Theoretical chemical study on NLO properties of polypyridinopyridine and its derivatives

With quantum chemical PM3/FF method, effects of strucure and substituents -NO2 and -NH2 on nonlinear optical properties of polypyridinopyridine(PPY) were discussed. The results showed that the beta and gamma values were -5.54 x 10(-29) esu and -1.544 x 10(-32) esu, respectively. In three stable structures of equal-bond length structure (a), cis-structure (b) and trans-structure (c), the beta and gamma values of(a) and (c) is larger than (b). More specially, beta and gamma values of (c) increased promptly as the number of repeat unit increased. When the number of unit was over four, (c) gave the biggest beta and gamma. In structures of PPY substituted by NO2 and NH2, the effects of pull-push electron and pi -electron delocalization became stronger, beta increased effectively to about 1.6 x 10(-27) esu. PPY is a promising candidate of nonlinear optical (NLO) materials.