Synthesis and spectroscopic characterization of meso-tetraarylporphyrins with fused phenanthrene rings

Article abstract of DOI:10.1016/j.tetlet.2005.11.162

A series of meso-tetraaryl porphyrins with fused phenanthrene rings have been synthesized from boron trifluoride-catalyzed Lindsey condensation of phenanthro[9,10-c]pyrrole with various para-substituted arylaldehydes at low temperature. Their structures w

Full text of DOI:10.1016/j.tetlet.2005.11.162

Tetrahedron
Letters
Tetrahedron Letters 47 (2006) 931–934
Synthesis and spectroscopic characterization of
meso-tetraarylporphyrins with fused phenanthrene rings
Hai-Jun Xu,a Zhen Shen,a,* Tetsuo Okujima,b Noboru Onob and Xiao-Zeng Youa,*
aCoordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China
bDepartment of Chemistry, Faculty of Science, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan
Received 1 September 2005; revised 29 November 2005; accepted 30 November 2005
Available online 19 December 2005
Abstract—A series of meso-tetraaryl porphyrins with fused phenanthrene rings have been synthesized from boron trifluoride-catal-
yzed Lindsey condensation of phenanthro[9,10-c]pyrrole with various para-substituted arylaldehydes at low temperature. Their
1
structures were characterized by UV–vis, H NMR, and mass spectroscopies. The UV–vis spectra of these compounds showed
remarkable bathochromic shift of the Soret band to the wavelength around 577 nm and Q-bands into the near-infrared region.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Modified porphyrin chromophores with strong absorp-
tion in the red/near-infrared region have been exten-
sively investigated due to their potential biomedical
NH
N
N
application in photodynamic therapy,1 as well as a
remarkable number of important functions in material
science application, such as fluorescent probes,2 conduc-
tive materials,3 nonlinear optical materials,4 near-infra-
red (NIR) dyes.5 Increased conjugation usually induces
a red-shift for a given chromophore, and various strate-
gies including the synthesis of expanded porphyrins,6 the
introduction of meso-alkynyl substituents,7 multiply
connecting porphyrin oligomers,8 and core modifica-
tions9 have been reported to produce absorptions at
long-wavelength. In addition, conformational distor-
tions of the porphyrin macrocycle is responsible for
some extent of bathochromic shifts.10 Among them,
one of the most effective and promising synthetic
approaches might be the fusion of aromatic rings at
the b-pyrrolic position which can lead to a significant
alternation in the electronic and optical properties of
the porphyrin core through the expansion of its p-elec-
tronic system. Several modified porphyrin structures
with fused benzene, 1,2-naphthalene, acenaphthylene,
phenathroline, and 9,10-phenanthrenene rings have
been investigated.11
NH
N
N
HN
HN
1
2
Tetraacenaphthoporphyrin
Tetraphenanthroporphyrin
NH
N
N
NH
N
N
HN
HN
4
3
Dodecaphenylporphyrin
Tetraphenyltetraacenaphthoporphyrin
However, fusion with these aromatic subunits showed
relatively small influence on the values of Soret band,
even fusion with four phenanthrene moieties (1, Chart
1) produces the Soret band at 482 nm, which is only
80 nm red-shift compared to that of octaethylporphyrin
(OEP).11,12 The corresponding acenaphthoporphyrin 2
(Chart 1) shows a disproportionate longer Soret band
at 528 nm.12a,13a,b Lash and co-workers further
Keywords: Exocyclic rings; Phenanthrene ring; Ring-fused porphyrins;
Synthesis.
*
Corresponding authors. Tel.: +86 25 83686679; fax: +86 25
83314502; e-mail: zshen@nju.edu.cn
0040-4039/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.11.162

