Self-assembly of T-shape 2: H -benzo [d] [1,2,3]-triazoles. Optical waveguide and photophysical properties

Article abstract of DOI:10.1039/c6ra02473d

T-Shaped 2H-benzo[d][1,2,3]triazole derivatives have been synthesized by Sonogashira coupling reactions under microwave irradiation. DFT calculations were performed in order to understand the structure-property relationships-an aspect that is of vital imp

Full text of DOI:10.1039/c6ra02473d

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J. R. Carrillo, A. Diaz, R. Martín, M. V. Gómez, L. Stegemann, C. Strassert, J. Orduna, J. Buendía, E. E.
Greciano, J. S. Valera, E. Matesanz and L. Sanchez, RSC Adv., 2016, DOI: 10.1039/C6RA02473D.
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Self-assembly of T-shape 2H-benzo[d][1,2,3]-triazoles. Optical
wadeguide and photophysical properties
†
Received 00th January 20xx,
Accepted 00th January 20xx
I. Torres,a J. R. Carrillo,a A. Díaz-Ortiz,a R. Martín,a M. V. Gómez,a L. Stegemann,b C. A. Strassert,b J.
Orduna,c J. Buendía,d E. E. Greciano,d J. S. Valera,d E. Matesanz,e L. Sánchez* d and P. Prieto* a
DOI: 10.1039/x0xx00000x
www.rsc.org/
T-shaped 2H-benzo[d][1,2,3]triazole derivatives have been synthesized by Sonogashira coupling reactions under
microwave irradiation. DFT calculations were performed in order to understand the structure-property relationships – an
aspect that is of vital importance for the rational design of organic self-assemblies for optoelectronic applications.
Concentration-dependent 1H Pulse Field-Gradient Spin-Echo (PFGSE) NMR spectroscopy and UV/Vis spectrophotometry
indicated the absence of a tendency for the aggregation of single molecules in solution. In contrast, in the solid state these
compounds form organized aggregates and these were studied by scanning electron microscopy (SEM), which showed the
influence that the peripheral substitution has on the morphology of the aggregates. For example, methoxy-substituted
benzotriazoles self-assemble into thick and crystalline needle-like structures. However, the unsubstituted triazoles give
rise to flower-like aggregates. Interestingly, the aggregates formed by benzotriazole 1c exhibit waveguide properties.
Optical waveguides are structures that have a higher refractive
Introduction
index than the environment. As a consequence, these
materials can retain light as they transmit it internally by total
reflection at the interface. These materials are capable of
propagating and manipulating light efficiently on the
subwavelength scale. These 1D-nanostructures can be built by
self-assembly of organic molecules through non-covalent
bonds such as hydrogen bonds, van der Waals interactions, π-
π stacking or CH-π interactions, and they are highly ordered
systems.
Organic electronics is a research area that has had a significant
impact in the last two decades owing to the development of
semiconducting materials and innovation in technological
devices. This is expected to be a powerful and fascinating
technology that offers great differentiation from the
conventional electronic applications based on inorganic
materials.1 In this framework, organic materials that exhibit
strong emission in the solid state have received increasing
attention in recent years because of their potential
applications in optical and optoelectronic devices such as
optical waveguides,2 optically pumped lasers3 and light-
emitting diodes.4 The transmission of light in fibers is an
A common feature of organic waveguides is the presence of
heteroaromatic rings with nitrogen atoms, which have a
marked influence on the formation of supramolecular
structures.6 1,2,4-Triazole systems have proven to have
excellent electron-transporting and hole-blocking abilities due
to the presence of this highly electron-deficient moiety.
Another important feature of this moiety is its ability to form a
variety of non-covalent interactions. Accordingly, a large
number of 1,2,4-triazole derivatives have been described with
a variety of uses in materials science.7 Moreover, 1,2,4-triazole
rings tend to decrease the effective π-conjugation of aromatic
systems, thus facilitating the design of blue emitters.8
exciting challenge in the information age and, as
a
consequence, investigations in this field have become very
attractive.5
Recently, our research group has reported the synthesis of 4-
aryl-3,5-bis(arylethynyl)-4H-1,2,4-triazole9 and 4-aryl-3,5-
bis(arylethynyl)aryl-4H-1,2,4-triazole derivatives10 and their
aggregation, in which C–H···π interactions play a role.
In order to obtain such promising materials it is very important
to apply a rational design process. In this sense, computational
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chemistry11 is a powerful tool that allows us to determine
properties of the building blocks and aggregates to avoid
unnecessary synthesis, thereby minimizing the cost and
environmental impact. In this sense, the use of sustainable
methods is a factor that needs to be considered.
Table 1.
λ
and
λ
and energies of HOMO-LUMO
em
abs
calculated at CPCM-M06-2X/6-311+G(2d,p)
Compound
λ
λ
EHOMO
(eV)
ELUMO
(eV)
Band
gap (eV)
abs
em
(nm)
392.3
367.5
402.0
397.8
(nm)
484.6
485.8
498.3
494.2
1a
1b
1c
1d
–7.06
–7.06
–6.90
–6.89
–2.05
–2.07
–2.04
-2.07
5.01
4.99
4.86
4.82
As part of our ongoing research program, and in an effort to
increase our knowledge of optical waveguides, we carried out
the design, computational study and synthesis of 2H-
benzo[d][1,2,3]triazole derivatives. Due to the excellent
properties shown by the 4H-1,2,4-triazole derivatives, we
decided to study the benzotriazole moiety with the aim of
retaining the ability of these systems to self-assemble while
varying their emission: the benzotriazole system does not
break the effective π-conjugation of aromatic systems and it
could provide compounds with different photophysical
calculated λabs and λem values are collected in Table 1 (see
spectra in Electronic Supplementary Information, Fig. S1). The
electronic spectra were also calculated in dichloromethane
solution using the conductor-like polarizable continuum model
(CPCM)12 and the time-dependent density functional theory
(TD-DFT) approach.13 The M06-2X14 meta-exchange functional
was employed. The choice of this functional was based on the
accurate results obtained in the calculation of systems with
high spatial orbital overlap, which are even better than those
provided by the more widely used CAM-B3LYP.15 The energies
of frontier molecular orbitals are also collected in Table 1.
properties.
