ELECTRONIC EFFECTS OF SUBSTITUENTS ON INDOLE NITROGEN ON THE PHOTOCHROMIC PROPERTIES OF INDOLYLFULGIDES

The attempt to synthesize N-p-tolylsulfonylindolylfulgide by Stobbe co ndensation was unsuccessful because hydrolysis of the Stobbe-condensat ion product eliminated the sulfonyl moiety to give, after several step s, the N-unsubstituted fulgide. Pd(II)-catalyzed carbonylation of 2-bu tyne-1,4-diol derivative bearing the N-p-tolylsulfonylindole, however, afforded the desired N-p-tolylsulfonylindolylfulgide. A comparison of absorption spectroscopic and photochromic properties of these fulgide s with those of the known N-methylindolylfulgide gave the following re sults. The electron-withdrawing substituent on nitrogen (i) shortened the absorption maximum of the colored form, (ii) suppressed thermal E- Z isomerization, and (iii) enlarged quantum yields of photochromic rea ctions.