We wish to measure the ALCs of a series of polyacene molecules made of a different number of rings. We would like to identify the dependence of the electron spin relaxation rate on the length of the molecule. We have performed theoretical calculations on the expected dependence using a model, based on our previous results, that involves a local spin relaxation mechanism based on a thermally assisted spin-orbit coupling.The direct measurement of this dependence will allow the comparison with the model we have developed, and will give further insights into this spin relaxation mechanism. The understanding of the relevant spin scattering mechanism could lead to major breakthroughs in spin dynamics in organic semiconductors, possibly generalised to all disordered materials.