Abstract
The role of lateral terminal (X2 and X3) and terminal (X1) positions of aryl ring on the second-order nonlinear optical (NLO) properties of arylimido derivatives of hexamolybdates have been examined by using time-dependent density functional response theory (TD-DFT). This group of organic-inorganic hybrid compounds holds considerable large molecular second-order NLO response, especially [Mo6O18 (NC6H2 (NH2)3)]2- (system 4) with the static secondorder polarizability (βvec) computed to be 4406.60 au. Hence, [Mo6O18 (NC6H4NH2)]2- (system 2) and [Mo6O18 (NC6H2 (CH3)2 NH2)]2- (system 3) have also possibility to be good second-order nonlinear optical materials as compared to [Mo6O18 (NC6H5)]2- (system 1). The study of the major contribution to the βvec value suggests that the charge transfer from arylimido to molybdate (D – A) along the z-axis plays an important part in the NLO response, arylimido acts as a donor (D) whereas molybdate (POM-cluster) acts as an acceptor (A) in all the studied systems. The computed βvec values increase by incorporation of an electron donor (-NH2) at the terminus of phenyl ring. Moreover, substitution of amino (-NH2) at the lateral terminal positions and the terminus of aryl ring is simultaneously dominant to increase the optical nonlinearity. The present exploration offers significant physical insight into the considerable large NLO properties of arylimido substituted hexamolybdates.
Keywords: Polyoxometalates, inorganic-organic hybrid composites, second-order polarizability, charge transfer, density functional calculations (DFT), Aryl Ring, second-order nonlinear optical, arylimido, (POM-cluster), Si-O bonds, zero-order regular approximation (ZORA), generalized-gradient approximation (GGA), sum-over-states (SOS), HOMO-LUMO energy gap, hexamolybdates
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