Synthesis and optical properties of multibranched and C3 symmetrical oligomers with benzene or triphenylamine core and diazines as peripheral groups

Article abstract of DOI:10.1016/j.tet.2014.02.044

We report therein the synthesis and photophysical properties of a new series of two- and tribranched compounds built up from benzene or triphenylamine as central core and electron-withdrawing diazine rings as peripheral group. The arms allowing connection between these two parts are constituted by an ethynylene linker. All these compounds are fluorescent and are of particular interest with generally good quantum yields and good Stokes shifts. Some of them have been tested for two-photon absorption (TPA) properties and had revealed interesting performances.

Full text of DOI:10.1016/j.tet.2014.02.044

Tetrahedron 70 (2014) 2546e2555
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and optical properties of multibranched and C3
symmetrical oligomers with benzene or triphenylamine core and
diazines as peripheral groups
,
,
a
Flavia-Adina Martin a b, Christine Baudequin a , Catherine Fiol-Petit ,
*
b
a
,
ꢀ a
*
Mircea Darabantu , Yvan Ramondenc , Nelly Ple
Normandie Univ, COBRA, UMR 6014 et FR 3038; Univ Rouen, INSA Rouen; CNRS, IRCOF, 1 rue Tesniere, 76821 Mont Saint Aignan Cedex, France
a
ꢁ
b
ꢁ
Department of Chemistry, Babes-Bolyai University, 11 Arany Janos St., 400028 Cluj-Napoca, Romania
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 October 2013
Received in revised form 10 February 2014
Accepted 19 February 2014
Available online 25 February 2014
We report therein the synthesis and photophysical properties of a new series of two- and tribranched
compounds built up from benzene or triphenylamine as central core and electron-withdrawing diazine
rings as peripheral group. The arms allowing connection between these two parts are constituted by an
ethynylene linker. All these compounds are fluorescent and are of particular interest with generally good
quantum yields and good Stokes shifts. Some of them have been tested for two-photon absorption (TPA)
properties and had revealed interesting performances.
Keywords:
Diazine
Ó 2014 Elsevier Ltd. All rights reserved.
Fluorescence
Two-photon absorption
Cross-coupling
Conjugation
1. Introduction
conjugation length, planarity of the p-center and the donor/ac-
ceptor strength.12 Among the factors, which influence the photo-
physical properties, electron conjugation, and intramolecular
charge transfer (ICT) play an important role; therefore by changing
the design of compounds it is possible to tune their photophysical
and their TPA properties. In this context, a convenient strategy to
achieve the desired properties of the chromophores is to optimize
Organic materials with extended-
p conjugation along their
backbone have received high interest owing to their applications in
a wide range of electronic and optoelectronic devices.1 In recent
years, a variety of dipolar (donorebridgeeacceptor, De
quadrupolar (Ae eA, De eD, Ae eDe eA or De eAe
peA),
p
p
p
p
p
peD)
and multibranched molecules have been synthesized and in-
vestigation of their structure-properties relationships has been
achieved. Among them, star-shaped and bent-shaped molecules
have highlighted applications in various fields, such as liquid
crystals,2 light-emitting,3 self-assembling,4 and octupolar non-
linear optical properties.5 Another interest of such structures is
their potential two-photon absorption (TPA) properties,6 defined
by their cross-sections (dTPA). These structures could find applica-
tions in a large number of new areas, including the fluorescence
imaging of biological samples,7 optical limiting,8 photodynamic
therapy,9 the three-dimensional optical data storage,10 and micro-
fabrication.11 In a general way, the electro-optical properties of the
chromophores with such applications increase mainly with the
the individual fragments of the architecture, such as the core, the
linkers and the peripheral groups.
p-
In continuation of our work dealing with the synthesis and the
study of optical properties of star-shaped conjugated compounds
incorporating diazine moieties, we have studied a series of octu-
polar compounds. These compounds have been built up from an
electron-donating or a withdrawing central unit exhibiting a C3
symmetry. To insure an intramolecular charge transfer (ICT) be-
tween the core and the peripheral groups, which must be of dif-
ferent electronic character, the three arms are constituted by an
ethynylene linker, allowing either a periphery-to-core or core-to-
periphery multidimensional charge transfer. Incorporation of a tri-
ple bond as linkage in the backbone has been chosen because it
gives a good stability, and leads to coplanar conjugated structures.
A planar scaffold is not always observed with aromatic rings as
transmitter, because they could generate twisted structures. For
compounds of type I (Fig. 1), when the core is constituted by the
* Corresponding authors. Tel.: þ33 (0) 235522406; fax: þ33 (0) 235522962
(C.B.); tel.: þ33 (0) 235522902; fax: þ33 (0) 235522962 (N.P.); e-mail addresses:
ꢀ
christine.baudequin@univ-rouen.fr (C. Baudequin), nelly.ple@insa-rouen.fr (N. Ple).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.02.044

F.-A. Martin et al. / Tetrahedron 70 (2014) 2546e2555
2547
4-ethynylaniline.20 One other way, reaction of 4-substituted aryl-
benzenes or 4-iodopyridine with 1,3,5-triethynylbenzene has led to
various compounds of type I.21,22
The synthetic route to the target compounds BY3 takes advan-
tage of a Sonogashira cross-coupling reaction between the 1,3,5-
triiodobenzene and the corresponding 3-methoxy- or 3-di-n-
butylamino-6-(trimethylsilyl)ethynylpyridazine leading to the
three-branched BY3 compounds 1 and 2 in moderate yields. In this
case the desilylation of the ethynyl part has been carried out in situ
by reaction with tetrabutylammonium fluoride (TBAF). A similar
reaction with the 2-ethynyl-4,6-dimethylpyrimidine gave the BZ3
compound 3 in 42% yield (Scheme 1).
D
N
N
N
N
Fig. 1. C3 symmetrical oligomers incorporating diazine moieties.
3 eq. Me Si
a, b
D
N
N
D
BY3
pyrimidine ring, known for its p-deficient character, the peripheral
1 D = OMe
55%
groups are phenyl groups para-substituted with electron-donors. In
contrary, when the central unit is an electron-donating moiety,
such as triphenylamine core or benzene ring may behave as mod-
erate donor and acceptor, the peripheral groups are electron-
2 D = N(n-Bu)2 62%
N
N
D
I
CH3
attracting p-deficient diazines (pyridazine or pyrimidine).
Compounds of type I with a triphenylamine core and peripheral
strong electron-withdrawing groups as substituents of phenyl rings
have been previously reported. Such compounds have highlighted
various applications, such as fluorescence,13 two-photon absorp-
tion,14 Organic Light Emitting Diodes (OLEDs),15 DNA strainers.16
Originality of this work is the synthesis of a new series of com-
pounds of type I with incorporation of diazines, known to be good
H3C
N
I
I
N
N
CH
CH
N
N
3 eq.
H
CH3
CH3
N
N
c
BZ3
3
42%
p-deficient moieties.
H3C
N
Dendritic materials alternating double and single bonds have
CH3
been synthesized and interesting fluorescence properties were
obtained.17 With the aim to modulate the optical properties of
these octupolar compounds, structures of type II have been syn-
thesized. In this case, each arm is constituted by a bis(arylvinyl)
pyrimidine linked to the triphenylamine central unit through an
ethynylene linker (Fig. 1).
a. TBAF
b. PPh3, CuI, Pd2(dba)3, Et3N / Toluene, 50 °C, 48 h.
c. PdCl2(PPh3)2, CuI, Et3N, 90 °C, 24 h.
Scheme 1. Synthesis of compounds BY3 and BZ3.
2.1.1.3. Compounds incorporating a triphenylamine core CY3 and
The choice of these peripheral
p-conjugated chains has been
CZ3. A series of star compounds CY3 and CZ3 with C3-fold symmetry
and the triphenylamine as central unit could be synthesized either
starting from the tris-(4-iodophenyl)amine 4,23,24 which un-
derwent Sonogashira cross-coupling reaction with diazinylethynes
(Scheme 2) or starting from the tris-[4-(2-trimethylsilylethynyl)
phenyl]amine 9,24 which was coupled with iododiazines (Scheme
4). In the first case, coupling reaction of 4 with 6-methoxy- or 6-
n-dibutylamino-3-ethynylpyridazine25 afforded compounds 5 and
6 in moderate yields (63e68%).
determined by ability of the V-shaped 4,6-bis(arylvinyl)pyrimidine
oligomers, previously described, to induce interesting optical
properties and to be used as fluorescent sensors.18
2. Results and discussion
2.1. Synthesis
2.1.1. Compounds of type I
When the reaction was performed under the same conditions
with the 3-ethynyl-6-phenylpyridazine, only the dicoupled
2.1.1.1. Compounds incorporating a pyrimidine core AX3. The
synthesis and optical properties of compounds of type I that we can
designate, for example, as AX3 (i.e., 2,4,6-triphenylpyrimidines)
have been previously reported.19 Using molecular orbital calcula-
tions at the DFT 6-31* level theory on these compounds, the en-
ergies of their frontier orbitals have been calculated and their
geometry fully optimized and established as absolutely planar
structures.
