Excited-state enhancement of the third-order optical nonlinearity of a square planar complex

Abstract

Excited-state enhancement of the third-order nonlinear optical susceptibility of a square planar complex, (2,2′-bipyridine)Pt(1,2-dicyano-1,2-ethylene-dithiolate), was observed when the sample was optically pumped by either a picosecond or a nanosecond pump beam of 355 nm wavelength. For the picosecond case, the temporal behavior of the enhancement was investigated, and found to be characterized by a slow and a fast components, which are attributed to populations of the first excited state S 1 and the second excited state S 2, respectively. For the nanosecond case, the enhancement of the nonlinearity is attributed predominantly to the population of the first excited state S 1. The molecular hyperpolariabilities of the S 1 state and the S 2 state, γ S1 and, γ S2, were determined to be 1.9 × 10 −31 and 1.0 × 10 −30 esu, respectively, which are much larger than the γ 8 of the ground state ( γ g < 5.6 × 10 −33 esu).