2-PHOTON ABSORPTION-SPECTRA OF LUMINESCENT CONDUCTING POLYMERS

We report the two-photon absorption (TPA) spectra of poly(2,5-dibutoxy -p-phenylene acetylene) (PPA-DBO), poly(2,5-dioctyloxy-p-phenylene vin ylene) (PPV-DOO), and poly(3-hexylthiophene) (PAT6) in the spectral ra nge extending from 576 nm to 846 nm. Using the Z-scan technique on the polymers in solution, we measured a strong two-photon allowed transit ion in all three materials which we attribute to the mA(g) essential s tate. The mA(g) in all three polymers occurs at, approximately, 1.2 ti mes the optical bandgap, E-g [E(1B(u))]. The excitonic nature of the A (g)-character states is indicated by the lack of a TPA band at or near E-g. Calculated chi((3)) spectra, using the mAg state, two additional states above the 1B(u) exciton, and a lineshape function to account f or chain length distribution, exhibit the same spectral features obser ved in the TPA spectra.