Furthermore,
our
previously
described
compounds9,10 are V-shaped whereas benzotriazoles adopt a
T-shape. It is known that optoelectronic properties are highly
dependent on the chemical structure and on the
supramolecular aggregation. Theoretical models can be used
to predict optical properties and are useful for the efficient in
silico design of new compounds.
The topologies of the FMO are very similar in compounds 1a
–
d
. The HOMO is located in the horizontal branch and the
LUMO in both branches, mainly in the vertical one (Fig. 2).
Additionally, the introduction of methoxy-substituents only
affects the value of the HOMO and this leads to a decrease in
the bandgap (Table 1, entry 1 vs 3, and 2 vs 4).
Results and discussion,
The work described here was focused on the synthesis and
applications of different 2H-benzo[d][1,2,3]triazole derivatives
(Fig. 1).
Computational study
Prior to carrying out the chemical synthesis, our initial goal was
to determine the properties and propensity for self-assembly
of
R1
R1
R1
R1
R1
R1
N
N
N
R
1a, R=H,
1b, R=Ph,
1c, R=H
R1=H
R1=H
R1=OCH3
R1=OCH3
,
1d, R=Ph,
Fig.
2
Fig. 1 2H-Benzo[d][1,2,3]triazole derivatives
HOMO-LUMO topologies of compound 1c.
Secondly, the structure of the molecular stacks was studied by
applying Grime’s B97D functional,16 which includes the
these compounds using computational chemistry. We initially
calculated the UV-vis absorption spectra of compounds 1. The
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dispersion forces. The 6-31G* basis set was employed.17 In between these electron-rich fragments. The aromatic C–H
order
to
simplify
this
2a
study,
and
2-phenyl-2H- bond in the ortho position of the N-phenyl unit of one
2-biphenyl-2H- molecule is involved in weak H-bonding (2.97 Å) with the sp2
benzo[d][1,2,3]triazole
benzo[d][1,2,3]triazole
(
)
(
2b
)
were chosen as model nitrogen atom of the adjacent molecule, and a CH-π
compounds. The π
-stacking arrangement considered for the interaction also occurs with another N-phenyl unit (3.52 Å).
calculations is depicted in Fig. 3. The relevant intermolecular CH-π interactions can also be observed between the ortho
parameters are as follows: (i) the distance R refers to the protons of one benzotriazole ring and the benzotriazole ring of
distance between the centers of mass of the two triazole rings a neighbouring molecule.
and indicates the separation between the two benzotriazole In the dimer of compound 2b, the π
rings; (ii) is the dihedral angle between the two rings and biphenyl units (3.36 Å) and H-bonding (2.8 Å) of the ortho-H of
denotes the relative orientation of the rings, i.e., the the biphenyl of one molecule with the sp2 nitrogen atom of the
benzotriazoles are parallel and antiparallel when = 0º and adjacent molecule are the non-covalent forces that direct the
180º respectively; (iii) corresponds to the angle formed by self-assembly of this compound. This outcome is consistent
the planes of the two rings and indicates the degree of tilting, with our previous study on the optical waveguide properties of
i.e., the two rings are coplanar when = 0º, while
= 180º triazole derivatives.9,10
corresponds to a perpendicular T-shaped configuration; (iv) We subsequently introduced the arylacetylenic fragment in
the parameter d defines the displacement of the two the basic models and the two possible aggregates were
benzotriazole moieties in the dimer. optimized, head-to-head and vertical ones. The calculated
The optimized dimers of 2-phenyl-2H-benzo[d][1,2,3]triazole structures (Fig. S2) showed that the triple bonds play an
2a) and 2-biphenyl-2H-benzo[d][1,2,3]triazole (2b) are shown important role in the stabilization of both aggregates, due to
in Fig. 4. The presence of the phenyl or biphenyl units results in the formation of CH-π interaction between the sp carbon and
−π stacking between the
θ
θ
θ =
,
φ
φ
φ
ꢀ
(
different aggregation pathways.
the aromatic ortho-proton and the benzotriazole protons.
Another stabilizing interaction is the CH-π between different
aromatic protons and aromatic carbons. It is interesting to
note that in these structures there are no hydrogen bonding
interactions. Thereby, it can be deduced that the triple bond
plays a more important role than the presence of nitrogen
atoms in the stabilization of the aggregates. Only the head-to-
head aggregate of the biphenyl derivative
(1b) showed
different behaviour. In this case, π−π stacking and H-bonding
are the most important interactions. Finally, the next goal was
to analyse the role played by the methoxy framework. The
optimized horizontal and vertical aggregates for phenyl (1c
)
and biphenyl derivatives (1d) are depicted in Fig. 5. It is
interesting to note that in this case the H-bonding between the
oxygen of one methoxy group and the hydrogen of the
methoxy group of the adjacent molecule (2.54 Å) and the CH-π
interaction of the sp carbon of the triple bond and the CH3
methoxy group are the most important interactions that
govern the formation of aggregates. The dimer of 1c was used
as a model and careful analysis of the optimized structures
again led to the conclusion that the head-to-head aggregate is
more organized and stable than the vertical one.
