The thermofluoric behavior of poly(fluorenetolyldiphenylamine)–oxadiazole pair in a polymer matrix

Abstract

Under UV irradiation, 1,4-bis(5-(4-octan-2-ylphenyl)-1,3,4-oxadiazol-2-yl)naphthalene (NOXD) and poly(fluorenetolyldiphenylamine) (PFT) are blue light emissive in solid film. When NOXD and PFT were blended to form a neat thin-film, yellowish exciplex emission was observed. The emissive properties vary when the materials were blended into different kinds of polymeric hosts; while polystyrene–NOXD–PFT (5 : 1 : 1) and PMMA–NOXD–PFT (5 : 1 : 1) showed blue light emission, poly(acrylonitrile-co-methyl acrylate) (P(AN-co-MA))–NOXD–PFT (5 : 1 : 1) showed blue and yellow dual emissions. When the film was heated at 140 °C for 2 min, the yellow light exciplex emission was enhanced. However, upon cooling to ambient temperature, the exciplex emission intensity gradually dropped back. Similar thermofluoric behaviors were observed when the thermally crosslinked polyepoxy-polymercaptan–NOXD–PFT film (20 : 1 : 1) was heated at 160–170 °C; the blue light emissive film showed yellow light emission, and turned white when cooling down to ambient temperature. This thermofluoric phenomenon is recyclable. We attributed the observation of the yellow emission to the segregation of NOXD from the polymeric host at high temperature that allows NOXD to aggregate with PFT, leading to exciplex emission.