COUPLING BETWEEN PHOTOCHROMISM AND 2ND-HARMONIC GENERATION IN SPIROPYRAN-DOPED AND SPIROOXAZINE-DOPED POLYMER-FILMS

The photochemical ring opening of spiropyrans in polymethylmethacrylat e (PMMA) host films in the presence of a high-voltage electric field ( 2-5 MV/cm) leads to a photo-orientation of photomerocyanines. Since ph otomerocyanines have rather high first-older hyperpolarizabilities, th is photo-orientation leads to second-harmonic generation (SHG). The se cond-order susceptibility d(33) Of PMMA films doped with ',3'-trimethy lspiro[2H-1-benzopyran-2,2'-indoline] (25% w/w) has been measured at 1 0 pm/V. If a PMMA film doped with spiropyran and preoriented by corona poling at 90 degrees C is irradiated in the UV, an SHG signal of phot omerocyanine is also observed as a result of a memory effect of the or ientation of spiropyran molecules. The photoswitching of this nonlinea r optical property can be inverted by visible light irradiation. Only partially reversible switching is observed because of a gradual light- induced disorientation of photomerocyanine dipoles. Photochemical quan tum yields of the spiropyran reversible arrow photomerocyanine reactio n have also been determined in PMMA for one system. Dipole moments and hyperpolarizabilities of closed and open forms have been calculated b y semiempirical and finite field methods for an analogous system.