Photoacoustic study of the photochemistry of adsorbed indigoid dyes

Abstract

The photochemistry of thioindigo, 6,6'-diethoxythioindigo, and N,N'-diacetylindigo adsorbed on alumina has been investigated. The results are compared with those obtained in solution. Unsubstituted thioindigo can be isomerized at the surface. In contrast to the findings in solution the cis isomer is stabilized at the surface and cannot be backconverted. If thioindigo is substituted in 6,6'-positions, only the trans form is found in the surface spectrum, and no trans ? cis photoisomerization is observed. The results on N,N'-diacetyl-indigo indicate that this compound decomposes at the surface. The spectrum obtained is identical to that of indigo.