Photorefractive polymers have been the subject of intense research activities in the past few years.[' -3 1 These materials have potential applications in the field of all-optical switching and are of considerable interest in the field of optical communication and computing techniques.The photorefractive effect is a light-induced change of the refractive index involving the creation of space charges. A spatially modulated light intensity pattern within the sample produced by a standing wave pattern of two laser beams generates charge carriers which are subsequently separated and trapped to produce a periodic space-charge distribution. The resulting space-charge field modulates the refractive index by virtue of the electro-optic effect. The refractive index grating can then be detected experimentally utilizing holographic techniques such as degenerate four-wave mixing and two-beam coupling.The most promising materials investigated so far are polymers based on charge-transporting hosts such as poly-Nvinylcarbazole (PVK) molecularly doped with compounds which act both as sensitizers and as NLO chromophores. To our knowledge the polymer composite with the largest reported refractive index change and optical gain is the system PVK:DMNPAA:ECZ:TNF 33:50:16:1 W~% [~I (DMN-PAA = 2,5-dimethyl-4-(p-nitrophenylazo)anisole) ; ECZ = ethylcarbazole; TNF = 2,4,7-trinitro-9-fluorenone). The refractive index change of this material has been reported as d n z 5 x yielding a gain coefficient of I ' z 2 2 0 cm-' at an electric field strength of E z 80 V/pm for p-polarized readout and p-polarized writing beams, respectively. In this material large volume fractions of both DMNPAA and ECZ are necessary as plasticizers in order to provide poling properties at room temperature and for ease of sample preparation.In this paper we present a new charge-transporting polymer backbone which is based on polysiloxane with pendant carbazole groups and which provides both transport and room-temperature poling properties without additional plasticizing components. We have prepared a large number of carbazole containing polymers.[5 In these polymers, the carbazole groups are linked to a polysiloxane-1, polyacrylate-2 or polymethacrylate 3 backbone by spacers of various length (Fig. 1). Depending on the stiffness of the polymer backbone and the spacer length, the glass transition

A number of novel nonlinear optically (NLO) active polymethacrylates were prepared from the NLO active methacrylates 2a-d with azobenzene side groups and the bulky comonomer 1-adamantyl methacrylate. The polymers exhibit unusually high glass transition temperatures between 160 "C and 190°C. The copolymerization parameters of the monomer pair 1-adamantyl methacrylate (1)lDisperse red methacrylate 2 b (r, = 1,l t 0,2, r2 = 0,s f 0,2) show that the two monomers are incorporated almost statistically into the polymer chain. Polymers 3a-d are soluble in common organic solvents and excellent films can be obtained by spin coating. After poling in an electric field of 120 V/pm polymer 3b shows a large electrooptic (EO) coefficient (r33) of 25 pm/V at 633 nm. Within two weeks, only a negligible decay of 7% of the EO coefficient was observed at room temperature. On-line monitoring of the second harmonic generation (SHG) at 100 O C showed a fast initial drop (10%) of the SHG signal and subsequently a slow decay of 20% within 10 h. Afterwards, the signal remained almost constant for further 5 h at 100°C. The novel polymers can thus be considered as easy processible NLO materials with a high thermal stability of the chromophore orientation obtained by poling.

We investigated both time and temperature dependence of chromophore movements by means of in situ second-harmonic generation (SHG) measurements. Using real-time detection of the SHG intensities during and after poling of various nonlinear-optical polymer films we observed differences between main-chain and side-chain polymers regarding the nonlinear coefficients d33 and the glass transition dynamics. We present experimental data on new main-chain polymers with polar stilbene chromophores attached in the most common transverse position to the backbones (MC-T) or incorporated in a linear fashion where they are a part of the main-chain (MC-L). The side-chain polymer (SC) presented here has been developed for photorefractive applications and is a copolymer containing Disperse Red 1 and a photoconducting carbazole unit in the side chain. The influence of the macromolecular structure on the chromophore dynamics is striking. This is verified by means of in situ corona poling experiments and thermal experiments based on temperature ramps on poled polymers. MC-T and especially MC-L polymers show a better thermal stability of the chromophore orientation relative to the glass transition temperature than SC polymers; however, chromophores of main-chain polymers are, as can be expected, less mobile during the poling process. We obtained resonance enhanced nonlinear optical coefficients d33 of 100 pm/V in a SC polymer, 90 pm/V in a MC-T polymer, and 30 pm/V in a MC-L polymer.

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