Zhongyu Li

Photoresponsive J-Aggregation Behavior of a Novel Azobenzene−Phthalocyanine Dyad and Its Third-Order Optical Nonlinearity

The photoresponsive J-aggregation behaviors of a novel azobenzene-substituted zinc phthalocyanine (azo-ZnPc dyad) were studied by UV/vis, fluorescence, and (1)H NMR spectroscopy. Upon illumination with 365 nm UV light, the trans-cis isomerization of azobenzene can efficiently reduce the steric hindrance around the peripheral oxygen atom of azo-ZnPc, shortening the possible distance between two phthalocyanine molecules and, consequently, greatly improving the tendency of J-aggregation of azo-ZnPc dyad. The third-order optical nonlinearities of the photoresponsive J-aggregates (before and after illumination) were measured by a Z-scan technique at 532 nm with a pulse duration of 25 ps. The Z-scan spectra revealed that all the samples possessed large positive nonlinear refraction and positive nonlinear absorption, exhibiting a self-focusing effect and reverse saturable absorption, respectively. The second molecular hyperpolarizabilities of the dyad in two conditions were measured to be 3.87 x 10(-30) and 4.82 x 10(-30) esu, respectively. All the results suggest that the azo-ZnPc dyad has potential in the field of nonlinear optics applications.

Large Third-Order Optical Nonlinearities of a Croconium Dye in Tetrahydrofuran Solution and in Poly(methyl methacrylate) Coating Films Measured Using Resonant Femtosecond Degenerate Four-Wave Mixing Technique

The third-order optical nonlinearities of a croconium dye in tetrahydrofuran (THF) solution and in poly(methyl methacrylate) (PMMA) coating films were measured using the femtosecond degenerate four-wave mixing (DFWM) technique under resonant conditions. The temporal profiles of the DFWM signal of the croconium dye were obtained with a time resolution of 0.3 ps (FWHM), and were found to consist of at least two components, i.e., the coherent instantaneous nonlinear response (electronic response) and the slow response due to the formation of excited molecules for both the THF solution and PMMA coating films. The electronic component of molecular hyperpolarizability, γe, of the croconium dye in the THF solution was determined to be ca. 4.6×10-29 esu at 817 nm. The electronic component of third-order nonlinear optical susceptibility, χ(3)e, of one of the present PMMA coating films containing the croconium dye was ca. 1.3×10-8 esu at 824 nm.

Photophysical properties of sulfonated dihydroxy phosphorus(V) tetrabenzotriazacorrole.

The photosensitizing properties of a novel phthalocyanine analogue, sulfonated dihydroxy phosphorus(V) tetrabenzotriazacorrole [P(OH)2TBCSn] and a non-sulfonated one [P(OH)2TBC] are reported in this paper. Different from other phthalocyanine derivatives, P(OH)2TBCSn shows little aggregation in aqueous solution. The fluorescence quantum yield (PhiF) of P(OH)2TBCSn is lower than that of the non-sulfonated one. Studies of triplet state photophysics show that the presence of peripheral substituents on the macrocycle enhances the quantum yield of the triplet state. The sulfonated derivative, P(OH)2TBCSn, has a longer triplet lifetime (tauT = 0.234 ms) and higher singlet oxygen quantum yield (PhiDelta = 0.88) than P(OH)2TBC. Together with the ground-state absorption properties, the photosensitizing properties of the new compound suggest that it may be used as an excellent photosensitizer for photodynamic therapy (PDT).

FABRICATION OF SQUARAINE DYE SENSITIZED SPHERICAL ZINC OXIDE NANOCOMPOSITES AND THEIR VISIBLE-LIGHT INDUCED PHOTOCATALYTIC ACTIVITY

A 1,3-bis[(3,3-dimethylindolin-2-ylidene)methyl]squaraine (ISQ) dye sensitized ZnO nanocomposites via two different preparation methods including hydrothermal and ultrasonic sensitization processes are discussed in this paper. The as-prepared composites were characterized by the X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), Raman spectroscopy, and transmission electron microscopy (TEM). Based on the XRD patterns and TEM images, the ISQ/ZnO nanocomposites still kept the characteristic peaks and the basic morphology of ZnO and ISQ dye. The photocatalytic activity of ISQ/ZnO nanocomposites was investigated by degrading methylene blue (MB) under visible-light illumination. Compared with the MB self-degradation rate, the photocatalytic activity of the ISQ/ZnO composites was enhanced remarkably. The ISQ/ZnO nanocomposites fabricated by ultrasonic sensitization method exhibited excellent photocatalytic degradation rate, approximately 20% higher than that of the hydrothermal sensitization one.

Third-Order Optical Nonlinearities of Novel Phthalocyanines and Related Compounds

