Synthesis of Oligo(1,8-pyrenylene)s: A Series of Functional Molecular Liquids

Article abstract of DOI:10.1002/cplu.201900133

A monomer-through-pentamer series of oligo(1,8-pyrenylene)s was synthesized using a two-step iterative synthetic strategy. The trimer, tetramer, and pentamer are mixtures of atropisomers that interconvert slowly at room temperature (as shown by variable-temperature NMR analysis). They are liquids well below room temperature, as indicated by POM, DSC and SWAXS analysis. These oligomers are highly fluorescent both in the liquid state and in dilute solution (λ_F,max = 444–457 nm, φ_F = 0.80) and an investigation of their photophysical properties demonstrated that delocalization plays a larger role in their excited states than it does in related pyrene-based oligomers.

Full text of DOI:10.1002/cplu.201900133

Accepted Article
Title: Synthesis of Oligo(1,8-pyrenylene)s: A Series of Functional
Molecular Liquids
Authors: Joshua C. Walsh, David T. Hogan, Kerry-Lynn M. Williams,
Simon D. Brake, Gandikota Venkataramana, Tara A.
Misener, Brandon J. Wallace, Richard P. Johnson, David W.
Thompson, Yuming Zhao, Brian D. Wagner, and Graham J.
Bodwell
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ChemPlusChem
10.1002/cplu.201900133
FULL PAPER
Synthesis of Oligo(1,8-pyrenylene)s: A Series of Functional
Molecular Liquids
[
a]
[a]
[a]
[a]
Joshua C. Walsh, David T. Hogan, Kerry-Lynn M. Williams, Simon D. Brake, Gandikota
[
a]
[b]
[b]
[c]
Venkataramana, Tara A. Misener, Brandon J. Wallace, Richard P. Johnson, David W.
[
a]
[a]
[b]
[a]
Thompson, Yuming Zhao, Brian D. Wagner * and Graham J. Bodwell*
Dedicated to the memory of Rajendra Rathore
Abstract:
A
monomer-through-pentamer series of oligo(1,8-
unusual for an aromatic molecule of its size. Combined with
their luminescence, this property renders them functional
pyrenylene)s was synthesized using a two-step iterative synthetic
strategy. The trimer, tetramer and pentamer are mixtures of
atropisomers that interconvert slowly at room temperature (VTNMR
analysis). They are liquids well below room temperature, as
indicated by POM, DSC and SWAXS analysis. The oligomers are
highly fluorescent both in the liquid state and in dilute solution and
an investigation of their photohysical properties demonstrated that
delocalization plays a larger role in their excited states than it does in
related pyrene-based oligomers.
[
8]
molecular liquids (FML).
Organic FMLs have been described
as “the third generation of liquid chemicals after the first and
second generations of solvent liquids and ionic liquids,
[
8b]
respectively” and are a rapidly-emerging class of compounds
owing to their ease of processability in device fabrication (e.g.
using painting and printing), ease of deformation within devices,
high thermal stability and their ability to act as solvents for
[
8]
dopants.
FMLs have also been used as the basis for the
[
8e]
formation of white-emitting luminescent inks.
Introduction
R*O
R*O
Pyrene is an increasingly useful building block for the synthesis
of designed pi systems, due mainly to its intense fluorescence
and the sensitivity of its fluorescence to its microenvironment.
Although pyrene has featured prominently in a large number of
4 n=x–y
n
X
X
R
R
R
[
1]
designed pi systems, only a few oligoarylenes composed
5 R=1-octyl
n=1–3
X
exclusively of pyrene units have been reported. This includes,
n
6
a X=H, R*=2-hexyl-
[
2]
but is not limited to, dendrimers 1 and 2, cyclic oligo(1,3-
1-decyl
6b X=2,5-di(2-hexyl-
decyloxy)phenyl
R
R
R
[
3]
[4]
pyrenylene) 3,
poly(2,7-pyrenylene)
4
and oligo(1,6-
[
5]
Target
Compounds
RO
OR
pyrenylene)s 5 (Figure 1).
Some poly(pyrene)s with varying
R*=2-hexyl-1-decyl
degrees of polydispersity and integrity of the substitution pattern,
as well as oligomers with mixed substitution patterns have also
Key FML Design Features
n
• strong fluorophores
• effective solublizing groups
[
6]
been reported.
Oligopyrenes 1-5 all exhibit strong
•
biaryl bonds
fluorescence, which makes them candidates for use as
luminescent materials in organic optoelectronic devices.
Unlike oligo(pyrenylene)s 1-5, which are all solids, some
recently reported pyrene-containing oligoarylenes, e.g. 6, were
7
• atropisomerism
(FML candidates)
RO
OR
RO
OR
[
7]
found to be liquids at room temperature. This property is very
X
X
t-Bu
R
R
R
R
[a]
J. C. Walsh, D. T. Hogan, K.-L. M. Williams, S. D. Brake, Dr. G.
Venkataramana, Prof. D. W. Thompson, Prof. Y. Zhao, Prof. G. J.
Bodwell
t-Bu
t-Bu
R
R
R
R
Chemistry Department
Memorial University of Newfoundland
283 Prince Philip Drive, St. John’s, NL, Canada, A1B 3X7
E-mail: gbodwell@mun.ca
[
b]
c]
T. A. Misener, B. J. Wallace, Prof. Brian D. Wagner
Chemistry Department
t-Bu
t-Bu
University of Prince Edward Island
550 University Ave, Charlottetown, PE, Canada, C1A 4P3
R
R
R
R
E-mail: bwagner@upei.ca
Prof. R. P. Johnson
X
X
t-Bu
[
1
R=H, X=t-Bu
Department of Chemistry and Materials Science Program
University of New Hampshire
Durham, NH 03824, USA
2 R=7-t-Bu-pyren-1-yl, X=H
3
Figure 1. Oligo(pyrenylene)s 1-5, pyrene-based FMLs
pyrenylene)s 7.
6
and oligo(1,8-
Supporting information for this article is given via a link at the end of
the document.
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Nakanishi’s guidelines for the design of FMLs address
certain key structural features that disfavor π–π interactions and
contributor to the suppression of solidification. It was therefore
decided to employ decoxy groups for the synthesis of the
targeted oligo(1,8-pyrenylene)s.
[
7]
thus suppress solidification. These include biaryl bonds, alkoxy
substituents with branching and low symmetry in the pi skeleton.
The notion that some combination of the these structural
features underpins the room temperature liquid behavior and our
recent interest in the synthesis of designed π systems featuring
RO
OR
RO
OR
RO
OR
[
9]
1
,8-pyrenylene units fuelled work in our group aimed at the
*
*
*
B(OR)2
*
synthesis of oligo(1,8-pyrenylene)s 7. Like 6, these purely
pyrene-based oligoarylenes have biaryl bonds and are adorned
with alkoxy substituents. Furthermore, the high barrier to
8
9
10
(dimer)
(
monomer)
1
. Regioselective halogenation
1st iteration
1st iteration
2. Suzuki-Miayura with 9
RO
OR
[
10]
rotation about the 1,1’-bipyrenyl bond (25.8 kcal/mol)
means
11 n=1 (trimer)
RO
OR
12 n=2 (tetramer)
14 n=4 (hexamer)
16 n=6 (octamer)
2
nd iteration
2nd iteration
3rd iteration
1
1
3 n=3 (pentamer)
5 n=5 (heptamer)
that atropisomerism comes into play and mixtures of
diastereomers will be expected starting with the trimer (7, n=1).
These (or any) diastereomers will have different shapes, which
would be expected to disfavor long-range ordering and thus
inhibit solidification. In fact, Nakanishi’s FMLs are also mixtures
of diastereomers due to the presence of a stereorandom
stereogenic centre in each of the eight Guerbet-alcohol-derived
side chains. For example, there are eight side chains in 6b,
which gives rise to 44 diastereomers (see Supporting
Information). Thus, diastereoisomerism is a separate issue from
branching alone, which may or may not bring with it
stereochemical consequences. Finally, with multiple pyrene
units in the oligo(1,8-pyrenylene)s 7, strong fluorescence would
be expected, so they appear to be promising candidates for new
FMLs. We report here the synthesis and characterization of the
monomer through the pentamer.
3rd iteration
n
*
*
RO
OR
RO
OR
Scheme 1. Iterative strategy for the synthesis of oligo(1,8-pyrenylene)s.
RO
OR
RO
OR
MeO
OMe
Br
2
(
R)
(S)
CH Cl
2
2
H
H
rt, 2-5 min Br
Br
meso-19b
8
a R=Dec
17a R=Dec, 96%
17b R=Me, 95%
8b R=Me
Pd(PPh
1,4-dioxane, H
0-100 °C, 16-19 h
3 4 2 3
) , K CO
1
8
2
O
MeO
OMe
8
HO
B
OH
RO
OR
(R)
(R)
Results and Discussion
H
H
MeO
OMe
[
5]
Akin to Rathore’s synthesis of the oligo(1,6-pyrenylene)s 5, an
iterative strategy was envisioned for the synthesis of the
oligo(1,8-pyrenylene)s 7 (Scheme 1). Each iteration consists of
a regioselective bromination (at the starred positions) followed
by a Suzuki-Miyaura cross-coupling with an appropriate boronic
(S)
(S)
H
H
(
±)-19b
1
1
9a R=Dec, 27% (liquid at rt)
9b R=Me, 38% (mp >233 °C, dec.)
[
11]
ester 9. Application of this strategy to the monomer 8 would
successively give rise to the odd-numbered oligomers (11, 13,
Scheme 2. Synthesis of 1,8-dipyren-1-ylpyrenes 19a and 19b and a depiction
of the two diastereomers of 19b.
1
5, etc.) and dimer 10 would serve as a starting point for the
synthesis of the even-numbered oligomers (12, 14, 16, etc.).
The success of this strategy hinges on the maintenance of the
complete regioselectivity of the bromination step for the starred
positions of each oligomer and the development of a way to gain
access reliably to synthetically usefully quantities of a boronic
acid/ester 9, which comes into play during every iteration.
