Development Of Organic Electron Transport Materials-perylene Derivatives

Novel materials are the bases of New Scientific & Technical Revolution in matters. With the rapid developments of organic optoelectronic devices, such as organic solar cells, organic light-emitting diodes (OLEDs) and organic field-effect transistors (OFETs), et al., organic n-type materials with high mobility, good stability and facile processability are in impending need. In this dissertation, basing on molecular and material designs, strong electron-withdrawing F atoms were introduced to the traditional organic n-type materials of perylene diimides and benzimidazole perylene. The fluorination on optical properties, energy levels, aggregation structure, electron mobility and air-stability of these fluorinated derivatives were investigated in details. The soluable organic semiconductors were prepared by chemical modification, and the organic semiconductor composite materials were fabricated by solution method. The optoelectronic properties of the composites were also investigated.First of all, a series of fluorinated aromatic substituted perylene diimides were synthesized through the nucleophilic reactions between 3,4,9,10-perylene tetracarboxylic dianhydride (PTDA) and fluorinated amines: N,N'-di-(2-fluorophenyl)-3,4,9,10-perylenetetracarboxylic diimide (D2MFPP), N,N'-di-(3-fluorophenyl)-3,4,9,10-perylenetetracarboxylic diimide (D3MFPP), N,N'-di-(4-fluorophenyl)-3,4,9,10-perylenetetracarboxylic diimide (D4MFPP), N,N'-di-(2,4-difluorophenyl)-3,4,9,10-perylenetetracarboxylic diimide (D24DFPP), N,N'-di-(2,5-difluorophenyl)-3,4,9,10-perylenetetracarboxylic diimide (D25DFPP), N,N'-di-(2,4,6-trifluorophenyl)-3,4,9,10-perylenetetracarboxylic diimide (DTFPP), N,N'-di-(3-trifluoromethanephenyl)-3,4,9,10-perylenetetracarboxylic diimide (DTFMPP),N,N'-diperfluorophenyl-3,4,9,10-perylenetetracarboxylic diimide (DPFPP). Their molecular structures were fully characterized by elementary analyses and FTIR measurements.The influence of the fluorination on the energy levels of perylene diimides wasinvestigated. Cyclic voltammetry (CV) and UV-Vis absorption measurements were performed to get the LUMO energy levels. The results indicated that introducing fluorine groups to perylenee diimides lowered the LUMO energy level. It was noticed that the half-wave reduction potentials of the fiuorinated perylene diimides were more positive than that of O2, suggesting that the fiuorinated compounds were air-stable organic electron acceptors.The influence of the fluorination on the aggregation structure of perylene diimides was studied through UV-Vis absorption spectra, the quantum chemical simulation of the molecular conformation, CV, SEM and XRD measurements. It was found that the fluorination induced the change of the molecular conformation of the fluorinated perylene diimides: for mono-fluorinated perylene diimides, the aggregation structure of ortho fluorinated derivatives was similar to the un-substituted compound of N,N'-diphenyl-3,4,9,10-perylenetetracarboxylic diimide (DPP), however, the fluorination on meta or para position was favor of the n-n coupling interaction, which was good for molecular stacking tightly;for di-, tri-, or penta- fluorinated derivatives, a new type of aggregation structure could be formed in the solid film that molecules stacked with the fluorinated phenyl groups straightly over or below the perylene cores of the adjacent fluorinated molecules.The electron mobilities of fluorinated perylene diimides films prepared by vacuum deposition were measured through OFETs. It was observed that the electron mobilities of fluorinated derivatives were higher than that of DPP film with good air stability. Among all the derivatives, the electron mobilities of D24DFPP, D25DFPP and DPFPP films were at the order of 10"2 cm2V"1s"1. These results proved that fluorinated perylene diimides were a kind of potential organic electron transport materials. With optimization of processing conditions, the electron mobility of DPFPP film was 0.068 cmV's'1.Another kind of organic electron transporting material of benzimidazole perylene (BZP) and its fluorinated compound (FBZP) were synthesized and characterized by elementary analysis and FTIR spectra. It was found that the effect of the fluorination on energy level ofBZP was stronger than that of fluorinated perylene diimides due to the reason that the fluorine group was directly introduced to the conjugated system. The influence of the fluorination on the energy level, electronic and aggregation structures, and thermal stability of the BZP derivatives were studied through UV-Vis absorption spectra, CV, TGA, DSC, SEM and XRD measurements. It was found that the LUMO energy level of FBZP was 0.13 eV lower than that of its parent compound of BZP. The electron mobilities of BZP and FBZP films prepared by vacuum deposition were measured through OFETs. The results indicated that these two compounds were good electron transporting materials. Fluorination is favor of electron mobility and air-stability. With optimization of processing conditions, the electron mobility of FBZP was 0.01 anV's"1.A series of 3,4,9,10-tetra-(n-alkoxy-carbonyl)-perylene (PTAC, n = 4, 6, 8, 10, 12) derivatives were synthesized via a simple and efficient phase transfer catalysis method, which had good solubility. The influences of the length of the alkyls attached to the perylene core on the optical properties, thermal stability, energy level and aggregation structures, and liquid crystal behaviors of PTACs were studied through UV-Vis absorption, PL, TGA, CV, DSC, POM and XRD measurements. The molecular aggregation structure of PTAC could be modulated by changing the length of the attached alkyl chains. It was interesting to observe that it was easier for PTAC derivatives with shorter alkyl chain to form crystal film, when n < 10. Meanwhile, the ordered liquid crystal structure of PER6 and PER8 could be held by quench. The photoconductivity of these materials was investigated by xerographic photoinduced discharge technique, and the results showed that the photosensitivity increased with decreasing the length of alkyl chain attached to perylene core.Copper tetra-(octyl-alkoxy-carbonyl)-phthalocyanine (CuPc-C8) attached with long alkyl chains by covalent bonds were synthesized. The novel composite of CuPc-C8/PER8 was prepared by the solution-blending method. Atomic force microscopy (AFM) demonstrated the formation of the bulk heterojunction structure in their cast-coated films. Enhanced photosensitivity was observed in the photoreceptor made from theCuPc-C8/PER8 composite, which was interpreted in terms of the large interfacial area between the two components due to the existence of the bulk heterojunction structure. Furthermore, the absorption spectra of ester substituted CuPc and ester substituted perylene were complementary, which might contribute to the improved efficiency of light absorption.