Morphology-dependent exciton diffusion length in PPE-PPVs thin films as revealed by a Forster mechanism based-study

- Forster energy transfer mechanism FRET has been invoked to determine the exciton diffusion length.
- Optical properties (PL and Absorbance spectra) of a statistical copolymer poly(p-phenyleneethynylene)-alt-poly(p-phenylenevinylene)s (PPE-PPVs) thin films for different thicknesses and alkoxy side chains have been used as experimental data.
- Exciton-diffusion length was found dependent on the thickness and the morphology, witch it is in turn dependent on the spectral overlap.
- The side-chain length was found to increase the crystallinity, hence enhanced the exciton diffusion process.
- The highest diffusion length value (the lowest donor-acceptor distance value) corresponds to the thickest polymer film, with the longer alkoxy chain grafted on the PPV section.

The effect of thickness and alkoxy side chains on the optical properties of poly(p-phenyleneethynylene)-alt-poly(p-phenylenevinylene)s (PPE-PPVs) have been investigated in parallel fashion. A Forster energy transfer mechanism has been invoked in order to infer the exciton diffusion length (LD). The latter parameter has been determined for six differently alkoxy-substituted PPE-PPVs for different thicknesses. The dependence of LD upon the donor-acceptor (D-A) distance (d) has been assessed as well. The results reveal an increase of LD up to 25 nm, with the increase of the sample thickness and side chain length.