Synthesis of Polyaryl-substituted Bisquinazolinones with potential photophysical properties

Abstract

3,5-Dibromo-2-aminobenzamide was reacted with 1,3-cyclohexanedione derivatives in the presence of iodine as catalyst in toluene under reflux to afford novel 6,8-dibromo-2-[3-(2´-alkyl-1´,2´,3´,4´-tetrahydro-6´,8´-dibromo-4´-oxoquinazoline-2yl)propyl]quinazolin-4(3H)-ones in high yields. Suzuki-Miyaura cross-coupling of the latter with arylboronic acids in the presence of Pd(PPh3)2Cl2–Xphos catalyst complex and K2CO3 as a base in dioxane-water mixture (3:1, v/v) afforded the corresponding polyaryl-substituted bis-heterocycles in a single step operation. The resultant compounds were characterized using a combination of NMR (1H and 13C) and IR spectroscopic techniques, as well as mass spectrometry. The electronic absorption and emission properties of these polyaryl-substituted bis-heterocycles comprising 2,3-dihydroquinazolin-4(1H)-one and quinazolin-4(3H)-one moieties linked by a flexible carbon chain were measured in dimethylsulfoxide (DMSO) and acetic acid by means of UV-Vis and fluorescence spectroscopic techniques. The absorption spectra of the resultant polyaryl-substituted bis-heterocycles showed blue-shift in acetic acid and red-shift in DMSO, while their emission spectra are blue-shifted in DMSO and red-shifted in acetic acid. The 4-methoxy groups on aryl-substituents caused red shift on π‒π* transition of the aryl-substituents. Moreover, it was also observed that as the propyl linkage becomes more substituted, the absorption and emission intensities decrease.