Heterogeneous Charge Mobility in Individual Conjugated Polyelectrolyte Nanoparticles Revealed by Two-Color Single Particle Spectroelectrochemistry Studies

Abstract

The optoelectronic properties of conjugated polymers and conjugated polyelectrolytes (CPEs) depend on their chain conformation and packing. Correlations between emission color, charge mobility, and extent of aggregation in these materials have been previously established from bulk studies. Here we describe the preparation of stable nanoparticle suspensions of the CPE poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene (MPS-PPV) where changes in the solvent composition enable tuning their emission spectra and quantum yield. By employing a newly developed color-sensitive single-molecule spectroelectrochemistry (SMS-EC) technique, the effect of chain conformation on the optoelectronic properties of MPS-PPV nanoparticles is monitored at the single particle level. Within a single particle the photoluminescence and redox response is chromatically correlated reflecting on the differing contributions that coiled and deaggregated vs extended and packed segments have on their optoelectronic properties. We also observe a heterogeneous response among nanoparticles to externally applied electrochemical potentials, which further correlates with their emission color (chain packing). We rationalize our observations on differential charge injection, energy and charge transport, and ion migration as a consequence of chain conformation, packing effects, and the presence of electrochemically reducible quenching sites. Our work provides a way to unravel the intrinsic heterogeneity of CPE materials to better understand the relationship between chain conformation and optoelectronic properties.