Basic Photophysical Properties of meso-Bis(pyren-2-yl)porphyrin: An Isomer of Pyrene-Substituted Porphyrins

Article abstract of DOI:10.1055/s-0036-1588715

The Suzuki-Miyaura coupling reaction of pyren-2-yl boronic acid ester with a meso-dibromodiphenylporphyrin derivative was carried out to give another pyrene-substituted porphyrin. The electrophilic substitution reaction occurred selectively on the porphyr

Full text of DOI:10.1055/s-0036-1588715

SYNTHESIS
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
© Georg Thieme Verlag Stuttgart · New York
2017, 49, A–E
paper
A
S. Tomita et al.
Paper
Synthesis
Basic Photophysical Properties of meso-Bis(pyren-2-yl)porphyrin:
An Isomer of Pyrene-Substituted Porphyrins
Ar
Shohei Tomitaa
Kazunori Hirabayashia
Toshio Shimizua
Kenta Gotob
N
N
N
N
O
O
Br
Br
B
tBu
M
+
Ken-ichi Sugiura*a
Ar
M
a Department of Chemistry, Graduate School of Science and Engineering,
Tokyo Metropolitan University, 1-1 Minami-Ohsawa, Hachi-Oji, Tokyo
192-0397, Japan
Ar
N
N
N
N
b Institute for Materials Chemistry and Engineering, Kyushu University,
744 Moto-oka, Fukuoka 819-0395, Japan
tBu
tBu
sugiura@porphyrin.jp
Ar
Received: 22.12.2016
Accepted after revision: 23.01.2017
Published online: 02.03.2017
The greatest motivation for this study was the compari-
son with the chemistry of the pyren-1-yl porphyrins 1 be-
cause the HOMO and LUMO coefficients of the 1- and 2-po-
sitions of pyrene are markedly different; that is, the 1-posi-
tion has large coefficients whereas the 2-position is the
node (Scheme 1, c).7 Here we report the synthesis of 3(M)
and describe its electrophilic reactivity and basic proper-
ties.
The reactions are summarized in Scheme 2. The key re-
action is the Suzuki–Miyaura reaction. In contrast to the
synthesis of pyren-1-yl porphyrins 1,7 which involved the
coupling of a porphyrin having a boronic acid ester with
bromopyrenes, the reaction of boronic acid of pyrene 68
with meso-dibromoporphyrin 59 was designed. The reac-
tion proceeded smoothly (50% yield) and gave a similar
yield to that of 1 (ca. 70%).7 The six tert-butyl groups on
pyrenes and phenyls led to a reasonable solubility of 3 in
common organic solvents. The corresponding free base
3(2H) was obtained by treatment of 3(Zn) with mineral
acid.10
The functionalization of 3(2H) was examined with an
eye to the future application of 3. Given that the 1-, 3-, 6-,
and 8-positions of pyrene have high reactivities in the elec-
trophilic aromatic substitution reaction, a concerted reac-
tion between pyrene and/or porphyrin functionalizations
was examined. We then carried out the bromination of
3(2H). To our surprise, the substitution occurred selectively
on the β-position of the porphyrin. Treatment with NBS (6
equiv) afforded tetrabromo derivative 7 as the main prod-
uct in an acceptable yield (63%) along with byproducts 8a
and 8b (20% yield).11,12
DOI: 10.1055/s-0036-1588715; Art ID: ss-2016-f0878-op
Abstract The Suzuki–Miyaura coupling reaction of pyren-2-yl boronic
acid ester with a meso-dibromodiphenylporphyrin derivative was car-
ried out to give another pyrene-substituted porphyrin. The electrophilic
substitution reaction occurred selectively on the porphyrin nucleus of
this molecule. The introduced pyrenes acted as a light-harvesting an-
tenna.
