Role of Crystal Packing and Weak Intermolecular Interactions in the Solid State Fluorescence of <i>N</i>-Methylpyrazoline Derivatives

Abstract

Six compounds containing an N-methylpyrazoline ring fused with flavanone derivatives have been synthesized and characterized by X-ray structural studies and fluorescence spectroscopy. The influence of molecular arrangement on the emission properties, including fluorescence lifetime and quantum yield, was discussed on the basis of structural data and detailed analysis of the Hirshfeld surfaces. The correlation of fluorescence and crystal packing reveals that solid state emission of this class of compounds strongly depends on intermolecular interactions present in a different crystal lattice. It was observed that the inverse of fluorescence lifetime (1/τavg) is dependent on a percentage contribution of H···O and H···N contacts in the Hirshfeld surface. In addition, the lipophilicity (log P) of these compounds is related to contribution of C···H interactions as well as noncovalent bonding involving a halogen atom.