Photophysical tuning of the aggregation-induced emission of a series of para-substituted aryl bis(imino)acenaphthene zinc complexes

Article abstract of DOI:10.1039/c5dt01529d

Bis(imino)acenaphthene (BIAN) zinc complexes with para-substituted aryl groups have been synthesized and investigated from the standpoint of their photophysical properties. Each complex was found to be nonemissive in solution. However, complexes 1-6 turne

Full text of DOI:10.1039/c5dt01529d

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Photophysical Tuning of the Aggregation-
Induced Emission of a Series of para-
Substituted Aryl Bis(imino)acenaphthene Zinc
Complexes
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
Daniel A. Evans,a Lucia Myongwon Lee,b Ignacio VargasꢀBaca,b Alan H.
Cowley,a
DOI: 10.1039/x0xx00000x
www.rsc.org/
Bis(imino)acenaphthene (BIAN) zinc complexes with paraꢀsubstituted aryl groups have been synthesized
and investigated from the standpoint of their photophysical properties. Each complex was found to be
nonemissive in solution. However, complexes 1-6 turned out to be emissive in the solid state, while
complexes 7 and 8 remained nonemissive. The emissions for complexes 1-8 displayed color tunability
ranging from redꢀyellow. A detailed crystallographic study of the “asꢀsynthesized” structures revealed a
distinct difference in the crystal packing environments of the emissive and nonemissive complexes.
Furthermore, a solvatomorphic study provided further emission tunability via changes in the crystal
packing environments of each solvatomorph. Lastly, TDꢀDFT calculations were performed in order to
investigate the effect of different paraꢀsubstituents on the flanking aryl rings of the BIAN ligand.
fascinating phenomenon that is now known as aggregationꢀ
induced emission (AIE). In turn, AIE has been shown to be a
Introduction
viable option for circumvention of the problems that are
typically encountered in the fabrication of solid state emissive
materials.7–9 As a consequence, the obstacle of ACQ, that
heretofore had arrested the development of OLED technologies,
could now be overcome by the utilization of AIE materials.
Moreover, in a more recent study by Tang et al., the color
tunability of pyran based AIE active compounds was achieved
by means of similar chemical modifications.10 Furthermore, in
a related study by Chujo and Kokado, the emissive properties
The design and fabrication of organic light emitting diodes
(OLEDs) for use in solid state optoelectronic devices is one of
the most rapidly advancing fields of current research today.1 A
significant advantage of OLED technologies relates to the facile
solution based tunability of the organic emissive layer by
means of chemical modification. Moreover, the availability of
such chemical modifications of the small molecule organic
emissive layer allows for a variety of luminescent properties to
be achieved within a single chemical framework, an outcome
that is not possible with semiconductor LED materials. The
viability of this approach was elegantly demonstrated by
Anzenbacher et al., who succeeded in tuning the emission of
the ubiquitous tris(8ꢀquinolinate)Al(III) (Alq3) complex,
thereby achieving excellent color tunability that spanned the
entire visible spectrum from red to blue emission.2,3 The
foregoing result was made possible by the installation of
electron donating/withdrawing groups in the C5 position of the
quinolinate ligand, thereby permitting manipulation of the
HOMOꢀLUMO gap. In turn, the use of the foregoing chemical
modifications resulted in the generation of distinct emissive
properties for each Alq3 derivative. Furthermore, photophysical
tunability of this type has emerged as a viable method for the
development of solid state OLED technologies.4,5
of a diphenylꢀoꢀcarborane were manipulated successfully by the
installation of electronic donating/withdrawing groups on the
periphery of the ligand framework. Additionally, full color
emission was achieved by electronic tuning of the diphenylꢀoꢀ
carborane ligand framework.11 Given these promising
preliminary results, it seemed clear that the further development
of colorꢀtunable AIE compounds could result in significant
technological improvements in solid state optoelectronic
devices.
The stereoelectronic tunability and excellent redox properties
of the bis(imino)acenaphthene (BIAN) ligand class has
rendered such compounds very useful in the contexts of
synthetic, structural, and catalytic chemistry.12 Interestingly,
there are only a few instances in which BIAN ligands have
been used for photoluminescent applications.13–16 However, in a
recently published study from our laboratory, it was reported
that the BIAN ligand can be used as a support for AIE
materials.17 In this particular study, the emissions of a series of
methylated aryl substituted BIAN (ArꢀBIAN) zinc complexes
Although the majority of organic based emissive materials
are highly luminescent in solution, they frequently suffer from a
dramatic decrease in emission intensity in the solid state, a
problem that is typically referred to as aggregationꢀcaused
quenching (ACQ).6 ACQ is particularly troublesome for the
fabrication of solid state optoelectronic devices since the
emissive material is typically quenched upon formation of its
aggregate state. Fortunately however, Tang et al. discovered the
with flanking
Me), 2,4,6ꢀtrimethylphenyl (Mes), and
p
ꢀmethylphenyl (4ꢀMe), 3,5ꢀdimethylphenyl (3,5ꢀ
ꢀmethylphenyl (2ꢀMe)
o
substituents were investigated. It was discovered that the
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emissions from these complexes were quenched in solution and trifluoromethyl (4ꢀCF3) substituents. Although the 4ꢀOMe18, 4ꢀF19,
21
only became emissive in the aggregated state. Furthermore, on 4ꢀBr20, and 4ꢀCF3 BIAN ligands had been synthesized previously,
the basis structural studies that were supported by subsequent their luminescent properties had not been investigated. Furthermore,
DFT calculations, it became evident that the foregoing in order to broaden the scope of the present study the new 4ꢀOBu, 4ꢀ
emissions resulted from the intramolecular πꢀstacking dimeric SMe, 4ꢀOPh, and 4ꢀOCF3 BIAN complexes were synthesized and
interactions that were present in the crystal lattices of the para added to the list of complexes to be examined.
and meta substituted complexes. Interestingly however, the
The synthesis of each ArꢀBIAN zinc complex was performed by
ortho substituted complexes exhibited different packing means of a facile condensation reaction, the details of which have
environments, presumably due to steric effects, and hence did already been described in the literature (Scheme 1).22 The ArꢀBIAN
not feature this specific interaction. As a consequence, these Zn(II) chloride complex was generated as a precipitate that had
complexes were found to be nonemissive in the solid state. formed during the condensation reaction in acetic acid. Complexes
(Figure 1).
1ꢀ8 were synthesized in high yields and isolated as dark red to
yellow crystalline powders, the photophysical properties of which
were subsequently investigated.
Initially, the absorption properties of complexes 1ꢀ8 were assessed
by means of UV/vis absorption spectroscopy studies that were
carried out in DCM solution (Figure 2). As displayed in Figure 2,
each spectrum for complexes 1ꢀ8 featured similar absorption bands.
