Optical Kerr Effect for Asymmetric Pentaazadentate Macrocyclic Metal Complexes

Asymmetric pentaazadentate macrocyclic metal complexes consist of pentaazadentate ligand containing 18 ~22π electrons, which coordinate with numerous metal ions to form near coplanar configuration with expanded π-electron delocalization, and are easy to be modified, in which a great deal of derivatives with versatile properteis including excellent thermal and light stabilities can be obtained by changing the central metal ions and the peripheral substituents of the ligand, therefre, they can be used as organic nonlinear optical materials with fast response for the potential application, such as all optical switching, optical power limiting and so forth. The time-resolve optical Kerr response signals were measured by using pump-probe method of femetosecond pulses laser for nine pentaazadentate macrocyclic metal complexes in methanol. Their third-order optical nonlinear polarizabilities X₁₁₁₁³=1.19~3.38×10^-13 esu were obtained, from which the molecuar second order hyperpolarizabilities γ₁₁₁₁=8.0 × 10^-32~2.83 × 10^-31 esu wer calculated and their response times of optical Kerr effect were about 165 fs.The linear correlation between the molecular second-order hyperpolarizabilities γ₁₁₁₁ and Hammett substituent constants of complexes was obtained with correlation coefficient 0.97, which shown the peripheral substituents centre metal ions and the conjugated π electrons to influence the third-order optical nonlinearities of the complexes, which arised from the excited state population.