MOLMOTDYN · Understanding the dynamics behind the photoisomerization of light-driven molecular rotary motors and switches

Light-driven molecular rotary motors derived from chiral overcrowded alkenes represent a central class of compounds for which photochemical rearrangements play a crucial role in their function. The mode of action of these motors is based on the periodic repetition of photo-isomerization and thermal relaxation steps, which lead to a uni-directional rotation of one part of the molecule (rotor) with respect to another (stator). A considerable increase in the rotation speed (ca. 10⁸ times) has been achieved due to a lowering of the activation energy of the thermal helix inversion step. The photo-isomerization step however still remains poorly understood. It is the primary purpose of this project to fill this gap and to study the dynamics of photo-isomerization in light-driven rotary molecular motors. I will use excited state methods developed in my group to investigate the fluorene-based and phenanthrylidene-based molecular motors and assemblies of motor molecules.The theoretical study of the substituent effects and the hetero-atom effects on the properties of the ground and excited state potential energy surfaces, on the occurrence and position of conical intersections and avoided crossings and on the non-adiabatic couplings between the states will provide information necessary for designing new molecular motors. The effect of anchoring of the motor units on a substrate suitable for practical applications, such as surfaces of conducting or insulating materials, or (bio-)polymer substrates, on the mode of function of the motor will be theoretically investigated. In this regard, special attention will be paid to the possibility of increasing the power output by combining several molecular motor units within a single molecular device.""