Fig. 3 Structure of the π-stacked benzotriazole dimer and indication
of the intermolecular parameters according to Ref. 18
It can be concluded that these compounds have several non-
covalent interactions that allow them to form good molecular
aggregates. So, the identification of optoelectronic and self-
assembly properties in these derivatives prompted us to
address the chemical synthesis of these compounds.
Fig. 4 Different stacking of 2a (left) and 2b (right) dimers
computed at B97D/6-31+G*.
The benzotriazole units in the dimer of N-phenylbenzotriazole
2a are rotated slightly in order to avoid electrostatic repulsion
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Fig. 5 Optimized structures of the vertical aggregate (top) and head-
to-head aggregate (bottom) of compounds 1c and 1d computed at
B97D/6-31G*
Scheme 1. Synthesis of 2H-benzo[d][1,2,3]triazole derivatives 1.
Isolated yields in brackets.
Chemical synthesis
Benzotriazoles 2a,b were prepared from 1-nitro-2-
nitrosobenzene and aniline or (1,1'-biphenyl)-4-amine,
respectively, according to the synthetic procedure described
by Höger.19 Bromination of these compounds afforded the
bromobenzotriazoles 3a,c in 80% and 97% yield, respectively.
However, while 2a gave only a dibromo-derivative, 2b led to a
tribromobenzotriazole (3c) although the excess of bromine
had been significantly reduced. Compound 3b (4,7-dibromo-2-
phenyl-2H-benzo[d][1,2,3]triazole) could not be obtained
under any of the reaction conditions employed (Scheme 1).
The Sonogashira C–C cross-coupling reaction between
Photophysical characterization
A thorough photophysical study was carried out in order to
demonstrate experimentally the theoretical predictions. The
UV/Vis absorption and emission spectra in solution at room
temperature were studied first (Fig. 6).
bromobenzotriazoles
3 and arylacetylenes 4 using reusable Pd-
EnCat™ TPP30, 1,5-diazabicyclo[5.4.0]undecene-5-ene (DBU),
CuI and MW irradiation as the energy source afforded
arylalkynylbenzotriazoles
1 within 20 minutes in good yields
(up to 88%)10 (Scheme 1). We recently developed this
sustainable procedure for the preparation of arylalkynylaryl-
1,2,4-triazoles.9 The cross-coupling reaction between 3c and 5-
ethynyl-1,2,3-trimethoxybenzene (4b) under more energetic
reaction conditions (170 ºC) provided the trisubstituted
benzotriazole 1g, albeit in moderate yield. However, a similar
reaction with phenylacetylene was unsuccessful, perhaps due
to the high degree of polymerization under these reaction
conditions. All of the compounds described above gave
satisfactory spectroscopic and analytical data.
Fig. 6 a) Absorption spectra in DCM. b) Emission spectra at room
temperature in DCM.
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Table 2. Photophysical data for the benzotriazole derivatives in
dichloromethane at room temperature.
solution
λabs
(nm)
374
397
352
λem
(nm)
442
503
441
513
522
Τ[a]
(ns)
Φ
1a
1c
1e
2.586
3.434
2.665
3.735
3.785
0.55
0.65
0.54
0.57
0.82
1f 349 / 408 (sh)
1g 372
[a] Intensity weighted average lifetime
Excitation and emission spectra of frozen glassy matrices at 77
K and of the amorphous solids, along with the corresponding
excited state lifetime decays, are depicted in Fig. S3 in the
Supporting Information. The most significant photophysical
data are summarized in Table 2. It can be clearly observed that
the introduction of MeO-groups on the phenyl substituents
leads to destabilization of the HOMO, as also observed from
the computational results, and thus to red-shifted absorption
1
Fig. 7 Collection of H NMR spectra of compound 1c in CDCl3 at 298
K. Some regions (8.40–7.70; 7.43–7.00 ppm; 6.90–4.05 ppm; 3.90–0
ppm) have been removed in order to show all of the signals within
the Fig. TMS was used as internal standard.
and emission spectra for 1c, 1f and 1g as compared to 1a and
1e. In contrast, the introduction of the Br-phenyl group does
not appreciably affect the photophysical properties. The
concomitant broadening of the emission spectra of 1c, 1f and
1g is caused by an enhanced charge-transfer character due to
the presence of the MeO-groups, which favours the relocation
of the electronic density from the side arms (HOMO) and the
dipole-mediated coupling with the surrounding solvent
molecules. Interestingly, these electron-donating groups also
lead to prolonged excited state lifetimes and higher
photoluminescence quantum yields, which indicate that the
radiationless deactivation rate is decreased. At 77 K the
structured vibrational progression is recovered as the charge-
transfer character is less favoured due to the lack of solvent
reorientation to stabilize the polar excited state.
Similarly, clear evidence for a tendency to aggregation of
benzotriazole 1c in a solution of CDCl3 cannot be seen in Figure
7. Two peaks (marked with an asterisk in Fig. 7) show a
negligible chemical shift change of only 0.01 ppm with respect
to the spectra of the more dilute samples when the
concentration reaches very high values (150–200 mM).
Concentration-dependent 1H Pulsed Field-Gradient Spin-Echo
(PFGSE) NMR spectroscopy experiments20 were performed on
compound 1c in CDCl3 at 298 K using CHI3 as internal standard.
The aim of these experiments was to confirm the absence of
any tendency to aggregation of single molecules in solution, as
The agreement between the theoretical and experimental
absorption and emission spectra is excellent.
1
shown by the concentration-dependent H NMR experiments.
