the ortho position. In general, no fluorescence is observed at the
second harmonic wavelength for these compounds with red-
shifted absorption and fluorescence, with respect to the C3(β) or
meta substitution.
For the V-shaped compounds 7, we see the combined effect of
the inefficient meta substitution with the extended conjugation
along the two arms resulting in intermediate properties, both for
the wavelength of maximal absorption and for the hyperpolariz-
ability. Also in agreement with the observation for compounds 4,
C3(β) substitution, we observe again two-photon fluorescence,
and correct for this contribution with the fluorescence lifetime
indicated in Table 3.
The theoretically calculated βHRS (see Table 4) also follow the
same behaviour and the agreement between experimental and
theoretical βHRS values for compounds 6a and 6d warrants par-
ticular mention. Furthermore, the 2D or V-shaped D-π-A+-π-D
chromophores, in comparison with the 1D D-π-A+
1664 | Org. Biomol. Chem., 2012, 10, 1659–1669
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theory.31 No solvent effects were considered in our quantum
chemical calculations.
were determined by HRS. The results show that a large first
hyperpolarizability was obtained in compounds 5b, 6a, 6b and
6d. The low transition energy and high level of CT are the deci-
sive factors that give a large first hyperpolarizability in com-
pounds substituted at C4. Theoretical calculations support the
experimental results obtained.
βMP2ð0; 0; 0Þ
βMP2ðꢀ2ω; ω; ωÞ ꢁ βHFðꢀ2ω; ω; ωÞ
ð1Þ
βHFð0; 0; 0Þ
The Hartree–Fock (HF) values were calculated analytically
and the MP2 values were obtained numerically. The calculated
hyperpolarizability tensor elements are given in the molecular
axes basis βijk and these must be transformed to the laboratory
axes βXYZ by applying the expressions of Civin et al.32 The
theoretical βZZZ values are lower than the βHRS values since the
former values are only part of the latter. However, in the exper-
imental determination of the βZZZ values the old two states
model approximation is applied. The molecular hyperpolarizabil-
ity tensors βijk can be reduced to vector components βi (eqn (2)
depolarization ratio ρ (eqn (3)) and βHRS (eqn (4)) are given by:
X
The synthesis and study of these new compounds are allowing
us to deduce valuable structure–activity relationships for use in
ongoing studies focused on the optimization of 2D-TPA and
applications in bioimaging.
Experimental
General procedure for the synthesis of D-π-A+ pyridinium salts
Method A (4, 5, 6c–d). A flame-dried flask was charged under
argon with 1 equiv. of bromopyridinium iodide or hexaflouro-
phosphate, 10 mol% CuI (0.0667 mmol, 0.0127 g) and 5 mol%
PdCl2(PPh3)2 (0.0333 mmol, 0.0234 g) in dry DMF (10 mL).
1.2 equiv. of the corresponding acetylene heterocycle
(0.7551 mmol) and 1.5 equiv. of Et3N (0.9438 mmol,
0.1315 mL) were added. The mixture was heated at 65 °C for
4 h and the solution was filtered through a small pad of celite
and washed with methanol. The solution was concentrated,
treated with saturated aqueous NaHCO3 and extracted with
CH2Cl2. The organic phase was dried over MgSO4, the solvent
was evaporated under reduced pressure, and the solid was
purified by flash chromatography on silica gel in CH2Cl2/MeOH
(9.5 : 0.5) as eluent.
βi ¼
ðβijj þ βjij þ βjjiÞ
ð2Þ
jꢀx;y;z
kβ2ZZZ
kβ2XZZ
l
l
ρ ¼
ð3Þ
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
βHRS
¼
kβ2ZZZl þ kβ2XZZ
l
ð4Þ
All theoretical data calculated for selected compounds are
shown in Table 4. The data in this table include the theoretically
predicted λmax values for the first excited electronic state. The
calculated wavelengths for compounds containing pyrrole
groups as donors (4a–7a) show positive and negative deviations
from the experimental values by less than 7%, whereas for the
compounds containing indazole groups the calculations under-
estimate the experimental values, with deviations in the range
8–14%. The estimated βHRS also follows a similar trend and
depolarization ratio at 800 nm, ρ800 take values close to 5 or 3 as
it should be for linear and dipol chromophores, respectively.
