Hydrogen bonding- and stacking-induced stereospecific [2 + 2]-photocycloaddition within a pseudodimeric complex of two styryl dyes

A new N-ammoniopropyl styryl dye and 18-crown-6 ether styryl dye of the pyridine series form a head-to-tail pseudodimeric complex through host-guest hydrogen bonding; the complex undergoes stereospecific [2 + 2]-photocycloaddition due to the stacking-induced pre-organization of the ethylene bonds of dye chromophores.