The branched (chiral) alkyl groups employed by Nakanishi,
which rendered his FMLs mixtures of diastereomers, were not
considered here because the atropisomerism of the 1,1’-
bipyrenyl system was expected to result in the formation of
1
mixtures of diastereomers. Indeed, the H NMR spectra of 19a
Synthetic work aimed at realizing the iterative strategy
commenced with 4,5-dialkoxypyrenes 8a and 8b, which were
and 19b (Figure 2) exhibit two sets of signals, which is
consistent with the presence of two slowly interconverting
atropisomeric diastereomers, i.e. meso-19a and (±)-19a. For
both compounds, the highest-field aromatic signals are a pair of
singlets (no COSY cross-peaks, see Supporting Information)
attributable to the K-region protons of the central pyrene unit (δ
[
12]
synthesized from pyrene by K-region oxidation and reductive
[
11]
alkylation as previously described (Scheme 2).
Br afforded the corresponding dibromides 17a and 17b in high
yield. The Suzuki-Miyaura step was first tested using
Reaction with
2
commercial pyrene-1-boronic acid (18) and this afforded 1,8-
dipyren-1-ylpyrenes 19a and 19b. The yields were modest, but
the observation that 19b is a high-melting solid (mp >233 °C,
dec) and 19a is a room-temperature liquid was striking. For
these compounds, side chain length is clearly an important
7
.53 and 7.49 ppm for 19a; δ 7.50 and 7.47 ppm for 19b). In
both cases, the higher-field signal is slightly more intense and
integration points to a 53:47 ratio of the two diastereomers.
Some broadening was observed upon heating to 110 °C (Figure
S1), but the system was clearly not close to coalescence. This
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[
10]
is in line with the calculated barrier of 25.8 kcal/mol.
For 19b,
temperature, which would require the separation of just two
compounds and not three. For practical purposes, slow addition
where Δν = 14.7 Hz for the two K-region singlets, this barrier
would correspond to a coalescence temperature (T ) of 217 °C.
c
2 2 2
of a solution of 1.3 equivalents Br in CH Cl was also found to
Progress with the iterative strategy could not be made with
result in the complete consumption of 8a and the reaction could
be scaled up to 5 g of 8a. At this scale, a 73% yield of 20 was
obtained along with 19% of 17a (Scheme 3). It is worth noting
that the chromatographic separation of 20 from 17a was found
to be easier than the separation of 20 from 8a, even though the
1
9a and 19b because each of the terminal pyrene units has
three sites available for electrophilic aromatic substitution.
Accordingly, attention was turned to the synthesis of a boronic
acid or ester of the general structure 9. The main challenge in
accomplishing this was the selective monofunctionalization of
f
differences in R values did not suggest this.
4
,5-didecoxypyrene (8a).
DecO
ODec
DecO
ODec
HBPin
Pd(dppf)Cl2
KOAc
DecO
ODec
Br2
1.3 equiv)
(
CH2Cl2
rt, 5 min
1,4-dioxane
80 °C, 4 h
91%
X
Y
BPin
8
a
22
17a or 21
2
1
0
X=H, Y=Br, 73%
7a X=Y=Br, 19%
I2, Hg(OAc)2
CH2Cl2, rt
2
1
X=Y=I, 88%
Pd(PPh3)4, Ba(OH)2
toluene, EtOH, H2O
80 °C, 4–24 h
2
0 min
DecO
ODec
11a n=1, X=H
7
9
7% from 17a
1% from 21
Br2, CH2Cl2
rt, 5 min, 78%
X
n
X
2
3 n=1, X=Br
2
2, Pd(PPh3)4
Ba(OH)2
toluene, EtOH, H O
2
8
0 °C, 24 h
1
13a n=3, X=H DecO
ODec
DecO
ODec
Figure 2. Aromatic region of the 300 MHz H NMR spectrum of 19b in CDCl
3
highlighting the clearly identifiable pairs of signals due to the meso and (±)
Scheme 3. Synthesis of boronic ester 22, trimer 11a and pentamer 13a.
diastereomers.
With access to multigram quantities of 20, its conversion to
boronic ester 22 was investigated. Lithiation-borylation
Monobromination of 8b with Br
2
at –78 °C has been
[
13]
reported, but the compound was used without purification and
no indication of the distribution between unbrominated,
monobrominated and dibrominated products was given.
protocols were found to be unsatisfactory and, after screening
various sets of conditions, it was found that Miyaura borylation
2
using HBpin, Pd(dppf)Cl and KOAc in 1,4-dioxane enabled the
Nevertheless,
monobromination of 8a was achievable. Preliminary attempts to
monobrominate 8a using Br , CuBr and NBS all gave mixtures
this
result
suggested
that
selective
synthesis of 22 in 91% yield on a 1.5 g scale. The synthesis of
the odd-numbered oligomers then commenced with the Suzuki-
Miyaura cross-coupling between dibromide 17a and boronic
ester 22, which afforded trimer 11a (77%) (Scheme 3). The use
2
2
of unbrominated, monobrominated and dibrominated products
under a variety of conditions. To better understand the progress
2 2 3
of Ba(OH) instead of K CO was found to give much better
of the reaction, an experiment was performed in which Br
2
was
yields. No dimeric species arising from incomplete Suzuki-
Miyaura reaction or protodebromination were observed (TLC,
added to a CH Cl solution of 8a (500 mg) in 0.1 equivalent
2
2
portions at room temperature. TLC analysis following each
addition showed that the expected new spot for monobromide
1
NMR analysis). As in the case of 19a and 19b, the H NMR
spectrum of 11a showed the presence of two diastereomers
2
0 (R
addition, a little ahead of the one for 8a (R
new faster-moving spot corresponding to dibromide 17a
=0.20) appeared after the addition of just 0.3 equivalents of
. The starting material 8a was fully consumed only after the
addition of 1.3 equivalents of Br and the last vestiges of
monobromide 20 disappeared after the addition of 2.2
equivalents. The addition of 10 equivalents of Br or the use of
neat Br as the solvent does not result in further bromination.
f
=0.10, 20% CH
2
Cl
2
/hexanes) appeared after the first
(
see Supporting Information). Singlets for the central K-region
f
=0.15). A second,
protons were observed at δ 7.50 and 7.48 ppm, but this time the
lower-field signal was slightly more intense (51:49). Again,
broadening of the signals was observed at 110 °C, (Figure S1),
but nothing approaching coalescence.
(R
f
Br
2
2
No TLC conditions could be found that resulted in even the
slightest separation of the two diastereomers of 11a, so the
determination of which isomer is dominant presented a stiff
challenge. Structures of the meso and (±) diastereomers (using
MeO substituents instead of DecO for computational ease) were
calculated at the B3LYP/6-31G(d) level of theory using a
chloroform solvent model (Figure S4-5). The meso isomer
2
2
In an attempt to delay the onset of dibromination, the
reaction was performed at lower temperatures. At 0 °C and –
2
0
0 °C, dibromide 17a again appeared after the addition of just
.3 equivalents of Br At –40 °C and –78 °C, 8a precipitated
2
.
(µcalc=0.57 D) was calculated to be 0.12 kcal/mol lower in energy
from the reaction. Based on these results, it was decided to
move forward with the addition of 1.3 equivalents of Br at room
than the (±) isomer (µcalc=0.22 D), which corresponds to a 55:45
2
ratio.
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The bromination of 11a was not as straightforward as that
of 8a. As with 8a, TLC monitoring of the addition of successive
.1 equivalent portions of Br revealed the appearance of first
compound with a much lower R
f
value began to form. It was
never formed in sufficient quantities to enable the acquisition of
0
2
an NMR spectrum, but MS analysis (m/z = 902; most abundant
one faster-moving spot and then another corresponding to the
2 4
signal for C52H54Br O ) was consistent with one of the 4,5-
formation of a monobromide and then dibromide 23. The
didecoxypyrene units having been converted to a pyrene-4,5-
dione unit. Tetramer 12a was obtained in 71% yield upon
Suzuki-Miyaura reaction of dibromide 24 with boronate 22. This
oligomer has four possible diastereomers (statistical ratio =
1:1:1:1, see Supporting Information) arising from the three axes
of asymmetry.
f
differences in the R values, however, were smaller than before,
which did not bode well for chromatographic separation, and the
starting material spot persisted until the addition of 1.9
equivalents of Br
a was found to be resistant to over-bromination, exceeding 2
equivalents of Br almost immediately resulted in over-
2
(cf. 1.2 equivalents for 8a). Additionally, while
8
2
The use of aryl iodides instead of bromides was
investigated as a possible way of improving the yields of the
Suzuki-Miyaura cross-coupling reactions. Monomer 8a was
found to undergo rapid (20 min) and fully regioselective
bromination of 11a, as indicated by TLC (appearance of a new
spot ahead of dibromide 23). The best result was obtained
when 11a was reacted with 2.03 equivalents of Br
2
.
This
afforded dibromide 23 in 78% yield after repeated
chromatography. Suzuki-Miyaura reaction of 23 with boronic
ester 22 then afforded pentamer 13a (84%), which has six
2 2
diiodination upon reaction with I , Hg(OAc) to afford diiodide 21
(88%). Upon increasing the reaction time to 2 h, the yield
plummeted to 50%. The drop in yield is clearly due to a
dealkylation/oxidation reaction as pyrene-4,5-dione was isolated.
In fact, this diketone is also present at the end of the 20-minute
possible diastereomers (statistical ratio
= 1:2:2:1:1:1, see
Supporting Information) arising from the four axes of asymmetry.
For the even-numbered oligomers, dimer 10a was required. reaction (TLC analysis). The use of the diiodide 21 in the
This compound was synthesized using three methods (Scheme
). First, Suzuki-Miyaura coupling of bromide 20 with boronic
ester 22 gave 10a in 64% yield. Second, Feringa’s PEPPSI-iPr-
Suzuki-Miyaura reaction with boronic ester 22 led to a significant
improvement of the yield trimer 11a (91%) (Scheme 3). The
same improvement could not be achieved for higher oligomers
because attempted iodination of dimer 10a and trimer 11a
resulted in rapid and complete consumption of the starting
materials to give mainly TLC immobile compounds. Clearly, the
ease of the dealkylation/oxidation process increases with the
size of the oligomer.
