Superbenzene–Porphyrin Gas-Phase Architectures Derived from Intermolecular Dispersion Interactions

Article abstract of DOI:10.1002/chem.201803684

A systematic series of superbenzene–porphyrin conjugates was synthesized and characterized. All conjugates show a high degree of cluster formation that correlates to the amount of tert-butylated hexa-peri-hexabenzocoronenes (tBuHBCs) attached to the porphyrin's periphery. Determined by mass spectrometry and X-ray diffraction, van der Waals (vdW) interactions like London dispersions (LD), stemming from solubilizing tert-butyl groups, were identified to be the major reason for the cluster formation. Cluster sizes comprised of more than twenty molecules with masses up to 70 000 Da were observed, which are rare examples of large architectures based on synthetic functional molecules, assembled by dispersion interactions. Novel strategies towards the design of solution processable functional materials, capable of dynamic transformations based on non-covalent synthesis can be envisioned.

Full text of DOI:10.1002/chem.201803684

A Journal of
Accepted Article
Title: Superbenzene-Porphyrin Gas-Phase Architectures Derived from
Intermolecular Dispersion Interactions
Authors: Dominik Lungerich, Jakob F. Hitzenberger, Frank Hampel,
Thomas Drewello, and Norbert Jux
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To be cited as: Chem. Eur. J. 10.1002/chem.201803684
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Supported by

Chemistry - A European Journal
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Superbenzene–Porphyrin Gas-Phase Architectures Derived from
Intermolecular Dispersion Interactions
Dominik Lungerich,[a,c] Jakob F. Hitzenberger, Frank Hampel, Thomas Drewello* and Norbert
[b]
[a]
[b]
Jux*[a]
Abstract:
A
systematic series of superbenzene-porphyrin
dispersion (LD),[12,13] are the foundation of – interactions in
DEDs, as they are true for tert-butyl groups. Still, on paper tBu
groups appear as bulky substituents and indeed, usually
solubilizing effects are mostly observed. However, these
nonpolar, though highly polarizable groups were found to be the
key for the preparation and intramolecular stabilization of
unprecedented and putatively bulky all-meta-t-butylated
conjugates was synthesized and characterized. All conjugates show
a high degree of cluster formation that correlates to the amount of t-
butylated hexa-peri-hexabenzocoronenes (tBuHBCs) attached to the
porphyrin’s periphery. Determined by mass spectrometry and X-ray
diffraction, van der Waals (vdW) interactions like London dispersions
(LD), stemming from solubilizing t-butyl groups, were identified to be
the major reason for the cluster formation. Cluster sizes comprised
of more than twenty molecules with masses up to 70.000 Da were
observed, which are rare examples of large architectures based on
hexaphenylethane
through
attractive
CH–CH
(–)
interactions.[10] Similarly, intermolecular LD interactions were
found to be the main driving force for the record holder of the
…
synthetic functional molecules, assembled by dispersion interactions. smallest observed H H bond, which was obtained for all-meta-t-
Novel strategies towards the design of solution processable
functional materials, capable of dynamic transformations based on
non-covalent synthesis can be envisioned.
butylated triphenylmethane dimers.[9] Further, precise crystal
engineering of tert-butylated triptycene derivatives showed also
[
14]
very close tBu-tBu interactions in the solid state. By means of
gas-phase experiments,[
15-18]
molecular balance studies,
[8,19-27]
and advances in computational methodologies,[4,28,29] the view
on London dispersion clearly changed during the last
decade.[2,30] The scientific community realized how nature is
Introduction
taking advantage of these interactions for the assembly of large
architectures.[6] To our surprise, aside from molecular balance
models, experimentally, LD and related vdW interactions were
The impact on the formation of condensed matter by means of
dispersion interactions, as it is true for e.g., alkanes, was known
since the early explorations by van der Waals (vdW) in the late
mainly investigated in rather “small” and “innocent”
1
9th century and was subsequently recognized by a Nobel prize
[9,10,31-34]
-6
molecules.