For all these systems the βHRS is given mainly by the spatially
averaged βZZZ. In contrast, for the 1D and 2D systems only the
diagonal βzzz and off-diagonal βzxx elements of the molecular
first hyperpolarizability tensor are meaningful, respectively.
When the molecular hyperpolarizability is reduced to a vector
according to eqn (2), only the parallel component βz is presented
either for 1D or 2D systems because this has values that are 10
times larger than those of the orthogonal βx or βy. The angles
between dipole moments and the reduced first hyperpolarizabil-
ity vectors are 0.4° and 0.7° for 7a and 7d, respectively, showing
that both are parallel in these 2D or dipolar chromophores. In
contrast, for the 1D or linear chromophores this angle ranges
from 10° to 30°, being 11° and 12° for 6a and 6d, respectively,
and 30° for 5a.
1-Methyl-3-(1-trityl-1H-pyrazol-4-ylethynyl) pyridinium iodide
(4c). Following the general procedure A, from 1a and 4-ethynyl-
1-trityl-1H-pyrazol (0.7551 mmol, 0.2626 g), afforded 0.1812 g
(48%) of 4c as a yellow solid: mp 246–247 °C; IR (KBr): υmax
1
(cm−1) 2231, 1443; H NMR (200 MHz, DMSO-d6) δ (ppm)
9.23 (s, 1H), 8.90 (d, 1H, J = 6.2 Hz), 8.59 (d, 1H; J = 8.0 Hz),
8.11 (t, 1H, J = 8.4 Hz), 8.01 (m, 9H), 7.38 (m, 6H), 7.38 (m,
9H, J = 2.5 Hz), 7.06 (m, 6H, J = 3.6 Hz), 4.28 (s, 3H); 13C
NMR (300 MHz, acetone-d6) δ (ppm) 148.2, 147.1, 143.5,
142.8, 137.3, 130.9, 129.0, 128.8, 125.7, 100.9, 84.1, 80.4,
73.4, 61.9, 45.3, 41.0; MS (ESI+) m/z (relative intensity) 426
(M+, 100); Anal. Calcd for C30H24N3I: C, 65.11; H, 4.37; N,
7.59. Found: C, 65.13; H, 4.39; N, 7.57.
1-Methyl-3-(1-tert-butoxycarbonyl-1H-indazol-3-ylethynyl) pyri-
dinium iodide (4d). Following the general procedure A, from 1a
and 3-Ethynyl-indazole-1-carboxylic acid tert-butyl ester
(0.7551 mmol, 0.1736 g), afforded 0.1705 g, (57%) of 4d as a
brown solid: mp 134 °C; IR (KBr): υmax (cm−1) 3419, 2230,
1
1742; H NMR (200 MHz, CD3OD) δ (ppm) 9.45 (s, 1H), 9.01
(d, 1H, J = 6.2 Hz), 8.88 (d, 1H, J = 8.1 Hz), 8.25 (d, 1H, J =
8.4 Hz), 8.19 (dd, 1H, J = 6.2 Hz), 8.03 (d, 1H, J = 7.7 Hz),
7.74 (t, 1H, J = 7.3 Hz), 7.55 (t, 1H, J = 6.9 Hz), 4.51 (s, 3H),
1.78 (s, 9H); 13C NMR (300 MHz, CD3OD) δ (ppm) 209.1,
149.6, 148.4, 146.6, 141.1, 133.7, 131.3, 129.2, 127.7, 126.2,
124.5, 121.4, 115.9, 88.1, 87.7, 87.5, 48.4, 28.2; HRMS Calcd
for C20H20N3O2I: (M+) 334.1555. Found 334.1523.
