Utilizing the π-acidity of boron subphthalocyanine to achieve novel solid-state arrangements

Article abstract of DOI:10.1021/cg4012795

The ability to control the solid-state structure of organic electronic materials can have a large effect on the quality of the devices to which they are applied. In this paper, we describe the use of π-π interactions to direct the crystal structure/solid-state arrangement of boron subphthalocyanine (BsubPc) derivatives by taking advantage of the π-electron-deficiency (π-acidity) of the BsubPc molecular fragment. First, we outline why BsubPc is a π-acid by looking at its chemical characteristics and the structure of crystals formed with other π-acidic moieties. Then we show how the solid-state arrangement of BsubPc can be purposefully altered by adding π-basic substituents. We found that adding a naphthoxy substituent provides an interaction that is strong enough to direct BsubPc into a novel solid-state arrangement made up of ribbons (or catemers) of molecules linked through π-stacking interactions between the naphthoxy and neighboring BsubPc molecular fragments. A similar effect was also seen when the naphthoxy fragment was added to the stronger π-acid perfluoro-BsubPc (F₁₂BsubPc).

Full text of DOI:10.1021/cg4012795

Article
pubs.acs.org/crystal
Utilizing the π‑Acidity of Boron Subphthalocyanine To Achieve Novel
Solid-State Arrangements
Andrew S. Paton,† Graham E. Morse,† Alan J. Lough,‡ and Timothy P. Bender*,†,‡,§
†Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, Ontario, Canada
M5S 3E5
‡Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6
§Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario, Canada M5S 3E4
S
* Supporting Information
ABSTRACT: The ability to control the solid-state structure
of organic electronic materials can have a large effect on the
quality of the devices to which they are applied. In this paper,
we describe the use of π−π interactions to direct the crystal
structure/solid-state arrangement of boron subphthalocyanine
(BsubPc) derivatives by taking advantage of the π-electron-
deficiency (π-acidity) of the BsubPc molecular fragment. First,
we outline why BsubPc is a π-acid by looking at its chemical
characteristics and the structure of crystals formed with other
π-acidic moieties. Then we show how the solid-state
arrangement of BsubPc can be purposefully altered by adding
π-basic substituents. We found that adding a naphthoxy
substituent provides an interaction that is strong enough to
direct BsubPc into a novel solid-state arrangement made up of ribbons (or catemers) of molecules linked through π-stacking
interactions between the naphthoxy and neighboring BsubPc molecular fragments. A similar effect was also seen when the
naphthoxy fragment was added to the stronger π-acid perfluoro-BsubPc (F12BsubPc).
The potential benefit from control of π−π interactions has
been established in the field of organic electronics. There have
been a number of studies correlating intermolecular π−π
distances with charge carrier mobility.3 The pioneering work by
Anthony and co-workers on silyl-derivatized pentacenes has
shown that smaller intermolecular distances in the solid state
lead to an increase in electron mobility and better performance
of the material in organic electronic devices such as organic
light-emitting diodes (OLEDs) and organic photovoltaics
(OPVs).4 Others have shown that the crystal polymorph,5
the crystal orientation,6 the quality of the crystal,6 and the solid-
state packing density of the material7 used in an organic
electronic device all affect the device performance. For example,
OPV devices have been fabricated with active layers consisting
of mixtures of C60 and boron subphthalocyanine (BsubPc). It
was shown that BsubPc forms crystallites in the devices that are
linked with an increase in the device performance versus the
same BsubPc in an amorphous form.8
INTRODUCTION
■
Crystal engineering can use non-covalent interactions of
varying strength (such as hydrogen bonding, dipole−dipole
interactions, van der Waals interactions, and π−π interactions)
to rationally plan and acquire specific solid-state arrangements
of targeted materials. Such interactions can be designed and
incorporated into a targeted molecular material if a certain
amount of information is known in advance about the molecule
and/or its fragments. Although these interactions may be
relatively weak in energetic terms, having many weak, non-
covalent intermolecular interactions can provide sufficient
impetus for stabilization of specific and desired solid-state
arrangements.
