An unusual single-crystal-to-single-crystal [2 + 2] photocyclisation reaction of a TTF-arylnitrile derivative.

4-([2,2'-Bi(1,3-dithiolylidene)]-4-yl)benzonitrile undergoes a [2 + 2] photocycloaddition reaction upon irradiation with polychromatic light, an unusual single-crystal-to-single-crystal transformation for a TTF derivative. In contrast, the closely related pyridylnitrile derivative adopts a different packing motif and is stable to light under the same conditions. [ABSTRACT FROM AUTHOR]