In order to analyse the dependence of charge transport m conjugated mate&s on thclr strue tural orgamxatlon, three sexlthlophene denvatlves were studied, unsubstttuted 6T and Its dl-hexyl subs& tuted compounds, both on the termmal a poslhons (a,uDH6T) and as pendant groups m B posttion (8, /J'DHGT) X-ray drffractlon charactenzatlon of vacuum evaporated thm films of these obgomers shows that 6T and K,wDH~T consist of layered structures m a monoclmlc arrangement, wtth all-trans planar molecules standmg on the substrate A large increase of molecular orgamzatlon at the mesoscoplc level IS observed when passmg from 6T to goDH6T, as shown by a much longer range ordermg Electrical cbaractenxattons show that the condutivtty of u,mDH6T IS amsotropq with a raho of 120 m favor of the conductlvtty parallel to the substrate plane, K along the stackmg axis The charge tamer mobtbty, determmed on field-effect transistors reahxed from these conjugated ohgomers, also shows a large mcrease when passmg from 6T to a,wDH6T, reachmg a value of 5 x 10-zcmz V-l s-l, m contrast with B$'DH6T wh~cb presents very low conductrvlty and mob&y These results are attnbuted to the selfassembly properks brought by alkyl groups m the a,w poatlon