The use of π−π interactions in crystal engineering is not as
common as the use of other non-covalent interactions such as
hydrogen bonding, which might be due to the debate
surrounding the nature of these interactions.1 Nonetheless,
the ubiquity of π−π interactions in the crystal structures of
aromatic molecules, as well as the recognition of the
contribution of other intermolecular interactions involving π-
electron systems in crystal structures (for example N···π, C−
H···π, and X···π), has undoubtedly demonstrated the
importance of π electrons in directing the solid-state arrange-
ment of molecules. Thus, more recently, the use of π−π
interactions in crystal engineering has been gaining broader
acceptance.2
Most crystal engineering techniques to control the solid-state
arrangement of small molecules rely on the addition of
functional groups, which adds additional molecular mass that
dilutes the concentration of π electrons in the resulting
Received: August 23, 2013
Revised: October 11, 2013
Published: October 17, 2013
© 2013 American Chemical Society
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materials. The use of π−π interactions alone to control the
solid-state arrangement of aromatic materials such as BsubPcs
would be ideal, as one could then minimize the number of
nonaromatic groups in the molecular structure. There is
evidence to suggest that a combination of electron-rich (π-
basic) and electron-deficient (π-acidic) aromatic groups present
within a single molecule can be used to engineer the solid-state
arrangement of the material; one example resulted in a material
with a hole mobility greater than 2 cm2 s−1 V−1.9 In that
reported crystal structure, the π-rich thiophene and the π-
deficient pyridinyl fragments stack on top of each other,
displaying a π-electron acid−base/acceptor−donor interaction.
Another study showed that a mixture of tetracene with phenyl
substituents (π-bases) and tetracene with fluorinated pendant
groups (π-acids) co-crystallizes in a 1:1 ratio with alternating
units of halogenated and non-halogenated pendant groups in a
π-stacked motif within the solid state.10 This type of arene−
perfluoroarene interaction is well-known, and many studies in
crystal engineering have used it to obtain desired solid-state
arrangements through co-crystallization.2,9,11,12 That the
perfluoroarene molecules alternate with the corresponding
non-halogenated arenes demonstrates a preference for an
energetically attractive π-stacking interaction between different
molecules of differing π-acidity/π-basicity rather than between
two of the same molecule. Thus, one can conclude on the basis
of these two representative examples that the π-acid/π-base
association preferentially occurs when π-acids and π-bases are
present together either within the same molecule or as co-
crystallites.
Figure 1. (a) Scheme of generic BsubPcs showing C3v symmetry lines,
the peripheral and bay positions, and the difference between the
perhydrogenated (BsubPc) and perfluorinated (F12BsubPc) variants.
(b) Previously reported phenoxy-BsubPcs containing π-acidic phenoxy
molecular fragments.26−28
Br19 (Figure 1a), arrange in columns running in a direction
perpendicular to the plane of the F12BsubPc fragment. The
halide is located immediately underneath the boron atom in the
concave face of the BsubPc at a distance of less than the sum of
the van der Waals radii. Finally, phenoxy-F12BsubPcs (X =
RPhO; Figure 1a) arrange in a similar fashion to their halide
counterparts, except that is the phenoxy fragment that occupies
the concave face and displays π−π interactions with the
F12BsubPc moiety.20 A similar structure was found for 4-
methylphenoxy-F12 BsubPc,21 pentafluorophenoxy-
F12BsuBPc,22 and 4-ferrocenylphenoxy-F12BsubPc.23
Recently, our group outlined how the charge-carrier
mobilities of a series of BsubPc derivatives with various
numbers of fluorine atoms in their chemical structures could be
correlated to their solid-state arrangement and the associated
crystallographic parameters. The series of BsubPcs had a
consistent packing motif in the solid state, but variation in the