Key words porphyrin, pyrene, Suzuki–Miyaura coupling, light-
harvesting
The molecular design and synthesis of porphyrinoid
compounds have been attracting much attention1 and,
thanks to advances in analytical instrumentation, the syn-
thetic chemistry of large porphyrin-based advanced mate-
rials has become an interdisciplinary science.2 To enhance
the functions of porphyrins, the introduction of a suitable
substituent on the meso-position is a promising approach
because this position has large HOMO and LUMO coeffi-
cients. Various functional groups have been introduced, in-
cluding arenes such as oligo-p-phenylenes3 and polycyclic
aromatic hydrocarbons (PAHs), namely anthracene,4
perylene,5 coronene,5 and hexa-peri-hexabenzocoronene.6
We have also contributed to this research field: our pyren-
1-yl-substituted porphyrin 1 opened the door to PAH-fused
porphyrin chemistry (Scheme1); thus, the oxidation of 1 af-
forded extremely π-expanded porphyrins 2.7 After the pub-
lication of our work, many reports of PAH-fused π-expand-
ed porphyrins appeared, which used PAH-substituted por-
phyrins as precursors.2 In this study, we designed another
pyrene-substituted porphyrin, namely meso-bis(pyrene-2-
yl)porphyrin derivative 3(M) (Scheme 1).
The absorption spectra of 3(Zn) and reference com-
pound 4 are shown in Figure 1 (a). A sharp and intense ab-
sorption band was observed at 429 nm (23,300 cm–1) for
3(Zn).
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–E

B
S. Tomita et al.
Paper
Synthesis
(a)
Ar
(b)
(c)
Ar
M
node
(OMe)n
N
N
N
N
tBu
tBu
H
H
Ar
1
LUMO
node
N
N
N
N
PhI(OTf)2
(OMe)n
tBu
tBu
M
Ar
N
N
N
N
Ar
M
tBu
tBu
3(M)
(M = Zn or 2H)
Ar
2
HOMO
Scheme 1 (a) Molecular structure of 1 and its oxidative intramolecular ring-closure reaction. (b) Molecular structure of 3(M). (c) Frontier orbitals
(HOMO and LUMO) of pyrene.
This Soret band was shifted 1100 cm–1 to the lower en-
tBu
tBu
ergy region compared with that of 4 (409 nm, 24,400 cm–1).
Although the substitution position of pyrene is the node of
this molecule and the pyrene molecules are connected
nearly perpendicularly to porphyrin, a small but significant
conjugation occurred between the porphyrin. The Q-band
also showed bathochromic shifts (see the Supporting Infor-
mation, SI1). Along with the absorptions characteristic of
zinc porphyrins, three new bands were observed in the UV
region, which were attributable to the excitations of
pyrene; namely, Band-I, with structures around 339 nm
(29,500 cm–1), Band-II, with structures around 278 nm
(35,000 cm–1), and broadened Band-III around 249 nm
(39,000 cm–1). Compared with the known photophysical
properties of pyrene,13,14 those bands were assigned to the
N
N
N
N
2)
3)
4)
X
X
3(Zn)
3(2H)
Zn
(from 5)
O
B
tBu
tBu
tBu
O
6
4 (X = H)
5 (X = Br)
1)
tBu
tBu
Br
1
transitions of La (transition from the pyrene HOMO to the
1
pyrene LUMO; i.e., LUMO ← HOMO), Bb (LUMO ← HOMO-
1), and 1Ba (LUMO+1 ← HOMO-1), respectively.
Br
NH
N
One of the important functions of PAH-substituted por-
phyrin is light harvesting; that is, the photoexcited energies
of PAH moieties are transferred to porphyrin and the
formed excited state of porphyrin emits light. Steady-state
qualitative experiments of 3(Zn) were carried out (Figure 1,
b). Irradiation of the Q-band of 3(Zn) at 551 nm afforded
emissions at 601 and 649 nm, which are characteristic of
tBu
tBu
N
HN
Z
Y
tBu
7
tBu
1
zinc porphyrins. Irradiation of the Bb band of the pyrenes
(Y = Z = Br)
8a (Y = Br, Z = H)
8b (Y = H, Z = Br)
at 277 nm also afforded a similar emission with 48% inten-
sity. The irradiation at 277 nm of 4, the reference com-
pound having no pyrene, gave a very weak emission. This
suggests that the two pyrenes acted as antenna chromo-
phores in 3(Zn).15
Scheme 2 Synthesis of pyren-2-yl-substituted porphyrins. Reagents
and conditions: (1) NBS, pyridine, CHCl3; (2) 6, Pd(PPh3)4, K2CO3, DMF;
(3) HCl, toluene/THF; (4) NBS, CHCl3.
