Investigation of the Self-Assembly Behavior of Organic Photoelectric Functional Molecules on Solid Surface
Author:Zhang Si Qi
Supervisor:duan wu biao zeng qing dao
Organic photoelectric functional molecules are a class of organic molecular materials with photoelectric activity and photoelectric conversion functions,they are widely used in a various of organic photoelectric devices.In general,the performance of photoelectric device is not only related to the structure of the organic photoelectric functional molecule,but also related to the aggregated structure of the photoelectric functional molecules in the active layer,including molecular orientation,arrangement,and structural defects.The ordered arrangement of photoelectric functional molecules in the nanometer range will facilitate carrier mobility and can significantly improve the optical and electrical properties of the device.Supramolecular self-assembly driven by non-covalent interactions between organic molecules is an effective way to obtain large-scale ordered molecular structures.It is of great significance to realize the controllable self-assembly of organic photoelectric functional molecules,which is beneficial to the development of various new photoelectric materials and optimize the performance of organic photoelectric functional devices.In this dissertation,supramolecular self-assembly behavior of some organic optoelectronic functional materials on highly oriented pyrolytic graphite(HOPG)surface was studied using scanning tunneling microscopy(STM)and density functional theory(DFT)calculation.A variety of ordered self-assembled structures were constructed on the surface of the substrate,and the effects of solution concentration,temperature,host-guest factors on the self-assembled structure were investigated.On the one hand,the mechanism of the self-assembly was discussed theoretically.On the other hand,the practical application of self-assembly was explored.The main research works are as follows:(1)Concentration controlled experiments have been performed to investigate the H3TTCA/COR host-guest system with structural polymorphism phenomenon on the surface of HOPG.The H3TTCA molecules could exclusively form honey-comb networks via inter-molecular hydrogen bonds between carboxyl groups.Three new reconstructed structures of H3TTCA/COR host-guest systems were subsequently formed as a response to the addition of COR guest molecules.The steric matching and concentration-dependent effects play a significant role in the structural transformation of the H3TTCA host-network after the introduction of COR guest molecules.The results presented here give us a better comprehension of the fabrication of multicomponent molecular assemblies,which are favorable for the construction of functional nanostructures.(2)The supramolecular self-assembly and co-assembly of two rigid linear molecules(H1 and H2)with different skeleton lengths were studied on the surface of HOPG.The results suggested that they were able to self-assemble into defined temperature-dependent nanostructures profiting from the strong amino functional end groups,with the hydrogen bond between the end amino groups being the most contributing factor.Furthermore,a pure hydrogen bonding co-assembled nanonetwork was constructed on HOPG by the two spatially matching molecules.In this study,we have got one step closer to the adequate control and tuning of molecular structures to construct desired supramolecular structures.(3)The supramolecular self-assembly of a series of cyclic oligo(phenylene-ethynylene)(OPE)molecules and their Pt(II)diimine complexes with different backbone and side chains lengths were studied on HOPG surface.Orderly self-assembled nanopatterns of square-planar Pt(II)complexes with OPE ligands were achieved on HOPG.In this study,we have get an strategy of controlling 2D Pt(II)metallacycles arrangements on a surface.The length of side alkoxyl chains compare to the rigid backbones was crucial to the self-assembled structures.This work revealed a supramolecular approach to the metal-organic complexes nano-materials,which might be applied in fabricating next generation functional films and nano-electronic devices.(4)We alternately installed typical TPA as an electron-rich unit and BTTh2 as an electron-deficient unit into acetylene-linked conjugated macrocycles(3B2A and 4B2A).The two shape-persistent cyclic molecules showed interesting concentration-controlled self-assembly behavior at the solid/liquid interface and could capture fullerenes within their inner cavities to form stable complexes in solution.To get further insight into the electronic structures of 3B2A-C70 and 4B2A-2C70 complexes,the frontier molecular orbitals(MOs)of 3B2A—C70 and 4B2A—2C70 were calculated,results suggested that the favored photoinduced charge separation exists in these complexes.This work can provide theoretical guidance for the design of donor materials in the active layer of organic solar cells.