distances between neighboring molecules and the overall crystal
density could be correlated to variations in their measured
charge-carrier mobilities in thin films.3b
Typically, BsubPcs exist in two common varieties, a
perhydrogenated version that we will denote simply as BsubPc
and a perfluorinated version that we will denote as F12BsubPc
(see Figure 1a). If one considers how the more common
BsubPcs arrange in the solid state, then BsubPcs can be
grouped into one of four categories depending on the nature of
their axial and peripheral substituents: halo-BsubPcs, phenoxy-
BsubPcs, halo-F12BsubPcs, and phenoxy-F12BsubPcs. Halo-
BsubPcs (X = F,13a Cl,13b Br;13a see Figure 1a) are all
practically isostructural in the solid state, crystallizing into a
head-to-tail concave-face to concave-face arrangement in well-
defined rows. When the halide group is replaced with a
phenoxy group (X = −OC6H5 in Figure 1a), the arrangement is
entirely different, with phenoxy-BsubPcs generally arranged in
such a manner that they form head-to-head concave−concave
dimers that repeat throughout the extended solid state.14 We
have recently published two studies illustrating that halides
present on the phenoxy molecular fragment can produce novel
solid-state arrangements of phenoxy-BsubPc. This first was
observed in the solid-state arrangement of p-bromophenoxy-
BsubPc, which has one novel polymorph stabilized by a π-Br
interaction.15 The second was observed for a wide variety of m-
halophenoxy-BsubPcs (halo = iodo, bromo, chloro) that
exhibited novel solid-state arrangements through the formation
of halogen bonds.16 Halo-F12BsubPcs, whether X = F,17 Cl,18 or
In this paper, we demonstrate a method for crystal
engineering of BsubPc derivatives using π-acid/π-base inter-
actions to generate an entirely unique and novel solid-state
arrangement of the BsubPc molecular fragment. We begin by
outlining why we believe BsubPc is a π-acid. This is supported
by several observations, including the electrochemical behavior
of BsubPcs and the positions of the hydrogen resonances in the
1H NMR spectrum of a BsubPc. Following that discussion, we
outline the synthesis and crystallization four novel BsubPc
compounds with π-basic substituents (Scheme 1): 4-methox-
yphenoxy-BsubPc (1), α-naphthoxy-BsubPc (2a), β-naphthoxy-
BsubPc (2b), and β-naphthoxy-F12BsubPc (3). We show that
attachment of π-basic substituent groups axially to the boron
atom of a BsubPc molecular fragment creates a π-acid/π-base
interaction within the crystal. This interaction results in a novel
solid-state arrangement for a BsubPc, as the concave-face to
concave-face π-stacking motif seen in many phenoxy-BsubPc
crystal structures14,15,20,24 is replaced with a ribbonlike (or
catemeric) arrangement.
RESULTS AND DISCUSSION
■
To make the case that BsubPcs are π-acids, we begin by
considering the electrochemical behavior of BsubPcs. We have
previously shown that BsubPc is preferentially an n-type
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a
observed to be nonreversible. The inclination to accept an
electron without degradation yet degrade upon giving up an
electron is a property of a π-acidic molecule (i.e., a molecule
that is deficient in π-electron density).
Scheme 1. Synthesis of BsubPcs 1−3
1
Second, when we consider the H NMR spectrum of a
typical phenoxy-BsubPc, we observe that the peripheral and bay
protons (defined in Figure 1a) resonate at ∼7.85 and ∼8.85
ppm, respectively (confirmed also in DMSO-d6).14,20,24 Each of
these resonances lies either at or well beyond the downfield
boundary of what would be expected for a standard aromatic
1
compound. As H NMR analysis can be considered a measure
1
of the acidity of a particular proton, the positions of the H
resonances of the peripheral protons of a typical BsubPc
suggest that they are acidic relative to other aromatic
compounds, including other phthalocyanines. We would note
that the significant ring currents of BsubPc and more generally
phthalocyanines also play a role in the downfield positions of
the proton resonances relative to other aromatic compounds.
