Study Of Aggregate Structure Of Organic Electron Transport Materials

In order to meet the requirements of organic optoelectronic devices, organic electron transport materials have been widely studied due to their low-cost, facile processing, large area and complete flexible devices. On the one hand, we need to find out new n-type organic materials with good solubility, high mobility and air-stability. On the other hand, the relationship between structures and properties of materials should be investigated carefully to improve the device performance.Perylene diimide is a kind of widely used cheap n-type organic materials with good optical and thermal stability properties, and has broad potential applications in organic photovoltaic devices and field-effect transistors. A series of perylene derivatives were synthesized in our lab,, including fluorinated perylene diimide where F atom was introduced into the molecular structure at different positions and with different number and 3,4,9,10-tetra-(n-alkoxy-carbonyl)-perylene (PTAC) with different length of alkyl chains. Their aggregate structure has been studied preliminarily in terms of configuration and optical properties. This work investigated further the aggregate structure of fluoronated perylene diimide and PTAC in solution and crystal form.Crystals of fluorinated perylene diimide were grown by different methods, including solvent-nonsolvent exchanging, reprecipitation, casting, nonsolvent inpouring into saturated solution, controlled cooling of hot saturated solution and solvent-vapor annealing. One-dimensional crystals were achieved through several means.Topographies of crystals were characterized by polarized microscope. It was found that the more introduced F atoms, the better the solubility, and the easier the crystal growth due to the improved polarity produced by the strong electron with-drawing F group. The increased solubility has a great influence on the size of crystals. More importantly, single crystal of N,N'-diperfluorophenyl-3,4,9,10-perylenetetracarboxylic diimide (DPFPP) was achieved by solvent-nonsolvent exchanging, and the unit cell-dimensions of triclinic structure were determined bysingle-crystal XRD as a=7.12 (?), b=10.72 (?), c=29.14 (?), α = 97.0° , β = 89.6° , γ= 93.4° . When considering that most of the longest c-axis orients nearly vertical to the long axis of the needle crystal, the molecular plans are expected to be vertical to the needle axis.UV-Vis absorption and fluorescence spectra of 3,4,9,10-tetra-(12-alkoxy-carbonyl)-perylene (Per12) in different solvents were studied. It was found that the spectra would be influenced by the polarity of the solvents. Absorption spectra were blue-shifted with increasing the polarity of the solvents.Crystals of PTAC with different length of alkyl chains were grown by casting and solvent-vapor annealing methods. Topographies of crystals were characterized by polarized microscope. It was found that it was very easy to get different shapes of crystals of PTAC, such as spherulites, snowflake and macroscopical one-dimensional crystals. The topographies of crystals were little dependent on the length of alkyl chains.