4
[
14]
catalyzed homocoupling of bromide 20 delivered 10a in 94%
yield. Finally, intermolecular Scholl reaction of monomer 8a
[
15]
using Rathore’s DDQ/MeSO
3
H method
proceeded in 37%
yield. Although the yield of the latter reaction is substantially
lower than those of the first two, it is attractive from a practical
perspective. It uses a less precious starting material, is trivially
A key concern with tetramer 12a and pentamer 13a was
the ability to assess purity. The presence of four and six
diastereomers, respectively (see Supporting Information),
complicates the NMR spectra to the point that it is impossible to
tell whether they are contaminated with lower oligomers (with or
without bromine atoms), which might arise from incomplete
Suzuki-Miyaura reaction and/or protodebromination. Using a
number of standard TLC solvent systems, e.g. 10:90
dichloromethane / hexanes, dimer 10a through pentamer 13a
were barely distinguishable (Figure 3A, left). After extensive
experimentation, it was found that the use of 5:5:90 toluene /
dichloromethane / hexanes gave far better separation (Figure 3A,
right). This allowed for more effective chromatography and,
coupled with the intense fluorescence of the oligomers (see
below), enabled visual assessment of purity. To demonstrate
this point, a 1:100 mixture of 11a:12a was prepared and the
minor component was clearly visible to the naked eye (Figure
easy to perform and is finished within seconds.
Higher
oligomers (up to hexamer) could also be observed by MALDI-
MS and trimer 11a could be reliably isolated from this reaction in
up to 17% yield.
DecO
ODec
DecO
ODec
2
3 4 2
2, Pd(PPh ) , Ba(OH) , toluene
2
EtOH, H O, 80 °C, 4–24 h, 64%
X
Br
n-hexane, rt, 10 min, 94%
DDQ, MeSO H, CH Cl
t-BuLi, PEPPSI-iPr
X
2
0
1
2
0a X=H
4 X=Br
Br
CH
rt, 5 min
8%
2
2
Cl
2
DecO
ODec
3
2
2
8
rt, 1 min, 37%
DecO
2
3 4
2, Pd(PPh )
Ba(OH)
toluene
2
DecO
ODec
ODec
DecO
ODec
EtOH, H
2
O
8
0 °C, 24 h, 71%
3
B).
MS analysis using various techniques was initially very
8
a
problematic due to extensive fragmentation, but it was ultimately
discovered that LC-MS with APPI(+) ionization gave very reliable
spectra, but only when the standard solvent system (90%
acetonitrile / toluene) was changed to 90% isopropanol / toluene
and the injection temperature was maximized. Under these
conditions, no signals attributable to dealkylated compounds or
lower oligomers arising from biaryl cleavage were observed.
1
2a
DecO
ODec
DecO
ODec
Scheme 4. Synthesis of dimer 10a and tetramer 12a.
Dimer 10a underwent bromination smoothly using 2.0
equivalents of Br to afford dibromide 24 in 88% yield. When a
small excess (up to 3 equiv) of Br was employed, over-
bromination was not a problem. Instead, a new bright yellow
2
2
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Figure 3. A) Thin-layer chromatograms of monomer 8a (M), dimer 10a (D),
trimer 11a (T), tetramer 12a (Te), pentamer 13a (P) and a co-spot (C) of the
Figure 5. Optical microscopy (top) and polarized optical microscopy (bottom)
for 11a (left), 12a (middle) and 13a (right).
five oligomers developed with 365 nm light, run with 10:90 CH
2 2
Cl /hexanes
(
left) and with 5:5:90 toluene/CH Cl /hexanes (right). B) Thin-layer
2
2
chromatogram of trimer 11a at ca. 0.1 (A), 0.01 (B) and 0.001 (C) mg/mL,
followed by tetramer 12a at ca. 0.1 mg/mL (D) and then a 1:100 mixture of
Small- and wide-angle X-ray scattering (SWAXS)
measurements of trimer 11a showed no features at all in the
small-angle range and just very broad peaks at 21.0° and 42.5°
in the wide-angle region (Figure 6). The former corresponds to
1
1a:12a (E).
It is interesting to note that Rathore’s monomer through
[
8d]
[
5]
a distance of 4.23 Å, which is typical of an alkyl halo, and the
peak at 42.5° is likely the corresponding second order peak
pentamer series of oligo(1,6-pyrenylene)s 5, which may also
appear to be candidates for FMLs, are all solids with melting
points that increase steadily from monomer (92–93 °C) to
pentamer (198–200 °C). The oligo(1,8-pyrenylene)s 8a, 10a–
(
corresponds to a distance of 4.25 Å). The absence of any
sharp peaks is indicative of the absence of long-range molecular
ordering, which speaks to 11a being a liquid. SWAXS was not
measured for 12a and 13a due to insufficient sample sizes, but
the consistency of their DSC and POM suggest that they are
also liquids.
1
3a behave very differently. The monomer 8a is a low-melting
solid (mp=38.4–39.5 °C) and the dimer remains a supercooled
liquid for as long as six months after purification before
eventually crystallizing (mp=30–34 °C). The trimer 11a, tetramer
1
2a and pentamer 13a are all liquids that have never solidified.
One sample of trimer 11a has remained a liquid after ambient
aging for over 7 years. No crystallization peaks were observed
in DSC traces for 11a–13a even after annealing at –42 °C for 12
[
8c]
hours (Figure 4), which further supports the notion that these
compounds are in fact room temperature liquids and not
supercooled liquids.
Figure 4. DSC thermograms for trimer 11a (top pair), tetramer 12a (middle
pair) and pentamer 13a (bottom pair) without annealing (black lines) and after
annealing at –42 °C for 12 h (red lines). Scale bar = 0.2 W/g for 11a, 0.2 W/g
for 12a and 0.3 W/g for 13a.
Figure 6. Small- (inset) and wide-angle X-ray scattering of trimer 11a.
An aspect of Nakanishi’s FMLs, e.g. 6, that does not
appear to have been addressed is that they are mixtures of
diastereomers by virtue of the presence of a stereorandom
stereogenic centre in each of the side chains. Oligo(1,8-
pyreneylene)s 11a–13a are also mixtures of diastereomers, but
this arises due to axial chirality (atropisomerism in the pi
skeleton. Atropisomerism in the oligo(1,6-pyrenylene)s 5 was
also not addressed, but based on the appearance of their NMR
spectra, the trimer, tetramer and pentamer are clearly mixtures
The total absence of birefringence in samples of 11a-13a,
as observed by polarized optical microscopy (POM) (Figure 5),
provided further evidence that these compounds are isotropic
liquids at room temperature.
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of diastereomers. The fact that they are increasingly high-
melting solids may be attributable to the presence of alkyl
instead of alkoxy side chains and the more linear (1,6)
substitution pattern of the pyrene units vs. the more bent (1,8)
for 11a-13a. Based on the existing evidence, it is difficult to
assess the relative importance of the various factors that
contribute to keeping 11a-13a in the liquid state.
photophysics of the neat liquids 11a-13a will be undertaken in
the near future.
High thermal stability and low volatility of 11a was revealed
by thermogravimetric analysis (TGA), where no loss of mass
was observed until ca. 325 °C (Figure 7). A 35% loss of mass
was observed starting at 325 °C, followed by an 18% loss of
mass starting at 560 °C. The first event is consistent with the
loss of four of the six decyl side chains (36.7% of the initial
mass) and the second loss of mass agrees very well with the
cleavage of the remaining two decyl groups (18.3% of the initial
mass). TGA of the tetramer 12a and pentamer 13a (Figures S2,
S3) were similar to that of 11a, showing the ultimate loss of ca.
Figure 8. Normalized absorption spectra of trimer 11a (green), tetramer 12a
(purple) and pentamer 13a (black) as neat liquid thin films in transmission
mode.
5
5% of the original mass (all of the alkyl groups). For these
compounds, a slight (3-6%) loss of mass was observed prior to
25 °C.
3
Figure 9. Normalized fluorescence spectra of trimer 11a (green), tetramer
1
2a (purple) and pentamer 13a (black) as neat liquid thin films measured
using front-face emission. λexc = 350 nm.
Figure 7. TGA trace for trimer 11a.
UV-vis and emission spectra obtained from dilute solutions
The UV-vis and emission spectra for pure liquid samples
of 8a and 10a-13a in cyclohexane are shown in Figures 10 and
are shown in Figures 8 and 9. The neat liquid oligomers 11a-
1
1, and spectroscopic data are summarized in Tables 1 and 2.
1
3a appear highly fluorescent to the naked eye under a UV lamp
The UV-vis spectrum of 8a is dominated by three intense
and also fluoresce visibly in ambient light. These optically
opaque liquids present experimental challenges in the
acquisition of spectroscopic data to characterize their ground
and excited state properties. The absorption spectra (Figure 8,
Table 1) were obtained using a thin film on the surface of a
cuvette and the emission spectra (Figure 9, Table 2) were
acquired using a front-face geometry as described in the
experimental section. The determination of quantum yields in
this manner can have large errors and often there are issues
with the reproducibility of the quantum yield data. Thus, initial
characterization of the excited states using dilute solutions in
cyclohexane and conventional protocols was undertaken. As
discussed below, the absorption and emission spectra closely
resemble those obtained using dilute solutions in terms of band
shapes and energetics. More detailed studies of the
*
overlapping π–π transitions (Bands 1–3) and their associated
vibronic progressions. The most intense transitions for the
structured band envelopes are observed at at 243 nm (41152
–
1
–1
–1
cm ), 281 nm (35587 cm ), and 347 nm (28820 cm ) along
–
1
with weak transitions at 357 nm (28011 cm ) and 376 nm
-
1
(
26595 cm ). The emission spectrum for 8a (Figure 10) is
complex and highly structured, comparable to the emission
spectrum of pyrene. Taken together, the photophysical
[
16]
properties of 8a are analogous to those found for pyrene.
