Aggregation-Induced Emission of Bis(imino)acenaphthene Zinc Complexes: Photophysical Tuning via Methylation of the Flanking Aryl Substituents

Article abstract of DOI:10.1021/om501191c

Bis(imino)acenaphthene zinc complexes with methylated aryl substituents have been examined from the standpoint of their photoluminescent properties. Although complexes 1-4 proved to be nonemissive in solution, complexes 1 and 2 were found to emit via an a

Full text of DOI:10.1021/om501191c

Article
pubs.acs.org/Organometallics
Aggregation-Induced Emission of Bis(imino)acenaphthene Zinc
Complexes: Photophysical Tuning via Methylation of the Flanking
Aryl Substituents
Daniel A. Evans,† Lucia Myongwon Lee,‡ Ignacio Vargas-Baca,‡ and Alan H. Cowley*,†
†Department of Chemistry, The University of Texas at Austin, 1 University Station A5300, Austin, Texas 78712-0165, United States
‡Department of Chemistry and Chemical Biology, McMaster University, Hamilton, Ontario, Canada L8S 4M1
S
* Supporting Information
ABSTRACT: Bis(imino)acenaphthene zinc complexes with
methylated aryl substituents have been examined from the
standpoint of their photoluminescent properties. Although
complexes 1−4 proved to be nonemissive in solution,
complexes 1 and 2 were found to emit via an aggregation-
induced emission pathway. On the other hand, complexes 3
and 4 were found to be nonemissive in the solid state. Detailed
crystallographic studies of complexes 1−4 provided valuable
insights into the structural differences between the emissive (1
and 2) and nonemissive complexes (3 and 4), particularly with
respect to their molecular structures and crystal-packing
environments. TD-DFT theoretical calculations were carried
out and were found to support the hypothesis that the phosphorescent emissions of 1 and 2 are due to the existence of
intermolecular π-stacking interactions within the crystal lattices. Finally, a series of solvatomorphs of complexes 1 and 2 were
synthesized and their emissive properties were studied.
dynamic intramolecular rotations, become restricted in the solid
state. As a consequence, the foregoing restrictions of intra-
molecular rotations (RIR) provide a radiative decay pathway.6
Currently, AIE materials represent an exciting new approach to
solid-state emissive materials.7
INTRODUCTION
■
Organic-based emissive materials continue to attract significant
attention due to their applications in a variety of solid-state
optoelectronic devices.1 Unfortunately, however, the intensities
of the emissions for such materials are typically reduced in the
solid state in comparison with those of their solution-based
counterparts.2 Quenching of this type is generally attributed to
noncovalent intramolecular interactions such as π−π inter-
actions or hydrogen bonding and is commonly referred to as
“aggregation-caused quenching” (ACQ).3 In particular, ACQ
represents a serious problem for the fabrication of solid-state
optoelectronic devices. As a consequence, numerous ap-
proaches have been taken in an effort to overcome this
obstacle. One such approach involves the installation of
sterically encumbered groups in order to inhibit aggregate
formation.4 However, despite such efforts, the ACQ effect
remains a serious problem because aggregate formation is an
inherent process that takes place spontaneously upon formation
of a solid-state material.
In a major 2001 breakthrough, Tang et al. discovered
materials that exhibited enhanced emissions in the aggregate
state and referred to this type of behavior as aggregate-induced
emission (AIE).5 In contrast to the behavior of materials that
display ACQ, the propeller-shaped phenyl-substituted silole
materials synthesized by Tang et al. were found to inhibit π−π
interactions upon aggregation. Furthermore, the phenyl rotors,
which provide a nonradiative pathway in solution due to
An excellent example of the value of AIE is evident in the
elegant work of Hariharan et al.8 In this study, the pyrene
lumiphore was acylated in a stepwise fashion, thereby changing
the crystal packing environments in a controlled manner. In
turn, this stepwise acylation resulted in a steady decrease of the
interplanar angle between the adjacent pyrene units, thereby
causing an increase in π−π orbital overlap. In turn, the
foregoing structural modifications resulted in an alteration in
the crystal packing, thus effecting an overall change in the
photophysical properties of each acylated pyrene molecule.
