Intramolecular excimer fluorescence from folded ground state rotamers of <i>N</i>,<i>N</i><i>'</i>dimethyl-<i>N</i>,<i>N</i><i>'</i>-dipyrenylurea protophanes
Bibliographic record
Abstract
The molecular structure, absorption, and fluorescence spectra of N,N'-dimethyl-N,N'-di-1-pyrenylurea and N,N'-dimethyl-N,N'-di-2-pyrenylurea have been investigated and compared to the properties of N,N,N'-trimethyl-N'-pyrenylurea model compounds. Di-1-pyrenylurea exists as a mixture of folded (E,E) syn- and anti-rotamers that interconvert via flipping of one of the pyrene rings to an unfolded (E,Z) rotamer geometry. The symmetric di-2-pyrenylurea exists as a single folded (E,E) conformation which is in equilibrium with a less-stable, unfolded (E,Z) rotamer. The absorption and fluorescence spectra of the dipyrenylureas at 77 K in a rigid glass are similar to those of monopyrenylurea model compounds. However, in fluid solution, the dipyrenylureas exhibit excimer fluorescence and very weak monomer fluorescence which have identical decay times. This behavior is attributed to fast rotational equilibrium between folded rotamers which exhibit excimer fluorescence and unfolded rotamers which exhibit monomer fluorescence. The behavior of the dipyrenylureas is compared with that of other systems that form intramolecular pyrene excimers and diarylureas.Key words: excited state rotamers, dipyrenylureas, pyrene excimers, ureaphane.
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How this classification was reachedexpand
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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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 teacher head, 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".