ORGANIC LETTERS
Porphyrin−Perylene Bisimide Dyads and Triads: Synthesis and Optical and Coordination Properties
2004 Vol. 6, No. 14 2401-2404
Chang-Cheng You and Frank Wu1 rthner* Institut fu¨r Organische Chemie, UniVersita¨t Wu¨rzburg, Am Hubland, 97074 Wu¨rzburg, Germany
[email protected] Received April 29, 2004
ABSTRACT
Novel porphyrin perylene dyad and triad dyes have been prepared by the coupling of aminophenyltrisphenylporphyrin and tetraphenoxysubstituted perylenetetracarboxylic acid bisanhydrides in a one-step synthesis. Fluorescence spectra of these compounds reveal features that are attributable to emission of perylene bisimides as well as porphyrin excited states. The self-assembly behavior of zinc-metalated compounds with 4,4′-bipyridine and diazabenzoperylene has been investigated by 1H NMR spectroscopy in CDCl3, showing that oligomeric zigzag assemblies are formed.
Transition-metal-mediated coordination has been used to construct supramolecular assemblies with a wide variety of topologies from linear polymers to two-dimensional macrocycles and three-dimensional cages/boxes over the past decade.1 The tremendous interest on this topic lies on the expectation that it provides not only aesthetic entities but also versatile functional materials. By employing kinetically labile coordinative interactions, supramolecular polymers with the characteristics of dynamic reversibility might be readily achieved from relatively simple organic building blocks.2 Some representative examples are the self-assembled * Corresponding author. Fax: +49-931-8884756. Tel: +49-9318885340. (1) For some recent reviews see: (a) Wu¨rthner, F.; You, C.-C.; SahaMo¨ller, C. R. Chem. Soc. ReV. 2004, 33, 133-146. (b) Seidel, S. R.; Stang, P. J. Acc. Chem. Res. 2002, 35, 972-983. (c) Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001, 34, 759-771. (d) Fujita, M.; Umemoto, K.; Yoshizawa, M.; Fujita, N.; Kusukawa, T.; Biradha, K. Chem. Commun. 2001, 509-518. (e) Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40, 2022-2043. (f) Swiegers, G. F.; Malefetse, T. J. Chem. ReV. 2000, 100, 3483-3537. (g) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. ReV. 2000, 100, 853-908. 10.1021/ol049206l CCC: $27.50 Published on Web 06/18/2004
© 2004 American Chemical Society
porphyrin polymers sewn up by complementary nitrogenmetal (Zn, Co) interactions, which show potential applications toward artificial photosynthesis and nonlinear optics materials as well.3,4 Our specific interest currently involves the self-assembly of perylene bisimide dyes which have found widespread applications in either industrial pigments or molecular/supramolecular devices due to their unique photo- and electrochemical properties.5 Recently, photoluminescent supramolecular polymers based on the coordinative interaction (2) (a) Yount, W. C.; Juwarker, H.; Craig, S. L. J. Am. Chem. Soc. 2003, 125, 15302-15303. (b) Brunsveld, L.; Folmer, B. J. B.; Meijer, E. W.; Sijbesma, R. P. Chem. ReV. 2001, 101, 4071-4097. (3) (a) Michelsen, U.; Hunter, C. A. Angew. Chem., Int. Ed. 2000, 39, 764-767. (b) Burrell, A. K.; Officer, D. L.; Reid, D. C. W.; Wild, K. Y. Angew. Chem., Int. Ed. Engl. 1998, 37, 114-117. (c) Fleischer, E. B.; Shachter, A. M. Inorg. Chem. 1991, 30, 3763-3769. (4) (a) Philips-McNaughton, K.; Groves, J. T. Org. Lett. 2003, 5, 18291832. (b) Ogawa, K.; Zhang, T.; Yoshihara, K.; Kobuke, Y. J. Am. Chem. Soc. 2002, 124, 22-23. (c) Ogawa, K.; Kobuke, Y. Angew. Chem., Int. Ed. 2000, 39, 4070-4073. (5) Wu¨rthner, F. Chem. Commun. 2004, in press.
