Experimental and theoretical investigations of absorption and emission spectra of the light-emitting polymer MEH-PPV in solution

We report the absorption and photoluminescence spectra of the MEH-PPV polym er in a chloroform solvent. In the analysis, we assume that the polymer con sists of short conjugated segments which are called oligomers with differen t lengths. The appearance of each chain length is controlled by a distribut ion function. Based an the conformational disorder caused by torsional moti on, we found that the distribution function should take a Gaussian form wit h its center and width being adjustable parameters. While the energy level of the emissive S-1 state of the oligomer and the corresponding oscillator strength are calculated from exciton theory. In addition, the associated vi brational motions are considered in determining the spectral shape in which both displacement and distortion of the potential surfaces are taken into account. With this information, the calculation result can fit the experime nt reasonably well. (C) 2000 Elsevier Science B.V. All rights reserved.