Tuning the solid-state fluorescence of chalcone crystals via molecular coplanarity and J-aggregate formation

Abstract

Four chalcones bearing the 1,3-diarylpropenone moiety 3-(9-anthryl)-1-(4-chloro)prop-2-en-1-one (I), 3-(1-pyrenyl)-1-(4-chlorophenyl)prop-2-en-1-one (II), 1-phenyl-3-(1-pyrenyl)prop-2-en-1-one (III) and 3-(1-pyrenyl)-1-(4-nitrophenyl)prop-2-en-1-one (IV) were synthesized and different crystal forms were obtained from different solvents by slow evaporation including I (I_a, I_b), II (II_a, II_b, II_c), III (III_a, III_b, III_c, III_d) and IV (IV_a, IV_b). Their structures and optical properties were characterized by single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), UV-Vis absorption spectroscopy and fluorescence spectroscopy. Hirshfeld surface calculations were also used for intermolecular interaction analysis. It has been found that polymorphism and conformational isomorphism exist in these crystals. I_b and III_a adopt a cis configuration with respect to the central CC bond while the other forms exhibit a trans configuration, except for those without single crystal X-ray analysis. Both I_b and II_b have two crystallographically independent molecules in their asymmetrical unit which has not been found in reported chalcone crystals. Those crystals with a cis configuration show a higher melting point and no fluorescence. Crystals with a trans configuration are fluorescent and their emission wavelengths are mainly effected by the torsion extent of the molecules and J-aggregate formation.