J. Am. Chem. Soc. 1996, 118, 8767-8768
8767
Scheme 1
Synthesis of Tetraphenyltetraacenaphthoporphyrin:
A New Highly Conjugated Porphyrin System with
Remarkably Red-Shifted Electronic Absorption
Spectra
Timothy D. Lash* and Pushpa Chandrasekar
Department of Chemistry
Illinois State UniVersity
Normal, Illinois 61790-4160
Scheme 2
ReceiVed April 15, 1996
Red-shifted porphyrinoid chromophores have been the subject
of extensive studies over the last few years. This is due in part
to their potential utility as photosensitizers in photodynamic
therapy (PDT).1 However, these pigments have many additional
applications including uses as fluorescent probes and near-
infrared dyes, and as components of photosynthetic antenna
arrays.2 A number of approaches for the construction of
porphyrinoid systems with high-wavelength absorptions have
been reported, including the synthesis of expanded porphyrins,3
porphyrin linkage isomers,4 and heterocyclic analogs.5 The
intriguing observation that sterically crowded (and hence
distorted) porphyrin structures, such as dodecaphenylporphyrin
1, have significantly red-shifted major absorption bands provides
an alternative avenue to systems of this type.6 We have
previously investigated the influence of fused aromatic subunits
on the porphyrin chromophore.7-10 Regretfully, the influence
of one or more fused naphthalene,7 phenanthrene,8 or 1,10-
phenanthroline9 rings gave surprisingly small red shifts in the
UV-vis absorption spectra, and even the highly symmetrical
tetraphenanthroporphyrin 2 showed smaller bathochromic shifts
porphyrins and report, in striking contrast to the previous studies,
on the extraordinarily red-shifted UV-vis absorption spectra
exhibited by these tetraannelated porphyrins.
Nitroarenes that have a significant amount of nitroalkene
character have been shown to condense with esters of isocy-
anoacetic acid in the presence of a non-nucleophilic base to
give polycyclic c-annelated pyrroles.12,13 For instance, 9-ni-
trophenanthrene afforded phenanthropyrroles in excellent yields,11
and these tetracycles were utilized in our syntheses of phenan-
throporphyrins (e.g., 2).8,10 Similarly, 1-nitroacenaphthylene,
obtained by nitrating acenaphthylene with nitryl chloride in
carbon tetrachloride at 0 °C,14 condensed with ethyl or tert-
butyl isocyanoacetate in the presence of DBU to give acenaph-
thopyrroles 3 in good yields (Scheme 1). Reduction of 3a with
lithium aluminum hydride afforded the related carbinol 4
(Scheme 2). Following the same procedure used in the
preparation of tetraphenanthroporphyrin 2,10 4 was treated with
boron trifluoride etherate in chloroform, stirred at room tem-
perature for 2 h, and oxidized with 2,3-dichloro-5,6-dicyano-
1,4-benzoquinone (DDQ). Following workup, the highly
insoluble porphyrin 5 was obtained in impure form and low
yield (approximately 5%). The new porphyrin system was
than might have been expected.10,11 Indeed, these fused
aromatic ring systems behave more like auxochromes than part
of truly extended chromophores.9 We have now extended our
investigations to encompass the synthesis of tetraacenaphtho-
somewhat soluble in TFA-chloroform, producing green solu-
(1) Brown, S. B.; Truscott, T. G. Chem. Br. 1993, 29, 955. Dolphin, D.
Can. J. Chem. 1994, 72, 1005. Bonnett, R. Chem. Soc. ReV. 1995, 24, 19.
(2) E.g., see: Prathapan, S.; Johnson, T. E.; Lindsey, J. S. J. Am. Chem.
Soc. 1994, 115, 7519.
(3) Sessler, J. L.; Burrell, A. K. Top. Curr. Chem. 1991, 161, 177-273.
Franck, B.; Nonn, A. Angew. Chem., Int. Ed. Engl. 1995, 34, 1795.
(4) E.g., see: Vogel, E.; Kocher, M.; Schmickler, H.; Lex, J. Angew.
Chem., Int. Ed. Engl. 1986, 25, 257. Chmielewski, P. J.; Latos-Grazynski,
L.; Rachlewicz, K.; Glowiak, T. Angew. Chem., Int. Ed. Engl. 1994, 33,
779. Furuta, H.; Asano, T.; Ogawa, T. J. Am. Chem. Soc. 1994, 116, 767.
(5) Broadhurst, M. J.; Grigg, R.; Johnson, A. W. J. Chem. Soc. C 1971,
3681. Vogel, E.; Haas, W.; Knipp, B.; Lex, J.; Schmickler, H. Angew.
Chem., Int. Ed. Engl. 1988, 27, 406. Lash, T. D. Angew. Chem., Int. Ed.
Engl. 1995, 34, 2533.
(6) (a) Shelnutt, J. A.; Medforth, C. J.; Berber, M. D.; Barkigia, K. M.;
Smith, K. M. J. Am. Chem. Soc. 1991, 113, 4077. (b) Medforth, C. J.; Senge,
M. O.; Smith, K. M.; Sparks, L. D.; Shelnutt, J. A. J. Am. Chem. Soc.
1992, 114, 9859.
(7) (a) Lash, T. D. Energy Fuels 1993, 7, 166. (b) Lash, T. D.; Roper,
T. J. Tetrahedron Lett. 1994, 35, 7715. c. Lash, T. D.; Denny, C. P.
Tetrahedron 1995, 51, 59.
2+
tions of the corresponding dication 5H2
. The UV-vis
spectrum for the dication showed absorptions that were shifted
to unusually high wavelengths; the Soret band appeared at 525
nm, and two smaller bands were evident at 628 and 701 nm.
Although the low yields and purity obtained for 5 were
disappointing at best, the remarkable bathochromic shifts
2+
exhibited for the corresponding dication 5H2 suggested that
the acenaphthylene ring system is particularly effective at
inducing desirable long-wavelength absorptions. In order to
further investigate this phenomenon, the related meso-tetraphe-
nylporphyrin 6 was targeted for synthesis (Scheme 3). It was
anticipated that there would be sufficient room for phenyl groups
to be sandwiched between the acenaphthylene rings. As the
(12) Ono, N.; Hironaga, H.; Simizu, K.; Ono, K.; Kuwano, K.; Ogawa,
T. J. Chem. Soc., Chem. Commun. 1994, 1019.
(8) Lash, T. D.; Novak, B. H. Tetrahedron Lett. 1995, 36, 4381.
(9) Lin, Y.; Lash, T. D. Tetrahedron Lett. 1995, 36, 9441.
(10) Lash, T. D.; Novak, B. H. Angew. Chem., Int. Ed. Engl. 1995, 34,
683.
(13) See also: Barton, D. H. R.; Kervagoret, J.; Zard, S. Z. Tetrahedron
1990, 46, 7587. Lash, T. D.; Bellettini, J. R.; Bastian, J. A.; Couch, K. B.
Synthesis 1994, 170.
(14) Iida, H.; Kajiyama, I.; Yamada, K. Nippon Kagaku Kaishi 1972,
137; Chem. Abstr. 1972, 76, 99395m.
(11) Lash, T. D.; Novak, B. H.; Lin, Y. Tetrahedron Lett. 1994, 35, 2493.
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