New bis(18-crown-6) and bis(aza-18-crown-6) bisstyryl dyes of pyridine series 1a,b and 2a,b containing a xylyl spacer were synthesized and their spectral and binding properties with ammonium compounds were studied by spectroscopic methods.
Homoditopic receptors 1a,b have strong absorption at 410 nm and form stable pseudocyclic 1 : 1 complexes (lgK≥5.5) with NH₃⁺(CH₂)_nNH₃⁺ (n = 2-10, 12) resulting in hypsochromic shift of their absorbance by upto 27 nm. Irradiation with visible light leads to stereospecific reaction of [2+2]-photocycloaddition (PCA) in the pseudocyclic complexes of 1a with formation of cyclobutan derivative 3. Contrarily, receptors 2a,b (λ_max=490 nm) were found to form only non-cyclic 1 : 1 complexes with diammonium compounds.

Financial support from the Russian Foundation for Basic Research, the Russian Academy of Sciences and the Ministry of Education and Science of Russia is gratefully acknowledged.

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