Theoretical study of the photochemical isomerization process of perfluoroaryltetrahedrane to perfluoroarylcyclobutadiene mediated by 9,10-dicyanoanthracene

The photoisomerization process between tetrahedrane (THD) and cyclobutadiene (CBD) has attracted tremendous attention during the past two decades due to its potential application toward designing new materials. Recently, an experimental study found that perfluoroaryl-substituted tetrahedrane could isomerize to its cyclobutadiene derivative under irradiation > 420 nm. In this paper, the detailed mechanism of this photoisomerization process will be investigated using density functional theory and time-dependent density functional theory. These results suggest that the chromophore 9,10-dicyanoanthracene is first activated under light irradiation, and then, electron transfer occurs from perfluoroaryltetrahedrane to the chromophore to form its cation derivative. The electron transfer process has been theoretically confirmed by the location of the crossing point between two excited states of the perfluoroaryltetrahedrane and 9,10-dicyanoanthracene complex in which the higher excited state can be denoted as the local excitation of 9,10-dicyanoanthracene and the lower excited state is characterized as the charge transfer state. After that, the cation of perfluoroaryltetrahedrane can easily isomerize to the perfluoroarylcyclobutadiene cation with a barrier of 6.2 kcal/mol. After isomerization, the electron could transfer back from perfluoroarylcyclobutadiene to 9,10-dicyanoanthracene, and thus, 9,10-dicyanoanthracene can be considered as the photocatalyst of the isomerization process. The studied mechanism in this work could be helpful to reveal the nature of the isomerization process between THD and CBD and instructive for the design of new light control materials.