Synthesis and Photophysical Properties of a 13,13′-Bibenzo[b]perylenyl Derivative as a π-Extended 1,1′-Binaphthyl Analog

Article abstract of DOI:10.1021/acs.orglett.6b00747

A 13,13′-bibenzo[b]perylenyl derivative-an axially chiral π-extended compound in which two perylene subunits fused to 1,1′-binaphthyl scaffold-has been synthesized from 1,8-dibromophenanthrene using an anionic cyclodehydrogenation reaction in the presence

Full text of DOI:10.1021/acs.orglett.6b00747

Letter
pubs.acs.org/OrgLett
Synthesis and Photophysical Properties of a 13,13′-
Bibenzo[b]perylenyl Derivative as a π‑Extended 1,1′-Binaphthyl
Analog
†
,†
‡
‡
,†
Yosuke Uchida, Takashi Hirose,* Takuya Nakashima, Tsuyoshi Kawai, and Kenji Matsuda*
†Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura,
Nishikyo-ku, Kyoto 615-8510, Japan
‡
Graduate School of Materials Science, Nara Institute of Science and Technology, NAIST, 8916-5 Takayama, Ikoma, Nara 630-0192,
Japan
*
S Supporting Information
ABSTRACT: A 13,13′-bibenzo[b]perylenyl derivativean axially chiral π-extended compound in which two perylene subunits
fused to 1,1′-binaphthyl scaffoldhas been synthesized from 1,8-dibromophenanthrene using an anionic cyclodehydrogenation
reaction in the presence of potassium metal as the key step. The pair of enantiomers can be separated by chiral high-performance
−
1
−1
liquid chromatography (HPLC), which showed a strong circular dichroism (CD) (Δε = 330 M cm at 449 nm, |g | = 5.8 ×
CD
−3
3
10
0
at 453 nm), high fluorescence quantum yield (Φ = 64%), and strong circular polarized luminescence (CPL) (|gCPL| = 5 ×
f
−
1
at 454 nm) in solution phase.
ontrolling the interchromophoric interaction can provide
design principles for diverse photophysical and chiroptical
C
properties that are difficult to realize using only one
1
−4
chromophore.
Spatial arrangement of two chromophores is
a determining factor in their interchromophoric interactions
including interactions between transition electronic/magnetic
5
−7
dipole moments.
Extension of the π-electron system by condensing aromatic
rings is a current emerging yet challenging issue in the field of
8
−11
organic chemistry.
By expanding π-conjugation, desired
Figure 1. Chemical structures of 1,1′-binaphthyl-based polycyclic
properties for application to functional materials can be expected,
such as high photoluminescence quantum yield, photophysical
response in the visible and near-infrared wavelength regions, low
redox potentials, and adequate π−π stacking in the solid state
causing a high carrier transportation.
aromatic hydrocarbons.
chiroptical properties (i.e., circular dichroism (CD) and circular
polarized luminescence (CPL)) can be successfully achieved by
1
2−15
23−25,32,35
1
,1′-Binaphthyl
is a typical scaffold having axial chirality,
introducing the axial chirality.
which has been widely used as a chiral ligand for asymmetric
organic syntheses,
cules,
In this context, we envisioned that further strong chiroptical
properties could be achieved while retaining good photophysical
properties in the monomer state by connecting even more π-
extended PAHs. We focused on perylene as fluorescence
chromophores because of its high fluorescence quantum yield
1
6−18
a recognition unit of chiral mole-
1
9−21
22−25
and a skeleton for asymmetric compounds.
Several 1,1′-binaphthyl-based polycyclic aromatic hydrocarbons
2
6,27
28,29
(
PAHs), such as 1,1′-bianthryl,
1,1′-biphenanthryl,
1,1′-
1
,33,36,37
3
0−32
33,34
bipyrenyl,
(
and 3,3′-biperylenyl,
Figure 1) and are reported to have weak intramolecular
have been synthesized
and outstanding photostability.
Here, we report the
synthesis and photophysical properties of a 13,13′-bibenzo[b]-
perylenyl derivative 1 (Scheme 1).
interaction between the two aromatic subunits connected by a
single C−C bond, especially in the ground state, due to the
dihedral angle between the two π-conjugation planes close to 90°
in solution. On the other hand, significant induction of
Received: March 15, 2016
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.6b00747
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 1. Synthesis of 8,8′,11,11′-Tetra-tert-butyl-13,13′-
bibenzo[b]perylenyl
1
Figure 2. H NMR spectra of compounds 1 (top) and 2 (bottom) in
CDCl at room temperature (for details of chemical shifts, see Table S1,
3
Supporting Information).
were observed for the signals of protons H-g and H-h (0.05 and
0
.08 ppm, respectively), which were more prominent for the
protons H-j, H-k, and H-l (0.14, 0.30, and 0.63 ppm,
respectively). The prominent upfield shifts for the protons H-j,
H-k, and H-l imply that these protons locate on top of the π-
plane of the other benzo[b]perylene unit. Therefore, the dihedral
angle between the two benzo[b]perylene moieties (ϕ) is less
than 90° and the two perylene subunits of compound 1 are in
proximity in solution, which was consistent with the optimized
structure calculated by a DFT method (ϕ = 77.5°) in the gas
phase (Figure S1, Supporting Information).