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S. Tomita et al.
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Synthesis
as the internal standard. Infrared spectra were recorded with a Shi-
madzu FTIR-8400 instrument using KBr pellet techniques in the range
of 500 to 4000 cm–1. The absorption spectra were recorded with a
Shimadzu UV-3600 using spectrophotometric grade CH2Cl2. The fluo-
rescence spectra were recorded with a JASCO FP-6500. Mass spectra
were recorded with a Bruker micrOTOF II SDT1. Melting points were
measured with a YANAKO MP-S3 apparatus. The observed melting
points are uncorrected. Silica gel thin-layer chromatography (Merck &
Co., Inc.) was performed using Silica Gel 60 F254 aluminum sheets
from Merck Co. Ltd. Column chromatography was performed using
Neutral Silica Gel 60N from Kanto Chemical Co., Inc. Full crystallo-
graphic details, excluding structure factors, have been deposited at
the Cambridge Crystallographic Data Centre (CCDC). Other experi-
mental details were reported previously.17
(a)
7
Wavelength / nm
429 nm
in CH2Cl2
3(Zn)
6
5
409 nm
4
4
3
2
1
Band-III
249 nm
1Ba
Band-II
278 nm
1Bb
Band-I
339 nm
1La
Compound 3(Zn)
0
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
A mixture of dibromoporphyrin 5 (90.8 mg, 100 μmol),9 boronic acid
of pyrene 6 (96.1 mg, 250 μmol, 2.5 equiv),8,18 K2CO3 (55.4 mg, 400
μmol, 4 equiv), and freshly distilled DMF (20 mL) was introduced into
a Schlenk flask and purged with N2. Against the stream of N2,
Pd(PPh3)4 (11.6 mg, 10 μmol, 0.1 equiv) was added. The reaction mix-
ture was stirred and heated at 70 °C under N2 for 17 h. TLC analysis
showed the disappearance of 5 and the formation of a new product
(Rf = 0.21; n-hexane/CHCl3/pyridine, 2:1:0.02). The reaction mixture
was diluted with toluene and then washed with water three times
and brine once. The organic layer was dried and the solvent was re-
moved under reduced pressure. The crude product was purified by
chromatography on SiO2 (n-hexane/CHCl3/pyridine, 2:1:0.02) to give
the desired product. An analytical sample was obtained by recrystal-
lization from CHCl3.
Wavenumber / 104 cm–1
(b)
in CH2Cl2
3(Zn) (ex.: 551 nm)
3(Zn)
(ex.: 277 nm)
4
Yield: 63.0 mg (50%); purple solid; mp >300 °C.
(ex.: 277 nm)
1H NMR (500 MHz, CDCl3, TMS): δ = 9.06 (s, 4 H), 9.90 (d, J = 4.7 Hz,
4 H), 8.00 (d, J = 4.7 Hz, 4 H), 8.39 (s, 4 H), 8.29 (d, J = 8.8 Hz, 4 H), 8.25
(d, J = 8.8 Hz, 4 H), 8.11 (d, J = 1.9 Hz, 4 H), 7.77 (t, J = 1.9 Hz, 2 H), 1.68
(s, 18 H), 1.50 (s, 36 H).
550
600
650
700
750
Wavelength / nm
Figure 1 (a) Absorption spectra of 3(Zn) and 4 (in CH2Cl2). (b) Steady-
state emission spectra of 3(Zn) excited at 551 and 277 nm and 4 excit-
ed at 277 nm (in CH2Cl2).
IR (KBr): 3040 (m), 2963 (s), 2904 (m), 2868 (m), 1592 (m), 1363 (m),
1226 (m), 1004 (m), 941 (m), 801 (m), and 715 (s) cm–1
.
UV/Vis (CH2Cl2): λmax (ε, dm3mol–1cm–1) = 551 (26,600), 537 (98,800),
429 (631,800), 408 (shoulder, 62,200), 339 (41,400), 323 (42,300),
278 (56,800), 267 (46,100), 249 (131,400), 238 (78,500) nm.
