Synthesis and photochromic behavior of 1,2-bis(1,3-dimethylindol-2-yl)cycloalkenes

Two novel 1,3-bis(1,3-dimethylindol-2-yl)cycloalkanes(2) were designed and synthesized by intramolecular coupling reaction using low-valance titanium as catalyst. Photochromic properties of these compounds were initially inve stigated. The results show that the thermal stability of colored form of 2 is much better than that of 1,2-bis(1-ethyl-2-methylindol-13-yl)cycloalkene s(4), and the absorption maximum of them is shorter than that of 1,2-bis(1- ethyl-2-methylindol-3-yl)cycloalkenes.