Controllable Preparation Of Nanocrystals Based On SFX-Cz Molecules:Explore The Influence Of Molecular Structure And External Environment On Nanocrystalline Morphology And Application Of OFET Devices

Micro-and nano-crystals of organic semiconductors have attracted wide spread attention in recent years.Significant advances include rational design of molecules and self-assembly to form high quality micro/nano crystals,explain how molecular structures determine crystal growth and how external conditions affect the final crystal morphology,the microscopic description of the photoelectric properties and structure-property relationships of organic nanocrystals,as well as device applications based on micro and nanocrystals.As an important intermediate platform in the structure of photoelectric materials,nanoscale structures play an important role in distinguishing molecular properties,nanoeffects and bulk properties.Firstly,this paper introduces a pair of molecular fragments(supramolecular group and repulsive bulky group)with opposite characteristics into a molecular system based on the deep understanding of the four-element structure of molecules,and calls it SMART theory.Under this theory,the previous work that the TPA-PF molecule designed has been shown to be a result of the cooperative effect of attractive supramolecular segment(SS)TPA and repulsive bulky group(BG)PF.On this basis,considering the diversity and variability of the action of molecular fragments,in order to accurately control the self-assembly behavior of molecules and fully define and clarify the necessity of attractor/repulsive groups or other types of molecular fragments,we rationally designed three spiro-isomer molecules:SFX-2-Cz,SFX-3'-Cz and SFX-2'-Cz,systematically study the combination of supramolecular action and repulsive force in a molecular systemSecondly,we rationally designed non-planar spirocyclic aromatic hydrocarbon SFX-2,7-DCz molecules,and prepared nanocrystals by classical reprecipitation method.The experimental results revealed the transformation of crystal morphologies from two-dimensional nanosheets to three-dimensional octahedrons.Through a series of SEM,TEM and XRD morphology and structural characterization,it is revealed that the competition between the kinetic barrier(?G~?{11-1}s)and the driving force for the crystallization,effects the transformation of crystal morphology to a large extend.The control of growth kinetics is achieved by adjusting the supersaturation of the target compound during crystallization,resulting in a series of organic nanocrystals of uniform size and controllable morphology.Finally,we carried out supramolecular self-assembly of the SFX-3'-Cz to form an ultra-thin two-dimensional organic nanosheet structure with a thickness of less than 11 nm.A compact organic nanocrystalline film was prepared by pressing method,and applied into OFET as the floating gate layer of the organic thin film device.Compared with molecular vapor-deposited thin film devices,it exhibits lower mobility,but lower threshold voltage and larger switch,higher storage,showing a storage window of nearly 50V.However,the stability and repeatability of the device structure have not been fully demonstrated.