However, due to its R -dependency, the true
in 1910.[ Nowadays, vdW interactions are the foundation of
basic organic chemistry and taught in first-year undergraduate
level classes; however, these concepts are often forgotten when
it comes to structure design. Bulky substituents like e.g.,
cyclohexyl, adamantyl or tert-butyl (tBu) groups, are often
installed under the premise of Pauli repulsion, thus as sterically
demanding and potentially solubilizing groups.[2,3] However,
recent theoretical[4-7] and experimental work[8-11] led to the rise of
so-called dispersion-energy-donors (DEDs). The attractive
interactions based on oscillating dipole moments, called London
1]
power of LD starts to unfold in large systems with >100
atoms.[2,35] Nonetheless, the role of dispersion interactions, was
proposed to open unprecedented design strategies for
[36]
innovative supramolecular materials concepts.
These novel
perspectives let us re-investigate the possibility of LD
interactions in superbenzene–porphyrin conjugates,[37-40] which
we originally started to investigate as graphene-porphyrin hybrid
materials for the application in organic electronics. We reviewed
our findings from 2014, in which we showed peculiar gas–phase
cluster formations of the first bis–HBC-porphyrin conjugate
[
[
transHBC]P.[38] X-ray diffraction analysis (XRDA) of
transHBC]P did not show any intermolecular packing motifs,
since n-heptane molecules were found to be intercalated
between the –surfaces of the conjugate and thus, acted as
[
a]
Dr. D. Lungerich, Dr. F. Hampel, Prof. Dr. N. Jux
Department of Chemistry and Pharmacy & Interdisciplinary Center
for Molecular Materials (ICMM), Organic Chemistry II
Friedrich-Alexander-University Erlangen-Nuernberg
Nikolaus-Fiebiger-Str. 10, 90458 Erlangen, Germany
E-mail: norbert.jux@fau.de
“
insulator” between the molecules (see figure 1 bottom). On the
II
other hand, XRDA of the respective Zn -complex
[
transHBC]PZn,[ which was crystallized in the absence of n-
38]
[
[
b]
c]
Dr. J. F. Hitzenberger, Prof. Dr. T. Drewello
Department of Chemistry and Pharmacy, Physical Chemistry I
Friedrich-Alexander-University Erlangen-Nuernberg
Egerlandstr. 3, 90458 Erlangen, Germany
E-mail: thomas.drewello@fau.de
heptane, showed distinct HBC–HBC interaction in the solid–
state, despite the presence of “bulky” tBu–groups in the
periphery of the HBC moiety (see figure 1 bottom).
Herein, we communicate for the first time our comprehensive
and systematic study on the effect of tBuHBC units attached to a
central porphyrin core. By means of mass spectrometric and X-
ray diffraction experiments, dispersion interactions, promoting
the formation of radical cation–clusters in the gas phase could
be identified. The findings can lead to new design strategies for
non-covalent syntheses of larger architectures.‡
Dr. D. Lungerich
Department of Chemistry & Molecular Technology Innovation Chair
University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Supporting information for this article is given via a link at the end of
the document.
