Donor-Acceptor-Functionalized Tetraethynylethenes with Nitrothienyl Substituents: Structure-Property Relationships
Bibliographic record
Abstract
Tetraethynylethenes (TEEs) functionalized with donor (4-(dimethylamino)phenyl) and acceptor (5-nitro-2-thienyl) groups were prepared by Pd0-catalyzed Sonogashira cross-coupling reactions (Schemes 1 – 6). The physical properties of these novel chromophores were examined and compared with those of analogous systems containing 4-nitrophenyl instead of 5-nitro-2-thienyl acceptor groups. X-Ray crystal-structure analyses showed the π-conjugated frameworks of 2, 11, and 13, including the TEE core and all aryl moieties, to be nearly perfectly planar (Figs. 1, 3, and 4). In contrast, one 4-(dimethylamino)phenyl group in 10 is rotated almost 90° out of the molecular plane, presumably due to crystal-packing effects (Fig. 2). The analysis of bond lengths and bond angles revealed little, if any, evidence of intramolecular ground-state donor-acceptor interactions. The electrochemical behavior of nitrothienyl-substituted TEEs is similar to that of the corresponding nitrophenyl-functionalized derivatives (Table 3). The nitrothienyl groups were reduced at −1.23 V (vs. the ferrocene/ferricinium couple, Fc/Fc+), regardless of the degree or pattern of other substitutions. For nonsymmetrical TEE 13, the reduction of the nitrothienyl group at −1.23 V is followed by a reduction of the nitrophenyl group at −1.40 V, a potential typical for the reduction of other nitrophenyl-substituted TEEs, such as 17 – 20. UV/VIS Spectroscopy showed a consistently lower-energy absorption cutoff for nitrothienyl derivatives compared with the analogous nitrophenyl-substituted TEEs that confirms a lowering of the HOMO-LUMO gap as a result of nitrothiophene substitution (Figs. 5 and 6). A comparison of the tetrakis-arylated TEEs 11, 13, and 20 clearly showed a steady bathochromic shift of the longest-wavelength absorption maximum and the end-absorption upon sequential replacement of nitrophenyl by nitrothienyl groups. Quantum-chemical computations were performed to explain a number of complex features of the electronic absorption spectra. All empirical features of relevance in the experimental UV/VIS spectra for 2, 5, 6, and 17 – 19 were correctly reproduced by computation (Tables 4 and 5). The combination of theory and experiment was found to be very useful to explain the particular acceptor properties of the 5-nitro-2-thienyl group.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.071 | 0.001 |
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; both teacher heads agree on what is shown here.
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".