Synthesis, characterization, photophysical and intramolecular energy transfer properties of oxy-naphthylchalcone appended cyclotriphosphazene cores

In this study, three novel oxy-naphthylchalcone appended cyclotriphosphazene derivatives (3, 4 and 5) were obtained by the nucleophilic substitution reactions of cyclotriphosphazene cores (1, 1a and 1b) with (E)-3-(4-hydroxyphenyl)-1-(naphthalene-2-yl) prop-2-en-1-one (2) in presence of K2CO3/acetone. Novel compounds 3, 4 and 5 were characterized with using NMR (H-1 and P-31), elemental analysis, mass and FT-IR spectroscopies. In addition, molecular and crystal structures of 2 and 3 were determined by single crystal X-ray crystallography. The photophysical and intramolecular energy transfer properties of novel oxy-naphthylchalcone appended cyclotriphosphazene derivatives (3, 4 and 5) and their precursors (1a and 1b) were examined by steady state-/time resolved fluorescence spectroscopy, UV-Vis absorption spectroscopy and excitation-emission matrix (EEM) analysis. According to obtained results, novel target compounds (4 and 5) demonstrate a highly efficient intramolecular fluorescence resonance energy transfer (FRET) between excited phenol/naphthol groups and oxy-naphthylchalcone group.