In accord with previously published BIAN UV/vis studies, the high
energy bands (< 350 nm) were assigned to πꢀπ* transitions that stem
from both the aryl moieties and the naphthalene backbone.23–25
Based on the TDꢀDFT studies reported by ZysmanꢀColman et al.,26
the lower energy bands can be tentatively assigned to intraligand
charge transfers (ILCT) that emanate from the flanking aryl
substituents and the naphthalene backbone. A summary of the
pertinent UV/vis absorption spectroscopic data is presented in Table
1.
Figure 1. Emissive behavior of methylated ArꢀBIAN Zinc(II)
chloride complexes.17
The methylated aryl substituents discussed above were selected in
order to investigate and thereby determine the origins of the
emissions from the BIAN zinc complexes while holding the
electronics of each sample constant. Accordingly, the overall
objective of the present work was to investigate the effects that
electronic and structural modifications could have on the solid state
photoluminescent properties of a series of BIAN zinc complexes.
Results and Discussion
Photophysical Properties of ArꢀBIAN Complexes 1ꢀ8
NH2
Acetic Acid
+ 2
ZnCl2
Figure 2. UV/Vis absorption spectra of 1ꢀ8 in DCM solution. A
photograph of each solution was taken in both ambient light and also
under UV irradiation.
O
O
R
N
N
R
Reflux
1 h
Zn
R
Cl
Cl
Table 1. Solution based UV/vis data for complexes 1ꢀ8.
R = butoxy (1), methoxy (2), methylthio (3), phenoxy (4), fluoro (5),
bromo (6), trifluoromethoxy (7), trifluoromethyl (8)
Complex
ꢀmax
ꢁ
(nm)
(x 104 Mꢀ1 cmꢀ1)
1.49, 1.19, 1.60, 4.06
1.14, 0.98, 1.10, 3.46
1.30, 1.24, 5.78
1.30, 1.17, 1.46, 4.44
0.47, 1.23, 2.99
0.49, 1.15, 2.80
0.43, 1.44, 3.02
0.28, 1.44, 2.93
Scheme 1. Syntheses of ArꢀBIAN zinc chloride complexes 1ꢀ8.
1
2
3
4
5
6
7
8
484, 411, 298sh, 262
478, 408, 315sh, 264
495, 307, 260
467, 405, 315, 263sh
435, 333, 263
440, 333, 267
428sh, 328, 263sh
423sh, 327, 271
The photoluminescent behavior of a series of methylated Arꢀ
BIAN zinc(II) chloride complexes has already been explored and
reported in a preliminary publication from our laboratory.17 Given
that the results proved to be interesting, it was decided to expand this
study to include a significantly broader series of ArꢀBIAN zinc(II)
chloride complexes. Accordingly, the present work is focused on
tuning of the electronic properties of a series of para substituted aryl
substituents. The electronic series of aryl substituents that were
employed in this investigation comprise the 4ꢀbutoxy, (4ꢀOBu), 4ꢀ
methoxy (4ꢀOMe), 4ꢀmethylthio (4ꢀSMe), 4ꢀphenoxy (4ꢀOPh), 4ꢀ
fluoro (4ꢀF), 4ꢀbromo (4ꢀBr), 4ꢀtrifluoromethoxy, (4ꢀOCF3), and 4ꢀ
2 | J. Name., 2015, 00, 1-3
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Figure 3. (TopꢀLeft) Solid state UV/vis diffuse reflectance spectra for complexes 1ꢀ8. (TopꢀRight) Solid state emission spectra for
complexes 1ꢀ8. (BottomꢀLeft) Hammett relationship between the ꢂp value and the ꢀmax value in the absence of the 4ꢀSMe outlier. (Bottomꢀ
Center) Hammett relationship between the ꢀmax and ꢂp values including the 4ꢀSMe outlier. (BottomꢀRight) Photographs of complexes 1ꢀ8 in
ambient light and under UV irradiation.
Table 2. Solid state diffuse reflectance UV/Vis spectroscopic data complex 3 which displayed a significantly redꢀshifted emission. A
for complexes 1ꢀ8.
summary of the pertinent solid state UV/vis reflectance
spectroscopic data is presented in Table 2.
Complex
ꢀmax
Intensity
(Kubelka-Munk)
10.24
%w/w of
BaSO4
The next phase of the work was focused on the
photoluminescence properties of 1ꢀ8. As displayed in Figure 2, all
eight complexes were found to be nonemissive in DCM solution.
Interestingly, however, complexes 1ꢀ6 turned out to be emissive in
the solid state, while complexes 7 and 8 retained their nonemissive
behavior (Figure 3). The emissions of complexes 1ꢀ6 were identified
as being phosphorescent based on their microsecond lifetimes (ꢃ).
Furthermore, the emissions of the foregoing complexes also
exhibited relatively low absolute quantum yields (ꢄ).
Interestingly, the emissions that were detected for complexes 1ꢀ6
exhibited an overall color tunability that changed progressively from
red to orange to yellow. This particular tunability was achieved by
modification of the electronic properties of the paraꢀsubstituted aryl
substituents. Overall, it was found that electron donating groups such
as 4ꢀBuO, 4ꢀMeO, and 4ꢀSMe exhibited emissions in the red region
of the spectrum. On the other hand, the 4ꢀOPh and 4ꢀF substituted
(nm)
514
517
540
502
501
493
446
452
1
2
3
4
5
6
7
8
50
50
50
90
90
90
90
90
11.36
13.67
9.38
9.34
7.25
2.36
2.79
Inspection of the solid state diffuse reflectance spectra for
complexes 1ꢀ8, revealed that complexes 1ꢀ6 exhibited intense broad
absorption peaks. On the other hand, complexes 7 and 8 featured less
intense blue shifted peaks in comparison with those of complexes 1ꢀ
6. The latter absorption bands blue shifted progressively as the
electron withdrawing character increased. The sole exception was
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complexes exhibited orange based emissions. Finally, the 4ꢀBr nonꢀsolvent hexanes.
substituted complex was found to display a yellow based emission.
A
representative example of an AIE
experiment with a DCM solution (~10ꢀ4 M) of 1 is presented in
Figure 4. Further details regarding the AIE experiments of 2ꢀ6 can
be found in the Supplementary Information.
Table 3. Solid state emission data for complexes 1ꢀ8.
As evident from Figure 4, the DCM solution of complex 1 was
found to be nonemissive in the DCM/hexanes fraction range of
100% DCM to 50% DCM : 50 % hexanes. These volumetric
fractions were completely translucent. However, upon formation of
the 40% DCM : 60 % hexanes mixture, complex 1 began to
precipitate. This particular fraction exhibited a very faint emission as
evident from both the photographs and also from the emission
spectra that are presented in Figure 4. However, the emission was
found to be intensified in the range of the 30% DCM : 70% hexanes
to 10% DCM : 90 % hexanes, at which point the precipitation had
increased significantly.
