Role of Side Chains in the Packing Structure and Dynamics of Conjugated Polymers

Charge transport in conjugated polymers is affected notonly bythe static structure but also the dynamics of backbone segments. Aseries of regiorandom poly(3-alkylthiophenes) (P3ATs) with 6-12alkyl carbons per side chain are studied by the all-atom moleculardynamics simulations. By investigating the effect of temperature andside chain length on the static structure, we identify that the peakof neutron scattering at q & SIM; 0.42 & ANGS;(-1) is from the backbone's edge-to-edge packingalong the side-chain direction and shifts to the lower q with the increasing side chain length. The peak at q & SIM; 1.35 & ANGS;(-1) is contributed by boththe intrachain side chain-side chain correlation and the interchaincorrelation on the face-to-face stacking direction. In addition, theincrease in side chain length can lead to faster backbone dynamics.The farther the carbon atom is from the backbone, the faster it moves.Based on the dynamic analysis, the faster motion of the backbone ismainly attributed to the last three atoms close to the end of thealkyl side chain, which have distinct dynamics compared with the carbonsin the inner part of side chains close to the rigid backbone.