Rational Design,Synthesis And Characterization Of Organic Semiconductors Having Extended Heterocyclic Aromatic Compounds

Research on the n-functional materials, such as thiophene-based and thiazole-based molecules and polymers, has been attracting considerable interests in view of their wide applications on organic semiconducting materials and electronic devices, such as dye-sensitized solar cells (DSSCs), organic solar cells (OSCs), organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), chemosensors, biosensors, and electrochromic devices. In particular, linear conjugated oligomers share many of the properties of conjugated polymers with certain advantages including their well-defined chemical structures, monodispersity, better solubility, easier purification, fewer defects, and the possibility to introduce versatile functionalities. However, rational design and synthesis of extended heterocyclic aromatic compounds and supramolecular systems for constructing high-performance electronic materials are still very important and challenging issues.Limited by the tremendous gap that still exists between the structures and the properties, these problems have not been completely solved. In this thesis, many theoretical and experimental efforts have been made on the studies of a variety of linear conjugated oligomers and complexes. On the one hand, an effective strategy for designing experimentally low band-gap oligomers is to use the miscellaneous conjugated donor-acceptor (D-A) concept because different D-A units in the linear aromatic heterocyclic semiconducting compounds show different band gaps. On the other hand, theoretical study is helpful for understanding the differences from short conjugated oligomers to polymers whose properties are calculated by the extrapolation of oligomeric properties to infinite chain lengths.The aim of incorporating various D/A substituents into one molecule is to finely tune their electronic structures and compare their spectroscopic, electrochemical, and thermal properties. The acquirement of these linear heterocyclic aromatic compounds especially the single-crystal structures prompts us to further explore the possible rules between their structures and properties, for example, the relationship between the number of aromatic heterocycles and the electronic and fluorescence spectra, energy gap alterations, the limitation of solubility of compounds which is also influenced by the substituent effects. As a result, we have quite a lot of work to do from a theoretical and experimental perspective. In summary, the thesis consists of eight sections as follow:Chapter1:Organic materials with semiconducting properties are regarded as organic semiconductors, that is, with an electrical conductivity between that of insulators and that of metals. Single molecules, oligomers, complexes and polymers can be semiconductive. Semiconducting small molecules (aromatic hydrocarbons) include the polycyclic aromatic compounds pentacene, anthracene, and rubrene. Polymeric organic semiconductors include poly(3-hexylthiophene), poly(p-phenylene vinylene), as well as polyacetylene and its derivatives. Recently,π-functional materials have been widely used in many areas, due to their notable characteristics of adjustable structures and energy bands, flexible nature, and easy processing. In this chapter, we summarized some optoelectronic properties of π-conjugated molecular materials, especially, the effects of length, structure modification and metal coordination are described in detailed. The aim of review provides an intuition for understanding the structure-function relationships in molecular materials, which could lead to new design concepts for the development of new high-performance electronic materials and devices on supramolecular nanostructures. Chapter2:Syntheses, characterizations, optical, electrochemical, and thermal properties of a family of linear oligothiophene-based heterocyclic aromatic fluorescent compounds are described herein. They all have effective π-conjugated systems with D-π-D or A-π-A structures as well as different bromo, thiocyano, formyl, and triphenylamino tails. X-ray single-crystal structure of2-72methanol semisolvate reveals a trans configuration with different dihedral angles between adjacent aromatic heterocycles. Theoretical and experimental studies have been made to reveal the differences from related compounds with adjustable electronic properties. The influences of introducing different D/A functionalized tails on the band-gap convergence have also been discussed, where the convergence behavior corrected via the thienyl ring coefficient (ncorr) shows better correlation of linear fitting based on the extrapolation of HOMO-LUMO gaps at the B3LYP/6-31G*level.Chapter3:A rigid oligothiazole dithiol molecule is first introduced to fabricate the self-assembled granular thin films with gold nanoparticles (Au-NPs) covering1μm gap gold electrodes by means of the Au-S bonded contacts, where the nanocomposite thin films prepared from different concentrations of dithiol and Au-NPs (1.0,0.5, and0.1mmol/L) exhibit temperature-dependent semiconducting I-V behavior in the order of μA, nA, and pA and photoresponsive properties in the temperature range8-300K. Compared with the nanodevices fabricated from similar oligothiophene dithiols, it is interesting to mention that the oligothiazole dithiol based ones show analogous morphologies and temperature-dependent I-V characteristics