Bis(imino)acenaphthene (BIAN) ligands are well-known
bidentate nitrogen donors that have many important
applications, most notably as ligand frameworks for the support
of olefin polymerization catalysts.9 Moreover, BIAN ligands
have been shown to possess several features that are desirable
for photophysical applications such as a π-conjugated
naphthalene backbone, structural rigidity, and the presence of
tunable flanking aryl substituents. Nevertheless, despite the
Special Issue: Mike Lappert Memorial Issue
Received: November 25, 2014
© XXXX American Chemical Society
A
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foregoing advantages, BIAN ligands have seldom been used in a
photophysical context.10 We have previously used the BIAN
ligand extensively, and therefore interest was generated in the
use of this ligand for potential photoluminescent applications.11
Accordingly, the work reported herein is focused on the
systematic tuning of a series of methylated aryl-substituted
BIAN Zn(II) complexes that exhibit solid-state photolumines-
cence via aggregation-induced emissions.
RESULTS AND DISCUSSION
■
The syntheses of the pertinent Ar-BIAN zinc complexes were
carried out by means of the facile condensation reactions of
acenaphthenequinone with two equivalents of the appropriate
methyl-substituted anilines in the presence of anhydrous zinc
chloride.12 Each of the resulting mixtures was subsequently
refluxed in acetic acid for 1 h, thus forming the corresponding
BIAN zinc complex as a precipitate. Decomplexation can be
achieved readily by refluxing each BIAN zinc complex in an
aqueous solution of potassium oxalate for an appropriate period
of time.
Figure 1. UV/vis absorption spectra of complexes 1−4 in DCM
solution.
(>350 nm) have been assigned as π−π* transitions that
emanate from both the flanking aryl groups and the
acenaphthene backbone.14 As described by Zysman-Colman
et al., on the basis of DFT calculations, the lower energy bands
were tentatively attributed to intraligand charge transfer
(1ILCT) between the flanking arlyimine fragments and the
acenaphthene backbone.15 A summary of the pertinent
solution-based UV/vis spectroscopic data is presented in
Table 1.
As mentioned previously, the free BIAN ligand platform is
used extensively. However, the BIAN zinc chloride complex
that is generated during the synthesis of the BIAN ligand is
typically viewed as merely a synthetic stepping stone that is
necessary for the preparation of the more widely used free
BIAN ligand. It therefore came as a pleasant surprise to
discover that the typically neglected BIAN zinc chloride
intermediate complexes exhibited some very interesting
photoluminescent properties.
Table 1. Solution-Based UV/Vis Spectroscopic Data for
Complexes 1−4
Scheme 1. Syntheses of Ar-BIAN Zinc Complexes 1−4
complex
λmax (nm) (ε × 104 M−1 cm−1
)
1
2
3
4
447 (0.68), 334 (1.12), 259 (2.89)
437 (0.86), 333 (1.76), 262 (4.30)
408 (0.32), 332 (1.21), 318 (1.38), 263, (4.09)
387 (0.42), 334 (1.39), 321 (1.56), 264 (4.17)
Subsequent investigations were focused on the solid-state
diffuse reflectance spectra of complexes 1−4. As displayed in
Figure 2, the reflectance spectra for all four BIAN zinc
complexes are characterized by the presence of an intense
absorption band between 450 and 550 nm. In the case of 3, the
absorption band features a prominent shoulder at 520 nm.
Interestingly, despite the similarities in their absorption spectra,
the 4-Me and 3,5-Me BIAN zinc chloride complexes were
found to exhibit yellow emissions centered at 570 and 575 nm,
respectively. On the other hand, the Mes and 2-Me BIAN zinc
complexes turned out to be nonemissive in the solid state. The
emissions from 1 and 2 were identified as being phosphor-
escent on the basis of their microsecond lifetimes (τ) both at
room temperature and also at liquid nitrogen temperature, as
displayed in Table 2. Complexes 1 and 2 exhibited low absolute
quantum yields (Φ) (see Table 2). Furthermore, all four BIAN
zinc complexes were found to be nonemissive in solution.
In order to gain further insight into the characteristics of the
emissions from complexes 1 and 2, it became necessary to
perform a series of AIE experiments. For this purpose, a
dichloromethane (DCM) stock solution of 1 was used for the
preparation of the various volumetric fractions of DCM/
hexanes, the overall objective being to confirm the existence of
an AIE mechanism for the emission of complex 1. As evident
from Figure 3, complex 1 is nonemissive in translucent DCM/
hexanes mixtures up to a volumetric ratio of 50% DCM/50%
The serendipitous discovery of the foregoing photo-
luminescent complexes prompted our investigation into an
enhanced understanding of the origin of such emissions. The
BIAN ligand platform is noted for facile tunability via
modification of the stereoelectronic properties of the flanking
aryl substituents. However, the present work is confined to the
photoluminescent properties of the BIAN complexes that
feature methylated aryl substituents, namely, p-methylphenyl
(4-Me), 3,5-dimethylphenyl (3,5-Me), 2,4,6-trimethylphenyl
(Mes), and o-methylphenyl (2-Me) substituents. The foregoing
aryl substituents were selected in order to probe the
photoluminescent properties of each individual BIAN zinc
complex while holding the electronic effects relatively constant.