The translational self-diffusion coefficients (Dt) can be
evaluated by PFGSE NMR experiments to provide information
concerning the molecular size in solution and therefore about
the existence of an aggregation process as the concentration
increased.21 The diffusion coefficients for each solution of
compound 1c are shown in Table 3. The Dt values (m2 s–1) for
the different concentrations are not significantly different,
thus confirming the lack of aggregation in solution. The
changes in solution viscosity within the concentration range
studied (75–10 mM) are expected to be negligible21 and within
the error observed for the diffusion coefficient Dt (m2s–1).
Self-assembly study
Following our initial goal, the aggregation of the reported 2H-
benzo[d][1,2,3]triazoles was investigated both in solution and
solid state. As in our previous reports on 4H-1,2,4-triazoles,
compounds 1 had a very low tendency to aggregate in
solution.9,10 In good analogy with those reports, appreciable
1
changes in the H NMR spectra of 2H-benzo[d][1,2,3]triazole
1
were not observed on varying the concentration in a good
solvent like chloroform.
Concentration-dependent 1H NMR measurements were
carried out on compounds 1a and 1c (Fig. S4 and Fig. 7,
respectively) in CDCl3 at 298 K. Variation in chemical shifts
cannot be observed in Fig. S4 for the different protons of
Table 3. Diffusion coefficients (10–10 Dt, m2 s–1) and concentrations
(C, mM) for compound 1c in CDCl3 at 298 K
C [mM]
10
25
50
75
Dt [m2 s–1
]
compound 1a
.
5.0 ± 0.36
5.6 ± 0.43
5.5± 0.46
5.1 ± 0.5
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Importantly, the aggregates formed by the self-assembly of
benzotriazole 1c were suitable for X-ray analysis. The
geometry
of
the
2-phenyl-4,7-bis-(phenylethynyl)-2H-
benzo[d][1,2,3]benzotriazole moiety is practically planar, with
the phenyl attached to N-2 of the triazole ring rotated by 17º
(Fig. 9a). The methoxy groups plays a crucial role in the
formation of the organized supramolecular structure. An array
of four C–H···π interactions between one of the methoxy
groups and one of the sp3 carbons and another four with the
sp-carbon of the ethynyl linker, results in a head-to-head
dimers, as proposed in the computational study. Thereby, one
of the protons of the phenyl group attached to N-2 of the
triazole and the peripheral trimethoxybenzene and an H-bond
between the methoxy groups of adjacent molecules results in
a Z-like trimer
Fig. 8 SEM images (glass substrate, 298 K) of the aggregates of
1c (a and b) and 1f (c and d) obtained by slow diffusion of
CHCl3/MeCN and CHCl3/MeOH, respectively. The scale bar in
(a), (c) and (d) is 10 micrometers and in (b) is 1 micrometer.
The formation of organized aggregates from compounds
1 was
investigated further by the slow diffusion technique using
CHCl3 as a good solvent and a variety of poor solvents such as
acetronitrile, hexane or methanol. The as-prepared organized
aggregates were visualized by scanning electron microscopy
(SEM) on glass substrates. Unfortunately, benzotriazoles 1a
and 1e, which do not contain methoxy substituents,
precipitated as amorphous solids. However, methoxy-
substituted benzotriazoles 1c and 1f readily self-assembled
into organized aggregates, as demonstrated by the
corresponding SEM images (Fig. 8 and S5). It is noteworthy
that the aggregate of trisubstituted compound 1g showed
similar behavior to 1a and 1e, probably due to the
interdigitation of the methoxy groups.
Benzotriazoles 1c and 1f both self-assemble into well-defined
rod-like microcrystalline structures that are hundreds of
micrometers in length and ~10
ꢁm in width. These rod-like
aggregates have structured edges. The use of MeCN as the
poor solvent in the slow diffusion process of benzotriazole 1c
resulted in an amorphous material. However, in the case of
compound 1f, large flower-like structures were obtained when
MeOH was replaced by hexane or MeCN as poor solvents (Fig.
S5). Closer inspection on the ensembles that aggregate to give
these flower-like structures demonstrates that they are
constituted by superimposed lamellae in
arrangement (Fig. S5c).
a hexagonal
The outcomes obtained from the aggregation of compound 1f
indicated that the presence of polar solvents like MeOH as bad
solvent induced the formation of well-defined structures. In
contrast, the replacement of MeOH by a non-polar or less
polar solvent like hexane or acetonitrile induces the formation
of less-defined flower-like structures.
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Fig. 9 (a) X-ray crystal structure of compound 1c. (b-d) C–H···π
intermolecular interactions operating in the aggregation of
compound 1c
Fig. 10 Polarized light (PL) microscopy images of the
aggregates of 1c (a, b); and 1f (c, d) obtained by irradiating the
(Fig. 9b). The unit cell consists of two of these trimers entirety (left) or a portion (right) of the aggregate
interacting, once again, through C–H···π interactions between
the methoxy groups and one of the sp carbons of the ethynyl
linker, with the benzotrizole units rotated by 180º (Fig. 9c).
Unfortunately, the thick aggregates obtained from
benzotriazole 1f were not suitable for X-ray analysis.
The calculated dimer and the structure obtained by X-ray
analysis are consistent with one another (Fig. 5b and 9c). It can
therefore be concluded that the computational calculations,
although unable to determine the exact structure of the
aggregates, represent an excellent tool to predict the
interactions that govern the formation of aggregates and for
the design of cores with possible auto-aggregation behavior.
