The pH-dependent fluorescence of pyridylmethyl-4-amino-1,8-naphthalimides
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Bibliographic record
Abstract
Regioselective photoinduced electron transfer (PET) has been previously observed in aminoalkyl-4-amino-1,8-naphthalimide 'fluorophore-spacer-receptor' systems. PET from the amine to the fluorophore was only observed when the electron entered the fluorophore in the region of its 4-NH group. This has received two related but distinct explanations. The first is a directing effect of the molecular-scale electric field of internal charge transfer (ICT) excited state of the fluorophore. The second is a peculiarity of 4-amino-1,8-naphthalimides in possessing a node at the imide nitrogen in its frontier orbitals. The six isomeric pyridylmethyl-4-amino-1,8naphthalimides 1-3 and 4-6 are configured as 'fluorophore-spacer-receptor' systems in order to test the relative importance of these two explanations. The two regioisomeric sets are designed such that PET is thermodynamically feasible when they are protonated, which should lead to fluorescence quenching by protons. In practice, the proton-induced fluorescence quenching is moderate and more clearly observed in the set 1-3. This evidence points to the PET-accelerating effect of the molecular-scale electric field being mitigated by the presence of the node at the imide nitrogen in the frontier orbitals. Compound 4 also shows this proton-induced fluorescence quenching effect but to a still smaller extent. In this instance, the PET is hampered by the electric field alone. Compounds 5 and 6 show an excited state intramolecular proton transfer (ESIPT) involving water-mediated hydrogen-bonded rings, which dominates over any residual PET to produce proton-induced fluorescence enhancement. Again, the effect is moderate. The two mechanisms of PET regioselectivity can now be understood to operate additively in the aminoalkyl-4-amino-1,8-naphthalimides and subtractively in the protonated pyridylmethyl-4amino-1,8-naphthalimides.
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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 | 0.000 | 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 it