PhD ceremony Mr. O. Ivashenko: Dual photo- and redox active molecular switches for smart surfaces
| When: | Fr 24-05-2013 at 16:15 |
PhD ceremony: Mr. O. Ivashenko, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen
Dissertation: Dual photo- and redox active molecular switches for smart surfaces
Promotor(s): prof. P. Rudolf, prof. B.L. Feringa
Faculty: Mathematics and Natural Sciences
Molecular switches are organic molecules that can change their structure or conformation upon interaction with light or electrical potential. In the introduction of this dissertation a route towards the development of smart surfaces is illustrated based on a few important examples of such dual responsive molecular switches.
Bis-thiaxanthylidene overcrowded alkene shows light- and redox-switching of its luminescent properties in solution. Remarkably, when immobilized as a monolayer on gold or indium tin oxide, it exhibits a higher stability of the unstable conformational states, explained by intermolecular interactions in the monolayer. Moreover oxidation to a dicationic state allows reversible modification of the surface’s wetting properties (contact angle change > 30°), which can be used as a volatile molecular memory.
Spiropyrans are photochemically and electrochemically switching molecules known for more than 60 years. UV/Vis photochemical switching is typically used to change between the ring-open and ring-closed forms of this compound in solution. In this thesis reversible switching was also achieved in self-assembled monolayers on gold; in addition a near-IR beam was successfully employed to induce ring-opening.
According to literature, the oxidation of spiropyrans is irreversible due to ring-opening and subsequent dimerization. Based on several spectroscopic measurements, in this dissertation we demonstrate that indeed dimerization of oxidized spiropyran in solution occurs, however not in the ring-open but in the ring-closed form. Remarkably in monolayers on gold intermolecular interactions are also favourable for such oxidative dimerization. Therefore together photo- and redox-responsive spiropyran monolayers can be used to develop a molecular write-read-erase memory device.