Design,Synthesis And Application Of Organic Semiconductors Based On Nitrogen Heterocycles

Organic semiconducting materials include conjugated small molecules and polymers which have the advantages of light weight,solution-processing,flexibility,etc.,and have made great progress in fields such as organic field effect-transistors,organic light-emitting diodes,and organic solar cells.Enhancing the planarity of the molecule can broaden the?conjugate and adjust the molecular energy level,which is an effective strategy to improve the performance of organic semiconductors.The fused-ring molecules have rigid skeleton and excellent planarity,which can enhance the delocalization of?electrons,regulate the molecular energy levels,inhibit non-radiative transition,and increase the carrier mobility.However,fused-ring molecules also have some disadvantages,such as in the active layer of organic solar cells,they may form excessive aggregation,which results in unsatisfactory phase separation size and affects device performance.The non-covalent interactions can lock the molecular conformation and enhance the molecular planarity.However,the commonly used F···S,O···S interactions also have some drawbacks.For example,the introduction of fluorine atoms on the thiophene is relatively expensive,and the alkoxy-chain has a strong electron donating ability,which is harmful for improving the n-type property of the organic semiconductors.In view of the above problems in the design of planar molecular,the research work of this thesis was carried out,and the nitrogen heterocycle was selected as the basic unit.In view of the above problems,the research work of this thesis was carried out,and the nitrogen heterocycle was selected as the basic unit,because the nitrogen heterocycle has the following advantages:?1?Wide range of sources;?2?Nitrogen heterocycle has electron-deficient properties,which is beneficial to reduce the energy level of organic semiconductors,realizing the n-type property;?3?In six-membered nitrogen heterocycle,the sp²hybridized N atom replaced C-H,which not only can reduce the steric hindrance effect,but also can form intramolecular hydrogen bonds,N···S interactions to enhances the molecular planarity;?4?In five-membered nitrogen heterocycle,the alkyl-chain can be introduced into the N atom which not only improves the solubility of the molecule,but also inhibits their excessive aggregation in solid states.In this dissertation,a series of novel organic semiconductors based on nitrogen heterocycles was designed,synthesized and applied due to the above advantages of them.The main contents are listed as follows:1.Two novel fused-ring building-blocks BTh P-Br and BTr P-Br were received by introducing the derivatives of benzotriazole or benzothiadiazole into the bay-position of perylene.BTh P-Br and BTr P-Br were used as as donor units and capped with DPP,resulting in two receptor-donor-acceptor type?A-D-A?small molecules BTh P-DPP and BTr P-DPP.Thermogravimetric analysis and photophysical tests reveal that the two molecules have good thermal stability and broad spectral absorption.Electrochemical tests show that two molecules have oxidative stability and suitable frontier orbital energy levels for use as a donor material in organic solar cells.Morphological characterization shows that the blended film of BTr P-DPP/PC₇₁BM has an ideal phase separation size,and the PCE of the device based on them is 2.88%.2.Three new donor-acceptor-donor?D-A-D?small molecules Py DCz,Pym DCz and Pya DCz were gained through the capping of pyridine,pyrimidine and pyrazine with carbazoles,respectively Thermogravimetric analysis proves that they have good thermal stability.Photophysical testing reveals that the three molecules have a higher triplet energy level and can be used as blue host material.Theoretical calculations show that intramolecular N···H interactions can lock their conformations and affect their aggregation mode in the solid state.Single crystal data analysis shows that Py DCz and Pya DCz have a tighter packing structure in the solid state,which is in favour of forming the transporting channels for electrons and holes.Three molecules were applied as host materials to organic light-emitting diodes.Consequently,by using Py DCz as the host,the high-efficiency blue Ph OLED based on FIrpic was successfully fabricated,showing a maximum EQE of 16.3%.3.Two novel acceptor-acceptor?A-A?conjugated polymers PDPP-Pyi and PDPP-Pya were obtained by copolymerization of pyridazine or pyrazine with pyrrolopyrroledione?DPP?.The two polymers have high thermal stability according to thermogravimetric analysis.Electrochemical tests reveal that they have high oxidative stability and suitable frontier orbital energy levels for applying bipolar organic field effect transistors.Through theoretical analyses,the backbone of the polymers exhibits high planarity and different curvature owing to the intramolecular N···S attractive interactions that can effectively restrict the chain rotation.Morphological characterization shows that the PDPP-Pya film has a highly ordered structure,and the molecules prefer to be mainly in an edge-on orientation which facilitates the transport of carriers along the conjugated skeleton and the of?-?stacking direction.PDPP-Pya is applied to organic field-effect transistors,and the hole/electron mobility can reach 0.39/0.30 cm² V^-1 s^-1,respectively.4.Two novel polymers PDPP5bi Py,PDPP6bi Py were obtained by copolymerization of5,5'-dibromo-2,2'-bipyridine or 6,6'-dibromo-2,2'-bipyridine with pyrrolopyrroledione,respectively.Thermogravimetric analysis shows that they have good thermal stability.Electrochemical tests have shown that they have high oxidative stability and suitable frontier orbital energy levels for use in organic field effect transistors.Theoretical calculations show that the backbone of PDPP5bi Py has local planarity due to the intramolecular N···H interactions restrict the rotation of single bond,and the whole main chain of PDPP6bi Py has excellent planarity because of the synergistic effect of N···H and S···N interactions lock its conformations.The PDPP5bi Py and PDPP6bi Py have potential application for organic field-effect transistors due to their suitable frontier orbital energy levels and excellent planarity of their backbones.