2.1.1.2. Compounds incorporating
a benzene core BY3 and
BZ3. The synthetic strategy to access compounds, BY3 or BZ3 with
a benzene core involves Sonogashira cross-coupling reactions
achieved either with 1,3,5-triiodo- or with 1,3,5-triethynyl- ben-
zene as starting materials. This first methodology has been pre-
viously used to synthesize compounds of type BX3 with
Scheme 2. Synthesis of compounds CY3 starting from compound 4.

2548
F.-A. Martin et al. / Tetrahedron 70 (2014) 2546e2555
compound 7 was obtained in 32% yield. On the other hand, when
the coupling reaction was achieved between 4 and only two
equivalents of 3-ethynyl-6-methoxypyridazine, under modified
experimental conditions, the dicoupled compound 8 was obtained
in similar low yield (Scheme 3).
Scheme 5. Glaser’s dimerization leading to the compound 13.
Scheme 3. Synthesis of two-branched compounds 7 and 8.
2.1.2. Compounds of type II. As previously, to access compounds of
type II with a triphenylamine as central moiety, two strategic
pathways could be considered either starting from the triiodo
compound 4 or from the triethynyl derivative 9. The choice of 4 as
starting material seemed to us more appropriate since this com-
pound is easily available. In this case coupling reaction would be
TMS
achieved between
4
and appropriate substituted 2-
N
ethynylpyrimidines. Synthesis of various 2-iodo-4,6-bis(arylvinyl)
pyrimidines 14e16 have been performed by solvent free conden-
sation of 2-iodo-4,6-dimethylpyrimidine with corresponding aro-
TMS
TMS
9
matic aldehydes, under the conditions described by Li et al.26
A
further coupling with TMSA and a subsequent desilylation with
TBAF afforded the expected 2-ethynyl-4,6-bis(arylvinyl)pyrimi-
dines 17e19 in good yields (Scheme 6).
3.5 eq.
3.5 eq.
a
b
I
D
I
N
N
D
CHO
2.2 eq.
H C
CH
N
N
N
N
N
N
5 eq. t-BuOK, r.t., 2 h
H C
CH
D
D
CY3
14 D = NMe
15 D = N(n-Bu)
16 D = OMe
57%
37%
37%
CZ3
N
N
H
N
H C
N
N
CH
a, b
N
N
N
N
D
N
6
D = N(n-Bu) 57%
D
10 71%
11 D = Ph 48%
CH
CH
N
N
a. TBAF, Pd(PPh ) , CuI, Et N / Toluene, 50 °C, 24 h.
b. TBAF, PPh , CuI, Pd (dba) , Et N / Toluene, 50 °C, 24 h.
D
D
17 D = NMe
18 D = N(n-Bu)
19 D = OMe
81%
83%
77%
Scheme 4. Synthesis of compounds CZ3 and CY3 starting from compound 9.
a. 2 eq. TMSA, PPh , CuI, PdCl (PPh ) , Et N / THF, 50 °C, 48 h.
b. TBAF, THF, r.t., 3 h.
In the second route, the tris-[4-(2-trimethylsilylethynyl)phenyl]
amine 9 has been used as starting material. Compound 9 was ob-
tained by a triple coupling of trimethylsilylacetylene (TMSA) with 4.
A one-pot TMS deprotection and subsequent standard Sonogashira
coupling reaction with iododiazines afforded the compound 10
with a structure CZ3 and the compounds 6 and 11 of type CY3 in
moderate yields (Scheme 4).
With the aim to access C3 star-shaped compounds with a tri-
phenylamine core and peripheral groups constituted by a sub-
structure of compound 8, a new p-aminophenylacetylene 12 has
been synthesized. The iodo derivative 8 was functionalized with
TMSA, a further removal of the TMS group giving 12 in 60% yield. An
attempt to perform a Sonogashira coupling between 4 and 12 under
standard conditions, previously used, has failed and only com-
pound 13, resulting from a Glaser’s dimerization reaction has been
obtained (Scheme 5).
Scheme 6. Synthesis of 2-ethynyl-4,6-bis(arylvinyl)pyrimidines.
Attempts to obtain tribranched compounds by coupling reaction
between 4 and compound 17 or 18 have been performed under
classical conditions. Nevertheless, by use of these experimental
conditions, only a mono-coupling occurred, leading to compounds
20 and 21 in low yields (Scheme 7).
These results urged us to choose another synthetic way, to ob-
tain the expected C3 compounds of type II. Starting from the CZ3
compound 10, it would be possible to carry out condensation under
basic conditions with aromatic aldehydes, this methodology having
been used with success to access compounds 14e16. Condensation
reaction of 10 with 4-dimethylamino- or 4-methoxybenzaldehyde

F.-A. Martin et al. / Tetrahedron 70 (2014) 2546e2555
2549
The UV/Vis and fluorescence spectroscopic data of various
oligomers measured in dichloromethane at 25 ꢀC are summarized
in Table 1.
Table 1
Photophysical data for octupolar chromophores 1e3, 5, 6, 10, 11, 24e26 in di-
chloromethane at 25 ꢀC
a
Type Compound
D
labs
ε
lem
FF
Stokes
[nm] [Mꢁ1 cmꢁ1
]
[nm]
shift [cmꢁ1
]
AX3 2418
AX3 2518
AX3 2618
H
341 38,539
335 45,073
433 26,155
286 47,177
370
406
522
0.06
0.48
0.24
2298
5220
3938
OMe
NMe2
OMe
Scheme 7. Synthesis of compounds 20 and 21 resulting from
reaction.
a mono-coupling
BY3
BY3
BZ3
CY3
CY3
CY3
CZ3
1
2
3
5
6
460 <0.01 13,226
425 <0.01
350 <0.01
449
450
488
449
N(n-Bu)2 326 24,573
d
7145
4764
4395
4094
4889
3702
has been achieved with an excess of aldehyde, and 9 equiv of t-
BuOK as base, at reflux of THF by a classical thermal heat for 24 h
(Method A). Under these conditions only traces of expected com-
pounds 22 and 23 have been observed. When this reaction has been
performed with use of microwaves and shorter reaction time
(Method B), compounds 22 and 23 were obtained, respectively, in
14% and 29% yields (Scheme 8).
300 58,573
375 64,597
OMe
0.60
0.29
0.03
0.57
N(n-Bu)2 380 56,112
Ph
d
11
10
394 52,601
385 56,908
a
ꢂ10%, harmane (0.1 M in H2SO4) was used as reference (FF¼0.58).
All the three-branched compounds collected in Table 1 have
their absorption wavelengths (labs) in the UV region (286e394 nm)
and their emission absorption wavelengths (lem) in the UV or blue
region (350e460 nm), an exception was observed for compound
AX3 26 with D¼NMe2 whose absorption and emission wavelengths
are in visible region. Amplitude of the charge transfer has a great
influence on the quantum yield, the highest values for FF are ob-
served with the cores A or C, which have a strong electron-with-
drawing or donating effect, whereas the lowest values are obtained
with the benzene core. It could be noticed that these results are in
agreement with the fact that triphenylamine derivatives are well-
known as fluorescent materials and exhibit high quantum yields
and Stokes shifts when they are included in scaffolds with
p-con-
Scheme 8. Synthesis of compounds of type II.
jugation extension and with strong acceptor groups in periphery.
For compounds CY3 5, 6, 11, such as for compounds AX3 24e26,
presence of an electron releasing group on the peripheral rings
increases the light-emitting properties. However, in this case and
unexpectedly, the methoxy group, which is prone to be less
electron-donor than dialkylamino groups is more efficient on the
quantum yields. We can notice that compound CZ3 10, with
a dimethylpyrimidine as peripheral substituent exhibits a moder-
ate Stokes shift but a great quantum yield.
With the aim to establish the influence of the number of arms,
comparison of optical properties of compounds 5, 7, 8, 11e13 with
a triphenylamine as core and 6-methoxy- or 6-phenylpyridazine as
peripheral groups have been studied and are reported in Table 2. All
these compounds have similar absorption values in UV
(367e394 nm), emission wavelengths in blue region (438e488 nm)
and similar Stokes shifts, the main difference is observed for the
quantum yields.
2.2. Linear UV/Vis absorption and single-photon excited
fluorescence
In order to determine the influence of the intramolecular charge
transfer (ICT) between the core and the peripheral groups, de-
termination and comparison of the spectroscopic properties of
various compounds of type I has been achieved. Compounds AX3
24e26,19 with the electron-withdrawing pyrimidine as central unit,
bearing on each arm
a benzene ring para-substituted with
a methoxy or a dimethylamino group, present a multidimensional
charge transfer from periphery-to-core. In the case of compounds
BY3 and BZ3, where a benzene ring is the central part, the external
diazine moieties Y (pyridazine) or Z (pyrimidine) induce the charge
transfer from core-to-periphery. Same kind of ICT is observed with
compounds CY3 and CZ3 where the central unit is the strong elec-
tron releasing triphenylamine (Fig. 2).
Table 2
Photophysical data for multibranched chromophores 5, 7, 8, 11e13 in dichloro-
methane at 25 ꢀC
a
Compound
labs
ε
lem
FF
Stokes
[nm]
[Mꢁ1 cmꢁ1
]
[nm]
shift [cmꢁ1
]
5
7
8
11
12
13
375
390
375
394
367
386
64,597
29,012
64,785
52,601
27,992
82,594
449
487
455
488
460
438
0.60
0.02
0.16
0.03
0.49
0.48
4395
5108
4688
4889
5509
3075
a
ꢂ10%, harmane (0.1 M in H2SO4) was used as reference (FF¼0.58).