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changes indicates
interactions.
a
very low degree of pyrene-pyrene
Table 1. Wavelength maxima λA,max for 8a and 10a-13a in cyclohexane
solution and for 11a-13a as neat liquids [in square brackets].
Compound
Band 1 (nm)
Band 2 (nm)
Band 3 (nm)
Monomer 8a
Dimer 10a
347
281
243
357
287
247
Trimer 11a
357 [365]
357 [365]
358 [366]
288 [291]
288 [291]
289 [292]
247 [248]
247 [250]
248 [250]
Tetramer 12a
Pentamer 13a
Figure 10. Absorption spectra of monomer 8a (blue), dimer 10a (red), trimer
1
1a (green), tetramer 12a (purple) and pentamer 13a (black) in oxygen-purged
cyclohexane solution.
Table 2. Fluorescence and photophysical data for 8a and 10a-13a in
deoxygenated cyclohexane solution and fluorescence data for 11a-13a as
neat liquid thin films (in square brackets).
–
1
–1
Compound
λ
F,max (nm)
φ
F
τ
F
(ns)
k
R
(s
)
kNR (s )
6
7
Monomer 8a
379, 401,
24
0.20±0.01
39±3
5.1×10
2.0×10
4
8
8
8
8
7
7
7
7
Dimer 10a
Trimer 11a
Tetramer 12a
Pentamer
429
0.74±0.08
0.80±0.04
0.80±0.04
0.80±0.01
2.80±0.03
2.71±0.01
2.2±0.1
2.6×10
3.0×10
3.6×10
3.6×10
9.3×10
7.4×10
9.5×10
9.5×10
444 [463]
453 [467]
457 [471]
2.2± 0.1
1
3a
The emission spectral profiles for 10a-13a are distinctly
Figure 11. Emission spectra of cyclohexane solutions of monomer 8a (blue),
dimer 10a (red), trimer 11a (green), tetramer 12a (purple) and pentamer 13a
different from the highly structured emission spectrum of 8b. The
emission spectra for 10a-13a have similar emission band
shapes, which shift to longer wavelength as the oligomer grows
(
black) in oxygen-purged cyclohexane solution.
λexc = 340 nm (8a, 10a, 11a)
or 350 nm (12a, 13a).
–
1
in size: 10 (λem = 429 nm (23310 cm ): 11 (λem = 444 nm (22520
–
1
–1
cm ): 12 (λem = 453 nm (22075 cm ): and 13 (λem = 457 nm
–
1
The following observations are discernable from the UV-vis
spectral data: (a) the vibronic resolution observed in 8a
diminishes in successive oligomers and is essentially all gone
once the trimer 11a has been reached, (b) the band maxima at
(
21880 cm ). For 10a-13a, the following trends are evident
from the data given in Table 2: (a) φ increases from 0.74 to 0.80
and levels off at trimer 11a; (b) τ decreases from 2.8 ns to 2.2
ns and levels off at tetramer 12a; (c) the radiative rate constant
F
F
8
–1
8
–1
3
57±1 nm, 288±1 nm and 247±1 nm for 10a-13a are all red-
(
k
r
) increases from 2.6 x 10 s to 3.6 x 10 s and levels off at
–
1
shifted from the analogous bands in 8a by 834±34 cm ,
tetramer 12a; and (d) the rate constant for non-radiative decay,
–
1
–1
7
–1
865±121 cm and 707±82 cm , respectively; (c) the spectral
band envelope at 355 nm gains intensity on going from 10a to
(knr ~ 9 x 10 s ) is more or less constant even though the
–
1
–1
energy gap changes from 23310 cm for 10a to 21880 cm for
3a. A quantitative analysis of the spectroscopic data to
*
1
2a and then levels off; (d) the energetics of the π–π transitions
1
–
1
–1
at 247 nm (40485 cm ), 288 nm (34722 cm ), and 357 (28010
delineate the microscopic origin that underlies the photophysical
properties is accommodated by the proposed mechanism
described below.
–
1
cm ) for 10a-13a do not change significantly (Table 1).
The absorption spectra of 11a-13a as neat liquids closely
resemble those obtained from dilute solutions, exhibiting three
broad and intense bands at 365±1 nm, 291±1 nm and 249±1 nm.
These bands are only slightly red-shifted from the corresponding
In going from the monomer 8a to the oligomers 10a-13a, a
broad absorption feature at ca. 360 nm emerges, which is
absent in 8a. The oligomers contain pyrene units that are linked
by C–C bonds, thereby providing a structural basis for π
interchromophoric coupling that mediates electron delocalization.
–
1
–1
bands in the solution spectra, i.e. by 613±38 cm , 357±59 cm
–
1
and 324±162 cm , respectively. The small magnitude of these
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In the ground state, each 1,1’-bipyrenyl unit of the oligomers
which is very close to the slope reported by Rathore for
[
5]
1
0a-13a adopts a non-coplanar orientation characterized by a
oligo(1,6-pyrenylene)s 5 (–0.56) (Figure S9).
Additionally,
dihedral angle (θ) between pyrenyl planes, which represents a
compromise between steric repulsion and π-electron
plots of the emission energies vs cos[π/(n+1)] for 10a-13a were
also found to be linear with a slope of –0.50, but this is a factor
[
17]
delocalization.
Absorption of a photon occurs on an ultrafast time scale
of
2
larger than the corresponding slope for oligo(1,6-
These observations
pyrenylene)s 5 (–0.26) (Figure S10).
-
15
(
~10
s) to form the Franck Condon excited state, which
indicate that delocalization plays a larger role in the excited
states of 10a-13a than it does in 5. The more extensive
delocalization in the excited states of 10a-13a may ultimately
prove to be important when these compounds are used as
materials in organic electronic devices.
possesses the electronic coordinates appropriate for the excited
state with the nuclear and solvent coordinates still in their
ground state coordinates. The absorption energy is given by:
ꢀ!"#
= ∆ꢀ!" + ꢀ + ꢀ ꢀ
[1]
!
where ΔGes is the free energy of the excited state and λ
total reorganization energy, which includes the vibrational (λvib
and solvent reorganization (λ ) energies. The parameter E(θ) is
t
is the Conclusions
)
o
Oligo(1,8-pyrenylene)s 8a, 10a–13a were synthesized using a
two-step iterative synthetic strategy. The trimer 11a, tetramer
the energy component that depends on the dihedral angle. E(θ)
contains contributions for the extent of π delocalization between
the ring systems and reflects the distribution of rotational
1
2a and pentamer 13a are room temperature liquids, which are
intensely fluorescent in dilute solution (φ = 0.80) and also in the
F
[
18]
conformers that exist in the ground state.
liquid state. Like other FMLs, several factors likely contribute to the
suppression of solidification in 11a-13a. The 1,8 substitution
pattern of pyrene units and the presence of mixtures of 2, 4 and
With time, the atomic nuclei that make up the chromophore
and the solvent orientations in the Franck-Condon excited states
will adjust their orientations to minimize the potential energy of
the thermalized excited state. The lowest lying excited states of
6
diastereomers (atropisomers), respectively, may well be
among them. With regard to the issue of diastereoisomerism, it
is distinct from side chain branching (an existing guideline for the
design of FMLs) and a prominent feature of other FMLs. As
such, it deserves to be considered in the context of future FML
design. Photophysical studies of 11a-13a in dilute solution
indicate that interchromphoric coupling manifests itself in
radiative decay and that delocalization plays a larger role in the
excited states than for Rathore’s oligo(1,6-pyrenylene)s 5. Work
aimed at the use of 11a-13a as solvents for chemical reactions
and as functional materials is underway.
1
0a-13a decay primarily through radiative decay (Table 2). The
emission energies move to longer wavelength as the number of
monomer units of the oligomer increases. The kinetics are
mono-exponential, which is consistent with emission coming
from a very narrow conformational distribution. Taken together,
it can be inferred that there is a substantial structural change on
going from the Franck-Condon state to the emitting state,
presumably due to a reduction of the dihedral angle.
A
decrease of the dihedral angle in the excited state would allow
the system to more effectively delocalize the excited electron.
Delocalization reduces bond length changes in the excited state
and thus lowers the excited state energy on going from 10a to
Experimental Section
1
3a. If true, one would anticipate that the transition moment (ꢀ)
should correlate with the number of monomer units in the
oligomers. The rate constant for radiative decay is given by
Commercial reagents and solvents were used without purification.
[
20]
Pd(PPh
3
)
4
was prepared
and used before discoloration occurred
1
13
(
within 7 d; storage under Ar in a freezer). H and C NMR spectra were
!
"!!!!
!
recorded on a Bruker 300 MHz AVANCE III or Bruker AVANCE 500 MHz
ꢀ!
=
ꢀ
ꢀ!! !!
[2]
ꢀℏ
spectrometers. High-resolution APPI−TOF−MS were recorded on a GCT
Premier Micromass Technologies instrument.
analysis was performed on Waters TGA−Q−500 instrument.
Differential scanning calorimetry was measured using a Mettler Toledo
DSC STAR system. Absorption spectra were measured in
cyclohexane solutions using Cary Bio UV-vis spectrophotometer
manufactured by Varian. Fluorescence spectra were measured in
oxygen-free cyclohexane solution, using Photon Technologies
Thermogravimetric
where ꢀ!! !! ≅ ꢀ!" !, and the transition moment ꢀ is given
a
by:
∗
1
ꢀ
= ꢀ ꢀ ꢀ
[3]
a
The transition moments were calculated for 10a (1.31 D), 11a
1.48 D), 12a (1.60 D) and 13a (1.74 D) using the experimental
a
(
International (PTI) RF-M2004 fluorescence spectrometer, with excitation
wavelengths of 340 nm (8a, 10a and 11a) or 350 nm (12a and 13a).
Oxygen was removed from these solutions by sparging with Ar.
