The self-assembly and photo-induced structural transformation of a diarylethene derivative 1,2-bis(3,5-dimethyl dithioene [3,2-6:2',3'-d]thiophene-2-yl) perfluorocyclopentene (BDDTP) have been investigated by cyclic voltammetry and electrochemical scanning tunneling microscopy (EC-STM) on a Au(1 1 1) substrate. BDDTP was found to form two ordered adlayer structures on Au(1 1 1) surface. STM observation revealed that the original ordered structures transformed into disordered adlayers after ex situ and in situ ultraviolet (UV) irradiation. Such a dramatic difference in the self-assembly behavior of BDDTP before and after UV irradiation results from the conformational transformation induced by photo-irradiation and the associated molecule-substrate interaction change. The result provides useful information to understand the self-assembly behavior and photochromic reaction of diarylethenes compounds on solid supports. (C) 2010 Elsevier B.V. All rights reserved.