Nano-Glasses Formed by Ensembles of Confined Conjugated Polymers: Molecular Dynamic Simulation Study

Confined conjugated polymers form long-lived far from equilibrium highly luminescent nano particles (NPs or polydots) with an immense potential for nanomedicine. Their photophysics strongly depends on chain conformation and the number of chains within the assemblies. Single molecule NPs are characterized by glass-like dynamics with time constants of micro seconds. Here fully atomistic molecular dynamics simulations was used to study the effects of the number of polymer molecules confined, and their relative orientation on ensemble structure and stability, using dialkyl poly (para-phenylene ethynylene)s (PPEs) as a model system. Increasing number PPE molecules were confined into one particle in implicit poor solvent while their initial orientation in the confining cavity was randomly varied, maintaining the total number off monomers per particle constant ( N= 240). We find that independent of the number of chains and their relative orientation, at early times the particles assume a close to spherical configuration. However, the initial orientation and the number of chains affect the internal structure and the unwinding process the polymers assume as the temperature is increased.