The field of nonlinear optics has been developing for a few decades as a promising field with important applications in the domain of optoelectronics and photonics. Materials that exhibit nonlinear optical (NLO) behavior are useful because they allow manipulation of the fundamental properties of laser light beams, and are hence of great technological importance in areas such as photonic switching, optical computing and other optical data processing systems (Perry et al., 1994, 1996; Shirk et al., 2000). NLO activity was first found in inorganic crystals (Zyss, 1994), such as LiNbO3, but the choice of these materials is rather limited. Also, most of them have either low NLO responses or important drawbacks for processing into thin films and being incorporated into micro-optoelectronic devices. By the mid-1980s, organic materials emerged as important targets of choice for nonlinear optical applications because they exhibit large and fast nonlinearities and are, in general, easy to process and integrate into optical devices. Moreover, organic compounds offer the advantage of tailorability: a fine-tuning of the NLO properties can be achieved by rational modification of the chemical structure. Finally, they are ideal to achieve the ultimate goal of device miniaturization by going into the molecular level. Large optical nonlinearities in organic molecules usually arise from highly delocalized electron systems. During the last two decades, phthalocyanines (Pcs) have been intensively investigated for their third-order NLO properties both in solutions and as thin films because of their extensively delocalized two dimensional 18-electron system (Ho, 1987; Shirk, 1989; Kambara, 1996; Ma, 2003; Zhou, 2004; He, 2007). They also exhibit other additional advantages, namely, exceptional stability, versatility, and processability features. The architectural flexibility of phthalocyanines is well exemplified by the large number of metallic complexes described in the literature, as well as by the huge variety of substituents that can be attached to the phthalocyanine core. Furthermore, some of the four isoindole units can be formally replaced by other heterocyclic moieties, giving rise to different phthalocyanine analogues. All these chemical variations can alter the electronic structure of the macrocyclic core, and therefore, they allow the fine-tuning of the nonlinear response. Aside from their practical interest, Pc-related molecules present very attractive features for fundamental NLO studies. Since the unsubstituted and many substituted compounds are planar (2D, two dimensional), they offer the possibility of investigating of the role of

Resonant Enhanced Large Third-Order Optical Nonlinearities and Responses of Polyvinyl Alcohol Coating Films Containing J-like Aggregates of a Cyanine Dye

The third-order optical nonlinearities and responses of polyvinyl alcohol (PVA) coating films containing J-like aggregates of a cyanine dye called NK-3261 were measured by a femtosecond degenerate four-wave mixing (DFWM) technique under resonant conditions. The temporal profiles of the DFWM signal of the PVA coating films containing the J-like aggregates of NK-3261 consisted of three components, i.e., the coherent instantaneous nonlinear response (electronic response) and two slow responses with decay time constants of ca. 1.2 ps and ca. 5.6 ps. The electronic component of the effective third-order nonlinear optical susceptibility, χe(3), of one of the films was as high as ca. 1.1 ×10-7 esu at 850 nm.

Third-Order Optical Nonlinearity of a 1,3-Bis(2,4,6-Trihydroxy-Phenyl)Squaraine

The magnitude and dynamic response of the third-order optical nonlinearity of a 1,3-bis(2,4,6-trihydroxy-phenyl)squaraine was measured by femtosecond degenerate four-wave mixing (DFWM) technique at 800 nm. Ultrafast optical response has been observed and the magnitude of the second-order hyperpolarizability of the studied squaraine was measured as large as 3.8 ×10-31 esu. The large optical nonlinearities of the squaraine can be attributed to their rigid and intramolecular charge transfer structure, and the instantaneous NLO response of squaraine is mainly contributed from the electron delocalization.

Self-Assembled Stratified Structure in Polyalkylthiophene-6 and Polyvinylcarbazole Blend Film

Layered films of polyalkylthiophene-6 (PAT-6) and polyvinylcarbazole (PVK) which are expected to be a photo-electronic device were fabricated from blend solution by self-assembly at only one casting process. Cross-section structure of the blend polymer films were observed by digital microscope and analyzed by using Energy Dispersive Spectroscopy (EDS) and FT-IR spectrometer. Stratified structure with component distribution along thickness direction was found to be self-assembly at the suitable casting condition. It was considered that the structure was controlled by the evaporation speed of solvent and properties of the solubility parameter and density of the polymer.

Dibenzotetraaza [14] annulene materials for recordable blue laser optical disc

Phthalocyanine materials have successfully been applied in infrared ray optical disc systems. Seeking for the phthalocyanine-analogous materials with great conjugate macrocyclic π bond system is the key for new materials research of super high density blue laser optical storage. Dibenzotetraaza [14] annulene have the similar macrocyclic structure. It was used as a building block for the preparation of multi-component materials matched the requirement of recordable blue laser optical disc. Ester substituents have been generated with oxalyl dichloride (or phosgene) and appropriate HO-function-containing substrates. A range of new complexes equipped with ester groups derived from various alcohols and phenols have been prepared. The new products have been characterized by UV-Vis spectrometer, TGA, refractive index of the organic films. These kinds of materials have suitable light and thermal sensitivity, and it is a valuable material for blue laser optical storage.

Synthesis and dual fluorescence property of novel dihydroxy phosphorus tetrabenzotriazacorrole derivates

Photodynamic diagnosis (PDD) is of increasing interest for diagnosis in oncology. It is based on the selective accumulation of photosensitizers in tumours, such as porphyrin and phthalocyanine. In the present study, novel dihydroxy phosphorus tetrabenzotriazacorrole derivates have been synthesized. And photophysical properties of these derivates have been studied. Dihydroxy phosphorus tetrabenzotriazacorrole derivates display a fluorescence which is from the higher S2 electronic state. With excitation at 614 nm, the fluorescence maximum is at 668 nm for dihydroxy phosphorus(V)-2,9,16,23-tetranitrotetrabenzotriazacorrole {P(OH)2TBC(NO2)4} in N,N-dimethylformamide (DMF). But with excitation at 310 nm for P(OH)2TBC(NO2)4 in DMF, in addition to S1 fluorescence a new fluorescence peak appears at 490 nm, which is attributed to S2-state fluorescence. It indicates that the dihydroxy phosphorus tetrabenzotriazacorrole derivates might have a potential application as a dual fluorescent marker for photodynamic diagnosis.