Abstract
This short review outlines the main results obtained in the field of molecular materials based on zinc coordination compounds for second-order nonlinear optics. It presents an overview of the main classes of second-order nonlinear optical (NLO) active complexes bearing monodentate, bidentate, tridentate, or tetradentate π-delocalized ligands such as substituted stilbazoles, bipyridines, phenanthrolines, terpyridines, and Schiff bases. Macrocyclic ligands such as porphyrins and phthalocyanines are not covered. This paper shows how coordination to the Zn(II) center of π-delocalized nitrogen donor ligands produces a significant enhancement of their quadratic hyperpolarizability. Dipolar complexes are mainly presented, but octupolar zinc complexes are also presented. The coverage is mainly focused on NLO properties that are measured at the molecular level, working in solution, by means of the electric field-induced second harmonic generation (EFISH) or the hyper-Rayleigh scattering (HRS) techniques.
Highlights
Second-order nonlinear optical (NLO) coordination complexes are of great interest for nonlinear optics [1,2,3], mostly due to the unique characteristics associated with the metal center [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
They possess intense, low-energy metal-to-ligand charge-transfer (MLCT), ligand-to-metal charge-transfer (LMCT), or intraligand charge-transfer (ILCT) transitions, and the metal can act as a donor, acceptor, or polarizable bridge of a dipolar donor–π–bridge–acceptor system
The quadratic hyperpolarizability determined with an incident wavelength λ by the electric field-induced second harmonic generation (EFISH) and hyper-Rayleigh scattering (HRS) techniques will be indicated as βλ (EFISH) and βλ (HRS), respectively
Summary
Second-order nonlinear optical (NLO) coordination complexes are of great interest for nonlinear optics [1,2,3], mostly due to the unique characteristics associated with the metal center [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]. We report an overview on the dipolar and octupolar second-order NLO active zinc complexes bearing stilbazole, bipyridine, phenanthroline, terpyridine, or Schiff bases as ligands, focusing on the relevant aspects associated to each class of complexes. Macrocyclic ligands such as porphyrins and phthalocyanines are not presented, being already covered in excellent papers and reviews [15,19,26,27,28]
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