Discrimination between Conglomerates and Pseudoracemates Using Surface Coverage Plots in 2D Self-Assemblies at the Liquid-Graphite Interface.

The two-dimensional (2D) molecular ordering of two photochromic diarylethenes was investigated using scanning tunneling microscopy at the liquid-graphite interface. The racemic mixture of the closed-ring isomer of one of the diarylethenes showed spontaneous separation of its enantiomers upon 2D crystallization, whereas that of the other diarylethene formed a pseudoracemic crystal in which two enantiomers coexist in a 2D ordering domain. The mixing of enantiomers in 2D assemblies can be analyzed by the dependence of the surface coverage on the concentration of enantiomers at different enantiomeric ratios.