HRMS (ESI): m/z [M + 1]+ calcd for C88H84N4Zn + H: 1261.6060; found:
1261.5991 (100%).
In conclusion, pyren-2-yl-substituted porphyrin 3(M)
was designed and prepared. Similar to our other pyren-2-
yl-substituted arenes,14 the corresponding boronic acid es-
ter of pyrene 6 acted as a good synthon of pyrene and con-
veniently afforded 3(2H). PAH-substituted porphyrins 3(M)
show much potential in advanced materials chemistry be-
cause they can be used as light-harvesting materials, PAH-
fused porphyrins,7,16 sponge molecules incorporating sol-
vents,10 and so on. We are investigating these topics further
with emphasis on the comparison of pyren-1-yl porphy-
rins.
Anal. Calcd for C88H84N4Zn: C, 83.68; H, 6.70; N, 4.44. Found: C, 82.97;
H, 6.72; N, 4.41.
Compound 3(2H)
A mixture of 3(Zn) (45.0 mg, 0.035 mmol), toluene (80 mL), and THF
(10 mL) was stirred at r.t. Five drops of concd HCl were added and the
reaction mixture was stirred at r.t. The color of the reaction mixture
changed from red-purple to dark-purple and finally green. After 15
min, the reaction mixture was washed with water, aq. NaHCO3, and
brine. This solution was passed through a short SiO2 column to afford
3(2H) (170.6 mg, 95%). An analytical sample was obtained by recrys-
tallization from CHCl3.
The syntheses of dibromoporphyrin 4 and 59 and boronic acid ester 68
were carried out according to the reported method. The following re-
agents were used as received: K2CO3 (Nacalai Tesque, Inc.), Pd(PPh3)4
(Tokyo Chemical Industry Co., Ltd.), conc. HCl (Kanto Chemical Co.,
Inc.), THF (Kanto Chemical Co., Inc.), NaHCO3 (Kanto Chemical Co.,
Inc.), and NBS (Wako Pure Chemical Industries, Ltd.). DMF (Wako Pure
Chemical Industries, Ltd.) was distilled over KOH under N2. The
1H NMR spectra were recorded with a Bruker Avance III 500 (500
MHz for 1H) spectrometer in CDCl3 (Acros Organics Co., Inc.) with TMS
Purple solid; mp >300 °C.
1H NMR (500 MHz, CDCl3, TMS): δ = 9.05 (s, 4 H), 9.89 (d, J = 4.7 Hz,
4 H), 8.77 (d, J = 4.7 Hz, 4 H), 8.39 (s, 4 H), 8.29 (d, J = 8.8 Hz, 4 H), 8.26
(d, J = 8.8 Hz, 4 H), 8.11 (d, J = 1.9 Hz, 4 H), 7.77 (t, J = 1.9 Hz, 2 H), 1.68
(s, 18 H), 1.50 (s, 36 H), –2.40 (s, 2 H).
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IR (ATR): 3312 (m), 3042 (m), 2961 (s), 2925 (m), 2854 (m), 1597 (m),
1477 (m), 1362 (m), 1240 (m), 916 (m), 885 (m), 803 (s), and 713 (s)
Supporting Information
cm–1
.
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0036-1588715.
S
u
p
p
ortiInfogrmoaitn
S
u
p
p
o
nrtogI
f
rmoaitn
UV/Vis (CH2Cl2): λmax (ε, dm3mol–1cm–1): 649 (6,100), 592 (7,400),
555 (12,800), 519 (23,300), 428 (469,500), 408 (shoulder, 104,800),
369 (30,300), 339 (53,200), 324 (49,000), 300 (33,000), 278 (65,600),
267 (56,800), 249 (124,600), 241 (90,400) nm.
References
HRMS (ESI): m/z [M + 1]+ calcd for C88H86N4 + H: 1199.6925; found:
1199.6847 (100%).
(1) Kadish, K.; Guilard, R.; Smith, K. M. The Porphyrin Handbook Vol.
1-20; Academic Press: Amsterdam, 2003.