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Results and Discussion
the inner nitrogen atoms.[39] Additionally, possible intermolecular
oxidative dimerization reactions at the unsubstituted meso-
position (in case of 5 and 6) could be suppressed, since the
electron density at the electron-rich meso-positions was reduced
due to the protonation of the porphyrin core.[45] Overall one can
say that the condensation with HPB-CHO followed by Scholl
oxidation works more efficiently, then the direct condensation of
HBC–CHO. However, in case of 1, a successful isolation could
be only achieved starting directly from HBC–CHO, because the
respective HPB–porphyrin showed incredibly poor solubility and
isolation from the other statistical isomers failed.[42] The higher
solubility of 1 compared to its HPB-analogue can be explained
by the out-of-plane rotation of the HBC moiety, whereas the
respective HPB remains in plane with the porphyrin. The meso–
aryl (aryl = 3,5-di-t-butylphenyl) conjugates were prepared
We approached our investigations by the preparation of mono–,
bis–, tris– and tetra–substituted HBC–porphyrin scaffolds (see
figure 1 top and scheme 1), which were synthesized by modified
Lindsey–type condensation protocols[41-44] of formylated
hexaphenylbenzene HPB-CHO or hexabenzocoronene HBC-
CHO.[ Briefly, in case of conjugates 1–4 (scheme 1 top), a fast
microwave-assisted porphyrin condensation method, which
allows to work in ten times higher concentrations (100 mM)
worked efficiently for HPB-CHO.[43,44] On the other hand, the
solubility of HBC-CHO revealed to be too low and therefore
typical Linsey conditions at 10 mM concentration had to be
carried out.[41] The outcome of the Scholl oxidation of the
hexaphenylbenzene–porphyrin conjugates (5–7) could be
38]
analogously, in
a
microwave-assisted statistical mixed
44]
[
condensation reaction; only mono–HPB–porphyrin 8 and cis-
bis–HPB–porphyrin 9 could be successfully isolated from trans-
bis–, tris– and tetra-conjugates 10, 11 and 7. 8 and 9 were
converted to the desired HBC-conjugates 1a and cis-2a in a
Scholl oxidation reaction under standard conditions. Attempts to
separate the mixture of HPB-porphyrin conjugates 10, 11 and 7
2
by column chromatography on SiO as well as by size-exclusion
chromatography on sephadex SX1 failed. Scholl oxidation of the
mixture to the respective HBC-porphyrin mixture, followed by a
II
chromatographic separation remained unsuccessful as well. Ni -
complexes 1aNi, cis-2aNi and 4Ni were obtained from the
conversion of the free-base conjugates with Ni(acac) in toluene
2
at 130 °C. Further synthetic details can be extracted from the
supporting information.
In order to avoid inherent substituent effects from moieties other
than HBCs attached to the porphyrin, the aryl–free, meso–H
porphyrins were considered first and subjected to matrix-
assisted laser desorption/ionization (MALDI) mass spectrometry
(
MS).
DCTB
(trans-2-[3-(4-tBu-phenyl)-2-methyl-2-
propenylidene]malononitrile) was used as matrix and resulted in
the formation of HBC–porphyrin radical cations. In order to avoid
the detection of concurrent dissociations of metastables,[
which would result in the distortion of the cluster distribution, the
ions were detected in a time of flight (ToF) detector in linear
mode. As a simple criterion for the cluster formation ability, we
46]
defined the ratio D between the signal intensities of the dimer I
D
versus the intensity of the monomer I , D = I /I . A clear
M
D M
correlation between the amount of HBC units and D can be
identified. As depicted in figure 2a, the mono-HBC–porphyrin
conjugate 1 shows a D ratio of 8%. D further increases to 14%
for bis–conjugate 2 and reaches its maximum with 24% for 3
and 4. Interestingly, while the D/HBC seems to average at a
value of 8 ± 1%, the fourth HBC unit seems not to have an
additional effect on the clustering ability. We attribute this to the
spacial coverage of HBCs into all three dimensions already for 3,
and obviously, it does not further improve with four HBCs as in
case of 4.
Figure 1. Top: herein investigated superbenzene–porphyrin scaffolds; R = H
for 1, 2, 3; R = 3,5-di-t-butylphenyl for 1a and cis-2a; bottom: solid–state
packing of [transHBC]P with intercalated n-heptane molecules indicated in
yellow and green; below: solid–state packing of [transHBC]PZn.
