Novel Photoswitchable Receptors:  Synthesis and Cation-Induced Self-Assembly into Dimeric Complexes Leading to Stereospecific [2+2]-Photocycloaddition of Styryl Dyes Containing a 15-Crown-5 Ether Unit

• Published in: Journal of organic chemistry 2003-08, Vol.68 (16), p.6115-6125
• Main Authors: Gromov, Sergey P, Ushakov, Evgeny N, Fedorova, Olga A, Baskin, Igor I, Buevich, Alexei V, Andryukhina, Elena N, Alfimov, Michael V, Johnels, Dan, Edlund, Ulf G, Whitesell, James K, Fox, Marye Anne
• Format: Article
• Language: English
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo034460x

Styryl dyes 4a − e containing a 15-crown-5 ether unit and a quinoline residue with a sulfonatoalkyl or sulfonatobenzyl N-substituent were synthesized. The relationship between the photochemical behavior of these dyes and their aggregates derived from complexation with Mg2+ in MeCN was studied using 1H NMR and absorption spectroscopy. The E-isomers of 4a − e were shown to form highly stable dimeric (2:2) complexes with Mg2+. Upon irradiation with visible light, the dimeric complexes undergo two competing photoreactions, viz., geometric E → Z isomerization, resulting in an anion-capped 1:1 complex of the Z-isomer with Mg2+ and stereospecific syn-head-to-tail [2+2]-cycloaddition, affording a single isomer of bis-crown-containing cyclobutane. The N-substituent in the dye has a dramatic effect on the photochemical behavior of the dimeric complex. Molecular dynamics and semiempirical quantum-chemical calculations were carried out to interpret the observed photocycloaddition in the dimer. Conformational equilibria for the dimer of (E)-4b were analyzed using 1H NMR spectroscopy.