In order to analyze the spectra of inseparable chemical mixtures, many mathematical methods have been developed to decompose them into the components relevant to species from series of spectral data obtained under different conditions. We formulated a method based on singular value decomposition (SVD) of linear algebra, and applied it to two example systems of organic dyes, being successful in reproducing absorption spectra assignable to cis/trans azocarbazole dyes from the spectral data after photoisomerization and to monomer/dimer of cyanine dyes from those during photodegaradation process. For the example of photoisomerization, polymer films containing the azocarbazole dyes were prepared, which have showed updatable holographic stereogram for real images with high performance. We made continuous monitoring of absorption spectrum after optical excitation and found that their spectral shapes varied slightly after the excitation and during recovery process, of which fact suggested the contribution from a generated photoisomer. Application of the method was successful to identify two spectral components due to trans and cis forms of azocarbazoles. Temporal evolution of their weight factors suggested important roles of long lifetimed cis states in azocarbazole derivatives. We also applied the method to the photodegradation of cyanine dyes doped in DNA-lipid complexes which have shown efficient and durable optical amplification and/or lasing under optical pumping. The same SVD method was successful in the extraction of two spectral components presumably due to monomer and H-type dimer. During the photodegradation process, absorption magnitude gradually decreased due to decomposition of molecules and their decaying rates strongly depended on the spectral components, suggesting that the long persistency of the dyes in DNA-complex related to weak tendency of aggregate formation.
For many optical semiconductor fields of study, the high photoconductivity of amorphous organic semiconductors has strongly been desired, because they make the manufacture of high-performance devices easy when controlling charge carrier transport and trapping is otherwise difficult. This study focuses on the correlation between photoconductivity and bulk state in amorphous organic photorefractive materials to probe the nature of the performance of photoconductivity and to enhance the response time and diffraction efficiency of photorefractivity. The general cooling processes of the quenching method achieved enhanced photoconductivity and a decreased filling rate for shallow traps. Therefore, sample processing, which was quenching in the present case, for photorefractive composites significantly relates to enhanced photorefractivity.
Light-driven supramolecular chiral materials containing an azobenzene moiety as a photoresponsive part and binaphthyl moiety as a chiral part were designed. We found that the dynamic molecular twisting motion of the binaphthyl moiety could be achieved by irradiation of UV or visible light to cause photoisomerization of the azobenzene moiety. The twisting motion induced by the photochromic reaction gave rise to large change in the molecular structure and the value of optical rotation. The chiral materials were demonstrated to behave uniquely as photomodulation of liquid-crystalline helical structures and non-destructive erasable chiroptical memory through photoinduced switching of the dihedral angle of the binaphthyl moiety.
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.
We synthesized novel ligand-based mixed valence (LBMV) CrIII-dioxolene complexes, [Cr(X4SQ)(X4Cat)(4,4'-di-tert-butyl-2,2'-bpy)] (SQ = semiquinone, Cat = catecohol, 2,2'-bpy = 2,2'-bipyridine; X = Cl (2a) and Br (2b)) and [Cr(X4SQ)(X4Cat)(4,4'-dinonyl-2,2'-bpy)] (X = Cl (3a) and Br (3b)), and prepared thin films for investigating their third-order nonlinear optical (NLO) properties in terms of the mixed valence states. Electronic absorption spectra of these complexes in solution and solid states showed an intervalence charge-transfer (IVCT) band from Cat2- to SQ•- at the IR region, indicating of a coexistence of SQ and Cat ligands, namely, LBMV state of the complexes. These complexes were well soluble in nonpolar organic solvent, which allowed us to prepare thin films by spin coating. The obtained films showed the electronic absorption spectra similar to those in solution and were amorphous because of steric hindrance of halogen and alkyl substituents in o-dioxolene and 2,2'-bpy moieties, respectively. The x(3) values of the films of 3a and 3b with a thickness of 30 ~ 40 nm were determined for 1.0 × 10-12 esu at 1.907 μm.
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 discussed the electric and optical properties of three types of conjugated carbazole polymers: substituted polyacetylene with carbzole moiety, main-chain polymers having conjugated carbazole trimer units, and triindole units. Substituted polyacetylenes can be expected to show the enhanced optoelectronic responses due to the extended conjugated systems in the main chain and the additional chromophores in the side chain. The hole mobility of a substituted polyacetylene containing carbazole moiety was determined to be about 10-4 cm2/Vs with the electric field of 4 x 105 V/cm by time-of-flight technique, while polyvinylcarbazole showed hole mobility of about 10-6 cm2/Vs. The carrier mobility is presumably enhanced by the extended conjugation system. Hyperbranched polymers with carbazole trimer units exhibited the enhanced two beam coupling gain of 60 cm-1 in comparison with main-chain polymer with carbazole units. Since triindole is an electron-donative molecule containing three carbazole substructures with smaller ionization energy than that of carbazole, we can expect the application to a variety of optical and electrical materials. Main-chain polymers with triindole units exhibited the two-beam coupling gain of over 100 cm-1. Therefore, theses conjugated carbazole polymers are one of the good candidates for the new class of electronic and photonic materials.