However, if one considers the position of the proton
resonances of zinc phthalocyanine, for example,25 the
peripheral proton resonances appear at ∼5.8 and ∼6.8 ppm
(DMSO-d6), still significantly upfield from those of BsubPc.
Therefore, we would suggest that it is not simply ring current
considerations that place the proton resonances of BsubPc this
far downfield.
Third, evidence for the π-acidity of BsubPc can be obtained
by looking at the crystal structures of its derivatives with other
π-acidic moieties. We previously reported the synthesis and
crystal structure of 4-cyanophenoxy-BsubPc (R = p-CNPhO;
Figure 1b).26 The 4-cyanophenoxy unit is π-acidic because of
the strong electron-withdrawing character of the cyano group.
By coupling it with the BsubPc unit, we observed the formation
of large void spaces in the single crystal (which were filled with
disordered solvent). Benzene/heptane and acetone/heptane
gave identical crystals, thus indicating that the disordered
solvent is likely heptane. A distorted B−O−C bond angle of
128.89(11)° was also observed, which is significantly different
than the typical 115°. One can explain these unique
observations by considering that within this molecule there
a
Conditions: (i) toluene, 4-methoxyphenol, reflux, 48 h; (ii) toluene,
naphthol, reflux, 24−72 h; (iii) chlorobenzene, 2-naphthol, reflux, 20
h.
organic electronic semiconductor in an OLED, an observation
supported by the fact that BsubPc generally accepts an electron
rather than giving up an electron under cyclic voltammetry
conditions.22 A reversible reduction is seen for a typical
phenoxy-BsubPc over many cycles, whereas an oxidation is
Figure 2. (a) Displacement ellipsoid plot of compound 1 at the 50% probability level and (b) its populated unit cell showing π-stacking interactions
between BsubPcs (red) and between methoxy (green) and a BsubPc. H atoms have been omitted for clarity. Colors: carbon, gray; nitrogen, blue;
oxygen, red; boron, yellow. The isoindoline units are colored in red in (b) for clarity of presentation.
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Figure 3. (a, b) Displacement ellipsoid plots of (a) compound 2a and (b) compound 2b at the 50% probability level. (b, c) Extended packing
structures showing π-stacking interactions between naphthoxy units and BsubPcs (red and green lines) for (c) 2a and (d) 2b. H atoms have been
omitted for clarity. Colors: carbon, gray; nitrogen, blue; oxygen, red; boron, yellow.
are two π-acidic fragments that do not benefit from associating
with one another. Rather, the molecule in the solid state seeks
to associate with heptane instead (likely by C−H···π
interactions), but this requires a significant distortion of its
molecular conformation. Similar observations regarding the
distortion of the B−O−C bond angle can be seen when other
π-acidic groups are present on the phenoxy fragment of a
phenoxy-BsubPc. For example, B−O−C bond angles of
124.6(1)° and 130.3(2)° are seen for 4-nitrophenoxy-BsubPc
(R = p-NO2PhO)27 and 4-acetylphenoxy-BsubPc (R = p-
CH3COPhO),28 respectively, although in these cases there is
not an accompanying solvent-filled void volume present within
the crystal.
units that could be placed in the axial position of BsubPc (see
Figure 1) to complement the π-acidity of the BsubPc and form
robust π-acid/π-base interactions in the solid state.
We began by considering 4-methoxyphenoxy-BsubPc (1)
which was synthesized using previously published proce-
dures14,20,24 (Scheme 1). Briefly, Cl-BsubPc was reacted with
4-methoxyphenol in toluene at reflux. The reaction was
monitored by HPLC until complete. Purification via Kauffman
column chromatography on standard basic alumina with
dichloromethane as the eluent gave the final product. Full
experimental details for all of the compounds are provided in
the Supporting Information. Crystals suitable for X-ray
diffraction were obtained via vapor diffusion using benzene/
heptane (solvent/antisolvent, a system we have used before).
Within 2 weeks, high-quality single crystals suitable for X-ray
diffraction were grown, diffracted, and solved (Figure 2a).
