SPECTRAL DISPERSION OF 3RD-HARMONIC GENERATION IN THIN-FILMS CONTAINING TRANSITION-METAL COMPLEXES

The optical third-harmonic generation technique has been used in a stu dy of several transition metal complexes having different near-infrare d (NIR) absorption features. The complexes were dispersed in polymer m atrices, and the molecular second hyperpolarizabilities gamma(3 omega; omega,omega,omega) were derived from thin film Maker fringe measuremen ts at 1064 and 1907 nm. Dispersion measurements of the complexes TBA[N i(dmit)(2)] and TBA[Pd(dmit)(2)], both having strong NIR transitions, were performed in the region from 1065 to 1480 nm, revealing resonance s in the NIR. For the TBA[Ni(dmit)(2)] complex a maximum gamma-value o f 20 x 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 p eak 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 gamma-value of the Pd-complex was more than 2.5 times that of the Ni-complex. The gamma-values were str ongly influenced by a number of resonances (one-, two-, and three-phot on resonances); however, no clear correlation with the near-infrared t ransition was observed.