Effect of particle insertion on Poly(3-hexylthiophene) brush’s π-π stacking

Abstract

A key mechanism in organic thin film transistor based biosensors is the change in charge carrier mobility caused by the disruption of π-π bonds in the selfassembled monolayers of conjugated polymers due to the attachment of the target analyst. We study the particle induced conformational changes of a π-π stacked Poly(3-hexylthiophene) (P3HT) brush using Molecular Dynamics simulations to mimic this event. The polymer brush is modeled using a Martini coarse-grained forcefield and Lennard-Jones particles of different sizes (0.5 nm < Rp < 3 nm) are inserted up to different heights in the brush. We quantify the disruption of the initially perfectly aligned π-π stack network using three properties: (i) the spatial P3HT monomer density profile, (ii) the spatial distribution of π-π bound monomer pairs, and (iii) the connectivity of the disrupted network. The perturbation of the brush leads to a short-ranged depletion of monomers at the particle position and the subsequent rearrangement of the entire π-π stack network. Interestingly, we find that the ratio of π-π -bound monomer pairs compared to unbound pairs increases in the neighborhood of the particle. We attribute this observation to crowding effects occurring in the brush when the particle penetrates. In general, we find stronger effects for deeper penetration.