Photochromic diarylethene derivatives 1o–6o bearing long alkyl chains (⩾ seven carbon atoms) have been synthesized and their structures with the exception of compound 3o have been determined by single-crystal X-ray diffraction analysis. The effect of alkyl chain length on their properties, including photochromism both in solution and in PMMA film and their electrochemical properties were investigated in detail. All of these diarylethenes showed ...