Tuning Second-Order Non-linear (NLO) Optical Response of Organoimido-Substituted Hexamolybdates through Halogens: Quantum Design of Novel Organic-Inorganic Hybrid NLO Materials

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The second-order non-linear optical (NLO) response of organoimido-substituted hexamolybdates has been tuned from 218.61 × 10–30 to 490.10 × 10–30 esu. The dipole polarizabilities and second-order nonlinear optical (NLO) properties of organoimido derivatives of hexamolybdates have been investigated by using the time-dependent density functional response theory (TDDFT). The electron withdrawing ability of F (fluorine) has played an important role in tuning the second-order NLO response in this class of organic-inorganic hybrid compounds; particularly system 6 [Mo6O18(NC16H8F2(CF3)2I)]2– with the static second-order polarizability (βvec ) computed to be 490.10 × 10–30 esu. Thus, our studied systems have the feasibility to be excellent tuneable second-order NLO materials. The analysis of the major contributions to the βvec value suggests that the charge transfer (CT) from POM to organic ligand (D-A) along the z-axis has been enhanced with addition of F atoms at the end phenyl ring which directs head (POM) to tail (fluorinated ring) charge transfer. The computed βvec values have been tuned by incorporation of different halogen atoms at the end phenyl ring of organoimido segment. Furthermore, substitution of two trifluoromethyl (–CF3) groups sideways along with iodine (I) at the terminus of end phenyl ring in the organoimido ligand has a striking influence on tuning the optical non-linearity, as CT from POM to the organoimido ligand was significantly increased. These systematic small changes in molecular composition by substitution of different halogen groups leads to a tuning the NLO response; the so-called ‘ripple effect’ catches this point nicely. Thus, the present investigation provides thought provoking insight into the tuneable NLO properties of organoimido-substituted hexamolybdates.