Charge recombination of electron-cation pairs formed in polymer solids at 20 K through two-photon ionization

The charge recombination at 20 K of a photoejected electron with the parent dopant cation formed in polymer solids through two-photon ionization was examined in terms of long-range electron transfer by electron tunneling. The decay kinetics of isothermal luminescence (ITL) was quantitatively compared with that of the radical cation observed directly by absorption spectroscopy. The comparison showed good agreement for polystyrene but not for poly(alkyl methacrylate)s, which are classified as scission type polymers to high energy radiation. In the latter case, the decrease in radical cations observed at 20 K by absorption measurement was less than that expected from the ITL decay. This disagreement suggests that photoejected electrons in poly(alkyl methacrylate)s are captured in a chemical trap as well as in a physical trap even at 20 K. An electron in a physical trap participates in the charge recombination and emits ITL, but that in a chemical trap does not.