A facile route to bis(pyridyl-1,3,5-triazine) ligands with fluorescing properties

Article abstract of DOI:10.1002/ejoc.201403521

We present a general method for the preparation of bis(pyridyl-1,3,5-triazine) (dpt) ligands via Stille coupling chemistry. The synthetic procedure surpasses known trimerisation procedures in terms of yield, flexibility, and diversity, as ditopic ligands with different spacers are now available. Polythiophene spacers give rise to different colours by extending the conjugated system and increasing HOMO energy levels. The luminescence properties can be tuned by the spacers, the emission is found in the region from 300-550 nm with nanosecond lifetimes. Preliminary experiments indicate thermochromic properties for the dpt-Fe^II complexes.

Full text of DOI:10.1002/ejoc.201403521

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FULL PAPER
DOI: 10.1002/ejoc.201403521
A Facile Route to Bis(pyridyl-1,3,5-triazine) Ligands with Fluorescing
Properties
Matthias F. Geist,[a] Daniel Chartrand,[b] Mihaela Cibian,[b] Fabian Zieschang,[c]
Garry S. Hanan,*[b] and Dirk G. Kurth*[a,d]
Keywords: Supramolecular chemistry / Synthetic methods / Cross-coupling / N ligands / Luminescence
We present a general method for the preparation of bis(pyr-
idyl-1,3,5-triazine) (dpt) ligands via Stille coupling chemistry.
conjugated system and increasing HOMO energy levels. The
luminescence properties can be tuned by the spacers, the
The synthetic procedure surpasses known trimerisation pro- emission is found in the region from 300–550 nm with nano-
cedures in terms of yield, flexibility, and diversity, as ditopic
ligands with different spacers are now available. Polythio-
phene spacers give rise to different colours by extending the
second lifetimes. Preliminary experiments indicate thermo-
chromic properties for the dpt-FeII complexes.
mentioned photophysical properties[4] dpt-based complexes
also show thermochromic properties[5] and can be used as
hosts for assorted molecules.[6] Ligands with two dpt units
are promising candidates for photoactive coordination
polymers[7] or metal–organic frameworks.[8] Metallo-poly-
mers based on the analogous ditopic tpy are well-known
for their tunable and stimuli-responsive properties.[9]
In contrast to expectation based on their many potential
uses, only a few ditopic dpt molecules are known in the
literature.[10] The synthesis is based on the trimerisation re-
action of the central ring and generally affords low yields
of only about 10%. For example, dpt-phenyl-dpt is pre-
pared by reaction of 2-cyanopyridine and 1,4-dicyanobenz-
ene resulting in a product yield of 16%.[10a] These low yields
limit full characterization and exploitation of material
properties (e.g. rheological measurements); larger amounts
of material are clearly needed for the potential of these spe-
cies to be realized. The low synthetic flexibility hinders the
preparation of a wide range of related structures, which are
necessary to investigate structure–property relationships.
For these reasons we established an improved synthetic
route to ditopic dpt ligands. This route should be both
highly adaptable and effective. In this report we focus on
the incorporation of oligothiophenes into the dpt frame-
work inspired by their remarkable fluorescence proper-
ties.[11,12]
Introduction
2,2Ј:6Ј,2ЈЈ-Terpyridine (tpy) and related metallo-supra-
molecular assemblies have attracted remarkable interest
over the last 20 years. In fact, tpy is now one of the most
important motifs in metallo-supramolecular chemistry.[1]
Although tpy binds many transition metal ions, ruthenium
tpy complexes have attracted considerable attention due to
their photophysical properties.[2] These properties are al-
tered by exchanging the central pyridine in tpy with 1,3,5-
triazine (trz).[3] For example, the ruthenium complex of the
ligand 2,4-(dipyridyl-2Ј-yl)-6-phenyl-1,3,5-triazine (Ph-dpt)
possesses a longer metal-to-ligand charge transfer (MLCT)
luminescence lifetime than in Ru-tpy complexes. The ad-
ditional nitrogen atoms in trz are co-planar with the 6-
phenyl group, which increases the electronic delocalization.
As a result, the energy difference between the emitting
3MLCT state and the deactivating triplet metal-centered
state (3MC) is increased, thus lowering Franck–Condon
factors and improving emission properties. As a second
positive effect, the π-accepting nature of the trz ligand fur-
3
ther reduces the energy of the MLCT state and the energy
gap ΔE between the MLCT and MC states. Besides the
3
3
[a] Chemical Technology of Advanced Materials, Julius-
Maximilians University Würzburg,
Röntgenring 11, 97070 Würzburg, Germany
E-mail: dirk.kurth@matsyn.uni-wuerzburg.de
http://www.matsyn.uni-wuerzburg.de
[b] Department of Chemistry, Université de Montréal,
2900 Edouard Mont-Petit, H3T-1J4, Montréal, Canada
http://www.greenenergygroup.ca
Results and Discussion
[c] Institut für Organische Chemie and Center for Nanosystems
Chemistry, Julius-Maximilians University Würzburg,
Am Hubland, 97074 Würzburg, Germany
The known syntheses featuring the 2,4-di(pyridin-2-yl)-
1,3,5-triazine (dpt) motif are usually based on trimerisation
of nitriles.[13] For example, three equivalents of 2-cyanopyr-
idine react under ring closure conditions to afford 2,4,6-
tri(pyridin-2-yl)-1,3,5-triazine.[14] This approach is conve-
[d] Fraunhofer-Institut für Silicatforschung ISC,
Neunerplatz 1, 97082 Würzburg, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201403521.