Fig. 11 The UV/Vis absorption and emission spectra of the
Considering the previously reported data on the optical
waveguiding features of related triazoles,9,10 we investigated
the propagation of light in the aggregates formed by
benzotriazoles 1c and 1f. These studies were carried out using
a confocal optical microscope and the aggregates of 1c and 1f
were irradiated with a laser beam. The resulting fluorescence
images were collected with a camera. Interestingly, only the
aggregates formed by benzotriazole 1c showed propagation of
the incident light along the rod-like aggregate. Thus,
propagated light was observed at the extremes of the
aggregates of 1c when the light was directed on the middle of
such aggregates (Fig. 10). However, the supramolecular
crystalline aggregates 1a-g
Table 4. Photophysical data for benzotriazole aggregates
λabs
(nm)
λem
(nm)
524
505
537
490
542
Τ[a]
Φ
(ns)
1a
1c
1e
1f
374
397
352
1.936
2.246
1.799
1.572
2.175
0.10
0.16
0.13
0.05
0.01
349 / 408 (sh)
372
1g
[a] intensity weighted average lifetime.
structure formed by 1f did not exhibit any optical waveguiding solid state spectra (both amorphous powders and crystalline
behavior and irradiation with a laser beam of the aggregates aggregates) show narrower emission ranges and lower fluorescence
formed by this benzotriazole did not result in the propagation quantum yields than the corresponding solutions, probably due to
of the incident light (Fig 10b).
the lower charge-transfer character of the excited state in the
Finally, a photophysical study of these aggregates was absence of stabilizing solvent molecules. Notably, the emission
performed. The UV/Vis absorption and emission spectra of the maxima of 1a and 1c appear red-shifted into the spectral region of
crystalline aggregates are shown in Fig. 11. The most 1e, 1f and 1g with comparable excited state lifetimes. In the case of
significant photophysical data are summarized in Table 4. 1f the emission peak is blue-shifted when compared to fluid
Interestingly, a clear vibrational progression can be observed solutions, unchanged for 1c and slightly red-shifted for 1g. It is clear
for 1e also in amorphous solid, whereas the broad, that the intermolecular interactions in the solid state affect 1a and
unstructured emission is recovered in the aggregated form. In 1e to a greater extent than for the MeO-substituted species.
general, the
Conclusions
In
summary,
after
computational
design,
2H-
benzo[d][1,2,3]triazoles were synthetized using sustainable
methods where possible, i.e., a marked decrease in the amount of
solvent employed, a reusable catalyst and microwave irradiation as
the energy source.
DFT calculations at the B397D/6-31G* level on these T-shaped
heterocyclic derivatives provided
a dimer structure that is
consistent with that determined by X-ray analysis. The findings
indicate that the compounds are able to form supramolecular
structures through CH-π interactions and H-bonding arrays.
Regarding the photophysical properties of the compounds, the
introduction of MeO groups on the phenyl rings led to
destabilization of the HOMO according to the computational results
and thus to red-shifted absorption and emission spectra.
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Concentration-dependent 1H Pulse Field-Gradient Spin-Echo (m/z determination) detection method was the threshold
(PFGSE) NMR spectroscopy indicated the absence of any tendency centroid at 50% height of the peak maximum.
to aggregation for single molecules in solution.
SEM images were obtained on a JEOL JSM 6335F microscope
As observed previously, these compounds aggregate in the solid working at 10 kV. The samples for SEM imaging were prepared
state – as determined by the slow diffusion technique on using by a controlled precipitation using the appropriate solvent or
CHCl3 as good solvent and a variety of poor solvents such as by slow diffusion by using mixtures of solvents, depending on
acetonitrile, hexane or methanol. The as-prepared organized their solubility properties (see the corresponding Figure
aggregates were visualized by scanning electron microscopy (SEM) Caption for a detailed description). The corresponding solid
on glass substrates and this demonstrated the influence exerted by was deposited onto a glass substrate and the remaining
the peripheral substitution on the morphology of these aggregates. solvent was evaporated slowly.
Methoxy-substituted benzotriazoles 1c and 1f self-assemble to form PL
photomicrographs
and
optical
waveguide
thick and crystalline needle-like structures. However, SEM images photomicrographs were obtained on
a
Zeiss Axioplan-2
show that the unsubstituted triazoles give rise to flower-like microscope with a CCD camera. A laser with an excitation
aggregates. It is noteworthy that the aggregate of compound 1g source of 488 or 532 nm wavelength was employed for the
shows similar behavior, probably due to the interdigitation of the measurements. Illumination of the aggregates of
1 with a laser
methoxy groups. beam generated a strong emission in the irradiated area. In
Interestingly, the aggregates formed by benzotriazole 1c exhibit addition, a brilliant emission point was clearly observed at the
waveguide properties that allow the propagation of incident light extremes/edges of the aggregates due to the propagation of
along the rod-like aggregate. Thus, propagated light is observed at laser light.
the extremes of the aggregates of 1c when the light is directed onto
the middle of such aggregates
Photophysical Data
Absorption spectra were measured on a Varian Cary 5000
double-beam UV-Vis-NIR spectrophotometer and were
baseline-corrected. Steady-state excitation and emission
spectra were recorded on a FluoTime300 spectrometer from
PicoQuant equipped with a 300 W ozone-free Xe lamp (250–
900 nm), a 10 W Xe flash-lamp (250–900 nm, pulse width <
10µs) with repetition rates of 0.1–300 Hz, an excitation
monochromator (Czerny-Turner 2.7 nm/mm dispersion, 1200
grooves/mm, blazed at 300 nm), diode lasers (pulse width < 80
ps) operated by a computer-controlled laser driver PDL-820
(repetition rate up to 80 MHz, burst mode for slow and weak
decays), two emission monochromators (Czerny-Turner,
selectable gratings blazed at 500 nm with 2.7 nm/mm
dispersion and 1200 grooves/mm, or blazed at 1250 nm with
5.4 nm/mm dispersion and 600 grooves/mm), Glan-Thompson
polarizers for excitation (Xe-lamps) and emission, a Peltier-
thermostatized sample holder from Quantum Northwest (–40
°C–105 °C), and two detectors, namely a PMA Hybrid 40
(transit time spread FWHM < 120 ps, 300–720 nm) and a
R5509-42 NIR-photomultiplier tube (transit time spread FWHM
1.5 ns, 300–1400 nm) with external cooling (–80 °C) from
Hamamatsu. Steady-state and fluorescence lifetimes were
recorded in TCSPC mode by a PicoHarp 300 (minimum base
Experimental
General methods. Reagents were used as purchased. All air-
sensitive reactions were carried out under an argon
atmosphere. Microwave irradiations were performed in a
Discover® (CEM) focused microwave reactor. Measurements
and temperature control were performed with an infrared
reader and parameters were recorded using the program
designed by CEM. Flash chromatography was performed using
silica gel (Merck, Kieselgel 60, 230–240 mesh or Scharlau 60,
230–240 mesh). Analytical thin layer chromatography (TLC)
was performed using aluminium-coated Merck Kieselgel 60
F254 plates. NMR spectra were recorded on a Varian Unity 500
(1H: 500 MHz; 13C: 125 MHz) spectrometer at 298 K using
partially deuterated solvents as internal standards. Coupling
constants (J) are denoted in Hz and chemical shifts (δ) in ppm.