(2) Mori, H.; Tanaka, T.; Osuka, A. J. Mater. Chem. C 2013, 1, 2500.
(3) Mikami, S.; Sugiura, K.-i.; Sakata, Y. Chem. Lett. 1997, 833.
(4) Wasielewski, M. R.; Johnson, D. G.; Svec, W. A.; Kersey, K. M.;
Minsek, D. W. J. Am. Chem. Soc. 1988, 110, 7219.
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Zimmerman, J. D.; Forrest, S. R.; Thompson, M. E. J. Org. Chem.
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(6) Englert, J. M.; Malig, J.; Zamolo, V. A.; Hirsch, A.; Jux, N. Chem.
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(7) Yamane, O.; Sugiura, K.-i.; Miyasaka, H.; Nakamura, K.;
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Chem. Lett. 2004, 33, 40.
(8) Crawford, A. G.; Liu, Z.; Mkhalid, I. A. I.; Thibault, M.-H.;
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J. Am. Chem. Soc. 1998, 120, 10764.
(10) We were unable to obtain good elemental analysis values for
pyrene-substituted porphyrins. meso-Tetraphenylporphryin
(TPP) and its metal complexes are known to behave as porphy-
rin sponges in which the TPP lattices incorporate solvent mole-
cules like a sponge, see: (a) Byrn, M. P.; Curtis, C. J.; Khan, S. I.;
Sawin, P. A.; Tsurumi, R.; Strouse, C. E. J. Am. Chem. Soc. 1990,
112, 1865. (b) Byrn, M. P.; Strouse, C. E. J. Am. Chem. Soc. 1991,
113, 2501. (c) Byrn, M. P.; Curtis, C. J.; Goldberg, I.; Hsiou, Y.;
Khan, S. I.; Sawin, P. A.; Tendick, S. K.; Strouse, C. E. J. Am. Chem.
Soc. 1991, 113, 6549. (d) Byrn, M. P.; Curtis, C. J.; Hsiou, Y.;
Khan, S. I.; Sawin, P. A.; Tendick, S. K.; Terzis, A.; Strouse, C. E.
J. Am. Chem. Soc. 1993, 115, 9480. Because pyrene is larger than
benzene, the space of the lattice produced by 3(M) and/or 7
should be larger than that produced by TPP. For example, the
crystal of 7 incorporated two toluene molecules in its unit cell.12
The incorporation of solvent molecules could be one of the
reasons for the inaccurate EA values. The characterization of
new products was based on high-resolution mass spectroscopic
analysis.
Anal. Calcd (%) for C88H86N4: C, 88.10; H, 7.23; N, 4.67. Found: C,
87.02; H, 7.33; N, 4.58.
Compound 7
A solution of purified NBS (85.7 mg of NBS dissolved in 6 mL of dis-
tilled CHCl3, 481.5 mol, 6 equiv) was added to a solution of 3(2H)
(96.1 mg, 80.1 μmol, dissolved in 50 mL of distilled CHCl3) at r.t. over
10 min. After the addition of the NBS solution, the reaction mixture
was heated to reflux for 8 h. TLC analysis indicated the disappearance
of 3(2H) (Rf = 0.17; n-hexane/toluene, 2:1) and the formation of de-
sired product 7 (Rf = 0.14) and tribromo compound (see below). The
mixture was cooled to r.t. and the reaction was terminated by adding
acetone (15 mL). The solvent was removed under reduced pressure
and imide was removed by short SiO2 column chromatography using
CHCl3 as eluent. Further purification was carried out by SiO2 column
chromatography (n-hexane/CHCl3, 1:2) to give 7 (75.7 mg, 63%) and
trisubstituted derivative (22.7 mg, 20%). An analytical sample of 7
was obtained by recrystallization from hot toluene.
Purple solid; mp > 300.0 °C.
1H NMR (500 MHz, CDCl3, TMS): δ = 8.99 (s, 4 H), 8.78 (d, J = 4.7 Hz,
2 H), 8.62 (d, J = 4.7 Hz, 2 H), 8.39 (s, 4 H), 8.31 (d, J = 8.8 Hz, 4 H), 8.29
(d, J = 8.8 Hz, 4 H), 8.01 (d, J = 1.9 Hz, 4 H), 7.80 (t, J = 1.9 Hz, 2 H), 1.68
(s, 18 H), 1.52 (s, 36 H), –2.74 (s, 2 H).
