Synthesis And Supramolecular Self-assembly Properties Of Thiophene/indole-fused Phenazines Derivatives

Organic one-dimensional(1D)functional nano/microstructures based on ?-conjugated molecules have been employed as important building blocks for advanced materials and smart miniature devices,due to their unique advantages involving high aspect ratio,processability,compatibility with flexible and lightweight substrates,low-cost and large-area fabrication,etc.Furthermore,organic nano/micro materials can exhibit various and tunable optoelectronic properties by synthesizing new molecules or controlling the size and shape of their structures,providing lots of possibilities for their multi-functional applications.To achieve desired nano/micromaterials with specific geometric structures and properties,we need to devote ourselves to further exploring this promising field,especially the relationship among molecules,assembly,structures and properties.Benefitting from the present development status,we have known that the optoelectronic properties of the nano/micromaterials are sensitively dependent on their structures.Considering that noncovalent interactions play a crucial role in dominating the supramolecular assembly characteristics,the precise regulation of noncovalent interactions within organic nano/micromaterials is thus the fundamental issue.Well-defined molecular self-assembly systems with multi types of interactions are needed,in which the type and strength of the driving force could be manipulated through molecular structure engineering,which will beneficial for obtaining in-depth knowledge of the self-assembly process as well as the design principles from molecular structure to functional assembled nanostructures.In this thesis,we carried out a systematic investigation on molecular self-assembly based on series of halogen-and alkyl-substituted thiophene/indole-fused phthazine derivatives.The construction strategy of these molecular building blocks is based on the following considerations:(i)A T-shaped coil-plate-coil structure composed of a ?-conjugated plate and two flexible side chains may promote the anisotropic assembly of building blocks.(ii)The D-A character of the ?-conjugated plate with electron-deficient phenazine fused by electron-rich thiophene rings may provide desirable optoelectronic functions.(iii)The large ?-conjugated plate modified with alkyl chains and sulfur and halogen atoms potentially affords intermolecular van der Waals,C-H···?,?···?,S···S,and halogen-bonding interactions which are expected driving forces for supramolecular self-assemblies.(iv)The abundant molecular building blocks with various halogen atoms and other possible groups provide an opportunity for in-depth understanding of the mechanism of supramolecular assembly.We mainly focus on the relationship among molecules,assembly characteristics,structures and properties,which is divided into four parts.1.In chapter II,a class of halogenated 2,5-dihexyldithieno[3,2-a:2?,3?-c]phenazine derivatives(XDTP-C6,X = F,Cl,Br,I)were synthesized and used as building blocks to assemble luminescent 1D nano/micromaterials.This class of luminescent organic molecules exhibits a unique halogen-dependent 1D self-assembly property.By varying the halogen atoms,luminescent 1D wires with twisted,straight,and zigzag morphologies have been obtained.Detailed single-crystal X-ray analyses and theoretical calculations demonstrated that halogen-dependent anisotropic noncovalent interactions dominate the 1D-assembly behaviors and crystal structures of XDTP-C6.The unprecedented 1D zigzag self-assemblies of organic molecules Br DTP-C6 and IDTP-C6 is attributed to the mirror-symmetrical crystallization based on specific lattice planes.We have thus developed an efficient strategy,i.e.alternation of halogen substituents,for regulating geometric shapes of 1D organic nano/micromaterials.2.In chapter III,two series of dithienophenazine derivatives,9,10-difluoro-2,5-dialkyldithieno[3,2-a:2',3'-c]phenazine(F-n,n = 4,5,6,7 and 8)and 9,10-dichloro-2,5-dialkyldithieno[3,2-a:2',3'-c]phenazine(Cl-n,n = 4,5,6,7 and 8),modified with various lengths of linear alkyl chains were synthesized and used as building blocks to assemble luminescent nano/micromaterials.It was demonstrated that the side-chain length can dramatically influence the self-assembled morphologies of the F-n and Cl-n based micromaterials.F-4,F-6 and F-7 molecules assembled into 1D twisted microwires and F-8 molecules generated long flat microribbons.Significantly,F-5 can self-assemble into