The molecular photochromic switch 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluoro-cyclopentene, abbreviated as DMPT-PFCP, has been commanding much attention recently in the fields of nanotechnology and optical data storage for 2D and 3D media applications. This recent attention of DMPT-PFCP is mainly attributed to the diarylethene’s high optical fatigue resistance and photo-isomerative nature, which allows the molecule to assume open and closed-ring conformations when irradiated with visible or UV light, respectively. Since it has been found that not all open-ring conformations of DMPT-PFCP can be readily converted to their closed-ring isomers upon photo-excitation, quantum yield for the photo-isomerization process has been limited to only ~50%. This ~50% quantum yield can be attributed to the existence of two classes of open-ring conformations of DMPT-PFCP in the ground-state: reactive (R) and non-reactive (NR). In order to better understand the photo-isomerization process, we utilize time-dependent density functional theory (TD-DFT) to study the photo-physical pathways of the open-ring, ground-state conformers of DMPT-PFCP and identify factors that promote or inhibit electrocyclization of the molecule. We have found that reactive conformers decay non-radiatively through conical intersections allowing for optimal photo-isomerization, whereas non-reactive conformers have large barriers on the S1 pathway that inhibit photo-isomerization upon UV excitation. Further, multi-configurational self-consistent field (MCSCF) calculations have been implemented to verify the presence of these conical intersections. Through this fundamental understanding of DMPT-PFCP, experimental procedures can be modified, when creating optical data storage devices, in order to provide more efficient means of data storage for the advancement in nanotechnology.

Excited-state investigation of the ultrafast electrocyclization reaction for a molecular photochromic switch

253rd National Meeting (2017)

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