Solutions for the fluorescence measurements were prepared to obtain an
absorbance of 0.25 to 0.35 at the excitation wavelength. Fluorescence
spectral data and Eq. 2, and they do indeed correlate with the
number of monomer units in the oligomers.
The spectroscopic properties of π-conjugated oligomers
[
19]
are often used to predict the properties at the polymeric limit.
[
21]
quantum yields were determined using the relative method,
using
The basis of the analysis is the linear evolution of the
spectroscopic energies with cos[π/(n+1)] where n is the number
of monomer units that make up the oligomer. Plots of the onset
energies for the 360 nm absorbance vs cos[π/(n+1)] for 10a-13a
were found to exhibit a linear trend with a slope of –0.60 (±0.05),
9
,10-diphenylanthracene in cyclohexane as the quantum yield standard
[21]
(
φ
F
= 0.90).
Fluorescence lifetimes were measured on the same
samples used for fluorescence spectra measurements, using a Photon
Technologies International instrument, which is based on the
[
22]
stroboscopic optical boxcar technique.
Absorption spectra of the neat
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liquids of 11a-13a were measured on samples prepared by depositing
highly concentrated solutions of the liquids in cyclohexane on the front
surface of thin 1 mm path length quartz cuvettes layed flat, with the
solvent allowed to evaporate to leave a thin, transparent film of the liquid,
which allowed for the measurement of the absorption spectrum in
transmission mode. Fluorescence spectra of the neat liquids of the 11a-
removed under reduced pressure and the residue was subjected to
column chromatography (2% CH
2 2
Cl /hexanes) to yield 1,8-dipyren-1-yl-
4,5-didecoxypyrene (19a) (0.037 g, 27%) as a pale yellow-green viscous
1
liquid.
f 2 2 3
R (20% CH Cl /hexanes) = 0.60; H NMR (CDCl , 500 MHz) δ
=8.760 and 8.757 (2×d, J=8.0 Hz, 2H), 8.283 and 8.278 (2×d, J=7.8 Hz,
2H) or 8.28 (dd, J=7.8, 12.8 Hz, 2H), 8.22–8.18 (m, 2H), 8.21 (d, J=7.9
Hz, 2H), 8.14–8.08 (m, 8H), 8.00 and 7.99 (2×t, J=7.6 Hz, 2H), 7.872 and
7.866 (2×d, J=9.3 Hz, 2H), 7.73 and 7.67 (2×d, J=9.3 Hz, 2H), 7.53 and
7.49 (2×s, 2H), 4.54 (t, J=6.7 Hz, 4H), 2.17–2.10 (m, 4H), 1.78–1.72 (m,
1
3a were measured as thin films manually spread directly on the front
surface of the thin 1 mm path length quartz cuvettes, which were placed
in the fluorimeter sample holder at 45° to the both the excitation light and
emission collection path, in a front-face emission configuration with 350
1
3
4H), 1.56–1.50 (m, 4H), 1.48–1.25 (m, 20H), 0.95–0.85 (m, 6H);
C
nm excitation.
Density functional theory (DFT) calculations were
NMR (CDCl , 125 MHz) δ = 144.32, 136.22, 136.19, 135.78, 131.45,
3
[
23]
performed with the Gaussian 16 software package,
using the B3LYP
130.98, 130.88, 130.07, 129.96, 129.30, 129.24, 129.05, 129.03, 128.94,
128.87, 127.57, 127.45, 126.03, 125.78, 125.21, 125.02, 124.79, 124.48,
123.31, 123.25, 119.36, 119.28, 74.12, 32.02, 30.83, 29.84, 29.76, 29.48,
26.51, 22.80, 14.22 ppm (only 27 of the 48 expected aromatic signals
functional in conjunction with the 6-31G(d) basis set. SWAXS data were
collected on a 2 mm thick sample held horizontally using a Siemens D-
5
000 θ-θ diffractometer equipped with a copper target X-ray tube and a
diffracted beam monochromator. The divergence and anti-scatter slits
were set to 1° and the receiving slit was set to 0.6 mm. Data was
collected every 0.05° in scattering angle with a 4 s count time.
and only 9 of the 20 expected aliphatic signals observed); HRMS
+
[APPI(+)], calcd for C68
H
66
O
2
([M] ): 914.5063, found: 914.5070.
1
,8-Dipyren-1-yl-4,5-dimethoxypyrene (19b): A 50 mL round-bottomed
1
,8-Dibromo-4,5-didecoxypyrene (17a): To
a
solution of 4,5-
Cl (250 mL) was
flask equipped with a side arm and capped with a rubber septum was
[
11]
didecoxypyrene (8a)
(5.00 g, 9.71 mmol) in CH
2
2
charged with pyrene-1-boronic acid (18) (0.469 g, 1.91 mmol), 1,8-
added bromine (3.41 g, 21.4 mmol). The reaction was stirred at room
temperature for 5 min. Excess bromine was quenched by the addition of
saturated sodium thiosulfate solution (150 mL). The layers were
dibromo-4,5-dimethoxypyrene (17b) (0.200 g, 0.476 mmol), K
g 15.3 mmol), 1,4-dioxane (10 mL) and water (2 mL). The resulting
slurry was subjected to three freeze-pump-thaw cycles before Pd(PPh
(0.0176 g, 0.152 mmol) was added under a positive pressure of N . The
2 3
CO (2.11
3 4
)
separated and the aqueous phase was extracted with CH
2
Cl
2
(3×100
SO
2
mL). The combined organic layers were dried over anhydrous Na
2
4
flask was then resealed with a rubber septum and heated at 100 °C in an
oil bath for 19 h. After cooling to room temperature, the mixture was
and the solvent was removed under reduced pressure. The resulting
brown solid was subjected to column chromatography (10%
diluted with CH
O (3×100 mL), washed with brine (200 mL), dried over anhydrous
MgSO and the solvent was removed under reduced pressure. The
residue was preadsorbed on silica gel and subjected to column
chromatography (40% CH Cl /hexanes) to yield 1,8-dipyren-1-yl-4,5-
dimethoxypyrene (19b) (0.194 g, 38%) as a pale yellow solid. (40%
2 2 3
CH Cl /hexanes) = 0.31; H NMR (CDCl , 300 MHz) δ = 8.729 and 8.727
2 2
Cl (100 mL). The resulting solution was washed with
CH
2
Cl
6%) as a pale-yellow solid.
9.3–80.5 °C (recrystalized from ethanol); H NMR (CDCl
.52 (s, 2H), 8.36 (d, J=8.5 Hz, 2H), 8.27 (d, J=8.5 Hz, 2H), 4.31 (t, J=6.7
2
/hexanes) to afford 1,8-dibromo-4,5-didecoxypyrene (17a) (6.27 g,
(20% CH Cl /hexanes) = 0.90; mp =
, 300 MHz) δ =
H
2
9
7
8
R
f
2
2
4
1
3
2
2
Hz, 4H), 2.00–1.90 (m, 4H), 1.64–1.56 (m, 4H), 1.45–1.23 (m, 24H), 0.89
R
f
1
3
1
(
t, J=6.7 Hz, 6H); C NMR (CDCl
3
, 75 MHz) δ = 143.78, 130.72, 129.43,
1
2
C
28.70, 127.47, 123.48, 120.85, 119.91, 73.90, 31.92, 30.53, 29.67,
(2×d, J=8.0 Hz, 2H), 8.251 and 8.245 (2×d, J=7.8 Hz, 2H) or 8.25 (dd,
J=7.8, 1.7 Hz, 2H), 8.20–8.13 (m, 2H), 8.19 (d, J=8.0 Hz, 2H), 8.12–8.04
(m, 8H), 7.97 and 7.96 (2×t, J=7.6 Hz, 2H), 7.84 and 7.83 (2×d, J=9.3 Hz,
9.61, 29.55, 29.36, 26.27, 22.70, 14.13 ppm; HRMS [APPI(+)], calcd for
8
1
79
+
36 2
H48 Br BrO ([M] ): 674.2034, found: 673.2004.
2
6
1
1
1
1
H), 7.69 and 7.63 (2×d, J=9.2 Hz, 2H), 7.50 and 7.47 (2×s, 2H), 4.38 (s,
1
3
3
H); C NMR (CDCl , 75 MHz) δ = 144.95, 136.07, 136.04, 135.98,
1
,8-Dibromo-4,5-dimethoxypyrene (17b): To
a
solution of 4,5-
Cl (30 mL) was
[
11]
35.91, 131.42, 130.92, 130.86, 130.01, 129.95, 129.94, 129.29, 129.23,
28.86, 128.80, 128.43, 128.41, 127.54, 127.41, 127.40, 126.01, 125.96,
25.92, 125.68, 125.19, 125.00, 124.78, 124.73, 124.43, 124.35, 123.24,
dimethoxypyrene (8b)
(1.00 g, 3.81 mmol) in CH
2
2
added bromine (1.34 g, 8.37 mmol). The reaction was stirred at room
temperature for 5 min. Excess bromine was quenched by the addition of
saturated sodium bisulfite solution (25 mL). The layers were separated
23.18, 119.13, 119.06, 61.38 ppm (only 34 of the 48 expected aromatic
+
signals observed); HRMS [APPI(+)], calcd for C50
found: 662.2299.
H
30
O
2
([M] ): 662.2246,
and the aqueous phase was extracted with CH
combined organic layers were washed with water (30 mL), washed with
brine (30 mL), dried over anhydrous Na SO and the solvent was
removed under reduced pressure. The resulting brown solid was
subjected to column chromatography (10% CH Cl /hexanes) to afford
,8-dibromo-4,5-dimethoxypyrene (17b) (1.52 g, 95%) as a white solid.
