It was shown by ¹H NMR spectroscopy that symmetrical bis(crown)stilbenes (L) and small alkali and alkaline-earth metal cations form 1(L) ∶ 1(M^m+) and 1(L) ∶ 2(M^m+) complexes in MeCN solutions. In the case of large or hydrated metal cations such as Cs⁺, Rb⁺, K⁺, Ba²⁺, Sr²⁺, [Ca(H₂O)_x]²⁺ and stilbenes with a small crown-ether cavity as compared with the metal cation size, stable bis-sandwich complexes 2(L) ∶ 2(M^m+) can also be formed. A stable bis-pseudosandwich 2 ∶ 2 complex is also produced from bis(18-crown-6)stilbene with the propanediammonium ion. The effect of the crown-ether size and the cation size and nature on the route of stilbene phototransformation and product composition was elucidated. The bis-(pseudo)sandwich complexes undergo effective stereoselective [2+2] photocycloaddition giving mainly rctt isomers of new 1,2,3,4-tetracrown cyclobutanes. The structures of complexes of bis(crown)stilbenes and obtained cyclobutanes were confirmed by X-ray diffraction.

A series of new viologen analogues bearing two ammonioalkyl groups (2–4) were synthesized in order to study their complexation with bis(18-crown-6)stilbene (1b). Electronic spectroscopy and ¹H NMR measurements show that in acetonitrile, bis(crown) stilbene 1b forms highly stable 1 : 1 and 2 : 1 charge-transfer (CT) complexes with π-acceptors 2–4 owing to host–guest bonding. The influence of geometric and electronic factors on the complex formation constants are discussed. The structures of the supramolecular CT complexes are analyzed on the basis of ¹H and ¹³C NMR data obtained in solution and in the solid state. X-Ray diffraction data for 1b and for model tetramethoxystilbene are also reported.