Carbazole-Based Helicene Compounds:Synthesis,Characterization And Properties

Helicenes are unique polycyclic aromatic compounds that possess the characteristic of the chirality.The chirality and nonlanar ?-electronic delocalization of helicenes are derived from their screw-shaped aromatic skeletons.The helicene molecules,which have physical properties including optical rotation activity,circular dichroism,nonlinear optics and the ability of self-assemble to construct supramolecular architectures,exhibit remarkable photoelectric properties and redox properties.Potential applications of helicenes have been found in the fields of non-linear optics(NLO),circularly polarized luminescence,liquid crystal displays and organic electroluminescence.Hetero[n]helicenes are a special type of helicenes,where one or more aromatic heterocyclic rings replace corresponding benzene rings.Hete ro[n]helicenes are currently arousing researcher's interest owing to the fact that they exhibited self-assembly behavior in the solid state and their complexes with transition metal ions show interesting properties in harvesting light and reemitting it at wavelengths depending on the metal ions.It means that hetero[n]helicene can be utilized in the development of light-emitting devices,chemosensors,photovoltaic dye-sensitized devices,etc.This dissertation mainly focuses on the design,synthesis,characterization and properties of two novel hetero[5]helicenes:8-Hexyl-8H-thieno[3',2':3,4]benzo[1,2-c]carbazole and 9-Hexyl-9H-4,9-diaza-indeno[2,1-c]phenanthrene.Furthermore,the quantum chemical calculation of 2,12-dithiophene-5,15-dihexy1-5,15-diaza[7]helicene was also included.8-Hexyl-8H-thieno[3',2':3,4]benzo[1,2-c]carbazole was first reported as a hetero[5]helicene based on groups of carbazole and thiophene.Carbazole and thiophene derivatives as the starting materials were used to synthesize the target compound by three sequent reactions:N-alkylation,Heck reaction and Photocyclization The compound was verified by1H NMR,13C NMR and HRMS and its optical properties,electrochemical properties and thermal properties were also investigated.The maximum absorption peaks and emission peaks in solvents such as hexane,toluene,dichloromethane,ethyl acetate,acetonitrile and methanol ranged from 298 to 301 nm and 402 to 406 nm,respectively.In contrast,the maximum emission peak in the film state was loated at 407 nm.The maximum fluorescence quantum yield of 33.7%was measured in dichloromethane among various solvents.In the electrochemical test,the compound underwent an irreversible redox process and its HOMO energy level and LUMO energy level was determined at-4.81 eV and-1.67 eV,respectively.The thermal measurement indicated that the decomposition temperature of compound was 236.16?.9-Hexyl-9H-4,9-diaza-indeno[2,1-c]phenanthrene based on groups of carbazole and pyridine was the first synthesized.Carbazole and pyridine derivatives were used to synthesize the diaza[5]helicene by three sequent steps:N-alkylation,Heck reaction and Photocyclization.Not only the compound was confirmed by 1H NMR,13C NMR and HRMS,but its optical properties,electrochemical properties and thermal properties were investigated.The maximum absorption peaks and emission peaks in solvents such as hexane,toluene,dichloromethane,ethyl acetate and acetonitrile were measured from 306 to 321 nm and 400 to 427 nm,respectively.However,the maximum emission peak in the film state was found at 518 nm.The fluorescence quantum yields in various solvents ranged from 9.0%to 13.3%.In the electrochemical measurement,the compound underwent an irreversible redox process and its HOMO energy level and LUMO energy level was located at-5.28 eV and-2.26 eV,respectively.The thermal curves indicated that the decomposition temperature was 206.31?,To gain an insight into the electronic properties of 2,12-dithiophene-5,15-dihexyl-5,15-diaza[7]helicene,quantum-chemical calculations were carried out by using the Gaussian 09 program.Vertical electronic transitions for compound were investigated by using TD-DFT methods at the B3LYP/6-31G(d)level.The transition energies,oscillator strength,and assignments for the most-relevant singlet excited states were obtained.The results of quantum chemical calculations were well consistent with the experimental data.The main absorption bands with energy gaps of 4.0449,3.9051 and 3.8296 eV originated from HOMO-2?LUMO,HOMO-1?LUMO and HOMO?LUMO+1 electronic transitions.