The four methylated Ar-BIAN zinc chloride complexes in
question, namely, 4-Me (1), 3,5-Me (2), Mes (3), and 2-
Me(4), were synthesized according to the pertinent literature
procedures.12,13 Although these complexes had been synthe-
sized previously, their emissive properties and solid-state
structures had yet to be investigated.
Initially, the photophysical properties of complexes 1−4 were
probed by means of UV/vis absorption spectroscopy that was
carried out in DCM solution at room temperature. As exhibited
in Figure 1, each of the spectra displays similar features. In
accord with previously published studies, the high-energy bands
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Figure 2. Absorption (top) and emission (bottom) spectra of complexes 1−4 in the solid state along with optical images of these complexes under
both ambient light and UV irradiation.
Table 2. Solid-State Fluorescence Data for 1 and 2
crystal X-ray diffraction studies was obtained directly from the
precipitate that had formed in the refluxing acetic acid solution.
In contrast, satisfactory single crystals of complex 4 could be
grown by slow evaporation of a DCM solution.
Initial inspection of the crystal structures of complexes 1−4
revealed an obvious structural dichotomy between the emissive
complexes 1 and 2 and those of the nonemissive complexes 3
and 4, as evident from Figure 4. Complexes 1 and 2 were found
λem
λex
(nm)
Φ (%)
complex (nm)
τ (μs)
(absolute)
1
570
470
2.60 0.79 (298 K)
3.99 1.26 (77 K)
1.69 0.06
2
575
470
6.21 0.70 (298 K)
6.88 1.17 (77 K)
1.01 0.13
Figure 3. AIE emission spectra and photographs of the corresponding
volumetric fractions (∼10−4 M) of the DCM/hexanes mixtures of
complex 1 under ambient light and UV irradiation.
Figure 4. POV-Ray diagrams for complexes 1−4 with thermal
ellipsoids displayed at 50% probability. All hydrogen atoms have been
removed for clarity. Note, however, that complex 2 crystallized with
two molecules in the asymmetric unit. One of these molecules has
been removed for clarity.
hexanes. However, upon formation of a 40% DCM/60%
hexanes mixture, complex 1 began to precipitate and only faint
emission was detectable. Furthermore, this emission was found
to be intensified in the 30−10% DCM fractions as displayed in
Figure 3. A similar behavior was evident for the AIE experiment
that was carried out on complex 2 using a series of THF/
hexanes volumetric mixtures. Additional details regarding the
latter experiment can be found in the Supporting Information.
The question that arose regarding the origins of the solid-
state emissions of 1 and 2 (as opposed to their nonemissive
behavior in solution) was addressed by means of a series of AIE
experiments. Unfortunately, however, the acquired information
failed to provide a satisfactory explanation for the nonemissive
behavior of complexes 3 and 4 either in solution or in the solid
state. In order to address this issue, the structure−property
relationships of all four complexes were investigated by means
of single-crystal X-ray diffraction studies. Surprisingly, in the
cases of complexes 1−3, a crop of crystals suitable for single-
to exhibit average acenaphthene−aryl interplanar torsion angles
of 58.76° and 69.77°, respectively. In contrast, complexes 3 and
4 feature average acenaphthene−aryl interplanar torsion angles
of 80.47° and 81.79°, respectively. The foregoing differences in
the molecular structures could be attributed to the presence of
methyl groups on the 2- and/or 6-positions of the flanking aryl
substituents of complexes 3 and 4, which are of course absent
in the cases of 1 and 2. In turn, the presence of the latter
methyl substituents restricts the rotation of the flanking aryl
rings. In contrast to the behavior of complexes 1 and 2, the
restricted intramolecular rotations of 3 and 4 orient the flanking
aryl substituents and the naphthalene backbone in a virtually
orthogonal manner.
As a consequence of the presence of different methylated aryl
substituents, the crystal packing environments for complexes
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1−4 fall into two distinct catagories. As displayed in Figure 5,
complexes 1 and 2 are closely packed and feature parallel
Figure 6. Transition density for the first triplet → singlet transition.
Polymorphism represents an effective way of tuning the
photophysical properties of solid-state materials by engineering
the crystal packing environments. Not surprisingly, this
approach has been used extensively as a successful pathway
for tunability.17 Moreover, in related work, solvatomorphism
has been employed for effecting subtle changes in the solid-
state luminescent properties by the incorporation of different
solvent molecules into the crystal lattice.18
Figure 5. Crystal packing diagrams for complexes 1−4.