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FULL PAPER
nient for monotopic ligands, but has several drawbacks for forms a bond to the dpt pincer as well as to the oxygen
ditopic molecules; drawbacks include low yields and diffi- atom. Notably, this structure had already been reported by
culty in attaining non-D3-symmetric molecules. We per- Cao et al.[17] In contrast to the Cao procedure, which in-
formed a retrosynthetic analysis of 1ЈЈ,4ЈЈ-bis[2,4-di(pyr- volves precipitation with NaCl, our results indicate that the
idin-2-yl)-1,3,5-triazine-6-yl]benzene (dpt-Ph-dpt) as a ref- NaO-dpt linkage is formed during the synthesis from urea,
erence molecule. To improve the variability of ditopic li- 2-cyanopyridine and sodium hydride. Our examination
gands as well as the reaction yield, we chose to employ a suggests that NaO-dpt forms a type of aggregate in solu-
cross-coupling reaction as the last step, which is compatible tion. Indeed, NMR experiments revealed a concentration
with the electron poor triazine ring. The coupling takes dependence of the proton signals. Figure 1 shows the con-
1
place between a bis-metal–organic spacer reagent and 6- centration-dependent H NMR spectra of NaO-dpt from
chloro-dpt, which is available through a nucleophilic substi- 0.18–0.001 m. Higher concentrations resulted in salt precipi-
tution of HO-dpt. This approach can be easily applied to tation. Signal H3Ј was found to be shifted upon increasing
different ligands with different spacers as a large number concentrations to lower field, whereas H6Ј was shifted to
of metal–organic reagents are commercially available. This higher field. These concentration-dependent shifts can be
approach is favored over the synthesis of tin- or boron tri- explained by inter- and intramolecular interactions.[18]
A
azines since these species are considered too unstable.[15] downfield shift is related to the formation of hydrogen
Here, we focus on two main aspects: i) the angle between bonds.[19]
the two dpt receptors, and ii) the incorporation of conju-
gated systems. Furthermore, we synthesize precursors and
reference molecules based on the dpt motif.
The entire synthetic pathway is shown in Scheme 1. In
the first step, 4,6-bis(pyridin-2-yl)-1,3,5-triazine-2-ol (HO-
dpt) is obtained as its sodium salt, 4,6-di(pyridin-2-yl)-
1,3,5-triazine-2-olate (NaO-dpt) 1a in 60% yield by the re-
action of urea and 2-cyanopyridine.[16] Intermediate 1a is
converted to 2-chloro-4,6-di(pyridin-2-yl)-1,3,5-triazine (Cl-
dpt) 2 and subsequent coupling with the stannyl reagents
gives desired products 3–11 (see Scheme 3). The NaO-dpt
salt is characterized by NMR spectroscopy and ESI-MS
1
(positive mode). H NMR is in accordance with previously
reported spectra.[16]
Figure 1. Top: NaO-dpt and assignment of protons. Bottom: Con-
1
centration-dependent H NMR spectra of NaO-dpt in [D6]DMSO
from 0.18 m to 0.001 m at 20 °C.
Most likely, proton H3Ј forms a bond with one of the
nitrogen atoms (N3 or N5) in the triazine ring at high con-
centrations. A shift to a higher field results from evolving
π–π interactions and the increased shielding as discussed
above (see Figure 1).[20] Although concentration-dependent
1H NMR spectra of triazine derivatives are presented in the
literature,[3a] no explanations are given. During crystalli-
zation experiments we discovered the hydrolytic instability
of the NaO-dpt species. Over several months N,NЈ-carbon-
yldipicolinamide 1b is formed via hydrolysis in chloroform/
methanol, probably catalyzed by trace amounts of chloro-
form-derived HCl (see Scheme 2). We confirmed the
identity of product 1b by NMR spectroscopy and X-ray
crystallography (Supporting Information, Figure S18). Al-
though it is mentioned in the literature, there is currently
Scheme 1. Synthetic pathway for dpt-based ligands.
no reported analytical data for 1b.[21]
The decomposition temperature of 1a determined with
After the preparation of NaO-dpt, we proceeded with
differential scanning calorimetry is 410 °C, which is excep- the chlorination. Initial chlorination experiments featured
tionally high. This finding led us to consequently examine thionyl chloride as the chlorinating agent and the pyridine
the solid-state structure of 1a. X-ray crystallography con- unit in dpt as an intramolecular trapping agent for the HCl
firmed the corresponding sodium salt NaO-dpt. The struc- resulting from chlorination. Cl-dpt could be deprotonated
ture represents a one-dimensional coordination polymer using the sterically hindered Hünig’s base, followed by neu-
(Supporting Information, Figures S16 and S17). Sodium tral buffers during work-up. This reaction proceeded in a
2
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A Facile Route to Fluorescent Bis(pyridyl-1,3,5-triazine) Ligands
Scheme 2. Degradation of 1a to N,NЈ-carbonyldipicolinamide 1b.
1
yield of 72%; the product was fully characterized by H-
1
and 13C-NMR spectroscopy as well as by ESI-MS. The H
NMR spectrum revealed the pyridine pattern of Cl-dpt,
whereas 13C displayed a significant shift of C6 in the tri-
azine ring due to the chloro group (see Supporting Infor-
mation/Experimental). ESI-MS further validates the
suggested structure with a distinctive chlorine isotope
pattern at 270.11 and 272.11 m/z. Due to the lability of Cl-
dpt in basic conditions typically employed for Suzuki-cou-
pling reactions,[22] the Stille coupling was performed under
neutral conditions.[23] With this synthetic procedure in
hand, we were able to prepare the following dpt-based li-
gands (see Scheme 3). Whereas the yields of the coupling
step are moderate to good, the overall yields range from 13
to 23%. The only known synthesis of 7 using a trimeri-
sation reaction results in a yield of 16% whereas the pre-
sented method gives a slightly better overall yield of 20%.
