J. Am. Chem. SOC.1994,116, 5741-5746
5741
Supramolecular Photochemistry and Photophysics. A Cylindrical Macrotricyclic Receptor and Its Adducts with Protons, Ammonium Ions, and a Pt(I1) Complex Roberto Ballardini,*J' Vincenzo Balzani,'Jb Albert0 CrediiIb Maria Teresa Gandolfi,Ib Florence Kotzyba-Hibert,lCJean-Marie Lehn,*~lC and Luca Prodilb Contribution from the Istituto FRAE-CNR, 40126 Bologna, Italy, Dipartimento di Chimica "G. Ciamician", Universith di Bologna, 40126 Bologna, Italy, and Institut Le Bel, UniversitL Louis Pasteur, 67000 Strasbourg, France Received January 25, 1994"
Abstract: The absorption spectrum and the luminescence properties of a cylindrical macrotricyclicreceptor (l), which is made of two diazatetraoxa macrocyclic [ 18]-N204 units linked by two 2,6-dimethylnaphthalene (DMN) bridges, have been investigated. Comparison with the behavior of the 2,6-dimethylnaphthalenereference chromophore shows that in CH2Cl2 solution at room temperature, the covalent bond between the DMN units and the nonabsorbing and nonemitting [ 18]-N204macrocycles causes the appearance of a charge-transfer (CT) absorption tail below 310 nm, the disappearanceof the structured DMN fluorescence at 342 nm, and the appearance of a broad and weak CT emission band at 438 nm. In rigid matrix at 77 K, however, 1 behaves similarly to DMN, showing a structured fluorescence band with maximum at 342 nm and a structured phosphorescence band with maximum at 518 nm and 7 = 2.6 s. Addition of CF3COOH to a CHzCl2 solution of 1 causes the successive protonation of the four amine units of the two [18]-N204 macrocycles which are responsible for the CT transitions to the naphthalene rings. As a consequence, the CT absorption tail disappears, the absorption spectrum of the macrotricycle becomes very similar to that exhibited by the isolated DMN chromophore, and the DMN-type fluorescence reappears. The luminescence intensity at 342 nm increases by at least 800 times upon protonation. Therefore, 1 is a fluorescence sensor highly responsive to protons. Upon adduct formation with a,w-alkanediyldiammoniumion NHp+(CHz)sNHp+(cadaverinecation), for which a molecular inclusion into the receptor 1 was previously demonstrated, the intensities of the CT absorption tail below 310 nm and the CT luminescence band at 438 nm decrease by -50%, but the fluorescence DMN band at 342 nm is negligibly small. Similar results are obtained upon adduct formation with NH4+ ions. The [Pt(NH&(bpy)]2+ complex, which can be used as a guest for a variety of crown ethers, forms a 1:l adduct with unprotonated 1. The absorption spectrum of the adduct is noticeably different from that expected for the sum of the two separated components, particularly because of the presence of an absorption in the 340-420-nm region. At room temperature, the luminescence bands exhibited by the two separated components are no longer observed in the adduct. In rigid matrix at 77 K, the phosphorescence band of 1 can be observed in the adduct regardless of the excitation wavelength, but its lifetime (0.8 ms) is considerably shorter than that (2.6 s) of the phosphorescence of 1. As suggested by observation of CPK models, the above results indicate that [Pt(NH~)2(bpy)]~+ is hosted in the cylindrical cavity of 1 with an amine ligand which interacts with a [ 18]-N204 macrocycle unit via hydrogen bonds and the Pt(bpy)2+electron-deficient moiety involved in a CT interaction with the DMN chromophoric units.
Introduction In the past few years, there has been an increasing interest in the photophysics and photochemistry of supramolecular species for both basic and applicativereasons.2-10 In host-guest systems, the photochemical and photophysical properties of each partner can be profoundly modified on adduct formation. Such changes can be useful for obtaining information on the structure of the adduct and, at the same time, for designing photochemical molecular devices for a variety of light-induced functions. Abstract published in Advance ACS Absrracrs, May 15, 1994. (1) (a) FRAE-CNR Institute, Bologna, Italy. (b) University of Bologna,
Italy. (c) University of Strasbourg, France. (2) SupramolecularPhotochemistry;Balzani, V., Ed.;Reidel: Dordrecht, The Netherlands, 1987. (3) Lehn, J.-M. Angew. Chem., Int. Ed. Engl. 1988, 27, 89. (4) Lehn, J.-M. Angew. Chem., Inr. Ed. Engl. 1990, 29, 1304. (5) Balzani V.; Scandola, F. Supramolecular Photochemistry; Horwood: Chichester, U.K., 1991. ( 6 ) Frontiers in Supramolecular Organic Chemistry and Photochemistry; Schneider, H. J., Dllrr, H., Eds.; VCH: Weinheim, Germany, 1991. (7) VOgtle, F.SupramolecularChemisrry;Wiley: Chichester,U.K.,1991. (8) Balzani, V. Tetrahedron 1992, 48, 10443. (9) Bissell, R. A.; de Silva, A. P.; Gunaratne, H. Q.N.; Lynch, P. L. M.; Maguire, G. E. M.; Sandanayake, K. R. A. S.Chem. Soc. Rev. 1992, 187. (10) Desvergne, J.-P.;Fages, F.;Bouas-Laurent, H.; Manau, P. Pure Appl. Chem. 1992.64, 1231.
