Spectroscopic Study of a Symmetrical Bis-crown Fluoroionophore of the Diphenylpentadienone Series Nathalie Marcotte, Suzanne Fery-Forgues,* and Dominique Lavabre Laboratoire des Interactions Mole ´ culaires Re ´ actiVite ´ Chimique et Photochimique, UMR CNRS 5623, UniVersite ´ Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex, France Sylvie Marguet SerVice de Chimie Mole ´ culaire, URA CNRS 331, CEA/Saclay, 91191 Gif-sur-YVette Cedex, France Vasyl G. Pivovarenko Chemistry Department, National Taras SheVchenko UniVersity, Volodymyrska 64, KieV 252017, Ukraine ReceiVed: December 4, 1998; In Final Form: February 16, 1999 A new fluoroionophore bearing two crown ethers on the conjugated system, 1,5-bis[4N-(aza-15-crown-5)- phenyl]-1,4-pentadien-3-one (II), was synthesized together with model compound I where the crown ethers are replaced by diethylamino groups. The behavior of molecules I and II in the presence of alkali and alkaline- earth perchlorates was investigated in acetonitrile solution by absorption and emission spectroscopy (including picosecond techniques), mass spectrometry, and NMR spectroscopy. Two types of interaction must be distinguished: on the one hand, the expected complexation of the crown ether moieties, which generated strong spectroscopic effects with Na + , Li + , Ba 2+ , and Ca 2+ ions, and on the other hand, an interaction between the unsaturated ligand core and the cation, particularly noticeable with magnesium. The absorption data were correctly fitted by taking into account three different stoichiometries and the corresponding association constants were calculated. The emissive properties of the species involved were discussed. 1. Introduction Crown-ether derivatives incorporating a fluorescent moiety are attractive tools for optical sensing of metal ions. During the past decade, numerous fluoroionophores have been built to this pattern. This abundance of structures allowed a classification of the compounds to be established according to the photo- physical mechanisms involved: photoinduced electron transfer, alteration of the conjugated system, excimer formation, etc. 1-7 However, very little information is available about molecules in which two ionophore groups are directly linked to a conjugated electron system. Few compounds of this type are mentioned in the literature. Most have been designed so that the two crown-ether moieties are spatially close and display a synergistic effect. Crowns incorporating biphenanthryl 8 or anthracenoyl 9,10 residues have been used as fluorescent probes for chiral molecular recognition and lipid phase-transition sensing, respectively, but their behavior in the presence of ions has not been reported. As far as cation recognition is concerned, several bis-crown-ether derivatives have been synthesized in the aim of favoring intramolecular sandwich structures. In fact, according to Ped- ersen and Frensdorff, 11 the stability of the cation/crown-ether complex depends on how the cation matches the crown cavity. It has been noticed that when the cation is too big to be accommodated by the crown, sandwich structures are formed where two ligands coordinate the same cation. In order to regulate the relative positions of the two crown-ether moieties, a photochromic group has been introduced between them. Such molecules are modified upon light irradiation which results in bringing the crown ethers close together or in moving them apart, and thus modulates their affinity for cations. Examples are Lindsten’s stilbenic derivatives, 12 Shinkai’s azoic com- pound, 13 and the malachite green derivative of Kimura. 14 These systems are potentially useful for light-driven cation pumps, although they have not been extensively investigated from a photophysical viewpoint. Actually, it seems that fluoroionophores bearing two crown ethers remaining far apart in space have been very rarely studied until now. Exceptions are the phenanthroline derivative of Schmittel 15 whose spectral properties have not been reported, and the red-emitting squaraine dye studied by Das et al. 16 and Akkaya. 17 The latter compound, symmetrically substituted by two crown ethers, undergoes a moderate decrease of the fluorescence quantum yield attributed to complexation and has been proposed for the analysis of alkali cations in solution. These considerations prompted us to conceive and study an original bis-crown-ether fluoroionophore devoid of any pos- sibility of forming a sandwich-type intramolecular complex with cations. We retained the idea of a symmetrical structure, but with a bis-chromophoric dye where each chromophore contains a cation chelator. The chromophores are conjugated and thus interact with one another. 18,19 It is expected that binding to a cation breaks the dye symmetry, which could result in striking changes in the spectroscopic properties. In this case, the dye may become a sensor for the analysis of cations in solution. 1,5-Bis[4-(diethylamino)phenyl]-1,4-pentadien-3-one ( I) (Scheme 1) was therefore chosen as the fluorophore because the dyes in * To whom correspondence should be sent. E-mail: sff@gdp.ups-tlse.fr. Fax.: +335 61 25 17 33. 3163 J. Phys. Chem. A 1999, 103, 3163-3170 10.1021/jp9846328 CCC: $18.00 © 1999 American Chemical Society Published on Web 04/10/1999