Fig. 2. Compounds of type I.

2550
F.-A. Martin et al. / Tetrahedron 70 (2014) 2546e2555
Comparison between the three-branched compounds 5 and 11
17 and 18, were determined in the wavelengths range
(730e920 nm) by investigating their two-photon induced fluo-
rescence (TPIF) measurements, with a femtosecond (fs) Ti:sapphire
laser source. In all cases, the output intensity of two-photon excited
fluorescence was linearly dependent on the square of the input
laser intensity, thereby confirming the TPA process. The results of
some fluorophores having the better quantum yields are summa-
rized in Table 4 and Fig. 3.
and the two-branched analogous iodo derivatives 8 and 7 high-
lights that compounds 5 and 8, with a methoxy group on the pyr-
idazine ring, exhibit better quantum yields than their analogous
bearing a phenyl group. We can observe that presence of a third
arm increases strongly the quantum yields. Comparison of the
values for 8 and 12 reveals that replacement of the iodine atom by
a triple bond has the effect of large increasing the FF (0.49 vs 0.16).
The low quantum yields observed for the compounds 7e8 can be
explained by the presence of the iodine atom, which can quench
the fluorescence. For the dimeric compound 13, which could be
considered as two three-branched moieties, the FF value is close to
that observed for 12. The better quantum yield is obtained for the
tripodal C3 symmetric compound 5.
Table 4
Photophysical and two-photon absorption data for selected fluorophores 5,10,12,17,
18
a
Compound
labs
ε
lem
FF
dmax (GM)
dmax/MW
[nm]
[nm]
Recently synthesis of a series of bis(arylvinyl)pyrimidine oligo-
mers have been reported highlighting interesting photophysical
properties (absorption, fluorescence and quantum yields).18a In-
corporation of such moieties on triphenylamine core through
ethynyl linkage leads to compounds of type II. The photophysical
properties of the two-branched building blocks 14e19, mono
coupled compounds 20e21 and three coupled compounds 22e23
are collected in Table 3.
5
375
385
367
440
455
64,597
56,908
27,992
43,916
65,407
449
449
460
545
547
0.60
0.57
0.49
0.47
0.52
126 (730 nm)
425 (730 nm)
143 (730 nm)
86 (830 nm)
146 (880 nm)
0.19
0.67
0.27
0.22
0.26
10
12
17
18
a
10%, harmane (0.1 M in H2SO4) was used as reference (FF¼0.58).
Table 3
Photophysical data for multibranched chromophores 14e23 in dichloromethane at
25 ꢀC
a
Compound
D
labs
ε
lem
FF
Stokes
[nm]
[Mꢁ1 cmꢁ1
]
[nm]
shift [cmꢁ1
]
14
15
16
17
18
19
20
21
22
23
NMe2
N(n-Bu)2
OMe
NMe2
N(n-Bu)2
OMe
NMe2
N(n-Bu)2
NMe2
450
470
374
440
455
364
430
450
408
376
46,535
60,651
21,387
43,916
65,407
35,244
24,897
39,625
77,057
134,084
561
560
459
545
547
457
545
545
553
518
0.04
0.08
0.01
0.47
0.52
0.02
0.42
0.52
0.19
0.03
4397
3419
4951
4378
3696
5590
4907
3874
6427
7291
Fig. 3. Two-photon absorption spectra of selected fluorophores 5, 10, 12, 17, 18 de-
termined by femtosecond TPIF measurements.
OMe
a
ꢂ10%, harmane (0.1 M in H2SO4) was used as reference (FF¼0.58).
The two-branched or V-shaped 2-ethynyl-4,6-bis(arylvinyl)py-
rimidines 17e18 with significant quantum yields present moderate
two-photon absorption cross-sections dmax reaching, respectively,
86 and 146 GM. The TPA performances of the compounds 5, 10, and
12 with a triphenylamine as central unit allow to observe that if the
two-branched compound 12 and the three-branched compound 5,
bearing both a peripheral 6-methoxypyridazine moiety, have sim-
ilar dmax around 125e145 GM, replacement of a pyridazine ring
with a pyrimidine one increases from one to threefold the cross-
sections dmax values, which reaches 425 GM for 10. This result
seems indicate that the nature of the peripheral diazine is more
important than the number of branches. It is interesting to note
that among the TPA performance the two-photon absorption/mo-
As previously, we observed that for the iodo derivatives 14e16
as well for the ethynyl compounds 17e19, replacement of the
methoxy group by a dialkylamino one induces a bathochromic ef-
fect for both absorption and emission wavelengths. For the amino
derivatives, replacement of the iodine atom in 14e15 by an ethynyl
group in compounds 17e18 resulted in higher quantum yield
(0.04e0.08 vs 0.47e0.52) whereas a slightly higher emission was
observed for the methoxy derivatives 16 and 19 (0.01 vs 0.02).
When a bis(arylvinyl)pyrimidine moiety is incorporated in one arm
of the triphenylamine unit leading to compounds 20 and 21, similar
photophysical properties are observed for the both series 17,18, and
20, 21. This result seems indicate that such incorporation do not
allow an extension of conjugation. When each arm of the three-
branched triphenylamine is substituted by a bis(arylvinyl)pyrimi-
dine moiety, a comparison on the one hand between 20 and 22 and
one the other hand between 19 and 23, allows to observe a slight
hypsochromic effect for the absorption and emission wavelengths
lecular weight ratio (
regard, compound 10 with a
d
/MW) is a relevant figure of merit. In this
d
/MW ratio around 0.67 GM gꢁ1 mol
falls in the range of the very good chromophores reported so far,
compared to values of 0.5e1.0 GM gꢁ1 mol described for large-sized
systems optimized for two-photon absorption.27
3. Conclusion
(labs and lem) whereas a dramatic decrease of the quantum yield is
noted, with a very low value when the external substituent is
a methoxy group 23.
In this paper, we have described the synthesis of novel multi-
polar fluorophores with benzene or a triphenylamine core and
electron-withdrawing diazine rings as peripheral group, these two
parts are connected through ethynyl linker to extend the conju-
gation. Various two- and three-branched compounds have been
obtained and their photophysical properties have been determined
and compared with those of C3 symmetrical compounds (AX3) with
2.3. Two-photon absorption (TPA)
Two-photon absorption cross-sections (dTPA) spectra of the
three-branched 5, 10, and 12 and the two-branched chromophores

F.-A. Martin et al. / Tetrahedron 70 (2014) 2546e2555
2551
a pyrimidine core. All these compounds are fluorescent and those
of C3 symmetry with a core having a strong character of electron-
withdrawing or electron releasing, such as pyrimidine or triphe-
nylamine (AX3, CY3, and CZ3) exhibit the better quantum yields. The
TPA performances of some compounds with good quantum yields
have been performed, the best result was obtained for the suitable
photostable compound 10 (structure CZ3) with a triphenylamine
core and dimethylpyrimidines as peripheral groups. This com-
pound with a moderate molecular weight exhibits an interesting
cross-section (425 GM) in the NIR region with a high figure of merit
to 0 ꢀC and TBAF (1 M in THF, 1.53 mL) was added dropwise and the
reaction mixture was stirred for 10 min. The solution was heated to
50 ꢀC for 48 h. The reaction was cooled, filtered through CeliteÒ and
evaporated under reduced pressure. The crude product was puri-
fied by column chromatography on silica gel (petroleum ether/
ethyl acetate¼2:1) to give the title compound 1 as a brown solid
(0.055 g, 55%). Mp: >260 ꢀC. IR (cmꢁ1, neat): 1400, 2952, 2219,
1582, 1538, 1466, 1423, 1403, 1335, 1296, 1166, 1133, 1098, 1010, 965,
873, 841, 759, 673; 1H NMR (300 MHz, CDCl3)
d (ppm): 4.19 (s, 9H),
7.00 (d, J¼9.3 Hz, 3H), 7.54 (d, J¼9.3 Hz, 3H) 7.84 (s, 3H); 13C NMR
(d
/MW ratio around 0.67 GM gꢁ1 mol).
(75 MHz, CDCl3) d (ppm): 55.3, 87.3, 89.8, 116.8, 123.3, 132.6, 135.6,
143.3, 163.7; MS (TOF MS ESIþ); m/z (rel int. %): (MþHþ) 475 (100),
4. Experimental section
4.1. General methods
516 (MþHþþacetonitrile).
4.1.2. 1,3,5-Tris-[6-(3-di-n-butylaminopyridazinyl)ethynyl]benzene
(2). According to the procedure described for 1, a mixture of
3-n-dibutylamino-6-(trimethylsilyl)ethynylpyridazine (0.232 g,
0.766 mmol), 1,3,5-triiodobenzene (0.100 g, 0.219 mmol), and TBAF
(1 M in THF, 1.53 mL) gave after purification by column chroma-
tography on silica gel (petroleum ether/ethyl acetate¼2:1) the title
All chemicals were purchased from commercial sources and
were used without further purification unless otherwise specified.