As shown in Scheme 3, our method is versatile in terms
of the variability of the central bridge. Furthermore, we
were able to incorporate thiophene rings into the dpt system
(3a, 8–11). Analogous terpyridine systems are known for
their photophysical properties.[18] To increase the number
of thiophene rings in the bridge, we expanded our method-
ology to the molecules shown in Scheme 4. For example, 2-
thiophenyl-4,6-di(pyridin-2-yl)-1,3,5-triazine (Th-dpt) 3a is
brominated in the 5ЈЈ position with N-bromosuccinimide
(NBS). Acetic acid was used as solvent to control the re-
gioselectivity.[24] The resulting product 3b is coupled with
the corresponding stannyl reagent. In this way, we prepared
dpt-trithiophene-dpt 10 and dpt-quaterthiophene-dpt 11,
having three or four thiophene rings as spacer units, respec-
tively. A useful feature of our synthetic pathway proved to
be the simple work-up. Monotopic ligands 3–5 are simply
Scheme 3. Overview of new dpt ligands assembled via Stille cou-
pling chemistry.
extracted from the reaction mixture and washed with The triazine related carbon peaks are observed at high fre-
toluene, hexane and Et2O; no further purification is quencies around 170 ppm, whereas the spacer and pyridine
necessary. Workup proved to be even easier with ditopic units occur between δ = 120 and 150 ppm. ESI-MS con-
ligands 6–11. Due to the second dpt pincer ligand, these firms the structure of 1–11. Molecules 1–11 display the
molecules have an increased tendency to π stack which distinctive triazine vibrational modes near 1300 and
diminishes solubility[25] and enables facile precipitation 1500 cm–1.[26]
from the hot reaction solutions. After washing with toluene,
hexane and Et2O, such ditopic compounds were found to 11 have a distinctive color. Monodentate th-dpt (3a) is off-
be analytically pure. white, whereas 8 is greenish white, 9 is yellow and 10 and
In contrast to 4–7, the thiophene containing ligands 8–
All new compounds were fully characterized with dif- 11 are dark red. This redshift is apparent in UV/Vis spectra
ferent NMR techniques, FT-IR and ESI-MS (for details see recorded in DCM solution as seen in Figure 2. The thio-
Supporting Information). The proton shifts are listed in phene related peak is shifted from 309 nm (3a) to 463 nm
Table S1. The distinctive pyridine pattern (H3Ј–H6Ј) was ob- (11) depending on the number of thiophene rings.
served in all of the molecules. Depending on electron den-
For an examination of the HOMO–LUMO gap we per-
sity of the spacer, the corresponding protons are shifted to formed TD-DFT calculations (for details see Supporting
higher (thiophene and furanyl derivatives) or lower fields Information Figures S19–S36). Ligands 3a, 8, 9, 10 and 11
(e.g. H3ЈЈЈ in 6). The 13C spectra show similar characteristics. are modelled with pyridine groups pointing inward (Sup-
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G. S. Hanan, D. G. Kurth et al.
FULL PAPER
it is relatively independent of the triazine (8 vs. 3a) (see
Figure 3). The LUMO shows the reverse trend; major con-
tribution is made by both triazine groups and increases only
slightly with the addition of thiophene units. However, the
removal of a triazine moiety pushes the MO to a higher
energy leading to its transition into LUMO+1. These two
effects contribute to a smaller energy gap with each added
thiophene and triazine. The calculated transition follows
closely the experimental data, with a greater redshift for
the larger molecules due to an exaggeration of the
extended delocalization in the modelled system.
Scheme 4. Synthetic pathway for dpt-trithiophene-dpt 10.
Figure 3. Calculated frontier MO energies of ligands 3 and 8–11
obtained from DFT PBE1PBE/6-311G(d,p) with CPCM(CH2Cl2).
As seen in Figures 4 and 5, dpt-based polythiophenes
show distinctive fluorescence. As expected, the expansion
of the π-system results in a redshifted emission. As is
evident in Figure 4 tunable emission colours are available.
Figure 2. Absorption spectra of 3a and 8–11 in DCM at 25 °C
with calculated oscillator strength from TD-DFT as symbols of
matching colour.
porting Information, Figure S19). This orientation is not
always observed in the solid state and to evaluate the im-
portance of this, the ten possible conformers of ligand 8 are
also modelled. The results show that the orientation has
little effect on both the calculated transition energies (varia-
tion of 2 nm) and the total energy of the molecules, which
is smaller than 2 kcal/mol (Supporting Information, Fig-
ures S20 and S21). The two absorption bands in the UV
region (245 and 280 nm), which are present in all examined
samples, are related to the π-π* and n-π* transitions in-
herent to dpt.[5a] The calculated spectra show absorptions
near 230 and 270 nm. The TD-DFT calculations of the
thiophene-containing ligands display the same batho-
chromic shift of the thiophene related band observed in the
measured spectra. This transition is attributed to the thio-
phene conjugated π-system. For 8–11 these transitions
correspond to the HOMO to LUMO transitions in the
molecule. The HOMO has a major contribution of density
coming from the thiophene backbone and showed an in-
Figure 4. Compounds 9–11 in DCM showed under UV light a dis-
tinctive fluorescence.
