Quinacridone And Aromatic-Amine Compounds: Self-Assemblies, Luminescence And Packing Structures

Organic semiconductor materials, possessing several notable advantages including easy design and synthesis, mechanical flexibility, and low cost, have been used as active elements in optoelectronic devices such as organic light emitting diodes (OLEDs), solar cells, sensors, field effect transistors, optical waveguides and lasers. Recently, molecular materials fabricated from organic molecules through non-covalent interactions (hydrogen bondings,Ï€-Ï€interactions, metal-metal interactions, etc.), have gradually become a research hotspot. Organic molecules can be prepared into molecular materials (micro-/nano-materials, thin films, single crystals, etc.) with abundant functions such as electricity, light, sensor, energy conversion, molecular machines etc, because of intermolecular non-covalent interaction. For organic solid materials, the constituent molecules may form strong intermolecular interactions and assembly packing structures resulting in that the properties of these materials are governed by the whole collective rather than by individual molecules. The performance of organic molecule-based devices strongly depends on the molecular assembly structures. Therefore, understanding and controlling molecular arrangement in solid state are fundamental issues for obtaining the solid material with desired chemical and physical properties.1. In chapter II, four fluorinated quinacridone compounds (Cn-DFQA, n = 4, 8, 10, 16), four quinacridone derivatives substituted with trifiuoromethyl (Cn-DTFMQA, n = 4, 8, 12, 16) and two trifluoromethyl substituted aromatic amine compounds (AA-1 and AA-2) have been synthesized. All the compounds are obtained in high yields and characterized by ¹H NMR spectroscopy, mass spectra, and element analysis. The concentration-dependent photophysics properties (absorption spectra, emission spectra and the Photoluminescence quantum efficiency) of synthesized compounds in solutions have been studied in detail.2. In chapter III, it was demonstrated that Cn-DFQA could be used as building blocks to fabricate organic luminescent micro-materials. The assembly properties of Cn-DFQA have obvious alky chain length dependent characteristic. The alky chain length has dramatic effect on the morphology of the resulted micro-materials. The molecules C4-DFQA and C8-DFQA with shorter alky chains could assemble into 1-D micro-materials, while C10-DFQA and C16-DFQA with longer alky chains aggregate into diamond and hexagonal micro-particle crystals, respectively. The emission spectra of the 1-D micro-materials formed by C4-DFQA or C8-DFQA exhibited red shift compared with that of the micro-particle crystals composed of C10-DFQA or C16-DFQA. The single crystal structure analysis revealed that in the crystals C4-DFQA and C8-DFQA there are 1-D molecular columns based on intermolecularπ…πand hydrogen bond interactions, while 2-D hydrogen bond molecular sheets are observed in the crystals C10-DFQA and C16-DFQA. The molecular packing properties of the four crystals suggest that C4-DFQA and C8-DFQA molecules have the tendency to form 1-D structure, while C10-DFQA and C16-DFQA molecules posses the characteristic to generate the sheet structures. The single crystal structures give a rational explanation for the alky chain length dependent morphology properties of the Cn-DFQA based micro materials. Therefore, it is possible to control the morphologies and emission properties of the organic micro and nano-materials through varying the molecular structures.Self-assembled 1D nanostructures with distinct morphologies are fabricated by the deposition of Cn-DTFMQA solutions (1.0×10^-3M). The microstructures fabricated from C8-DTFMQA and C12-DTFMQA give ultralong 1D nanowires (more than 1 mm) with high aspect ratios. The investigation of the crystal structure suggests that DTFMQA-C8 molecules should have the tendency to aggregate into a straight liner 1-D structure in nature. The single crystal structure feature of C8-DTFMQA provided a rational explanation for the formation of the flat fibers. It is known that the energy of hydrogen bong is C=O…H-C >π…π> C-F…H-C, so the 1D aggregate tendency of C8-DTFMQA molecules is the kay factor to form ultralong micromaterials.3. In chapter IV, we show that two achiral center-symmetrical quinacridone (QA) derivatives, N,N'-di(n-hexyl)-1,3,8,10-tetramethylquinacridone (C6TMQA) and N,N'-di(n-decyl)-1,3,8,10-tetramethylquinacridone (C10TMQA), could be employed as building blocks to fabricate well-defined twisted nanostructures by controlling the mixture solvent's composition and concentration. The bowknot-like bundles with twisted fiber arms were prepared based on C6TMQA. The uniform twisted fibers were generated from C10TMQA in ethanol/THF solution. The scanning electron microscope (SEM), UV-Vis spectra, differential scanning Calorimetry (DSC), X-ray diffraction, infrared (IR), nuclear magnetic resonance (NMR), single crystal and molecule simulations characterizations revealed that the introduction of ethanol molecules in the solution systems could induce the staggered aggregation of C6-TMQA (or C10-TMQA) molecules and the formation of twisted nanostructures. The twisted materials generated from achiral organic functional molecules may be valuable to the design and fabrication of new materials for optoelectronic applications. The twisted materials generated from achiral organic functional molecules may be valuable to the design and fabrication of new materials for optoelectronic applications.4. In chapter V, AA-1 and AA-2 display thermo-induced and revisable solid sate phase transformation properties, which are accompanied by the switches between the different emission colors. For AA-1 or AA-2, the different phases could be obtained by controlling the solidification speed of the melted AA-1 or AA-2 sample. The red phases of AA-1 and AA-2 can undergo solid phase transfer into corresponding yellow phase of AA-1 and green AA-2 phase, respectively. The single crystal to single crystal transformation from red crystal AA-1 to yellow crystal AA-1 has been achieved. The phase dependent emission properties of AA-1 and AA-2 have been attributed to the different molecular packing properties and changeable molecular geometry for different solid phases of AA-1 and AA-2. The novel organic luminescence materials AA-1 and AA-2, which could be efficiently switched between two different luminescent phases based on the external thermal stimulation, may be employed to fabricate the display, sensing, memory devices. In summary, we have synthesized and characterized ten novel organic light-emitting materials. Their concentration-dependent photophysical properties in solution were investigated, and nine single crystals were grown and their structures were analyzed. Through investigating the self-assembly behaviors of Cn-DFQA, Cn-DTFMQA and Cn-TMQA and the thermal induced solid-state luminescent switch behaviors of AA-1 and AA-2, the relationship between the morphologies and luminescent properties of solid materials and molecular packing structures was elucidated.