Multiplicities are denoted as follows: s = singlet, d = doublet, t
= triplet, m = multiplet, br = broad.
MALDI-TOF mass spectra were measured on a Bruker Autoflex
II TOF/TOF spectrometer (Bremen, Germany) using dithranol
as the matrix. Samples co-crystallized with the matrix on the
probe were ionized with a nitrogen laser pulse (337 nm) and
accelerated under 20 kV with time-delayed extraction before
entering the time-of-flight mass spectrometer. Matrix (10
mg/mL) and sample (1 mg/mL) were separately dissolved in
methanol and mixed in a matrix/sample ratio ranging from
100:1 to 50:1. Typically, a 5 μL mixture of matrix and sample
resolution
4 ps). Emission and excitation spectra were
corrected for source intensity (lamp and grating) by standard
correction curves. Lifetime analysis was performed using the
commercial FluoFit software. The quality of the fit was
assessed by minimizing the reduced chi-squared function (χ2)
and visual inspection of the weighted residuals and their
autocorrelation. Luminescence quantum yields were measured
with a Hamamatsu Photonics absolute PL quantum yield
measurement system (C9920-02) equipped with a L9799-01
CW Xenon light source (150 W), monochromator, C7473
photonic multi-channel analyzer, integrating sphere and
was applied to
a MALDI-TOF MS probe and air-dried.
MALDITOF MS in positive reflector mode was used for all
samples. External calibration was performed by using Peptide
Calibration Standard II (covered mass range: 700–3200 Da),
Protein Calibration Standard I (covered mass range: 5000–
17500 Da) and Protein Calibration Standard II (covered mass
range: 20000–70000 Da) from Care (Bruker). The applied peak
employing
U6039-05
PLQY
measurement
software
8 | J. Name., 2012, 00, 1-3
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ARTICLE
(Hamamatsu Photonics, Ltd., Shizuoka, Japan). All solvents chromatography, eluting with hexane/ethyl acetate (9:1), to give
used were of spectrometric grade.
analytically pure products 1.
2-Phenyl-4,7-bis(phenylethynyl)-2H-benzo[d][1,2,3]triazole
(1a): From 4,7-dibromo-2-phenyl-2H-benzo[d][1,2,3]triazole
Computational study
All calculations included in this paper were carried out using
(3a) (0.100 g, 0.28 mmol), ethynylbenzene (4a) (0.058 g, 0.56
the GAUSSIAN 0922 series of programs. In order to include mmol), DBU (0.086 g, 0.56 mmol), CuI (0.003 g, 0.014 mmol)
electron correlation at a reasonable computational cost, and Pd-EncatTM TPP30 (0.025 g, 0.009 mmol), derivative 1a
Density Functional Theory (DFT)23 was used. The structures (0.083 g, 75%) was obtained as an orange solid. M. p.: 100–102
were fully optimized by means of the B97D16 method with the ºC. 1H-NMR (CDCl3, ppm)
δ: 8.49 (d, J = 7.8 Hz, 2H, o-NPh),
standard 6-31G(d) basis set 17 until the minima were achieved. 7.67–7.69 (m, 4H, o-Ph), 7.60 (s, 2H, H-5 and -6), 7.56 (t, J = 7.8
The nature of all the stationary points was checked by Hz, 2H, m-NPh), 7.47 (t, J = 7.8 Hz, 1H, p-NPh), 7.36–7.42 (m,
computing vibrational frequencies, and all the species were 6H, m,p-Ph). 13C-NMR (CDCl3, ppm)
δ
: 145.1, 140.1, 131.9,
found to be true potential energy minima, as no imaginary 130.6, 129.3, 128.8, 128.4, 128.3, 122.9, 121.0, 114.2, 96.7,
frequency was obtained (NImag = 0).