2 2
Cl (3×100 mL). The
2
4
1-Bromo-4,5-didecoxypyrene (20): To a solution of 4,5-didecoxypyrene
[
11]
2
2
(8b)
bottomed flask was added dropwise a solution of bromine (2.03 g, 12.7
mmol) in CH Cl (127 mL, 0.1 M) over 35 min. The resulting solution was
2 2
(5.00 g, 9.77 mmol) in CH Cl (100 mL) in a 500 mL round-
1
1
R
f
(40% CH
2
Cl
2
/hexanes) = 0.60; mp = 212–214 °C; H NMR (CDCl
3
,
2
2
3
00 MHz) δ = 8.51 (s, 2H), 8.35 (d, J=8.4 Hz, 2H), 8.27 (d, J=8.4 Hz, 2H),
transferred to a separatory funnel, washed with water (100 mL), washed
with brine (100 mL), dried over anhydrous magnesium sulfate and
concentrated under reduced pressure. The resulting pale pink-orange
solid was adsorbed on silica gel and subjected to column
1
3
4
.19 (s, 6H); C NMR (CDCl
28.14, 127.46, 123.46, 120.70, 120.09, 61.18 ppm; HRMS [APPI(+)],
3
, 75 MHz) δ = 144.45, 130.79, 129.45,
1
8
1
79
+
2
calcd for C18H12 Br BrO ([M] ): 419.9185, found: 419.9184.
chromatography (1% CH
didecoxypyrene (17a) (1.26 g, 19%) and 1-bromo-4,5-didecoxypyrene
20) (4.20 g, 73%) as a waxy white solid. (1% CH Cl /hexanes) =
.10; mp=45.4–46.8 °C (recrystallized from ethanol); H NMR (CDCl
00 MHz) δ = 8.52 (dd, J=7.8, 1.0 Hz, 1H), 8.42 (d, J=9.2 Hz, 1H), 8.33
2 2
Cl /hexanes) to afford 1,8-dibromo-4,5-
1
,8-Dipyren-1-yl-4,5-didecoxypyrene (19a): A 50 mL round-bottomed
(
R
f
2
2
flask equipped with a side arm and capped with a rubber septum was
1
0
3
3
,
charged with pyrene-1-boronic acid (18) (0.091 g, 0.037 mmol), 1,8-
dibromo-4,5-didecoxypyrene (17a) (0.101 g, 0.150 mmol), K
g 3.00 mmol), 1,4-dioxane (4 mL) and water (1 mL). The resulting slurry
was subjected to four freeze-pump-thaw cycles before Pd(PPh (0.0036
g, 0.031 mmol) was added under a positive pressure of N The flask
2 3
CO (0.414
(
d, J=8.5 Hz, 1H), 8.24 (d, J=8.5 Hz, 1H), 8.17 (dd, J=7.8, 0.7 Hz, 1H),
8
2
.15 (d, J=9.0 Hz, 1H), 8.05 (t, J=7.7 Hz, 1H), 4.34 (t, J=6.7 Hz, 4H),
.01–1.88 (m, 4H), 1.64–1.58 (m, 4H), 1.41–1.22 (m, 24H), 0.87 (t, J=6.7
3 4
)
2
.
1
3
Hz, 6H); C NMR (CDCl
3
, 75 MHz) δ = 144.15, 143.76, 130.94, 130.11,
was then resealed with a rubber septum and heated at 80 °C in an oil
bath for 16 h. After cooling to room temperature, the solvent was
1
29.51, 129.11, 128.93, 128.54, 126.55, 125.88, 124.85, 124.07, 122.26,
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ChemPlusChem
10.1002/cplu.201900133
FULL PAPER
1
2
20.18, 120.18, 119.34, 73.88, 73.85, 31.95, 30.61, 30.59, 29.71, 29.64,
9.60, 29.59, 29.38, 26.33, 22.72, 14.15 ppm (only 13 of the 20 expected
resulting solution was washed with H
MgSO
yellow oil. The residue was subjected to column chromatography (1:1:10
toluene/CH Cl /hexanes) to yield 4,5-didecoxy-1,8-bis(4,5-
didecoxypyren-1-yl)pyrene (11a) (1.77 g, 77%) as a bright yellow viscous
2
O (200 mL), dried over anhydrous
4
and the solvent was removed under reduced pressure to afford a
8
1
aliphatic signals observed); HRMS [APPI(+)], calcd for C36
H
49 BrO
2
+
(
[M] ): 592.2916, found: 592.2893.
2
2
1
f 2 2 3
oil. R (7.5:7.5:85, toluene/CH Cl /hexanes) = 0.60; H NMR (CDCl , 300
2
-(4,5-Didecyloxypyren-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
MHz) δ = 8.720 and 8.718 (2×d, J=8.1 Hz, 2H), 8.56 and 8.55 (2×d,
J=8.1 Hz, 2H), 8.49 and 8.48 (2×dd, J=7.6, 1.5 Hz, 2H), 8.17 (d, J=8.1,
(
22): A 250 mL round-bottomed flask equipped with a side arm and
capped with rubber septum was charged with 1-bromo-4,5-
didecoxypyrene (20) (1.50 g, 2.53 mmol), 1,4-dioxane (50 mL), KOAc
0.744 g, 7.58 mmol) and HBPin (0.970 g, 7.58 mmol). The mixture was
subjected to three freeze-pump-thaw cycles before Pd(dppf) Cl (0.092 g,
.13 mmol) was added under a positive pressure of nitrogen. The
a
2
H), 8.09 and 8.08 (2×d, J=8.1 Hz, 2H), 8.04 and 8.02 (2×dd, J=7.7, 1.3
Hz, 2H), 7.98 and 7.97 (2×t, J=7.6 Hz, 2H), 7.82 (d, J=9.3 Hz, 2H), 7.68
and 7.62 (2×d, J=9.2 Hz, 2H), 7.50 and 7.46 (2×s, 2H), 4.51 (t, J=6.7 Hz,
(
2
2
4
H), 4.35 (m, 8H), 2.12–2.08 (m, 12H), 1.75–1.71 (m, 12H), 1.45–1.20
0
1
3
(
m, 72H), 0.93–0.83 (m, 18H); C NMR (CDCl
3
, 75 MHz) δ = 144.43,
mixture was heated at 80 °C in an oil bath for 4 h. The rubber septum
was then replaced with a distillation head and the majority of the solvent
was removed by distillation. After cooling, the resulting brown sludge
1
1
1
1
2
1
1
44.28, 144.25, 135.92, 135.91, 135.63, 135.60, 131.03, 130.15, 139.48,
29.42, 129.29, 139.27, 129.14, 129.12, 128.77, 127.61, 126.17, 125.80,
24.45, 123.47, 123.42, 123.19, 123.12, 119.79, 119.45, 119.37, 119.09,
19.00, 74.15, 73.99, 73.94, 32.14, 32.11, 30.94, 30.82, 29.96, 29.87,
2 2
was dissolved in CH Cl (200 mL) and the resulting solution was washed
with water (100 mL), washed with brine (100 mL), dried over anhydrous
magnesium sulphate. The solvent was removed reduced pressure and
the crude mixture was subjected to column chromatography (20%
9.80, 29.87, 29.80, 29.78, 29.60, 29.55, 26.63, 26.52, 22.91, 22.88,
+
4.31, 14.30, 14.28 ppm; HRMS [APPI(+)], calcd for C108
539.1119, found: 1539.1109.
H
146
O
6
([M] ):
CH
2
Cl
2
/hexanes) to afford 2-(4,5-didecoxypyren-1-yl)-4,4,5,5-tetramethyl-
(50%
, 300 MHz) δ = 9.05 (d, J=9.1
Hz, 1H), 8.55 (d, J=7.9 Hz, 1H), 8.51 (d, J=7.9 Hz, 1H), 8.46 (d, J=7.9 Hz,
1
,3,2-dioxaborolane (22) as a pale brown oil (1.47 g, 91%).
R
f
1
CH
2
Cl
2
/hexanes) = 0.60; H NMR (CDCl
3
Method B (using diiodide 21) – Using the procedure described above,
(4,5-didecoxypyren-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (22)
(2.51 g, 3.91 mmol), 1,8-diiodo-4,5-didecoxypyrene (21) (1.00 g, 1.30
mmol), anhydrous Ba(OH) (4.47 g, 26.1 mmol), toluene (80 mL), ethanol
(20 mL), water (10 mL) and Pd(PPh (0.015 g, 0.013 mmol) were used
1
4
1
H), 8.16 (d, J=7.7 Hz, 1H), 8.11 (d, J=9.3 Hz, 1H), 8.02 (t, J=7.7 Hz, 1H),
.37 (t, J=6.7 Hz, 2H), 4.30 (t, J=6.7 Hz, 2H), 2.01–1.94 (m, 4H), 1.62–
2
1
3
.57 (m, 4H), 1.49 (s, 12H), 1.40–1.28 (m, 24H), 0.91–0.87 (m, 6H);
, 75 MHz) δ = 145.05, 143.79, 136.33, 134.03, 131.37,
30.71, 128.66, 127.93, 127.70, 125.73, 124.70, 122.88, 122.59, 119.61,
C
3 4
)
NMR (CDCl
3
to afford 4,5-didecoxy-1,8-bis(4,5-didecoxypyren-1-yl)pyrene (11a) (1.83
1
1
2
g, 91%) as a bright yellow viscous oil.
18.36, 83.85, 73.85, 73.81, 31.93, 30.63, 30.57, 29.70, 29.63, 29.59,
9.37, 26.34, 26.31, 25.06, 22.71, 14.13 ppm (only 15 of the 16 expected
1
,8-Bis(8-bromo-4,5-didecoxypyren-1-yl)-4,5-didecoxypyrene
To solution of 4,5-didecoxy-1,8-bis(4,5-didecoxypyren-1-yl)pyrene
11a) (0.050 g, 0.032 mmol) in CH Cl (3 mL) was added a solution of
bromine (0.010 g, 0.065 mmol) in CH Cl (3 mL) and the reaction was
(23):
aromatic signals and only 15 of the 22 expected aliphatic signals
a
+
4
observed); HRMS [APPI(+)], calcd for C42H61BO ([M] ): 640.4669, found:
(
2
2
6
40.4716.