Surprisingly, four solvatomorph structures could be grown
for each complex merely by changing the solvent that was used
for recrystallization. As displayed in Figure 7, each solvato-
displaced, head-to-tail π−π stacking. Moreover, complex 1
comprises an extended array of π−π stacking columns that are
arranged in an overall staircase motif. Furthermore, the latter
staircase formation packs in a head-to-tail fashion as a result of
the π−π stacking of two naphthalene units in conjunction with
a close contact interaction between a chlorine atom and both
carbons of the N−C−C−N fragment. Similarly, complex 2 also
packs in a parallel displaced π−π stacking motif along with two
other BIAN complexes that flank this arrangement in an
orthogonal manner. The foregoing face-to-face π−π stacking of
the naphthalene moieties is known to be conducive to excimer
formation.16
Interestingly, complexes 3 and 4 do not involve π−π stacking
and consequently pack in a less dense, herringbone fashion. As
mentioned earlier, the ortho-substituted aryl groups orient the
molecular structure in an orthogonal fashion. In turn, this
orthogonal orientation apparently inhibits π−π stacking due to
the existence of steric repulsion. By contrast, steric repulsion of
this type is absent in complexes 1 and 2; hence these complexes
possess more acute interplanar aryl-acenaphthene torsion
angles. Overall, the differences in these torsion angles result
in the formation of a less dense crystal packing environment for
both 3 and 4 in comparison with those for 1 and 2.
Collectively, the herringbone packing environments of 3 and
4 do not feature π−π stacking and could therefore inhibit
excimer formation, thus resulting in nonemissive behavior.
In an effort to further elucidate the nature of the emissions
from complexes 1 and 2, it became desirable to carry out some
pertinent theoretical calculations. By means of TD-DFT
calculations (ADF, TZP, SAOP), it was possible to confirm
the viability of intermolecular electron excitations within the π-
stacked dimer of 1. Furthermore, it was determined that the
lowest triplet states lie below those of the first singlet states.
The triplet to singlet transitions that would radiatively relax can
be visualized by plotting the transition densities (Figure 6)
according to the expression ρge(r) = ψg*(r) ψe(r).
Figure 7. Stacking interactions of solvatomorphs for complexes 1 and
2 (top). Slipped stacked π−π interactions (bottom): a = interplanar
distance, b = slip distance of naphthalene centroids, c = distance
between naphthalene centroids, θ = slip angle between naphthalene
centroids.
morph of 1 and 2 features a similar packing arrangement of
parallel displaced π−π stacking interactions. In this respect,
each solvatomorph of complex 1 is reminiscent of the
nonsolvated lattice of 1 in the sense that each lattice features
infinite π−π stacking columns that are arranged in a staircase
formation. Interestingly, each solvatomorph of complex 2
features an alternate parallel slipped π−π stacking staircase
formation. The solvatomorphs of complex 2 stack in this
fashion as a consequence of both the π−π contacts between
naphthalene units and the Cl−H contacts of the flanking aryl
groups. The calculated crystallographic details involving the
distances and angles of the slipped π−π-stacked naphthalene
rings are summarized in Table 3.
As a result of the TD-DFT calculations, it can be surmised
that small changes in the crystal packing environments could
perturb the intramolecular electron excitations and thus change
the emissive properties of complexes 1 and 2. With this in
mind, polymorphism was investigated as a means of tuning the
emissions of complexes 1 and 2.
As displayed in Table 3, each solvatomorph features a slightly
different crystal packing environment and consequently exhibits
different photophysical properties. Figure 8 exhibits the various
crystalline samples that were examined by both fluorescence
spectroscopy and fluorescent microscopy. A summary of the
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complex 1. Specifically, the solvatomorphs of complex 2 that
contain CHCl3 and MeCN were found to be red-shifted by
approximately 10 nm in comparison with those of the THF and
DCM solvatomorphs (Table 4).
