Synthesis, structure, and stereospecific cross-[2+2] photocycloaddition of pseudodimeric complexes based on ammonioalkyl derivatives of styryl dyes

New 4-pyridine-derived styryl dyes having an ammonioalkyl N-substituent in the pyridine moiety and various substituents in the benzene moiety were synthesized. The formation of pseudodimeric complexes of ammonioalkyl styryl dye derivatives with 18-crown-6-containing styryl dyes of the 4-pyridine, 4-quinoline, and 2-benzothiazole series was studied by 1H NMR in MeCN-d3. It was found that the stability of supramolecular complexes is mainly determined by the monotopic interaction of the ammonioalkyl group with the crown ether moiety via hydrogen bonding. The components of pseudodimeric complexes undergo stereospecific cross-[2+2] photocycloaddition reaction to give unsymmetrical rctt isomers of cyclobutane derivatives owing to the syn-head-to-tail arrangement of components in the initial complex. The efficiency of photoreaction is affected by the N-substituent length, the nature of the substituent in the benzene ring of the ammonioalkyl component, and the nature of the heterocyclic residue of the crown-containing component. The structures of dyes, pseudodimeric complexes, and the cyclobutane derivative were studied by X-ray diffraction.