Figure 6.

Mechanism for photocrosslinking of PEMAA modified with 3-hydroxypropyldimethylmaleimide. Upon excitation to the bright singlet state some population is transferred to the triplet state by intersystem crossing. Electron transfer leads to quenching of the triplet population and allows spectroscopic identification of the maleimide anion. Photocrosslinking occurs by recombination of the ions to the dimer. Our spectroscopic results do not exclude a parallel reaction path via direct cross linking of favorably oriented maleimides in the excited singlet state, see text. Transient species which were detected spectroscopically (triplet state, radical anion) are marked in green.