Third-order nonlinear optical properties of sulfur-rich compounds

The molecular third-order optical nonlinearity gamma(R) (second hyperpolari zability or nonlinear refractive index) was measured for a series of sulfur -rich molecules: sulfur (Ss), carbon-sulfur compounds, and metal thiolate c lusters. Z-scan techniques (pulse width 27 ps, wavelength 527 nm) were used to measure these properties in solution by comparing the solution to the p ure solvent. Our approach is an efficient way to evaluate a number of diffe rent compounds and to quickly direct synthetic strategies for improved nonl inear and linear optical properties. The optical nonlinearities were evalua ted in terms of figures of merit, \W\I-0 and [T](-1), where \W\I-0 is the r atio of nonlinear refraction to linear absorption and [T](-1) is the ratio of nonlinear refraction to nonlinear absorption. Among the carbon-sulfur co mpounds, C6S8O2 had the largest figures of merit: /W/I-0 = 4.3 x 10(-13) m( 2) W-1 and [T](-1) > 5. The metal thiolate cluster with the largest second hyperpolarizability was [Zn10S4(SPh)(16)](4-) (gamma(R) = -7.8 x 10(-56) C m(4) V-3, -6.3 x 10(-31) esu). This cluster exhibited no measurable linear or nonlinear absorption, so the figures of merit were effectively infinite. Previous work on the second hyperpolarizability of sulfur-rich compounds e xamined species that were hampered by substantial linear absorption coeffic ients. The present work shows that high figures of merit can be achieved wi thout significant linear or nonlinear absorption.