Near-Infrared Absorbing Azo Dyes: Synthesis and X-ray Crystallographic and Spectral Characterization of Monoazopyrroles, Bisazopyrroles, and a Boron−Azopyrrole Complex
Bibliographic record
Abstract
Symmetric 2,5-bisazopyrroles 2(a-d) were synthesized by a one-step reaction of substituted phenyl diazonium salts [R'(Ph)N2(+)Cl-] [a, R' = 4-N(CH3)2; b, R' = 2-OH; c, R' = 2-CO2H; d, R' = 4-NO2] with pyrrole under basic conditions. Asymmetric 2,5-bisazopyrroles 3(a-d) were synthesized by reacting substituted phenyl diazonium salts [R''(Ph)N2(+)Cl-] (a, R'' = 4-OCH(3); b, R'' = H; c, R'' = 4-Br; d, R'' = 4-NO2) with 2-(4-dimethylaminophenylazo)-1H-pyrrole (1a) under the same conditions. The reactions of 2a with boron trifluoride and iodomethane provided a BF2-azopyrrole complex of 1H-pyrrolo[2,1-c]-1,2,4,5-boratriazole (4) and 2,5-bisazo-1-methylpyrrole 5. X-ray crystallographic and spectral analysis of 1a, 2a, 2b, and 4 showed that 1a has three crystal forms: 1a(I), 1a(II), and 1a(III), the latter two bearing a bicyclic ring system formed via intermolecular hydrogen bonding. Complex 4 was found to be the most planar due to a rigid trans-azo configuration and has the longest N horizontal lineN bond distances (1.322 and 1.300 Angstrom) and wavelength of maximum absorption (754 nm). The N horizontal lineN bond distances increase in the sequence of monoazopyrrole [1a(I): 1.253 Angstrom], bisazopyrrole (2a: 1.283 Angstrom), bisazopyrrole with intramolecular hydrogen bonding (2b: 1.293 and 1.293 Angstrom), and the BF2-azopyrrole complex. Their maximum absorptions shift bathochromically in the sequence of monoazopyrrole (1a: 443 nm), bisazopyrroles [2(a-d), 3(a-d), 5: 486-615 nm], and the BF2-azopyrrole complex. These results are important for the design of near-infrared absorbing azo dyes and suggest an efficient path for the preparation of near-infrared absorbing azo dyes by effectively enhancing pi-electron delocalization.
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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) | 0.001 | 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".