We investigated the carrier transport and photorefractive properties in multi-component materials containing 9-(2-ethylhexyl)carbazole (EHCz), so-called liquid carbazole. The electric-field dependence of the carrier mobility for EHCz and polyvinylcarbazole (PVK) was measured by the time-of-flight (TOF) technique. We obtained the higher carrier mobility of 4.2 x 10-6 cm2/Vs with an electric field of 2.5 x 105 V/cm for EHCz than that of 6.4 x 10-7 cm2/Vs for PVK. We also performed the two-beam coupling (TBC) technique to investigate photorefractive responses for the guest-host polymers containing PVK, EHCz, the electro-optic chromophore 4-piperidinobenzylidene malonitrile (PDCST), and the sensitizer C60. The measurement showed that the TBC gain depended on the mixture ratio of PVK and EHCz. The TBC gain was enhanced from 31 to 85 cm-1 at an electric field of 60 V/μm by increasing the concentration of EHCz from 10 to 15 wt%. These results show that EHCz plays important role for the optoelectronic and photorefractive materials as a hole transport materials as well as a plasticizer.
Vanadyl phthalocyanine derivatives having optically active side chains and the corresponding racemic isomers were synthesized and examined as nonlinear optical materials. These dyes were soluble in organic solvents and gave uniform thin films using spin coating. The thin films (neat or polymer doped) of each phthalocyanines showed the second- and third-order nonlinear optical responses under appropriate experimental conditions. The nonlinear optical susceptibilities of the optically active derivatives are larger than those of the corresponding racemic isomers. To clarify this enhancement phenomenon, we measured the electronic absorption- and circular dichloic spectra, and X-ray diffraction of the thin films. These results suggested that the optically active dyes forms one-dimensional columnar aggregates with one-handed helical sense and the columns further aligned into honeycomb-like chiral superstructures. It was surmised from the experimental results that the chiral superstructures enhance the nonlinear optical responses relative to the racemic analogues.
We studied linear and nonlinear optical properties of four different phthalocyanines: vanadyl and copper phthalocyanines substituted with chiral branched side chains, (S)(OMeBu)8VOPc, (S)(OMeBu)8CuPc; a racemic analogue (R,S)(OMeBu)8VOPc; vanadyl phthalocyanine substituted with linear side chains, (OBu)8VOPc. We investigate the molecule packing and their third-order nonlinear optical response in terms of chirality, planarity, and side chain structures. Molecular arrangement of (S)(OMeBu)8VOPc in the thin films was determined to be a columnar phase with rectangular 2D crystals by X-ray diffraction studies. The thin films of (S)(OMeBu)8VOPc diplayed CD activity. While, a chloroform solution of this compound did not show any CD. Therefore, we conclude that the CD in the films must result from the chiral aggregation of the molecules. The Χ(3) value of the flims of (S)(OMeBu)8VOPc was determined for 6.7×10-11 esu by third harmonic generation at 1.907 μm and this value was larger than those of (R,S)(OMeBu)8VOPc, (R,S)(OMeBu)8CuPc, and (OBu)8VOPc.