improved by the addition of small amounts of TFA, because the
solubility of the conjugates increased due to the protonation of
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Scheme 1. Top: Synthesis of meso-H substituted HBC-porphyrin conjugates 1–4: a) CH
2
Cl
2
, 1 equiv. DPM, 2 equiv. pyrrole-2-carbaldehyde, cat. TFA, rt, 18 h,
then DDQ, rt, 1.5 h, (4%); µW: CH
HPB), 0 °C to rt, 18 h, 2 cycles (2 95%, 3 93%, 4 87%); d) µW: CH
2
Cl
2
, 1 equiv. DPM, cat. I
2
, 40 °C, 10 min, then para-chloranil, 40 °C, 2 min, (29%); c) CH
CL , 0.33 equiv. DPM, 0.66 equiv. pyrrole, cat. I , 40 °C, 10 min, then para-chloranil, 40 °C,
, 40 °C, 10 min, then para-chloranil, 40 °C, 1 min, (39%); f) CH
, 16 equiv. FeCl /MeNO , 0 °C, 3 h, (88%); Bottom: Statistical synthesis of meso-arylated HBC-
Cl , 2 equiv. pyrrole, cat. I2, 40 °C, 5 min, then para-chloranil,
(per HPB), 0 °C to rt, 18 h, (1a 99%, cis-2a 80%); j) µW: toluene, 20 equiv. Ni(acac)
30 °C, 1 h, (1aNi 99%, 2aNi 99%, 4Ni 99%); acac = acetylacetonate, DDQ = 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, DPM = dipyrromethene µW =
2 2 3 2
Cl , TFA, 16 equiv. FeCl /MeNO (per
2
2
2
.
2 2 3 2
Cl , 1 equiv. pyrrole, cat. BF OEt ,
2
min, (6 9%, 7 21%); e) µW: CH
2
Cl
2
, 1 equiv. pyrrole, cat. I
Cl
2
cat. EtOH, rt, 1 h, then DDQ, rt, 1.5 h, (4 11%); g) CH
porphyrin conjugates 1a, cis-2a and the nickel complexes 1aNi, cis-2aNi and 4Ni: h) µW: CH
2
2
3
2
2
2
40 °C, 1 min (8 18%, 9 24%); i) CH
2
Cl
2
, TFA, 16 equiv. FeCl
3
/MeNO
2
2
,
1
microwave reactor, TFA = trifluoroacetic acid.
Alteration of the analyte-to-matrix ratio from 1:50 to 1:5000 does
not affect the appearance of the mass spectra. Laser
desorption/ionization (LDI) on the other hand, gives nothing
except monomers of the respective conjugates and thus in-gas-
phase cluster formations can be ruled out. It is reasonable to
expect that the clusters are pre-formed during the crystallization
on the target plate; MALDI then transfers these clusters into the
gas phase. The harsh conditions of direct laser irradiation in LDI
leads to the complete dissociation of the pre-formed clusters and
no evidence could be found that support an in-gas-phase cluster
formation. Intermolecular covalent bond formations could be
excluded as well, since the clusters dissociate upon changing
from linear to reflectron mode while passing through the
spectrometer.[38] With an increasing I
/I ratio, an inherent
D M
increase of cluster sizes can be observed. The largest clusters
that were identified for 1 contained up to six molecules, whereas
a steady increase for 2 with up to nine molecules, and 3 and 4
with >20 molecules could be detected, hence forming nano–
architectures reaching masses way beyond 50.000 Da or 70.000
Da, respectively, (see figure 2b for 4 and figures S1–S4 for 1, 2
and 3).
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To identify the active part in the cluster formation, observed for
the conjugates, we performed electrospray ionization (ESI) of
tetraphenylporphyrin (TPP) and hexa-t-butyl-HBC (tBuHBC),
which undergo cluster formations in ESI (compare figure S5). By
performing energy–resolved collision–induced dissociation (CID)
of the dimer cation from tBuHBC, TPP and a mixture of both
occupation of higher lying orbitals increases their polarizability
and hence, leads to increased dispersion interactions in the
cluster material.[47]
This hypothesis is further supported by the ultrafast energy-
transfer from the HBC to the porphyrin upon excitation of the
HBC’s -band (compare absorption and emission spectra in
(
TPP/tBuHBC) the role of the porphyrin moiety as the active
figure 5; discussion of the optical spectra can be found at the
end of the manuscript).[
37,38]
Unfortunately, reliable and high level
cluster part could be ruled out. As shown in figure 2c, TPP
shows only very weak interactions and fragmentation takes
place already at low energies. In comparison, the cluster
strength increases drastically for the TPP/tBuHBC dimer and
finds its maximum for the pure tBuHBC dimers. However, at that
DFT computations, which include dispersion contributions
require large basis sets and electron correlation corrections;
common functionals like e.g., B3LYP are inefficient in describing
the LD contributions in supramolecular gas-phase assemblies.
