Excimer state of a conjugated polymer (MEH-PPV) in thin films

In this paper, the spectral properties of a conjugated polymer poly [2-methoxy-5-(2′-ethylhexyloxy)-1, 4-phenylene vinylene] (MEH-PPV) in thin films have been studied. The results obtained were compared with MEH-PPV in liquid states. First, MEH-PPV was dissolved in tetrahydrofuran (THF) for different concentrations. These solutions were deposited on glass substrates to form thin films with different thicknesses ranging from 0.85 to 1.40 μm. The absorption spectra showed no new peak when the thickness of the thin film increased, which indicates no dimer formation in these thin films. The photoluminescence (PL) spectrum for the thickness 0.85 μm showed two peaks; one at 572 nm as dominant and the other at 615 nm as shoulder. The dominant and the shoulder peaks are attributed to monomeric and excimeric states. However, when the thickness increased, the intensity of the peak at 572 nm decreased and the intensity of the peak at 615 nm increased. At a thickness of 1.40 μm the peak at 572 nm was almost absent and there was only one peak at 615 nm. These dramatic changes in PL spectra could be due to the formation of the excimer in the thin film. The results obtained were compared with the spectral properties of MEH-PPV dissolved in THF for different concentrations. It was found that the thin film of MEH-PPV could exist in an excimeric state similar to that of the liquid state.

► MEH-PPV deposited in thin films for different thicknesses. ► MEH-PPV could exist in excimeric states. ► MEH-PPV in thin films were compared with MEH-PPV in solution.