1-Methyl-2-(1-trityl-1H-pyrazol-4-ylethynyl) pyridinium iodide
(5c). Following the general procedure A, from 2 and 4-ethynyl-
1-trityl-1H-pyrazol (0.7551 mmol, 0.2626 g), gave 0.08 g,
(45%) of 5c as a brown solid: mp 233 °C. IR (KBr): υmax
Conclusions
The C2v symmetric 2D (D-π-A+-π-D) systems and their 1D
(D-π-A+) analogues were synthesized in moderate to good yields
by Sonogashira cross-coupling reactions from bromopyridinium
salts and ethynylheterocycles. The first hyperpolarizabilities of
the series of charged chromophores (D-π-A+) and (D-π-A+-π-D)
This journal is © The Royal Society of Chemistry 2012
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(cm−1) 2215, 1615, 1443; 1H NMR (200 MHz, CD3OD) δ
(ppm) 8.93 (d, 1H, J = 5.8 Hz), 8.51 (t, 1H, J = 8.1 Hz), 8.21
(d, 1H, J = 7.8 Hz), 8.08 (s, 2H), 7.96 (t, 1H, J = 6.2 Hz), 7.41
(t, 9H, J = 3.6 Hz), 7.18 (m, 6H), 4.45 (s, 3H); 13C NMR
(300 MHz, CD3OD) δ (ppm) 146.3, 144.0, 142.4, 141.4, 137.4,
137.0, 130.2, 129.1, 127.6, 125.5, 116.5, 98.8, 98.4, 81.8, 78.7,
46.6; MS (ESI+) m/z (relative intensity) 426 (M+, 100); Anal.
Calcd for C30H24N3I: C, 65.11; H, 4.37; N, 7.59. Found: C,
65.14; H, 4.34; N, 7.63.
6.44 (dd, 1H, J = 1.2, 1.4 Hz), 4.89 (s, 3H); 13C NMR
(300 MHz, CD3OD) δ (ppm) 145.7, 144.6, 132.9, 129.7, 127.5,
124.6, 120.5, 118.3, 112.9, 106.8, 47.8; MS (ESI+) m/z (relative
intensity) 341 (M+, 100); Anal. Calcd for C12H11N2I: C, 46.32;
H, 3.89; N, 9.00. Found: C, 46.29; H, 3.87; N, 9.03.
1-Methyl-3-[1-(toluene-4-sulfonyl)-1H-indol-3-ylethynyl] pyridi-
nium iodide (4b). Following the general procedure B, from 1a
and 3-ethynyl-1-(toluene-4-sulfonyl)-1H-indole (0.7551 mmol,
0.2231 g), gave 0.1489 g, (61%) of 4b brown solid: mp 208 °C;
1
IR (KBr) : υmax (cm−1) 3505, 2231, 1378; H NMR (200 MHz,
1-Methyl-2-(1-tert-butoxycarbonyl-1H-indazol-3-ylethynyl) pyri-
dinium iodide (5d). Following the general procedure A, from 2
and 3-ethynyl-indazole-1-carboxylic acid tert-butyl ester
(0.7551 mmol, 0.1736 g), gave 0.1705 g, (53%) of 5d as an
orange solid: mp 185 °C; IR (KBr): υmax (cm−1) 3418, 2350,
CD3OD) δ (ppm) 8.84 (d, 2H, J = 6.7 Hz), 8.34 (s, 1H), 8.14 (d,
2H, J = 6.9 Hz), 8.03 (t, 2H, J = 8.6 Hz), 7.94 (d, 2H; J = 8.4
Hz), 7.80 (d, 1H; J = 0.9 Hz), 7.70-7.58 (m, 4H), 4.4 (s, 3H),
2.38 (s, 3H); 13C NMR (300 MHz, CD3OD) δ (ppm) 147.3,
146.3, 134.8, 133.7, 133.0, 132.6, 132.5, 131.2, 129.7, 129.6,
129.5, 128.1, 127.0, 126.6, 125.4, 121.2, 114.6, 90.57, 48.8,
47.6, 21.4; MS (ESI+) m/z (relative intensity) 388 (M+, 100);
Anal. Calcd for C23H20N2O3SI: C, 51.99; H, 3.79; N, 5.27.
Found: C, 51.97; H, 3.83; N, 5.25.
1
1628; H NMR (200 MHz, CD3OD) δ (ppm) 9.18 (d, 1H, J =
6.6 Hz), 8.79 (t, 1H, J = 6.6 Hz), 8.38 (d, 1H, J = 8.1 Hz), 8.19
(t, 1H, J = 7.7 Hz), 7.94 (d,1 H, J = 8.1 Hz), 7.73 (td, 2H, J =
1.1, 7.3 Hz), 7.60 (td, 1H, J = 1.8, 4.4 Hz), 4.44 (s, 3H), 1.25 (s,
9H); 13C NMR (300 MHz, CD3OD) δ (ppm) 209.0, 148.3,
148.3, 146.5, 141.1, 136.0, 130.3, 126.9, 126.7, 125.5, 125.1,
120.8, 111.4, 100.2, 95.6, 46.8, 17.8, 11.2; HRMS Calcd for
C20H20N3O2I: (M+) 334.1555. Found 334.1547.