Table 3. Calculated Crystallographic Details of
Solvatomorph π−π Interactions
solvatomorph
a
b
c
θ
1
3.504 Å
3.418 Å
3.421 Å
3.569 Å
3.549 Å
3.725 Å
3.431 Å
3.404 Å
3.400 Å
3.450 Å
1.439 Å
1.266 Å
1.415 Å
1.604 Å
1.400 Å
1.763 Å
1.300 Å
1.246 Å
1.328 Å
1.228 Å
3.788 Å
3.645 Å
3.702 Å
3.787 Å
3.815 Å
4.121 Å
3.668 Å
3.625 Å
3.650 Å
3.662 Å
22.33°
20.33°
22.47°
19.54°
21.52°
25.32°
20.71°
20.10°
21.33°
19.59°
In summary, four methylated Ar-BIAN complexes have been
investigated from the standpoint of their photophysical
properties. Complexes 1 and 2 were found to be emissive via
AIE pathways. In contrast, complexes 3 and 4 proved to be
nonemissive in both the solid state and in solution. Analyses of
the crystal packing diagrams for complexes 1−4 provided
valuable insights into the possible reasons for both the emissive
behavior of complexes 1 and 2 and also for the nonemissive
behavior of complexes 3 and 4. The hypothesis for the origin of
the emissions of complexes 1 and 2 was supported on the basis
of TD-DFT calculations. Furthermore, a solvatomorph study
was performed in order to investigate the effect that subtle
changes in crystal packing environments would have on the
emissive properties of each complex. Future effort will be
focused on tuning the stereoelectronic properties of the BIAN
ligand class in order to modify and control the photophysical
properties of the BIAN zinc complexes.
1-CHCl3
1-THF
1-DCM
1-MeCN
2
2-CHCl3
2-THF
2-DCM
2-MeCN
EXPERIMENTAL SECTION
■
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. The p-methylphenyl (1),12 3,5-dimethylphenyl
(2),12 2,4,6-trimethylphenyl (3),12 and o-methylphenyl (4)13 BIAN
zinc chloride complexes were synthesized according to the pertinent
literature procedures.
Physical Measurements. All of the NMR spectra were recorded
at 298 K on either a Varian DirectDrive instrument (1H NMR, 599.75
MHz; 13C NMR, 150.82 MHz) or a Varian INOVA instrument (1H
NMR, 499.87 MHz; 13C NMR, 125.71 MHz), using residual solvent as
the internal reference. The deuterated chloroform solvent was
procured from Cambridge Isotopes Laboratories, Inc., and stored
over 4 Å molecular sieves prior to use. The high-resolution chemical
ionization mass spectral data (HRMS-CI) were collected on a
Micromass Autospec Ultima mass spectrometer. The melting points
of 1−4 were determined using a Mel-Temp apparatus. Samples of
complexes 1−4 were sent to Midwest Microlab, LLC, for C, H, and N
elemental analyses.
Fluorescence Spectroscopy. All solid-state fluorescence spec-
troscopy experiments were performed on a Photon Technology
International QM 4 spectrophotometer equipped with a 6 in. diameter
K Sphere-B integrating sphere. The crystalline powders of 1−4 were
loaded into quartz EPR tubes for measurement purposes, and their
chemical identities were confirmed by powder X-ray crystallography.
All solvatomorph samples were loaded into quartz EPR tubes and
subsequently covered with mineral oil to maintain crystallinity. The
absolute quantum yield measurements were made by using a 6 in.
diameter K Sphere-B 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.
[(Areasample emission/(AreaBaSO4 blank excitation − Areasample 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
nonsolvated complex, for which the absolute quantum yield had
been measured directly. All graphs were constructed using the
OriginPro 9.1 Student Version 64bit program.
Figure 8. Emission spectra, optical, and fluorescent images for the
solvatomorphs of complexes 1 and 2.
photophysical data for each solvatomorph can be found in
Table 4.
Table 4. Solid-State Fluorescence Data for Solvatomorphs of
Complexes 1 and 2
a
complex
λem (nm)
λex (nm)
τ (μs)
Φ (%) (relative)
1-CHCl3
1-THF
590
567
569
569
587
576
578
585
470
470
470
470
470
470
470
470
4.59 1.12
2.97 0.96
6.23 1.17
2.86 0.57
4.94 0.09
4.51 0.75
4.54 1.02
6.41 1.33
3.78 0.13
1.52 0.14
0.35 0.01
0.63 0.02
1.03 0.13
2.59 0.32
2.42 0.30
0.84 0.10
1-DCM
1-MeCN
2-CHCl3
2-THF
2-DCM
2-MeCN
a
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
nonsolvated complex, for which the absolute quantum yield had
been measured directly.
The most significant change in photophysical properties was
observed in the case of the CHCl3 solvatomorph of complex 1.
This particular solvatomorph was found to be red-shifted by
approximately 20 nm in comparison with those of the other
three solvatomorphs of complex 1. This outcome is presumably
due to the increased π−π orbital overlap of this solvatomorph
in comparison with the other solvatomorphs of complex 1.