Complex
ꢀem
(nm)
634
620
682
606
589
574
ꢀꢀꢀ
ꢀex
(nm)
470
470
470
470
470
470
ꢀꢀꢀ
ꢃ
(ꢁs)
ꢄ (%)
(Absolute)
1.06 ± 0.09
1.20 ± 0.05
1.33 ± 0.18
1.30 ± 0.08
1.72 ± 0.03
1.80 ± 0.06
ꢀꢀꢀ
1
2
3
4
5
6
7
8
3.12 ± 0.70
4.04 ± 0.96
1.24 ± 0.66
4.01 ± 1.39
4.38 ± 1.29
2.43 ± 0.66
ꢀꢀꢀ
ꢀꢀꢀ
ꢀꢀꢀ
ꢀꢀꢀ
ꢀꢀꢀ
As evident from Table 3, the emissions for complexes 1ꢀ6
followed a general trend, namely that as the electron withdrawing
strength of the paraꢀsubstituted flanking aryl group increased, the
emission progressively underwent a blue shift. In order to confirm
Single Crystal Xꢀray Diffraction Studies of 1ꢀ8
Subsequent to probing the photophysical properties of each
complex, the question that had arisen as to why complexes 7 and 8
were found to be nonemissive both in solution and also in the solid
state remained unanswered. In our previous study involving
methylated ArꢀBIAN complexes, the nature of the solid state
structure was found to have a strong influence on the emissive
properties of each BIAN complex.17 The subsequent use of TDꢀDFT
calculations revealed the existence of an intramolecular electron
excitation that took place between the πꢀπ interactions of the two
adjacent naphthalene units in the 4ꢀMe BIAN zinc chloride complex.
Furthermore, the transition density of this intermolecular excitation
was used to visualize the T1 ꢀ S0 transition that was delocalized
across an intermolecular πꢀπ stacked dimer. The nonemissive
complexes that were investigated in our previous study did not
feature this intramolecular arrangement in their crystal packing
environments. Interestingly, our previous study was based on a steric
congestion hypothesis, namely, that the orthoꢀsubstituted complexes
inhibit the aforementioned intramolecular interactions due to steric
repulsion. On the other hand, the less sterically bulky para and metaꢀ
substituted complexes permit the foregoing intermolecular πꢀπ
interactions. However, since complexes 1ꢀ8, feature very similar
steric properties, this cannot be the factor that is responsible for the
emissive/nonemissive behavior. Accordingly, it became necessary to
conduct a thorough structural analysis of each complex in order to
determine if structural differences were apparent between the
emissive and nonemissive complexes in question.
and quantify this observation,
a Hammett relationship was
investigated with the objective of determining whether a correlation
existed between the ꢂp and ꢀmax values of the emissions. As
displayed in Figure 3, if the 4ꢀSMe substituted complex 3 is omitted
from the series, complexes 1, 2, 4, 5, and 6 were found to exhibit a
linear Hammett relationship between the ꢂp value and the ꢀmax of
each emission. This relationship was confirmed on the basis of a
Pearson regression value of R2 = 0.984. However, if the 4ꢀSMe
substituted complex 3 is included in this series it is clearly an outlier
with a new Pearson regression value of R2 = 0.486. Overall, complex
3 exhibited both significantly red shifted absorption and emission
peaks with respect to the ꢂp value when compared with those of the
other complexes in this series.
Akin to the work described in our previous publication,17
recrystallization of this class of complexes was found to be
particularly sensitive to the nature of the solvent that had been used
for recrystallization. Fortunately, however, the crystalline powders
that had precipitated directly from the acetic acid reaction mixture
proved to be suitable for a series of single crystal Xꢀray diffraction
experiments with complexes 1ꢀ8. The sole absence to this series was
complex 6. This omission is attributable to the fact that it was not
possible to obtain a single crystal directly from the aforementioned
precipitation reaction. Nevertheless, analysis of the “asꢀsynthesized”
crystalline powder of each complex provided a useful insight into the
initial structure of each complex. However, since the “asꢀ
synthesized” crystalline powders could not be recrystallized for fear
of altering their initial structures via solvatomorphism, the overall
quality of the some of the structures was not high.
Figure 4. AIE emission spectra and photographs of the
DCM/hexanes volumetric fractions (~10ꢀ4 M) of 1 (the above
percentage values are relative to the DCM content).
Although the color tunability described above represented an
exciting discovery, it became necessary to employ aggregationꢀ
induced emission (AIE) experiments in order to gain further insight
into the nature of the emissions of all six complexes. With this in
mind, each BIAN zinc chloride complex was dissolved in a stock
solution of DCM and volumetric fractions were prepared with the
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Figure 5. (Top) POVꢀRay diagrams for complexes 1ꢀ5, 7 and 8 with thermal ellipsoids displayed at 50% percent probability. All hydrogen
atoms have been removed for clarity. Note however, that complexes 7 and 8 crystallized with only half of the dimeric complex in the
asymmetric unit. The expanded complex is displayed for clarity. (Bottom) Representative packing diagrams for the emissive (5) and the
nonemissive complexes (7 and 8) are also presented above.
Despite the foregoing difficulties, the crystal structures of these complexes each possess
complexes 1ꢀ5 were studied and the results thereof are presented in bipyramidal structure with respect to the zinc metal center.
Figure 5. All five of these complexes exhibit a similar tetrahedral As discussed in our previous publication, the packing environment
a dimeric bridging trigonal
geometry with respect to the zinc metal center. However, complexes of each BIAN Zn complex was found to have a significant impact on
2 and 3 both feature the presence of an acetic acid molecule in their the emissive properties of the corresponding complex.17 Therefore, it
respective lattice. On the other hand, complexes 1, 4, and 5 were is proposed that complexes 7 and 8 are nonemissive due to their
found to be nonꢀsolvated. Surprisingly, structural analyses of the different molecular geometries which in turn resulted in the
nonemissive complexes 7 and 8 led to the discovery that these formation of an overall different crystal packing environment.
complexes do not form analogous tetrahedral structures. Instead,
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Figure 6. (TopꢀLeft) Solid state emission spectra for the DCM solvatomorphs 1ꢀDCMꢀ8ꢀDCM (TopꢀRight). Photographs of all
solvatomorphs under ambient light and UV irradiation. (Bottom) POVꢀRay diagrams for solvatomorphs 1ꢀDCMꢀ8ꢀDCM with thermal
ellipsoids displayed at 50% percent probability. All hydrogen atoms have been removed for clarity. Note however, that solvatomorph 7ꢀ
DCM crystallized along with two BIAN complexes and two DCM solvent molecules in the asymmetric unit. Only one such complex is
displayed in the interest of clarity.