Figure 5. Fluorescence spectra of 8–11. Spectra were recorded at
25 °C in deaerated DCM. The excitation wavelength is 410 nm for
crease in energy with each thiophene unit added, although 9–11 and 350 nm for 8. All spectra were normalized.
4
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A Facile Route to Fluorescent Bis(pyridyl-1,3,5-triazine) Ligands
The influence of the dpt unit could be estimated by com-
parisons with neat oligothiophenes (see Table 1). The dpt
unit shifts the absorbance as well as the fluorescence to
higher wave numbers.[27] Garcia reported for 2,2Ј-bithio-
phene an absorption at 302 nm and an emission at
361 nm.[27a] The corresponding ditopic dpt ligand 9 was
found to be shifted to 411 nm (absorption) and 460 nm
(emission). The same trend was observed for 10 and 11 and
the corresponding polythiophenes. The bathochromic shifts
show clearly the influence of the electronegative dpt pincers
on the luminescence properties of oligothiophenes. Further-
more, the quantum yield is clearly boosted by the dpt units.
Compound 9 possesses a very high quantum yield Φ in rela-
tive to bithiophene. The fluorescing molecules possess
quantum yields of 60% (9), 9% (10) and 11.7% (11). The
lower quantum yields of 10 and 11 are most likely caused
by π-π stacking interactions at play in solution. In fact, ESI-
MS of 10 revealed the presence of a dimer, whereas 9 does
not show any type of aggregation in the gas phase as exam-
ined by mass spectrometry. Such π-π interactions in ex-
tended π-conjugated systems are associated with an effect
called aggregation-caused quenching (ACQ), which is also
responsible for weak or non-emissive luminescence proper-
ties in solid state.[28]
Conclusions
In this report we describe a versatile methodology by
which to synthesize several new bis-pyridyl-1,3,5-triazine li-
gands. The newly synthesized Cl-dpt, 2, is the central build-
ing block for further derivatization by organotin reagents
via Stille coupling chemistry. We prepared mono- and
ditopic ligands with moderate to good yields, with workup
generally being straight forward. The introduction of thio-
phene spacers of different lengths leads to tunable absorp-
tion and emission properties. The chelating motive of these
ligands, similar to the well-known terpyridines, makes them
potential tectons for metallo-supramolecular architectures.
Since the bite angle of DPT is larger than that of TPY, it is
expected that the ligand field stabilizing energy is lower
giving rise to interesting material properties of the resulting
metallo-supramolecular assemblies.[29]
Experimental Section
Materials and Instrumentation: Nuclear magnetic resonance
(NMR) spectra were recorded in CDCl3 or [D6]DMSO at 25 °C
with a Bruker Fourier 300 spectrometer at 300 MHz for H NMR
1
and at 75 MHz for 13C NMR spectroscopy. Chemical shifts are
reported in part per million (ppm) relative to residual solvent pro-
tons (δ =7.26 ppm for [D]chloroform) and the carbon resonance of
the solvent. The assignment of the protons and carbons as well as
the corresponding spectra are available in the Supporting Infor-
mation (Figures S1–S15). Melting points were determined using
a Krüss KSP1N. FT-IR Spectra were recorded as KBr pellets in
transmission using a Jasco FT/IR-4100. Absorption spectra and
emission spectra were measured in deaerated dichloromethane at
25 °C with a Varian Cary 50 UV/Vis-NIR Spectrophotometer and
Table 1. Spectroscopic and photophysical data of 3a and 8–11 in
DCM at 25 °C.[a]
Absorption
λmax thiophene
[nm]
Emission
Δλmax
λmax
Φ
[%]
τ1/2
[ns]
[nm]
3a
8
9
309
346
411
302
445
354
463
390
–
–
–
–
402
460
361
509
411, 413
550
56
49
59
64
79
87
94
Ͻ 0.1 0.45
a
JASCO FP-8300 Spectrophotometer, respectively. For the
60
1.8
9
5.5
11.7 1.42
16 n.r.
1.30
n.r.
0.98
0.14
luminescence lifetimes, Photon Technology International
a
Bithiophene[27a]
TimeMasterTM Model TM-2/2003 fluorescence lifetime spectrom-
eter was used, employing a Hamamatsu PLP2 laser diode as pulse
(wavelength output, 415 nm; pulse width, 59 ps). Emission quan-
tum yields were measured at room temperature using the optically
dilute method.[30] Coumarin 6 for 9–11 and Coumarin 2 for 8 in
deaerated dichloromethane solution were used as quantum yield
standards, assuming values of 0.78 and 0.68 respectively.[31] Experi-
mental uncertainties are as follows: absorption maxima, Ϯ2 nm;
molar absorption coefficient, 10%; emission maxima, Ϯ5 nm; ex-
cited state lifetimes, 10%; luminescence quantum yields, 20%. Sol-
vents were removed under reduced pressure using a rotary evapora-
tor unless otherwise stated. All chemicals including the organotin
compounds were purchased from Sigma–Aldrich and used as re-
ceived.
10
Terthiophene[27a]
11
Quaterthiophene[27a]
454, 484
[a] n.r.: not reported.
Indeed 8–11 showed no fluorescence in the solid state, in
accordance with our hypothesized π–π interactions attribut-
able to the second dpt unit.
