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Photochromic Torsional Switch (PTS): a lightdriven actuator for the dynamic tuning of π-conjugation extension


Fazzi,  Daniele
Research Department Thiel, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Maciejewski, J., Sobczuk, A., Claveau, A., Nicolai, A., Petraglia, R., Cervini, L., et al. (2016). Photochromic Torsional Switch (PTS): a lightdriven actuator for the dynamic tuning of π-conjugation extension. Chemical Science, (8), 361-365. doi:10.1039/C6SC03196J.

Here we present a molecular architecture that can reversibly change the geometric conformation of its π-system backbone via irradiation with two different wavelengths. The proposed ‘molecular actuator’ consists of a photoswitchable azobenzene orthogonally connected to a π-conjugated bithiophene by both direct and aliphatic linker-assisted bonding. Upon exposure to 350 nm light, the trans azobenzene moiety isomerizes to its cis form, causing the bithiophene to assume a semiplanar anti conformation (extended π-conjugation). Exposure to 254 nm light promotes the isomerization of the azobenzene unit back to its initial extended trans conformation, thus forcing the bithiophene fragment to twist out of coplanarity (restricted π-conjugation). The molecular conformation of the bithiophene was characterized using steady-state UV-vis and nuclear magnetic resonance spectroscopy, as well as ab initio computations. The proposed molecular design could be envisaged as a π-conjugation modulator, which has potential to be incorporated into extended linear π-systems, i.e. via the terminal α-thiophene positions, and used to tune their optical and electronic properties.