Photoelectric Properties Of Organic Molecular Materials Research

Metal phthalocyanine is two-dimensional p-π conjugated macrocyclic system substance. Due to the unique properties such as high quantum yield, high singlet oxygen yield and intense absorption in the red and rear infra-red region of solar spectrum, metal phthalocyanine, as a kind of photosensitizer, become very popular on photodynamic therapy (PDT) field in recent years. In addition, metal phthalocyanines have been extracted a wide range of applications in optical communication, optical switching, data storage, harmonic generators and dynamic holography, for their good thermal stability and chemical stability, especially good linear and nonlinear optical properties. With the developing of the mode-locked technology and ultrashort pulse laser, the femtosecond laser technology has been widely used in experimental studies. The properties of metal phthalocyanines gradually aroused great research interest in the laser field. At present, lots of researches on nonlinear optical properties of metal phthalocyanines have already been done by the nanosecond and picosecond laser. However, few studies have been done by the femtosecond laser. As well known, phthalocyanine compounds have very poor solubility, so it’s significant to find phthalocyanines which could be dissolved in the solvent and study their properties in laser field.CuPc(COOH)4, CoPc(COOH)4, RuPc(COOH)4and FePc(COOH)8are metal phthalocyanines easily soluble in DMSO. In the thesis, the nonlinear optical properties of the above four phthalocyanines were characterized by means of the Z-scan technique with femtosecond pulses at800nm. Four samples exhibited good nonlinear optical properties, such as obvious self-defocusing effect and reverse saturable absorption. We had also evaluated the values of the third-order nonlinear optical parameters. It was found that the central metals have big effects on their nonlinear optical properties, and their third-order nonlinear parameter n2,β and χ(3) all increased with the increase of metal atomic number. The number of carboxyl groups also affects the nonlinear optical properties. More carboxyl groups enhanced the nonlinear optical effects and nFB/nRu≈2. The experimental results were analyzed based on the theory about the delocalized electronic conjugated structure and charge transfer in the system.We did systematic researches in femtosecond field, for the first time, on the third-order nonlinear optical parameters of different carboxyl metal phthalocyanines lied in the same cycle/main group in the Periodic Table of the elements. The nonlinear optical properties of phthalocyanines were affected by the choice of central metal ion and substituents on the edge, which appeared certain regularity. This work provides a certain reference value for the synthesis of carboxyl substituted metal phthalocyanine compounds."Thickness Dependence of Ferroelectricity in Langmuir-Blodgett Multilayer Films of Hemicyanine Dyes" is another work in this paper. The Langmuir-Blodgett (LB) film is a well-organized ultrathin molecular film. Moreover, LB deposition technique can be used to fabricate artificially ordered ultrathin organic molecular films at molecular levels and the thickness can be controlled precisely. The hemicyanine dyes were fabricated to Z-type LB films with10,20and40monolayers, and the ferroelectric hysteresis loops were observed in all the LB films. It was indicated that ferroelectricity is existed in LB films of small organic molecules. In the experiment, it was demonstrated the typical ferroelectricity exists in hemicyanine dye LB films with different thickness and the relationship can be approximated by a power law Ec∝N-4/3in the range from30～200nm, which is consistent with other conventional ferroelectric materials. Through the measurement of dielectric properties, the optimum thickness of about60nm was obtained as storage devices in these LB films. The innovation of this work is to prove the organic hemicyanine LB films satisfy the power law Ec∝N-4/3, and to solve the optimal thickness problem of the hemicyanine LB films as a storage device.