Nonlinear harmonic generation

LeBozec and co-workers have reported nonlinear behavior in a series ofterpyri-dyl and dipicolinic acid complexes, with further studies on these complexes by Maury and co-workers [83, 84]. Their research was on new molecular materials for optoelectronics, with studies based on octupolar nonlinear optical molecules showing that molecular quadratic hyperpolarizability values were strongly influenced by the symmetry of the complexes [85]. Other studies on organic-lanthanide complexes with nonlinear optics have also reported second- and third-harmonic generation behavior with simultaneous multiphoton absorption properties [50]. Such studies have shown the importance of coordination chemistry as a versatile tool in the design of nonlinear materials. 

The primary objective of this section is to show the importance of lanthanides to nonlinear harmonic generation. This work, which is unpublished, evolved from earlier studies that have shown the correlation of nonlinear optical effects in dipolar and octupolar compounds which involve the use of one or more electron-donating groups connected via a conjugated tt-linker to an electron acceptor group. 

The first half or more of the series, known as the early and mid-lanthanides (La-Tb), are referred to here as type I the later or second half of the lanthanide period (Dy-Lu), and also for Y complex, are known as type II. The type I complexes all have larger ionic radii (1.10—1.22 A) than type II, which are typically between 0.92 and 0.97 A. The size of the metals was found to govern their coordination to the cinnamic acid, thus giving rise to the two different coordinations and space 

The lanthanide complexes measured here were measured in the solid state due to the effect of the polymeric nature of the complexes, which reduced their solubility in virtually all solvents, with limited solubility shown in dimethyl sulfoxide. 

To condude, it is recognized that electronic and geometric parameters both affect the nonlinear activity however, for lanthanide complexes the electronic parameters have been to date been found to be more significant for the nonlinear activity in second-harmonic generation. Such a hypothesis is outlined by previous studies by other groups on direct f electron contributions and by this work, which suggests that the number of unpaired electron can act as an additional factor 

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Multiphoton Processes and Nonlinear Harmonic Generations in Lanthanide Complexes... 

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