Initial complexation experiments with ligands 3a–7 and
iron(II) acetate resulted in compounds with a distinctive
blue colour. In contrast, dpt-dithiophene-dpt 9 and FeII
give, under the same reaction conditions, a dark green com-
pound. Until now it was not possible to determine the mo-
lecular structures with NMR, MS or crystallography. Ac-
cordingly, it was difficult to identify the molecular reasons
for these colour differences. Notably, some of the prepared
complexes feature thermochromatic properties. For in-
stance, in going from 10 to 70 °C FeII-7 complex (in EtOH)
underwent a color change from blue to colorless and UV/
Vis measurements (see Supporting Information) revealed a
weakening of the MLCT band at 600 nm at temperatures
above 40 °C.
CCDC-1014477 (for 1a) and -1014478 (for 1b) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Computational Methods: All calculations were performed with
Gaussian software (G09).[32] The geometry optimization and IR
frequency determination was carried out with the DFT method
using the PBE1PBE functional[33] and The 6-311G(d,p) basis set[34]
associated with the polarized continuum model (CPCM)[35] using
DCM as solvent. No imaginary frequencies were observed for all
optimized structures confirming the model reached a stable local
minimum in energy. The electronic absorption l properties were cal-
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G. S. Hanan, D. G. Kurth et al.
FULL PAPER
culated by TD-DFT approach using the method, basis set and sol-
vent model previously stated. Gaussview 3.09 was used to visualize
MOs with an isodensity of 0.02; GaussSum 2.2 was employed to
extract the absorption energies, oscillator strengths and molecular
orbital energies and Chemissian program was used to sketch ener-
gies of MOs with their colour coded atomic orbital (AO) contri-
butions, using 0.001 eV as the threshold for degeneracy for the
MO.[36]
270.05421. C13H8N5Cl: C, 57.90; H, 2.99; N, 25.97; found C, 57.45;
H, 3.29; N, 25.00. IR (KBr): ν = 1541, 1370 (triazine) cm–1.
˜
General Synthesis of Monotopic dpt Ligands 3a–5: A solution of
Cl-dpt 2 (1.00 g, 3.71 mmol), the corresponding tributylstannyl
Bu3SnR (4.45 mmol) and Pd(PPh3)4 (0.200 g, 5 mol-%) in degassed
toluene (40 mL) were heated for 15 h under an inert atmosphere at
100 °C. The mixture was cooled to room temperature and 1 m
NaOH (30 mL) were added. The biphasic mixture was vigorously
stirred for 1 h to remove the tin compounds.[38] The phases were
separated and the aqueous phase was extracted with chloroform
(3ϫ 30 mL). The combined organic phases were washed with 1 m
NaOH (30 mL) and brine (30 mL), dried with MgSO4, filtered and
evaporated under reduced pressure. The residue was washed with
hot hexane and Et2O to purify the product.
Synthesis
Synthesis of 1a: Urea (7.50 g, 0.125 mol) was dissolved in dry
DMSO (100 mL) under an inert atmosphere. Sodium hydride
(6.00 g, 0.150 mol) (60% dispersion in paraffin oil) was slowly
added and the mixture was stirred under an inert atmosphere at
25 °C for 2 h. 2-Cyanopyridine (26.02 g, 0.250 mol) was added to
the grey dispersion. The reaction mixture was stirred for 21 h at
75 °C. The resulting black mixture was cooled to 25 °C, poured
into ice-water (100 mL) and carefully neutralized with 1 m H2SO4.
The mixture was cooled for 12 h to increase the yield. The crude
product was filtered off and washed with acetone to remove by-
products as sodium methylsulfinylmethylide. The filtered solution
was saved and stored in the fume hood. After 2–3 days additional
product was formed. The two crystallisations fractions were com-
bined and washed with acetone. The resulting product was used
without further purification, yield 68% (colourless powder); m.p.
Ͼ 300 °C. 1H NMR (300 MHz, [D6]DMSO): δ = 8.59 (ddd, J =
4.8, 1.8, 0.8 Hz, 2 H6Ј), 8.42 (ddd, J = 7.7, 1.3, 1.1 Hz, 2 H3Ј), 7.97
(td, J = 7.7, 1.8 Hz, 2 H4Ј), 7.51 (ddd, J = 7.5, 4.8, 1.3 Hz, 2
H5Ј) ppm. 13C{1H} NMR (75 MHz, [D6]DMSO): δ = 170.51 (C2,6),
169.42 (C4), 156.15 (C2Ј), 150.05 (C6Ј), 138.23 (C4Ј), 126.35 (C5Ј),
123.59 (C3Ј) ppm. HRMS (ESI): m/z: calcd. for C3H10N5O:
3a: Yield 58% (off-white powder); m.p. 188–190 °C (dec.). 1H
NMR (300 MHz, CDCl3): δ = 8.93 (ddd, J = 4.9, 1.8, 1.1 Hz, 2 H,
H6Ј), 8.77 (ddd, J = 7.9, 1.3, 1.3 Hz, 2 H, H3Ј), 8.48 (dd, J = 3.8,
1.3 Hz, 1 H, H3ЈЈ), 7.95 (td, J = 7.8, 1.8 Hz, 2 H, H4Ј), 7.69 (dd, J
= 4.9 Hz, 1.3 2 H, H5ЈЈ), 7.54 (ddd, J = 7.6, 4.9, 1.2 Hz, 2 H, H5Ј),
7.26 (t, J = 4.2 Hz, 2 H, H4ЈЈ) ppm. 13C{1H} NMR (75 MHz,
CDCl3): δ = 171.30 (C2,6), 168.89 (C4), 152.95 (C2Ј), 150.19 (C6Ј),
141.01 (C2ЈЈ), 137.13 (C4Ј), 133.07 (C5ЈЈ), 132.57 (C3ЈЈ), 128.67 (C4ЈЈ),
126.45 (C5Ј), 124.84 (C3Ј) ppm. HRMS (ESI): m/z: calcd. for
C17H11N5S: 318.08017 [M + H]+ found 318.08149. IR (KBr): ν =
˜
1522, 1373 (triazine) cm–1.
