PHOTOCHROMIC REACTIONS OF PYRRYL SUBSTITUTED FULGIDES AND FULGIMIDES

Photochromic behaviour of six pyrryl substituted fulgides and one fulg imide has been examined. The substituents have significant effects on their photochromic processes. The results of steady state kinetics sho w that the photodecoloration of the colored form, 7,7a-dihydroindole d erivatives (II) follows the first-order kinetics. The substituents hav e certain effects on the rate constant of the photodecoloration. As fo r the colored form (II), compounds with the substituent at 2- or 3-pos ition have larger rate constants of the decoloration than those of non -substituted ones. The photocoloration reactions are more complicated and do not fit the simple kinetics. Introduction of the electron donat ing substituent into the 2 or 3-position leads to bathochromic shift o f the maximum of absorption (lambda(max)) of 7,7a-dihydroindole deriva tives. For example, the lambda(max) of compound II 7 is 720 nm in acet onitrile. The increasing of the polarity of the solvent caused a marka ble bathochromic shift of lambda(max) of the colored form, but the sol vent polarity has little effect on the absorption spectra of fulgides.