Scheme 1
between terpyridine-functionalized perylene bisimide dyes and metal ions have been fabricated.6 Also, it has been reported that coordination polymers can be generated from dimetalloporphyrin monomers and dipyridine monomers7 or from pyridyl-substituted metalloporphyrins.3 Therefore, we became interested in zinc porphyrins as functional receptor dyes which can be used to self-assemble zinc porphyrinperylene bisimide-zinc porphyrin triads. In this paper, we describe our first results on the synthesis and optical and coordination properties of this class of compounds. Perylene bisimide derivatives that incorporate zinc porphyrins have been prepared usually through the imidization of perylene anhydrides with aminoporphyrins8,9 followed by metalation with zinc(II) acetate.8 In the current report, however, zinc porphyrin-perylene-zinc porphyrin triads 3a and 3b were obtained as purple powders (yields 28% and 39%) in a one-step synthesis by the coupling of 5-(4-aminophenyl)-10,15,20-trisphenylporphyrin 110 and corresponding 1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarboxylic acid bisanhydride 2a or 2b11 in quinoline in the presence of (6) Dobrawa, R.; Wu¨rthner, F. Chem. Commun. 2002, 1878-1879. (7) Twyman, L. J.; King, A. S. H. Chem. Commun. 2002, 910-911. (8) (a) Andersson, M.; Sinks, L. E.; Hayes, R. T.; Zhao, Y.; Wasielewski, M. R. Angew. Chem., Int. Ed. 2003, 42, 3139-3143. (b) van der Boom, T.; Hayes, R. T.; Zhao, Y.; Bushard, P. J.; Weiss, E. A.; Wasielewski, M. R. J. Am. Chem. Soc. 2002, 124, 9582-9590. (9) Quante, H. Ph.D. Thesis, University of Mainz, 1995. (10) (a) Sakaki, S.; Koga, H.; Tao, K.-i.; Yamashita, T.; Iwashita, T.; Hamada, T. J. Chem. Soc., Dalton Trans. 2000, 1015-1017. (b) Kruper, W. J., Jr.; Chamberlin, T. A.; Kochanny, M. J. Org. Chem. 1989, 54, 27532756. 2402
zinc(II) acetate (Scheme 1). The latter serves herein not only as an efficient catalyst for the coupling reaction, but also as the metalation reagent of porphyrin. In a similar way, the reaction of perylene monoimide monoanhydride and 5-(4aminophenyl)-10,15,20-trisphenylporphyrin afforded zinc porphyrin-perylene dyad 4 (yield 16%). The treatment of 4 with HCl (6 M) followed by neutralization with NaHCO3 afforded exclusively metal-free dyad 5. The desired products were purified through silica gel column chromatography and their structures were established by 1H and 13C NMR, elemental analysis, and MALDI-TOF mass spectrometry (Supporting Information). The absorption and emission properties of the metal-free as well as the zinc-metalated porphyrin perylene bisimides were investigated in chloroform. Figure 1a illustrates the absorption spectra of 3b and 4 and the emission spectrum of 4 as well. As can be seen, both zinc porphyrin-perylene dyad and triad show intense absorption at 425 nm that is assignable for the Soret band of porphyrin chromophore. The sharp Soret band of the zinc porphyrin (fwhm ) 13 nm) is in accord with that of porphyrin (without perylene moieties), implying insignificant ground-state electronic interaction between perylene bisimides and porphyrins.12 The Q-band of porphyrin overlaps with the first absorption band (S0 f (11) Wu¨rthner, F.; Sautter, A.; Schmid, D.; Weber, P. J. A. Chem. Eur. J. 2001, 7, 894-902. (12) (a) Tomizaki, K.; Thamyongkit, P.; Loewe, R. S.; Lindsey, J. S. Tetrahedron 2003, 59, 1191-1207. (b) Tomizaki, K.; Loewe, R. S.; Kirmaier, C.; Schwartz, J. K.; Retsek, J. L.; Bocian, D. F.; Holten, D.; Lindsey, J. S. J. Org. Chem. 2002, 67, 6519-6534. Org. Lett., Vol. 6, No. 14, 2004
bisimides with diaza ligands, which would lead to multichromophoric assemblies. Although polymeric coordination assemblies are the desired products, in principle the stoichiometric combination of compounds 3a or 3b with ditopic ligands would afford either discrete rectangles (Figure 2a)
Figure 1. UV/vis absorption spectra of 3b (a, solid line), 4 (a, dashed line) and 5 (b, solid line) and fluorescence spectra of 4 (a, dotted line, λex ) 545 nm) and 5 (b, dotted line, λex ) 545 nm) in CHCl3.
