A Semi-empirical Theory of the Conjugated Systems II. Bond Alternation in Conjugated Chains

The problem of the convergence of the absorption wave-lengths of chain conjugated systems, polyenes, and merocyanines, is discussed, by using the method developed in the previous paper. It is shown that the bond alternation as the cause of the convergence of the absorption wave-lengths, which has been presumed from the view of the resonance theory but cannot be deduced in terms of the ordinary molecular orbital theory, do actually occurs even for an infinite polyene chain, but the calculated limiting wavelength does not agree with the experiment quantitatively, possibly because of the coulomb attraction between the excited electron and the hole.