85.3. HRMS calcd for C28H17N3 M+ 395.465, found 395.903.
For the electronic study the equilibrium geometries were 2-Phenyl-4,7-bis((3,4,5-trimethoxyphenyl)ethynyl)-2H-
obtained using the M06-2X14 hybrid meta-GGA exchange- benzo[d][1,2,3]triazole (1c): From 4,7-dibromo-2-phenyl-2H-
correlation functional with the 6-31G(d) basis set both for benzo[d][1,2,3]triazole (3a) (0.100 g, 0.28 mmol), 5-ethynyl-
ground and first excited states. Solvent effects were estimated 1,2,3-trimethoxybenzene (4b) (0.109 g, 0.56 mmol), DBU
using the Conductor-like Polarizable Continuum Model (0.086 g, 0.56 mmol), CuI (0.003 g, 0.014 mmol) and Pd-
(CPCM)12 with dichloromethane as solvent. Excitation energies EncatTM TPP30 (0.025 g, 0.009 mmol), derivative 1c (0.133 g,
1
were calculated by time-dependent single point calculations 82%) was obtained as a yellow solid. M. p.: 85–86 ºC. H-NMR
using the M06-2x/6-311+G(2d,p) model chemistry. Vertical (CDCl3, ppm) δ: 8.49 (d, J = 7.6 Hz, 2H, o-NPh), 7.62 (s, 2H, H-5
excitation energies were calculated at the optimized ground and -6), 7.59 (t, J = 7.6 Hz, 2H, m-NPh), 7.50 (t, J = 7.6 Hz, 1H,
(Absorption) or Excited (Emission) state geometry. Molecular p-NPh), 6.93 (s, 4H, o-Ph), 3.93 (s, 12H, m-OCH3), 3.91 (s, 6H, p-
orbital contour plots were obtained using the Gausview OCH3). 13C-NMR (CDCl3, ppm)
δ: 153.0, 144.9, 140.0, 139.3,
130.6, 129.4, 129.3, 120.9, 117.7, 114.0, 109.1, 96.7, 84.3,
software.
Concentration-dependent 1H NMR experiments were carried 60.9, 56.2. HRMS calcd for C34H29N3O6 M+ 575,621 found
out for compounds 1a and 1c at 298 K. Concentration- 575.176.
dependent 1H PFGSE (Pulsed Field Gradient Spin Echo) 2-(4'-Bromo-[1,1'-biphenyl]-4-yl)-4,7-bis(phenylethynyl)-2H-
measurements were performed on compound 1c in CDCl3 at benzo[d][1,2,3]triazole (1e): From 4,7-dibromo-2-(4'-bromo-
298 K using the DOSY bipolar pulse pair stimulated echo with [1,1'-biphenyl]-4-yl)-2H-benzo[d][1,2,3]triazole (3b) (0.100 g,
convention compensation (Dbppste_cc in the Varian DOSY 0.2 mmol), ethynylbenzene (4a) (0.041 g, 0.40 mmol), DBU
package) in a concentration range from 10 mM to 75 mM. The (0.060 g, 0.39 mmol), CuI (0.002 g, 0.010 mmol) and Pd-
Doneshot pulse sequence was used for the gradient calibration EncatTM TPP30 (0.020 g, 0.007 mmol), derivative 1e (0.083 g,
1
by means of the diffusion of HDO in D2O at 298 K. The 88%) was obtained as a brown solid. M. p.: 194–196 ºC. H-
correction for gradient non-uniformity was employed to NMR (CDCl3, ppm) δ: 8.57 (d, J = 8.7 Hz, 2H, o-NPh), 7.75 (d, J =
process each spectrum. The signal intensities as a function of a 8.7 Hz, 2H, m-NPh), 7.69–7.71 (m, 4H, o-Ph), 7.62 (s, 2H, H-5
delay parameter (del2) (velocity map) were measured to and -6), 7.61 (d, J = 8.3 Hz, 2H, m-BrPh), 7.54 (d, J = 8.3 Hz, 2H,
corroborate the absence of convention using the Dbppste_cc o-BrPh), 7.40–7.42 (m, 6H, m,p-Ph). 13C-NMR (CDCl3, ppm)
δ:
pulse sequence. The same acquisition parameters were used 145.1, 140.9, 139.4, 138.7, 132.0, 131.9, 130.7, 128.8, 128.6,
for the whole concentration range: 30 increments in the 128.4, 127.7, 122.9, 122.2, 121.4, 114.1, 96.7, 85.3. HRMS
gradient strength (3000–22000), 64 averages per increment calcd for C34H20BrN3 M+ 550.459, found 550.984.
step, duration of the magnetic field pulse gradient (
a diffusion time ( ) of 40 ms, and a pre-acquisition delay of 3 s. trimethoxyphenyl)ethynyl)-2H-benzo[d][1,2,3]triazole
Reference deconvolution (FIDDLE) on CHI3 (internally added) From 4,7-dibromo-2-(4'-bromo-[1,1'-biphenyl]-4-yl)-2H-
was used to correct the line shapes.
δ) of 2 ms, 2-(4'-Bromo-[1,1'-biphenyl]-4-yl)-4,7-bis((3,4,5-
ꢀ
(1f):
benzo[d][1,2,3]triazole (3c) (0.100 g, 0.2 mmol), 5-ethynyl-
1,2,3-trimethoxybenzene (4b) (0.058 g, 0.40 mmol), DBU
Preparation
of
2-aryl-4,7-bis(arylethynyl)-2H- (0.060 g, 0.39 mmol), CuI (0.002 g, 0.010 mmol) and Pd-
benzo[d][1,2,3]triazoles. General procedure: A mixture of 2-aryl- EncatTM TPP30 (0.020 g, 0.007 mmol), derivative 1f (0.122 g,
1
the 83%) was obtained as a yellow solid. M. p.: 128–130 ºC. H-
4,7-dibromo-2H-benzo[d][1,2,3]triazole
(3)
(1
eq),
corresponding acetylene derivative (4) (2 or 3.5 eq), DBU (2 eq), CuI NMR (CDCl3, ppm)
δ
: 8.56 (d, J = 7.8 Hz, 2H, o-NPh), 7.75 (d, J =
(0.05 eq) and Pd-EncatTM TPP30 (0.035 eq) was charged under 7.8 Hz, 2H, m-NPh), 7.63 (s, 2H, H-5 and -6), 7.61 (d, J = 7.5 Hz,
argon to a dried microwave vessel. CH3CN (1 mL) was added. The 2H, m-BrPh), 7.53 (d, J = 7.5 Hz, 2H, o-BrPh), 6.93 (s, 4H, o-Ph),
vessel was closed and irradiated at 130 ºC (170 ºC in the case of 1g) 3.93 (s, 12H, m-OCH3), 3.91 (s, 6H, p-OCH3). 13C-NMR (CDCl3,
for 20 min. The crude product was purified by column ppm) δ: 153.1, 145.1, 141.0, 139.4, 139.3, 138.6, 132.1, 130.8,
128.6, 127.8, 122.3, 121.5, 117.7, 113.9, 109.2, 96.9, 84.3,
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61.0, 56.2. HRMS calcd for C40H32BrN3O6 M+ 730.615, found
729.147.
