Subgap absorption and quantum lattice fluctuation in polymers: effects of the ground-state degeneracy

By using a simple model of soliton-antisoliton pairs to simulate the quantu m lattice fluctuations in one-dimensional conjugated polymers, the subgap o ptical absorption results from the transitions between the lowest unoccupie d and the highest occupied levels off the conduction and valence bands, res pectively, in the soliton-antisoliton excitations. There is no gap in the a bsorption induced by the quantum fluctuation It is shown that the ground-st are nondegeneracy suppresses the quantum fluctuations, so that the subgap a bsorption is reduced and then there appears a clear onset in the absorption spectrum of nondegenerate polymers. The result is in good agreement with e xperiments. (C) 2001 Elsevier Science B.V. All rights reserved.