Electronic structure of a glassy poly(9,9-dioctylfluorene) thin film determined using linear and nonlinear spectroscopies

The electronic structure of glassy thin films of poly(9,9-dioctylfluorene) (F8) has been studied by absorption, polarized absorption, two-photon absorption (TPA), and electroabsorption (EA) measurements. The TPA and EA spectra of F8 can be well reproduced by a sum-over-states calculation based on a four-level model in which a dipole-forbidden state is located between two dipole-allowed states. The electronic structure of F8 has many features in common with those of other pi-conjugated polymers; the main difference in the electronic structures is in the properties of the fourth level. Photocurrent measurements revealed that the fourth level is also the lowest charge separation state in F8.