Guiding The Molecular Design,Assembly And Photoelectronic Properties Of Diarylfluorene-based Organic Micro/nano-crystal By Supramolecular Steric Hindrance Effect

Organic nanocrystals have attracted increasing attention recently because of their obvious advantages,such as light weight,molecular structural diversity,long-range ordered structures,and small size effect,which are considered as strong candidates beyond carbon materials and inorganic nanomaterials for next-generation micro-nano scale flexible optoelectronics.With the rapid development of organic optoelectronic materials,we tend to pay more attention to realize the multidimensional morphology and versatile function of micro-nano crystals via appropriate molecular design.One predictable trend is that,by covalently grafting inactive bulky groups with steric hindrance and planar segments with supramolecular forces,is expected to fabricate morphology and dimension controllable micro-nano crystals,thus obtain assembly building block with specific supramolecular steric hindrance?SSH?effect and opto-electrical property.In this dissertation,we learn from nature,and rationally design the types and amounts of steric substituents,which reflected on the change of organic micro-nano crystals morphologies from 1D to 2D and even multi-dimension.We systematically investigate the relationship among molecular structure,micro-nano crystals morphology and optoelectronic properties,and the dynamic assembly behavior under the control over different external influencing factors such as temperature and pH.The major research findings as following:?1?Under the bioinspired lipid bilayer paradigm,we customized amphiphilic monobulk-substituted“SS-BG”building block named TPA-PF under the guideline of synergistically molecular attractor-repulsor theory?SMART?.The PF group is the repulsive bulky 9-phenyl-fluorene,similar to a hydrophobic segment,and is expected to provide steric hindrance during the self-assembly process.TPA group?triphenylamine?is analogous to hydrophilic segment with abundant supramolecular interaction sites,and is supposed to provide most of the attractive forces.The supramolecular interaction analysis based on single crystal data verified our hypothesis.TPA groups with strong supramolecular interactions present tight interdigital layer arrangement for shape and force complementation.PF segments with large repulsive force as end-capped groups locate on the both sides of TPA.TPA-PF molecular packing motifs reveal an interdigital lipid bilayer-like?ILB?molecular arrangement with TPA attractor networks in the middle and bulky PF at the outboard of the bilayers.The unique packing mode promotes the preferential growth direction along a and b-axis,and the stacking along c-axis will be suppressed,dominating the formation of high quality 2D nanosheets.The TPA-PF nanosheets show the long time charge retention when inject electrons and holes into the nanosheets,which is expected to be used as charge trap layer in memory devices.?2?In order to further clarify the effect of SSH on packing modes,morphologies and optoelectronic properties of organic semiconductors,three pyrene-based spirocyclic aromatic hydrocarbons?PSAHs?were designed to systematically explore self-assembly and property.Single crystal analysis show that the different bulky groups on pyrene core gave distinct synergistic effect of steric repulsion and attractive supramolecular interaction,which further results in different packing and morphologies in aggregate:one-dimensional?1D?nanowire for Py-SBF,two-dimensional?2D?rectangular microplate for Py-SFX and rhombic nanosheets for Py-SFDBX.Furthermore,the various structures show apparent differences in lasing properties by reason of the distinct molecular orientation and optical microcavity of the aggregated nanostructures.?3?In order to explore the self-assembly rule of dibulk-substituted dumbbell-shaped molecules,we designed and synthesized four diarylfluorene derivatives?BSBF,BDPhF,T?PF?₂ and T₂?PF?₂?.For the single crystal structures,BDPhF and BSBF own the same core linkage?CL,“bar”?,but functionalized with different supramolecular bulky group?SBG,“bell”?;T?PF?₂ and T₂?PF?₂ have the same SBG of 9-phenyl-fluorene,but distinguished by their length of CL.Such molecular systems provide an ideal platform to study the role of molecule segments during assembly.Two kinds of packing modes were adopted in their nanocrystal fabrication:layer stacking and herringbone stacking,which reflected on the change of nanocrystal morphologies from 2D to 1D,which is attributed to molecular orientation.Finally,the regularly shaped microcrystals of BDPhF show lower laser threshold of 49.4 W/cm² due to the uniaxial molecular orientation.These contributions pave the way for the rational design of dumbbell-shaped molecules toward desired morphology and photoelectric properties.?4?Multidimensional complex micro-nano crystals based on organic small molecules are rarely reported due to the weak intermolecular interactions and simple molecular structures.Extension of supramolecular interaction in 3D space via molecular design could become a feasible and effective alternative.We synthesized a windmill-shaped bulky diazafluorene molecule T?DAF?₃,and investigated the self-assembly behavior in neutral and acid environment.An unprecedented biomimetic organic microcrystal with butterfly shape can be obtained with the absence of surfactant.Time-resolved morphology evolution together with single crystal analysis clearly revealed the formation mechanism of butterfly-shaped microcrystal?BM?and the relationships between the molecular geometries and shape appearance.Additionally,the aggregates are pH-sensitive and can be converted reversibly between two morphologies of butterfly shape and cube shape.Further characterizations suggest the two distinct morphologies are polymorphism and the pH-sensitive conversion of conformation from asymmetrical motif to symmetrical one is responsible for the morphology transformation.Finally,the conductive properties of the BM were measured by conductive AFM,which revealed organic semiconducting properties.?5?The research of organic semiconductor materials is finally going to be applied to devices.At present,the production of organic semiconductor optoelectronic devices is still dominated by high-energy and expensive vacuum evaporation films.Combined with organic semiconductor materials,it can be processed at low cost and easy to prepare in large areas.The development of a wet film process route with good controllability and repeatability has become the key to the development of the organic electronics industry.Using the controllable features of molecular materials from bottom to top to achieve hierarchical control of the thin film process is an important research idea to realize the wet film process route.Based on the above problems and considerations,in this chapter,we first studied the influence of kinetic environmental factors on the morphology and homogeneity of organic nanomaterials with the steric hindrance molecule TPA?PF?₂ as the molecular model and successfully obtained a batch of uniform zero.Dimensional nanospheres,one-dimensional nanowires and two-dimensional nanosheets.Secondly,we explored the preparation of ordered nano-films based on the uniform nanomaterials.The ordered array film of nanospheres was obtained based on the"base tilt method",and the ordered film array of nanowires was obtained by the"L-B"method,combined with surfactant-assisted re-precipitation method and liquid-liquid interface self-assembly method.A nanosheet film was obtained.Finally,these three films were used as dielectric layers of OFET devices,and their applications in devices were tried.This work has opened up new ideas for the high-precision assembly of ordered thin films and their further application in devices in the future.