In examining the solid-state arrangement of 1 (Figure 2b),
we see that in addition to the typical molecular pairing between
adjacent isoindoline fragments (colored in red in Figure 2b)
observed in other phenoxy-BsubPcs, there is an extra π−π
interaction between the methoxyphenoxy (shown in green) and
BsubPc fragments in the neighboring molecule at a distance of
3.5124(8) Å (Figure 2b). In this structure, the distance of the
π−π interaction between the isoindoline fragments of adjacent
The crystallographic data for cyanophenoxy-BsubPc, the
1
typical electrochemical behavior, and the H NMR spectro-
scopic behavior of BsubPcs are all consistent with the idea that
BsubPcs are π-acids. Given this, we can then move to the
rational design of novel BsubPc derivatives that utilize the π-
acidity to obtain previously unknown solid-state arrangements
for BsubPc derivatives.
As stated above, it is best to use the most mass-efficient
means to alter the solid-state arrangement of BsubPcs in order
to avoid diluting the specific concentration of the BsubPc
chromophore. For this reason, we considered π-basic aryloxy
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Figure 4. continued
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Figure 4. (a, b) Displacement ellipsoid plots for (a) compound 3 and (b) compound 3 benzene solvate at the 50% probability level. (c, d) Extended
solid-state arrangement of 3 showing π−π interactions between naphthoxy units and F12BsubPcs. (e, f) Extended solid-state arrangement of 3
benzene solvate showing π−π interactions between naphthoxy units and F12BsubPcs and between the benzene solvent and F12BsubPcs. H atoms
have been omitted for clarity. Colors: carbon, gray; nitrogen, blue; oxygen, red; boron, yellow; fluorine, purple.
BsubPcs is 3.5512(9) Å, which is slightly shorter than that
observed in other phenoxy-BsubPcs. In view of the relative π-
basicity of the methoxyphenoxy fragment over a standard
phenoxy fragment, the presence of a new π−π interaction not
otherwise seen in crystals grown under identical conditions
initially demonstrated to us the potential for using π-acid/π-
base interactions to alter the solid-state arrangement of aryloxy-
BsubPcs, although this example still contains the often seen
dimerization of adjacent BsubPc fragments.14
We then turned our attention to other π-basic substituents
that may be slightly less mass-efficient yet provide for a wider π-
basic footprint. Specifically, we incorporated α-naphthoxy and
β-naphthoxy fragments into the BsubPc molecular structure.
The naphthoxy group is only slightly larger than the 4-
methoxyphenoxy group (144 vs 124 amu, respectively) yet
provides for a larger π-system by area. The synthesis was as
described above. Reaction of Cl-BsubPc with commercially
available α-naphthol and β-naphthol gave the two naphthoxy-
BsubPcs 2a and 2b, respectively (Scheme 1; same conditions as
for 1). Again, single crystals of 2a and 2b were obtained by slow
vapor diffusion using a benzene/heptane solvent system, and
their X-ray crystal structures are shown in Figures 3a,b,
respectively.
The solid-state arrangements of 2a and 2b do not at all
resemble the typical phenoxy-BsubPc arrangement. The
BsubPc molecules are arranged in one-dimensional ribbons
(or catemers) parallel to the crystallographic axis, directed by
the presence of a π−π interaction between the naphthoxy
fragment and the concave face of the BsubPc (Figure 3c,d).
These ribbons show close-packing N···π distances of 3.876(2)
and 3.807(6) Å between the centroid of the outermost ring of
the naphthoxy unit and the closest imine nitrogen in the next
BsubPc ligand in the crystal structures of 2a and 2b,
respectively. Interestingly, in the structures of both the α-
and β-naphthoxy derivatives there exists disorder in the
naphthoxy unit across the mirror plane of each row. This
disorder does not affect the region in which there is
intermolecular close contact between the naphthoxy group
and the neighboring BsubPc ligand. Furthermore, there is no
disorder in the BsubPc ligands themselves. Taken together,
these results suggest a strong intermolecular interaction
between the naphthoxy and BsubPc.
crystal structure. While some BsubPc structures show varying
crystal structure or solvates15,29 with variation of the
crystallization conditions, a polymorph search on the
naphthoxy-derivatized BsubPcs yielded only the crystal
structure described above. We attempted crystallization by
liquid-layering, classic crystallization, evaporation, and slow
vapor diffusion using a variety of different solvents. We also
formed crystals of the naphthoxy derivatives using sublimation.