Furthermore, the solvatomorphs of complex 2 exhibit a more
subtle shift in lambda max with respect to the solvatomorphs of
Single-Crystal X-ray Crystallography. In the cases of com-
pounds 1−3, suitable single crystals could be obtained directly from
each reaction mixture. Suitable crystals of complex 4 were grown via
slow evaporation of a dichloromethane solution of this complex. Each
solvatomorph crystal was grown from the appropriate solvent. In each
case, the single crystals were removed from their respective vials,
covered with mineral oil, and mounted separately on nylon thread
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loops. The X-ray diffraction data (powder and single crystal) were
collected on an Agilent Technologies SuperNova Dual Source
diffractometer using a μ-focus Cu Kα radiation source (λ = 1.5418
Å) equipped with collimating mirror monochromators. Crystals 1 and
2 were collected at 100 K, and crystals 3 and 4 were collected at 147 K.
All solvatomorphs were collected at 133 K. Crystallographic details for
all structures can be found in the Supporting Information. Data
collection, unit cell refinement, and data reduction were performed
using the Agilent Technologies CrysAlisPro V 1.171.37.31 program.19
The structure of each complex was solved by direct methods using the
SIR9720 program and refined by full-matrix least-squares on F2 with
anisotropic displacement parameters for all non-H atoms using
SHELXL-2013.21 The structural analyses were performed using the
PLATON9822 and WinGX23 programs, and all non-hydrogen atoms
were refined anisotropically. The hydrogen atoms were placed in fixed,
calculated positions with isotropic displacement parameters set to 1.2
× Ueq with respect to the attached atom (1.5 × Ueq for methyl
hydrogens). All powder XRD graphs were constructed using the
OriginPro 9.1 Student Version 64 bit program. The POV-Ray images
were created using the Mercury version 3.3 program. The crystallo-
graphic details concerning the solvatomorph π−π interactions were
calculated using the Mercury version 3.3 program.
Diffuse-Reflectance and UV/Vis Absorption Spectroscopy.
All diffuse-reflectance measurements were performed with an
illuminated (tungsten-halogen light source) integrating sphere
(Ocean Optics ISP-REF) attached to a photodiode array spectropho-
tometer (Ocean Optics SD 2000), and all data are reported relative to
a BaSO4 standard. Each measurement was integrated over 3 ms and
corrected for stray light and dark current. The raw data were used to
calculate the reflectance (R) using Grams/AI (version 8.0). The
Kubelka−Munk function ([1 − R]2/2R) was evaluated in Excel, and
the resulting spectra were smoothed by calculating the weighted
averages of the values at neighboring points using the Cauchy density
function as implemented within SigmaPlot (version 9). The final
illustration was composed in PowerPoint. All UV/vis absorption
experiments were performed using a Varian Vary 6000i UV−vis−NIR
spectrophotometer. All UV/vis graphs were constructed using the
OriginPro 9.1 Student Version 64bit program.
7.598 (t, 2H, Ar−H, J = 7.7 Hz), 7.650 (d, 2H, Ar−H, J = 7.2 Hz),
8.132 (d, 2H, Ar−H, J = 8.1 Hz). 13C NMR (CDCl3): δ 21.35, 121.69,
125.33, 125.96, 128.56, 130.66, 131.14, 132.26, 139.20, 141.07, 144.88,
161.85. MP: 344 °C. Anal. Calcd for C26H20N2ZnCl2: C, 62.87; H,
4.06; N, 5.64. Found: C, 62.84; H, 3.99; N, 5.54.
3,5-Dimethylphenyl-BIAN Zinc Chloride (2). 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 latter yellow
suspension was heated to 60 °C, and 3,5-dimethylaniline (1.49 mL,
12.63 mmol) was added, following which the resulting solution was
refluxed for 1 h. The precipitate that had formed during the latter
reaction was filtered off and washed sequentially with water and diethyl
ether. The resulting crystalline yellow powder was collected and used
without further purification for a single-crystal X-ray diffraction study
(1.84 g, 64%).
HRMS (CI, CH4): calcd for [M − Cl]+ [C28H24N2ZnCl]+ m/z
487.0919; found 487.0913. 1H NMR (CDCl3): δ 2.404 (s, 12H, CH3),
7.102 (s, 2H, Ar−CH3), 7.179 (s, 4H, Ar−CH3), 7.536 (d, 2H, Ar−H,
J = 6.5 Hz), 7.607 (d, 2H, Ar−H, J = 7.8 Hz), 8.147 (d, 2H, Ar−H, J =
8.2 Hz). 13C NMR (CDCl3): δ 21.38, 118.82, 125.27, 126.05, 128.60,
130.37, 131.08, 132.19, 140.03, 162.12. MP: 321 °C. Anal. Calcd for
C28H24N2ZnCl2: C, 64.08; H, 4.61; N, 5.34. Found: C, 64.06; H, 4.62;
N, 5.28.
