Photochromism of Spiropyrancarboxylic Acid and the Effect of Base on it

Abstract

Reverse photochromic 1, 3, 3-trimethylspiro indoline-2, 2'-benzopyran-8'-carboxylic acid (1) turned from the colored to the colorless state on the addition of NaOH. This change was considered to occur by neutralization of the carboxylic acid group of (Z) with NaOH which resulted in the unstabilization of the colered structure by destruction of hydrogen bonding.
In the presence of NaOH, two colored isomers, (Bt) and (B2), were separated spectroscopically after fiash irradiation on the colorless species (A') of (1). lncreasing the concentration of NaOH added, another colored species (Bs) was formed, its quantity being proportional to the concentration of NaOH excess to the amount ef spiropyran (1).
Two colored species (B') and (Bs) in neutral ethanolic solution, and another colered (B6) species in basic solution were feund also in the case of 6'-carboxylic acid derivatives (2), and its reaction scheme was discussed.
In the absence of NaOH, relative photo-coloration efficiency of (2) was larger in polar alcohlic solvents than in nonpolar solvents. lt increased on the addition of NaOH. These results show great influences of the dissociative proton on cc. The effect of proton on co of C1 was also discussed.