1-Methyl-4-(1-trityl-1H-pyrazol-4-ylethynyl)pyridinium hexafluoro
phosphate (6c). Following the general procedure A, from 3 and
4-ethynyl-1-trityl-1H-pyrazol (0.7551 mmol, 0.2626 g), afforded
0.2485 g, (77%) of 6c as an orange solid: mp 249–251 °C; IR
(KBr): υmax (cm−1) 2215, 1637, 1447; 1H NMR (200 MHz,
DMSO-d6) δ (ppm) 8.89 (d, 2H, J = 6.7 Hz), 8.09(d, 2H, J =
7.1 Hz), 7.93 (s, 1H), 7.39 (m, 10H), 7.06 (m, 6H), 4.25 (s, 3H);
13C NMR (300 MHz, acetone-d6) δ (ppm) 146.2, 143.3, 141.2,
138.3, 130.8, 129.3, 128.9, 128.7, 100.7, 97.8, 80.0, 73.3, 48.7;
MS (ESI+) m/z (relative intensity) 426 (M+, 100); Anal. Calcd
for C30H24N3PF6: C, 63.05; H, 4.23; N, 7.35. Found: C, 63.07;
H, 4.27; N, 7.33.
1-Methyl-4-(1-tert-butoxycarbonyl-1H-indazol-3-ylethynyl) pyri-
dinium hexafluoro phosphate (6d). Following the general pro-
cedure A, from 3 and 3-ethynyl-indazole-1-carboxylic acid tert-
butyl ester (0.7551 mmol, 0.1736 g), gave 0.2066 g, (69%) of
6d as a black solid: mp 144 °C; IR (KBr): υmax (cm−1) 3418,
2207, 1636; 1H NMR (200 MHz, CD3OD) δ (ppm) 9.02 (d, 2H,
J = 6.6 Hz), 8.37 (d, 2H, J = 6.9 Hz), 8.28 (d, 1H, J = 8.4 Hz),
8.06 (d, 1H, J = 8.1 Hz), 7.75 (t, 1H, J = 7.3 Hz), 7.57 (t, 1H, J
= 7.3 Hz), 4.47 (s, 3H), 1.78 (s, 9H);13C NMR (300 MHz,
CD3OD) δ (ppm) 209.1, 145.5, 143.0, 140.6, 139.8, 129.0,
127.6, 125.1, 122.9, 119.6, 117.1, 110.9, 95.5, 88.7, 69.4, 47.0,
29.9; MS (ESI+) m/z (relative intensity) 253 (M+, 100).; Anal.
Calcd for C20H21N3O2PF6: C, 49.90; H, 4.61; N, 8.73. Found:
C, 49.95; H, 4.57; N, 8.76.
1-Methyl-2-(1H-pyrrol-3-ylethynyl) pyridinium iodide (5a). Fol-
lowing the general procedure B, from 2 and 3-ethynyl-1-triiso-
propylsilanyl-1H-pyrrole (0.7551 mmol, 0.1875 g), gave
0.0381 g, (26%) of 5a as an orange dark oil: IR (KBr): υmax
(cm−1) 3434, 2206, 1619; 1H NMR (200 MHz, CD3OD) δ
(ppm) 8.88 (d, 1H; J = 7.2 Hz), 8.45 (t, 1H, J = 6.8 Hz), 8.13
(d, 1H, J = 8.0 Hz), 7.87 (t, 1H, J = 6.2 Hz), 7.50 (t, 1H, J = 1.6
Hz), 6.89 (dd, 1H, J = 0.9, 2.0 Hz), 6.53 (dd, 1H, J = 1.4, 2.9
Hz), 4.46 (s, 3H); 13C NMR (300 MHz, CD3OD) δ (ppm)
147.1, 145.2, 141.1, 131.5, 128.2, 125.7, 120.9, 113.0, 109.5,
101.3, 81.6, 47.86; MS (ESI+) m/z (relative intensity) 341 (M+,
100); Anal. Calcd for C12H11N2I: C, 46.32; H, 3.89; N, 9.00.
