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The spirocyclic compounds bis[2`,3`-bis(methoxycarbonyl)-5`,6`,6`-trimethylspirofluoren-9,4`-(1`-aza-2`-cyclopentene)][1`,5`-a]indolino[4,5-e]indoline and bis[2`,3`-bis(methoxycarbonyl)-5`,6`,6`-trimethylspirofluoren-9,4`-(1`-aza-2`-cyclopentene)][1`,5`-a]indolino[7,6-g]indoline exhibit photochromic properties with various half-lifes. The AM1 method was used to correlate the structural and electronic properties, on the one hand, and photochromic properties, on the other, and to explain reasons for the difference in the photochromism of the two compounds.