Synthesis of styrylcoumarins from coumarin diazonium salts and studies on their spectra characteristics

A facile synthesis of styrylcoumarins based on Palladium-catalyzed reaction of coumarin diazonium salts with substituted styrenes is described. The reactions produced a series of 7-styrylcoumarins in good yields under mild conditions. The absorption and emission spectra of different styrylcoumarins were compared and discussed. Although the λa,max of the styrylcoumarins changed only slightly with a p-substituted styrene, the λe,max produced a blue shift which increased with the electron-withdrawing ability of the p-substituted group. The p-CH3 of styrylcoumarin caused a red shift of ca. 20 nm and also a higher fluorescence quantum yield. Styrylcoumarins with o, p-CN obtained well-resolved vibrational bands and the latter possessed higher fluorescence quantum yield. In addition, a coumarin extended at both the 3-positions with benzene and 7-position with p-chlorostyrene had better fluorescence properties. [Copyright &y& Elsevier]