Figure 2. Schematic representation of the two possible species that could form by self-assembly between zinc porphyrin perylene triads and rigid bidentate ligands.
S1) of perylene dye in the region of 500-650 nm resulting in two absorption maxima around 555 and 595 nm. The emission spectra of the zinc porphyrin-perylene bisimide dyads and triads show typical perylene bisimide emission at 619 nm (Figure 1a for 4) upon irradiation at 500-560 nm. To further assess the fluorescence, the emission spectra were also recorded upon excitation at 420 nm where perylenes are relatively transparent. Virtually identical fluorescence spectra were obtained indicating an energy transfer from zinc porphyrin to perylene rather than from perylene to zinc porphyrin. Remarkably, this situation changes dramatically for the demetalated compound 5. Here, perylene-type emission (λmax ) 621 nm) and free base porphyrin-type emission (λmax ) 648 nm, 718 nm) could be detected in similar amounts upon excitation at 545 nm (Figure 1b).13 The fluorescence quantum yields14 of 4 and 5 were quantitatively determined to be 2.6% and 1.9%, respectively, while the values of 3a and 3b decreased by about 1 order of magnitude (ΦF ) 0.4% and 0.3%, respectively). Since porphyrins are easily oxidizable and may act as excellent electron donors, a concomitant photoinduced electron transfer seems to account for the observed fluorescence quenching.15,16 Our further interest is concerned with the self-assembly behavior of these diporphyrinatozinc(II)-substituted perylene
or infinite zigzag polymers (Figure 2b). Molecular modeling studies suggest that twisted perylene bisimide unit with its bulky phenoxy substituents disfavors the formation of rectangular assemblies.17 The coordination interaction of 3b with 4,4′-bipyridine (6a) was first investigated in CDCl3 using 1H NMR titration. From the representative titration spectra depicted in Figure 3, it
(13) For comparison, tetraphenylporphyrin exhibits fluorescence maxima at 651 and 715 nm and ΦF ) 0.07 in CH2Cl2. (14) Measured under dilute conditions with N,N′-(2,6-diisopropylphenyl)1,6,7,12-tetraphenoxyperlyene-3,4:9,10-tetracarboxylic acid bisimide (ΦF ) 0.96 in CHCl3) as a reference; see: Gvishi, R.; Reisfeld, R.; Burshtein, Z. Chem. Phys. Lett. 1993, 213, 338-344. Org. Lett., Vol. 6, No. 14, 2004
Figure 3. Selected 1H NMR spectra for the titration of 4,4′bipyridine with 3b in CDCl3. The arrows indicate the change in chemical shift of protons in 4,4′-bipyridine: (a) 4,4′-bipyridine (1.3 mM); (b) (a) + 3b (1.8 mM); (c) (a) + 3b (4.1 mM).
can be noticed that the R- and β-protons in bipyridine are drastically shifted upfield with the gradual addition of zinc porphyrin perylene triad 3b. The chemical shift change is 2403
undoubtedly caused by the shielding effect of the ring current of porphyrins, confirming the coordination of pyridyl units to zinc porphyrins.18 Nonlinear least squares curve-fitting analysis19 on the titration data reveals that the site binding constant is 7400 M-1. Similarly, the binding constant between 3b and the highly luminescent ligand diazadibenzoperylene 6b (λmax ) 496 nm, λem ) 522 nm, and ΦF ) 0.75 in CH2Cl2)20 was obtained as 3050 M-1. Although these data are somewhat higher than those for the coordination of diaza ligands with simple zinc tetraphenylporpyhrin (ZnTPP),21 structurally well-defined assemblies such as rectangles cannot be considered as the predominant species. A control experiment revealed that the coordination between monotopic compound 4 and 4,4′-bipyridine gives a binding constant of 4060 M-1. Thus, the slight enhancement of stability constant seems to originate most likely from the effect of perylene moiety upon coordination. On the basis of the binding constants, it is calculated that for a 10 mM solution of the 1:1 mixture of 3b and 4,4′bipyridine more than 90% monomers are involved in the selfassembled state. These two types of ditopic building blocks AA and BB are considered to associate to