Analytical thin layer chromatography was performed on silica gel
plates (MerckÒ TLC Silica gel 60 F254) and compounds were
detected by irradiation with UV light (254 and 365 nm). Chro-
matographic purification of compounds was achieved with silica
compound 2 as a brown solid (0.104 g, 62%). Mp: 60 ꢀC. IR (cmꢁ1
,
neat): 2957, 2928, 2871, 2214, 1734, 1701, 1654, 1578, 1540, 1484,
1425, 1371, 1333, 1232, 1171, 1112, 1017, 960, 926, 878, 822, 733, 681;
gel (mesh size 60e80 mm). IR spectra were recorded with a uni-
versal attenuated total reflectance (ATR) sampling accessory on
a PerkineElmer FTIR Spectrum 100 spectrometer. Absorption bands
are given in cmꢁ1. HRMS spectra (ESIþ) were recorded on a LC
Waters Acquity coupled to a Waters LCT Premier XE instrument.
Elemental analyses were performed on a Carlo Erba 1106 apparatus.
Measurement accuracy is around ꢂ0.4% on carbon. Melting points
(ꢀC) were measured on a Kofler hot-stage with a precision of 2ꢀ
(ꢂ2 ꢀC). The 1H and 13C NMR spectra were recorded on a Bruker
Advance spectrometer operating at 300 MHz and 75 MHz, re-
1H NMR (300 MHz, CDCl3)
d
(ppm): 0.95 (t, J¼7.4, 18H), 1.24e1.43
(m, 12H), 1.55e1.66 (m, 12H), 3.53 (t, J¼7.6, 12H), 6.64 (d, J¼9.4 Hz,
3H), 7.29 (d, J¼9.4 Hz, 3H), 7.69 (s, 3H); 13C NMR (75 MHz, CDCl3)
d
(ppm): 14.1, 20.3, 29.6, 48.9, 88.4, 88.8, 109.8, 123.7, 130.5, 134.5,
136.9, 156.7; HRMS: calcd for C48H64N9 [MþH]þ 766.5285; found
766.5295.
4.1.3. 1,3,5-Tris-[2-(4,6-dimethylpyrimidinylyl)ethynyl]benzene
(3). A solution of 1,3,5-triiodobenzene (0.226 g, 0.497 mmol),
2-ethynyl-4,6-dimethylpyrimidine (0.229 g, 1.739 mmol),
Pd(PPh3)2Cl2 (0.034 g, 0.049 mmol), CuI (0.018 g, 0.097 mmol) in
Et3N (15 mL) was stirred at 90 ꢀC for 24 h under nitrogen atmo-
sphere, the TLC monitoring indicated the consumption of starting
materials. The reaction mixture was cooled, filtered through CeliteÒ
and evaporated under reduced pressure. The crude product was
purified by column chromatography on silica gel (EtOH was used
for the first purification followed by a second one with ethyl acetate
as eluent) to afford the title compound 3 as brown solid (0.097 g,
42%). Mp: 230 ꢀC. IR (cmꢁ1, neat): 2962, 2923, 2900, 2172, 1949,
1738, 1587, 1535, 1441, 1346, 1251, 1176, 1036, 956, 943, 845, 788,
spectively. The chemical shifts
d are reported in parts per million
(ppm) relative to the residual solvent peak (7.26 and 77.16, re-
spectively, for CDCl3, 0.00 for CFCl3). Data appear in the following
order: chemical shifts in ppm, number of protons, multiplicity (s,
singlet; d, doublet; dd, doublet of doublet; t, triplet; m, multiplet),
coupling constant J in Hertz. Fluorescence spectroscopic studies
were performed with a Varian Cary Eclipse spectrophotometer.
Compounds were excited at their absorption maxima for recording
the emission spectra; however different wavelengths were used to
determine fluorescence quantum yields in cases where compounds
and standards absorbed significantly. All solutions were measured
with optical densities below 0.1. The TPA cross-sections in the range
790e950 nm were obtained by up-conversion fluorescence using
a mode locked Ti:sapphire femtosecond laser (Tsunami Spectra-
Physics) with pulse duration 100 fs and at a repetition rate of
82 MHz. The measurements were done at room temperature in
DCM and at concentration of ca. 5$10ꢁ6 Me10ꢁ5 M. The excitation
beam (5 mm diameter) is focused with a lens (focal length 10 cm) at
the middle of the fluorescence cell (10 mm). The fluorescence,
collected at 90ꢀ to the excitation beam, was focused into an optical
761, 704, 634, 619; 1H NMR (300 MHz, CDCl3)
d
(ppm): 2.52 (s, 18H),
(ppm): 24.0,
7.01 (s, 3H), 7.88 (s, 3H); 13C NMR (75 MHz, CDCl3)
d
84.3, 89.4, 119.5, 122.8, 136.6, 152.2, 167.3; HRMS: calcd for
C
30H25N6 [MþH]þ 469.2141; found 469.2144.
4.1.4. Tris-(4-iodophenyl)amine(4). A mixture of triphenylamine
(1 g, 0.004 mmol), HgO (4.06 g, 0.019 mmol) and I2 (5.08 g,
0.020 mmol) in EtOH (50 mL) was stirred overnight at room tem-
perature. The solvent was removed, and the product was separated
from mercuric salts with boiling toluene. The solution was filtered
through the short column of Al2O3, and the product was pre-
cipitated from hot toluene with MeOH to afford the title compound
4 as white solid (2.33 g, 90%). Mp: 170 ꢀC. 1H NMR (300 MHz, CDCl3)
fiber (diameter 600
mm) connected to an Ocean Optics S2000
spectrometer. The incident beam intensity was adjusted to 50 mW
in order to ensure an intensity-squared dependence of the fluo-
rescence over the whole range. The detector integration time was
fixed to 1 s. Comparison of the spectra was performed with the
published Fluorescein and Rhodamine B two-photon absorption
spectra.
d
(ppm): 7.53 (d, J¼8.8 Hz, 6H), 6.81 (d, J¼8.8 Hz, 6H); 13C NMR
(75 MHz, CDCl3)
d
(ppm): 86.76, 126.12, 138.53, 146.59.23
4.1.5. Tris-[4-(6-methoxypyridazin-3-yl)ethynylphenyl]amine (5). A
solution of tris-(4-iodophenyl)amine 4 (0.200 g, 0.321 mmol), 3-
ethynyl-6-methoxypyridazine (0.150 g, 1.123 mmol), Pd(PPh3)2Cl2
(0.017 g, 0.090 mmol), CuI (0.063 g, 0.090 mmol), PPh3 (0.047 g,
0.180 mmol) in 30 mL of a mixture of 1/1 THF/Et3N was stirred at
65 ꢀC for 48 h. The reaction was cooled, filtered through CeliteÒ and
evaporated under reduced pressure. The crude product was
4.1.1. 1,3,5-Tris-[6-(3-methoxypyridazinyl)ethynyl]benzene
(1). To
a
mixture of 3-methoxy-6-(trimethylsilyl)ethynylpyridazine
(0.185 g, 0.766 mmol), 1,3,5-triiodobenzene (0.100 g, 0.219 mmol),
Pd2(dba)3 (0.020 g, 0.021 mmol), CuI (0.004 g, 0.021 mmol), PPh3
(0.005 g, 0.021 mmol) under nitrogen atmosphere were added dry
Et3N (10 mL) and toluene (10 mL). The reaction mixture was cooled

2552
F.-A. Martin et al. / Tetrahedron 70 (2014) 2546e2555
purified by column chromatography on silica gel (petroleum ether/
ethyl acetate¼1:2) to give the title compound 5 as a yellow solid
(0.129 g, 63%). Mp: 223 ꢀC. IR (cmꢁ1, neat): 3039, 2949, 2360, 2345,
2218, 1735, 1655, 1594, 1542, 1505, 1462, 1410, 1338, 1318, 1288,
1180, 1153, 1110, 999, 833, 731, 682, 635, 531, 485, 420; 1H NMR
1/1 THF/Et3N cooled at 0 ꢀC, 11.2 mL of TBAF (1 M in THF, 11.2 mmol)
were introduced dropwise under nitrogen atmosphere and the
reaction mixture was stirred for 10 min. The solution was heated to
50 ꢀC for 24 h. The reaction was cooled, filtered through CeliteÒ and
evaporated under reduced pressure. The crude product was puri-
fied by column chromatography on silica gel (petroleum ether/
ethyl acetate¼1:4) to give the title compound 10 as a yellow solid
(0.850 g, 71%). Mp: >260 ꢀC. IR (cmꢁ1, neat): 2203, 1701, 1653, 1581,
1529, 1503, 1437, 1370, 1343, 1314, 1274, 1220, 1175, 1108, 1028, 958,
(300 MHz, CDCl3)
d
(ppm): 4.17 (s, 9H), 6.96 (d, J¼9.2 Hz, 3H), 7.11
(d, J¼8.7 Hz, 6H), 7.51 (d, J¼9.2 Hz, 3H), 7.53 (d, J¼8.8 Hz, 6H); 13C
NMR (75 MHz, CDCl3)
d (ppm): 55.2, 85.9, 92.0, 116.7, 116.9, 124.2,
132.4, 133.4, 143.8, 147.3, 163.4; HRMS: calcd for C39H28N7O3
[MþH]þ 642.2254; found 642.2263.
