Tris(dimethylamino)-Phosphan-Phenylimine as an Photoluminescent Organophosphorus Additive for Polylactic Acid

The photophysical properties of the known organophosphorus compound tris(dimethylamino)-phosphan-phenylimine, (Me2N)3P=NPh, were investigated experimentally and computationally, and its potential as a multifunctional additive for polylactic acid (PLA) was evaluated. The compound exhibits excitation-dependent dual emission, with bands centred at 409 and 533 nm. Lifetime measurements allowed these bands to be assigned to fluorescence and phosphorescence, respectively, while the electronic states involved were rationalized using time-dependent density functional theory calculations. The compound was subsequently incorporated into biodegradable PLA films to assess its potential as an optical authentication marker and its influence on the thermal stability and fire behaviour of the polymer. The doped films retained a pronounced photoluminescent response, dominated by the lower-energy emission band. Thermogravimetric analysis showed that the additive anticipated the onset of PLA degradation by approximately 30 °C and did not promote the formation of a stable char residue. Consistently, flammability tests showed no appreciable improvement in flame resistance. These findings identify (Me2N)3P=NPh as a potential luminescent marker for PLA, although its molecular structure requires further modification to achieve combined optical and flame-retardant functionality.