Found: C, 46.33; H, 3.85; N, 9.02.
1-Methyl-2-[1-(toluene-4-sulfonyl)-1H-indol-3-ylethynyl] pyridi-
nium iodide (5b). Following the general procedure B, from 2 and
3-ethynyl-1-(toluene-4-sulfonyl)-1H-indole (0.7551 mmol,
0.2231 g), afforded 0.2387 g, (70%) of 5b as a yellow solid: mp
192 °C. IR (KBr): υmax (cm−1) 3500, 2220, 1378; 1H NMR
(200 MHz, CD3OD) δ (ppm) 9.02 (d, 1H, J = 6.7 Hz), 8.58 (t,
1H, J = 7.1 Hz), 8.49 (s, 1H), 8.37 (d, 1H, J = 7.7 Hz), 8.09 (d,
1H, J = 7.8 Hz), 8.03 (t, 1H, J = 6.2 Hz), 7.97 (d, 2H, J = 8.4
Hz), 7.83 (d, 1H, J = 7.5 Hz), 7.54–7.47 (m, 2H), 7.44 (t, 3H, J
= 8.4 Hz), 4.59 (s, 3H), 2.41 (s, 3H); 13C NMR (300 MHz,
CD3OD) δ (ppm) 148.0, 147.9, 145.9, 135.6, 135.5, 135.1,
132.7, 131.4, 130.8, 128.4, 127.4, 125.8, 121.3, 115.0, 102.3,
101.1, 85.2, 48.1, 47.9, 21.5; MS (ESI+) m/z (relative intensity)
388 (M+, 100); Anal. Calcd for C23H20N2O3SI: C, 51.99; H,
3.79; N, 5.27. Found: C, 51.97; H, 3.83; N, 5.25.
1-Methyl-4-(1H-pyrrol-3-ylethynyl) pyridinium hexafluoro phos-
phate (6a). Following the general procedure B, from 3 and 3-
Method B (4, 5, 6a–b). Analogously to Method A, with
addition of l% LiCl (0.0667 mmol, 0.0026 g and stirring the
reaction mixture for 20 h at room temperature.
1-Methyl -3-(1H-pyrrol-3-ylethynyl) pyridinium iodide (4a). Fol-
lowing the general procedure B, from 1a and 3-ethynyl-1-triiso-
propylsilanyl-1H-pyrrole (0.7551 mmol, 0.1875 g), afforded
0.1351 g, (63%) of 4a as a brown solid: mp 133 °C; IR (KBr):
υmax (cm−1) 3444, 3131, 2208, 1637; 1H NMR (200 MHz,
CD3OD) δ (ppm) 8.66 (d, 2H, J = 6.7 Hz), 7.90 (d, 2H, J = 6.7
Hz), 7.36 (t, 1H, J = 1.4 Hz), 6.85 (dd, 1H, J = 0.7, 2.0 Hz),
ethynyl-1-triisopropylsilanyl-1H-pyrrole
(0.7551
mmol,
0.1875 g), gave 0.0379 g, (32%) of 6a as a brown solid: mp
133 °C; IR (KBr): υmax (cm−1) 3444, 3131, 2208, 1637; 1H
NMR (200 MHz, CD3OD) δ (ppm) 8.66 (d, 2H, J = 6.7 Hz),
7.89 (d, 2H, J = 6.7 Hz), 7.36 (t, 1H, J = 1.4 Hz), 6.85 (dd, 1H,
J = 0.7, 2.0 Hz), 6.44 (dd, 1H, J = 1.3, 1.4 Hz), 4.89 (s, 3H);
13C NMR (300 MHz, CD3OD) δ (ppm) 145.7, 144.6, 132.9,
129.7, 127.5, 124.6, 120.5, 118.3, 112.9, 106.8, 47.8; MS (ESI+)
m/z (relative intensity) 341 (M+, 100); Anal. Calcd for
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1-Butyl-3,5-(1-trityl-1H-pyrazol-4-ylethynyl)pyridinium hexafluo-
rophosphate (7c). Following the general procedure C, from 1b
and 4-ethynyl-1-trityl-1H-pyrazol (1.6401 mmol, 0.5711 g),
gave 0.5317 g, (80%) of 7c as a brown solid: mp decomposes at
230 °C; IR (KBr): υmax (cm−1) 2223, 1618; 1H NMR
(200 MHz, DMSO-d6) δ (ppm) 9.20 (s, 2H), 8.59 (s, 1H), 7.80
(s, 2H), 7.70 (s, 2H), 7.41–7.38 (m, 15H), 7.17– 7.14 (m, 10H),
7.30–7.28 (m, 5H), 4.79 (t, 2H, J = 3.6 Hz), 4.28 (s, 3H); 13C
NMR (300 MHz, acetone-d6) δ (ppm) 147.9, 146.8, 144.4,
142.6, 141.9, 136.5, 131.8, 130.0, 128.1, 127.9, 127.8, 127.5,
126.7, 125.1, 99.9, 90.4, 83.1, 79.5, 62.6, 19.1, 12.7; MS (ESI+)
m/z (relative intensity) 801 (M+, 100); Anal. Calcd for
C57H46N5PF6: C, 72.37; H, 4.90; N, 7.40. Found: C, 72.34; H,
4.94; N, 7.42.