Compound 1 was synthesized according to the route shown in
Scheme 1. 1,8-Dibromo-3,6-di-tert-butylphenanthrene (3) was
prepared from commercially available 4-tert-butyltoluene in five
The structure of compound 1 was unambiguously determined
by X-ray crystallography. A single crystal suitable for X-ray
analysis was obtained by a liquid−liquid diffusion method using a
toluene solution of a racemic mixture of 1 and acetonitrile as a
poor solvent. The dihedral angle (ϕ) was 119.8° (Figure 3a).
38
steps according to the literature. Mononaphthyl-substituted
phenanthrene derivative 4 was synthesized by Suzuki−Miyaura
coupling of compound 3 with 1-naphthylboronic acid. One half
of compound 4 was lithiated, borylated, and then reacted with
the other half of 4 in the presence of Pd(PPh ) and potassium
1
Considering the results of H NMR and DFT calculation, the
large dihedral angle in the crystal structure is likely due to a
packing effect.
3
4
carbonate, affording 8,8′-di(1-naphthyl)-1,1′-biphenanthryl (5).
For the cyclodehydrogenation of the precursor 5, a conventional
photochemical reaction was attempted in the presence of iodine
X-ray analysis revealed that compound 1 is arranged in a 1-D
chain through a slipped π−π stacking along the c-axis, in which
the axially chiral enantiomers (i.e., (P)- and (M)-isomers) are
alternately stacked with the π−π distance of 3.28−3.47 Å (Figure
3b,c). Besides the π−π stacking interaction, the CH···π
interaction was observed between the tert-butyl group and
benzo[b]perylene moiety in the crystal structure (see Figure S2,
Supporting Information).
3
9
as an oxidant; however, no reaction occurred upon UV
irradiation during 12 h in cyclohexane. The Scholl reaction (i.e.,
oxidative aryl−aryl coupling reactions) of 5 using iron(III)
4
0
chloride resulted in a complicated mixture of unidentified
byproducts. Instead, the intramolecular aryl−aryl bond for-
mation of compound 5 was successfully achieved by an anionic
The absorption and steady state fluorescence spectra of
compounds 1 and 2 were recorded in methylcyclohexane
(MCH) (Figure 4 and Table 1). The absorption and
fluorescence spectra of 1 were quite similar in shape to those
of 2. Absorption and fluorescence maxima of 1 (446 and 454 nm,
respectively) appeared at slightly longer wavelengths by ca. 10
nm than those of 2 (438 and 445 nm, respectively). The Stokes
41
cyclodehydrogenation induced by potassium metal, affording
the desired compound 1 in 42% yield. In this reaction, the two
C−C bonds between the naphthyl and phenanthryl groups (i.e.,
the carbon atoms at the 8-position of the naphthyl group and at
the 9-position of the phenanthryl group) were selectively formed
4
2
and the 10- and 10′-positions of the product were not reacted.
−1
Reference compound 2 was synthesized by lithiation of
compound 4 followed by the same anionic cyclodehydrogena-
tion induced by potassium metal. The structure of compounds 1
and 2 was fully characterized by H NMR, C NMR, and
HMQC/HMBC measurements and high-resolution mass
spectrometry (see the Supporting Information).
shifts for both 1 and 2 were very small (only 395 and 359 cm ,
respectively), suggesting a remarkably small geometrical
relaxation of 1 in the excited state. The similarity in the ground-
and excited-state geometries of 1 is in marked contrast to the
1
13
34
previously reported 3,3′-biperylenyl derivative. The fluores-
cence quantum yield and fluorescence lifetime of 1 (Φ = 0.64,
f
1
The axially chiral structure of 1 was suggested by H NMR
⟨τ ⟩ = 3.4 ns) were comparable to those of 2 (Φ = 0.74, ⟨τ ⟩ = 3.6
f
f
f
spectroscopy in CDCl (Figure 2). The proton signals of H-a, H-
ns). Thus, the photophysical properties of the benzo[b]perylene
subunit can be well retained after dimerization by linking with a
single C−C bond at the 13,13′-positions.
3
c, and H-f, which are laterally distant from the C−C bond at the
1
0
3,13′-positions of compound 1, were shifted to downfield by
.18, 0.04, and 0.01 ppm, respectively, compared to the chemical
Enantiomers of compound 1 were separated from a racemic
solution by a chiral high-performance liquid chromatography
shifts of compound 2. On the other hand, slight upfield shifts
B
DOI: 10.1021/acs.orglett.6b00747
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Table 1. Photophysical Properties of Compounds 1 and 2 in
MCH
λ
/nm
−1
max,abs
compd (ε/M cm
−1
a
⟨τ ⟩/ns kf/ns−1 knr/ns−1
b
c
c
)
λmax,FL/nm Φf
f
1
446
454
0.64
3.4
3.6
0.19
0.21
0.11
(
7.3 × 104)
2
438
445
0.74
0.073
(
3.9 × 104)
a
b
Measured by an absolute method using an integrating sphere. The
area-weighted mean fluorescence lifetime ⟨τ ⟩ was calculated as
f
2
n
follows: ⟨τ ⟩ = Σ(A τ )/Σ(A τ ), where A is the coefficient of the
exponential function for the nth component. Fluorescence emission
rate constant (k ) and nonradiative decay rate constant (k ) were
f
n
n
n
n
c
f
nr
calculated as follows: k = Φ /⟨τ ⟩, k = (1 − Φ )/⟨τ ⟩.
