Effective conjugation length and UV/vis spectra of oligomers

On the basis of an extended series of monodisperse oligomers of the dialkoxy-substituted phenyleneethenylenes 1a–i the Eqs. (3) and (4) were conceived in order to determine the limiting values of the energies E_i and the wavelengths λ_i of the UV/vis absorption. The convergence of the E_i, and λ_i values with a growing number n of repeating units permits a precise prediction of the E_i,∞ and λ_i,∞ values of the corresponding polymer 1j as well as a statement about the overall effect of conjugation ΔE_i and the effective conjugation length ECL. A great variety of different conjugated oligomers 2–14 can be evaluated by the same algorithm.