A Study on the Synthesis and Spectra Characteristics of Coumarins

o-Methoxy stilbene and 3- or 4-phenylcoumarins rigidified by a lactone configuration were synthesized by Wittig reaction, Perkin reaction, and Pechmann reaction respectively. The absorption-emission spectra and the fluorescence quantum yields in THF were determined and the structure-spectra relationships were discussed. The rigidification of 3-phenylcoumarin caused a 2 nm bathochromic shift for the absorption maximum (λa,max), 20 nm for the emission maximum (λc,max), and 18 nm increase of Stokes shift (△λ). It also gave a higher fluorescence quantum yield than its open chain analog. The introduction of methoxy at the 7-position in 3-phenylcoumarin caused a 16 nm bathochromic shift for λa, max, 21 nm for λc, max, and resulted in an excellent fluorescence quantum yield approaching 100%. The phenyl group at the 4-position produced blue shifts of λa.max and λc.max and decreased the fluorescence quantum yield significantly.