The effects of donor-acceptor substitution symmetry on the nonlinear absorption of two-dimensionally-conjugated isomeric chromophores
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Bibliographic record
Abstract
Differential optical Kerr effect (DOKE) detection is a powerful tool for studying the ultrafast time-resolved dynamics of 3<sup>rd</sup>-order nonlinear processes. In this study, DOKE was used to measure the nonlinear absorption properties of tetraethynylphenylene (TEP) solutions in THF using 800 nm, 80 fs laser pulses. These two-dimensional, highly-conjugated chromophores (also known as TPEBs) show high instantaneous two-photon absorption (TPA) for relatively small chromophores. The TPA cross section is strongly dependent on the donor-acceptor geometry in these materials: a quadrupolar, all-donor TEP shows the smallest TPA, with a cross-section of σ<sup>(2)</sup>= 90 ± 15 GM. <i>ortho</i>-TEP, for which the donors (and acceptors) are conjugated via the <i>ortho</i> position across the central phenyl ring, is dipolar and displays the largest cross-section, of σ<sup>(2)</sup>= 260 ± 30 GM. <i>para</i>-TEP, which is quadrupolar, and <i>meta</i>-TEP, which is dipolar, display similar cross-sections of σ<sup>(2)</sup>= 160 ± 10 GM and σ<sup>(2)</sup>= 150 ± 10 GM, respectively. In addition to an instantaneous TPA response, these isomers show unique two-photon assisted excited-state absorption (ESA), with the <i>ortho</i>- and <i>meta</i>-TEP displaying a clear 3-10 ps rise to an ESA peak, and subsequent decay. The differences in the nonlinear absorption behaviour of these materials may be partially explained by selection rules and UV-vis spectroscopy. In addition, the polar geometries, coupled to the various in-plane conjugation paths, may further influence their optical nonlinearities. Understanding these trends impacts both the design of materials with desirable nonlinear absorption properties and our understanding of the electronic landscape in functionalized organic materials.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.002 |
| 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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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 it