Constitutional Isomers of Dendrimer-like Pyrene Substituted Cyclotriphosphazenes: Synthesis, theoretical calculation, and fluorescence receptor for the detection of explosive nitroaromatics
Two constitutionally isomeric bis-pyrenyl phenole dendrons (4 and 6) and their dendrimer-like cyclotriphosphazene derivatives (5 and 7) with different architectural motifs on the periphery of the cyclotriphosphazene ring are designed, synthesized, and their structural characterizations are established by means of standard spectroscopic techniques (elemental analysis, 1H, 31P and 13C NMR spectroscopies and MALDI-TOF mass spectrometry). The thermal and photophysical properties of these newly synthesized compounds are also investigated. The geometric optimizations of the constitutional isomeric dendrons and their dendrimer-like derivatives, HOMO-LUMO energy levels and molecular interactions are performed by density functional theory calculation at wB97XD/6-31G(d) level. Fluorescence detection behaviors of 5 and 7 are evaluated for nitro aromatic compounds (NACs). Results of measurements show that explosive nitroaromatics efficiently quenched fluorescence emission, while other tested competitive species (toluene, RDX, picric acid, benzene and 20 metal ions) induced no spectral changes, suggesting that these dendrimer-like cyclotriphosphazene derivatives (5 and 7) can be promising candidate for sensor applications of explosive nitro aromatics with high selectivity and sensitivity.