847, 830, 785, 773, 730, 627; 1H NMR (300 MHz, CDCl3)
2.48 (s, 18H), 6.94 (s, 1H), 7.05 (d, J¼8.7 Hz, 6H), 7.56 (d, J¼8.7 Hz,
6H); 13C NMR (75 MHz, CDCl3)
(ppm): 24.1, 87.1, 88.5, 116.5, 119.0,
d (ppm):
4.1.6. Tris-[4-(6-N,N-dibutylaminopyridazin-3-yl)ethynylphenyl]
amine (6). According to the procedure described for 5, a mixture of
tris-(4-iodophenyl)amine 4 (0.200 g, 0.321 mmol) with the 6-n-
dibutylamino-3-ethynylpyridazine (0.260 g, 1.123 mmol) gave after
purification by column chromatography on silica gel (petroleum
ether/ethyl acetate¼1:2) the title compound 6 as a dark yellow
solid (0.203 g, 68%). Mp: 68 ꢀC. IR (cmꢁ1, neat): 3308, 3660, 3469,
3188, 3040, 2956, 2928, 2870, 2343, 2211, 1596, 1542, 1504, 1424,
1372, 1318, 1288, 1270, 1230, 1168, 1112, 1015, 925, 830, 767, 724,
d
124.2, 134.2, 147.5, 152.8, 167.2; MS (TOF MS ESIþ); m/z (rel int. %):
(MþHþ) 636 (90).
4.1.11. Tris-[4-(6-phenylpyridazin-3-yl)ethynylphenyl]amine (11). To
a mixture of 3-iodo-6-phenylpyridazine (0.277 g, 0.980 mmol),
compound
9 (0.150 g, 0.280 mmol), Pd2(dba)3 (0.025 g,
0.028 mmol), CuI (0.005 g, 0.028 mmol), PPh3 (0.007 g,
0.028 mmol) under nitrogen atmosphere were added dry Et3N
(10 mL), and toluene (10 mL). The reaction mixture was cooled to
695, 646, 540, 409; 1H NMR (300 MHz, CDCl3)
d (ppm): 0.95 (t,
J¼7.3 Hz, 18H), 1.31e1.40 (m, 12H), 1.57e1.63 (m, 12H), 3.52 (t,
J¼7.6 Hz, 12H), 6.63 (d, J¼9.6 Hz, 3H), 7.06 (d, J¼8.6 Hz, 6H), 7.27 (d,
J¼9.4 Hz, 3H), 7.46 (d, J¼8.6 Hz, 6H); 13C NMR (75 MHz, CDCl3)
0
ꢀC and TBAF (1 M in THF, 1.68 mL) was added dropwise and the
reaction mixture was stirred for 10 min. The solution was heated to
50 ꢀC for 24 h. The reaction was cooled, filtered through CeliteÒ and
evaporated under reduced pressure. The crude product was puri-
fied by column chromatography on silica gel (petroleum ether/
ethyl acetate¼3:1) to give the title compound 11 as a yellow solid
(0.104 g, 48%). Mp: 216 ꢀC. IR (cmꢁ1, neat): 2216, 1773, 1735, 1701,
1648, 1595, 1570, 1535, 1503, 1449, 1400, 1316, 1288, 1268, 1179,
1160, 1108, 1032, 1011, 830, 787, 763, 747, 690; 1H NMR (300 MHz,
d
(ppm): 14.1, 20.4, 29.7, 48.9, 87.1, 90.5, 109.8, 117.6, 124.1, 130.2,
133.1, 137.5, 146.9, 156.5; HRMS: calcd for C60H73N10 [MþH]þ
933.6020; found 933.6021.
4.1.7. N,N0-Bis-[4-(6-phenylpyridazin-3-yl)ethynylphenyl]-4-
iodoaniline (7). According to the procedure described for 5, a mix-
ture of tris-(4-iodophenyl)amine 4 (0.200 g, 0.321 mmol) with the
3-ethynyl-6-phenylpyridazine (0.202 g, 1.123 mmol) gave after
purification by column chromatography on silica gel (petroleum
ether/ethyl acetate¼2:1) the title compound 7 as a yellow solid
(0.0074 g, 32%). Mp: 216 ꢀC. IR (cmꢁ1, neat): 3052, 2921, 2849, 2218,
1597, 1579, 1541, 1450, 1400, 1316, 1287, 1269, 1163, 1113, 1004, 919,
856, 825, 788, 749, 691, 547, 509; 1H NMR (300 MHz, CDCl3)
CDCl3)
d
(ppm): 7.15 (d, J¼8.4 Hz, 6H), 7.58 (d, J¼8.4 Hz, 6H),
7.51e7.54 (m, 9H), 7.68 (d, J¼8.7 Hz, 3H), 7.85 (d, J¼9.0 Hz, 3H), 8.11
(d, J¼6.0 Hz, 6H); 13C NMR (75 MHz, CDCl3)
d (ppm): 86.5, 94.2,
116.8,123.1,124.3,127.3,129.2,130.0,130.4,133.7,136.0,146.8,147.5,
157.0; HRMS: calcd for
780.2876.
C
54H34N7 [MþH]þ 780.2871; found
d
(ppm): 6.92 (d, J¼8.9 Hz, 2H), 7.10 (d, J¼8.9 Hz, 4H), 7.52e7.55 (m,
4.1.12. 4-Ethynyl-N,N-bis[4-{(6-methoxypyridazin-3-yl)ethynyl}phe-
nyl]aniline (12). First step: In a 50 L two necked round bottom flask,
6H), 7.55 (d, J¼8.9 Hz, 4H), 7.63 (d, J¼8.9 Hz, 2H), 7.67 (d, J¼8.9 Hz,
2H), 7.85 (d, J¼8.9 Hz, 2H), 8.10e8.14 (m, 4H); 13C NMR (75 MHz,
compound
8 (0.410 g, 0.645 mmol), Pd(PPh3)2Cl2 (0.013 g,
CDCl3)
d
(ppm): 86.3, 88.2, 94.3, 116.3, 123.1, 123.6, 127.3, 127.5,
0.019 mmol, 3%), CuI (0.007 g, 0.038 mmol, 6%), dry toluene
(15 mL), and trimethylsilylacetylene (0.17 mL, 1.290 mmol, 2 equiv)
were introduced under dry nitrogen atmosphere. Dry Et3N (15 mL)
was added and the mixture was heated at 60 ꢀC for 48 h. The re-
action mixture was cooled, filtered through CeliteÒ and evaporated
under reduced pressure. The crude product was purified by column
chromatography on silica gel (petroleum ether/ethyl acetate¼2:1)
to afford the title compound as a brown solid (0.296 g, 76%). Mp:
146 ꢀC. IR (cmꢁ1, neat): 2950, 2218, 2152, 1596, 1543, 1504, 1461,
1409, 1339, 1319, 1286, 1175, 1151, 1104, 1008, 912, 864, 839, 759,
129.2, 130.0, 130.4, 136.0, 138.9, 146.3, 146.8, 147.7, 157.0; HRMS:
calcd for C42H27IN5 [MþH]þ 728.1311; found 728.1313.
4.1.8. N,N0-Bis-[4-(6-methoxypyridazin-3-yl)ethynylphenyl]-4-
iodoaniline (8). According to the procedure described for 1, a mix-
ture 3-methoxy-6-(trimethylsilyl)ethynylpyridazine (0.097 g,
0.470 mmol), tris-(4-iodophenyl)amine (0.136 g, 0.219 mmol), and
TBAF (1 M in THF, 0.94 mL) gave after purification by column
chromatography on silica gel (petroleum ether/ethyl acetate¼1:2)
compound 8 as a yellow solid (0.040 g, 29%). Mp: 64 ꢀC. IR (cmꢁ1
,
725, 656; 1H NMR (300 MHz, CDCl3)
d (ppm): 0.25 (s, 9H), 4.17 (s,
neat): 2942, 2217, 1719, 1596, 1542, 1505, 1483, 1460, 1409, 1339,
1317, 1286, 1178, 1153, 1100, 1061, 1006, 909, 835, 722, 638, 537, 512;
6H), 6.95 (d, J¼9 Hz, 2H), 7.06 (d, J¼8.7 Hz, 2H), 7.07 (d, J¼8.7 Hz,
4H), 7.40 (d, J¼8.7 Hz, 2H), 7.50 (d, J¼8.4 Hz, 2H), 7.60 (d, J¼8.7 Hz,
1H NMR (300 MHz, CDCl3)
d
(ppm): 4.17 (s, 6H), 6.89 (d, J¼8.9 Hz,
4H); 13C NMR (75 MHz, CDCl3)
d (ppm): 0.0, 55.0, 85.7, 92.1, 94.3,
104.7, 116.4, 116.6, 118.5, 123.7, 124.4, 132.2, 133.3, 143.7, 146.4, 147.3,
163.3.
