Synthesis and photochromism of isomeric unsymmetrical diarylethenes bearing both naphthalene and thiophene moieties

Three new isomeric unsymmetrical diarylethenes bearing both naphthalene and thiophene moieties were synthesized. Their photochromism, fluorescence and electrochemistry properties were investigated in detail. Each of the diarylethene derivatives showed notable photochromism and functioned as an effective fluorescent switch both in solution and in PMMA films. The cyclization quantum yield and the molar absorption coefficients of both the open- and closed-ring isomers were found to decrease based on the position of the chloro substituent attached to the terminal benzene ring as follows: para- > meta- > the ortho-position. Consequently, the cycloreversion quantum yield would increase para- to meta- to ortho-chloro substitution. When compared with the unsubstituted parent compound, the presence of the chloro substituent on the terminal benzene ring of these diarylethenes, regardless of the substitution position, would considerably lower the band gaps of the open- and closed-ring isomers. Our results indicated that the chlorine atom and its substitution position have significant influence on the optical and electrochemical properties of the diarylethenes bearing a naphthalene moiety.