On the fluorescence depolarization and the calculation of rotational relaxation times of rigid rod molecules.

The rotational relaxation times of rod like molecules like poly[arylene-ethynylene]s and their low molecular weight model compounds calculated from a simple model agree well with the experimental ones as long as the axial ratio of the corresponding rotational ellipsoid is less than 8. For the polymer (axial ratio > 10) the fluorescence depolarization cannot be described by rotational motion perpendicularly to the long molecular axis. One has to take into consideration bending motions in connection with energy transfer along the bent backbone.