Studies On The Synthesis And Spectral Properties Of Novel 1,8-Naphthalimides

Fifty-eight novel 1,8-naphthalimide derivatives with a π-conjugated group at the C-4 position are synthesized using 4-bromo-l,8-naphthalimides as starting materials and catalyzed by a Pd(PPh3)2Cl2 / CuI system. Their structures are characterized using IR, NMR, EA and HRMS. The absorption-emission spectra and fluorescence quantum yields are determined and the relationships between molecular structure and fluorescence properties are studied.Five 4-alkylalkynyl-1,8-naphthalimides and twenty-three 4-arylalkynyl-1,8-naphthalimides are prepared in high yields by Sonogashira reaction, which employed Pd(PPh3)2Cl2 as catalyzer, CuI as co-catalyzer and Ph3P as ligand. According to their spectral data, 4-arylalkyne-1,8-naphthalimides present excellent fluorescent characteristics and most of them had a blue-purple fluorescence. λUV, max are in the range 372-380 nm and λFL, max are in the range 428-460 nm. Changing substituted groups at the arylethyne had a great effect on spectral properties. Introducing an electron-donor group (-CH3) at the p-position of phenylethynyl of 1,8-naphthalimide caused a significant bathochromic shift of the absorption maximum. The largest red shift occurred when a methoxy is at the p-position of the phenylethynyl (λUV, max = 399 nm and λFL, max = 531-533 nm) and an obvious hypsochromic shift occurred when there is an electron-acceptor (-CN) at the p-position of phenylethynyl of 1,8-naphthalimide. In addition, extending the conjugated chain caused a greater bathochromic effect on the absoiption and emission maximum. Most of the 4-arylalkynyl-1,8-naphfhalimides showed higher fluorescence quantum yields than those of 4-alkylalkynyl-1,8-naphthalimides. From the electroluminescent characteristics, it can be expected that 4-arylalkynyl-1,8-naphthalimides have potential applications as electroluminescent devices.Fourteen N-alkyl 4-(2-benzo[b]furanyl)-l,8-naphthalimides and nine N-alkyl-4-(2-indol)-1,8-naphthalimides are prepared by Pd(PPh3)2Cl2-catalyzed Sonogashira-type cycloaddition reaction from 4-ethynyl-N-alkyl-1,8-naphthalimide and substituted ο-iodophenol or ο-iodo-aniline in dioxane with TMG as base. It is shown from the absorption and fluorescent spectra that benzofuranyl-substituted compounds present better fluorescence properties than those of the indol-substituted compounds. The UV/vis absoiption spectra of benzofuranyl-substituted compounds are in the range of 380-400 nm and the emission spectra are in the range of 500-520 nm. The changing of substituents at the benzo[b]furan ring had remarkable effects on the λUV. max and λFL, max. The introduction of an electron-donor group (-CH3) at the benzo[b]furan ringcaused a bathochromic shift in the absorption and emission peaks of these compounds, but the introduction of an electron-withdrawing group (-CN) caused a hypsochromic shift in the spectrum. It is interesting to note that with each addition of a methyl to the benzo[b]furan ring, the wavelength of fluorescence emission maximum increased about 4 nm. On the other hand, the indole substituted compounds presented lower fluorescence quantum yields. For N-tosyl indole compounds, the λFL, max are in the range of 500-510 nm, and for N-H compounds, the λFL, max are in the range of 580-590 nm. In addition, it can be expected, from the mensurement of electroluminescent properties, that 4-benzo[b]furan-1,8-naphthalimides have potential applications as electroluminescent devices.Two 4-(2-phenyl-benzo[b]mran-3-yl)-l,8-naphthalimides and four 4-(2-aryl-benzo[b]furan-3-ethynyl)-1,8-naphthalimides are synthesized by palladium-catalyzed cycloaddition reaction from ο-iodophenol and 4-bromo-l,8-naphthalimide. Study of the spectral characteristics shown that extending the conjugated chain caused a red shift in the UV / vis and FL spectra. The UV/vis absorption spectra of the foraier are in the range of 300-320 nm and there are two peaks in the emission spectra, one in the range of 400-425 nm, the other near 550 nm. For the latter, the λUV, max is in the range of 400-420 nm, with the absorption maxima...