Second- and third-order nonlinear optical properties of multilayer and composite C60-based thin films

The nonlinear optical properties of C60-based composites and multilayered charge-transfer structures with 5,10,15,20-tetraphenyl-21H,23H-porphine (TPP) and 5,6,11,12-tetraphenylnaphthacene (rubrene) (TPN) acting as electron donors are studied by transverse optical second- and third-harmonic generation. The results are compared with those obtained on pristine and vacuum-photolyzed C60 thin films. Second-harmonic generation (SHG) is observed from composite films containing C60 molecules. A significant enhancement in SHG signal is observed in the multilayered structures. This result is interpreted in terms of a ground state permanent electron transfer from the electron-donating molecules to C60. The third-harmonic generation experiments show an enhancement of the cubic susceptibility from vacuum-photolyzed C60 thin films.