Prediction of remarkably large second-order nonlinear optical properties of organoimido-substituted hexamolybdates

The dipóle polarizabilities, dipóle moments, density of states, and second-order nonlinear optical (NLO) properties of organoimido derivatives of hexamolybdates have been investigated by using time-dependent density functional response theory. This class of organic-inorganic hybrid compounds possesses remarkably large and eye-catching molecular second-order NLO response, especially [Mo₆O₁₇(NC₁₆H ₁₂NO₂)(FeNC₁₀H₉)]²(7) and [MO₆O₁₇(NC₁₆H₁₂NO ₂)(NC₆H₂(NH₂)₃)] ²- (6) with static second-order polarizability (c_vec) computed to be 15766.27 × 10^-30 esu and 6299.59 × 10 ^-30 esu, respectively. Thus, these systems have the possibility to be excellent second-order nonlinear optical materials. Analysis of the major contributions to the β_vec value suggests that the charge transfer (CT) from polyanion to organic segment (D-A) along the z-axis plays the key role in NLO response; the polyanion acts as a donor (D) whereas organoimido acts as an acceptor (A) in all the studied systems. The computed β_vec values increase by incorporation of an electron acceptor (-NO₂) at the end of the phenyl ring of the organoimido segment. Furthermore, substitution of amino (-NH₂) or ferrocenyl (-FeC ₁₀H₉) at the outer side of polyanion and an electron acceptor (-NO₂) at the end of the phenyl ring in organoimido segment simultaneously is more important to enhance the optical nonlinearity. Orbital analysis shows that the degree of CT between the polyanion and organoimido segments was increased when ferrocenyl donor was introduced. The present investigation provides important insight into the remarkably large NLO properties of organoimido-substituted hexamolybdates.