Thermally stable glassy luminescent cyclotriphosphazenes

Abstract

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 416nm 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.