extended staircase array of intermolecular πꢀπ interactions between
In order to confirm the foregoing hypothesis, comparisons of the the adjacent naphthalene units. These staircase formations are
crystal packing environments of complexes 1ꢀ5 were made with attributable to the existence of close contacts that involve the
those of 7 and 8. All five of these emissive complexes were found to chloride ligands on the zinc metal center in conjunction with both of
possess crystal packing environments that were reminiscent of those the carbon atoms of the NꢀCꢀCꢀN fragment and the naphthalenic
that had been observed for the emissive BIAN complexes in our hydrogen atoms. The representative packing diagram, exhibited in
earlier study.17 Thus, each complex features a slipped stacked Figure 5, clearly displays the staircase packing formation of complex
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5. By contrast, the crystal packing environments of 7 and 8 do not
feature slipped stacked staircase dimeric πꢀπ arrangements. Instead,
each complex was found to exhibit infinite πꢀπ stacking in a
columnar formation which can, in fact be a deleterious arrangement
from the standpoint of emission.6
Photophysical Properties of the Solvatomorphs of
Complexes 1ꢀ8
Following the analysis of the “asꢀsynthesized” crystalline powder
samples (1ꢀ8), interest was generated in a solvatomorphic study. In
our previous study, different recrystallization solvents had been
employed in order to grow a series of solvatomorphs. Each
solvatomorph included a different solvent molecule in the crystal
lattice which in turn resulted in slight changes in the metrical
parameters of the crystal packing. In each case, however, these slight
modifications to the crystal packing environments resulted in
significant changes in the solid state photoluminescent properties of
each complex.
Given the foregoing result, a solvatomorphic study was performed
using DCM as the recrystallization solvent, the objective being the
formation of the DCM solvatomorphs of complexes 1ꢀ8. In each
case, the solvatomorphs (1ꢀDCMꢀ8ꢀDCM) were grown by means of
slow vapor diffusion of hexanes into a DCM solution. (It should be
noted, however, that a different DCM solvatomorph of complex 2
had been reported previously.27) Each of the resulting solvatomorphs
exhibited a tetrahedral molecular geometry with respect to the zinc
metal center. Moreover, with the exception of the 4ꢀF substituted
complex, each of the complexes incorporated a DCM solvent
molecule into the crystal lattice. Interestingly, recrystallization of the
dimeric bridged trigonal bipyramidal complexes 7 and 8 resulted in
the formation of the monomeric tetrahedral complexes that are
displayed in Figure 6.
Figure 7. Emission spectra for 5ꢀTHF and 5 with optical images
displayed under ambient light and UV irradiation (Right). (Left)
Optical and fluorescent microscope images of 5ꢀTHF and 5.
Finally, the solid state photoluminescent properties of the DCM
solvatomorphs were investigated. As displayed in Figure 6 and Table
4, it was discovered that the emissive properties of complexes 1ꢀ
DCMꢀ4ꢀDCM and 6ꢀDCM displayed somewhat similar properties
to those of the nonꢀsolvated crystalline powders, albeit in overall
higher relative quantum yields (ꢄ). Surprisingly however, complex
5
failed to incorporate
a
DCM solvent molecule upon
recrystallization, hence the photoluminescent properties remained
unchanged. Interestingly however, the previously studied
nonemissive complexes 7 and 8 were found to be emissive after
recrystallization from DCM solution. This outcome is presumably a
consequence of the formation of the slipped πꢀstacked staircase
formations in the monomeric tetrahedral DCM solvatomorphs 7ꢀ
DCM and 8ꢀDCM, both of which were absent in the respective “asꢀ
synthesized” crystalline lattices of 7 and 8
Table 4. Solid state emission data for solvatomorphs of complexes
1ꢀ8.
Complex
ꢀem
(nm)
645
631
684
625
562
564
574
576
ꢀex
(nm)
470
470
470
470
470
470
470
470
ꢃ
(ꢁs)
ꢄ (%)
(Relative)
5.99 ± 0.51
1.96 ± 0.08
3.24 ± 0.44
7.03 ± 0.43
2.89 ± 0.05
2.57 ± 0.09
1.80 ± 0.06
9.54 ± 0.32
1ꢀDCM
2ꢀDCM
3ꢀDCM
4ꢀDCM
5ꢀTHF
6ꢀDCM
7ꢀDCM
8ꢀDCM
5.13 ± 1.87
3.06 ± 1.06
3.58 ± 1.46
1.60 ± 0.57
2.12 ± 0.83
6.16 ± 1.37
3.71 ± 0.83
4.12 ± 0.70
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Computational Study
As evident from Figure 6, the 4ꢀF substituted complex failed to
incorporate DCM molecule into its crystal lattice upon
a
recrystallization from DCM. Fortunately however, recrystallization
of this complex from THF solution resulted in the isolation of a THF
solvatomorph of complex 5. As displayed in Figure 7, the
incorporation of a THF molecule into the crystal lattice had a
significant impact on the solid state emissive properties of the 4ꢀF
BIAN zinc chloride complex. The emission maximum for the THF
solvatomorph 5ꢀTHF was found to be blue shifted by approximately
30 nm in comparison with that of the nonꢀsolvated lattice of 5.
Furthermore, the inclusion of a THF solvent molecule in the crystal
lattice of 5ꢀTHF resulted in a change in the color of the emission
from orange to yellow, as displayed in Figure 7. The foregoing shift
in the emission is presumably due to changes in both the molecular
structure and the crystal packing environments of each
solvatomorph. For example, the average torsion angle between the
acenaphthene backbone and the flanking aryl rings of complexes 5
and 5ꢀTHF were found to be 53.88 and 65.21 degrees, respectively.
Overall, the differences in the emissive properties of the series of
tetrahedral solvatomorphic ArꢀBIAN zinc complexes can be best
understood by inspection of the metrical parameters of the slipped
stacked πꢀπ interactions due to the adjacent naphthalene backbones.
The foregoing differences, all of which have been visualized and
quantified, are listed in Table 5. Overall, the foregoing stacking
interactions can be separated into four components, namely, the
interplanar distance (a), the slip distance between naphthalene
centroids (b), the distance between naphthalene centroids (c), and the
slip angle between naphthalene centroids (ꢅ). The differences in
stacking interactions were most obvious in the cases of complexes 5
and 5ꢀTHF, which resulted in a large shift in ꢀmax from orange to
yellow, respectively.
Figure 8. Calculated frontier orbitals of selected ArꢀBIAN Zn
complexes. Pairs of orbitals that have similar energies are shown at
the same height for clarity. However, no degeneracy is implied.
Table 5. Calculated metrical parameters for the emissive tetrahedral
complexes: a = interplanar distance, b = the slip distance between
naphthalene centroids, c = the distance between naphthalene
centroids, ꢅ = slip angle between naphthalene centroids.