C12H11N2PF6: C, 43.92; H, 3.38; N, 8.54. Found: C, 43.97; H,
3.34; N, 8.55.
1-Methyl-4-[1-(toluene-4-sulfonyl)-1H-indol-3-ylethynyl] pyridi-
nium hexafluorophosphate (6b). Following the general procedure
B, from
3 and 3-ethynyl-1-(toluene-4-sulfonyl)-1H-indole
(0.7551 mmol, 0.0.2231 g), gave 0.1692 g, (50%) of 6b as a
brown solid: mp 208 °C; IR (KBr): υmax (cm−1) 3564, 2238,
1
1384. H NMR (200 MHz, CD3OD) δ (ppm) 8.84 (d, 2H, J =
6.7 Hz), 8.34 (s, 1H), 8.14 (d, 2H, J = 6.9 Hz), 8.03 (t, 2H, J =
8.6 Hz), 7.94 (d, 2H; J = 8.4 Hz), 7.80 (d, 1H; J = 0.9 Hz),
7.70–7.58 (m, 4H), 4.39 (s, 3H), 2.38 (s, 3H); 13C NMR
(300 MHz, CD3OD) δ (ppm) 147.3, 146.3, 134.8, 133.7, 133.0,
132.6, 132.5, 131.2, 129.7, 129.6, 129.5, 128.1, 127.0, 126.6,
125.4, 121.2, 114.6, 90.5, 48.8, 47.6, 21.4; MS (ESI+) m/z (rela-
tive intensity) 388 (M+, 100); Anal. Calcd for C23H20N2O2SPF6:
C, 50.37; H, 3.49; N, 5.11. Found: C, 50.42; H, 3.51; N, 5.07.
1-Butyl-3,5-(1-tert-butoxycarbonyl-1H-indazol-3-ylethynyl) pyri-
dinium hexafluoro phosphate (7d). Following the general pro-
cedure C, from 1b and 3-ethynyl-indazole-1-carboxylic acid tert-
butyl ester (1.6401 mmol, 0.3772 g), gave 0.2315 g, (55%) of
7d as a black solid: mp: decomposes at 240 °C; IR (KBr): υmax
General procedure for the synthesis of D-π-A+-π-D pyridinium
salts (7a–d)
1
(cm−1) 2229; 1744; 1382; H NMR (200 MHz, acetone-d6) δ
(ppm) 9.69 (d, 2H, J = 1.2 Hz), 9.37 (s, 1H), 8.27 (d, 2H, J =
8.5 Hz), 8.03 (d, 2H, J = 7.9 Hz), 7.73 (t, 2H, J = 6.9 Hz), 7.52
(t, 2H, J = 7.3 Hz), 4.90 (t, 2H, J = 7.6 Hz), 2.23–2.20 (m, 2H),
1.53–1.48 (m, 2H, J = 7.3 Hz), 1.02 (t, 3H, J = 7.6 Hz); 13C
NMR (300 MHz, CD3OD) δ (ppm) 150.0, 149.1, 147.8, 140.8,
132.8, 130.8, 127.5, 125.8, 124.7, 121.1, 115.8, 88.6, 87.4, 86.5,
64.0, 33.7, 28.2, 20.1, 13.7; MS (ESI+) m/z (relative intensity)
616 (M+, 100); Anal. Calcd for C37H43N5O4PF6: C, 58.04; H,
5.53; N, 9.15. Found: C, 58.02; H, 5.57; N, 9.12.