Figure 2. Cluster experiments in MS: a) determination of the cluster ability ratio D by MALDI MS in linear mode; b) zoom-in into the high mass region of [4] 
clusters; c) relative comparison of energy dependent CID of dimers from TPP (orange), TPP/tBuHBC mixture (green) and tBuHBC (blue).
+
n
point it should be noticed that neither tBuHBC clusters nor
TPP/tBuHBC mixed–clusters are formed during MALDI, and
thus, this phenomenon can be solely attributed to the HBC–
porphyrin conjugates (compare figure S6– S8). We believe this
could be related to induced polarization effects during electronic
excitation of the conjugates in the mass spectrometer, since the
Reasonable DFT functionals can be used for smaller molecules
(<200 atoms), but investigations of our smallest dimer (1 +•),
excluding the formation of multimers, would already include
>300 atoms; hence busting our computational capacities at the
moment.[36]
2
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Figure 3. Single crystal structure analysis of 1a; a) ORTEP model depicted with 50 % thermal ellipsoids; b) side–view on HBC–HBC packing interactions; c)
top–view on HBC–HBC packing interactions (from bottom to top: [green]–[red]–[blue]–[orange]; d) zero-dimensional dimer formation between [green] and [red]
through – and CH– interactions; e) one-dimensional propagation through CH–CH interactions between [red] and [blue].
We obtained a deeper understanding of the supramolecular
binding situation in superbenzene–porphyrin clusters, by
performing XRDA on selected examples. Regrettably,
n-alkylated HBCs, was found to undergo mere dimer formation
in a sandwich–herringbone packing.[48-50] While a herringbone
type packing cannot be observed for 1a, an attractive one-
dimensional CH–CH interaction of the tBu–groups at the
periphery of the HBCs with tBu–groups from the next dimer–pair
propagates through the crystal (compare figure 3b, c and e;
superbenzene–porphyrins 1, 2,
3 and 4 could not be
successfully analyzed. However, single crystals suitable for
XRDA of 1a could be obtained by layer diffusion from a
toluene/methanol mixture. In the solid state, the HBC plane is
tilted by 70° with respect to the porphyrin (compare figure 3a),
allowing a reasonable electronic communication between both
chromophores. As it can be extracted from figure 3b–3e, two
major interaction motifs can be elucidated for 1a, which can be
classified as zero–dimensional interactions and one–
dimensional propagation interactions. The 0D–interactions stem
from – and CH– interactions of two HBC planes and their tBu
groups (compare dimer pairs in figure 3b–d; [green–red] and
…
[red–blue]). Hereby, an average H H distance of 2.69 Å can be
observed, which is in the perfect range for attractive London
dispersion interactions (2.5– 3.0 Å).[ In case for Ni –complex
1aNi, which shows a saddle-shape distortion of the porphyrin
plane, the intermolecular interaction parameters change only
marginally to a – distance of 3.39 Å for the HBC planes and
8]
II
…
an averaged H H distance of 2.74 Å for the tBu–groups (see
figure S9 in the supporting information). Hence, changing the
electronic properties and the shape of the porphyrin by nickel
(and zinc as shown for [transHBC]PZn) complexation has no
significant impact on the intermolecular interactions, which is
[
blue–orange]). The distance of the respective HBC–dimers is
found to be around 3.47 Å, which is in good agreement with the
crystal structure analysis of tBuHBC (3.44 Å) and which, unlike
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also reflected in the gas–phase cluster formations of 1aNi
versus 1a (see figure S10 in the supporting information).
