Nanoscopy of Single Charge Carrier Jumps in a Conjugated Polymer Nanoparticle

Abstract

We present super-resolution (∼2 nm spatial resolution per frame, 1 ms time resolution) tracking of single charge carriers in nanoparticles of the conjugated polymer PFBT. The motion of the charge carrier is determined from fluctuations in the centroid position of the particle fluorescence spot arising from fluorescence quenching by the polaron. A single polaron is observed to hop between a few sites, consistent with dispersive charge transport in a disordered energy landscape. In some shorter segments of the trajectory, there is repeated hopping between two sites, whereas for longer segments and full trajectories, random walk-like behavior consistent with multiple sites is observed. The hopping times range from a few milliseconds to seconds, following a power law distribution, while the hopping distances range from 2 to 5 nm, roughly following an exponential distribution. From the polaron hopping time distribution, we estimate a barrier height of 430–570 meV, with a nearest-neighbor distribution ranging from 2 to 5 nm, consistent with the presence of deep traps often associated with structural or chemical defects.

Dual‐Mode Superresolution Imaging Using Charge Transfer Dynamics in Semiconducting Polymer Dots

“…[12] Thes low blinking dynamics that we observed is likely due to accumulation and elimination of holes occurring at charge carrier traps in the host polymer.T hus,w eh ypothesize that the "on" and "off" transitions reflect fluctuations in the population of trapped holes in the Pdots.T oq ualitatively visualize this effect, we simulated stochastic hole polaron population fluctuation using ap olaron generation rate determined from the singlestep "on" to "off" transitions ( Figures S2-4) and ar ecombination rate estimated from previously reported hole polaron lifetimes in semiconducting polymers ( Figure S5;d etails of modeling and analysis are provided in the Supporting Information). [5c,13] Based on previously estimated hole polaron quenching efficiency( % 10 %) in Pdots of similar sizes, [13,14] we assumed that roughly 10 polarons can completely quench the single-particle emission. As shown in Figure 2j,k, under the simulated experimental conditions,the hole polaron population is typically more than enough to completely quench the single-particle fluorescence,a nd only low-probability large fluctuations in the quencher population lead to rare fluorescence bursts.…”

Conjugated‐Polymer‐Based Nanoparticles with Efficient NIR‐II Fluorescent, Photoacoustic and Photothermal Performance

“…The conjugated polymer poly[9,9‐dioctylfluorenyl‐2,7‐diyl)‐co‐1,4‐benzo‐{2,1′‐3}‐thiadiazole)] (PFBT) doped with the fullerene derivative phenyl‐C61‐butyric acid methyl ester (PCBM) achieved about four times better resolution than dye molecules . At the same time, super‐resolution tracking of single charge carriers in the conjugated polymer PFBT was also displayed …”

π-Conjugated nanostructured materials: preparation, properties and photonic applications

“…69 In the subsequent study by McNeill and co-workers, the time resolution (1 ms) was improved substantially, and a broad range of polaron dynamics at kilohertz frame rates, ranging from the millisecond to second scale was investigated. 70 The position trajectories were analysed using multiscale segmented correlation and mean-square displacement (MSD) analysis to obtain the distribution of the polaron hopping dynamics. In long segments, the polaron was trapped in an area that roughly matched the size of a particle, whereas in short segments, the polaron was trapped in a much smaller region.…”