Method C. A flame-dried flask was charged under argon with
1 equiv. of the corresponding 3,5-dibromo-N-butylpyridinium
hexafluoro-phosphate salt (0.3 g, 0.6834 mmol), 10 mol% CuI
(0.013 g, 0.0683 mmol), 5 mol% PdCl(PPh3)2 (0.0239 g,
0.0341 mmol) in dry THF (10 mL) were added. The correspond-
ing acetylene heterocycle (2.4 equiv., 1.6401 mmol) and Et3N (3
equiv., 2.0502 mmol, 0.2815 mL) were added and the mixture
was stirred at room temperature for 1 h. Work-up following
Method A or B.
1-Butyl-3,5-(1H-pyrrol-3-ethynyl) pyridinium hexafluoropho-
sphate (7a). Following the general procedure C, 1b and 3-
ethynyl-1-triisopropyl silanyl-1H-pyrrole (1.6401 mmol,
0.4074 g), gave 0.1714 g, (55%) of 7a as a brown solid: mp
decomposed at 210 °C; IR (KBr): υmax (cm−1) 3444, 2965,
Acknowledgements
The authors acknowledge financial support from the Spanish
Ministerio de Ciencia
0431304313 and CTQ2009-07120), Comunidad de Madrid y
Universidad de Alcalá (CAM-UAH, project CCG10-UAH/
BIO-5974) and a grant from the CONACYT-144234/192425
(MAR).
e Innovación (project CTQ2008-
1
2215; H NMR (200 MHz, CD3OD) δ (ppm) 9.15 (d, 2H, J =
1.4 Hz), 8.54 (s, 1H), 7.32 (dd, 2H, J = 1.2, 1.4 Hz), 6.91 (dd,
2H, J = 2.0, 2.5 Hz), 6.35 (t, 2H, J = 2.5 Hz), 4.84 (t, 2H; J =
7.5 Hz), 2.22–2.20 (m, 2H, J = 8.0 Hz), 1.53–1.50 (m, 2H), 0.99
(t, 3H, J = 7.3 Hz); 13C NMR (300 MHz, CD3OD) δ (ppm)
145.7, 143.1, 126.1, 124.8, 119.4, 111.3, 101.5, 96.2, 80.8, 62.4,
32.9, 19.1, 12.8; MS (ESI+) m/z (relative intensity) 314 (M+,
100); Anal. Calcd for C21H20N3PF6: C 54.91; H, 4.39; N, 9.15.
Found: C, 54.92; H, 4.36; N, 9.14.
Notes and references
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hexafluorophosphate (7b). Following the general procedure C,
from 1b and 3-ethynyl-1-(toluene-4-sulfonyl)-1H-indole
(1.6401 mmol, 0.4846 g), afforded 0.4778 g, (83%) of 7b as a
1
brown solid: mp 177 °C. IR (KBr) υmax (cm−1) 2220; 1373; H
NMR (200 MHz, CD3OD) δ (ppm) 9.45 (d, 2H, J = 1.5 Hz),
9.02 (s, 1H), 8.21 (s, 2H), 8.09 (d, 2H, J = 8.2 Hz), 7.99 (d, 4H;
J = 8.5 Hz), 7.79 (d, 2H; J = 6.9 Hz), 7.54–7.37 (m, 9H), 4.92
(t, 2H, J = 7.6 Hz), 2.37 (s, 6H), 2.20–2.06 (m, 2H), 1.53–1.48
(m, 2H), 1.01 (t, 3H, J = 7.6 Hz); 13C NMR (300 MHz,
CD3OD) δ (ppm) 148.4, 147.3, 146.0, 135.2, 134.9, 132.4,
131.3, 130.8, 128.1, 127.1, 125.7, 125.3, 121.3, 114.7, 103.5,
90.6, 86.9, 63.7, 33.8, 21.5, 20.0, 13.7; MS (ESI+) m/z (relative
intensity) 722 (M+, 100); Anal. Calcd for C43H37N3O6S2PF6: C,
57.39; H, 4.03; N 4.67. Found: C, 57.37; H, 4.04; N, 4.68.
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 1659–1669 | 1667

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