Fused-Ring Heterocyclic Compounds Based On Carbazole:Syntheses,Crystal Structures And Properties

Fused heterocyclic compounds are polycyclic aromatic compounds with one or more benzene rings were replaced by the heterocycle,and with the additional properties due to the heteroatom could improve various optoelectronic properties.In this paper,through the introduction of bromine and thiophene groups into 9-Hexyl-9-carbazole-3-carbaldehyde.two new different types of fused-ring heterocycles based on carbazole and naphthalene,that is,10-bromine-7-hexyl-7-monoaza[6]helicence and 14-hexyl-11-(thiophen-2-yl)-14H-phenanthro[4,3-b]carbazole were successfully synthesized.10-bromine-7-hexyl-7-monoaza[6]helicene is an extension of the known monoaza[6]helicene.The carbazole moiety was modified at its 3-,6-,or 9-positions and covalently linked to other moieties of molecules.The compounds based on carbazole and naphthalene were synthesized by a series of classical chemical reactions such as phase transfer,Vilsmeier-Haack reaction,Wittig reaction,and photocyclization reaction.We investigated the 1H NMR,13C NMR,HRMS,single crystal structure,and studied the optical properties,electrochemical properties,thermal properties.The molecular structure is spiral,and the dihedral angle between carbazole and naphthalene is 41.3°.The compound had the maximum absorption peak near at 319 nm and maximum emission peak near at 435 nm in dichloromethane,and the maximum emission peaks were found near at 447 and 470 nm in the thin film state,respectively.The fluorescence quantum yields of compound in different solvents were measured in the range of 8%-18%,and the highest was in toluene up to 18%.Compound exhibited quasi-reversible oxidation and reduction behavior with HOMO energy level of-4.95 eV,LUMO energy level of-2.04 eV.The optical band gaps was 2.91 eV.The decomposition temperature was at 236.82 ?,indicating that compound had good solubility and thermal stability.14-hexyl-11-(thiophen-2-yl)-14H-phenanthro[4,3-b]carbazole had one more step Suzuki-Miyaura reaction to introduce thiophene compared with 10-bromine-7-hexyl-7-monoaza[6]helicene.We investigated the characterization with 1H NMR,13C NMR.HRMS and single crystal structure,and studied the optical properties,electrochemical performance and thermal properties.The molecular structure is coplaner,and the dihedral angle between carbazole and naphthalene is 155.8°.Single-crystal structures revealed that 14-hexyH l-(thiophen-2-yl)-14H-phenanthro[4,3-b]carbazole possessed less distortion,deformation and better planarity than 10-bromine-7-hexyl-7-monoaza[6]helicene.Compound had maximum absorption peak near at 337 nm and maximum emission peak near at 447 nm in dichloromethane,maximum emission peak near at 460 nm in the thin film state.The fluorescence quantum yields of compound in different solvents were measured in the range of 35%-74%,and the highest was in toluene up to 74%.Compound exhibited quasi-reversible oxidation and reduction behavior with HOMO energy level of-4.85 eV and LUMO energy level of -2.09 eV.The optical band gaps was 2.76 eV.The decomposition temperature was 214.96?,indicating that compound had good solubility and thermal stability.These results showed that introducing the functional substituent group of thiophene to the carbazole could not only transform photocyclization products from helicenes into other types of fused-ring heterocyclic compounds but also increase the fluorescence quantum yields of 14-hexyl-11-(thiophen-2-yl)-14H-phenanthro[4,3-b] carbazole by more than three and half times.The simple synthetic method would pave the way for obtaining fused-ring heterocycles with diverse types and various properties.