The Open and Closed Forms of a Perfluoro Diarylethene Photoswitch─Halogen Bonding, Network Topology, and CSD Analysis

Journal article, 2024

The structure of the perfluoro cyclopentene diarylethene photoswitch 3,3′-(perfluorocyclopent-1-ene-1,2-diyl)bis(2-ethyl-6-iodobenzo[b]thiophene 1,1-dioxide) (C25H16F6I2O4S2) 1 at 100 K has a tetragonal (I41/a) symmetry. The compound has a halogen-bonded network structure described by the uninodal five-connected joa net. This net is related to another uninodal six-connected net sfo. Analysis using the Cambridge Structural Database (CSD) shows that the majority of structures with the perfluoro cyclopentene diarylethene motif, >85%, have a C···C distance of around 3.5 Å where a new single bond will develop during photoswitching, whereas compound 1 falls in a second smaller category with C···C distances of around 4.2 Å. The photochemical reaction of 1 under UV light in ethanol gave a closed form that crystallized as ethanol solvate 2a in the P21/c space group, and recrystallization in acetone gave the nonsolvated form 2b crystallizing in the space group Fdd2. We did not observe, and do not believe that it is possible, to photoswitch 1 in the solid state as the C···C distance where a new single bond will develop is very long.