Photon-echo studies of collective absorption and dynamic localization of excitation in conjugated polymers and oligomers
Bibliographic record
Abstract
Investigations of the origins of line broadening and excited state dynamics for the conjugated polymer poly[2-methoxy,5-(2-ethyl-hexoxy)-1,4-phenylenevinylene] (MEH-PPV) and a model pentamer, $p$-bis{[$o,m$-di(2-ethylhexy)oxy-$p$-methylstyryl]styryl}benzene are reported. The time-integrated three-pulse stimulated echo peak shift (3PEPS) experiment is employed to elucidate dephasing, spectral inhomogeneity arising from conformational disorder, and dynamical processes, otherwise obscured by ensemble averaging. We progressively discuss three dynamical models to describe the experimental data. The multiphonon model describes coupling of the electronic transitions to high frequency vibrational modes, and is able to fit the absorption spectra well, highlighting the importance of a distribution of conjugation length. However, it fails to model the 3PEPS data. A two-level system approach is found to reproduce the absorption line shapes as well as 3PEPS data, however, it cannot simultaneously describe the fluorescence data since the homogeneous linewidth is grossly overestimated. In light of these analyses, we propose the three-stage relaxation model, that (1) describes absorption into delocalized states that arise from electronically coupled conformational subunits; (2) explains the fast decay of the 3PEPS data as a rapid dynamic localization of excitation; and (3) provides a homogeneous line broadening that is consistent for both the absorption and fluorescence processes. Simultaneous modeling of the 3PEPS, absorption, and fluorescence data, establishes a consistent picture to understand the line broadening, dephasing mechanisms, and excited state dynamics for conjugated polymers and oligomers.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".