MEH-PPV hypsochromic shifts in halogenated solvents induced by γ-rays

The development of materials, devices, and methods that allow for the detection of low doses of ionizing radiation is an important research area. In this sense, conjugated polymers have been proposed as promising dosimetric materials. In particular, polymer solutions and composites have been appointed as high-sensitivity systems, but there is no satisfactory understanding of the effects induced by radiation in these systems. Further investigations are therefore necessary for the achievement of more sensitive systems. In this paper, the effect of gamma-ray radiation on different alkyl halide and toluene solutions of poly [2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) is reported. To this end, samples were irradiated with a 60Co gamma-ray source at room temperature, using doses of up to 30 Gy. Chloroform, dichloromethane, bromoform, dibromomethane, a mixture of dichloromethane and diiodomethane, and toluene were employed as solvents. The MEH-PPV concentration in the solutions fell in the range of 0.005–0.225 mg mL−1. Irradiation of the MEH-PPV alkyl halide solutions was followed by UV–vis spectroscopy measurements, and a blue shift in the main MEH-PPV UV–vis absorption peak was detected. The results revealed that the gamma-ray radiation effects depend on the nature of the solvent and on the concentration of the polymer, thereby indicating that they are associated with the formation of a radical. By selection of a suitable solvent and of an appropriate polymer concentration, a simple dosimeter can be constructed for medical applications as well as other uses.

► Solutions with halogenated solvents presented hypsochromic shifts.
► The effect is not observed in toluene, where halogen atoms are absent.
► The solvent performs a key role in the process.
► The shifts is associated to radical formation.