Complexes
a
b
c
ꢅ
(Å)
(Å)
(Å)
(°)
1
3.440
3.484
3.522
3.445
3.517
3.575
3.561
3.450
3.435
3.542
3.512
3.528
3.516
1.766
1.419
1.293
1.366
1.363
1.252
1.620
1.394
1.207
1.564
1.326
1.306
1.298
3.867
3.762
3.752
3.706
3.772
3.788
3.912
3.721
3.641
3.872
3.754
3.762
3.748
27.18
22.16
20.17
21.63
21.19
19.31
24.46
22.00
19.37
23.83
20.69
18.76
20.27
Figure 9. Isoꢀsurface plots of functions relevant to the first
excitation of 3. a) HOMO (0.03 a.u.); b) LUMO (0.03 a.u.);
c) transition density ρge(r) = ψg*(r)ψe(r) (0.0008 a.u.).
1ꢀDCM
2
2ꢀDCM
3
3ꢀDCM
4
4ꢀDCM
5
5ꢀTHF
6ꢀDCM
7ꢀDCM
8ꢀDCM
Timeꢀdependent density functional theory calculations in the gas
phase were carried in order to assess the ability of the substituents on
the aryl groups to tune the electronic absorption spectra of the Arꢀ
BIAN Zn complexes. The calculated parameters for the first
prominent excitation (f ≥ 0.04) for complexes 2, 3, 5, 6, and 8 are
presented in Table 6. (Note that only two excitations are presented
for complex 5 due to the small energy separation and similar
intensities). The calculated energies of the frontier orbitals of each
model are presented in Figure 8. Although this approximate method
underestimates the excitation energies by as much as 0.90 eV, the
8 | J. Name., 2015, 00, 1-3
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Journal Name
Dalton Transactions
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DOI: 10.1039/C5DT01529D
order of the excitation energies is in agreement with the
experimental observations and follows the trend of HOMOꢀLUMO
gaps. However, in each case the calculated excitation energy is
larger than the gap and the excitations are not simple twoꢀorbital
processes. As is typical for conjugated chromophores of this type,
each excitation features multiple contributions. Nevertheless, in all
cases the absorption originates from the excitation of π electrons
from the phenyl rings into the LUMO, which predominantly
contains contributions from the π*C=N orbitals. This is easier to
appreciate in the case of complex 3, the only compound for which
the HOMOꢀLUMO contribution to the first prominent excitation is
95%. The composition of the frontier orbitals and the first transition
density for this compound are displayed in Figure 9. The substituents
on the aromatic rings can influence such intramolecular charge
transfers in two ways. The first way is inductive in nature. As the
energy of the molecular orbitals decreases, the electron withdrawing
ability of the substituents increases. The second effect is a decrease
in the HOMOꢀLUMO gap that results from the interaction of
electrons of the substituents with the π manifold, which is noticeable
in the composition of the HOMO of complex 3. It is the combination
of these effects that places 8 and 3 at the extremes of the series.
Experimental
General Procedures. All reactions were performed in the
ambient atmosphere with glassware that had been oven dried
and flushed with argon gas prior to use. Each BIAN zinc
complex was synthesized according to the pertinent literature
procedures (4ꢀOMe18, 4ꢀF19, 4ꢀBr20, and 4ꢀCF321). The 4ꢀOBu,
4ꢀSMe, 4ꢀOPh, and 4ꢀOCF3 substituted ArꢀBIAN are new
complexes that have not been reported previously.
Physical Measurements. All NMR experiments were
performed at 298K on either a Varian DirectDrive instrument
(1H NMR, 599.75 MHz; 13C NMR, 150.82 MHz), a Varian
INOVA instrument (1H NMR, 499.87 MHz; 13C NMR, 125.71
MHz; 19F 469.85 MHz), an Agilent MR instrument (1H NMR,
399.77 MHz; 13C NMR, 100.52 MHz; 19F 469.85 MHz), or a
Varian Unity Instrument (1H NMR, 399.14 MHz; 13C NMR,
75.47 MHz; 19F 282.41 MHz) using residual solvent as the
internal
reference.
The
deuterated
chloroform,
dichloromethane, and dimethylsulfoxide solvents were
purchased from Cambridge Isotopes Laboratories, Inc. and
stored over 4 Å molecular sieves prior to use. The highꢀ
resolution chemical ionization mass spectral data (HRMSꢀCI)
were acquired on a Micromass Autospec Ultima mass
spectrometer. The melting points of 1ꢀ8 were determined using
a MelꢀTemp apparatus. Samples of complexes 1ꢀ8 were sent to
Midwest Microlab, LLC for C, H, and N elemental analyses.
Fluorescence Spectroscopy. All solid state fluorescence
spectroscopic data were collected on a Photon Technology
International QM 4 spectrophotometer equipped with a 6ꢀinch
diameter K SphereꢀB integrating sphere. The crystalline
powders of 1ꢀ8 were loaded into quartz EPR tubes for
measurement purposes and their chemical identities were
confirmed by powder Xꢀray crystallography. All solvatomorph
samples were loaded into quartz EPR tubes and subsequently
covered with mineral oil in order to maintain crystallinity. The
absolute quantum yield measurements were made by using a 6ꢀ
inch diameter K SphereꢀB integrating sphere. The absolute
quantum yield values were calculated by dividing the integrated
area under each emission curve by the respective excitation
peak of each sample. [(Area sample emission / (Area BaSO4 blank excitation
– Area sample excitation)]. The relative quantum yield values were
calculated based on the ratio of the emission intensities. The
intensity of the emission peak for each solvatomorph was
integrated and compared with that of the nonꢀsolvated complex
for which the absolute quantum yield had been measured
directly. All graphs were constructed using the OriginPro 9.1
Student Version 64bit program.
Table 6. Calculated parameters for the first prominent excitation (f ≥
0.04) for complexes 2, 3, 5, 6, and 8. H=HOMO, L=LUMO
Experimental
Calculated
Assignment
62% L ← H
26% L ← Hꢀ1
95% L ← H
R
4ꢀOMe
(2)
4ꢀSMe
(3)
E (eV)
Rank
1
E (ev)
1.90
f
2.59
2.50
2.85
0.15
1
4
1.61
2.09
0.35
0.07
4ꢀF
36% L ← Hꢀ1
35% L ← Hꢀ4
27% L ← Hꢀ2
(5)
5
53% L ← Hꢀ4
21% L ← Hꢀ1
11% L ← Hꢀ2
47% L ← Hꢀ4
42% L ← Hꢀ3
56% L ← H
2.24
0.07
4ꢀBr
(6)
4ꢀCF3
(8)
2.82
2.90
5
4
2.32
1.98
0.09
0.17
38% L ← Hꢀ3
Conclusions
In conclusion, the photophysical properties of eight para
ꢀ
substituted BIAN zinc chloride complexes have been examined.
All eight complexes were found to be nonemissive in solution.
