Molecular reorientation studies of ultra-violet light irradiated photosensitive polyimide films using two-dimensional infrared correlation spectroscopy

An organic solvent-soluble photosensitive polyimide (PSPI), bearing a cinnamate photoreactive moiety in its side group, was synthesized. The photochemical reactions of the PSPI in the films were investigated in detail using both UV-vis and IR spectroscopy, confirming that the cinnamate chromophores underwent photodimerization. Ultra-violet (UV) light irradiation of the polyimide thin films induced molecular reorientation of the chromophores as well as the main chain units. The molecular motions of the main chain units were induced by photoreaction before those of the photoreactive side groups in the UV irradiated films. Photo-induced molecular reorientation occurred in the following sequence: main chain → photodimerization → cinnamoyl chromophores.