Photochromic Diarylethenes with a Curved Aromatic Corannulene Unit

We report new photochromic diarylethenes incorporating a curved aromatic corannulene unit as a side aryl group: 1-(2-methoxycorannulenyl)-2-(2-methyl-5-phenyl-3-thienyl)-perfluorocyclopentene (<b>1</b>) and its sulfone derivative 1-(2-methoxycorannulenyl)-2-(1,1-dioxide-2-methyl-5-phenyl-3-thienyl)-perfluorocyclopentene (<b>2</b>). These compounds are compared with our previously reported compound 1,2-bis-(2-methoxycorannulenyl)-perfluorocyclopentene (<b>3</b>). Both <b>1</b> and <b>2</b> exhibited photochromic color changes with photochemical quantum yields of 0.44 (cyclization) and 0.025 (cycloreversion) for <b>1</b> and 0.54 (cyclization) and 0.034 (cycloreversion) for <b>2</b>. The open-ring isomers, <b>1o</b> and <b>2o</b>, displayed fluorescence at room temperature, which is attributed to locally excited (LE) and intramolecular charge transfer (ICT) states, respectively. Whereas the closed-ring isomer <b>1c</b> exhibited no fluorescence, <b>2c</b> showed orange fluorescence at 615 nm with a fluorescence quantum yield of 0.010 indicating fluorescence wavelength switching. Furthermore, <b>1o</b> and <b>3o</b> exhibited phosphorescence at 80 K in 2-methyltetrahydrofuran (2-MTHF) promoting a phosphorescence switching nature, while <b>2</b> <b>o</b> <b>/2c</b> did not. This difference can be rationalized by the LE character of the excited states and efficient intersystem crossing facilitated by the curved corannulene moiety.