2ND-ORDER AND 3RD-ORDER NONLINEAR-OPTICAL PROPERTIES OF MULTILAYER AND COMPOSITE C-60-BASED THIN-FILMS

The nonlinear optical properties of C-60-based composites and multilay ered charge-transfer structures with 5,10,15, 20-tetraphenyl-21H,23H-p orphine (TPP) and 5,6,11,12-tetraphenylnaphthacene (rubrene) (TPN) act ing as electron donors are studied by transverse optical second- and t hird-harmonic generation. The results are compared with those obtained on pristine and vacuum-photolyzed C-60 thin films. Second-harmonic ge neration (SHG) is observed from composite films containing C-60 molecu les. A significant enhancement in SHG signal is observed in the multil ayered structures. This result is interpreted in terms of a ground sta te permanent electron transfer from the electron-donating molecules to C-60. The third-harmonic generation experiments show an enhancement o f the cubic susceptibility from vacuum-photolyzed C-60 thin films. (C) 1998 Elsevier Science S.A. All rights reserved.