Efficient enhancement of second order nonlinear optical response by complexing metal cations in conjugated 7-substituted coumarin

Most of the coumarins have been found useful as non-linear optical chromophores. The four novel watersoluble coumarin-based compounds (006, NC6, 007, and NC7) and the metallic compounds of NC7 with different metal cations (Na+, K+, met Ca2+, Fe2+, and Zn2+) have been investigated by carrying out density functional theory (DFF). Our DFT calculations revealed that the second-order nonlinear optical properties have a pronounced enhancement by means of the introduction of it-conjugatd electron donor (dimethylamino phenyl alkynyl) in 7-position of the coumarin ring and metal cations, especially for transition metals. The further investigations of the larger first hyperpolarizability (atot) reveal that the NC7*Fe2+ and NC7*Zn2+ present the larger values as 1.151 x 10(-27) and 1.083 x 10(-27) esu owing to the lower transition energies and larger oscillator strengths of crucial electronic transitions. Moreover, time dependent DFF results show that the large intramolecular charge transfers exist in the NC7*Fe2+ and NC7*Zn2+. In addition, the natural bond orbital analysis demonstrated that the second-order stabilization energies is from the lone pair (LP) orbital on 0 atom to the LP* orbital of metal cations interaction correlate with the O-M} atomics distance. On the other hand, the atoms in molecules analysis showed that the O-Mn+ interactions can be characterized by the presence of a bond critical point (BCP) and the OFe2+ and O-Zn2+ interactions have partially ionic and partially covalent bonds rather than an electrostatic character for O-Mn+ (Na+, K+, Mg2+ and Ca2+). In addition, the delocalization indices of O-Mn+ bonds correlate reasonably well with electron density, kinetic and potential energy densities in these complexes. Thus, we hope this research will introduce a new relation between the structure and the property of chromophore nonlinear optical activity. (C) 2017 Elsevier B.V. All rights reserved.