In all cases, we were able to form high-quality crystals, and in all
cases the crystals exhibited the same structure.
We next looked at perfluorinated BsubPcs (F12BsubPcs),
which should be even more π-acidic than the perhydrogenated
BsubPcs discussed above. By attachment the naphthoxy
substituent to F12BsubPc, we again expected to see crystals
that possess π-acid/π-base interactions. β-Naphthoxy-
F12BsubPc (3) (Scheme 1) was synthesized using procedures
similar to those described above. We successfully grew crystals
via both sublimation and vapor diffusion of heptane into a
benzene solution. These methods gave two different structures,
the former a solvent-free structure and the latter a benzene
solvate. Displacement ellipsoid plots of these structures are
shown in Figure 4a,b, respectively. Interestingly, aside from the
benzene molecules in the solvate, the interactions seen in the
two structures are same, as described below.
In the solvent-free structure (Figure 4a,c,d), the naphthoxy
unit is located beneath the concave side of an indole unit and
interacts through π−π interactions at a distance of 3.735(2) Å;
however, the same indole unit also interacts through its convex
side with another naphthoxy group at a π−π stacking distance
of 3.556(2) Å. This second interaction joins two neighboring
columns within the structure. There are two sets of these
interactions in the structure because two molecules of the
compound in slightly different conformations appear in the
asymmetric unit. The Cg−Cg distances of the π−π interaction
in the second set are 3.762(2) and 3.683(2) Å, respectively.
These stacked molecules form two-dimensional sheets of
molecules that do not appear to have specific interactions
between them.
The benzene solvate of 3 (Figure 4b,e,f) shows identical π−π
interactions, but at separation distances of 3.603(2) and
3.570(2) Å. The main difference between the two crystals of
3 is that in the solvated structure there is also an equidistant
convex face to solvent (benzene) π−π stacking at 3.548(3) Å
that joins adjacent sheets of stacked molecules.
Further evidence of the strength of the naphthoxy−BsubPc
aromatic interactions is provided by the prevalence of the
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(3) (a) Gsanger, M.; Oh, J. H.; Konemann, M.; Hoffken, H. W.;
̈
̈
̈
The consistency between the two structures shows that the
preferred interaction in this molecule is between the π-acidic
F12BsubPc and the π-basic naphthoxy substituent. Both of these
arrangements are similar to what is typically observed in the
solid-state arrangements of phenoxy-F12BsubPcs (as described
above), but the structures of 3 show more π-stacking overlap.
In the structures of phenoxy-F12BsubPc20 and 4-methylphe-
noxy-F12BsubPc,21 the phenol π-stacks with the concave face of
the neighboring F12BsubPc unit at Cg−Cg distances of
3.6048(19) and 3.5320(18) Å, respectively. Because of the
smaller area of the π-basic phenoxy unit compared to the
naphthoxy group, however, there are no additional interactions
with the convex face of the F12BsubPc moiety. In other words,
the increased π-basicity of the naphthoxy substituent over the
phenoxy substituent allows greater π-acid/π-base interactions
for β-naphthoxy-F12BsubPc in the solid state.
Krause, A.-M.; Bao, Z.; Wurthner, F. Angew. Chem., Int. Ed. 2010, 49,
̈
740−743. (b) Castrucci, J.; Helander, M. G.; Morse, G. E.; Lu, Z.-H.;
Yip, C.; Bender, T. P. Cryst. Growth Des. 2012, 12, 1095−1100.
