Photophysical Investigations of the Organic Compounds Synthesised from Waste Poly(Ethylene Terephthalate)

This paper presents the photophysical investigations of two organic compounds synthesised directly by the aminolysis depolymerisation of the waste poly(ethylene terephthalate) (rPET) with aromatic amines, i.e., aniline and 3-amino-N-hexyl-1,8-naphthalimide without use of a catalyst. The chemical structure was confirmed by ¹H-NMR and ¹³C-NMR, as well as FT-IR. The thermal, electrochemical and optical studies of the obtained derivatives were performed. The presented compounds were thermally stable up to 360 °C, and the glass transition temperature (T_g) occurred for the compound with the 1,8-naphthalimide units. The electrochemical investigations of the synthesised compounds have revealed one oxidation process and two reduction processes for the compound with the 1,8-naphthalimide fragments. The tested derivatives were characterised by a low-lying highest occupied molecular orbital (HOMO) level (below –6.09 eV) and an energy-band gap (E_g) below 3.10 eV. The obtained molecules were absorbed in the range of 204 nm - 445 nm and emitted light from a purple to a green spectral region deepened on the used solvent with low quantum yields. The blends with poly(3-hexylthiophene-2,5-diyl) (P3HT), which is used as a donor in the bulk heterojunction solar cells (BHJ), and amide derivative with 1,8-naphthalimide fragments were made, and the emission quenching of poly(3-hexylthiophene-2,5-diyl) (P3HT) was recorded. The presented results of the photophysical investigations have opened new possibilities for obtaining functional materials from recycled poly(ethylene terephthalate) (rPET).