Microwave-Assisted Synthesis of Near-Infrared Chalcone Dyes: a Systematic Approach

(<i>E</i>)-3-[4-(Dimethylamino)phenyl]-1-(2-hydroxyphenyl)prop-2-en-1-one is an organic dye with potential application in dye-sensitized solar cells. In order to fully investigate and characterize this molecule, many synthetic approaches were applied, including base and acid-catalyzed synthetic methodologies. NaOH, KOH, Ba(OH)₂·8H₂O, K₂CO₃, Et₃N, SOCl₂, HCl, HOAc, and Ac₂O were utilized in different solvents and reaction conditions; however, all attempts failed to access the desired product in an efficient and productive way. A good success was achieved employing excess of piperidine, as base in refluxing ethanol. The reaction completed in 3 days; however, the product was obtained in 85% purity. In order to minimize the formation of side products, and taking in consideration a greener approach, such as shortening the extended reaction time and reducing excess production of organic wastes, the reaction was performed under controlled microwave reaction conditions. With greater success, the desired product was obtained in excellent isolated yield and high purity, in a shorter reaction time. This novel approach was then explored to investigate its scope and limitations to access other chalcone dyes.