(4) (a) Swartz, C. R.; Parkin, S. R.; Bullock, J. E.; Anthony, J. E.;
Mayer, A. C.; Malliaras, G. G. Org. Lett. 2005, 7, 3163−3166.
(b) Anthony, J. E. Chem. Rev. 2006, 106, 5028−5048.
(5) Pfattner, R.; Mas-Torrent, M.; Bilotti, I.; Brillante, A.; Milita, S.;
Liscio, F.; Biscarini, F.; Marszalek, T.; Ulanski, J.; Nosal, A.; Gazicki-
Lipman, M.; Leufgen, M.; Schmidt, G.; Molenkamp, L. W.; Laukhin,
V.; Veciana, J.; Rovira, C. Adv. Mater. 2010, 22, 4198−4203.
(6) Rivnay, J.; Jimison, L. H.; Northrup, J. E.; Toney, M. F.; Noriega,
R.; Lu, S.; Marks, T. J.; Facchetti, A.; Salleo, A. Nat. Mater. 2009, 8,
952−958.
́
(7) Bredas, J. L.; Calbert, J. P.; da Silva Filho, D. A.; Cornil, J. Proc.
Natl. Acad. Sci. U.S.A. 2002, 99, 5804−5809.
(8) Pandey, R.; Gunawan, A. A.; Mkhoyan, K. A.; Holmes, R. J. Adv.
Funct. Mater. 2012, 22, 617−624.
(9) Chang, Y.-C.; Chen, Y.-D.; Chen, C.-H.; Wen, Y.-S.; Lin, J.-T.;
Chen, H.-Y.; Kuo, M.-Y.; Chao, I. J. Org. Chem. 2008, 73, 4608−4614.
(10) Okamoto, T.; Nakahara, K.; Saeki, A.; Seki, S.; Oh, J. H.;
Akkerman, H. B.; Bao, Z.; Matsuo, Y. Chem. Mater. 2011, 23, 1646−
1649.
(11) Saunders, G. C. CrystEngComm 2011, 13, 1801−1803.
(12) Smith, C. E.; Smith, P. S.; Thomas, R. L.; Robins, E. G.;
Collings, J. C.; Dai, C.; Scott, A. J.; Borwick, S.; Batsanov, A. S.; Watt,
S. W.; Clark, S. J.; Viney, C.; Howard, J. A. K.; Clegg, W.; Marder, T.
B. J. Mater. Chem. 2004, 14, 413−420.
CONCLUSIONS
■
The addition of a π-basic substituent onto both BsubPc and
F12BsubPc produces increased π-stacking interactions at shorter
distances over those with less π-basic substituents. These
additional interactions produce variations in the crystal packing
motifs of typical phenoxy-BsubPcs14 and phenoxy-
F12BsubPcs,20,21 suggesting that an increase in the available π-
electron density interacts favorably with any BsubPc. It has
been shown that BsubPc is π-electron-deficient and thus is a π-
acid. For this reason, we believe that the increased π-electron
stacking is due to a π-acid/π-base interaction between the π-
basic axial derivatives of naphthoxy and methoxyphenoxy and
the π-acidic BsubPc and F12BsubPc. This conclusion is further
supported by the increased number of π−π interactions seen in
the crystal structure of compound 3 and the decreased number
of interactions seen in the structures of other phenoxy-BsubPc
derivatives having π-acidic phenols as the axial substi-
tuent.26−28This study provides evidence that π-acid/π-base
interactions can successfully be used in the crystal engineering
of BsubPc. In fact, the three naphthoxy derivatives display a
one- or two-dimensional infinite ribbon structure in the solid
state that may provide improved electronic properties. For this
reason, these materials possess great potential for use as
electronic materials.
(13) (a) Fulford, M. V.; Jaidka, D.; Paton, A. S.; Morse, G. E.;
Brisson, E. R. L.; Lough, A. J.; Bender, T. P. J. Chem. Eng. Data 2012,
57, 2756−2765. (b) Kietaibl, H. Monatsh. Chem. 1974, 105, 405−418.
