Tris(dimethylamino)-phosphan-phenylimine as photoluminescent organophosphorus additive for polylactic acid films

The organophosphorus compound tris(dimethylamino)-phosphan-phenylimine, (Me₂N)₃P=NPh, was synthesized through the Staudinger reaction between tris(dimethylamino)-phosphine (Me₂N)₃P and phenylazide PhN₃, according to a reported procedure [1]. The structure of the compound was confirmed by means of multinuclear NMR spectroscopy. The pure compound exhibits appreciable photoluminescence in the violet-blue region under irradiation with a Wood lamp. Spectrofluorimetric measurements revealed that (Me₂N)₃P=NPh is characterized by excitation-dependent dual emission. The two bands are centered at 409 and 533 nm, respectively. Photoluminescence excitation spectra allowed to conclude that the two bands are correlated and, according to time-correlated experiments, attributable to fluorescent and phosphorescent radiative decays. The excited states involved were rationalized by means of time-dependent density functional theory (TD-DFT) calculations. The presence of two distinct emission bands makes the emission of (Me₂N)₃P=NPh excitation dependent [2].

The unexpected luminescence features of (Me₂N)₃P=NPh and its appreciable stability prompted to consider this species as dopant for biodegradable plastics, polylactic acid (PLA) in particular. Thin PLA films containing variable amounts of (Me₂N)₃P=NPh were prepared through optimized procedures and characterized spectroscopically. The luminescence associated with the presence of the embedded dopant molecules was investigated in detail. Given the composition of (Me₂N)₃P=NPh, thermal measurements and flammability tests were also performed to verify whether the compound could behave as multifunctional dopant for PLA films [3].

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