nearly criss-cross(orthogonal)network patterns interconnected by 1D wires.The assembly properties of Cl-n molecules show more significant chain-length-dependent assembly characteristics.Microwires,microblocks and microzigzags were generated by Cl-4,Cl-5 and Cl-6,respectively.Twisted microwires were formed by Cl-7 and Cl-8 with longer alkyl chains.Single crystal X-ray structure studies of F-n and Cl-n(n = 4,5 and 6)demonstrated that alkyl chains with different lengths result in distinctly different intermolecular interactions and molecular packing structures,which provides a reasonable explanation for the alkyl chain length dependent morphologies of F-n and Cl-n based micromaterials.The unique F-5 based criss-cross network was associated with the mirrorsymmetrical crystallization by sharing lattice planes.The F-4 and F-5 based assembly samples exhibited phase-dependent luminescence properties,which is because different polymorphs have distinguished supramolecular structures.In this contribution,we present a possible approach to control the 1D assembly of organic nano/microstructures by regulating the length of alkyl chains that are attached to the rigid ?-conjugated core.3.In chapter IV,we designed and synthesized a series of halogenated(F,Cl,Br,or I)dihexyldithieno[2,3-a:3',2'-c]phenazine derivatives.Compared to the isomers investigated in Chapter II,this series of compounds generate different nano/microstructures,indicating that modifying the same substituent onto different positions in the molecules is also an effective way to regulate the self-assembled stuctures.In particular,the achiral fluorinated molecule shows the strong ability of helical 1D assembly.Under appropriate processing conditions,it is able to self-assemble into a variety of helical nano/microstuctures including twisted ribbons,spring-like helical coils,spiral-based microtubes and microrods.From the supramolecular point view,the fluorinated molecules adopt a one-dimensional layer-like arrangement based on planar molecular chains and ?-? stacking.The possible intermolecular H-bonding interaction between the solvent and solute molecule could break the symmetry of packing and trigger the form of helices.The actual mechanism of formation of the helical structures reported in this study is likely to be very complicated and this is an ongoing investigation.At this point,we have thoroughly investigated the chemical structure-dependent self-assembly properties of the dithienophenazine derivatives,which is referential value for the constuction of controllable organic nano/microstructures in the future.4.In chapter V,we designed and synthesized a series of halogenated dihydrodiindolophenazine derivatives(XDIP-C4,X = F,Cl,Br,I)to systematically investigate the supramolecular structures and the fluorescence emission properties in solution and in the solid state.For FDIP-C4 and IDIP-C4 solids,the molecules adopt the similar one-dimensional columnar structure driven by strong ?-? interactions,and thus exhibited similar emission and assembly properties with decent 1D nanowire morphology.While in the case of ClDIP-C4 and BrDIP-C4,their solids showed the same emission color and fluorescent quantum yield,and they displayed similar tendency of two-dimensional growth,which is attributed to their similar supramolecular structure resulting from the appearance of X···X halogen bonds.The study confirmed that predicting the solid-state properties of fluorophores is particularly challenging.The optical characteristics of dyes in solution are not directly transposable to the solid state,because the solid-state properties are influenced by many factors.In the present case,the intrinsic properties of the molecules,governed by heavy atom effect,were modulated by the influence of the molecular arrangement.It further confirmed the significant influence of halogen on the supramolecular structure and assembly morphology.In summary,we have designed and synthesized series of thiophene/indole-fused phthazine derivatives,and have investigated the dramatic effects of halogen,alkyl-chain length and position of sulfur atom on the supramolecular self-assembly property.As a result,diverse one-dimensional nano/microstructures involving twisted,helical,zigzag,and criss-cross shaped architectures have been obtained,which colud be good candidates for photonic/electronic devices when special structures are required.It is hoped that these results would help us to achieve a better comprehension of function-oriented material design and synthesis through molecular tailoring.