(14) Paton, A. S.; Morse, G. E.; Lough, A. J.; Bender, T. P.
CrystEngComm 2011, 13, 914−919.
(15) Paton, A. S.; Lough, A. J.; Bender, T. P. CrystEngComm 2011,
13, 3653−3656.
(16) Virdo, J. D.; Kawar, Y. H.; Bender, T. P. CrystEngComm 2013,
15, 3187−3199.
(17) Rodríguez-Morgade, M. S.; Claessens, C. G.; Medina, A.;
́ ́
Gonzalez-Rodríguez, D.; Gutierrez-Puebla, E.; Monge, A.; Alkorta, I.;
Elguero, J.; Torres, T. Chem.Eur. J. 2008, 14, 1342−1350.
(18) Claessens, C. G.; Gonzalez-Rodriguez, D.; del Rey, B.; Torres,
T.; Mark, G.; Schuchmann, H.-P.; von Sonntag, C.; MacDonald, J. G.;
Nohr, R. S. Eur. J. Org. Chem. 2003, 2547−2551.
(19) Morse, G. E.; Maka, J. F.; Lough, A. J.; Bender, T. P. Acta
Crystallogr. 2010, E66, o3057.
(20) Claessens, C. G.; Torres, T. Angew. Chem., Int. Ed. 2002, 41,
2561−2565.
(21) Paton, A. S.; Lough, A. J.; Bender, T. P. Acta Crystallogr. 2010,
E66, o3059.
ASSOCIATED CONTENT
* Supporting Information
Materials, synthetic procedures, crystallographic data, and CIFs.
This material is available free of charge via the Internet at
http://pubs.acs.org.
■
S
(22) Morse, G. E.; Helander, M. G.; Maka, J. M.; Lu, Z.-H.; Bender,
T. P. ACS Appl. Mater. Interfaces 2010, 2, 1934−1944.
́
(23) Gonzalez-Rodríguez, D.; Torres, T.; Olmstead, M. M.; Rivera, J.;
́
Herranz, M. A.; Echegoyen, L.; Castellanos, C. A.; Guldi, D. M. J. Am.
Chem. Soc. 2006, 128, 10680−10681.
AUTHOR INFORMATION
Corresponding Author
*E-mail: tim.bender@utoronto.ca.
Notes
■
(24) Morse, G. E.; Paton, A. S.; Lough, A.; Bender, T. P. Dalton
Trans 2010, 39, 3915−3922.
(25) Kobayashi, N.; Mack, J.; Ishii, K.; Stillman, M. J. Inorg. Chem.
2002, 41, 5352−5354.
(26) Paton, A. S.; Lough, A. J.; Bender, T. P. Acta Crystallogr. 2011,
E67, o505−506.
The authors declare no competing financial interest.
(27) Paton, A. S.; Lough, A. J.; Bender, T. P. Acta Crystallogr. 2011,
E67, o57.
REFERENCES
■
(1) (a) Grimme, S. Angew. Chem., Int. Ed. 2008, 47, 3430−3434.
(b) Hunter, C. A.; Sanders, J. K. A. J. Am. Chem. Soc. 1990, 112, 5525−
5534. (c) Janiak, C. J. Chem. Soc., Dalton Trans. 2000, 3885−3896.
(d) Wheeler, S. E.; Houk, K. N. J. Am. Chem. Soc. 2008, 130, 10854−
10855.
(28) Paton, A. S.; Lough, A. J.; Bender, T. P. Acta Crystallogr. 2010,
E66, o3246.
(29) Paton, A. S.; Lough, A. J.; Bender, T. P. Ind. Eng. Chem. Res.
2012, 51, 6290−6296.
(2) The Importance of Pi-Interactions in Crystal Engineering: Frontiers in
Crystal Engineering; Tiekink, E. R. T., Zukerman-Schpector, J., Eds.;
Wiley: West Sussex, U.K., 2012.
5374
dx.doi.org/10.1021/cg4012795 | Cryst. Growth Des. 2013, 13, 5368−5374