afford a supramolecular polymer [‚‚‚AA‚‚‚BB‚‚‚]n, in which the average (15) (a) D’Souza, F.; Deviprasad, G. R.; El-Khouly, M. E.; Fujitsuka, M.; Ito, O. J. Am. Chem. Soc. 2001, 123, 5277-5284. (b) Myles, A. J.; Branda, N. R. J. Am. Chem. Soc. 2001, 123, 177-178. (16) O’Neil, M. P.; Niemczyk, M. P.; Svec, W. A.; Gosztola, D.; Gaines, G. L., III; Wasielewski, M. R. Science 1992, 257, 63-65. (17) The discrete rectangle structurally resembles double-strand porphyrin ladders: (a) Screen, T. E. O.; Thorne, J. R. G.; Denning, R. G.; Bucknall, D. G.; Anderson, H. L. J. Am. Chem. Soc. 2002, 124, 9712-9713. (b) Taylor, P. N.; Anderson, H. L. J. Am. Chem. Soc. 1999, 121, 11538-11545. (c) Anderson, H. L. Inorg. Chem. 1994, 33, 972-981. (18) Significant UV/vis spectral changes of 3b were also observed upon addition of 4,4′-bipyridine ligand (see the Supporting Information). (19) In the evaluation of binding constants, an excellent fit was obtained for all data points with a simple model which assumes an equal K for all aza ligand-zinc porphyrin interactions, i.e., independent, and not cooperative binding. (20) (a) Wu¨rthner, F.; Sautter, A.; Thalacker, C. Angew. Chem., Int. Ed. 2000, 39, 1243-1245. (b) Wu¨rthner, F.; Sautter, A.; Schilling, J. J. Org. Chem. 2002, 67, 3037-3044. (21) The binding between ZnTPP and some diaza ligands has been investigated by isothermal titration calorimetry (ITC). In the system of ZnTPP and 4,4′-bipyridine, the ITC revealed the presence of two independent binding sites (1:2 complex formation) with two equal site binding constants of 2500 M-1. Similarly, the interaction between ZnTPP and diazadibenzoperylene 6b was characterized by independent site binding constants of 1950 M-1.
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degree of polymerization can be conveniently estimated by a well-established equation for nylon-type supramolecular polymers.22,23 Once the monomer concentration (10 mM) and the binding constant (7400 M-1) are introduced into the known equation, the mean degree of polymerization in the obtained assembly is deducible to be n ) 6. It means that the alternate coordination of six zinc porphyrin-perylene triads and six 4,4′-bipyridine leads to the polymeric assemblies incorporating 6 perylene and 12 porphyrin dyes. Although in the present case the degree of polymerization is not too big, due to the relatively weak pyridine-zinc porphyrin interaction, the polymer has an average molecular weight of as high as 16000 Daltons. With diazadibenzoperylene 6b as the bidentate bridging ligand (K ) 3050 M-1), the generated oligomers comprise three types of dyes, including in average four diazadibenzoperylenes, eight zinc porphyrins, and four perylene bisimides at a concentration of 10 mM. In summary, novel perylene-bridged diporphyrinatozinc(II) triads have been prepared by the coupling of perylenetetracarboxylic acid bisanhydrides with aminophenyltrisphenylporphyrin in the presence of zinc(II) acetate. The ditopic metalloporphyrin acceptors coordinate with bidentate ligands such as 4,4′-bipyridine and diazabenzoperylene to afford rigid zigzag oligomeric assemblies. The resultant entities comprise alternately the photo- and electrochemically active porphyrin and perylene dyes, thus, such assemblies have potentials for application in molecular devices and materials. Acknowledgment. We thank the Alexander von Humboldt Foundation (postdoctoral fellowship for C.C.Y.) and the Fonds der Chemischen Industrie for financial support. Supporting Information Available: General procedure for the preparation of 3, 4 and 5, characterization, and spectral properties. This material is available free of charge via the Internet at http://pubs.acs.org. OL049206L (22) Yamaguchi, N.; Nagvekar, D. S.; Gibson, H. W. Angew. Chem., Int. Ed. 1998, 37, 2361-2364. (23) Wu¨rthner, F.; Thalacker, C.; Sautter, A.; Scha¨rtl, W.; Ibach, W.; Hollricher, O. Chem. Eur. J. 2000, 6, 3871-3886.
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