Reversible surface morphology changes of a photochromic diarylethene single crystal by photoirradiation

The surface morphology of a diarylethene single crystal [1,2-bis(2,4-dimeth yl-5-phenyl-3-thienyl)perfluorocyclopentene determined by atomic force micr oscopy changed reversibly upon photoirradiation, The crystal underwent a th ermally irreversible but photochemically reversible color change (colorless to blue) upon alternate irradiation with ultraviolet (wavelength lambda = 366 nm) and visible (lambda > 500 nm) Light that drove reversible photocycl ization reactions, Upon irradiation with 366-nm Light, new steps appeared o n the (100) single-crystalline surface that disappeared upon irradiation wi th visible Light (lambda > 500 nm). The step height, about 1 nm, correspond s to one molecular Layer. Irradiation with 366-nm light formed valleys on t he (010) surface that also disappeared by bleaching upon irradiation with v isible Light (lambda > 500 nm). The surface morphological changes can be ex plained by the molecular structural changes of diarylethenes regularly pack ed in the single crystal. These crystals could potentially be used as photo driven nanometer-scale actuators.