When it comes to multi–HBC–porphyrin conjugates, these
interact with the porphyrin plane of an adjacent molecule via
CH– attractions. However, we believe that these particular
interactions are neglectable in the gas phase and are mere
interactions can be imagined to propagate not only in x–direction, findings arising from packing phenomena in the solid state. This
thus in one dimension, but also into the second– and third–
dimensional space. With that said, XRDA of cis-2a, which was
assumption is based on the fact that the clustering ability of 1a,
with detected cluster sizes of up to four molecules (see figure
S11), and cis-2a with clusters of a maximum size of six
molecules (figure 4b), are obviously smaller compared to their
respective meso–H conjugates 1 and 2 and thus the 3,5-di-tBu-
phenyl moieties at the porphyrin seem not to contribute to
crystallized by layer diffusion from a mixture of CH
methanol, provided an interesting view. As it is depicted in figure
a, the cis-configuration of cis-2a leads to the formation of 1D
zig-zag wires”. Even though the structure resolution does not
2 2
Cl and
4
“
Figure 4. a) Top-view on the two dimensional “carpet-formation” of cis-2a through – and CH– interactions; b) MALDI MS of cis-2a and the respective nickel-
complex cis-2aNi; c) top-view on the two-dimensional network of 4Ni; intercalated n–heptane molecules are highlighted in light blue as space filling model
structures; d) side-view on the three-dimensional network of 4Ni; [green] lies directly on top of [purple]; n-heptane molecules are omitted for clarity.
allow for detailed assignments of intra- and intermolecular bond
lengths, the interactions remind closely of the zero-dimensional
interplay, which was discussed above for 1a. Interestingly, in y-
direction the next set of zig-zag wire is found to be closely
attached via CH– interactions of the tBu-groups of the aryl
moiety at the porphyrin with the HBC plane, forming a “2D-
carpet” of linearly assembled zig-zag wires. Similarly, in case of
attractive interactions. This hypothesis is consistent with the
findings of Hwang et al., who demonstrated with their molecular
balance model that the nature of the interactions (attractive
versus repulsive) of “bulky” tBu–groups are highly dependent on
the location at the aryl moiety. Thus, meta- positioned tBu–
groups in our case did not show attractive interactions, which is
also reflected in the high solubility of conjugates 1a and cis-2a.[8]
1a a few of the tBu–groups of the aryl moiety were found to
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becomes the interaction motif, if the perspective is tilted onto the
z-axis, hence into the third dimension. Indicated in figure 4d, the
molecules interact in such way that the beneath lying layer is
interconnected by the respective HBC–HBC interactions,
accordingly leading to a dispersion-based 3D-network ([green]
molecule is lying directly on top of the [purple] molecule). With
this model in hand, the strong cluster formation ability of 3 and 4
becomes reasonable. Despite the sterically much more crowded
situation of 3 and 4, taking into account that all para-positions at
the HBC are t-butylated and the –surface of the porphyrin
plane is not available for any strong interactions, the large
clusters in MALDI and the structure analysis conclude that all
attractive interactions stem from the tBuHBC–tBuHBC interplay.
However, the powerful interplay is not solely based on intuitively
apparent – interactions but appears to benefit largely from –

and – interactions, originating from the peripheral DEDs.
Importantly, the cluster formation ability is not related to the
solubility of the molecules in e.g. CH Cl or CHCl , which does
2
2
3
not only allow the clear analysis by NMR spectroscopy in
solution (compare figures S12–S15 in the supporting
information), but correlates well to the latest observations by
Pollice et al., who found the attenuation of LD in CH Cl
2 2
solutions.[11] A qualitative depiction can be summarized as the
following: cluster size: 4 ≥ 3 > 2 > 1 ≥ 2a > 1a; solubility
(
2 2
CH Cl ): 1a ≥ 2a > 3 ≥ 4 > 1 >> 2. With that said, one can
clearly rule out mere aggregation phenomena due to low
solubility, which readily occur in –rich molecules like e.g., in
unsubstituted HBC–porphyrin conjugates,[ or large polycyclic
aromatic hydrocarbons. In fact, some of the HPB-porphyrin
conjugates like e.g., 5,15-bis-HPB-porphyrin (precursor of 2),
show to be almost insoluble in common solvents like e.g.,
37]
2 2
CH Cl , but no evidence for cluster formation in MALDI could be
detected.