f
f
f
nr
f
f
Figure 5. (a) Experimentally observed CD spectra of compounds in
MCH at 15 °C (red, (P)-(+)-1; blue, (M)-(−)-1). (b) Rotatory
strengths of (M)-(−)-1 calculated at M062X/6-311g(2d,p) level. Gray
dashed line denotes the simulated CD spectra from the calculated
rotatory strengths.
Figure 3. (a) ORTEP drawing of 1, showing 50% probability of thermal
ellipsoids. Hydrogen atoms are omitted for clarity. (b) Crystal packing
structure of 1 viewed normal to the (010) face. Red and blue represent
the (P)- and (M)-isomers, respectively. (c) Crystal packing viewed
̅
normal to the (110) face.
The rate of racemization of 1 was investigated by monitoring
the time course of CD signal intensity at 449 nm at different
temperatures (Figure S8, Supporting Information). Based on the
Eyring plot of the CD signal decay rate, the activation free energy
‡
−1
of the racemization was calculated as ΔG = 102.9 kJ·mol at 25
‡
−1
‡
−1
°
C (ΔH = 89.6 kJ·mol , ΔS = −44.5 kJ·mol ) (Figure S9,
Supporting Information). According to these parameters, the
half-life of the isolated enantiomers is τ1/2 = 18 h at 25 °C.
Circular polarized luminescence (CPL) is a powerful tool to
investigate the electronic structure of chiral molecules in the
24,35
excited state.
Both enantiomers, (P)-(+)-1 and (M)-(−)-1,
showed positive and negative CPL signals around 454 nm with a
dissymmetric factor of |gCPL| = (5 ± 3) × 10− (Figure 6). The
sign of the CPL signal was consistent with the sign of the first
Cotton effect observed in the CD spectra (Figure 5a).
Interestingly, the dissymmetric factors of luminescence were
3
Figure 4. Absorption and fluorescence spectra of compounds 1 (top)
and 2 (bottom) in MCH.
−3
comparable to that of absorption (|g | = 5.8 × 10 ) for
CD
(
HPLC) (Figure S6, Supporting Information), and then CD
compound 1, suggesting that the electronic structure of 1 in the
excited state is similar to that in the ground state.
spectra were measured in MCH (Figure 5a). The first fraction in
the chiral HPLC was (+)-1, which showed a positive Cotton
effect at the longest wavelength (Δε = 330 M cm at 449 nm,
In conclusion, 13,13′-bibenzo[b]perylenyl derivative 1 was
synthesized using 1,8-dibromo-3,6-di-tert-butylphenanthrene
(3) as a key intermediate. The photophysical properties of
benzo[b]perylene subunit can be well retained in the axially
chiral dimer 1 by linking with the C−C bond at the 13,13′-
positions. Bibenzo[b]perylenyl 1a π-extended molecule with
axial chirality consisting of only carbon and hydrogen atoms
−1
−1
−3
|
g | = 5.8 × 10 at 453 nm), while the second fraction was
−)-1 showing a negative Cotton effect as the mirror image. On
CD
(
the basis of the comparison of experimental CD spectra with
theoretically calculated rotatory strength (at the M062X/6-
311G(2d,p) level) (Figure 5b), the axial chirality of 1 was
determined as (P)-(+)-1 and (M)-(−)-1. The assignment of
without any heteroatomsexhibited a strong emission (Φ =
f
chirality is consistent with that estimated by the exciton chirality
0.64) and relatively large dissymmetric factors of both absorption
4
3−45
−3
−3
method.
and emission (|g | = 5.8 × 10 , |g | = 5 × 10 , respectively)
CD CPL
C
DOI: 10.1021/acs.orglett.6b00747
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
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AUTHOR INFORMATION
Corresponding Authors
̈ ̈
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■
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E-mail: thirose@sbchem.kyoto-u.ac.jp.
E-mail: kmatsuda@sbchem.kyoto-u.ac.jp.
́
Maroto, B.; Muller, G.; Ortiz, M.; de la Moya, S. Chem. - Eur. J. 2015, 21,
Notes
13488.
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36) Wu
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The authors declare no competing financial interest.
Qu, J.; Kohl, C.; Mu
̈
ACKNOWLEDGMENTS
This work was supported by a Grant-in-Aid for Scientific
Research on Innovative Areas “Photosynergetics” (No.
6107008) from the MEXT, Japan and a Grant-in-Aid for
Young Scientists (B) (No. 25810048) from the JSPS, Japan.
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0 , and 1 × 10 , respectively. A significantly large |g | value has been
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D
DOI: 10.1021/acs.orglett.6b00747
Org. Lett. XXXX, XXX, XXX−XXX