Prediction of second-order nonlinear optical properties of Wells-Dawson polyoxometalate derivatives [X-C(CH2O)3P2M3′M15O59]6- (X = NO2, NH2, and CH3, M′ = V and Nb, M = Wand Mo)

The geometrical structures of Wells-Dawson derivatives [X-C(CH2O)(3)P2M'3M15O59](6-) (X = NO2, NH2, and CH3, M' = V and Nb, M = W and Mo) have been calculated by the density functional theory (DFT) method. The results show that the distances of P...P and P...C are controlled by the {M'(3)} triads, and {M'(3)} triads also affect the sizes of W-6 hexagonal belts. The second-order polarizabilities and origin of nonlinear optical (NLO) properties of those clusters have been investigated by a time-dependent density functional theory (TDDFT) method. The NLO property analysis reveals that [X-C(CH2O)(3)P2V3Mo15O59](6-)(X = NH2) anions have the largest beta(vec) values, 75.064 x 10(-30) esu. Grafting electron donors to POM clusters is an efficient way to improve the NLO response. The major electron transition orbitals show that the charge transfer from the organic groups to the metal atoms is responsible for the NLO properties of these polyoxometalates.