2H), 6.95 (d, J¼9.0 Hz, 2H), 7.06 (d, J¼8.7 Hz, 4H), 7.48 (d, J¼8.7 Hz,
4H), 7.50 (d, J¼9.2 Hz, 2H), 7.60 (d, J¼8.7 Hz, 2H); 13C NMR (75 MHz,
CDCl3)
d
(ppm): 55.2, 85.8, 87.9, 92.2,116.5, 116.7, 123.6,127.4, 132.4,
Second step: To a solution of the compound described above
(0.170 g, 0.280 mmol) in THF (10 mL) cooled at 0 ꢀC, TBAF (1 M in
THF, 0.56 mL) was added dropwise. The reaction mixture was
stirred for 10 min at 0 ꢀC and for 3 h at room temperature. Then
water (10 mL) was introduced, and the crude mixture was extracted
with dichloromethane (2ꢃ15 mL). The organic layer was dried with
MgSO4, filtered and evaporated. The crude product was purified by
column chromatography on silica gel (petroleum ether/ethyl
acetate¼2:1) to afford the title compound 12 as a brown solid
(0.120 g, 80%). Mp: 146 ꢀC. IR (cmꢁ1, neat): 2922, 2850, 2355, 2218,
133.4, 138.8, 143.9, 146.4, 147.5, 163.5; HRMS: calcd for C32H23IN5O2
[MþH]þ 636.0897; found 636.0878.
4.1.9. Tris-[4-(2-trimethylsilylethynyl)phenyl]amine (9). See Ref. 24.
4.1.10. Tris-[4-{2-(4,6-dimethylpyrimidin-2-yl}ethynylphenyl)]amine
(10). To a solution of compound 9 (1 g, 1.873 mmol), 2-iodo-4,6-
dimethylpyrimidine (1.534 g, 6.550 mmol), Pd(PPh3)4 (0.211 g,
0.187 mmol) and CuI (0.035 g, 0.187 mmol) in 30 mL of a mixture of

F.-A. Martin et al. / Tetrahedron 70 (2014) 2546e2555
2553
2095,1596,1539,1504,1461,1410,1339,1318,1288,1173,1152,1106,
1008, 833, 726; 1H NMR (300 MHz, CDCl3)
(ppm): 3.08 (s, 1H), 4.17
165.0; C36H49IN4 (664.30): calcd. C 65.05, H 7.43, N 8.43; found C
64.97, H 7.58, N 8.86.
d
(s, 6H), 6.95 (d, J¼9.0 Hz, 2H), 7.06 (d, J¼8.7 Hz, 2H), 7.08 (d,
J¼8.4 Hz, 4H), 7.42 (d, J¼8.4 Hz, 2H), 7.48e7.51 (6H); 13C NMR
4.1.16. (E,E)-4,6-Bis-(4-methoxystyryl)-2-iodopyrimidine
(16). According to the procedure described for 15, using 4-
methoxybenzaldehyde (0.255 g, 1.878 mmol) gave after purifica-
tion by column chromatography on silica gel (petroleum ether/
ethyl acetate¼3:1) the title compound 16 as a yellow solid (0.147 g,
37%). Mp: 168 ꢀC. IR (cmꢁ1, neat): 2930, 2835, 1626, 1603, 1600,
1544, 1477, 1422, 1376, 1303, 1249, 1218, 1175, 1154, 1109, 1027, 969,
(75 MHz, CDCl3)
d (ppm): 55.1, 83.3, 85.7, 92.0, 116.5, 116.6, 117.4,
123.8, 124.4, 132.3, 133.3, 133.5, 143.7, 146.7, 147.3, 163.3; HRMS:
calcd for C34H24N5O2 [MþH]þ 534.1930; found 534.1926.
4.1.13. Bis-{[N,N-bis-[4-{2-(6-methoxypyridazin-3-yl)ethynyl}phe-
nyl]-N-(4-ethynylphenyl)} (13). In a 25 mL two necked round bot-
tom flask tris(4-iodophenyl)amine 4 (0.040 g, 0.064 mmol),
compound 12 (0.120 g, 0.224 mmol, 3.5 equiv), Pd(PPh3)2Cl2
(0.004 g, 0.005 mmol, 9%), CuI (0.002 g, 0.011 mmol, 18%), dry
toluene (8 mL), and dry Et3N (8 mL) were added and the mixture
was heated at 60 ꢀC for 48 h. The reaction mixture was cooled,
filtered through CeliteÒ and evaporated under reduced pressure.
The crude product was purified by column chromatography on
silica gel (petroleum ether/ethyl acetate 1.5:1, first purification;
petroleum ether/ethyl acetate 1:1, second purification) to afford the
title compound as dark yellow solid (0.029 g, 43%). Mp>260 ꢀC. IR
(cmꢁ1, neat): 2213, 1593, 1541, 1500, 1460, 1408, 1335, 1317, 1287,
891, 822, 769, 595, 537, 521; 1H NMR (300 MHz, CDCl3)
d (ppm):
3.85 (s, 6H), 6.80 (d, J¼15.8 Hz, 2H), 6.93 (d, J¼8.7 Hz, 4H), 7.15 (s,
1H), 7.55 (d, J¼8.7 Hz, 4H), 7.82 (d, J¼15.8 Hz, 2H); 13C NMR
(75 MHz, CDCl3) d (ppm): 55.5,114.5,114.7, 122.3,128.2,129.5, 138.1,
161.0, 164.8; HRMS: calcd for C22H20IN2O2 [MþH]þ 471.0570; found
471.0569.
4.1.17. (E,E)-4,6-Bis-(4-dimethylaminostyryl)-2-ethynylpyrimidine
(17). First step: In a two necked round bottom flask, compound 14
(0.200 g, 0.403 mmol), PPh3 (0.012 g, 0.048 mmol), CuI (0.004 g,
0.024 mmol), Pd(PPh3)2Cl2 (0.016 g, 0.024 mmol) were dissolved in
dry THF (6.25 mL) under nitrogen atmosphere. Trimethylsilylace-
tylene (0.11 mL, 0.806 mmol) followed by dry Et3N (10 mL) were
introduced via syringe. The resulting mixture was heated at 50 ꢀC
for 48 h and then filtered through CeliteÒ and evaporated under
reduced pressure. The crude product was purified by column
chromatography on silica gel (petroleum ether/ethyl acetate¼2:1)
to give the title product as a brown solid (0.170 g, 90%). Mp>260 ꢀC.
IR (cmꢁ1, neat): 1605, 1557, 1525, 1430, 1432, 1354, 1326, 1282, 1249,
1220, 1184, 1160, 1061, 1015, 979, 946, 845, 808, 758, 670, 520; 1H
1171, 1152, 1100,1006, 832, 725; 1H NMR (300 MHz, CDCl3)
d (ppm):
4.17 (s, 12H), 6.95 (d, J¼9 Hz, 4H), 7.06 (d, J¼8.7 Hz, 4H), 7.10 (d,
J¼8.7 Hz, 8H), 7.44 (d, J¼8.7 Hz, 4H), 7.50 (d, J¼9.3 Hz, 4H), 7.52 (d,
J¼8.7 Hz, 8H); 13C NMR (75 MHz, CDCl3)
d (ppm): 55.2, 74.3, 81.8,
86.0, 92.1, 116.7, 117.0, 124.1, 124.3, 132.4, 133.5, 134.0, 143.9, 147.3,
163.5; HRMS: calcd for C68H45N10O4 [MþH]þ 1065.3625; found
1065.3610.
4.1.14. (E,E)-4,6-Bis-(4-dimethylaminostyryl)-2-iodopyrimidine
(14). At room temperature, t-BuOK (0.479 g, 4.27 mmol) was
placed into a dry mortar and milled to very small, then 2-iodo-4,6-
dimethylpyrimidine (0.200 g, 0.854 mmol) and 4-dimethyl-ami-
nobenzaldehyde (0.438 g, 1.878 mmol) were added and mixed. The
mixture was milled vigorously for about 2 h. The mixture became
sticky and then continuously milled for 10 min. After completion
(monitored by TLC), the mixture was dispersed in 20 mL methanol.
The residual solid was filtered and recrystallized from anhydrous
dichloromethane/methanol (10:1) to afford the title compound 14
as a brown solid (0.240 g, 57%). Mp: 153 ꢀC. IR (cmꢁ1, neat): 2896,
2806, 2362, 1602, 1550, 1456, 1442, 1432, 1411, 1364, 1300, 1277,
1250, 1233, 1207, 1188, 1145, 1062, 971, 946, 891, 839, 809, 737, 668,
NMR (300 MHz, CDCl3)
d (ppm): 0.32 (s, 9H), 3.03 (s, 12H), 6.71 (d,
J¼8.7 Hz, 4H), 6.85 (d, J¼15.9 Hz, 2H), 7.16 (s, 1H), 7.50 (d, J¼8.7 Hz,
4H), 7.80 (d, J¼16.1 Hz, 2H); 13C NMR (75 MHz, CDCl3)
d (ppm):
ꢁ0.1, 40.3, 91.8, 103.7, 113.3, 120.8, 123.8, 137.8, 151.3, 152.2, 163.6;
MS (ESI); m/z (rel int. %): (Mþ) 467 (100), 391 (30), 247 (28), 178
(18), 157 (40).