W2-7863/94/1516-5741$04.50/0
Marked effects of protonation, metal ion binding, and diammonium substrate binding on luminescence properties have been observed for macrobicyclicll and macrotricyclic12 receptors incorporating anthracene groups. The cylindrical macrotricyclic receptor l , l z which is made of two diazatetraoxa macrocyclic [ 18]-N204 units linked by two 2,6-dmethylnaphthalenebridges, can encapsulateselectively a,w alkanediyldiammoniumions of compatiblelength,l2 as is also the case for similar macrotri~yclic~~ or bis-ma~rocyclic'~ receptors based on anthracene. 1 is expected to be an interesting host for photophysical studies because of its cylindrical cavity, the two (11) Fages, F.; Desvergne, J.-P.; Bouas-Laurent, H.; Marsau, P.; Lehn, J.-M.; Kotzyba-Hibcrt, F.; Albrecht-Gary, A.-M.; AI-Joubbeh, M. J. Am. Chem. Soc. 1989, 111,8612. (12) (a) Kotzyba-Hibert, F.; Lehn, J.-M.; Vierling. P. Tetrahedronk r r . 1980,21,941. (b) Pascard, C.; Riche, C.; Cesario, M.; Kotzyba-Hibcrt, F.; Lehn, J.-M. J . Chem. Soc., Chem. Commun. 1982,557. (13) (a) Fages, F.; Desvergne, J.-P.; Bouas-Laurent, H.; Lehn, J.-M.; Konopelski, J. P.; Marsau, P.; Barram, Y. J. Chem. Soc., Chem. Commun. 1990,655. (b) Fages, F.; Desvergne, J.-P.; Kampe, K.; Bouas-Laurent, H.; Lehn, J.-M.;Meyer,M.;Albrecht-Gary,A.-M.J. Am. Chem.Soc. 1993,115, IhSA.
(14) de Silva, A. P.; Sandanayake, K. R. A. S. Angew. Chem., Int. Ed. Engl. 1990, 29, 1173.
0 1994 American Chemical Society
5742 J. Am. Chem. SOC.,Vol. 116, No. 13, 1994
Ballardini et al. 0.2 -
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potentially luminescent naphthalene units, and the amine groups contained in the two [ 18]-N204 macrocycles. The [Pt(NH3)2(bpy)]2+ complex (bpy = 2,2'-bipyridine) is known to form adducts with crown ethers because its ammonia ligands give rise to hydrogen bonds with their oxygen sites.ls Furthermore, it has been shown that this complex exhibits characteristic absorption, emission,and photochemical properties that can be strongly modified upon A-A interaction between the Pt(bpy)2+moiety and aromatic rings.l6 CPK molecular models suggest that [pt(NH3)2(bpy)l2+ can be encapsulated into the macrotricyclic receptor 1. This has prompted us to investigate the photophysical behavior of 1 and the adduct of 1 with [pt(NH3)2(bpy)]2+. In order to better understand the properties of the receptor 1,we havealso investigated its photophysical behavior on protonation of the amine groups and on adduct formation with NH4+and NHs+(CH2)5NHs+(cadaverinecation). In doing that, we have found that 1is an excellent fluorescent sensor responsive to protons.I'-lg
Experimental Section Chemicals. Thereceptor 1and its [ 18]-N20~componentwereavailable from previous investigations.12 The synthesis of [Pt(NH3)z(bpy)](PF& has already been described.16b 2,6-Dimethylnaphthalene (DMN) and cadaverine chlorohydrate ( N H ~ ( C H ~ ) ~ N H ~were ) C I Zobtained from Aldrich. Dichloromethane and trifluoroacetic acid were Merck products. The former was distilled on PzO5 before use to remove water traces. Equipment. Absorption spectra were recorded with a Perkin-Elmer A6 spectrophotometer. Uncorrected emission spectra and corrected excitation spectra were obtained with a Perkin-Elmer LSSO spectrofluorimeter, which was also used to obtain phosphorescence lifetimes in the 10-ps to 5-s time region. In order to allow comparison of emission intensities, corrections for the different absorbance and phototube sensitivity were performed when necessary. An Edinburgh single-photon counting apparatusI6b was used for shorter lifetimes. Emission spectra at 77 K were obtained in CHZC12 matrix or MeOH/EtOH (4:1, v/v). Degassed solutions were obtained by the freeze-thaw-pump method. All (15) Colquhoun, H. M.; Stoddart, J. F.;William, D. J. Angew. Chem., Int. Ed. Engl. 1986, 25, 487. (16) (a) Ballardini, R.; Gandolfi, M. T.;Balzani, V.; Kohnke, F. H.; Stoddart, J. F.Angew. Chem., Int. Ed. Engl. 1988, 27,692. (b) Ballardini, R.;Gandolfi,M.T.;Prodi,L.; Ciano,M.; Balzani,V.;Kohnke, F.H.;ShahriariZavareh, H.; Spencer, N.; Stoddart, J. F.J. Am. Chem.Soc. 1989,111,7072. (c) Gandolfi, M. T.; Zappi, T.; Ballardini, R.; Prodi, L.;Balzani, V.; Stoddart, J. F.; Mathias, J. P.; Spencer, N. Gazz. Chim. Iral. 1991, 121, 521. (d) Ballardini, R.; Gandolfi, M. T.; Balzani, V.; Desvergne, J.