2,4,6-Trimethylphenyl-BIAN Zinc Chloride (3). 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 latter yellow
suspension was heated to 60 °C, and 2,4,6-trimethylphenylaniline
(1.64 mL, 12.63 mmol) was added, following which the resulting
solution was refluxed for 1 h. The precipitate that had formed during
the latter reaction was filtered off and washed sequentially with water
and diethyl ether. The resulting crystalline red powder was collected
and used without further purification for a single-crystal X-ray
diffraction study (2.69 g, 89%).
HRMS (CI, CH4): calcd for [M − Cl]+ [C30H28N2ZnCl]+ m/z
515.1232; found 515.1237. 1H NMR (CDCl3): δ 2.313 (s, 12H, CH3),
2.405 (s, 6H, CH3), 6.936 (d, 2H, Ar−H, J = 7.4 Hz), 7.063 (s, 4H,
Ar−H), 7.602 (dd, 2H, Ar−H, J = 7.8 Hz, 1.0 Hz), 8.153 (d, 2H, Ar−
H, J = 8.0 Hz). 13C NMR (CDCl3): δ 18.36, 21.02, 125.57, 125.87,
128.36, 129.33, 129.97, 130.97, 132.36, 137.24, 140.28, 144.43, 164.20.
MP: 384 °C. Anal. Calcd for C30H28N2ZnCl2: C, 65.18; H, 5.11; N,
5.07. Found: C, 65.18; H, 5.13; N, 5.02.
DFT Calculations. All DFT calculations were performed using the
ADF DFT package (version 2013).24,25 A model of the π-stacked
dimer of complex 1 was built from the crystallographic coordinates,
and the positions of all non-carbon atoms were optimized using the
exchange−correlation functional of Perdew, Burke, and Ernzerhof26
and corrected for dispersion27 with a triple-ζ all-electron basis set with
two polarization functions and applying the zeroth-order regular
approximation (ZORA)28−32 formalism with specially adapted basis
sets. In the interest of expediency, the lowest 80 singlet−singlet and
lowest 80 singlet−triplet electronic excitations33,34 were calculated
using time-dependent density functional theory (TD-DFT) under the
statistical average of different model potentials for occupied KS orbitals
(SAOP).35−37
2-Methylphenyl-BIAN Zinc Chloride (4). A mixture of acenaph-
thenequinone (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 latter yellow suspension was
heated to 60 °C, and o-toluidine (1.35 mL, 12.63 mmol) was added,
following which the resulting solution was refluxed for 1 h. The
precipitate that had formed during the latter reaction was filtered off
and washed sequentially with water and diethyl ether. The resulting
crystalline yellow powder was collected and subsequently recrystallized
from dichloromethane solution. The resulting crop of crystals proved
to be suitable for a single-crystal X-ray diffraction study (1.47 g, 53%).
HRMS (CI, CH4): calcd for [M − Cl]+ [C26H20N2ZnCl]+ m/z
Fluorescent Microscopy. The fluorescent microscopy was
performed on a Zeiss Axiovert200 M epifluorescent microscope.
The crystalline solvatomorph samples were excited using an FITC
filter cube. The fluorescent microscopy images were created using the
program Axiovision 4.6.
1
459.0606; found 459.0610. H NMR (CDCl3): δ 2.355 (s, 6H, CH3),
6.974 (apparent dd, 2H, Ar−H, J = 7.2 Hz), 7.391 (m, 8H, Ar−H),
7.573 (dd, 2H, Ar−H, J = 8.3 Hz, J = 1.0 Hz), 8.133 (d, 2H, Ar−H, J =
8.1 Hz); (CDCl3): δ 18.04, 18.28, 120.63, 120.93, 125.50, 125.51,
126.10, 127.74, 127.83, 128.08, 128.11, 128.76, 128.94, 129.12, 131.00,
132.02, 131.66, 131.68, 132.40, 132.42, 143.37, 143.41, 144.85, 144.89,
163.51, 163.52. MP: 359 °C. Anal. Calcd for C26H20N2ZnCl2: C,
62.87; H, 4.06; N, 5.64. Found: C, 62.80; H, 4.13; N, 5.59.
Syntheses of 1−4. 4-Methylphenyl-BIAN Zinc Chloride (1). 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 latter yellow
suspension was heated to 60 °C, and p-toluidine (1.42 mL, 12.63
mmol) was added, following which the resulting solution was refluxed
for 1 h. The precipitate that had formed during the latter reaction was
filtered off and washed sequentially with water and diethyl ether. The
resulting crystalline, yellow-orange powder was collected and used
without further purification for a single-crystal X-ray diffraction study
(2.18 g, 80%).
