Synthesis And Properties Of Perylene Tetracarboxylic Acid Diimide And Triazine Complexes

Perylene tetracarboxylic diimide(PDI) derivatives are important molecular building blocks that are currently being investigated for use in a variety of photoactive organic materials because of their low light and thermal fading rates, high luminescence efficiency,wide absorption and emission bands in visible region, and optoelectronic properties.They have been used in organic field-effect transistors, light-harvesting solar cells,photovoltaic devices,light emitting diodes,and robust organic dyes that are resistant to photobleaching.These dyes have generated great interest because of their outstanding photochemical and thermal stability,ease of synthetic modification,and desirable optical and redox characteristics.Driven by the demands of diverse applications,the modification on molecular structure of PDI aimed at changing the photophysical properties has attracted a lot of research interest in the past decade.Our research work has been focused on the following aspects:1.An Amphiphilic Perylenetretracarboxyl Diimide Dimer and its Application in Field Effect TransistorPerylene tetracarboxyl diimides(PDIs),a category of organic dyes with excellent thermal and photo stabilities,have recently been intensively studied as good n-type semiconductor due to the high electron affinity caused by the electron-withdrawing imide groups.Different functional groups have been introduced at the imide nitrogen atoms of PDIs aimed at modifying the packing in solid state and thus improving the OFETs performance.Electron withdrawing groups,such as cyanide groups,introduced to the bay positions have been proved to improve the n-type semiconductivity significantly.Solution processed films of PDIs has been fabricated into OFETs and ambipolar transport properties for PDI was observed for the first time. We report the design,synthesis of a novel PDI compound with phenoxy groups at the bay positions and hydrophobic alkyl subsitutents at one of the two imide nitrogens of the PDI molecule.More interestingly,two of these PDI tings were linked by a hydrophilic triazine ring to form a PDI double-decker dimer with very good amphiphilic properties.Good OFETs performance using Langmuir-Blodgett(LB) films of this compound as active layer has been achieved with the carrier mobility as high as 0.05 cm² V^-1 s^-1 and current modulation of 10³ which is much better than that of the LB films fabricated from the corresponding PDI monomer.Our result revealed that pre-organizing the organic molecules into a stacked structure in solution by covalent bond before the film fabrication might be an efficient way to improve its OFET performance.2.Fluorescence Quenching in a Perylenetetracarboxylic Diimide TrimerThe most important process in natural photosynthetic reaction center is the quick and efficient multiple-step electron and the energy transfer.This has attracted many researchers to look for ways to duplicate the reactions in simplified chemical systems.In order to expatiate the ET process,sample and effective structure is very necessary.We designed and synthesisd a PDI trimer,which composed of three PDIs connected by a triazine ring.The monomer-dimer structure was confirmed by the steady state absorption spectra and the H¹NMR apectra.The fluorescence spectra indicate that the fluorescence of monomer has been quenched,suggesting the presence of ET from monomer to dimer in this trimer.To gain an insight into the ET from monomer to dimer in compound trimer,time-resolved transient absorption spectra were recorded. Our finding suggests that the ET can happen efficiently and quickly between a pair of non-interacted PDI monomer and dimer.We believe that this observation is meaningful for the design and construction of novel artificial LH systems. 3.Particle-Size-Dependent Hydrophilicity of TiO₂ Nanoparticles Characterized by Marcus Reorganization Energy of Interfacial Charge RecombinationSize-dependent hydrophilicity of TiO2 nanoparticles has been investigated by an interface transient molecular probe method.The results show that the reorganization energy for the interfacial charge recombination of the probe molecule can be a specific parameter for characterizing the hydrophilicity of the nanoparticles which is in accordance with the density of the surface hydroxyl group as a parallel parameter.The observed hydrophilicity in terms of either reorganization energy or the density of the surface hydroxyl group decays monoexponential with the mean particle diameter.This determination of the reorganization energy of the interfacial charge recombination can be a practical method for evaluating the hydrophilicity of nanoparticles other than TiO₂.