Large negative hyperpolarizabilities (beta) of the protonated Schiff basesof the azulenic retinal analogues

The molecular first hyperpolarizabilities (beta) and electronic properties of some azulenic retinal analogues and their derivatives have been investig ated theoretically by employing semiempirical approaches. The results indic ate that the protonated Schiff bases (PSB) of the 2-substituted azulenic re tinal analogues possess extremely large negative beta values and very good transparency. These can be attributed to the large difference between the g round state dipole moment and the first excited state dipole moment accordi ng to the electronic property analysis. The characteristic blueshifted abso rption in polar solvents of the 2-substituted PSB chromophores can be well explained by the negative solvatochromic effects. The largest calculated \ mu beta \ value can reach the magnitude of 10(-44) esu, which is close to t he highest reported values of synthesized chromophores.