ASSOCIATED CONTENT
■
S
* Supporting Information
HRMS (CI, CH4): calcd for [M − Cl]+ [C26H20N2ZnCl]+ m/z
Fluorescence spectroscopy and crystallographic data are
provided in the Supporting Information. This material is
available free of charge via the Internet at http://pubs.acs.org.
1
459.0606; found 459.0605. H NMR (CDCl3): δ 2.464 (s, 6H, CH3),
7.363 (d, 4H, Ar−H, J = 8.0 Hz), 7.511 (d, 4H, Ar−H, J = 8.0 Hz),
F
DOI: 10.1021/om501191c
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(16) Zhang, H.; Zhang, Z.; Ye, K.; Zhang, J.; Wang, Y. Adv. Mater.
2006, 18, 2369−2372.
AUTHOR INFORMATION
Corresponding Author
*E-mail: acowley@cm.utexas.edu.
Notes
■
(17) (a) Li, R.; Xiao, S.; Li, Y.; Lin, Q.; Zhang, R.; Zhao, J.; Yang, C.;
Zou, K.; Li, D.; Yi, T. Chem. Sci. 2014, 5, 3922−3928. (b) Dong, Y.;
Xu, B.; Zhang, J.; Tan, X.; Wang, L.; Chen, J.; Lv, H.; Wen, S.; Li, B.;
Ye, L.; Zou, B.; Tian, W. Angew. Chem., Int. Ed. 2012, 51, 10782−
The authors declare no competing financial interest.
̌
̌
10785. (c) Galer, P.; Korosec, R. C.; Vidmar, M.; Sket, B. J. Am. Chem.
Soc. 2014, 136, 7383−7394. (d) Unesaki, H.; Kato, T.; Watase, S.;
Matsukawa, K.; Naka, K. Inorg. Chem. 2014, 53, 8270−8277.
(e) Kitamura, C.; Ohara, T.; Kawatsuki, N.; Yoneda, A.; Kobayashi,
T.; Naito, H.; Komatsu, T.; Kitamura, T. CrystEngComm 2007, 9,
644−647. (f) Talarico, A. M.; Aiello, I.; Bellusci, A.; Crispini, A.;
Ghedini, M.; Godbert, N.; Pugliese, T.; Szerb, E. Dalton Trans. 2010,
39, 1709−1712. (g) Field, J. S.; Ledwaba, L. P.; Munro, O. Q.;
McMillin, D. R. CrysEngComm 2008, 10, 740−747. (h) Quanrtapelle
Procopio, E.; Mauro, M.; Panigati, M.; Donghi, D.; Mercandelli, P.;
Sironi, A.; D’Alfonso, G.; De Cola, L. J. Am. Chem. Soc. 2010, 132,
14397−14399. (i) Luo, G.-G.; Xia, J.-X.; Fang, K.; Zhao, Q.-H.; Wu, J.-
H.; Dai, J.-C. Dalton Trans. 2013, 42, 16268−16271.
(18) (a) Fan, Y.; Zhao, Y.; Ye, L.; Li, B.; Yang, G.; Wang, Y. Cryst.
Growth Des. 2009, 9, 1421−1430. (b) Kuwabara, J.; Ogawa, Y.;
Taketoshi, A.; Kanbara, T. J. Organomet. Chem. 2011, 696, 1289−1293.
(c) Benito, Q.; Le Goff, X. F.; Maron, S.; Fargues, A.; Garcia, A.;
Martineau, C.; Taulelle, F.; Kahlal, S.; Gacoin, T.; Boilot, J.-P.;
Perruchas, S. J. Am. Chem. Soc. 2014, 136, 11311−13320.
(19) CrysAlisPro, version 1.171.37.31; Agilent Technologies UK Ltd.:
Oxford, UK, 2013.
ACKNOWLEDGMENTS
■
The authors are grateful for the generous financial support
provided by the Robert A. Welch Foundation (Grant F-0003)
(AHC) and the Natural Sciences and Engineering Research
Council of Canada (IVB Discovery Grant, LML Doctoral
Postgraduate Scholarship). This work was made possible by the
facilities of the Shared Hierarchical Academic Research
Computing Network (SHARCNET: www.sharcnet.ca) and
Compute/Calcul Canada.
DEDICATION
■
Dedicated to the memory of Professor Michael F. Lappert, an
outstanding scientist and a true gentleman.
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DOI: 10.1021/om501191c
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