Abstract

Since the development of preparative scale syntheses of the fullerenes,¹ we have examined the nonlinear optical (NLO) properties of C₆₀ in the solid state.²-⁴ Following the characterization of solid films of pure C₆₀, we have explored means of altering the optical and NLO properties of this molecule via chemical modification including photopolymerization, oxygen doping, and the creation of charge transfer (CT) complexes in both the ground and excited states.⁵-⁷ Studies on solutions of C₆₀ with the electron donor, N,N,N′,N′-tetramethyl-1,4-phenylene-diamine (TMPD) revealed the formation of a 1:1 CT complex where C₆₀ acted as the acceptor. NLO studies conducted on solutions of C₆₀/TMPD at 675 nm (near the λ_max of the CT absorption) showed a great enhancement in the third-order optical susceptibility, ${\text{χ}}_{xxxx}^{(3)}$, of the complex relative to C60 Direct optical excitation in the CT band accessed higher-lying excited states with larger absorption cross-sections than the ground state, which contributed to the enhanced NLO response observed for the TMPD:C₆₀ complex.⁵

© 1995 Optical Society of America