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Optical absorption spectrum of polydiacetylene (PDA) crystalline films shifts toward higher energies as irregularity in molecular ordering is increased. We view this behavior in terms of the reduced overlap of conjugated π-electron wave function among one-dimensional PDA molecular wires. This point is further discussed by using the Kronig–Penney model, in which the influence of irregularity in molecular ordering is assessed in terms of a change in the intermolecular distance which in turn shifts the fundamental absorption edge.

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