Quantum Chemical Design for Enhanced Second-Order NLO Response of Terpyridine-Substituted Hexamolybdates

A dramatic increase in the second-order nonlinear optical (NLO) response of terpyridine-substituted hexamolybdates has been observed from 886.55 × 10 -30 esu (system 1) to 4622.92 × 10 -30 esu (system 7). The dipole polarizabilities and second-order nonlinear optical (NLO) properties of terpyridine derivatives of hexamolybdates have been investigated by using time-dependent density functional theory (TDDFT). The quantum mechanical design suggests that [Mo 6 O 18 (N 4 C 25 H 14 (CF 3 ) 2 (CN) 2 )] 2- (system 7) is the best choice among all studied systems to improve nonlinearity. The electron-withdrawing ability of electron-acceptor groups (F, CI, Br, I, CF 3 , and CN) at the end of the terpyridine ligand directs the charge transfer (CT) from the POM cluster to the terpyridine segment along the z axis, which leads to an efficient second-order NLO molecular design. These small changes in molecular composition by substitution may have disproportionately huge effects on the NLO properties, which can be attributed to the so-called "butterfly effect".