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.
Recent development of dendron-containing NLO chromophores and polymers is summarized. By modifying the chromophore shape or applying the site isolation principle to these materials, we have systematically build up our understanding of how to molecular engineer the NLO materials. In this process, we have introduced the dentritic structures to these materials, varied from 3-D shaped dendritic chromophore, to fully-functionalized dendrimers with the center cores of NLO chromophores and crosslinkable periphery, and to side-chain dendronized NLO polymers. Compared to the conventional designed organic NLO materials, these nanoscale tailored NLO chromophores and macromolecules provide great opportunities for the simultaneous optimization of macroscopic electro-optic activity, thermal stability, and optical loss.
Monte Carlo simulations suggest that the functionalization of bulky side groups on highly efficient nonlinear optical chromophores will improve the poling efficiency of the electro-optic polymers by reducing the intermolecular electrostatic interactions from these large dipole moments (μ) chromophores. However, very little information has been provided from theoretical simulation to describe the optimal functionality of the bulky side group needed on individual chromophore in order to be compatible with its environment, e.g. neighboring chromophores and polymer matrix. To further understand the influence of side-chain modification of chromophore on both chromophore-chromophore and chromophore-polymer matrix interactions, we have synthesized a series of highly polarizable nonlinear optical chromophores with various side-chain modifications in terms of shape, rigidity and functionality. Linear E-O coefficients (r33) of these functionalized chromophores in amorphous poly(carbonate) were evaluated using the contact poling technique. Several important chromophore and polymer parameters, such as, steric hindrance and free volume were used to explain the overall results from chromophore-chromophore and chromophore-polymer matrix interactions on E-O property.
The polarization and depolarization behavior of electric field-induced polar alignment in a stable photorefractive polymer containing carbazole was measured by thermally stimulated current (TSC) and electro-optic (EO) modulation experiments. A relaxation peak was observed around the glass transition temperature (Tg) for the poled photorefractive polymer in a TSC experiment. The apparent TSC was not observed at room temperature. The polarization calculated from the relaxation peak linearly increased with the strength of the poling electric field. This result was consistent with the EO behavior which showed the linear dependence of the EO coefficients on the poling electric field. The polar alignment induced by the electric field at an elevated temperature was stable at room temperature, which could lead to the long-term stability of the photorefractive responses without an external applied electric field.
A series of dendron-modified nonlinear optical (NLO) chromophores and multiple chromophore-containing crosslinkable NLO dendrimers have been developed. The enhancement of poling efficiency (40%) in the dendritic NLO chromophore/polymer guest/host system was obtained due to the significant minimization of intermolecular electrostatic interactions among chromophores by the dendritic effect. Multiple NLO chromophore building blocks can be further placed into a dendrimer to construct precise molecular architecture with predetermined chemical composition. The site-isolation effect, through the encapsulation of NLO moieties by dendrons, can greatly enhance the performance of electro-optic (E-O) materials. A very large E-O coefficient (r33=60 pm/V at 1.55 micrometers ) and high temporal stability (85 degree(s)C for more than 1000 h) were achieved in a NLO dendrimer developed through the double-end functionalization of a 3D shape phenyl-tetracyanobutadienyl (Ph-TCBD)- containing NLO chromophore with thermally crosslinkable trifluorovinylether-containing dendrons.
As a new class of multi-functional compounds, three kinds of calix[4]arene molecules were newly synthesized: calix[4]arenes containing two 3-nitro-N-allyl carbazoles, two N- allyl carbazoles and one of each at the lower rim. These compounds take cone conformation in solution because of the 1,3-di-O-substitution at the lower rim. Those compounds take amorphous state as proved by differential scanning calorimetry and powder X-ray diffraction and they can be made into films without supporting the polymer matrix. Second- harmonic generation signals were observed in the films of the two calix[4]arenes containing nitro groups after electric poling at a temperature above glass transition point. Enhancement of d33 in the calix[4]arene with nitrocarbazole derivatives compared with the calix[4]arene with both carbazole and nitrocarbazole derivatives was observed, which might be attributed partially to some extent to the conformational regulation between the two carbazole chromophores. Using two beam couple experiment, photorefractive effect was observed in the film of the calix[4]arene with both carbazole and nitrocarbazole derivatives doped with 2,4,7-trinitro-9-fluorenone. This is the first report on the photorefractive property of calix[4]arene compound.
Two-beam coupling gain obtained from an orientational index grating was observed without applying an external field in a photorefractive polymeric material with ow glass transition temperature. A novel carbazole derivative with a photorefractive function was used as the material doped with a sensitizer for photocarrier generation. The mechanism to form the grating and to give the gain was investigated by two-beam coupling measurements.
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