Spectral Dispersion of Third-Harmonic Generation in Thin Films Containing Transition Metal Complexes

The optical third-harmonic generation technique has been used in a study of several transition metal complexes having different near-infrared (NIR) absorption features. The complexes were dispersed in polymer matrices, and the molecular second hyperpolarizabilities γ(3ω;ω,ω,ω) were derived from thin film Maker fringe measurements at 1064 and 1907 nm. Dispersion measurements of the complexes TBA[Ni(dmit)2] and TBA[Pd(dmit)2], both having strong NIR transitions, were performed in the region from 1065 to 1480 nm, revealing resonances in the NIR. For the TBA[Ni(dmit)2] complex a maximum γ-value of 20 × 10-33 esu was observed at approximately 1325 nm, red-shifted by 172 nm (0.14 eV) compared with the position of the NIR absorption peak at 1153 nm. For the TBA[Pd(dmit)2] complex the exact location of the resonance could not be determined definitively but was shifted to or even beyond 1480 nm. The maximum γ-value of the Pd-complex was more than 2.5 times that of the Ni-complex. The γ-values were strongly influen...