Triplet energies of pi-conjugated polymers

Using pulse radiolysis and triplet energy transfer has enabled us to measur e the triplet energies in a broad range of different pi -conjugated polymer s. In all eases we find that the 1(3)B(u) is Of order 0.6 to 1 eV below the 1 B-1(u), indicative of localized triplet states with strong electron-elec tron correlation. We also observe that the 1(1)A(g)-1(3)B(u), gap decreases linearly as the I(1)A(g)-1(1)B(u) gap decreases even though polymers with very different structure have been studied. This surprising result suggests that polymers with singlet gap <1.3 eV will have a triplet ground state.