Photochromism of fulgenates possessing crown-ether moiety

Three indolylfulgenates possessing diesters of 14-crown-4 (2). 17-crown-5 ( 3), and 20-crown-6 (4) groups were synthesized and their photochromic behav iors in the presence or absence of alkali metal cations (Li+, Na+, K+) were investigated. Notable features are: (1) The association constant of Na+ wa s the largest for 3, and that for K+ was the largest for 4, (2) The associa tion of E- and Z-forms are stronger than C-form. (3) In the cases of Na+-3 and K+-4, no photocoloration occurred. (4) As for the photochromism of 2, n o effects of alkali metal species were observed. These phenomena were eluci dated by molecular mechanics calculations.