-P.; Bouas-Laurent, H. J . P h p . Chem. 1991,95,2080. (e) Balzani, V.; Ballardini, R.; Gandolfi, M.T.;Prodi, L. In ref. 6, p 371. (17) For reviews on fluorescent sensors, sec refs 9 and 18. For some recent papers on proton-controlled fluorescence, see ref 19. (18) (a) Czamik, A. W. In ref 6. p 109. (b) Ueno, A.; Osa, T. In Photochemistry in Organized and Constrained Media;Ramamurthy, V., Ed.; VCH: New York, 1991; p 739. (c) Bissell, R.A.; de Silva, A. P.; Gunaratne, H.Q.N.; Lynch, P. L.M.; Maguire, G. E. M.; McCoy, C. P.; Sandanayake, K. R. A. S. Top. Curr. Chem., in press. ( 19) (a) Bissell, R. A.; Calle, E.; de Silva, A. P.; de Silva,S.A,; Gunaratne. H. Q.N.; Habib-Jiwan, J.-L.; Peiris, S. L. A.; Rupasinghe, R. A. D. D.; Samarasinghe, T.K. S.D.; Sandanayake, K. R. A. S.;Soumillion, J. P. J. Chem. Soc.,Perkin Trans. 1992,1559. (b) de Silva, A. P.; Gunaratne, H. Q. N.;McCoy, C. P. Nature 1993,364,42. (c) Grigg, R.;Norbert, W. D. J. A. J. Chem. Soc., Chem. Commun. 1992, 1298, 1300.
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(nm) Figure 1. Absorption spectra in CHzClz solution at room temperature of 1, b(H+)4, and 2,6-dimethylnaphthalene (DMN). For comparison purposes, the molar absorption coefficient of the last compound has been multiplied by a factor of 2.
I
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1(nm) Figure 2. Luminescence spectra in CHZCl2 solution at room temperature of 1, l.(H+),, and 2,6-dimethylnaphthalene (DMN). the experiments were performed in CHzClz at room temperature (-25 "C) unless otherwise noted.
Results and Discussion Receptor 1, a Fluorescent Sensor Responsive to Protons. The absorption spectrum of 1is shown in Figure 1. For comparison purposes, the spectrum of 2,6-dimethylnaphthalene (DMN) is also shown. The other component of 1, i.e., the macrocycle [ 181N204, shows a negligible absorption in the spectral region examined (e < 20 M-I cm-* at A, = 267 nm). Comparison between the spectrum of 1with the summation of the spectra of itscomponents (Le., with twice the absorption spectrum of DMN, Figure 1) shows that bonding with two [ 18]-N204 units causes the appearance of an absorption tail in the UV region and small changes in the structure and intensity of the ILb (A, = 323 nm) and 'La (A, = 274 nm) A- A* bands of DMN. The absorption tail (as well as the corresponding luminescenceband, vide infra) can be assigned to CT transitions from the nonbonding orbital of the amine groups of the [ 18]-N204 macrocycles to the A* orbitals of the naphthalene units. This assignment is confirmed by the disappearance of the absorption tail upon addition of 4 equiv of trifluoroacetic acid which, as will be discussed in more detail later on, causes full protonation of the amine groups of the two [ 18]-N204 units (Figure 1). The small differences observed between the absorption spectrum of l.(H+)4 and DMN can be attributed to perturbation of the A** naphthalene transitions by the nearby proton charges in l.(H+)4 (vide infra). Figure 2 shows the luminescence spectra of 1, ~ s ( H + )and ~, DMN in CH2Cl2 at room temperature. The [18]-N204 macrocycle does not show any luminescence. As one can see, l.(H+),
J. Am. Chem. SOC.,Vol. 116, No. 13, 1994 5743
A Cylindrical Macrotricyclic Receptor and Its Adducts Table 1. Luminescence Propertiesa
fluorescence, 293 K phosphorescence,77 K hnu
A m
(nm) Id* ~ ( n s ) (nm) T (s) DMN 342 100 14 jLY 1% 1 342