IR (KBr): 3373 (m), 3042 (m), 2960 (s), 1594 (m), 1475 (m), 1362 (m),
1226 (m), 1002 (s), 953 (m), 929 (m), 713 (m) cm–1
.
UV/Vis (CH2Cl2): λmax (ε, dm3mol–1cm–1) = 679 (10,900), 536 (20,400),
440 (289,000), 340 (63,500), 325 (49,000), 279 (66,400), 267 (65,800),
248 (105,200) nm.
HRMS (ESI): m/z [M + 1]+ calcd for C88H82Br4N4 + H: 1515.3327; found:
1515.3303 (100%).
Anal. Calcd for C88H82Br4N4: C, 69.75; H, 5.45; N, 3.70. Found: C, 70.06;
H, 5.75; N, 3.55.
The fraction eluting first having Rf = 0.22 was characterized as a mix-
ture of the isomers of tribiromo derivatives on the basis of mass spec-
tra and complicated 1H NMR signals; MS (ESI): m/z (%) = 1436.4 (100)
[M + 1]+.
(11) Crossley, M. J.; Burn, P. L.; Chew, S. S.; Cuttance, F. B.; Newsom, I.
A. Chem. Commun. 1991, 1564.
(12) Preliminary single-crystal diffraction study of 7 was carried out
(see Figure 2).
However, the marked disorder of solvent molecules prevented
the complete analysis. Provisional results are shown in the Sup-
porting Information SI2. CCDC 1520375 contains the supple-
mentary crystallographic data for this paper. The data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/getstructures.
Acknowledgment
This work was supported in part by the Tokyo Kasei Chemical Promo-
tion Foundation, the Cooperative Research Program of ‘Network Joint
Research Center for Materials and Devices: Dynamic Alliance for Open
Innovation Bridging Human, Environment and Materials’, and the Pri-
ority Research Program sponsored by the Asian Human Resources
Fund of Tokyo Metropolitan Government (TMG). We appreciate the
technical assistance provided by the Service Centre of the Elementary
Analysis of Organic Compounds at Kyushu University.
(13) (a) Yoshinaga, T.; Hiratsuka, H.; Tanizaki, Y. Bull. Chem. Soc. Jpn.
1977, 50, 3096. (b) Yamashita, K.-i.; Nakamura, A.; Sugiura, K.-i.
Chem. Lett. 2015, 44, 303.
(14) Yamashita, K.-i.; Nakamura, A.; Hossain, M. A.; Hirabayashi, K.;
Shimizu, T.; Sugiura, K.-i. Bull. Chem. Soc. Jpn. 2015, 88, 1083.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–E

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S. Tomita et al.
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Synthesis
(15) Similar experiments were carried out in polar solvent DMF and
similar results were obtained; that is, energy transfer occurred
from pyrenes to porphyrin.
(16) One of the objectives of this study was to synthesize pyrene-
fused porphyrins. Attempts to obtain such porphyrins under
oxidative conditions, such as FeCl3 in MeNO2, DDQ/Sc(OTf)3,
etc., were unsuccessful. Furthermore, Pd-catalyzed intramolec-
ular C–C bond formation reactions on tetrabromide 7 also
failed, see: Saegusa, Y.; Ishizuka, T.; Komamura, K.; Shimizu, S.;
Kotani, H.; Kobayashi, N.; Kojima, T. Phys. Chem. Chem. Phys.
2015, 17, 15001; details of the oxidation reactions of 3(M) will
be reported elsewhere.
(17) Dien, L. X.; Yamashita, K.-i.; Asano, M. S.; Sugiura, K.-i. Inorg.
Chim. Acta 2015, 432, 103.
(18) Hassan, K.; Yamashita, K.-i.; Hirabayashi, K.; Shimizu, T.;
Nakabayashi, K.; Imai, Y.; Matsumoto, T.; Yamano, A.; Sugiura,
K.-i. Chem. Lett. 2015, 44, 1607.
Figure 2
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–E