Highly Light‐Sensitive Luminescent Cyanostilbene Flexible Dimers

Switchable luminescent organic materials with unusual high light‐sensitivity in the bulk at room temperature are described. The compounds consist of two promesogenic photoactive cyanostilbene units linked by a flexible spacer with an odd number of carbon atoms, analogous to the structural design of a liquid crystal dimer. Experimental and computational studies support the formation of excimers in solution due to the characteristic geometry of the dimers. In their condensed phases they show a high tendency to pack in lamellar phases, exhibiting bent‐core lamellar liquid crystal phases and crystalline polymorphs with different photoluminescence and high quantum yields. The compounds are highly photoreactive, and their photoactivity in terms of photoisomerization and/or photocycloaddition reactions in solution and in the bulk is different. By irradiation of the compounds in the condensed phases at room temperature a fast photochemical process takes place, identified as a photocycloaddition reaction favored by the lamellar packing. Due to this photoreaction a luminescence modulation with green/blue color switching and an increase in quantum yield takes place.