Finally, the absorption and emission properties of conjugates 1–
4, shown in figure 5, are discussed. As depicted in figure 5a, the
absorption characteristics of the HBC-moieties remain, besides
an increased extinction coefficient upon increasing the number
of HBCs in the conjugate, unchanged; no shift of the -bands
(
358 nm) are observed. On the other hand, the porphyrins B-
Figure 5. Spectroscopic analysis of HBC–porphyrin conjugates 1–4; a)
and Q-bands exhibit distinct red shifts, with absorption maxima
for the B-band at 402 (1), 415 (2), 434 (3) and 441 nm (4).
Furthermore, a remarkable broadening of the B-band with rising
number of HBCs is observed. Additionally, conjugates 2, 3 and 4
show a split in the B-band. Upon excitation of the conjugates, a
very efficient energy transfer from the HBC-periphery to the
porphyrin core can be observed (figure 5b-e). Excitation of the -
band leads exclusively to the emission of the porphyrins Q-band
and no emission from the HBC moieties can be observed in any
of the conjugates. While the ratio of emission intensity for 1 is
higher upon excitation of the porphyin itself, conjugates 2, 3 and
4 show ratios close to one, underpinning the efficient energy
transfer. In fact, conjugates 3 and 4 show slightly higher
porphyrin Q-band emissions after excitation of the HBC’s
band, than after the B-band.
UV/vis spectra of 1 (black), 2 (red), 3 (green) and 4 (blue) in CH
emission spectra of 1 (b), 2 (c), 3 (d) and 4 (e); excitation of B-band (black)
and -band (red) in CH Cl at rt; insert values indicate the ratio of the
emission intensity of the porphyrin’s Q-bands after excitation of the B-band
versus the -band.
2 2
Cl at rt; b–e)
2
2
Lastly, a preliminary structure solution of 4Ni, crystallized from a
mixture of CS , CH Cl and n-heptane shows a consecutive
2 2 2
HBC–HBC stacking, as it is true for the 0D–dimer of 1a; though,
this time interrupted by intercalated and thus “insulating” n-
heptane molecules, as it was already observed for the
[
37]
[
transHBC]P conjugate in 2014. It was shown that n-heptane
molecules serve only as “insulators” between the HBC planes,
without really affecting the overall packing motif and therefore,
they cause a switching between a “conducting” to an “insulating
state”. Consequently, upon “virtual–exhaling” of the n-heptane
molecules, the actual packing pattern in x- and y-direction
becomes readily apparent (see figure 4c). Even more striking
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Chemistry - A European Journal
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Conclusions
‡
Results are taken in parts from: D. Lungerich, Doctoral Thesis,
Friedrich–Alexander–Universität Erlangen–Nürnberg, 2017.
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Keywords: Porphyrin • Hexabenzocoronene • Cluster • Mass
spectrometry • Dispersion Interaction
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Entry for the Table of Contents (Please choose one layout)
FULL PAPER
Non-covalent architectures
Superbenzene-porphyrin conjugates
were synthesized that show a high
cluster formation ability. The cluster
size correlates to the amount of tert-
butylated hexa-peri-hexabenzo-
coronenes attached to the
porphyrin’s periphery. Determined by
mass spectrometry and X-ray
diffraction, London dispersion
interactions stemming from the tert-
butyl groups were identified to be the
major reason for the cluster
D. Lungerich, J. F. Hitzenberger, F.
Hampel, T. Drewello,* N. Jux*
Page No. – Page No.
Superbenzene-porphyrins
MALDI
Superbenzene–Porphyrin Gas-
Phase Architectures Derived from
Intermolecular Dispersion
Interactions
Dispersion
forces
>70.000 Da
Gas-phase cluster
formation.
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