but enhanced photoresponsvie properties, which may arise from the improved charge separation ability of oligothiazole in stabilizing the photogenerated electron carriers. To the best of our knowledge, this is the first report in which an oligothiazole dithiol molecule acts as a bridging unit to link Au-NPs exhibiting photoresponse properties in the solid state.Chapter4:A family of stable and soluble bithiazole-centered heterocyclic aromatic fluorescent compounds is described herein. All these multiple N-donor containing compounds have effective π-conjugated systems and different imidazole, pyridine, thiophene, triphenylamino, benzoic acid, and ethyl benzoate tails showing distinguishable D-A-A-D and A-A-A-A structures. X-ray single-crystal structures of seven compounds indicate that all of the bithiazole cores have the same trans coplanar configuration but exhibit different dihedral angles with their adjacent aromatic heterocycles (4.5(6)-69.7(3)0). Optical and electrochemical results demonstrate that the TPA-terminated bithiazole compound4-6has yellow fluorescence and reversible redox activity as well as extraordinarily high thermal stability. Theoretical and experimental studies have been made to reveal the differences from related compounds with adjustable electronic properties. The internal reorganization energy (η) studies have been carried out to indicate the differences between the bithiazole-based derivatives and the corresponding bithiophene-based counterparts.Chapter5:The first structural Re(I)-bithiazole complexes are reported. Complexes with the general formulas,fac-[ReL(CO)3Cl] have been designed and prepared successfully, where L is one of a family of linear bithiazole-based aromatic heterocyclic fluorescent ligands with two chelating nitrogen atoms as the coordination sites, bearing the different Donor/Acceptor tails (proton, bromo, thienyl, dibenzo[6,d]thienyl phenylcarbazolyl and triphenylamino). X-ray single-crystal structures of five complexes indicate that the bithiazole cores have the same cis coplanar configuration, while the trans configuration is observed in the free ligands. Density function theory computational studies on comparing the different molecular conformations as well as spectral, electrochemical, and solid-state conductance properties for related compounds before and after the metal-ion complexation have also been carried out.Chapter6:A three-dimensional (3D) metal-organic framework having a unique tetradecanuclear{Zn1/2(μ3-OH)6Na2(μ2-O)}18+hetero-metal cluster core, formulated as {Zn12(BTDA)9(μ3-OH)6Na2(μ2-O)}(6-1)[H2BTDA=4,4’.(4,4’-dibutyl-2,2’-bithiazole-5,5’-diyl)dibenzoic acid (4-7)], has been described herein. The tetradecanuclear hetero-metal cluster core is composed of two heptanuclear{Zn6-(μ3-OH}Na}10trifolium-shaped subunits where the axle sodium(Ⅰ) ion is connected with three pairs of zinc(Ⅱ) ions by three μ3-OH ions and the two sodium(I) ions are further linked by a μ2-oxo bridge. Besides, the auxiliary BTDA ligand serves as a multi-dentate bridging mode linking adjacent tetradecanuclear hetero-metal clusters into a3D coordination polymer where a rhombohedral array with a new (418·8108·1227)·(4)9topology is observed.Chapter7:A family of linear asymmetrical D-π-A and symmetrical D-π-D types of thiazole-based aromatic heterocyclic fluorescent compounds bearing various electron-donating and electron-withdrawing tails (bromo, triphenylamino, pyridyl, thienyl and benzoic acid) have been designed and prepared successfully. Synthetic, structural, thermal, spectral and computational comparisons have been carried out for related compounds because of their adjustable electronic properties. It is interesting to mention that compound7-2can be prepared from5-bromothiazole by one-pot Suzuki-Miyaura coupling and subsequent C-H activation reactions via a5-TPA-substituted thiazole intermediate7-1. X-ray single-crystal structures of six compounds indicate that they all crystallize in the triclinic P1space group and the thiazole core exhibits different dihedral angles with its adjacent benzene ring of the triphenylamino group (3.6(3)-40.8(3)0). The photophysical and electrochemical results demonstrate that compound7-7exhibits high electrochemical activity with a green fluorescence emission. Meanwhile, compounds7-1,7-2, and7-6show high luminescence quantum yields, and compound7-8exhibits excellent thermal stability (Td10=503℃).Chapter8:Metal-directed assembly of naphthalene-1,4,5,8-tetracarboxylic acid (NTA) with different transition-metal salts in the presence of ammonia results in a series of one-dimensional metal-naphtnalenediimidato (M-NDI) coordination polymers with the formulas of {[Ag(NDI)](NH4)}n (8-P1),[Zn(NDI(NH3)2]n (8-P2),[Cd(NDI)(NH3)2]n (8-P3),[Co(NDI)(NH3)2]n (8-P4) and [Ni(NDI)(NH3)2]n (8-P5), respectively. It is worthwhile to mention that the1D straight-line NDI-Ag(Ⅰ) coordination polymer P1is formed stepwise from a dinuclear NDI-Ag(Ⅰ) intermediate [Ag2(NDI)(NH3)2](8-2AgNDI), where ammonia serves as a stabilizing reagent of Ag(Ⅰ) ion and a weak base to remove the protons of NDIH2simultaneously. Furthermore, 8-Pl exhibits semiconducting properties in the solid state which may originate from its all-parallel-aligned packing structure (AAAA) which is different from the common ABAB packing mode for8-P2-8-P5and8-2AgNDI. In addition, theoretic computational studies as well as X-ray photoelectron spectrometer spectra on8-Pl and8-2AgNDI have also been carried out.