2010, 22, 2159-2163; (c) M. L. Tang and Z. N. Bao, Chem.
Mater., 2011, 23, 446-455.
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2012, 51, 3556-3561.
A. Díaz-Ortiz, P. Prieto, J. R. Carrillo, I. Torres and R. Martín,
Curr. Org. Chem., 2015, 19, 568-584.
(a) T. Yasuda, K. Namekawa, T. Iijima and T. Yamamoto,
Polymer, 2007, 48, 4375-4384; (b) L.-R. Tsai and Y. Chen,
Macromolecules, 2007, 40, 2984-2992; (c) G. Aromí, L. A.
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Mamykin, R. R. Muslukhov, G. F. Iskhakova, S. P. Ivanov, S. A.
Meshcheryakova, E. E. Klen, F. A. Khaliullin and V. P. Kazakov,
Russ. J. Gen. Chem., 2011, 81, 1203-1210.
5
6
4,7-Bis((3,4,5-trimethoxyphenyl)ethynyl)-2-(4'-((3,4,5-
trimethoxyphenyl)ethynyl)-[1,1'-biphenyl]-4-yl)-2H-
benzo[d][1,2,3]triazole (1g): From 4,7-dibromo-2-(4'-bromo-
[1,1'-biphenyl]-4-yl)-2H-benzo[d][1,2,3]triazole (3c) (0.100 g,
0.2 mmol), 5-ethynyl-1,2,3-trimethoxybenzene (4b) (0.115 g,
0.69 mmol), DBU (0.060 g, 0.39 mmol), CuI (0.002 g, 0.010
mmol) and Pd-EncatTM TPP30 (0.020 g, 0.007 mmol), derivative
1g (0.053 g, 38%) was obtained as a pale yellow solid. M. p.:
7
8
145–146 ºC. 1H-NMR (CDCl3, ppm)
δ: 8.58 (d, J = 8.7 Hz, 2H, o-
NPh), 7.82 (d, J = 8.7 Hz, 2H, m-NPh), 7.64–7.69 (m, 4H, Harom),
7.63 (s, 2H, H-5 and -6), 6.93 (s, 4H, o-Ph), 6.81 (s, 2H, o-Ph),
3.93 (s, 12H, OCH3), 3.91 (s, 6H, OCH3), 3.90 (s, 6H, OCH3), 3.89
(s, 3H, OCH3). 13C-NMR (CDCl3, ppm)
δ: 153.2, 153.1, 145.2,
9
D. Cáceres, C. Cebrián, A. R. Rodríguez, J. R. Carrillo, A. Díaz-
Ortiz, P. Prieto, F. Aparicio, F. García and L. Sánchez, Chem.
Commun., 2013, 49, 621-623.
141.4, 139.5, 139.4, 139.3, 139.0, 132.1, 130.9, 127.9, 127.0,
122.9, 121.5, 118.1, 117.8, 114.0, 109.2, 108.9, 96.9, 90.7,
88.2, 84.4, 61.1, 61.0, 56.3, 56.2. HRMS calcd for C51H43N3O9
M+ 841.917, found 841.299.
10 M. J. Pastor, I. Torres, C. Cebrián, J. R. Carrillo, A. Díaz-Ortiz, E.
Matesanz; J. Buendía, F. García, J. Barberá, P. Prieto and L.
Sánchez, Chem.–Eur. J., 2015, 21, 1795-1802.
11 (a) W. Koch and M. C. Holthausen, A Chemist's Guide to Density
Functional Theory, (Ed. Wiley-VCH Verlag GmbH) Weinheim,
Germany, 2001; (b) C. J. Cramer, Essentials of Computational
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Germany, 2014.
Acknowledgements
Financial support from the MINECO of Spain (projects
12 (a) A. Klamt and G. J. Schürmann, J. Chem. Soc., Perkin Trans. 2,
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CTQ2012-35692
and
CTQ2014-52331-R),
Junta
de
Comunidades de Castilla-La Mancha (FEDER funded project
PEII-2014-002-A), and DFG (SFG-TRR 61, project C07) is
gratefully acknowledged. I. Torres and R. Martín are indebted
to MEC for a FPU studentship. M. V. G. thanks the MINECO of
Spain for funding her contract through the Ramón y Cajal
program and Parque Científico y Tecnológico de Castilla-La
Mancha. Moreover, the technical support from High
Performance Computing Service of University of Castilla-La
Mancha is gratefully acknowledged.
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DOI: 10.1039/C6RA02473D
Self-assembly of T-shape 2H-benzo[d][1,2,3]-triazoles.
Optical wadeguide and photophysical properties.
I. Torres,a J. R. Carrillo,a A. Díaz-Ortiz,a R. Martín,a M. V. Gómez,a
L. Stegemann,b C. A. Strassert,b J. Orduna,c J. Buendía,d
E. E. Greciano,d J. S. Valera,d E. Matesanz,e L. Sánchez* d and P. Prieto* a