Knowledge Bank

Recently, Akiyama and Nakagawa reported that in $1,1\prime$-dianthrylpoly-ynes, $C14H9-(C\equiv C)n-C14H9$, a fine linear relation was obtained by plotting the absorption maxima, $\lambda max$, of the longest wavelength absorption band against $n2(\lambda max\propto n2)$, which forms a striking contrast with a well known relation that in the series of polyenes and poly-ynes the square of $\lambda max$ varies linearly with the number of the conjugated multiple bonds $(\lambda max2\propto n)$. In order to elucidate this interesting relation, we have carried out some MO calculations on the electronic structures of 1,$1\prime$-dianthrylpoly-ynes. According to the present theory the existence of $\lambda max\propto n2$ relation indicates that the contribution of ionic configuration to the ground state of 1, $1\prime$-dianthrylpoly-yne should linearly increase with increasing the number of triple bonds, n. The electronic spectra of 9, $9\prime$-dianthrylpoly-ynes have also been studied theoretically.