932
H.-J. Xu et al. / Tetrahedron Letters 47 (2006) 931–934
ii
i
7
NO2
CO2Et
N
H
N
H
5
6
ArCHO
iii
Ar
NH
Ar
N
NH
HN
Ar
Ar
Ar
Ar
N
HN
Ar
NH
iv
HN
Ar
9
8
a. Ar = Ph; b. Ar = 4-FC6H4; c. Ar = 4-ClC6H4; d. Ar = 4-BrC6H4; e. Ar = 4-IC6H4
Scheme 1. Reagents and conditions: (i) CNCH2CO2Et, DBU, THF,
rt, 24 h; (ii) KOH, (CH2OH)2, 170 ꢁC, 2 h; (iii) BF3ÆOEt2, CH2Cl2, Ar,
À50 ꢁC, 24 h; (iv) DDQ, Et3N, 1 h.
1
Figure 1. Partial 500 MHz H NMR spectrum of 9a in deuterio-N,N-
increased this value to 556 nm by introducing meso-phen-
yl substituents (3, Chart 1).13b However, meso-aryl
phenanthroporphyrin could not be characterized due
to the difficulty of preparation under normal Lindsey
porphyrin condensation.13b Very recently, we reported
the synthesis of meso-tetraphenyl-ethynylporphyrins at
low temperature.7a Herein, we describe the synthesis
and the spectroscopic property studies of a series of
novel tetraaryltetraphenanthroporphyrins following our
previous method.
dimethylformamide.
protons which were consistent with the proposed highly
symmetrical porphyrin-like structure. The phenanthrene
protons closest to the phenyl subunits were shielded by
the adjacent phenyl rings and gave an upfield doublet
resonance at 6.93 ppm.12b The ortho-protons on the phen-
yl units were deshielded by the adjacent p-systems and
afforded a downfield doublet at 8.98 ppm. The remaining
protons fell into the typical aromatic range of 7.3–
8.0 ppm. The chemical shift of the internal NH appeared
at 1.11 ppm, indicating that 9a had a highly distorted
conformation in solution. The structure was further sup-
ported by MALDI-TOF mass spectrometry, which gave
the expected [M+H]+ peak at m/z = 1216.38. Porphyrins
9b–e gave satisfactory spectroscopic data that were in
accordance with their proposed structures.14
The general procedure for the preparation of meso-tetra-
aryl substituted tetraphenanthroporphyrins 9a–e was
summarized in Scheme 1. Ethyl phenanthro[9,10-c]pyr-
role-2-carboxylate 6 was readily obtained from the reac-
tion of 9-nitrophenanthrene 5 with ethyl isocyanoacetate
in the presence of the non-nucleophilic base 1,8-diazabi-
cyclo [5.4.0]undec-7-ene (DBU).12d The ethoxycarbonyl
group of 6 was removed by heating with potassium
hydroxide in ethylene glycol at 170 ꢁC to give the unsub-
stituted tetracycle 7 in excellent yield. To the solution of
7 in dry dichloromethane, argon was purged and the
flask was cooled to À50 ꢁC, a solution of benzaldehyde
in CH2Cl2 was added dropwise, followed by addition
of catalytic amount of BF3ÆOEt2. The reaction mixture
was stirred at low temperature for three hours and
warmed to room temperature overnight and after oxida-
tion with DDQ gave the desired tetraphenyltetra-
phenanthroporphyrin 9a in 17% yield. The successful
synthesis of 9a encouraged us to examine a series of
related compounds with para-substituted aryl subunits.
A series of para-substituted benzaldehydes (R = F, Cl,
Br, and I) were condensed with phenanthropyrrole 7 as
described above to give the corresponding porphyrins
9b–e in 10–15% yields. These compounds showed
increased solubility in comparison to meso-unsubstituted
tetraphenanthroporphyrin 1 in CHCl3. Their structures
The UV–vis spectrum of 9a in chloroform showed a
maximum peak at 577 nm which is typical for Soret
band, and two Q-bands were observed at 725 and
796 nm that extended into the near-infrared region
(Fig. 2). These values compared to those of the corre-
sponding tetraphenyltetraacenaphthoporphyrin 3 (556
(Soret), 638, 705 nm) were red-shifted by 21 nm for Sor-
et band and near 90 nm for the Q-bands. It is very inter-
esting to note that in the case of meso-unsubstituted
ring-fused porphyrins, the absorption of tetraacenaph-
thoporphyrins 2 (528 (Soret), 647, 702 nm) is more
red-shifted than that of tetraphenanthroporphyrin 1
(482 (Soret), 615, 668 nm). In addition, the Soret band
of 9a is around 100 nm red-shifted compared to the
value of 482 nm for the meso-unsubstituted tetra-
phenanthroporphyrin dication 1 and 468 nm for the
highly distorted dodecaphenylporphyrin 4,15 suggesting
that fusion with phenanthrene rings and the severe con-
formational distortions induced by the meso-aryl sub-
units with the relatively ꢀwiderꢁ phenanthrene rings are
responsible for such a remarkable bathochromic shift.
The UV–vis absorption spectra of 9b–e in chloroform
showed that as the electron withdrawing ability of the
1
were characterized by MALDI-TOF MASS, H NMR,
IR, and UV–vis spectroscopies.14
The proton NMR spectrum of 9a in deuterio-N,N-
dimethylformamide (Fig. 1) showed six types of aromatic

