3RD-ORDER NONLINEAR-OPTICAL POLARIZABILITY INDUCED BY REAL ELECTRONICEXCITATIONS IN TRANSITION-METAL DIIMINE AND DITHIOLENE COMPLEXES

The organo-transition metal complexes (Ni or Pt)bis(3,4-toluenediimine ), Ni-bis(3,4-benzophenonediimine) and Ni-bis( 1-phenyl-2-bulyl-1,2-di thiolene), which are generally considered to be good candidates for th ird order nonlinear optical (NLO) applications, have been examined by sub-picosecond induced transparency measurements. The electronic decay times are around 2 ns for each of the compounds, while the orientatio nal relaxation happens in the 100 ps range. High third order NLO param eters have been previously reported from degenerate four wave mixing e xperiments, but not confirmed by several other techniques. This dispar ity in results is clarified here in terms of noninstantaneous contribu tions from real electronic excitations.