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 (1) and its sulfone derivative 1-(2-methoxycorannulenyl)-2-(1,1-dioxide-2-methyl-5-phenyl-3-thienyl)-perfluorocyclopentene (2). These compounds are compared with our previously reported compound 1,2-bis-(2-methoxycorannulenyl)-perfluorocyclopentene (3). Both 1 and 2 exhibited photochromic color changes with photochemical quantum yields of 0.44 (cyclization) and 0.025 (cycloreversion) for 1 and 0.54 (cyclization) and 0.034 (cycloreversion) for 2. The open-ring isomers, 1o and 2o, displayed fluorescence at room temperature, which is attributed to locally excited (LE) and intramolecular charge transfer (ICT) states, respectively. Whereas the closed-ring isomer 1c exhibited no fluorescence, 2c showed orange fluorescence at 615 nm with a fluorescence quantum yield of 0.010 indicating fluorescence wavelength switching. Furthermore, 1o and 3o exhibited phosphorescence at 80 K in 2-methyltetrahydrofuran (2-MTHF) promoting a phosphorescence switching nature, while 2 o /2c 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.