,8-Diiodo-4,5-didecoxypyrene (21): To
2
2
stirred at room temperature for 5 min. Excess bromine was quenched by
the addition of saturated sodium thiosulfate solution (5 mL). The layers
1
a
solution of 4,5-
(100 mL) was added
didecoxypyrene (8a) (2.00 g, 3.88 mmol) in CH
iodine (2.96 g, 11.7 mmol) and Hg(OAc)
2
Cl
2
were separated and the aqueous phase was extracted with CH
2
Cl
2
(3×5
SO
2
(3.71 g, 11.7 mmol). The
mL). The combined organic layers were dried over anhydrous Na
2
4
reaction was stirred for 20 min at room temperature. The slurry was
and the solvent was removed under reduced pressure. The resulting
brown solid was subjected to column chromatography (10%
®
passed through short plug of silica gel and Celite (ca. 1:1). Water (150
mL) was added and the layers were separated. The organic phase was
CH
2
Cl
2
/hexanes) to afford 1,8-bis(8-bromo-4,5-didecoxypyren-1-yl)-4,5-
(20%
2 3
/hexanes) = 0.38; H NMR (CDCl , 300 MHz) δ = 8.740 and 8.738
dried over anhydrous Na
reduced pressure. The solid pink residue was subjected to column
chromatography (10% CH Cl /hexanes) to yield 1,8-diiodo-4,5-
didecoxypyrene (21) (2.62 g, 88%) as white solid. (20%
/hexanes) = 0.90; mp >95 °C dec.; H NMR (CDCl , 300 MHz) δ =
.53 (d, J=8.4 Hz, 2H), 8.35 (s, 2H), 8.21 (d, J=8.4 Hz, 2H), 4.30 (t, J=6.7
Hz, 4H), 2.02–1.86 (m, 4H), 1.65–1.50 (m, 4H), 1.42–1.23 (m, 24H),
2
SO
4
and the solvent was removed under
didecoxypyrene (23) (0.043 g, 78%) as a pale yellow liquid.
R
f
1
CH
2
Cl
2
2
(2×d, J=8.1 Hz, 2H), 8.609 and 8.606 (2×d, J=8.1 Hz, 2H), 8.33 and 8.32
(2×d, J=8.5 Hz, 2H), 8.24–8.10 (m, 8H), 7.80 and 7.74 (2×d, J=9.5 Hz,
2H), 7.49 and 7.45 (2×s, 2H), 4.52 (t, J=6.7 Hz, 4H), 4.39–4.29 (m, 8H),
2.17–2.04 (m, 4H), 2.01–1.89 (m, 8H), 1.78–1.66 (m, 4H), 1.66–1.17 (m,
a
R
f
1
CH
2
Cl
2
3
8
1
3
3
80H), 0.94–0.78 (m, 18H); C NMR (75 MHz, CDCl ): δ = 144.31,
1
3
0
1
2
.95–0.81 (m, 6H); C NMR (75 MHz, CDCl
3
): δ = 143.91, 137.47,
144.15, 143.80, 136.09, 136.04, 135.35, 130.24, 129.94, 129.91, 129.59,
129.32, 129.24, 129.12, 128.77, 127.33, 127.29, 125.99, 125.89, 124.18,
123.23, 123.17, 122.46, 122.38, 120.36, 119.71, 119.49, 119.41, 74.09,
73.94, 73.92, 31.98, 31.94, 31.92, 30.77, 30.59, 29.79, 29.70, 29.63,
32.94, 132.40, 129.38, 123.13, 121.31, 96.17, 73.90, 31.93, 30.52,
9.67, 29.61, 29.54, 29.36, 27.26, 22.70, 14.13; HRMS [APPI(+)], calcd
+
for C36
H
48
I
2
O
2
([M] ): 766.1744, found: 766.1757.
2
1
9.59, 29.43, 29.38, 26.46, 26.33, 22.75, 22.72, 22.70, 14.16, 14.14,
8
1
79
+
6
4.12; HRMS [APPI(+)], calcd for C108H144 Br BrO ([M] ): 1697.9343,
4
,5-Didecoxy-1,8-bis(4,5-didecoxypyren-1-yl)pyrene (11a): Method A
found: 1697.9330.
(
using dibromide 17a) – A 250 mL round-bottomed flask equipped with a
side arm and capped with a rubber septum was charged with 2-(4,5-
didecoxypyren-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (22) (2.84 g,
1,8-Bis(8-(4,5-didecoxypyren-1-yl)-4,5-didecoxypyren-1-yl)-4,5-
didecoxypyrene (13a): A 250 mL round-bottomed flask equipped with a
side arm and capped with a rubber septum was charged with 2-(4,5-
didecyloxypyren-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (22) (0.113
4
.46 mmol), 1,8-dibromo-4,5-didecoxypyrene (17a) (1.00 g, 1.49 mmol),
anhydrous Ba(OH) (5.09 g, 29.7 mmol), toluene (80 mL), ethanol (20
mL) and water (10 mL). The resulting slurry was subjected to three
freeze-pump-thaw cycles before Pd(PPh (0.017 g, 0.015 mmol) was
added under a positive pressure of N . The flask was then resealed with
2
3
)
4
g,
0.117
mmol),
1,8-bis(8-bromo-4,5-didecoxypyren-1-yl)-4,5-
(0.201 g,
2
didecoxypyrene (23) (0.100 g, 0.059 mmol), anhydrous Ba(OH)
2
a rubber septum and heated at 80 °C in an oil bath for 24 h. After cooling
to room temperature, the solvent was removed under reduced pressure
1.18 mmol), toluene (16 mL), ethanol (4 mL) and water (2 mL). The
resulting slurry was subjected to three freeze-pump-thaw cycles before
and the resulting brown oil was dissolved in CH
2
Cl
2
(2×100 mL). The
3 4
Pd(PPh ) (0.007 g, 0.006 mmol) was added under a positive pressure of
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ChemPlusChem
10.1002/cplu.201900133
FULL PAPER
N
2
.
The flask was then resealed with a rubber septum and heated at
0 °C in an oil bath for 24 h. After cooling to room temperature, the
solvent was removed under reduced pressure and the resulting brown oil
was dissolved in CH Cl (2×35 mL). The resulting solution was washed
with H O (50 mL), dried over anhydrous MgSO and the solvent was
removed under reduced pressure. The resulting yellow oil was subjected
to column chromatography (1:1:10 toluene/CH Cl /hexanes) to afford
,8-bis(8-(4,5-didecoxypyren-1-yl)-4,5-didecoxypyren-1-yl)-4,5-
didecoxypyrene (13a) (0.127 g, 84%) as a bright yellow viscous oil.
Method C (Scholl reaction) – To a solution of 4,5-didecoxypyrene (8a)
8
2 2
(0.100 g, 0.194 mmol) in CH Cl (10 mL) and methanesulfonic acid (1
mL) was added DDQ (0.022 g, 0.097 mmol). The deep green solution
was stirred at room temperature for 1 min and then quenched by the
addition of aqueous 10% sodium bicarbonate solution (10 mL). The
layers were separated and the organic phase was dried over anhydrous
magnesium sulphate. The solvent was removed under reduced pressure
and the resulting red solid was subjected to column chromatography (5%
2
2
2
4
2
2
1
R
f
2 2
CH Cl /hexanes) to afford 1,1’-bi(4,5-didecoxypyrenyl) (10a) as a bright
1
(
7.5:7.5:85, toluene/CH
2
Cl
2
/hexanes) = 0.50; H NMR (CDCl
3
, 300 MHz)
yellow viscous oil (0.037 g, 37%) and 4,5-didecoxy-1,8-bis(4,5-
didecoxypyren-1-yl)pyrene (11a) as a bright yellow viscous oil (0.017 g,
17%).
δ = 8.66–8.33 (m, 10H), 8.11–7.89 (m, 12H), 7.79–7.30 (m, 10H), 4.46–
4
1
1
1
1
1
7
3
2
.18 (m, 20H), 2.03–1.81 (m, 20H), 1.66–1.44 (m, 20H), 1.44–1.07 (m,
1
3
3
20H), 0.88–0.63 (m, 30H); C NMR (75 MHz, CDCl ) δ 144.17, 144.11,
44.11, 135.50, 135.47, 130.87, 129.89, 129.87, 129.14, 128.89, 128.81,
28.57, 128.05, 127.41, 126.07, 126.02, 125.91, 125.83, 125.79, 125.72,
25.12, 124.54, 124.33, 124.30, 123.28, 123.26, 123.23, 123.17, 123.15,
22.93, 122.16, 121.78, 121.39, 120.36, 119.08, 118.99, 118.85, 77.46,
7.04, 76.62, 74.03, 74.00, 73.95, 73.92, 73.87, 31.96, 31.91, 30.73,
1
,1’-Bi(8-bromo-4,5-didecoxypyrenyl) (24): To a solution of 1,1’-bi(4,5-
didecoxypyrenyl) (10a) (0.125 g, 0.122 mmol) in CH
2
Cl
2
(10 mL) was
2
(10 mL) and
added a solution of bromine (0.039 g, 0.24 mmol) in CH
2
Cl
the reaction was stirred at room temperature for 5 min. Excess bromine
was quenched by the addition of saturated sodium thiosulfate solution
0.70, 30.67, 29.76, 29.74, 29.68, 29.67, 29.41, 29.36, 26.42, 26.37,
(
25 mL). The layers were separated and the aqueous phase was
extracted with CH Cl (3×25 mL). The organic phase was dried over
anhydrous Na SO and the solvent was removed under reduced
pressure. The resulting brown solid was subjected to column
chromatography (10% CH Cl /hexanes) to afford 1,1’-bi(8-bromo-4,5-
didecoxypyrenyl) (24) (0.127 g, 88%) as a pale yellow solid. (20%
CH Cl /hexanes) = 0.60; mp=39.1–41.1 °C (crystallized from hexanes);
H NMR (CDCl , 300 MHz) δ = 8.70 (d, J=8.0 Hz, 2H), 8.40 (d, J=8.5 Hz,
+
2.74, 14.16; HRMS [APPI(+)], calcd for C180
H
242
O
10 ([M] ): 2563.8428,
2
2
found: 2566.8658.