H.-J. Xu et al. / Tetrahedron Letters 47 (2006) 931–934
933
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0.8
0.6
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0.2
0.0
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Chem. Commun. 2004, 374–375; (b) Stilts, C. E.; Nelen, M.
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Figure 2. UV–vis spectra of 9a in CHCl3.
para-subunits on the phenyl moieties decreased in the
order of F > Br > Cl > I, both the Soret band and Q-
bands were slightly red-shifted with respect to that of
9a, indicating that different substituents on meso-aryl
groups had minor additional influence on the porphyrin
electronic properties.
In conclusion, we synthesized a series of meso-aryl substi-
tuted tetraphenanthroporphyrins that showed strong
absorption in the red/infrared region. Introduction of
meso-aryl substituents and fusion with phenanthrene
rings to the porphyrin chromophore are responsible for
such a significant red-shift of the porphyrin absorption
spectra. These properties are desirable as photosensitiz-
ers for PDT application. Further studies on the construc-
tion of oligomeric porphyrin arrays based on these
conjugated structures are currently under investigation.
Acknowledgements
This work was supported by the National Natural Sci-
ence Foundation of China (No. 20401009), the Natural
Science Foundation of Jiangsu Province (No.
BK2004414) and the research Grant from the Ministry
of Chinese Education (No. 0205133119).
References and notes
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R.; Gibson, S. L.; Wagner, S. J. J. Med. Chem. 2004, 47,
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Chem. Soc. 2005, 127, 478–479; (d) Dichtel, W. R.; Serin,
12. (a) Ono, N.; Hironaga, H.; Ono, K.; Kaneko, S.;
Murashima, T.; Ueda, T.; Tsukamura, C.; Ogawa, T. J.
Chem. Soc., Perkin Trans. 1 1996, 417–423; (b) Lash, T.
D.; Novak, B. H. Angew. Chem., Int. Ed. Engl. 1995, 34,
683–685; (c) Lash, T. D.; Novak, B. H. Tetrahedron lett.
1995, 36, 4381–4384; (d) Novak, B. H.; Lash, T. D. J. Org.
Chem. 1998, 63, 3998–4010.
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14. Selected spectral data for 9a–e. Compound 9a: dark
red powder; 17% yield; mp > 300 ꢁC; 1H NMR (500
MHz, DMF-d7): d 1.11 (2H, b), 6.93 (8H, d, J = 8.2 Hz),
2. (a) Kubo, Y.; Yamamoto, M.; Ikeda, M.; Takeuchi, M.;
Shinkai, S.; Yamaguchi, S.; Tamao, K. Angew. Chem., Int.

