| Abstract: | The photocleavage reaction of dimer model compounds of photosensitive polyimides having cyclobutane rings in the main chain was studied. Efficient photocleavage was observed for the dimer models (CBAM2, CBAM4, and CBPM2) which had an electron-donating aromatic substituent at the electron-accepting imide group. On the other hand, the cleavage quantum yield was nearly zero for a dimer (CBCM2) which had a cyclohexane substituent instead of the aromatic ring. Solvent polarity effects on the cleavage quantum yield revealed that these dimers gave the largest photocleavage efficiency in medium-polar solvents. The transient absorption band of the excited triplet of CBPM2 was effectively quenched by oxygen, whereas no oxygen quenching was observed for the cleavage quantum yield. This leads to the conclusion that the cyclobutane ring in the polyimide is photocleaved via the excited singlet intramolecular CT state. |
