Abstract Three styryl dyes of the 4-pyridine series that form syn-head-to-tail dimeric pairs in polycrystalline films were synthesised. NMR and UV/Vis spectroscopic studies showed that this promotes stereospecific [2+ 2]-autophotocycloaddition (PCA) in the dimeric pairs to give rctt-isomers of cyclobutane derivatives. For the dye with an N-ammoniopropyl substituent, this transformation was accomplished according to the single-crystal-to-single-crystal ...
