A photochromic diarylethene with N,N-dimethyl substituted group 1a was prepared. 1a showed ring-opening and ring-closing photoisomerization with UV/vis light irradiation. Treatment of 1a with CF3COOH produced a protonated diarylethene 1aH. With UV light irradiation, 1aH photoconverted to protonated ring-closed isomer 1c, which is photoinactive. It is found that 1c is hydrophilic and 1aH is hydrophobic.