Glassy, Conjugated Polymer Nanoparticles Formed by a Semiflexible Polymer: A Molecular Dynamic Study*

Conjugated polymers confined into nano dimensions form long-lived luminescent particles (polydots), with potential as bio markers, where the chain dynamics and conformation determine the photophysics in the confined state. Here we probe the structure and dynamics of semiflexible polymers MEH-PPV confined to their nano dimension, using fully atomistic molecular dynamics (MD) simulations as the temperature is varied. We find that the polymer swells below T_g and R_g increases linearly with temperature. A transition takes place at 605-610 K. This transition is attributed to transformation of glass-like particle to a more dynamic state. The auto correlation function of the backbones of the confined chains, were calculated and analyzed in terms of KWW stretched exponentials, yielding correlation times of ~3.5 ms. This semiflexible polymer remains in its confined state over a broad temperature range. In comparison with polydots formed by rigid polymers, backbone flexibility results in a tighter packing and formation of internal correlations of the side chains.