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 polymer in a chloroform solvent. In the analysis, we assume that the polymer consists of short conjugated segments which are called oligomers with different lengths. The appearance of each chain length is controlled by a distribution function. Based on the conformational disorder caused by torsional motion, we found that the distribution function should take a Gaussian form with its center and width being adjustable parameters. While the energy level of the emissive S1 state of the oligomer and the corresponding oscillator strength are calculated from exciton theory. In addition, the associated vibrational 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 experiment reasonably well.