P K Bhowmik
University of Nevada Las Vegas, USA
P K Bhowmik is currently a Professor of Chemistry in the Department of Chemistry and Biochemistry at University of Nevada Las Vegas. He received the 2014 POLY Fellow and 2014 ACS Fellow Awards for his outstanding scientific/professional accomplishments and service to the American Chemical Society. He presently serves on the Editorial Board of 10 technical journals and is an academic Editor for Trends in Green Chemistry, Advances in Research, American Chemical Science Journal and Green and Sustainability Chemistry, and as well as an Advisory Board Member for InnoSense LLC, California, USA.
Pyrylium salts are an important class of organic molecules containing trivalent oxygen atom in six-membered aromatic ring. Versatile methods for the synthesis of a series of four 2,4,6-triaryl-substitued pyrylium tosylate salts with different substituents are reported. The synthesis methods use p-toluenesulfonic acid monohydrate instead of conventional acid catalysts including perchloric acid or boron trifluoride diethyl etherate that pose explosion danger and difficult storage problem, respectively. The chemical structures of these salts were established using Fourier transform infrared, 1H and 13C nuclear magnetic resonance spectroscopic techniques and elemental analysis. Their solubility in different organic solvents was dependent on the substituents in 2nd and 6th positions of phenyl groups. Their thermal stability and thermal property were studied using thermogravimetric analysis and differential scanning calorimeter, respectively. It was observed that, solutions of all four pyrylium tosylate salts absorbed strongly in the blue-near-ultraviolet spectral range and emitted efficiently in the blue-green spectral range depending on the substituent in 2nd and 6th positions of phenyl groups. The fluorescence quantum yield of the salts ranged from 0.56 to 0.33 and under intense ultrashort laser pumping, the solution of the salt, (2,4,6-triphenylpyrylium tosylate), which was having the highest quantum yield demonstrated stimulated emission and laser action with only nominal feedback.