Second step: To a solution of the compound described above
(0.150 g, 0.321 mmol) in THF (10 mL) cooled at 0 ꢀC, TBAF (1 M in
THF, 0.64 mL) was added dropwise. The reaction mixture was
stirred for 10 min at 0 ꢀC and for 3 h at room temperature. Then
water (10 mL) was introduced, and the crude mixture was extracted
with dichloromethane (2ꢃ15 mL). The organic layer was dried with
MgSO4, filtered and evaporated. The crude product was purified by
column chromatography on silica gel (petroleum ether/ethyl
acetate¼2:1) to afford the title compound 17 as a brown solid
(0.114 g, 90%). Mp: 212 ꢀC. IR (cmꢁ1, neat): 2104, 1603, 1553, 1483,
1431, 1360, 1297, 1229, 1183, 1147, 1061, 970, 945, 883, 835, 807, 724,
598, 520; 1H NMR (300 MHz, CDCl3)
d (ppm): 3.9 (s, 12H), 6.78 (d,
J¼15.6 Hz, 2H), 6.88 (d, J¼8.9 Hz, 4H), 7.13 (s, 1H), 7.52 (d, J¼8.9 Hz,
4H), 7.78 (d, J¼15.6 Hz, 2H); 13C NMR (75 MHz, CDCl3)
d (ppm):
40.3, 112.0, 113.7, 119.8, 123.4, 129.5, 130.8, 138.5, 151.3, 165.0;
HRMS: calcd for C24H26N4I [MþH]þ 497.1202; found 497.1183.
671, 639; 1H NMR (300 MHz, CDCl3)
d (ppm): 3.03 (s, 12H), 3.07 (s,
4.1.15. (E,E)-4,6-Bis-(4-n-dibutylaminostyryl)-2-iodopyrimidine
(15). At room temperature, t-BuOK (0.479 g, 4.27 mmol) was
placed into a dry mortar and milled to very small, then 2-iodo-4,6-
dimethylpyrimidine (0.200 g, 0.854 mmol) and 4-n-dibutyl-ami-
nobenzaldehyde (0.438 g, 1.878 mmol) were added and mixed. The
mixture was milled vigorously for about 2 h. The mixture became
sticky and then continuously milled for 10 min. After completion
(monitored by TLC), the mixture was dispersed in 20 mL methanol.
The residual solid was filtered and purified by column chroma-
tography on silica gel (petroleum ether/ethyl acetate¼7:1) to afford
the title compound 15 as a brown solid (0.210 g, 37%). Mp: 50 ꢀC. IR
(cmꢁ1, neat): 2955, 2942, 2868, 2360, 1601, 1551, 1520, 1466, 1431,
1401, 1366, 1276, 1223, 1205, 1181, 1144, 969, 925, 890, 838, 806,
1H), 6.71 (d, J¼8.7 Hz, 4H), 6.84 (d, J¼15.9 Hz, 2H), 7.14 (s, 1H), 7.51
(d, J¼8.7 Hz, 4H), 7.84 (d, J¼15.9 Hz, 2H); 13C NMR (75 MHz, CDCl3)
d
(ppm): 40.3, 73.8, 83.1, 112.1, 114.0, 120.6, 123.8, 129.4, 137.9, 151.3,
151.8, 163.7; MS (ESI); m/z (rel int. %): (MþþH) 395 (100), 316 (10),
264 (24), 196 (6).
4.1.18. (E,E)-4,6-Bis-(4-n-dibutylaminostyryl)-2-ethynylpyrimidine
(18). First step: According to the procedure described for 17, com-
pound 15 (0.200 g, 0.277 mmol), PPh3 (0.008 g, 0.033 mmol), CuI
(0.003 g, 0.016 mmol), Pd(PPh3)2Cl2 (0.011 g, 0.016 mmol) dry THF
(6.25 mL), and trimethylsilylacetylene (0.07 mL, 0.554 mmol) gave
after purification by column chromatography on silica gel (petro-
leum ether/ethyl acetate¼9:1) the title product as a dark green
solid (0.150 g, 86%). Mp<50 ꢀC. IR (cmꢁ1, neat): 3038, 2956, 2932,
2872, 1603, 1560, 1521, 1492, 1460, 1431, 1400, 1353, 1292, 1250,
1222, 1183, 1145, 1110, 1018, 976, 926, 844, 807, 759, 700, 671, 533;
535; 1H NMR (300 MHz, CDCl3)
d
(ppm): 0.97 (t, J¼7.3 Hz, 12H),
1.31e1.43 (m, 8H), 1.57e1.62 (m, 8H), 3.31 (t, J¼7.6 Hz, 8H), 6.62 (d,
J¼8.9 Hz, 4H), 6.67 (d, J¼15.8 Hz, 2H), 7.08 (s, 1H), 7.45 (d, J¼8.9 Hz,
4H), 7.73 (d, J¼15.8 Hz, 2H); 13C NMR (75 MHz, CDCl3)
d
(ppm): 14.1,
1H NMR (300 MHz, CDCl3)
12H), 1.38e1.35 (m, 4H), 1.59e1.56 (m, 4H), 3.31 (t, J¼7.4 Hz, 4H),
d
(ppm): 0.32 (s, 9H), 0.97 (t, J¼7.4 Hz,
20.4, 29.5, 50.8, 111.4, 113.5, 119.1, 122.4, 129.7, 130.8, 138.5, 149.3,

2554
F.-A. Martin et al. / Tetrahedron 70 (2014) 2546e2555
6.62 (d, J¼8.6 Hz, 4H), 6.81 (d, J¼16 Hz, 2H), 7.14 (s, 1H), 7.46 (d,
J¼8.7 Hz, 4H), 7.78 (d, J¼15.8 Hz, 2H); 13C NMR (75 MHz, CDCl3)
6.86 (d, J¼8.7 Hz, 4H), 6.87 (d, J¼15.8 Hz, 2H), 7.00 (d, J¼8.5 Hz, 2H),
7.16 (s,1H), 7.52 (d, J¼8.7 Hz, 4H), 7.56e7.59 (6H), 7.83 (d, J¼15.8 Hz,
d
(ppm): ꢁ0.1, 14.1, 20.4, 29.6, 50.9, 91.6, 103.7, 111.5, 113.1, 120.2,
2H); 13C NMR (75 MHz, CDCl3)
d (ppm): 40.4, 86.2, 87.3, 89.2, 112.2,
122.8, 129.5, 137.8, 149.2, 152.2, 163.7; MS (ESI); m/z (rel int. %):
112.9,116.0, 121.0, 122.6,123.9,126.9,129.3,134.1, 137.7, 138.7, 146.5,
147.6, 151.3, 153.1, 163.7; HRMS: calcd for C44H38I2N5 [MþH]þ
890.1217; found 890.1224.
(Mþ) 635 (100).
Second step: According to the procedure described for 17,
deprotection of the silylated compound reported above (0.150 g,
0.236 mmol) is achieved with TBAF (1 M in THF, 0.46 mL) and gave
after purification by column chromatography on silica gel (petro-
leum ether/ethyl acetate¼7:1) the title compound 18 as a dark
green solid (0.128 g, 97%). Mp: 55 ꢀC. IR (cmꢁ1, neat): 3038, 2956,
2932, 2872, 1603, 1560, 1521, 1492, 1460, 1431, 1400, 1353, 1292,
1250, 1222, 1183, 1145, 1110, 1018, 976, 926, 844, 807, 759, 700, 671,
4.1.21. N,N-Bis-(4-iodophenyl)-4-[4-bis-(E,E)-{4,6-(dibutylaminos-
tyryl)pyrimidin-2-yl}ethynyl]aniline (21). A solution of tris-(4-
iodophenyl)amine 4 (0.110 g, 0.177 mmol), compound 18 (0.350 g,
0.621 mmol), PdCl2(PPh3)2 (0.011 g, 0.016 mmol), CuI (0.006 g,
0.032 mmol) in a mixture of dry THF (15 mL) and Et3N (5 mL) was
stirred at 60 ꢀC for 72 h under nitrogen atmosphere. The TLC
monitoring indicated no significant evolution of the reaction. The
reaction mixture was cooled, filtered through CeliteÒ and evapo-
rated under reduced pressure. The crude product was purified by
column chromatography on silica gel (petroleum ether/ethyl
acetate¼6:1 was used for the first purification followed by a second
one with petroleum ether/ethyl acetate¼7:1) to give the title
compound 21 as a dark green solid (0.060 g, 32%). Mp: 63 ꢀC. IR
(cmꢁ1, neat): 3038, 2956, 2932, 2872, 1603, 1560, 1521, 1492, 1460,
1431, 1400, 1353, 1292, 1250, 1222, 1183, 1145, 1110, 1018, 976, 926,
533; 1H NMR (300 MHz, CDCl3)
d
(ppm): 0.97 (t, J¼7.3 Hz, 12H),
1.33e1.41 (m, 8H), 1.56e1.59 (m, 8H), 3.06 (s, 1H), 3.31 (t, J¼7.6 Hz,
8H), 6.62 (d, J¼8.7 Hz, 4H), 6.79 (d, J¼15.8 Hz, 2H), 7.12 (s, 1H), 7.46
(d, J¼8.8 Hz, 4H), 7.81 (d, J¼15.9 Hz, 2H); 13C NMR (75 MHz, CDCl3)
d
(ppm): 14.1, 20.4, 29.5, 50.8, 73.6, 83.1, 111.4, 113.8, 119.8, 122.7,
129.5, 137.8, 149.2, 151.6, 163.6; MS (ESI); m/z (rel int. %): (MþþH)
563 (100), 507 (50), 451 (20), 234 (2).
