J. Chem. Soc., Perkin Trans. 2, 1999, 601–607 601 Crown-containing styryl dyes: cation-induced self-assembly of multiphotochromic 15-crown-5 ethers into photoswitchable molecular devices Evgeny N. Ushakov, a Sergei P. Gromov,* b Alexei V. Buevich, c Igor I. Baskin, c Olga A. Fedorova, b Artem I. Vedernikov, b Michael V. Alfimov, b Bertil Eliasson d and Ulf Edlund * d a Institute of Chemical Physics Research, Russian Academy of Sciences, Chernogolovka, Moscow Region, 142432, Russia b Center of Photochemistry, Russian Academy of Sciences, 7a ul. Novatorov, Moscow, 117421, Russia c N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky prosp., Moscow, 117913, Russia d Department of Organic Chemistry, Umeå University, Umeå, S-901 87, Sweden Received (in Cambridge) 29th September 1998, Accepted 14th January 1999 The s-conformations of trans-1b–e were studied by 1 H NMR spectroscopy in CD 3 CN solution. It was shown that in trans-1b–e intramolecular ion pairs between the SO 3 - group and the positively charged nitrogen atom of the benzothiazolium residue are formed. In the case of trans-1a no ionic association was observed. The complex formation of the trans- and cis-isomers of crown-containing styryl dyes with Mg 2+ in CH 3 CN was studied spectrophotometrically. The anion-“capped” complexes formed by the cis-isomers were found to be more stable than the complexes formed by the corresponding trans-isomers. The stability constants of the complexes formed by the cis- isomers depend markedly on length and type of the N-substituent. Data from PM3 quantum-chemical calculations were used for the interpretation of some experimental data. Introduction Certain conditions must be fulfilled for a successful develop- ment of photoswitchable molecular devices. 1–5 The actual com- pounds must have the capability of self-organisation at the molecular level (self-assembly), 6–8 giving supramolecular struc- tures with a desirable architecture, and allow a photochemical control of their properties. Synthesis of multiphotochromic complexones susceptible to various types of molecular photo- switching is of prime importance in this respect. Previously, we developed a procedure for the synthesis of crown-containing styryl dyes (CSD). 9 The CSD of type trans- 1c–f (Scheme 1) proved to be the most promising among these compounds. These CSD are able to form anion-“capped” com- plexes (Scheme 2) upon trans–cis-photoisomerization owing to the interaction of the sulfo group of the N-substituent (spacer) with a metal cation in the crown-ether cavity. Studies of CSD in solution have shown that in the presence of metal cations, the trans-isomers of these molecules can exist as self-organised pairs according to the anti-“head-to-tail” pattern 10,11 (Scheme 2). The self-assembly of the dimeric Scheme 1 Crown-containing styryl dyes. complexes comprising two trans-1c,d molecules and two metal cations can become a unique tool for controlling the regio- and stereoselectivity of [2+2]-photocycloaddition (PCA) of CSD. 12–14 It is noteworthy that neither trans-1a–f without alkaline earth metal cations nor complexes of trans-1a with Mg 2+ , Ca 2+ , or Ba 2+ undergo PCA even in saturated solutions. The change from spacers with flexible polymethine chains to N-substituents in which the sulfo group is rigidly arranged in space, makes it possible to influence the efficiency of these photochemical reactions and also to change the route of trans- formation of CSD. 15 The anion-“capped” and dimeric complexes are the simplest photoswitchable molecular devices, since their ability to bind metal cations substantially changes on exposure to light, i.e. the complex-formation process can be controlled. 10,12,15–17 Scheme 2 Downloaded on 06 January 2012 Published on 01 January 1999 on http://pubs.rsc.org | doi:10.1039/A807565D View Online / Journal Homepage / Table of Contents for this issue