4: Yield 70% (colourless powder); m.p. 227 °C. 1H NMR
(300 MHz, CDCl3): δ = 8.97 (ddd, J = 4.7, 1.8, 0.9 Hz, 2 H, H6Ј),
8.82 (m, 4 H, H3Ј,2ЈЈ), 7.96 (td, J = 7.8, 1.8 Hz, 2 H, H4Ј), 7.58
(m, 5 H5Ј,3ЈЈ,4ЈЈ) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 173.02
(C2,6), 171.74 (C4), 153.54 (C2Ј), 150.53 (C6Ј), 137.01 (C4Ј), 135.41
(C1ЈЈ), 133.05 (C4ЈЈ), 129.52 (C2ЈЈ), 128.90 (C3ЈЈ), 126.58 (C5Ј), 125.08
(C3Ј) ppm. HRMS (ESI): m/z: calcd. for C19H14N5: 312.12437 [M+
+ H] found 312.12451. C19H13N5: C, 73.30; H, 4.21; N, 22.24;
252.08799 [M + H]+ found 252.08816. IR (KBr): ν = 1540, 1375
˜
(triazine) cm–1.
Synthesis of 1b: Compound 1a was dissolved in a CHCl3/MeOH
(3 mL) and recrystallized by diffusion of Et2O into the solution.
The closed vessel was in the fumehood for about 6 months. The
resulting white crystals were filtered off and dried at 25 °C. 1H
NMR (300 MHz, [D6]DMSO): δ = 11.85 (s, 2 H, H1), 8.77 (ddd, J
= 4.9, 1.7, 0.9 Hz, 2 H, H6Ј), 8.20 (ddd, J = 7.7, 1.3, 1.1 Hz, 2 H,
H3Ј), 8.12 (td, J = 7.7, 1.7 Hz, 2 H, H4Ј), 7.77 (ddd, J = 7.5, 4.9,
1.3 Hz, 2 H, H5Ј) ppm. 13C{1H} NMR (75 MHz, [D6]DMSO): δ =
163.68 (C2), 148.96 (C6Ј), 147.64 (C2Ј), 147.55 (C1), 138.57 (C4Ј),
128.40 (C5Ј), 123.19 (C3Ј) ppm.
found C, 72.69; H, 4.16; N, 22.49. IR (KBr): ν = 1525, 1365 (tri-
˜
azine) cm–1.
5: Yield 36% (off-white powder); m.p. 198–200 °C (dec.). 1H NMR
(300 MHz, CDCl3): δ = 8.94 (ddd, J = 4.7, 1.9, 1.0 Hz, 2 H, H6Ј),
8.77 (dd, J = 7.9, 0.9 Hz, 2 H,H3Ј), 7.95 (td, J = 7.8, 1.8 Hz, 2 H,
H4Ј), 7.83 (dd, J = 3.5, 0.8 Hz, 1 H, H3ЈЈ), 7.79 (dd, J = 1.8, 0.9 Hz,
1 H, H4ЈЈ), 7.52 (ddd, J = 7.7, 4.7, 1.1 Hz, 2 H, H5Ј), 6.68 (dd, J =
3.5 Hz, 1.8 2 H, H5ЈЈ) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ
= 171.56 (C2,6), 165.22 (C4), 153.13 (C2Ј), 150.51 (C2ЈЈ), 150.48
(C6Ј), 147.27 (C4ЈЈ), 137.06 (C4Ј), 126.39 (C5Ј), 124.90 (C3Ј), 118.19
(C5ЈЈ), 112.83 (C3ЈЈ) ppm. HRMS (ESI): m/z: calcd. for C17H11N5O:
Synthesis of 2: Freshly distilled thionyl chloride (85 mL, 1.24 mol)
was slowly added under an inert atmosphere to 3.50 g (13.9 mmol)
1 NaO-dpt in a Schlenk flask. The reaction mixture was heated
to reflux and stirred for 18 h. Thionyl chloride was removed by
distillation. Toluene (60 mL) was added and the mixture was dis-
tilled to dryness again. The process was repeated twice to remove
all thionyl chloride. The resulting off-white triazine salt was sus-
pended in chloroform (60 mL) and diisopropylethylamine (Hünigs
base) (4.4 mL, 3.34 g, 25.8 mmol) were added. The orange solution
was washed three times with phosphate buffer[37] (150 mL) and
brine (60 mL), dried with MgSO4, filtered and evaporated off. The
resulting off-white powder product was used without further purifi-
cation. The product can be recrystallized from hot toluene/hexane
(1:2), yield 65% (off-white powder); m.p. 166–172 °C (dec.). 1H
302.10364 [M + H]+ found 302.10417. IR (KBr): ν = 1525, 1365
˜
(triazine) cm–1.
