Dynamics of siloxane chains bearing phenyl chromophores

Abstract

Molecular dynamics simulations are used to model the conformational motions associated with transitions between rotational states which may be responsible for the coupling between chromophores (excimer forming states) in the chains of poly(methylphenylsiloxane). Analysis of the trajectories show that the rotations around backbone bonds occur much faster than the coupling-uncoupling between the lateral chromophores. Although fast, the rotations around backbone bonds are strongly coordinated, each pair of Si-O-Si bonds rotating in a concerted fashion, such that the lateral phenyl groups (attached to the Si atoms) remain coupled over long times (many backbone rotations). The quantitative assessment of these results is established by calculating the correlation times for the backbone rotational angles (Si-O), for the distance separating chromophores (Ph…Ph), and for the lateral Si-Ph bonds. The relevance for the kinetics of excimer emission is discussed.