Tuning The Crystal Polymorphism Of Organic Semiconducting Materials And Charge Transporting Property Investigation

Polymorphism refers to the phenomenon that a substance can exist in two or more different crystal structures.It is also known as homogenous polymorphism or homogenous heteromorphism.Compared to inorganic molecules,organic molecules are characterized by weak van der Waals interactions,which grant access to multiple crystalline packing states?crystal polymorphism?at near ambient conditions.The polymorphism of organic semiconductor materials is often accompanied by changes in molecular packing,and differences in semiconductor crystal packing are directly related to changes in charge carrier mobility.In the organic materials community,altering the molecular packing to study the sensitive relationship between packing and solid-state properties is known as crystal engineering,wherein the compound is slightly modified?Synthetic methods such as introducing electron-withdrawing groups such as Cl and F to change the polarity of molecules?to access different molecular packing states.However,this method also alters the chemical structure,making it difficult to establish a direct relationship between packing and charge transport.Polymorphism eliminates the need for chemical modification of the parent compound,and thus proves to be a valuable tool for investigating the effects of solid-state packing on charge transport.Since the chemical structures between the polymorphic forms are the same,the relationship between molecular packing and charge transfer can be clearly established.Organic field effect transistor?OFET?performance depends largely on the crystal packing structure,therefore,we can fine tune the polymorphs and advanced processing technology to achieve improve performance of the organic field effect transistor.What is certain is that polymorphism provides an excellent platform for examining the fundamental relationship between charge transport and crystal packing without changing the chemical structure.This thesis focuses on the research of polycrystalline preparation of organic semiconductor materials and their charge transport performance,and the main contents are as follows:1:A new crystal phase of a naphthalenediimide derivative??-DPNDI?has been prepared via a facial polymerassisted method.The stacking pattern of DPNDI can be tailored from the known one-dimensional?1D?ribbon??phase?to a novel two-dimensional?2D?plate??phase?through the assistance from polymers?P3HT?.We believe that the presence of polymers during crystal growth is likely to weaken the direct?-?interactions and favor side-to-side C-H···?contacts.Furthermore,?phase(2.59 cm²V^-1s^-1)architecture shows electron mobility higher than that of the?phase(1.16cm²V^-1s^-1)in the single-crystal-based OFET.Theoretical calculations not only confirm that?-DPNDI has an electron transport performance better than that of the?-DPNDI but also indicate that the?phase crystal displays 2D transport while the?phase possesses 1D transport.Our results clearly suggest that polymer-assisted crystal engineering should be a promising approach to alter the electronic properties of organic semiconductors.2:Herein,we present solvent-vapor annealing?SVA?made nanowires based on perylene tetracarboxylic diimide?PDI?derivative.It was found that the spin-coated thin films reorganized into nanowires distributed all over the substrate,as a result of the following solvent-vapor annealing effect.Cooperating with the atomic force microscopy and fluorescence microscopy characterization,the PDI₈-CN₂ molecules were supposed to conduct a long-range and entire transport to form the 1D nanowires through the SVA process,which may guarantee its potential morphology tailoring ability.Inaddition,the nanowire-based transistors displayed airstable electron mobility reaching to 0.15 cm²V^-1s^-1,attributing to effective in situ reassembly.Owing to the broader application of organic small-molecule nanowires,this work opens up an attractive approach for exploring new high-performance micro-and nanoelectronics.3:The crystal polymorphism study leads to an explosion of science research,related to many fields,such as organic semiconductors,pharmaceuticals,pigments,food,and explosives.Two different crystal phases of a perylene diimide derivative?4FPEPTC?have been prepared via a simple and efficient solution method.Via changing the concentration of the solution,we observed the polymorphisms clearly,wire-shape??phase?and ribbon-like??phase?crystals differed in the stacking mode and short-contacts.Moreover,the as-prepared n-channel microcrystal-based OFET demonstrated distinct electron mobilities that of?phase architecture higher than?phase structure and obvious photoresponse discrepancy.Theoretical calculations further confirmed this phenomena,which help us to understand the structure-property relationship in this crystal polymorph.Our study indicates that the investigation of polymorphisms could be considered as a very useful method to realize functional property modulation and benefits the development of organic?opto?electronics.