General Synthesis of Ditopic dpt Ligands 6–9: A solution of Cl-
dpt 2 (1.00 g, 3.71 mmol), the corresponding bis(tributylstannyl)
(Bu3Sn)2R (1.85 mmol) and Pd(PPh3)4 (0.200 g, 5 mol-%) in de-
gassed toluene (40 mL) was heated 15 h under an inert atmosphere
at 100 °C. After the reaction the mixture was cooled to room tem-
perature and the precipitate was filtered off and washed with tolu-
ene, hot hexane and Et2O.
1
6: Yield 32% (grey powder); m.p. Ͼ 300 °C. H NMR (300 MHz,
CDCl3): δ = 10.19 (m, 1 H, H2ЈЈ), 9.06 (dd, J = 7.7, 0.8 Hz, 2 H,
NMR (300 MHz, CDCl3): δ = 8.88 (ddd, J = 4.7, 1.8, 0.8 Hz, 2 H, H4ЈЈ), 8.99 (ddd, J = 4.8, 1.8, 1.0 Hz, 4 H, H6Ј), 8.92 (ddd, J = 7.9,
H6Ј), 8.68 (d, J = 7.9 Hz, 2 H, H3Ј), 7.90 (td, J = 7.9, 1.8 Hz, 2 H, 1.3, 1.0 Hz, 4 H, H3Ј), 8.00 (ddd, J = 7.9, 7.7, 1.8 Hz, 4 H, H4Ј),
H4Ј), 7.50 (ddd, J = 7.6, 4.7, 1.1 Hz, 2 H, H5Ј) ppm. 13C{1H} NMR 7.82 (dd, J = 3.5, 0.8 Hz, 1 H, H5ЈЈ), 7.57 (ddd, J = 7.6, 4.8, 1.1 Hz,
(75 MHz, CDCl3): δ = 173.65 (C2,6), 172.98 (C4), 151.63 (C2Ј), 4 H, H5Ј) ppm. 13C{1H} NMR (100 MHz, CDCl3): δ = 172.46 (C4),
150.83 (C6Ј), 137.36 (C4Ј), 127.27 (C5Ј), 125.55 (C3Ј) ppm. HRMS 171.75 (C2,6), 153.30 (C2Ј), 150.44 (C6Ј), 137.11 (C4Ј), 136.24
(ESI): m/z: calcd. for C13H9N5Cl: 270.05410 [M + H]+ found
(C1ЈЈ,3ЈЈ), 133.67 (C4ЈЈ), 130.39 (C5ЈЈ), 129.30 (C2ЈЈ), 126.50 (C5Ј),
6
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O43521
/KAP1
Date: 27-02-15 12:24:30
Pages: 9
A Facile Route to Fluorescent Bis(pyridyl-1,3,5-triazine) Ligands
125.05 (C3Ј) ppm. ESI-MS: m/z: calcd. for 545.19452 [M + H]+
= 7.6 Hz, 4 H, H3Ј), 8.40 (d, J = 3.9 Hz, 2 H, H3ЈЈ), 7.97 (t, J =
7.1 Hz, 4 H, H4Ј), 7.53 (t, J = 7.6 Hz, 4 H, H5Ј), 7.33 (d, J = 3.9 Hz,
4 H, H3ЈЈЈ,4ЈЈЈ), 7.21 (d, J = 3.9 Hz, 2 H, H4ЈЈ) ppm. 13C{1H} NMR
(75 MHz, CDCl3): δ = 171.46 (C2,6), 171.14 (C4), 153.21 (C2Ј),
150.48 (C6Ј), 139.33 (C2ЈЈ), 137.27 (C2ЈЈЈ), 137.02 (C4Ј), 136.16 (C5ЈЈ),
133.66 (C4ЈЈ) 126.33 (C5Ј), 126.12 (C3ЈЈ), 124.95 (C3ЈЈЈ,C4ЈЈЈ) 124.40
(C3Ј) ppm. HRMS (ESI): m/z: calcd. for C42H25N10S4: 797. 11410
found 545.19482. IR (KBr): ν = 1526, 1356 (triazine) cm–1.
˜
7: Yield 49% (off-white powder); m.p. Ͼ 300 °C. 1H NMR
(300 MHz, CDCl3): δ = 9.01 (s 4 H, H2ЈЈ), 8.98 (ddd, J = 4.7, 1.8,
1.0 Hz, 4 H, H6Ј), 8.88 (ddd, J = 7.9, 1.3, 1.0 Hz, 4 H, H3Ј), 8.01
(ddd, J = 7.9, 7.6, 1.8 Hz, 4 H, H4Ј), 7.57 (ddd, J = 7.6, 4.7, 1.1 Hz,
4 H, H5Ј) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 172.45 (C4),
171.86 (C2,6), 153.31 (C2Ј), 150.53 (C6Ј), 139.49 (C1ЈЈ), 137.15 (C4Ј),
129.68 (C2ЈЈ), 126.47 (C5Ј), 125.08 (C3Ј) ppm. ESI-MS: m/z: calcd.
[M + H]+ found 797.11385. IR (KBr): ν = 1509, 1371 (tri-
˜
azine) cm–1.
for 545.19452 [M + H]+ found 545.19485. IR (KBr): ν = 1525, 1364
Supporting Information (see footnote on the first page of this arti-
˜
1
cle): H and 13C spectra, crystallographic data, computational cal-
(triazine) cm–1.
culation data and UV/Vis spectra.