However, it was discovered that complexes 1ꢀ6 exhibited color
tunable solid state emissions that range from redꢀyellow. On the
Single Crystal Xꢀray Crystallography. In the cases of
compounds 1ꢀ5, 7, and 8, suitable single crystals could be
obtained directly from each reaction mixture. Unfortunately,
however, suitable single crystals of the asꢀsynthesized complex
other hand, complexes
7 and 8 were found to be nonemissive in
both the solid state and in solution. A detailed crystallographic
study revealed the structural differences between the emissive
6
were not obtainable. Each solvatomorph crystal was grown
complexes 1ꢀ6 versus those of the nonemissive complexes
7
from the appropriate solvent. In every case, the single crystals
were removed from their respective vials, covered with mineral
oil, and mounted separately on nylon thread loops. The Xꢀray
diffraction data were collected on either an Agilent
and . The overall structural difference resulted in the
8
formation of dissimilar crystal packing environments and hence
different photophysical properties. Solvatomorphism was also
investigated as a method to further tune the solid state
emissions of complexes 1ꢀ8. Eight emissive solvatomorphic
structures were grown and their photophysical properties were
determined to be different in comparison with those of the “asꢀ
synthesized” complexes 1ꢀ8. Finally, a TDꢀDFT study was
performed in order to gain further insight into the effects that
the paraꢀsubstituted flanking aryl substituents of the BIAN
ligand had on the overall photophysical properties.
Technologies SuperNova Dual Source diffractometer using a
ꢀꢀ
focus Cu K radiation source ( = 1.5418 Å) equipped with
α
λ
collimating mirror monochromators that operated at 147 K,
133K, or 100K, or on a Rigaku AFC12 Saturn 724+ CCD
diffractometer equipped with
temperature device that operated at 100 K, or on a Rigaku
SCXꢀMini diffractometer equipped with a Rigaku XStream low
a
Rigaku XStream low
This journal is © The Royal Society of Chemistry 2012
J. Name., 2015, 00, 1-3 | 9

Dalton Transactions
Page 10 of 13
VJieowuArrtnicalelONnlainme e
ARTICLE
DOI: 10.1039/C5DT01529D
temperature device that operated at 153 K. Both Rigaku HRMS (CI, CH4): calcd for [M ꢀ Cl]+ [C32H32N2O2ZnCl]+ m/z
1
instruments used a graphiteꢀmonochromated Mo Kα radiation 575.1444; found 575.1434; H NMR (CD2Cl2): δ 1.023 (t, 6H, CH3,
source (λ = 0.71075 Å). All powder Xꢀray diffraction data were J = 7.4 Hz), 1.542 (m, 4H, CH2), 1.840 (m, 4H, CH2), 4.095 (t, 4H,
collected on an Agilent Technologies SuperNova Dual Source CH2, J = 6.5 Hz), 7.122 (d, 4H, ArꢀH, J = 9.0 Hz), 7.632 (m, 6H,
diffractometer. Crystallographic details for all the structures can ArꢀH), 7.844 (d, 2H, ArꢀH, J = 7.4 Hz), 8.191 (d, 2H, ArꢀH, J = 7.8
be found in the Supplementary Information. Data collection, Hz). 13C NMR (CD2Cl2): δ 13.58, 19.20, 31.22, 68.30, 115.68,
unit cell refinement, and data reduction were performed using 123.65, 125.39, 125.61, 128.44, 131.18, 132.26, 136.22, 144.62,
the Agilent Technologies CrysAlisPro
V
1.171.37.31 159.96, 161.41. Anal. Calcd. for C32H32N2O2ZnCl2: C, 62.71; H,
program.28 The structure of each complex was solved by direct 5.26; N, 4.57. Found: C, 62.72; H, 5.24; N, 4.62. MP = 310 °C
methods and refined by fullꢀmatrix least squares on F2 with (decomp).
anisotropic displacement parameters for all nonꢀH atoms using 4ꢀmethoxyphenylꢀBIAN Zinc Chloride (2).
A mixture of
SHELXLꢀ201329 and PLATON9830. All nonꢀhydrogen atoms acenaphthenequinone (1.00 g, 5.49 mmol) and anhydrous zinc
were refined anisotropically. The hydrogen atoms were placed chloride (2.02 g, 14.82 mmol) was suspended in 10 mL of glacial
in fixed, calculated positions with isotropic displacement acetic acid, thereby generating a yellow suspension. The yellow
parameters set at 1.2 x Ueq with respect to the attached atom suspension was heated to 60 °C and pꢀanisidine (1.55 g, 12.63
(1.5 x Ueq for methyl hydrogens). All powder XRD graphs mmol) was added, following which the resulting solution was
were constructed using the OriginPro 9.1 Student Version 64 refluxed for 1 hour. The red precipitate that had formed during the
bit program. The POVꢀRay images were created using the reaction was filtered off and washed sequentially with water and
Mercury version 3.3 program and all the crystallographic diethyl ether. The resulting red crystalline powder was collected and
details concerning the solvatomorph πꢀπ interactions were used without further purification for
a single crystal Xꢀray
calculated using the Mercury version 3.3 program.
Diffuseꢀreflectance and UV/Vis Absorption Spectroscopy
diffraction study (2.17 g, 75%).
.
HRMS (CI, CH4): calcd for [M ꢀ Cl]+ [C26H20N2O2ZnCl]+ m/z
1
All diffuseꢀreflectance measurements were performed with an 491.0505; found 491.0497; H NMR (CDCl3): δ 3.923 (s, 6H, CH3),
illuminated (tungstenꢀhalogen light source) integrating sphere 7.095 (d, 4H, ArꢀH, J = 6.8 Hz), 7.642 (m, 6H, ArꢀH), 7.818 (d, 2H,
(Ocean Optics ISPꢀREF) attached to a photodiode array ArꢀH, J = 7.3 Hz), 8.158 (d, 2H, ArꢀH, J = 8.3 Hz). 13C NMR
spectrophotometer (Ocean Optics SD 2000) and all data are (CDCl3): δ 56.11, 115.63, 124.02, 125.74, 126.07, 128.88, 131.60,
reported relative to a BaSO4 standard. Each measurement was 132.72, 136.85, 145.09, 160.72, 161.99. Anal. Calcd. for
integrated over 3 ms and corrected for stray light and dark C26H20N2O2ZnCl2·C2H4O2: C, 57.12; H, 4.11; N, 4.76. Found: C,
current. The raw data were used to calculate the reflectance (R) 57.19; H, 3.94; N, 4.67. MP = 299 °C (decomp).
using Grams/AI (version 8.0). The KubelkaꢀMunk function ([1ꢀ 4ꢀ(methylthio)phenylꢀBIAN Zinc Chloride (3). A mixture of
R]2/2R) was evaluated in Excel and the resulting spectra were acenaphthenequinone (1.00 g, 5.49 mmol) and anhydrous zinc
smoothed by calculating the weighted averages of the values at chloride (2.02 g, 14.82 mmol) was suspended in 10 mL of glacial
neighboring points using the Cauchy density function as acetic acid, thereby generating a yellow suspension. The yellow
implemented within SigmaPlot (version 9). The final suspension was heated to 60 °C and 4ꢀ(methylthio)aniline (1.57 mL,
illustration was composed in PowerPoint. All UV/Vis 12.63 mmol) was added, following which the resulting solution was
absorption experiments were performed using a Varian Vary refluxed for 1 hour. The dark red precipitate that had formed during
6000i UVꢀVISꢀNIR spectrophotometer and all UV/Vis graphs the reaction was filtered off and washed sequentially with water and
were constructed using the OriginPro 9.1 Student Version 64bit diethyl ether. The resulting dark red crystalline powder was collected
program.
and used without further purification for a single crystal Xꢀray
DFT Calculations. All DFT calculations were performed using the diffraction study (2.86 g, 93%).
