“…The design and synthesis of new photochromic diarylethene compounds is an area of intense research because of their widespread potential application as optical memories and photoswitches (Pu, Li et al, 2006;Pu, Yang et al, 2006;Pu, Zheng et al, 2006) and their good thermal stability and fatigue resistance (Irie, 2000;Tian & Yang, 2004;Morimoto et al, 2006). For further background information, see Pu, Yang et al (2005).…”