The experience achieved by our group toward controlling the properties of molecular motors allowed to develop several systems able to reach high speed rotation and application for responsive materials. The rotary motion involves photochemical and thermal helix inversion steps. Previous results showed how in 2nd-generation molecular motors featuring a six-membered ring upper-half and a five-membered ring lower-half, the barriers for thermal helix inversion were found to be very high,while recent results on compound 1  suggest that the barriers for thermal E-Z isomerization and helix inversion are comparable, limiting their use as molecular motors. Nonetheless, due to the high thermal stability and high photostationary states (PSS), their behaviour could then be better described as light-triggered bistable molecular switches. Therefore, in order to extend the study to similar structures, overcrowded alkenes 2  , 3  and 4  have been synthesized and their photochemical and thermal isomerization processes have been extensively studied. They indeed revealed to be very stable molecular switches at low temperature. While at high temperatures alkene 2  still retains mainly its E-Z switching properties, alkene 3  shows a motor-like behaviour. Both compounds can be efficiently switched back and forth by irradiation with UV or visible light showing high PSS ratios. Due to these properties, they might provide a route toward a new family of chiral, bistable molecular switches with a large change in geometry, which could be applied in a wide range of responsive materials.

Molecular switches and motors based on highly efficient bistable overcrowded alkenes

248th National Meeting (2014)

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