8: Yield 33% (greenish white powder); m.p. Ͼ 300 °C. 1H NMR
(300 MHz, CDCl3): δ = 8.98 (ddd, J = 4.7, 1.8, 1.0 Hz, 4 H, H6Ј),
8.84 (ddd, J = 7.9, 1.3, 1.0 Hz, 4 H, H3Ј), 8.58 (s, 2 H, H3Ј Ј), 7.99
(ddd, J = 7.9, 7.6, 1.8 Hz, 4 H, H4Ј), 7.56 (ddd, J = 7.6, 4.7, 1.1 Hz,
4 H, H5Ј) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 171.70 (C2,6),
168.71 (C4), 152.87 (C2Ј), 150.46 (C6Ј), 146.89 (C2ЈЈ), 137.20 (C4Ј),
133.17 (C3ЈЈ), 126.62 (C5Ј), 125.13 (C3Ј) ppm. HRMS (ESI): m/z:
calcd. for C30H19N10S: 551.15094 [M+ + H] found 551.15079. IR
Acknowledgments
G. S. H. thanks the Natural Sciences and Engineering Research
Council of Canada (NSERC), the Centre for Self-Assembled
Chemical Structures and the Université de Montréal for financial
support. M. G. thanks the Bayerische Forschungsallianz (BayFor)
and the Bayerisch-Französisches Hochschulzentrum (BFHZ) for
funding the cooperation between Würzburg and Montréal. The au-
thors thank Stephanie Maas (University of Würzburg) for her help
preparing the dpt precursors. The authors thank Christoph Lam-
bert for valuable discussions.
(KBr): ν = 1514, 1360 (triazine) cm–1.
˜
9: Yield 55% (yellow powder); m.p. Ͼ 300 °C. 1H NMR (300 MHz,
CDCl3): δ = 8.96 (ddd, J = 4.7, 1.8, 1.0 Hz, 4 H, H6Ј), 8.79 (ddd,
J = 7.9, 1.3, 1.0 Hz, 4 H, H3Ј), 8.44 (d, J = 4.0 Hz, 2 H, H3ЈЈ), 7.97
(ddd, J = 7.9, 7.7, 1.8 Hz, 4 H, H4Ј), 7.54 (m, 6 H, H5Ј) ppm.
13C{1H} NMR (75 MHz, CDCl3): δ = 171.56 (C2, 6), 168.65 (C4),
153.12 (C2Ј), 150.50 (C6Ј), 143.82 (C2ЈЈ), 140.85 (C5ЈЈ), 137.05 (C4Ј),
133.60 (C3ЈЈ), 126.40 (C5Ј), 126.36 (C4ЈЈ), 125.00 (C3Ј) ppm. HRMS
(ESI): m/z: calcd. for C34H21N10S2: 633.13866 [M + H]+ found
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˜
Synthesis of 3b: Compound 3a (0.500 g, 1.58 mmmol) was dis-
solved in glacial acetic acid (10 mL). N-Bromosuccinimide (0.310 g,
1.73 mmol) was added to the solution and the mixture was stirred
at 40 °C for four days under exclusion of light. The resulting green-
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H3ЈЈ/4ЈЈ) ppm.
Synthesis of 10 and 11: A solution of 3b (0.267 g, 0.67 mmol), the
corresponding bis(tributylstannyl) (Bu3Sn)2R (0.34 mmol) and
Pd(PPh3)4 (0.08 g, 10 mol-%) in degassed toluene (20 mL) was
heated for 15 h under an inert atmosphere at 100 °C. After the
reaction the mixture was cooled to room temperature and the pre-
cipitate was filtered off and washed with toluene, hot hexane and
Et2O.
10: Yield 33% (dark red powder); m.p. 239 °C (dec.). 1H NMR
(300 MHz, CDCl3): δ = 8.97 (d, J = 4.9 Hz, 4 H, H6Ј), 8.78 (d, J
= 7.7 Hz, 4 H, H3Ј), 8.42 (d, J = 4.1 Hz, 2 H, H3ЈЈ), 7.98 (t, J =
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H4ЈЈ), 7.38 (d, J = 4.1 Hz, 2 H, H3ЈЈЈ) ppm. 13C{1H} NMR (CDCl3,
75 MHz): δ = 171.51 (C2,6), 168.65 (C4), 153.05 (C2Ј), 150.35 (C6Ј),
143.95 (C2ЈЈ), 139.61 (C5ЈЈ), 137.21 (C2ЈЈЈ), 137.06 (C4Ј), 133.58 (C4ЈЈ
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˜
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Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7

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/KAP1
Date: 27-02-15 12:24:30
Pages: 9
G. S. Hanan, D. G. Kurth et al.
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Received: November 25, 2014
Published Online: ᭿
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O43521
/KAP1
Date: 27-02-15 12:24:30
Pages: 9
A Facile Route to Fluorescent Bis(pyridyl-1,3,5-triazine) Ligands
Ligand Synthesis
Several bis(pyridyl-1,3,5-triazine) (dpt)
ligands are prepared via Stille coupling
with yields and scope of application su-
perior to known trimerisation procedures.
Ditopic ligands with different spacers are
prepared and incorporation of p- and m-
substituted phenyl rings enable access to
different isomers. The absorption and
emission properties can be tuned using
oligothiophene spacers.
M. F. Geist, D. Chartrand, M. Cibian,
F. Zieschang, G. S. Hanan,*
D. G. Kurth* ..................................... 1–9
A Facile Route to Bis(pyridyl-1,3,5-tri-
azine) Ligands with Fluorescing Properties
Keywords: Supramolecular chemistry / Syn-
thetic methods
/ Cross-coupling / N
ligands / Luminescence
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
9