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

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

The project aims at reaching thorough understanding of the effect of chemical modification on functional characteristics of light driven molecular devices, such as molecular motors and molecular switches. Chemistry is currently at an early stage of building artificial molecular machines, in which light driven molecular devices can serve as the means of movement. Designing molecular devices with application defined functionality requires thorough understanding of their mode of action where the photochemical rearrangement, which is the principal step in the working cycle of light driven molecular devices, still remained less amenable to judicial modulation by the means of synthetic chemistry. In my project, I use the computational tools of modern theoretical chemistry and molecular dynamics to model mechanistic aspects of the working cycle of light driven molecular devices and thereby to reach understanding of the ways of chemical modulation of their functionality. As a result of the computational work undertaken in the project, two new classes of light driven molecular devices with improved quantum efficiency were proposed. A key to improving their quantum efficiency is in changing the character of motion performed during their action; in particular, a precessional motion typical of early models of light driven molecular motors is replaced by pure axial rotation in the new molecular motors. Furthermore, a simple rule was proposed that helps to identify molecular fragments suitable for designing molecular photodriven devices with pure axial rotation, thus enabling a simple screening of potential precursors of such molecules. This opens up a perspective for rational design of photodriven molecular motors and switches suitable for application within specific molecular machines. It is important that some of the molecular motors studied theoretically in this project have been already synthesized and are currently under investigation by spectroscopic tools. Preliminary results of the spectroscopic investigation confirm the validity of theoretical models developed in the course of the project. To achieve the goals of the project required the development of novel computational tools of theoretical chemistry capable of providing reliable description of mechanistic features of the ground and excited electronic states of the target molecular systems, such as conical intersections which are crucial for non-adiabatic relaxation of the excited electronic states. The novel computational tools developed in this project are based ensemble density functional theory, an emerging concept within modern quantum chemistry. The developed computational tools considerably extend capabilities of the existing quantum-chemical methods and enable researchers to address problems that were beyond their reach heretofore. The work on further improvement and extension of the capabilities of the new computational means will be continued in the future. The results of the project were communicated in 7 research articles published in peer reviewed scientific journals, 3 lectures presented at the international scientific conferences and 4 research seminars given at universities and research institutes worldwide.

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