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. 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.

Nanohybrid conjugated polyelectrolytes: highly photostable and ultrabright nanoparticles

“…45 Very recently, a report by Godin et al described the fluorescence enhancement of MPS-PPV prepared in different solvent mixtures (H 2 O/THF). 46 In low water content, nanoparticles (110-212 nm) exhibited a redshift in the emission which was also attributed to the increase in the conjugation length of MPS-PPV.…”

Turning the heat on conjugated polyelectrolytes: an off–on ratiometric nanothermometer

“…Whether dissolved in hydrophobic or hydrophilic media, their fluorescence emission dramatically changes. [23][24][25] In particular phenylene based polymers exhibit a pronounced spectral emission shift when going from the aggregated to the free chain. 26 As such, they have been employed as piezochromic probes 27 and membrane reporters.…”

High Throughput Mapping of Single Molecules’ Redox Potentials on Electrode

“…Interfacial and intracellular redox states and processes have been extensively explored using fluorescent probes of redox proteins and dyes, − where mapping redox potentials (times) of interfacial and intracellular electron transfer processes in chemical and biological systems have become feasible due to recent technological developments. In contrast to conventional single-molecule confocal fluorescence microscopy, which only detects one single molecule at a time due to its limitation of a single point photon detector, single-molecule localization super-resolution fluorescence microscopy allows simultaneous fluorescence monitoring of multiple single molecules in the field of view by high-speed camera with high sensitivity, and thereby hundreds of single-molecule fluorescence intensity trajectories can be acquired with high throughput. − For more than a decade, single-molecule fluorescence microscopies have been combined with electrochemical modulation to develop single-molecule spectroelectrochemistry at single-molecule levels and nanoscales. − For example, heterogeneous charge mobility of individual conjugated polyelectrolyte nanoparticles was studied in organic solvent via two-color single particle spectroelectrochemistry; Jin et al reported the direct observation and quantitative analysis of single redox events of resorufin to the nonfluorescent dihydroresorufin via electrochemical modulation inside silica nanochannels . The modulation of the fluorescence as a function of electrochemical potential of the fluorescent dye Alexa Fluor 647 conjugated to bovine serum albumin was studied by total internal reflection fluorescence microscopy .…”

“…reviewed single-molecule fluorescence microscopy for probing the electrochemical interface . When the single-molecule fluorescence microscope is coupled with electrochemical potential scanning, − every redox-active single fluorescent molecule is expected to be laid out in an electrochemically modulated fluorescence intensity (vs time) trajectory. However, photodriven processes also cause single molecule fluorescence intensity fluctuations, which disguise the electrochemically driven fluorescence intensity changes. − In other words, it is difficult to tell the electrochemically modulated fluorescence change apart from other causes of fluorescence on/off blinking.…”

“…6−8 For more than a decade, single-molecule fluorescence microscopies have been combined with electrochemical modulation to develop single-molecule spectroelectrochemistry at single-molecule levels and nanoscales. 9−20 For example, heterogeneous charge mobility of individual conjugated polyelectrolyte nanoparticles was studied in organic solvent via two-color single particle spectroelectrochemistry; 13 Jin et al reported the direct observation and quantitative analysis of single redox events of resorufin to the nonfluorescent dihydroresorufin via electrochemical modulation inside silica nanochannels. 14 The modulation of the fluorescence as a function of electrochemical potential of the fluorescent dye Alexa Fluor 647 conjugated to bovine serum albumin was studied by total internal reflection fluorescence microscopy.…”