Self-assembly involving alkanediammonium ions and stereospecific [2+2] photocycloaddition of (18-crown-6)stilbene.

Complexation between (18-crown-6)stilbene and alkanediammonium ions +H3N(CH2)nNH3+ (n = 2−4) resulting in the pseudo-sandwich 2:1 stilbene—dication complexes and 1:1 stilbene—dication complexes was studied by NMR spectroscopy. The stability of the complexes decreases as the methylene chain length in the alkanediammonium ion increases. UV photolysis of the bis-ligand complexes produces two major products, viz., the rctt isomer of a biscrown-containing cyclobutane derivative formed as a result of intra-supramolecular [2+2] photocycloaddition and a crown-containing phenanthrene derivative (product of electrocyclization reaction). The effective quantum yields of both cyclization reactions occurring in the pseudo-sandwich complexes increase as the number of methylene units in the dication decreases. [ABSTRACT FROM AUTHOR]