Photostability and photobactericidal properties of porphyrin-layered double hydroxide–polyurethane composite films

Abstract

The photostability and photobactericidal properties of PdTPPC (Pd(II)-5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin)–Zn₂Al/PU (polyurethane) composite films have been studied in order to investigate their applicability as new photodynamic surfaces. These films comprise a PdTPPC porphyrin photosensitizer intercalated between the lamella of Zn₂Al layered double hydroxide and dispersed (1 wt%) into a polyurethane matrix. The study of the photophysical behaviour shows that the Zn₂Al LDH host enhances the chemical stability of the PdTPPC guest by minimizing photobleaching and quenching aggregation effects. The singlet oxygen production under irradiation of PdTPPC–Zn₂Al/PU composite films is confirmed by the observation of an O₂(¹Δ_g) emission band centered at 1274 nm. Furthermore, the value of the rate constant k_q for the PdTPPC phosphorescence quenching by oxygen k_q = (8.2 ± 0.3) 10⁻² s⁻¹ Pa⁻¹ indicates a slow diffusion of oxygen into and out of the PU polymer. In a second step, accelerating light ageing tests are conducted to determine the effect of singlet oxygen production on the chemical and mechanical stability of the PU matrix. Oxygen uptake experiments coupled with ATR-IR measurements indicate the probable formation of hydroxylated photoproducts but with no detrimental effects on the microstructure and the viscoelastic properties of the PU matrix as evidenced by dynamical mechanical analysis. Finally, in vitro preliminary antimicrobial tests show that PdTPPC–Zn₂Al/PU composite films are able to inhibit S. aureus growth with no release of PdTPPC biocide from the PdTPPC–Zn₂Al/PU composite film. We also observe a total inhibition of P. aeruginosa growth suggesting an efficacy against biofilm formation.