PHOTOCHEMICAL HOLE BURNING OF TETRAPHENYLPORPHIN IN AN AROMATIC POLYIMIDE

Photochemical hole burning (PHB) was performed in free-base tetraphenylporphin (TPP) doped into an aromatic polyimide (PI). The microscopic ordered structure of PI, low energy excitation modes, and thermal stability of a hole burnt at 4.2 K were studied with the PHB measurements. Low energy excitation modes reflected microscopic ordered structure. Thermal stability of a hole showed little dependence on the ordered structure. It could be interpreted that the structural relaxation leading to the instability of a hole is a larger scale relaxation than the low energy excitation modes. This interpretation is consistent with the fact that the thermal energy for annealing temperature (30-80 K) is larger than the low energy excitation modes (approximately 10 cm(-1)).