2
4
1
,1’-Bi(4,5-didecoxypyrenyl) (10a): Method A (Suzuki-Miyaura cross-
2
2
coupling) – A 250 mL round-bottomed flask equipped with a side arm and
capped with a rubber septum was charged with 2-(4,5-didecoxypyren-1-
yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborylane (22) (1.46 g, 2.27 mmol), 1-
bromo-4,5-didecoxypyrene (20) (0.450 g, 0.758 mmol), anhydrous
R
f
2
2
1
3
2H), 8.27 (d, J=8.5 Hz, 2H), 8.23 (d, J=9.5 Hz, 2H), 8.17 (d, J=8.0 Hz,
2H), 7.73 (d, J=9.5 Hz, 2H), 4.43 (t, J = 6.7 Hz, 4H), 4.39 (t, J = 6.7 Hz,
4H), 2.08–1.96 (m, 8H), 1.72–1.59 (m, 8H), 1.50–1.24 (m, 48H), 0.93–
Ba(OH)
2
(2.60 g, 15.2 mmol), toluene (40 mL), ethanol (10 mL) and water
(
5 mL). The resulting slurry was subjected to three free-pump-thaw
1
3
cycles before Pd(PPh
positive pressure of N
3
)
4
(0.009 g, 0.008 mmol) was added under a
. The flask was then resealed with a rubber
3
0.88 (m, 12H); C NMR (CDCl , 75 MHz) δ = 144.18, 143.90, 135.79,
2
130.36, 129.96, 129.56, 129.37, 128.97, 128.83, 127.21, 126.19, 124.21,
122.45, 120.49, 119.74, 119.56, 73.99, 31.96, 31.94, 30.67, 30.63, 29.73,
29.66, 29.63, 29.39, 26.37, 22.73, 22.71, 14.15, 14.13 ppm (only 14 of
the 20 expected aliphatic signals observed); HRMS [APPI(+)], calcd for
septum and heated at 80 °C in an oil bath for 24 h. After cooling to room
temperature, the solvent was removed under reduced pressure and the
resulting brown oil was dissolved in CH
solution was dried over anhydrous MgSO
under reduced pressure to afford a yellow oil. The residue was subjected
to column chromatography (1:1:10 toluene/CH Cl /hexanes) to afford
,1’-bi(4,5-didecoxypyrenyl) (10a) (0.498 g, 64%) as a bright yellow
viscous oil, which crystalized over 60 d. (20% CH Cl /hexanes) =
, 300 MHz) δ = 8.66 (d, J=8.0 Hz, 2H), 8.55 (dd,
J=7.5 Hz, 1.4 Hz 2H), 8.15 (d, J=8.0 Hz, 2H), 8.08 (d, J=7.2 Hz, 2H),
2
Cl
2
(2×100 mL). The resulting
8
1
79
+
4
and the solvent was removed
72 4
C H96 Br BrO ([M] ): 1182.5675, found: 1182.5669.
2
2
1
,1’-Bi(8-(4,5-didecoxypyrenyl)-4,5-didecoxypyrenyl (12a): A 250 mL
round-bottomed flask equipped with a side arm and capped with a rubber
septum was charged with 2-(4,5-didecyloxypyren-1-yl)-4,4,5,5-
1
R
f
2
2
1
0
.35; H NMR (CDCl
3
tetramethyl-1,3,2-dioxaborolane (22) (0.227 g, 0.354 mmol), 1,1’-bi(8-
bromo-4,5-didecoxypyrenyl) (24) (0.140 g, 0.118 mmol), anhydrous
8
4
0
1
1
2
.03 (t, J=7.7 Hz, 2H), 7.85 (d, J=9.3 Hz, 2H), 7.62 (d, J=9.3 Hz, 2H),
Ba(OH)
2
(0.404 g, 2.36 mmol), toluene (16 mL), ethanol (4 mL) and water
.42 (m, 8H), 2.07–2.00 (m, 8H), 1.79–1.54 (m, 8H), 1.46–1.26 (m, 48H),
(
2 mL). The resulting slurry was subjected to three freeze-pump-thaw
1
3
3
.92–0.81 (m, 12H); C NMR (CDCl , 75 MHz) δ = 144.18, 135.62,
cycles before Pd(PPh
positive pressure of N
3
)
4
(0.014 g, 0.012 mmol) was added under a
30.93, 130.07, 129.21, 128.98, 128.66, 127.47, 126.14, 125.75, 124.37,
23.00, 119.69, 118.99, 73.95, 73.90, 31.96, 31.94, 30.71, 30.68, 29.74,
9.66, 29.39, 26.39, 22.73, 22.71, 14.15, 14.13 ppm (only 14 of the 16
2
. The flask was then resealed with a rubber
septum and heated at 80 °C in an oil bath for 24 h. After cooling to room
temperature, the solvent was removed under reduced pressure and the
expected aromatic signals and only 14 of the 20 expected aliphatic
resulting brown oil was dissolved in CH
2 2
Cl (2×35 mL). The resulting
+
signals observed); HRMS [APPI(+)], calcd for C72
found: 1026.7466.
98 4
H O ([M] ): 1026.7465,
solution was washed with H O (50 mL), dried over anhydrous MgSO
2
4
and the solvent was removed under reduced pressure. The resulting
yellow oil was subjected to column chromatography (1:1:10
Method B (Feringa homocoupling) – To a 2-necked pear-shaped flask
equipped with a calcium chloride drying tube and a rubber septum was
charged with 1-bromo-4,5-didecoxypyrene (20) (0.250 g, 0.421 mmol), n-
toluene/CH
2 2
Cl /hexanes) to afford 1,1’-bi(8-(4,5-didecoxypyrenyl)-4,5-
didecoxypyrenyl (12a) (0.172 g, 71%) as a bright yellow viscous oil.
R
f
1
2 2 3
(7.5:7.5:85, toluene/CH Cl /hexanes) = 0.55; H NMR (CDCl , 300 MHz)
TM
hexane (5 mL), PEPPSI-iPr (0.003 g, 0.004 mmol) and the mixture was
δ = 8.70–8.46 (m, 8H), 8.16–7.94 (m, 10H), 7.86–7.40 (m, 8H), 4.51–
stirred at room temperature for 15 min. t-Butyllithium (0.3 M, 1.00 mL,
4.30 (m, 16H), 2.13–1.92 (m, 16H), 1.74–1.53 (m, 16H), 1.54–1.17 (m,
1
3
0
.3 mmol) was then added dropwise over a period of 10 min through the
rubber septum via syringe. The excess t-butyllithium was quenched by
the addition of aqueous NH Cl solution (1 mL). The water and n-hexane
were removed under reduced pressure and the resulting brown solid was
dissolved in CH Cl (15 mL) and passed through a plug of Celite and
3
96H), 0.95–0.78 (m, 24H); C NMR (75 MHz, CDCl ) δ = 144.21, 144.20,
144.15, 144.12, 135.65, 135.56, 135.53, 135.47, 130.89, 130.01, 129.89,
129.28, 129.15, 128.95, 128.87, 128.56, 127.45, 126.09, 126.05, 125.91,
125.88, 125.71, 124.34, 123.28, 123.20, 123.12, 122.99, 122.95, 119.66,
119.14, 118.94, 118.83, 74.01, 73.92, 73.89, 31.97, 30.73, 30.68, 29.75,
4
2
2
silica (ca. 1:1) The solvent was removed under reduced pressure to
afford 4,5-didecoxy-1-(4,5-didecoxypyren-1-yl)pyrene (10a) as a bright
yellow viscous liquid (0.203 g, 94%).
29.68, 29.42, 26.42, 26.39, 22.74, 14.16; HRMS [APPI(+)], calcd for
+
C
144
H
194
O
8
([M] ): 2051.4774, found: 2051.4704.
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ChemPlusChem
10.1002/cplu.201900133
FULL PAPER
that of 1,1’-binaphthyl, for which energy barriers of 24.1 kcal/mol (44 °C
in benzene) and 23.5 kcal/mol (55 °C in DMF) have been measured.
See: a) A. K. Colter, L. M. Clemens, J. Phys. Chem. 1964, 68, 651-654.
b) A. S. Cooke, M. M. Harris, J. Chem. Soc. 1963, 2365-2373. Our
calculated (M06-2X/6-31G*) barriers (see Supporting Information) for
1,1’-binaphthyl (26.2 kcal/mol) and 1,1’-bipyrene (25.8 kcal/mol) are
indeed similar.
Acknowledgements
Financial support of this work from the Natural Sciences and
Engineering Research Council (NSERC) of Canada (G.J.B., Y.Z.
and B.D.W.) and the National Science Foundation (R.P.J., CHE-
1
362519) is gratefully acknowledged. Compute Canada is
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This research used the Extreme Science and Engineering
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OCI-1053575 (R.P.J). The authors thank Prof. Jeff Dahn,
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Keywords: atropisomerism • iterative synthesis• functional
molecular liquids • oligoarylenes • pyrene
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rotation for 1,1’-bipyrene. It would, however, be expected to be close to
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Entry for the Table of Contents (Please choose one layout)
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FML?! Hardly a web-slang indictment
of one’s own existence! A new set of
intensely fluorescent (φ=0.80)
Joshua C. Walsh, David T. Hogan,
Kerry-Lynn M. Williams, Simon D.
Brake, Gandikota Venkataramana, Tara
A. Misener, Brandon J. Wallace, Richard
P. Johnson, David W. Thompson,
Yuming Zhao, Brian D. Wagner* and
Graham J. Bodwell*
atropisomeric pyrene-based oligomers
has been synthesized using a two-
step iterative strategy. They have
been shown to be room temperature
liquids by POM, DSC and SWAXS
analysis. As such, they join the
Page No. – Page No.
growing family of Functional Molecular
Liquids. Delocalization in their excited
states was found to be more extensive
than in other pyrene-based systems.
Synthesis of Oligo(1,8-pyrenylene)s –
A Series of Functional Molecular
Liquids
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