Conformation-Dependent Photostability among and within Single Conjugated Polymers

Abstract

The relationship between photostability and conformation of 2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) conjugated polymers was studied via excitation polarization modulation depth (M) measurements. Upon partial photobleaching, M distributions of collapsed, highly ordered MEH-PPV molecules shifted toward lower values. Conversely, M distributions of MEH-PPV molecules with random coil conformations moved toward higher values after partial photobleaching. Monte Carlo simulations of randomly distributed dipole moments along polymer chains subjected to partial photobleaching revealed that a statistical effect leads to an increase in peak M value. Decreases in M values seen experimentally in the population of MEH-PPV molecules with high M values, however, are due to conformation-dependent photostability within single MEH-PPV polymers. We show that, while folded MEH-PPV molecules are relatively more photostable than extended MEH-PPV molecules in an ensemble, extended portions of particular molecules are more photostable than folded domains within single MEH-PPV molecules.

Super‐resolution Fluorescence Imaging for Materials Science

“…[52] Applying this technique to single conjugated chains of a similar polymer, Park et al could confirm that polymers of compact conformation exhibit a rather stepwise photobleaching in contrast to continuous photobleaching behavior. [51] The distance between recombination sites was confirmed to be approx. 10 nm.…”

“…In a more recent study, the localization of single emitters after step‐wise bleaching allowed closely spaced emission sites to be resolved, using a technique called single‐molecule high‐resolution imaging with photobleaching (SHRImP) . Applying this technique to single conjugated chains of a similar polymer, Park et al could confirm that polymers of compact conformation exhibit a rather stepwise photobleaching in contrast to continuous photobleaching behavior .…”

“…[49] It was found that the emitting sites are distributed nearly uniformly within a single chain, and that, irrespective of the molecular weight of the polymer, the sites are on average 10 nm apart from each other. [50] In a more recent study, the localization of single emitters after step-wise bleaching allowed closely spaced emission sites to be resolved, [51] using a technique called single-molecule high-resolution imaging with photobleaching (SHRImP). [52] Applying this technique to single conjugated chains of a similar polymer, Park et al could confirm that polymers of compact conformation exhibit a rather stepwise photobleaching in contrast to continuous photobleaching behavior.…”

In Situ Optical Imaging of the Growth of Conjugated Polymer Aggregates

“…Coalescence events predominantly yield aggregates with lower M values, decreasing the median M to 0.43. While this finding suggests coalescence events attenuate optical (and presumably structural) anisotropy of aggregates, because changes in M values may also emerge from changes in number of emitting dipoles, complementary Monte Carlo simulations of coalescence were performed.…”

Resist or Oxidize: Identifying Molecular Structure–Photostability Relationships for Conjugated Polymers Used in Organic Solar Cells

“…[9] Furthermore, oxygen diffuses with non-negligible rates even through the best barrier foils used for encapsulation. [15] It has been shown that conjugated polymers, [16][17][18][19][20] fullerene derivatives, [21,22] and also non-fullerene acceptors (NFAs) [23] undergo facile photooxidation. The electron transfer from the photoexcited organic molecules to molecular oxygen and the generation of the reactive superoxide radical anion O 2…”