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H.-J. Xu et al. / Tetrahedron Letters 47 (2006) 931–934
7.36–7.38 (8H, m), 7.71–7.74 (12H, m), 7.95–7.97 (8H, m),
8.59–8.63 (8H, m), 8.98 (8H, d, J = 8.2 Hz); IR (KBr):
max/cmÀ1 3424, 3081, 1629, 1443, 1352, 1048, 759, 726;
UV–vis (CHCl3)
max/nm (e · 105) 577 (0.861), 725
(M+H+). Anal. Calcd for C92H50Cl4N4: C, 81.66; H, 3.72;
N, 4.14. Found: C, 81.45; H, 3.80; N, 4.21. Compound 9d:
dark red powder; 11% yield; mp > 300 ꢁC; 1H NMR
(500 MHz, DMF-d7): d 0.86 (2H, b), 6.99–7.03 (8H, m),
7.40–7.43 (8H, m), 7.55–7.59 (8H, m), 7.83–7.86 (8H, m),
m
k
(0.0574), 796 (0.149); MS (MALDI-TOF) m/z 1216.38
(M+H+). Anal. Calcd for C92H54N4Æ2H2O: C, 88.29; H,
4.67; N, 4.48. Found: C, 88.46; H, 4.68; N, 4.51.
Compound 9b: dark red powder; 10% yield; mp >
300 ꢁC; 1H NMR (500 MHz, DMF-d7): d 0.89 (2H, b),
6.91–6.94 (8H, m), 7.46–7.49 (8H, m), 7.60–7.63 (8H, m),
7.86–7.88 (8H, m), 8.65–8.67 (8H, m), 8.86–8.88 (8H, m);
IR (KBr): mmax/cmÀ1 3426, 3086, 1597, 1449, 1352, 1158,
1048, 758, 724; UV–vis (CHCl3) kmax/nm (e · 105) 576
(0.553), 721 (0.038), 796 (0.0941); MS (MALDI-TOF) m/z
1288.10 (M+H+). Anal. Calcd for C92H50F4N4Æ3H2O: C,
82.37; H, 4.21; N, 4.18. Found: C, 82.46; H, 4.28; N, 4.21.
Compound 9c: dark red powder; 13% yield; mp > 300 ꢁC;
1H NMR (500 MHz, DMF-d7): d 0.84 (2H, b), 7.02–7.05
(8H, m), 7.42–7.44 (8H, m), 7.57–7.59 (8H, m), 7.78–7.81
(8H, m), 8.68–8.71 (8H, m), 8.92–8.95 (8H, m); IR (KBr):
8.66–8.69 (8H, m), 8.85–8.88 (8H, m); IR (KBr): mmax
cmÀ1 3422, 3082, 1630, 1442, 1350, 1077, 1047, 759, 725;
UV–vis (CHCl3)
max/nm(e · 105) 583 (0.938), 726
/
k
(0.0711), 801 (0.163); MS (MALDI-TOF) m/z 1531.95
(M+H+). Anal. Calcd for C92H50Br4N4Æ3H2O: C, 69.71;
H, 3.56; N, 3.53. Found: C, 69.94; H, 3.59; N, 3.42.
Compound 9e: dark red powder; 15% yield; mp > 300 ꢁC;
1H NMR (500 MHz, DMF-d7): d 0.82 (2H, b), 6.98–7.05
(8H, m), 7.19–7.25 (8H, m), 7.38–7.46 (8H, m), 7.57–7.63
(8H, m), 8.02–8.10 (8H, m), 8.67–8.72 (8H, m); IR (KBr):
m
max/cmÀ1 3424, 3080, 1576, 1446, 1348, 1060, 758, 727
617; UV–vis (CHCl3) kmax/nm (e · 105) 585 (0.5998), 804
(0.1035), 857 (0.09); MS (MALDI-TOF) m/z 1719.99
(M+H+). Anal. Calcd for C92H50I4N4Æ1/2H2O: C, 63.94;
H, 2.97; N, 3.24. Found: C, 63.74; H, 2.99; N, 3.42.
15. Medforth, C. J.; Senge, M. O.; Smith, K. M.; Sparks, L.
D.; Shelnutt, J. A. J. Am. Chem. Soc. 1992, 114, 9859–
9869.
m
max/cmÀ1 3421, 3084, 1586, 1447, 1350, 1047, 1092 758,
726; UV–vis (CHCl3) kmax/nm (e · 105) 582 (0.833), 722
(0.0798), 799 (0.160); MS (MALDI-TOF) m/z 1353.86