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Langmuir 2001, 17, 4056-4060
Inclusion of Resorcinol-Based Acridinedione Dyes in Cyclodextrins: Fluorescence Enhancement† V. K. Indirapriyadharshini,‡,§ P. Karunanithi,‡ and P. Ramamurthy*,‡,§ Department of Inorganic Chemistry, School of Chemical Sciences, and National Centre for Ultrafast Processes, University of Madras, Chennai 600 025, India Received January 23, 2001. In Final Form: April 26, 2001 The inclusion of acridinedione dyes (ADR) with β-cyclodextrins (β-CD) in the presence of 0.6% methanol is studied using absorption and fluorescence techniques. The association constant was determined by using the Benesi-Hildebrand plot and also by nonlinear regression analysis. A stoichiometry of 1:1 was found for β-CD/ADR (3-5). The nonobservation of the changes in the absorption or the fluorescence in the case of dyes 1 and 2 clearly indicates that the phenyl substituent at the -N atom in the ADR (3-5) is included in the β-CD cavity. Thermodynamic parameters ∆H and ∆S values obtained from the temperaturedependent binding constants of the β-CD/ADR (3-5) system are reported. In the presence of β-CD, the fluorescence of ADR (4) dye shows single exponential decay, consistent with the completion of complex formation, and ADR (3, 5) showed a double exponential decay, consistent with the equilibrium between free and complexed forms. The binding constants and thermodynamic factors are systematically resolved through lifetime analysis.
Introduction Continuing inquiries into the fashion in which the systems have been found to provide so-called restricted microenvironment or cavities of molecular dimensions (on the order of 10 Å) capable of sequestering and controlling the chemistry of reactive molecules.1 Dynamic effects may result from the geometry restrictions imposed on the guest molecule resulting from the limited space in the host cavity. For example cyclodextrins (CDs) are water-soluble cyclic oligosaccharides consisting of six, seven, and eight glucopyranose units, and they are called R-CD (cyclohexaamylose), β-CD (cycloheptaamylose), and γ-CD (cyclooctaamylose) characterized by their increasing cavity diameter.2-4 Apart from the considerable amount of experiments and theoretical work on CD inclusion complexes, it still seems to be necessary for us to accumulate more basic data on the interaction-geometry relationship of the inclusion complexes by means of appropriate spectroscopic methods.5 The complex formation was rationalized in terms of spectral shift and enhancement in the fluorescence quantum yield.6-9 The binding force between CD and organic solutes has been assumed to be hydrogen bonding,10 van der Waals force,11,12 or hydrophobic interac-
tion.13,14 Since the absorption spectra of inclusion complexes differ from those of organic solutes dissolved in water, the absorption spectrophotometric method has been used for obtaining equilibrium constants.15 A series of thermodynamic and kinetic studies on the formation of inclusion complexes showed that a molecule could be included when the size of the molecule is smaller than that of the cavity inside the cyclodextrin molecule. The first observation of fluorescence enhancement upon inclusion was reported for the aqueous β-CD solution of 1-anilino-8-naphthalenesulfonate.15 Konda et al. studied fluorescence enhancement of 6-(p-toludino)naphthalenesulfonate for the purpose of detecting ring opening of CD catalyzed by Takaamylase.16 In the present study, we have used resorcinol-based acridinedione (ADR) dyes having substitution as shown.
† Dedicated to Dr. J. P. Mittal FASc, FNA, BARC, Mumbai, on the occasion of his 60th birthday. ‡ Department of Inorganic Chemistry, School of Chemical Sciences. § National Centre for Ultrafast Processes.
