Solvatochromic Behaviour and Prototropic Studies of some oxazolones of electron donor‐acceptor type

Abstract Solvatochromic and halochromic behaviour in the u.v.‐vis absorption spectra of some substituted 4‐arylidene‐2‐aryloxazol‐5‐ones ( 1–5 ) are studied. Positive and negative solvatochromism, depending on the substituent present, are observed in different hydrogen bonding donoracceptor (HBD‐A) and hydrogen bonding acceptor (HBA) solvents. However, in non hydrogen bonding (NHB) solvents all compounds show a positive solvatochromism. A considerable intramolecular charge transfer interaction, between the donor and acceptor parts in the oxazolones studied, is observed. Small fluorescence quantum yields are observed for the oxazolones. In triethanolamine‐acetone mixtures, the visible absorption spectra of the hydroxy substituted oxazolone shows an additional long‐wavelength band suggesting the existance of prototropic equilibria. The prototropic equilibrium constants at different temperatures are determined.