Photochromic behaviour of six pyrryl substituted fulgides and one fulgimide has been examined. The substituents have significant effects on their photochromic processes. The results of steady state kinetics show that the photodecoloration of the colored form, 7,7a-dihydroindole derivatives (II) follows the first-order kinetics. The substituents have certain effects on the rate constant of the photodecoloration. As for the colored form (II), compounds with the substituent at 2- or 3-position 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 donating substituent into the 2- or 3-position leads to bathochromic shift of the maximum of absorption (λmax) of 7,7a-dihydroindole derivatives. For example, the λmax of compound II 7 is 720 nm in acetonitrile. The increasing of the polarity of the solvent caused a remarkable bathochromic shift of λmax of the
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