Thermally stable glassy luminescent cyclotriphosphazenes

A series of thermally stable cyclotriphosphazenes, hexakis(4-(9,9-dihexthyl-fluoren-2-yl)phenoxy)cyclotriphosphazene (CPZ1), hexakis(4′-(9,9-dihexyl-fluoren-2-yl)-[1,1′-biphenyl]-4-oxy)cyclotriphosphazene (CPZ2), hexakis(4-(9,9,9′,9′-tetrahexyl-[2,2′-bifluoren]-7-yl)phenoxy)cyclotriphosphazene (CPZ3), and hexakis-(4′-(9,9,9′,9′-tetrahexyl-[2,2′-bifluoren]-7-yl)-[1,1′-biphenyl]-4-oxy)cyclotriphosphazene (CPZ4), were prepared by reacting hexachlorocyclotriphosphazene with suitable precursors in high yields. The chemical structures and properties of the compounds CPZ1-4 were characterized by thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, and UV–Vis and fluorescence spectroscopy. All CPZ compounds were amorphous in nature and showed very good thermal stability with decomposition temperatures of more than 429 °C in nitrogen and around 400 °C in air. CPZ3-4 emitted blue light with maxima of 403 and 416 nm with quantum yields of 0.69–0.56 in THF solution, respectively. Study on the thermal aging effect on the optical properties of CPZ2-4 revealed that three-dimensional hybrid organic–inorganic cyclotriphosphazene ring could suppress the undesirable green emission by obstructing π–π stacking. In addition, light-emitting diode devices of CPZ3 and CPZ4 were fabricated.