ADF DFT package (version 2013).31,32 Models of the complexes 2, HRMS (CI, CH4): calcd for [M ꢀ Cl]+ [C26H20N2S2ZnCl]+ m/z
1
3, 5, 6, and 7 were built from their crystallographic coordinates and 523.0048; found 523.0032; H NMR (CDCl3): δ 2.566 (s, 6H, CH3),
fully optimized using the exchangeꢀcorrelation functional of Perdew, 7.409 (d, 2H, ArꢀH, J = 8.6 Hz), 7.580 (d, 2H, ArꢀH, J = 9.0 Hz),
Burke, and Ernzerhof33 and corrected for dispersion34 with a tripleꢀζ 7.628 (t, 2H, ArꢀH, J = 8.1 Hz), 7.409 (d, 2H, ArꢀH, J = 8.6 Hz),
allꢀelectron basis set with two polarization functions and applying 8.158 (d, 2H, ArꢀH, J = 8.6 Hz). 13C NMR (CDCl3): δ 15.56,
the Zeroth Order Regular Approximation (ZORA)35–38 formalism 122.56, 125.23, 125.94, 127.82, 128.66, 131.19, 132.48, 140.27,
with specially adapted basis sets. In the interest of expediency, the 140.75, 144.81, 161.72. Anal. Calcd. for C26H20N2S2ZnCl2·C2H4O2:
lowest 50 singletꢀsinglet electronic excitations39,40 were calculated C, 54.16; H, 3.90; N, 4.51. Found: C, 54.22; H, 3.75; N, 4.80. MP =
using timeꢀdependent density functional theory (TDꢀDFT) under the 314 °C (decomp).
Statistical Average of different model Potentials for occupied KS 4ꢀphenoxyphenylꢀBIAN Zinc Chloride (4).
A mixture of
Orbitals (SAOP)41–43
.
acenaphthenequinone (1.00 g, 5.49 mmol) and anhydrous zinc
chloride (2.02 g, 14.82 mmol) was suspended in 10 mL of glacial
Syntheses of 1ꢀ8
4ꢀbutoxyphenylꢀBIAN Zinc Chloride (1).
A
mixture of acetic acid, thereby generating a yellow suspension. The yellow
acenaphthenequinone (1.00 g, 5.49 mmol) and anhydrous zinc suspension was heated to 60 °C and 4ꢀphenoxyaniline (2.34 g, 12.63
chloride (2.02 g, 14.82 mmol) was suspended in 10 mL of glacial mmol) was added, following which the resulting solution was
acetic acid, thereby generating a yellow suspension. The yellow refluxed for 1 hour. The orangeꢀred precipitate that had formed
suspension was heated to 60 °C and 4ꢀbutoxyaniline (2.10 mL, 12.63 during the reaction was filtered off and washed sequentially with
mmol) was added, following which the resulting solution was water and diethyl ether. The resulting orangeꢀred crystalline powder
refluxed for 1 hour. The red precipitate that had formed during the was collected and used without further purification for a single
reaction was filtered off and washed sequentially with water and crystal Xꢀray diffraction study (2.41 g, 67%).
diethyl ether. The resulting red crystalline powder was collected and HRMS (CI, CH4): calcd for [M ꢀ Cl]+ [C36H24N2O2ZnCl]+ m/z
used without further purification for
diffraction study (2.94 g, 88%).
a
single crystal Xꢀray 615.0818; found 615.0816; 1H NMR (CDCl3): 7.196 (m, 10H, ArꢀH)
7.432 (tꢀd, 4H, ArꢀH, J = 7.1 Hz, J = 1.8 Hz), 7.636 (dd, 4H, ArꢀH,
J = 6.8 Hz, J = 2.2 Hz), 7.666 (t, 2H, ArꢀH, J = 7.8 Hz), 7.773 (d,
10 | J. Name., 2015, 00, 1-3
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DOI: 10.1039/C5DT01529D
2H, ArꢀH, J = 7.1 Hz), 8.186 (d, 2H, ArꢀH, J = 8.3 Hz). 13C NMR 49.05; H, 2.22; N, 4.40. Found: C, 49.40; H, 2.07; N, 4.39. MP =
(CDCl3): δ 119.40, 119.80, 123.69, 124.40, 125.26, 125.87, 128.65, 291 °C (decomp).
130.09, 131.23, 132.59, 138.20, 144.86, 156.02, 158.37, 161.83. 4ꢀ(trifluoromethly)phenylꢀBIAN Zinc Chloride (8). A mixture of
Anal. Calcd. for C36H24N2O2ZnCl2: C, 66.23; H, 3.71; N, 4.29. acenaphthenequinone (1.00 g, 5.49 mmol) and anhydrous zinc
Found: C, 66.23; H, 3.61; N, 4.30. MP = 316 °C (decomp).
4ꢀfluorophenylꢀBIAN Zinc Chloride (5).
chloride (2.02 g, 14.82 mmol) was suspended in 10 mL of glacial
mixture of acetic acid and 2 mL of toluene, thereby generating a yellow
A
acenaphthenequinone (1.00 g, 5.49 mmol) and anhydrous zinc suspension. The yellow suspension was heated to 60 °C and 4ꢀ
chloride (2.02 g, 14.82 mmol) was suspended in 10 mL of glacial (trifluoromethyl)aniline (1.59 mL, 12.63 mmol) was added,
acetic acid, thereby generating a yellow suspension. The yellow following which the resulting solution was refluxed for 1 hour. The
suspension was heated to 60 °C and 4ꢀfluoroaniline (1.20 mL, 12.63 yellow precipitate that had formed during the reaction was filtered
mmol) was added, following which the resulting solution was off and washed sequentially with water and diethyl ether. The
refluxed for 1 hour. The orange precipitate that had formed during resulting yellow crystalline powder was collected and used without
the reaction was filtered off and washed sequentially with water and further purification for a single crystal Xꢀray diffraction study (2.29
diethyl ether. The resulting orange crystalline powder was collected g, 69%).
and used without further purification for a single crystal Xꢀray HRMS (CI, CH4): calcd for [M ꢀ Cl]+ [C26H14N2F6ZnCl]+ m/z
1
diffraction study (2.33 g, 84%).
