Tetrathienyl Corannulene Compounds with Highly Sensitive Photochromism.

We have designed and synthesized photochromic tetrathienyl corannulene compounds, 1,2,7,8-tetrakis(2-methyl-5-phenylthiophen-3-yl)corannulene (1) and 1,2,7,8-tetrakis(2,4-dimethyl-5-phenylthiophen-3-yl)corannulene (2), by fusing two units of photochromic terarylene with a curved aromatic corannulene with a promising antenna effect. Compound 1 exhibited highly sensitive photoreactivity, with a large molar absorption coefficient of 8.2×104  M-1 cm-1 and practically photon-quantitative photocyclization. On the other hand, a terarylene derivative with a planar aromatic phenanthrene, 9,10-bis(2,4-dimethyl-5-phenylthiophen-3-yl)phenanthrene (4) showed no photoreactivity. The reason for such a difference was attributed to the predominance of the photoreactive atropisomers amplified by energy migration, and the shortened distance between reactive carbons induced by the curved structure.