Irradiation with circularly polarized light of a film of an achiral azobenzene liquid crystalline polymer induces chirality. Circularly polarized light with opposite handedness produces enantiomeric structures. A chirooptical switch based on this phenomenon is reported.

The molecular and solid state nonlinear optical (NLO) properties of several (phenylazo)-azulenes are investigated. In particular, (4-nitrophenylazo)-azulene (2b) exhibits a quadratic hyperpolarizability (beta(vec)) of 80 x 10(-30) cm5esu recorded at 1.907 microm by the electric field-induced second-harmonic (EFISH) technique. This molecular material, which crystallizes in the monoclinic noncentrosymmetric space group Pc, exhibits an efficiency 420 times that of urea in second-harmonic generation. The origin of the optical nonlinearity in azo-azulene is discussed in relation with crystal structures and semiempirical calculations within the INDO/SOS formalism, and compared with that of the well known disperse red one (DR1) organic dye.

A series of chiral enantiomerically pure analogues of (E)-(2-(4-nitrophenyl)ethenyl)ferrocene (2), substituted by R (3, R = Me; 4, R = CH2OH; 5, R = SiMe3), in the 2-position on the cyclopentadienyl ring, were synthesized. Measurements by electric-field-induced second-harmonic generation (EFISH) and calculations by INDOS/CI-SOS show that the different chromophores have closely related molecular NLO responses. However, the crystal packings for the different compounds, observed by X-ray diffraction on a monocrystal, are completely different. In any case, the chirality of the constituting molecules avoids the centrosymmetry of the crystals and therefore preserves the NLO efficiency in the solid state. In the case of 3, the crystal packing is close to the centrosymmetry and so the bulk NLO efficiency is low (6 times that of urea, λ = 1.907 μm) but not nil, as is the case for 2. For 4, the crystal packing is much better for NLO (efficiency 20 times that of urea, λ = 1.907 μm) and is almost optimized for 5 (efficiency 100 times that of urea, λ = 1.907 μm). The correlation between molecular and bulk NLO responses was studied using the model proposed by Zyss.

The design of polymeric materials with optimized photoconductivity and nonlinear optical properties is of major interest for emerging optical applications using photorefractive properties. This paper reports the synthesis and preliminary optical characterization of a series of novel, fully functionalized, photorefractive polymers. They were synthesized by a post azo coupling reaction of a polyether carbonate polymer based on the charge transport N,N,N‘,N‘-tetraphenyl-diaminobiphenyl group with 4-nitrobenzene-diazonium tetrafluoroborate by phase transfer catalysis. The amount of the inserted 4-nitro-phenyl-azo group was between 0.1 and 1.7 per structural unit. These polymers absorb in the UV−vis range, because of the presence of donor−acceptor substituted azobenzene chromophores. Light induced change of the refractive index was studied by birefringence measurements (λprobe = 632.8 nm) as a function of azo content in thin films with thickness ranging from 200 to 500 nm. Surface relief grating inscription was also demonstrated in the same polymer thin films, with a weak surface relief amplitude and a low diffraction efficiency (<1%). These results indicate a relatively low mobility of the azobenzene chromophores. Photoconductivity was studied by measuring the photocurrent through 40 μm thick samples where a metal-free phthalocyanine layer deposited on electrodes served as charge generator. These samples have exceptionally high photoconductivity compared to other composite materials. In addition, preliminary two-beam coupling experiments demonstrated unambiguously the photorefractive effect under low poling field (2.5 V/μm) at room temperature, but no net gain was obtained because of a high absorption coefficient at 632.8 nm.