(1) Kalyanasundaram, K. Photochemistry in Microheterogeneous systems; Academic Press: London, 1987. (2) Bender, M. L.; Komiyama, M. Cyclodextrin chemistry; Springer Veriag: Berlin, 1978. (3) Szejtli, J. Cyclodextrins and their inclusion complexes; Akademiai Kiado: Budapest, 1982. (4) Saonger, W. Angew. Chem., Int. Ed. Engl. 1980, 19, 344. (5) Kamiya, M.; Mitsuhashi, S.; Makino, M. and Yoshioka, H. J. Phys. Chem. 1992, 96, 95. (6) Cenquera, E. J.; Aicart, E. J. Ind. Phenom. 1997, 29, 119. (7) Bergmark, W. R.; Davis, A.; York, C.; Macintosh, A.; Jones, G., II J. Phys. Chem. 1990, 94, 5020. (8) Veno, A.; Takahashiand, K.; Osa, T. J. Chem. Soc., Chem. Commun. 1980, 921. (9) Hamai, S. Bull. Chem. Soc. Jpn. 1982, 55, 2721. (10) Cramer, F.; Kampe, J. J. Am. Chem. Soc. 1965, 87, 1115.
These have been reported as a class of laser dyes.17 These dyes are important because of their structural similarity to 1,4-dihydropyridines and NADH, which act as coen(11) Bergeron, R. J.; Channing, M. A.; G. J. Gilbeily, G. J.; Pillor, D. M. J. Am. Chem. Soc. 1977, 99, 5146. (12) Cramer, F. Angew. Chem. 1967, 73, 49. (13) Hall, E. S.; Ache, J. J. Phys. Chem. 1979, 83, 1805. (14) Hoffman, J. L.; Bock, R. H. Biochemistry 1970, 9, 3542 (15) Cramer, F.; Saenger, W.; Spatz, H. J. Am. Chem. Soc. 1967, 89, 14. (16) Kondo, H.; Nakatani, H.; Hiromi, K. J. Biochem. 1976, 79, 393. (17) Shanmugasundaram, P.; Murugan, P.; Ramakrishnan, V. T.; Srividya, N.; Ramamurthy, P. Heteroat. Chem. 1996, 6, 17.
10.1021/la0101200 CCC: $20.00 © 2001 American Chemical Society Published on Web 06/01/2001
Acridinedione Dyes in Cyclodextrins
zymes in biological systems.18 The ADR dyes have a bichromophoric structure enabling them to act as both electron donors and acceptors in the ground and excited states.19-22 The photochemistry23 and photophysics24,25 of these dyes have been studied. These dyes are used as photosensitizers19 and initiators in photopolymerization.26 The solvent effect studies on the dyes used in this study show that they have high fluorescence quantum yield24 and deserve special attention due to their good lasing action17 comparable to coumarin 102. Benesi-Hildebrand plots can offer fundamental information concerning the binding strength and stoichiometry of binary systems.27,28 Such plots are used in this paper to estimate value of binding constant, thus providing further understanding of mechanisms characterizing the systems.
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Figure 1. Absorption spectra of ADR (3) dye in the presence of 0-0.008 M β-CD at 300 K: [β-CD] ) 0 (1), 0.0005 M (2), 0.001 M (3), 0.002 M (4), 0.004 M (5), and 0.008 M (6).
Experimental Section R-CD and β-CD (Fluka) were used as received. Acridinedione dyes were synthesized by the procedures reported in the literature and characterized.29 Methanol HPLC grade was obtained from Qualigens India Ltd. Water was triply distilled in an all-glass apparatus. Due to low solubility of these dyes in water, the solutions were prepared in 0.6% methanol. Approximately 0.2 mM dye solution in 6% methanol was prepared. From this 0.5 mL was added to different volumes of CDs and then made up to 5 mL with the triple-distilled water. The samples were shaken with a mechanical shaker for 8 h and then allowed to equilibrate overnight. The same was used to measure the fluorescence lifetime as well. Corresponding concentrations of the CDs were used as a reference for the absorption measurements. The absorption spectra were recorded in Hewlett Packard 8452A diode array spectrophotometer. Fluorescence measurements were done in a Perkin-Elmer LS-5B fluorescence spectrophotometer. Fluorescence lifetimes were measured using a time-correlated single photon counting (TCSPC) spectrometer comprised of a diode pumped Nd-VO4 laser of 532 nm that was used as the excitation source for a titanium-sapphire modelocked laser. This provides the wavelength tunable from 720 to 1000 nm operating at a 4 MHz repetition rate and pulse width of