4.1.19. (E,E)-4,6-Bis-(4-methoxystyryl)-2-ethynylpyrimidine
(19). First step: According to the procedure described for 17, com-
pound 16 (0.200 g, 0.425 mmol), PPh3 (0.013 g, 0.051 mmol), CuI
(0.004 g, 0.025 mmol), Pd(PPh3)2Cl2 (0.017 g, 0.016 mmol) dry THF
(6.25 mL), and trimethylsilylacetylene (0.12 mL, 0.850 mmol,
2 equiv) gave after purification by column chromatography on silica
gel (petroleum ether/ethyl acetate 2:1) the title product as a yellow
solid (0.140 g, 77%). Mp: 98 ꢀC. IR (cmꢁ1, neat): 2956, 2835, 2357,
844, 807, 759, 700, 671, 533; 1H NMR (300 MHz, CDCl3)
d (ppm):
0.97 (t, J¼7.3 Hz, 12H), 1.33e1.41 (m, 8H), 1.56e1.59 (m, 8H), 3.31 (t,
J¼7.5 Hz, 8H), 6.63 (d, J¼8.9 Hz, 4H), 6.83 (d, J¼15.3 Hz, 2H), 6.87 (d,
J¼8.7 Hz, 4H), 7.00 (d, J¼8.9 Hz, 2H), 7.13 (s, 1H), 7.47 (d, J¼8.9 Hz,
4H), 7.58 (d, J¼8.7 Hz, 6H), 7.80 (d, J¼15.6 Hz, 2H); 13C NMR
(75 MHz, CDCl3)
d (ppm): 14.1, 20.4, 29.5, 50.8, 85.9, 89.1, 112.4,
112.6, 116.0, 121.0, 122.6, 129.1, 129.5, 134.1, 137.8, 138.7, 146.5, 147.8,
149.2, 153.1, 163.6; HRMS: calcd for C56H62I2N5 [MþH]þ 1058.3095;
found 1058.3124.
1629, 1604, 1563, 1511, 1463, 1422, 1349, 1303, 1250, 1172, 1153, 1111,
1
1030, 975, 845, 821, 759, 534; H NMR (300 MHz, CDCl3)
d (ppm):
0.33 (s, 9H), 3.85 (s, 6H), 6.96e6.90 (m, 6H), 7.20 (s, 1H), 7.56 (d,
J¼8.7 Hz, 4H), 7.86 (d, J¼16.2 Hz, 2H); 13C NMR (75 MHz, CDCl3)
4.1.22. Tris[4-(2-{4,6-bis[4-(dimethylamino)styryl]pyrimidin-2-yl}
ethynyl)phenyl]amine (22). A stirred solution of compound 11
(0.100 g, 0.157 mmol), 4-dimethylaminobenzaldehyde (0.211 g,
1.413 mmol), t-BuOK (0.158 g, 1.413 mmol) in THF (30 mL) was
heated at 60 ꢀC for 1 h under microwave. The reaction mixture was
cooled and evaporated under reduced pressure. Then H2O was
added, and the crude mixture was extracted with DCM (4ꢃ10 mL).
The organic layer was dried with MgSO4, filtered, and evaporated.
The crude product was purified by column chromatography on
silica gel (petroleum ether/ethyl acetate¼1:1 was used for the first
purification followed by a second one with ethyl acetate) to give the
title compound 22 as a brown solid (0.030 g, 14%). Mp: >260 ꢀC. IR
(cmꢁ1, neat): 2209, 1617, 1601, 1560, 1556, 1523, 1508, 1500, 1364,
1321, 1273, 1177, 1114, 975, 883, 814; 1H NMR (300 MHz, CDCl3)
d
(ppm): ꢁ0.2, 55.5, 92.5, 103.4, 114.1, 114.5, 123.3, 128.5, 137.4,
152.4, 160.9, 163.5; MS (ESI); m/z (rel int. %): (Mþ) 441 (100), 379
(12), 279 (18).
Second step: According to the procedure described for 17,
deprotection of the silylated compound reported above (0.150 g,
0.340 mmol) is achieved with TBAF (1 M in THF, 0.68 mL) and gave
after purification by column chromatography on silica gel (petro-
leum ether/ethyl acetate¼7:1) the title compound 19 as a yellow
solid (0.125 g, conversion 100%). Mp: 235 ꢀC. IR (cmꢁ1, neat): 3270,
2930, 2834, 2117, 1625, 1603, 1564, 1511, 1455, 1436, 1421, 1374,
1346, 1311, 1283, 1249,1174,1151, 1110,1027, 973, 891, 845, 826, 806,
773, 723, 673; 1H NMR (300 MHz, CDCl3)
d (ppm): 3.11 (s, 1H), 3.85
(s, 6H), 6.92 (d, J¼16.1 Hz, 2H), 6.93 (d, J¼8.7 Hz, 4H), 7.19 (s, 1H),
7.56 (d, J¼8.7 Hz, 4H), 7.89 (d, J¼16.1 Hz, 2H); 13C NMR (75 MHz,
d
(ppm): 3.03 (s, 36H), 6.72 (d, J¼9.2 Hz, 12H), 6.89 (d, J¼15.9 Hz,
CDCl3)
d
(ppm): 55.5, 74.4, 82.8, 114.5, 114.9, 123.0, 128.5, 129.4,
6H), 7.14 (d, J¼8.9 Hz, 6H), 7.16 (s, 3H), 7.53 (d, J¼8.9 Hz, 12H), 7.66
137.5, 151.8, 160.9, 163.5; MS (TOF MS ESIþ); m/z (rel int. %):
(d, J¼8.7 Hz, 6H), 7.85 (d, J¼16.1 Hz, 6H); 13C NMR (75 MHz, CDCl3)
(MþHþ) 369 (100).
d
(ppm): 40.4, 86.2, 89.3, 112.2, 112.3, 116.9, 121.0, 124.0, 124.2,
129.4, 134.2, 137.8, 147.5, 151.3, 153.2, 163.7.
4.1.20. N,N-Bis-(4-iodophenyl)-4-[4-bis-(E,E)-{4,6-(dimethylaminos-
tyryl)pyrimidin-2-yl}ethynyl]aniline (20). A solution of tris-(4-
iodophenyl)amine 4 (0.112 g, 0.181 mmol), compound 17 (0.250 g,
0.633 mmol), PdCl2(PPh3)2 (0.021 g, 0.030 mmol), CuI (0.005 g,
0.030 mmol) in a mixture of dry toluene (20 mL), and Et3N (5 mL)
was stirred at 40 ꢀC for 72 h under nitrogen atmosphere. The TLC
monitoring indicated no significant evolution of the reaction. The
reaction mixture was cooled, filtered through CeliteÒ and evapo-
rated under reduced pressure. The crude product was purified by
column chromatography on silica gel (petroleum ether/ethyl
acetate¼1.5:1) to give the title compound 20 as a brown solid
(0.030 g,19%). Mp: >260 ꢀC. IR (cmꢁ1, neat): 2918, 2798, 2364, 2210,
1718,1701,1685, 1676,1648,1604,1551,1483,1432,1357,1312,1285,
1263, 1179, 1148, 1056, 1003, 970, 946, 883, 810, 744, 720, 692; 1H
4.1.23. Tris[4-(2-{4,6-bis[4-(methoxy)styryl]pyrimidin-2-yl}ethynyl)
phenyl]amine (23). A stirred solution of compound 11 (0.100 g,
0.157 mmol), 4-methoxybenzaldehyde (0.192 g, 1.413 mmol), t-
BuOK (0.158 g, 1.413 mmol) in THF (30 mL) was heated at 60 ꢀC for
1 h under microwave. The reaction mixture was cooled and evap-
orated under reduced pressure. Then H2O was added, and the crude
mixture was extracted with DCM (4ꢃ10 mL). The organic layer was
dried with MgSO4, filtered, and evaporated. The crude product was
purified by column chromatography on silica gel (petroleum ether/
ethyl acetate¼1:4 was used for the first purification followed by
a second one with DCM to give the title compound 23 as a dark
yellow solid (0.060 g, 29%). Mp: 235 ꢀC. IR (cmꢁ1, neat): 2364, 2207,
1634,1603,1563,1554,1511,1504,1456,1422,1368,1317,1250,1172,
NMR (300 MHz, CDCl3)
d
(ppm): 3.03 (s,12H), 6.71 (d, J¼8.9 Hz, 4H),
1104, 1029, 968, 818, 763, 724; 1H NMR (300 MHz, CDCl3)
d (ppm):

F.-A. Martin et al. / Tetrahedron 70 (2014) 2546e2555
2555
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3.81 (s, 18H), 6.93 (d, J¼8.7 Hz, 12H), 6.96 (d, J¼16.2 Hz, 6H), 7.14 (d,
J¼8.7 Hz, 6H), 7.18 (s, 3H), 7.57 (d, J¼8.7 Hz, 12H), 7.66 (d, J¼8.7 Hz,
6H), 7.88 (d, J¼15.9 Hz, 6H); 13C NMR (75 MHz, CDCl3)
d (ppm):
55.4, 86.6, 89.2, 113.8, 114.4, 116.7, 123.4, 124.1, 128.6, 129.4, 134.2,
137.2, 147.5, 153.1, 160.8, 163.5.
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Acknowledgements
The authors thank Dr. Patrice Baldeck and Mr. Jean Bernard
ꢀ
(Universite Joseph Fourier, Grenoble, UMR 5588) for their collabo-
ration and the two-photon absorption cross-section measurements.
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