567.0041; found 567.0046; H NMR (CD2Cl2): δ 7.438 (d, 2H, Arꢀ
HRMS (CI, CH4): calcd for [M ꢀ Cl]+ [C24H14N2F2ZnCl]+ m/z H, J = 7.4 Hz), 7.679 (t, 2H, ArꢀH, J = 7.8 Hz), 7.732 (d, 4H, ArꢀH,
467.0105; found 467.012; 1H NMR (D6ꢀDMSO): δ 6.823 (d, 2H, Arꢀ J = 8.2 Hz), 7.935 (d, 4H, ArꢀH, J = 8.2 Hz), 8.259 (d, 2H, ArꢀH, J
H, J = 7.3 Hz), 7.141 (m, 4H, ArꢀH, apparent complex coupling = 8.2 Hz). 19F NMR (CD2Cl2): δ ꢀ62.83 (s, ArꢀF, 6F). 13C NMR
from fluorine), 7.360 (m, 4H, ArꢀH, apparent complex coupling from (CD2Cl2): δ 122.27, 124.24 (q, 2C, J = 272.50 Hz (F)), 124.88,
fluorine), 7.559 (t, 2H, ArꢀH, J = 7.8 Hz), 8.115 (d, 2H, ArꢀH, J = 127.06, 128.03 (q, 4C, J = 4.14 Hz (F)), 129.37, 130.97 (q, 2C, J =
8.3 Hz). 19F NMR (D6ꢀDMSO): δ ꢀ119.83 (m (apparent septet), Arꢀ 33.60 Hz (F)), 131.70, 133.71, 146.02, 147.28, 164.00. Anal. Calcd.
F, 2F). 13C NMR (D6ꢀDMSO): δ 116.53 (d, 4C, J = 22.54 Hz (F)), for C26H14N2F6ZnCl2: C, 51.64; H, 2.33; N, 4.63. Found: C, 52.04;
119.91, 123.48, 127.65, 128.12, 129.77, 130.97, 141.17, 147.17, H, 2.27; N, 4.64. MP = 370 °C (decomp).
159.60 (d, 2C, J = 240.19 Hz (F)), 160.70. Anal. Calcd. for
C24H14N2F2ZnCl2: C, 57.12; H, 2.80; N, 5.55. Found: C, 56.83; H,
2.94; N, 5.44. MP = 362 °C (decomp).
Acknowledgments
We thank the Robert A. Welch Foundation for the generous financial
support (Grant Fꢀ0003) (A.H.C.) The support of Canada’s Natural
Sciences and Engineering Research Council is also gratefully
acknowledged. Portions of this work were made possible by using
the facilities of the Shared Hierarchical Academic Research
Computing Network (SHARCNET: www.sharcnet.ca) and
Compute/Calcul Canada.
4ꢀbromophenylꢀBIAN Zinc Chloride (6).
A
mixture of
acenaphthenequinone (1.00 g, 5.49 mmol) and anhydrous zinc
chloride (2.02 g, 14.82 mmol) was suspended in 10 mL of glacial
acetic acid, thereby generating a yellow suspension. This yellow
suspension was heated to 60 °C and 4ꢀbromoaniline (2.17 g, 12.63
mmol) was added, following which the resulting solution was
refluxed for 1 hour. The dark yellow precipitate that had formed
during the reaction was filtered off and washed sequentially with
water and diethyl ether. The resulting dark yellow crystalline powder
was collected and recrystallized from dichloromethane to obtain
yellow crystals of 19. (2.92 g, 85%).
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10 H. Tong, Y. Hong, Y. Dong, Y. Ren, M. Häussler, J. W. Y. Lam,
K. S. Wong and B. Z. Tang, J. Phys. Chem. B, 2007, 111, 2000–
2007.
11 K. Kokado and Y. Chujo, J. Org. Chem., 2011, 76, 316–319.
12 N. J. Hill, I. VargasꢀBaca and A. H. Cowley, Dalton Trans.,
2008, 240–253.
13 T. Kern, U. Monkowius, M. Zabel and G. Knör, Inorganica
Chim. Acta, 2011, 374, 632–636.
HRMS (CI, CH4): calcd for [M ꢀ Cl]+ [C24H14N2Br2ZnCl]+ m/z
586.8504; found 586.8515; 1H NMR (D6 ꢀDMSO): 6.493 (d, 4H, Arꢀ
H, J = 6.7 Hz), 7.090 (d, 4H, ArꢀH, J = 6.7 Hz), 7.886 (t, 2H, ArꢀH,
J = 7.5 Hz), 8.043 (d, 2H, ArꢀH, J = 7.0 Hz), 8.401 (d, 2H, ArꢀH, J
= 8.2 Hz). 13C NMR (D6ꢀDMSO): δ 106.84, 116.47, 121.88, 129.01,
129.06, 130.92, 131.79, 132.91, 144.88, 148.17, 173.26. Anal.
Calcd. for C24H14N2Br2ZnCl2: C, 46.01; H, 2.25; N, 4.47. Found: C,
45.96; H, 2.24; N, 4.36. MP = 352 °C (decomp).
4ꢀ(trifluoromethoxy)phenylꢀBIAN Zinc Chloride (7). A mixture
of acenaphthenequinone (1.00 g, 5.49 mmol) and anhydrous zinc
chloride (2.02 g, 14.82 mmol) was suspended in 10 mL of glacial
acetic acid, thereby generating a yellow suspension. The yellow
suspension was heated to 60 °C and 4ꢀ(trifluoromethoxy)aniline
(1.69 mL, 12.63 mmol) was added, following which the resulting
solution was refluxed for 1 hour. The yellow precipitate that had
formed during the reaction was filtered off and washed sequentially
with water and diethyl ether. The resulting yellow crystalline powder
was collected and used without further purification for a single
crystal Xꢀray diffraction study (2.44 g, 70%).
HRMS (CI, CH4): calcd for [M ꢀ Cl]+ [C26H14N2O2F6ZnCl]+ m/z
598.9939; found 598.9929; 1H NMR (CDCl3): δ 7.461 (d, 4H, ArꢀH,
J = 8.3 Hz), 7.526 (d, 2H, ArꢀH, J = 7.3 Hz), 7.669 (m, 6H, ArꢀH),
8.228 (d, 2H, ArꢀH, J = 8.3 Hz). 19F NMR (CDCl3): δ ꢀ58.18 (s, ꢀ
OCF3, 6F). 13C NMR (CDCl3): δ 120.42 (q, 2C, ꢀCF3, J = 258.2 Hz),
122.67, 123.25, 124.73, 126.30, 128.94, 131.30, 133.06, 141.76,
145.42, 149.20, 163.02. Anal. Calcd. for C26H14N2O2F6ZnCl2: C,
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