Aza[7]helicene And Its Thiophene Substituted Derivative:Synthesis,Crystal Structures And Properties

Fused polycyclic aromatic compounds,especially helicenes,which possess rigid molecular structure and unique optoelectronic properties,have been extensively used for potential applications in the field of organic electronics.These compounds that contain heteroatom in their aromatic skeletons considerably contributes to changing the electronic structure and helps fine-tune various optoelectronic properties.In this paper,carbazole was used as the starting material for the reactions,two new fused-ring aromatic compounds based on carbazole and anthracene,that is,15-hexyl-15H-tetrapheno[1,2-b]carbazole and 15-hexyl-12-(thiophen-2-yl)-15H-tetrapheno[1,2-b]carbazole were first successfully synthesized.15-hexyl-15H-tetrapheno[1,2-b]carbazole was synthesized via classical organic reactions such as Phase transfer catalyst reaction,Vilsmeier-Haack reaction,Witting reaction,Heck reaction,Photocyclization reaction.The compound was characterized by 1H NMR,13C NMR,Time-of-flight mass spectrometry,single crystal structure analysis.Furthermore,its thermal,electrochemical,optical properties as well as theoretical calculations were also investigated.In UV-visible absorption spectra,the strong peaks of the compound in different solvents ranged within the wavelength of of 294-295 and 323-338nm.In the PL spectra,the maximum fluorescence emission peak was in the range of 446-492 nm,and the highest fluorescence quantum yield of the compound in different solvents was up to 6%measured in dichloromethane.In the thermal spectrum,the decomposition temperature of compound was determined at 236.57 ?,indicating that compound had relatively good thermal stability.In the electrochemical spectrum,HOMO energy level of the compound was measured to be-4.93 eV,and LUMO energy level was determined at 2.71 eV by the band gap of-2.22 eV.This indicated that the compound had relatively good hole transporting ability.The results of theoretical calculations manefested that the 294-295 nm absorption peak of the molecule was mainly attributed to the H-1?L+2 electronic transition.Compared with the synthesis of the former compound,15-hexyl-2-(thiophen-2-yl)-15H-tetrapheno[1,2-b]carbazole was obtained via the introduction of the substituent of thiophene to the fused-ring skeleton.The compound was verified by 1H NMR,13C NMR,high resolution mass spectrometry,single crystal structure analysis,and its thermal,electrochemical,optical properties as well as theoretical calculations were also investigated.In optical spectra,the strong UV-visible absorption peaks in different solvents were in the range of 240-245 and 300-350 nm.Meanwhile,the maximum fluorescence emission peak ranged within 452-494 nm.The highest fluorescence quantum yield in different solvents was up to 50%in dichloromethane.The decomposition temperature of compound was measured at 249.84 ?,indicating that the compound had better thermal stability than the former.The HOMO energy level of the compound was at-4.82 eV while the LUMO energy level was determined to be-2.14 eV by the band gap of 2.68 eV.These results indicated that the compound had better hole transporting ability than the former.The results of theoretical calculations indicated that the 342 nm absorption peak of the molecule was ascribed mainly to the H?L+2 electronic transition.In summary,by comparision of two compounds results,the thermal,carrier transport and optical properties of the latter were enhanced,especially the fluorescence quantum yields,whose highest value amounted to eight times of the maximum in the former.The method of synthesis provides a new route to create or innovate functional materials in the field of organic optoelectronics.